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1.
  • Önnerfjord, Patrik, et al. (author)
  • Homogeneous sample preparation for automated high throughput analysis with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.
  • 1999
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 13:5, s. 315-22
  • Journal article (peer-reviewed)abstract
    • This work presents a simple method for obtaining homogeneous sample surfaces in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) for the automated analysis of peptides and proteins. The sample preparation method is based on applying the sample/matrix mixture onto a pre-deposited highly diluted matrix spot. The pre-deposited crystals act as seeds for the new sample containing crystals which become much smaller in size and more evenly distributed than with conventional methods. This 'seed-layer' method was developed, optimised and compared with the dried-droplet method using peptides and proteins in the 1000-20,000 Da range. The seed-layer method increases the surface homogeneity, spot to spot reproducibility and sample washability as compared with the commonly used dried-droplet method. This methodology is applicable to alpha-cyanohydroxycinnamic acid, sinapinic acid and ferulic acid, which all form homogeneous crystal surfaces. Within-spot variation and between-spot variation was investigated using statistics at a 95% confidence level (n = 36). The statistical values were generated from more than 5000 data points collected from 500 spectra. More than 90% of the sample locations results in high intensity spectra with relatively low standard deviations (RSDs). Typically obtained data showed an RSD of 19-35% within a sample spot as well as in-between spots for proteins, and an RSD of < or = 50% for peptides. Linear calibration curves were obtained within one order of magnitude using internal calibration with a point-RSD of 3% (n = 10). The sample homogeneity allows mass spectra (average of 16 laser shots) to be obtained on each individual sample within 15 sec, whereby a 100 spot target plate can be run in 25 min. High density target plates using the seed-layer method were prepared by spotting approximately 100 picoliter droplets onto the target, resulting in sample spots < or = 500 microns in diameter using a flow-through piezo-electric micro-dispenser. By using this automated sample preparation step lower standard deviations are obtained in comparison to manually prepared samples.
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2.
  • Palmblad, Magnus, et al. (author)
  • Analysis of Enzymatically Digested Proteins and Protein Mixtures using a 9.4 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer
  • 2000
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 14:12, s. 1029-1034
  • Journal article (peer-reviewed)abstract
    • A commercially available 9.4 Tesla Fourier transform ion cyclotron resonance (FTICR) mass spectrometer was applied in the analysis of tryptic digests of protein mixtures without any separation. First, the method was demonstrated on a mixture of tryptic digests of equine cytochrome c, equine myoglobin and bovine serum albumin. The same method was then applied to human plasma from a healthy blood donor. Computer programs were employed to simplify analysis of the complex spectra. The 2745 peaks in the human plasma electrospray ionization FTICR spectrum could be reduced to 1165 isotopic clusters and 669 unique masses. Out of these, 82 masses matched tryptic fragments of serum albumin with mass measurement errors less than 10 ppm, covering 93% of the sequence. Another 16 masses were assigned to tryptic fragments of transferrin, covering 41% of the sequence on the 10 ppm mass measurement error level (14 within 2 ppm). The mass measurement errors were approximately normal distributed with a standard deviation of 1.7 ppm. This demonstrates the feasibility of combining the ultra-high mass resolving power and accuracy of FTICR mass spectrometry with automated computer analysis for investigating complex biological matrices.
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3.
  • Zubarev, Roman A., et al. (author)
  • Delayed, gas-phase ion formation in plasma desorption mass spectrometry
  • 1997
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 11:9, s. 963-972
  • Journal article (peer-reviewed)abstract
    • The formation mechanisms of secondary ions from organic targets under MeV ion bombardment were studied with a high-resolution time-of-flight (TOF) mass spectrometer. Promptly formed ions Hn+, Cn+ and CnH+ were used for calibrating the TOF scale. Theoretical flight times of other ions were calculated according to the calibration curve and compared to experimentally determined values. The TOF values of non-specific low mass fragments formed via rearrangement or breaking of several bonds and/or abstraction of several atoms, agree well with the theoretical values. On the other hand, target-specific organic ions, including molecular ions of peptides, have longer TOF values than predicted by the calibration curve. Time delays of a few hundred picoseconds were found for low-mass specific fragments, and a few nanoseconds for peptide molecular ions. For protonated species and non-covalent clusters, the delays are larger than for pre-formed and radical molecular ions. Metals contained in organic samples, as contamination, also give delayed ions. For inorganic targets of LiBF4, significant delays were found for the clusters (LiF)nLi+ with n >3. A strong correlation was observed between the delay of an ion and the tailing of its kinetic energy distribution. The conclusion was made that the majority of target-specific ions are formed in the gas phase, at a distance from the target surface of the order of 1 μm.
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4.
  • Axelsson, Jan, et al. (author)
  • Electron Capture Dissociation of Substance-P using a Commercially Available Fourier Transform Ion Cyclotron Resonance Mass Spectrometer
  • 1999
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 13:6, s. 474-477
  • Journal article (peer-reviewed)abstract
    • Electron capture dissociation of the peptide Substance P is reported for the first time, with an unmodified, commercially available Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The fragmentation pattern is compared with that obtained with collisionally induced dissociation of the ions in the electrospray ion source, and note that electron capture dissociation gives a more easily interpreted spectrum, showing mainly C-fragments. With the exception of the proline residues, which require cleavage of two chemical bonds, we observe all C-fragmental we find the bias voltage of the electron gun not to be very critical.
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5.
  • Bergquist, Jonas, et al. (author)
  • Identification of catecholamines in the immune system by electrospray ionization mass spectrometry.
  • 1998
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 12:11, s. 683-8
  • Journal article (peer-reviewed)abstract
    • The first evidence that catecholamines might be present in the immune system was provided by capillary electrophoresis combined with electrochemical detection. Here, we present the first structural characterization of the endogenous catecholamines isolated from human peripheral blood mononuclear cells. Dopamine, L-DOPA and norepinephrine were detected and were identified with electrospray ionization mass spectrometry by determination of the protonated molecular species of each catecholamine and their major fragments generated in the electrospray source with a nozzle-skimmer voltage method. This technique, in conjunction with accurate mass measurement, allowed us to identify in an unfractionated sample the content of catecholamines in extracted cells in a quantitative manner, with structure-specific methodology. The data unambiguously confirm our previous tentative findings, and also strengthen the importance of the regulatory function of catecholamines in the immune system and the existence of an autocrine loop, where lymphocytes may down-regulate their own activity.
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6.
  • Stolyarova, V.L, et al. (author)
  • High-temperature Mass Spectrometric Study of the Vaporization of Dysprosium Trifluoride
  • 1996
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 10:5, s. 501-508
  • Journal article (peer-reviewed)abstract
    • The high-temperature Knudsen effusion method was used to study the vaporization processes and thermodynamic properties of dysprosium trifluoride in the temperature range 1280-1440 K. Data on the partial vapour pressure of DyF3 as a function of temperature and the enthalpy of sublimation of DyF3 were obtained. Using the value of the enthalpy of formation of solid DyF3, available in the literature, the enthalpy of formation of the gaseous molecule of dysprosium trifluoride and its atomization energy were calculated. At 1382 K, the partial vapour pressure of Dy2F6 over dysprosium trifluoride was obtained and the Gibbs energy of the gaseous reaction (Dy2F6)=(2DyF3) was evaluated.
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7.
  • Zubarev, Roman A., et al. (author)
  • Accurate monoisotopic mass measurements of peptides : Possibilities and limitations of high resolution time-of-flight particle desorption mass spectrometry
  • 1996
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 10:11, s. 1386-1392
  • Journal article (peer-reviewed)abstract
    • The possibilities and limitations of time-of-flight particle-desorption mass spectrometry are analysed from the standpoint of accuracy of monoisotopic mass determination. For an instrument with mass reflector, typical mass accuracy was found to be ca. 20 ppm (standard deviation). The main limitation was found to be the mechanism of secondary ion production itself. A fraction of biological ions are formed in the gas phase and therefore exhibit both time delay and energy deficit. This leads to a limited resolving power and non-symmetric ion peaks. A peak shape model, taking into account gas-phase ion formation, is built and analysed, and a simple correction procedure proposed. The application of the correction has increased the mass accuracy to 12 ppm (standard deviation). It is shown that further progress cannot be achieved by a correction procedure without instrumental improvements.
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8.
  • Zubarev, Roman A., et al. (author)
  • Kinetic energies of secondary ions in MeV and keV particle-induced desorption
  • 1996
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 10:15, s. 1966-1974
  • Journal article (peer-reviewed)abstract
    • Kinetic energy distributions of secondary ions produced by MeV or keV primary-ion bombardment of molecularsolids were measured in a reflectron time-of-flight mass spectrometer. It was found that the energy distributionsof many ions exhibit tails extending towards energies lower than the accelerating potential. The degree of tailingdepends upon the nature of the desorbed ion and the conditions of the target surface. Some light ions (H' andC' ), ions from inorganic (alkali halide) samples, radical molecular ions (Cg) and pre-formed molecuiar ions (e.g.complexes of valinomycin with alkali metal ions) exhibit almost no tailing. For positive adduct-type molecularions, such as MH', more extensive tailing was observed for MeV compared with keV primary ions. The originof the energy tailing is attributed to gas-phase formation of a fraction of the secondary ions. For molecular ionsof peptides, the characteristic time of formation of that fraction of ions (*lo% of the whole molecular-ionpopulation) was estimated to be of the order of 10 ns, while the characteristic distance from the target surfacewas of the order of 10 pm.
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9.
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10.
  • Adiels, Martin, 1976, et al. (author)
  • Optimization of N-methyl-N-[tert-butyldimethylsilyl]trifluoroacetamide as a derivatization agent for determining isotopic enrichment of glycerol in very-low density lipoproteins.
  • 2010
  • In: Rapid communications in mass spectrometry : RCM. - : Wiley. - 1097-0231 .- 0951-4198. ; 24:5, s. 586-592
  • Journal article (peer-reviewed)abstract
    • Stable isotope kinetic studies play an important role in the study of very-low density lipoprotein (VLDL) metabolism, including basic and clinical research. Today, [1,1,2,3,3-(2)H(5)]glycerol is the most cost-effective alternative to measure glycerol and triglyceride kinetics. Recycling of glycerol from glycolysis and gluconeogenesis may lead to incompletely labelled tracer molecules. Many existing methods for the measurement of glycerol isotopic enrichment involve the production of glycerol derivatives that result in fragmentation of the glycerol molecule after ionization. It would be favourable to measure the intact tracer molecule since incompletely labelled tracer molecules may be measured as fully labelled. The number of methods available to measure the intact tracer in biological samples is limited. The aim of this project was to develop a gas chromatography/mass spectrometry (GC/MS) method for glycerol enrichment that measures the intact glycerol backbone and is suitable for electron ionization (EI), which is widely available. A previously published method for N-methyl-N-[tert-butyldimethylsilyl]trifluoroacetamide (MTBSTFA) derivatization was significantly improved; we produced a stable derivative and increased recovery 27-fold in standards. We used the optimized MTBSTFA method in VLDL-triglyceride and found that further modification was required to take matrix effects into account. We now have a robust method to measure glycerol isotopic enrichment by GC/EI-MS that can be used to rule out the known problem of tracer recycling in studies of VLDL kinetics. Copyright (c) 2010 John Wiley & Sons, Ltd.
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11.
  • Allard, Erik, 1976-, et al. (author)
  • Quantitative aspects of analyzing small molecules - monitoring singly or doubly charged ions? : A case study of ximelagatran.
  • 2010
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 24:4, s. 429-435
  • Journal article (peer-reviewed)abstract
    • Precision, reproducibility and lower limit of quantitation (LLOQ) are important characteristics of a quantitative method. We have investigated these properties for Ximelagatran (Xi), which has a high tendency to form doubly charged ions in electrospray ionization (ESI), by studying the percentage of doubly charged species formed when varying the formic acid (FA) concentration, analyte concentration, amount of organic modifier and flow rate. It was found that the percentage of [Xi + 2H]2+ can be controlled to be more than 90% or less than 10% by varying the amount of FA present, and that the change between these values is dramatic. Furthermore, the percentage of [Xi + 2H]2+ formed decreases with increased analyte concentration and increased flow rate. No apparent relationship with the amount of organic modifier was found. The results have the implication that, by carefully controlling the selected parameters, the LLOQ, precision and reproducibility can be improved. We have compared the fragmentation of the singly and doubly charged species and concluded that the [Xi + 2H]2+ ion is more inclined to undergo fragmentation than [Xi + H]+. As a consequence, unusual instrumental settings had to be used for the experiments. The fragmentation patterns are to a great extent similar, but the doubly charged species is more inclined to generate low-mass product ions.
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12.
  • Alsberg, T., et al. (author)
  • Determination of hydroxyalkyl derivatives of cobalamin (vitamin B12) using reversed phase high performance liquid chromatography with electrospray tandem mass spectrometry and ultraviolet diode array detection
  • 2001
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 15:24, s. 2438-45
  • Journal article (peer-reviewed)abstract
    • Electrospray ionization tandem mass spectrometry (ESI-MS/MS) and ultraviolet diode array detection (UV-DAD), coupled on-line to reversed phase high performance liquid chromatography (HPLC), was used for the characterization of hydroxyalkyl derivatives of cob(I)alamin. The reduced form of vitamin B12, cob(I)alamin, denoted a supernucleophile due to its high nucleophilic strength, has shown promise as an analytical tool in studies of electrophilically reactive compounds in vitro and in vivo. A method for analysis of DNA-phosphate adducts was developed earlier utilizing the supernucleophilicity of cob(I)alamin to transfer alkyl groups from the phosphotriester configuration in DNA, with the formation of a Co-substituted alkyl-cobalamin (alkyl-Cbl) complex. For the purpose of identification and quantification of alkyl-Cbls at high sensitivity, an MS/MS method has been developed with application to a number of 2-hydroxyalkyl-cobalamins (OHalkyl-Cbls). The precursor oxiranes were reacted with cob(I)alamin, followed by clean-up and mass spectrometric analysis of the resulting OHalkyl-Cbls. It was found that ionization was highly dependent on solvent composition. By using acetonitrile/water/trifluoroacetic acid (TFA) (eluent I), the base peak was the doubly protonated molecule [M + 2H](2+), whereas acetonitrile/water/1-methylpiperidine (eluent II) yielded the singly protonated molecule [M + H](+) as the base peak. Excellent separation was obtained with eluent II, with good separation between stereoisomers, thus enabling the characterization of these by means of UV spectra. Limits of quantitation for 2-hydroxypropyl-cobalamin (OHPr-Cbl) were 0.2 and 2 pg/microL (or 0.1 and 1 fmol/microL) using selected ion recording (SIR) with eluent I and II, respectively. The obtained detection level should be sufficient for analysis of alkyl-Cbls from a wide range of toxicological applications.
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13.
  • Andersson, Maria, et al. (author)
  • Metabolic profiling of new synthetic cannabinoids AMB and 5F-AMB by human hepatocyte and liver microsome incubations and high-resolution mass spectrometry
  • 2016
  • In: Rapid Communications in Mass Spectrometry. - : WILEY-BLACKWELL. - 0951-4198 .- 1097-0231. ; 30:8, s. 1067-1078
  • Journal article (peer-reviewed)abstract
    • RationaleAMB (methyl (1-pentyl-1H-indazole-3-carbonyl)-L-valinate)) and its fluoro analog 5F-AMB (methyl (1-(5-fluoropentyl)-1H-indazole-3-carbonyl)-L-valinate) are two new synthetic cannabinoids that are structural analogs of AB-PINACA and 5F-AB-PINACA, respectively. 5F-AMB is scheduled as an illicit drug in China, Germany, Singapore and Japan, and no metabolism data are currently available for either drug. The aim of the present work was to investigate the metabolism of AMB and 5F-AMB and propose appropriate markers to identify their intake in clinical or forensic cases. MethodsAMB and 5F-AMB were incubated in human hepatocytes (10 mol/L) to generate phase I and II metabolites, which were identified with a TripleTOF 5600(+) high-resolution mass spectrometer. AMB and 5F-AMB metabolic stability studies also were performed with human liver microsomes (HLM) to evaluate metabolic clearances, and to adequately design the human hepatocyte experiment. ResultsAMB and 5F-AMB were quickly metabolized in HLM with a 1.1 0.1 and 1.0 +/- 0.2min T-1/2, respectively. The predominant metabolic pathway for AMB and 5F-AMB in hepatocytes was ester hydrolysis, and further oxidation and/or glucuronidation. In total, 19 metabolites were identified for AMB and 17 for 5F-AMB. We describe metabolites to differentiate AMB from 5F-AMB, and metabolites that are common to both analytes due to oxidative defluorination of 5F-AMB. ConclusionsFor the first time, AMB and 5F-AMB metabolism profiles were characterized, providing valuable data for identifying these two novel psychoactive substances. The difficulties of differentiating AMB and 5F-AMB from AB-PINACA/5F-AB-PINACA metabolites also were examined. These data improve the interpretation of urinary markers after AMB and 5F-AMB intake. Published in 2016. This article is a U.S. Government work and is in the public domain in the USA
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14.
  • Andersson, M., et al. (author)
  • Size and structure characterization of ethylhydroxyethyl cellulose by the combination of field-flow fractionation with other techniques. Investigation of ultralarge components
  • 2004
  • In: Biomacromolecules. - : Wiley. - 1525-7797 .- 1526-4602. ; 5:1, s. 97-105
  • Journal article (peer-reviewed)abstract
    • Ethylhydroxyethyl cellulose (EHEC) of three different viscosity classes (EHEC I, II, and III) was analyzed by programmed cross-flow asymmetrical flow field-flow fractionation coupled to multiangle light scattering and refractive index detectors to determine their size and molar mass distribution. Two size populations were detected in the two lower viscosity classes, EHEC I and II, one high molar mass and one ultrahigh molar mass (UHM). The two covered molar masses from 10(4) up to 10(9) g.mol(-1). The highest viscosity class EHEC III was less size-dispersed covering molar masses from 5x10(5) to 5x10(7) g.mol(-1). Filtering of the EHEC II solution removed small amounts of compact UHM material. Enzyme treatments were performed on EHEC II to further characterize it. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and anion ion-exchange chromatography coupled to pulsed amperometric detection showed that the UHM component contained EHEC.
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15.
  • Axén, Jakob, et al. (author)
  • Efforts to improve detection sensitivity for capillary electrophoresis coupled to atmospheric pressure photoionization mass spectrometry.
  • 2010
  • In: Rapid Communications in Mass Spectrometry. - : John Wiley & Sons Ltd. - 0951-4198 .- 1097-0231. ; 24:9, s. 1260-1264
  • Journal article (peer-reviewed)abstract
    • Electrospray ionization performs best with volatile buffers. However, generally the best separation performance for capillary electrophoresis (CE) is achieved with non-volatile buffers. Hyphenation of CE with mass spectrometry (MS) utilizing atmospheric pressure photoionization (APPI) enables use of a wider range of separation buffers without compromising detection sensitivity. As APPI is considered to be mass flow sensitive, the use of a larger inner diameter separation capillary (75 microm) allows larger volumes to be injected, without decreased separation performance, thus providing improved sensitivity (approx. a factor of 10), compared to the use of a 25 microm capillary. However, nebulizing gas flow and position of capillary tip in the sprayer have to be carefully optimized to prevent excessive band broadening. Further improvement in sensitivity (approx. a factor of 2) was obtained by decreasing the distance between the sprayer and ionization region, indicating that a specially designed CE/APPI-MS interface for low flow rates will be favourable.
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16.
  • Badea, Silviu‐Laurentiu, et al. (author)
  • Development of an enantiomer-specific stable carbon isotope analysis (ESIA) method for assessing the fate of α‐hexachlorocyclohexane in the environment
  • 2011
  • In: Rapid Communications in Mass Spectrometry. - : John Wiley & Sons, Ltd. - 0951-4198 .- 1097-0231. ; 25:10, s. 1363-1372
  • Journal article (peer-reviewed)abstract
    • α‐Hexachlorocyclohexane (α‐HCH) is the only chiral isomer of the eight 1,2,3,4,5,6‐HCHs and we have developed an enantiomer‐specific stable carbon isotope analysis (ESIA) method for the evaluation of its fate in the environment.The carbon isotope ratios of the α‐HCH enantiomers were determined for a commercially available α‐HCH sample using a gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS) system equipped with a chiral column. The GC‐C‐IRMS measurements revealed δ‐values of −32.5 ± 0.8‰ and −32.3 ± 0.5‰ for (−) α‐HCH and (+) α‐HCH, respectively. The isotope ratio of bulk α‐HCH was estimated to be −32.4 ± 0.6‰ which was in accordance with the δ‐values obtained by GC‐C‐IRMS (−32.7 ± 0.2‰) and elemental analyzer‐isotope ratio mass spectrometry (EA‐IRMS) of the bulk α‐HCH (−32.1 ± 0.1‰). The similarity of the isotope ratio measurements of bulk α‐HCH by EA‐IRMS and GC‐C‐IRMS indicates the accuracy of the chiral GC‐C‐IRMS method. The linearity of theα‐HCH ESIA method shows that carbon isotope ratios can be obtained for a signal size above 100mV. The ESIA measurements exhibited standard deviations (2σ) that were mostly < ± 0.5‰. In order to test the chiral GC‐C‐IRMS method, the isotope compositions of individual enantiomers in biodegradation experiments of α‐HCH withClostridium pasteurianum and samples from a contaminated field site were determined. The isotopic compositions of theα‐HCHenantiomers show a range of enantiomeric and isotope patterns, suggesting that enantiomeric and isotopefractionation can serve as an indicator for biodegradation and source characterization of α‐HCH in the environment.
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17.
  • Bengtsson, Jörgen, et al. (author)
  • On-line desalting and determination of morphine, morphine-3-glucuronide and morphine-6-glucuronide in microdialysis and plasma samples using column switching and liquid chromatography/tandem mass spectrometry
  • 2005
  • In: Rapid Communications in Mass Spectrometry. - : John Wiley & Sons. - 0951-4198 .- 1097-0231. ; 19:15, s. 2116-2122
  • Journal article (peer-reviewed)abstract
    • A sensitive and reproducible method for the determination of morphine and the metabolites morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) was developed. The method was validated for perfusion fluid used in microdialysis as well as for sheep and human plasma. A C18 guard column was used to desalt the samples before analytical separation on a ZIC HILIC (hydrophilic interaction chromatography) column and detection with tandem mass spectrometry (MS/MS). The mobile phases were 0.05% trifluoroacetic acid (TFA) for desalting and acetonitrile/5 mM ammonium acetate (70:30) for separation. Microdialysis samples (5 microL) were directly injected onto the system. The lower limits of quantification (LLOQ) for morphine, M3G and M6G were 0.50, 0.22 and 0.55 ng/mL, respectively, and the method was linear from LLOQ to 200 ng/mL. For plasma, a volume of 100 microL was precipitated with acetonitrile containing internal standards (deuterated morphine and metabolites). The supernatant was evaporated and reconstituted in 0.05% TFA before the desalting process. The LLOQs for sheep plasma were 2.0 and 3.1 ng/mL and the ranges were 2.0-2000 and 3.1-3100 ng/mL for morphine and M3G, respectively. For human plasma, the LLOQs were 0.78, 1.49 and 0.53 ng/mL and the ranges were 0.78-500, 1.49-1000 and 0.53-500 ng/mL for morphine, M3G and M6G, respectively.
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18.
  • Benkestock, Kurt, et al. (author)
  • Electrospray ionization mass spectrometry as a tool for determination of drug binding sites to human serum albumin by noncovalent interaction
  • 2005
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 19:12, s. 1637-1643
  • Journal article (peer-reviewed)abstract
    • Most proteins in blood plasma bind ligands. Human serum albumin (HSA) is the main transport protein with a very high capacity for binding of endogenous and exogenous compounds in plasma. Many pharmacokinetic properties of a drug depend on the level of binding to plasma proteins. This work reports studies of noncovalent interactions by means of nanoelectrospray ionization mass spectrometry (nanoESI-MS) for determination of the specific binding of selected drug candidates to HSA. Warfarin, iopanoic acid and digitoxin were chosen as site-specific probes that bind to the main sites of HSA. Two drug candidates and two known binders to HSA were analyzed using a competitive approach. The drugs were incubated with the target protein followed by addition of site-specific probes, one at a time. The drug candidates showed predominant affinity to site I (warfarin site). Naproxen and glyburide showed affinity to both sites I and II. The advantages of nanoE-SI-MS for these studies are the sensitivity, the absence of labeled molecules and the short method development time.
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19.
  • Benkestock, Kurt, et al. (author)
  • On-line microdialysis for enhanced resolution and sensitivity during electrospray mass spectrometry of non-covalent complexes and competitive binding studies
  • 2002
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 16:21, s. 2054-2059
  • Journal article (peer-reviewed)abstract
    • Many proteins and macromolecules easily form metal adduct ions which impairs their analysis by mass spectrometry. The present study describes how the formation of undesired adducts can be minimized by on-line microdialysis for non-covalent binding studies of macromolecules with low molecular mass ligands with electrospray ionization mass spectrometry (ESI-MS). The technique was indispensable for protein-ligand studies due to reduction of unwanted adduct ions, and thus gave excellent resolution and a sensitivity improvement of at least 5 times. The core of the analytical system was a modified microdialysis device, which was operated in countercurrent mode. A novel technique based on microdialysis for competitive binding studies is also presented. The noncovalent complex between a protein and a ligand was formed in the sample vial prior to analysis. The complex was injected into an on-line microdialysis system where a competitive ligand was administered in the dialysis buffer outside of the fiber. The second ligand competitively displaced the first ligand through transport via the wall of the dialysis fiber, and the intact complexes were detected by ESI-MS.
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20.
  • Bergh, Caroline, et al. (author)
  • Simultaneous selective detection of organophosphate and phthalate esters using gas chromatography with positive ion chemical ionization tandem mass spectrometry and its application to indoor air and dust
  • 2010
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 24:19, s. 2859-2867
  • Journal article (peer-reviewed)abstract
    • A selective and sensitive method for the simultaneous determination of 14 organophosphate and six phthalate esters using gas chromatography (GC) and mass spectrometry (MS) is presented. Both of these compound classes are frequently found in the indoor environment due to their use as bulk additives in numerous polymers, consumer products and building materials. GC/MS utilizing positive ion chemical ionisation (PICI) in selected reaction monitoring (SRM) mode with isobutane as the reagent gas was found to be the best of the tested methods; it proved superior to electron ionisation (EI) in selected ion monitoring (SIM) mode and to PICI using methane as the reagent gas. The method was applied to indoor air samples collected by active air sampling using solid-phase extraction (SPE) cartridges. Organophosphates and phthalates were simultaneously determined with method detection limits (MDLs) in the range of 0.1-47 ng m(-3). For most compounds the MDLs were <= 0.2 ng m(-3), but due to the presence of some of these ubiquitous indoor air pollutants in the blanks, significantly higher MDLs were observed for a few compounds. Finally, the method was also applied in the screening of a much more complex sample matrix, indoor dust.
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21.
  • Björklund, Jonas, et al. (author)
  • Selective determination of organophosphate flame-retardants and plasticizers in indoor air by gas chromatography, positive-ion chemical ionization and collision-induced dissosiation mass spectrometry
  • 2004
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 18:24, s. 3079-3083
  • Journal article (peer-reviewed)abstract
    • Gas chromatography/ion trap mass spectrometry with in-source ionization and dissociation was used in positive-ion chemical ionization (PICI) mode for the determination of organophosphate triesters in indoor air. These compounds are widely used as additive flame retardants and plasticizers in different types of materials and have become ubiquitous pollutants in indoor environments. When using collision-induced dissociation in PICI mode the fragmentation of the organophosphate triesters can be performed in a more controllable way than in electron ionization (EI) mode. The developed selected-reaction monitoring method provided high selectivity for the investigated compounds. For 8-h air measurements (corresponding to 1.5 m3 of sampled air) the limit of detection of the method was determined to be in the range 0.1–1.4 ng m−3, which is comparable with nitrogen-phosphorus detection and about 50-fold lower than when using EI in selected-ion monitoring mode. The presented method was applied to samples from three common indoor environments, in which a number of organophosphate triesters were identified and quantified. The dominating compound was found to be tris(2-chloropropyl) phosphate, which occurred at levels up to 0.8 μg m−3.
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22.
  • Bohlin, Madeleine, et al. (author)
  • High-precision determination of lithium and magnesium isotopes utilising single column separation and multi-collector inductively coupled plasma mass spectrometry
  • 2018
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 32:2, s. 93-104
  • Journal article (peer-reviewed)abstract
    • Rationale Li and Mg isotopes are increasingly used as a combined tool within the geosciences. However, established methods require separate sample purification protocols utilising several column separation procedures. This study presents a single-step cation-exchange method for quantitative separation of trace levels of Li and Mg from multiple sample matrices.Methods The column method utilises the macro-porous AGMP-50 resin and a high-aspect ratio column, allowing quantitative separation of Li and Mg from natural waters, sediments, rocks and carbonate matrices following the same elution protocol. High-precision isotope determination was conducted by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) on the Thermo Scientific NEPTUNE Plus fitted with 1013Ω amplifiers which allow accurate and precise measurements at ion beams <0.51 V.Results Sub-nanogram Li samples (0.3-0.5 ng) were regularly separated (yielding Mg masses of 1-70 μg) using the presented column method. The total sample consumption during isotopic analysis is <0.5 ng Li and <115 ng Mg with long-term external 2σ precisions of ±0.39‰ for δ7Li and ±0.07‰ for δ26Mg. The results for geological reference standards and seawater analysed by our method are in excellent agreement with published values despite the order of magnitude lower sample consumption. Conclusions The possibility of eluting small sample masses and the low analytical sample consumption make this method ideal for samples of limited mass or low Li concentration, such as foraminifera, mineral separates or dilute river waters.
  •  
23.
  • Boström, Emma, et al. (author)
  • The Use of Liquid Chromatography/Mass Spectrometry for Quantitative Analysis of Oxycodone, Oxymorphone and Noroxycodone in Ringer Solution, Rat Plasma and Rat Brain Tissue
  • 2004
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 18:21, s. 2565-2576
  • Journal article (peer-reviewed)abstract
    • Sensitive and reproducible methods for the determination of oxycodone, oxymorphone and noroxycodone in Ringer solution, rat plasma and rat brain tissue by liquid chromatography/mass spectrometry are described. Deuterated analogs of the substances were used as internal standards. Samples in Ringer solution were analyzed by direct injection of 10 microL Ringer solution diluted by an equal volume of water. The limit of quantification was 0.5 ng/mL and the method was linear in the range of 0.5-150 ng/mL for all substances. To analyze oxycodone and oxymorphone in rat plasma, 50 microL of plasma were precipitated with acetonitrile, and the supernatant was directly injected onto the column. To analyze oxycodone, oxymorphone and noroxycodone in rat plasma, 100 microL of rat plasma were subjected to a C18 solid-phase extraction (SPE) procedure, before reconstituting in mobile phase and injection onto the column. For both methods the limit of quantification in rat plasma was 0.5 ng/mL and the methods were linear in the range of 0.5-250 ng/mL for all substances. To analyze the content of oxycodone, oxymorphone and noroxycodone in rat brain tissue, 100 microL of the brain homogenate supernatant were subjected to a C18 SPE procedure. The limit of quantification of oxycodone was 20 ng/g brain, and for oxymorphone and noroxycodone 4 ng/g brain, and the method was linear in the range of 20-1000 ng/g brain for oxycodone and 4-1000 ng/g brain for oxymorphone and noroxycodone. All methods utilized a mobile phase of 5 mM ammonium acetate in 45% acetonitrile, and a SB-CN column was used for separation. The total run time of all methods was 9 min. The intra-day precision and accuracy were <11.3% and <+/-14.9%, respectively, and the inter-day precision and accuracy were <14.9% and <+/-6.5%, respectively, for all the concentrations and matrices described.
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24.
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25.
  • Burman, Johan, 1966, et al. (author)
  • A simplified method of preparing phosphoric acid for stable isotope analyses of carbonates
  • 2005
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 19:21, s. 3086-3088
  • Journal article (peer-reviewed)abstract
    • In order to produce CO2 for stable isotope analyses (delta(18)O and delta(13)C), carbonate samples are commonly digested in phosphoric acid. The acid recipe here presented is based on phase shifting crystalline orthophosphoric acid of pro-analysis quality to a liquid state through heating, followed by pre-vacuum treatment during a start-up procedure before mass analyses for common acid bath preparation, or adding a small amount of phosphoric pentoxide for single drop equipments, respectively. This methodology results in a final acid concentration of 104%. Copyright (C) 2005 John Wiley & Sons, Ltd.
  •  
26.
  • Chartrand, Michelle, et al. (author)
  • Compound specific isotope analysis of hexachlorocyclohexane isomers : a method for source fingerprinting and field investigation of in situ biodegradation
  • 2015
  • In: Rapid Communications in Mass Spectrometry. - : John Wiley & Sons. - 0951-4198 .- 1097-0231. ; 29:6, s. 505-514
  • Journal article (peer-reviewed)abstract
    • RATIONALE: The manufacturing and uses of hexachlorocyclohexane (HCH) have resulted in a serious environmentalchallenge and legacy. This study highlights the ability of compound specific isotope analysis (CSIA) to distinguishamong various HCH sources and to support the evaluation of the potential for in situ biodegradation in contaminatedgroundwater.METHODS: Tests were conducted to verify the absence of significant isotope fractionation during HCH sample preconcentrationincluding dichloromethane extraction, solvent exchange into iso-octane, and H2SO4 clean-up, and analysisby gas chromatography/combustion-isotope ratio mass spectrometry (GC/C-IRMS). The method was then applied tofour Technical Grade (TG) HCH mixtures procured from different sources and to groundwater samples from acontaminated site.RESULTS: The pre-concentration method enabled determination of carbon isotope ratios (δ13C values) of HCH isomerswith no significant isotopic fractionation. The TG-HCH mixtures had significantly different δ13C values. Moreover, forany given TG-HCH, all isomers had δ13C values within 1.1‰ of each other – a distinctly uniform fingerprint. At theHCH-contaminated field site, compared with source wells, downgradient wells showed significant (up to 5.1‰)enrichment in 13C and the δ13C values of the HCH isomers were significantly different from each other.CONCLUSIONS: A method was successfully developed for the CSIA of HCH isomers that showed potential for HCHsource differentiation and identification of HCH in situ biodegradation. At the HCH-contaminated site, the observedpreferential isotopic enrichment of certain isomers relative to others for a given source allows differentiation betweenbiodegraded and non-biodegraded HCH.
  •  
27.
  • Conrotto, Paolo, et al. (author)
  • Lys Tag : an easy and robust chemical modification for improved de novo sequencing with a matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometer
  • 2008
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 22:12, s. 1823-33
  • Journal article (peer-reviewed)abstract
    • Mass spectrometry using a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) instrument is a widespread technique for various types of proteomic analysis. Along with an expanding interest in proteomics, there is a strong requirement for the identification of proteins with high confidence from biological samples. Peptide modification by a wide variety of post-translational modifications (PTMs), the existence of different protein isoforms and the presence of uncharacterized genomes of many species, make protein identification through peptide mass fingerprinting (PMF) often unachievable. Peptide de novo sequencing has been proven to be a useful approach to overcome these variables, and efficient derivatization processes are important tools to achieve this goal. In the present work we describe the methodology and experimental applications of a fast, efficient and cheap lysine derivatization. This chemical modification improves the signals from lysine-terminated peptides and can be efficiently used as a lysine-blocking agent in combination with other derivatization techniques. Most importantly, upon peptide fragmentation it generates a neat series of predominantly y-ions, allowing the determination of unambiguous amino acid sequences. Moreover, this chemical compound was used with target-eluted samples, enabling a second, alternative analysis of the same sample in the MALDI mass spectrometer.
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28.
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29.
  • Ebhardt, H Alexander, et al. (author)
  • Enzymatic generation of peptides flanked by basic amino acids to obtain MS/MS spectra with 2× sequence coverage
  • 2014
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 1097-0231 .- 0951-4198. ; 28:24, s. 43-2735
  • Journal article (peer-reviewed)abstract
    • RATIONALE: Tandem mass (MS/MS) spectra generated by collision-induced dissociation (CID) typically lack redundant peptide sequence information in the form of e.g. b- and y-ion series due to frequent use of sequence-specific endopeptidases cleaving C- or N-terminal to Arg or Lys residues.METHODS: Here we introduce arginyl-tRNA protein transferase (ATE, EC 2.3.2.8) for proteomics. ATE recognizes acidic amino acids or oxidized Cys at the N-terminus of a substrate peptide and conjugates an arginine from an aminoacylated tRNA(Arg) onto the N-terminus of the substrate peptide. This enzymatic reaction is carried out under physiological conditions and, in combination with Lys-C/Asp-N double digest, results in arginylated peptides with basic amino acids on both termini.RESULTS: We demonstrate that in vitro arginylation of peptides using yeast arginyl tRNA protein transferase 1 (yATE1) is a robust enzymatic reaction, specific to only modifying N-terminal acidic amino acids. Precursors originating from arginylated peptides generally have an increased protonation state compared with their non-arginylated forms. Furthermore, the product ion spectra of arginylated peptides show near complete 2× fragment ladders within the same MS/MS spectrum using commonly available electrospray ionization peptide fragmentation modes. Unexpectedly, arginylated peptides generate complete y- and c-ion series using electron transfer dissociation (ETD) despite having an internal proline residue.CONCLUSIONS: We introduce a rapid enzymatic method to generate peptides flanked on either terminus by basic amino acids, resulting in a rich, redundant MS/MS fragment pattern.
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30.
  • Ek, Patrik, et al. (author)
  • Electrospray Ionization from a Gap with Adjustable Width
  • 2006
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 20:21, s. 3176-3182
  • Journal article (peer-reviewed)abstract
    • In this paper, we present a new concept for electrospray ionization mass spectrometry, where the sample is applied in a gap which is formed between the edges of two triangular-shaped tips. The size of the spray orifice can be changed by varying the gap width. The tips were fabricated from polyethylene terephthalate film with a thickness of 36 μm. To improve the wetting of the gap and sample confinement, the edges of the tips forming the gap were hydrophilized by means of silicon dioxide deposition. Electrospray was performed with gap widths between 1 and 36 μm and flow rates down to 75 nL/min. The gap width could be adjusted in situ during the mass spectrometry experiments and nozzle clogging could be managed by simply widening the gap. Using angiotensin I as analyte, the signal-to-noise ratio increased as the gap width was decreased, and a shift towards higher charge states was observed. The detection limit for angiotensin I was in the low nM range.
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31.
  • Ek, Patrik, et al. (author)
  • Electrospray ionization mass spectrometry from discrete nanoliter-sized sample volumes
  • 2010
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 24:17, s. 2561-2568
  • Journal article (peer-reviewed)abstract
    • We describe a method for nanoelectrospray ionization mass spectrometry (nESI-MS) of very small sample volumes. Nanoliter-sized sample droplets were taken up by suction into a nanoelectrospray needle from a silicon microchip prior to ESI. To avoid a rapid evaporation of the small sample volumes, all manipulation steps were performed under a cover of fluorocarbon liquid. Sample volumes down to 1.5 nL were successfully analyzed, and an absolute limit of detection of 105 attomole of insulin (chain B, oxidized) was obtained. The open access to the sample droplets on the silicon chip provides the possibility to add reagents to the sample droplets and perform chemical reactions under an extended period of time. This was demonstrated in an example where we performed a tryptic digestion of cytochrome C in a nanoliter-sized sample volume for 2.5h, followed by monitoring the outcome of the reaction with nESI-MS. The technology was also utilized for tandem mass spectrometry (MS/MS) sequencing analysis of a 2 nL solution of angiotensin I.
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32.
  • Enebro, Jonas, et al. (author)
  • Improved matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of carboxymethyl cellulose
  • 2006
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 20:24, s. 3693-3698
  • Journal article (peer-reviewed)abstract
    • A refined sample preparation procedure for matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) was developed for the evaluation of the degree of substitution (DS) in partially depolymerised carboxymethyl cellulose (CMC). By adding ammonium sulphate to the sample mixture prior to the analysis, good quality mass spectra could be acquired. The usual time-consuming search for 'sweet-spots' at the crystalline rim of the MALDI target spot was also avoided. This quality improvement made it possible to investigate whether various positions on the target spot generated mass spectra in which the measured DS varied. The accuracy and reproducibility of the sample preparation procedure were tested by applying it on three commercial CMCs. The study shows that the DS values that were calculated from the spectra acquired from the centre region of the MALDI target spot were in better agreement with the DS provided by the supplier than were the values obtained from the large crystals at the target spot rim. This observation could be one reasonable explanation for the higher DS values reported in other publications. By applying our refined MALDI sample preparation procedure DS values that were in good agreement with the values provided by the manufacturer could be obtained. This indicates that MALDI-TOFMS of partially depolyrnerised CMCs can be used for an estimation of the DS as a complement to the more established methods, e.g. NMR, titrimetry, and chromatographic techniques.
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33.
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34.
  • Eriksson, Cecilia, et al. (author)
  • Time-of-flight secondary ion mass spectrometric analysis of the interface between bone and titanium implants.
  • 2008
  • In: Rapid communications in mass spectrometry : RCM. - : Wiley. - 0951-4198 .- 1097-0231. ; 22:7, s. 943-9
  • Journal article (peer-reviewed)abstract
    • Implant healing into bone tissue is a process where the mature bone grows towards and eventually fuses with the implant. In this study we investigated implant healing during 4 weeks with focus on the implant-tissue interface. Our main interest was to study the mineralization process around the implant. Titanium discs were implanted in rat tibia for 2 and 4 weeks. After implantation cross sections of bone and implant were made using a low-speed saw equipped with a diamond wafering blade. One section from each sample was stained with basic fuchsin and micrographed by light microscopy (LM). The other section was analyzed with imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) using a Bi(3)(+) cluster ion source. This ion source has recently been shown to enable identification of high-mass hydroxyapatite (HA) fragment ions (m/z 291-653) in bone samples. The LM images were used to identify areas suitable for TOF-SIMS analysis. Three areas were selected for mass spectral analysis, corresponding to interface region, bone and soft tissue, from which positive ion spectra were recorded. In the areas identified as bone, high-mass HA fragments ions were found after both 2 and 4 weeks. In the soft tissue area, no high-mass ions were found after 4 weeks. However, after 2 weeks HA-related ions were identified in mineralized spots in areas defined as soft tissue. After 4 but not after 2 weeks, high-mass HA fragment ions were found in the interface region. In conclusion, differences were observed regarding mineralization between 2 and 4 weeks of implantation and between different regions surrounding the implants. Imaging TOF-SIMS analysis using a Bi(3)(+) cluster as ion source enables identification of high-mass HA fragment ions at implant-tissue interfaces in bone. This technique might therefore be useful for biocompatibility assessment and for studying the mineralization process at implant surfaces.
  •  
35.
  • Fedorova, Ganna, et al. (author)
  • Comparison of the quantitative performance of a Q-Exactive high-resolution mass spectrometer with that of a triple quadrupole tandem mass spectrometer for the analysis of illicit drugs in wastewater
  • 2013
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 27:15, s. 1751-1762
  • Journal article (peer-reviewed)abstract
    • RATIONALE Analysis of drugs in wastewater is gaining more interest, as new approaches to estimate drug consumption from the amount of drug residues in wastewater have been proposed. The aim of this study was to compare the quantitative performance of high-resolution mass spectrometry with that of triple quadrupole mass spectrometry.METHODS A Q-Exactive mass spectrometer was operated in full scan (HRFS) (70 000 FWHM) and product scan (HRPS) (17 500 FWHM) modes. The first and third quadrupoles of the QqQ MS/MS instrument were operated at 0.7 FWHM. A mass-extracted window of 5ppm around the theoretical m/z of each analyte was used to construct chromatograms. An HESI-II ion source was used for the ionization of target compounds. In-line-SPE-LC configuration was used for the extraction and separation of target analytes.RESULTS All three methods showed good linearity and repeatability. High-resolution detection of product ions exhibited better sensitivity and selectivity for some compounds. For most of the tested compounds, LOQs ranged from 0.46 to 20ngL(-1). Good agreement between measured and nominal concentrations was observed for most of the compounds at different levels of fortification. Both MS/MS methods showed good selectivity, while HRFS gave some false positive results.CONCLUSIONS The Q-Exactive mass spectrometer proved to be suitable for trace detection and quantification of most of the tested drugs in wastewater, with performance comparable to that of the commonly used MS/MS triple quadrupole, but with better selectivity.Copyright (c) 2013 John Wiley & Sons, Ltd.
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36.
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37.
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38.
  • Fred, Charlotta, et al. (author)
  • Adducts to N-terminal valines in hemoglobin from isoprene di-epoxide, a metabolite of isoprene
  • 2004
  • In: Rapid Communications in Mass Spectrometry. - : John Wiley & Sons, Inc. - 0951-4198 .- 1097-0231. ; 18:18, s. 2177-2184
  • Journal article (peer-reviewed)abstract
    • Isoprene (2-methylbuta-1,3-diene) is a multi-site carcinogen in rodents. To evaluate the role of the diepoxide metabolite (1,2:3,4-diepoxy-2-methylbutane) in carcinogenesis, measurements of in vivo doses of the diepoxide are needed. The in vivo dose may be inferred from levels of reaction products with hemoglobin (Hb adducts). This report presents in vitro studies of the adduct formation by the diepoxide of isoprene with valinamide and oligopeptides as model compounds of N-terminal valines in hemoglobin (Hb). In the reaction with valinamide it was shown that isoprene diepoxide forms as the main product a ring-closed adduct, which is a pyrrolidine derivative [N,N-(2,3-dihydroxy-2-methyl-1,4-butadiyl)valinamide, MPyr-Val]. The analysis was performed by gas chromatography/mass spectrometry (GC/MS) (EI and PICI) after acetylation. The ring-closed adduct was also identified by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) as the main product in the reaction between isoprene diepoxide and standard hepta- or (2H8)octapeptides, corresponding to the N-terminal peptides of the α-chains in mouse and rat Hb. These peptides, alkylated with isoprene diepoxide, to be used as internal standards and calibration standards for quantification of MPyr-adduct levels in vitro and in vivo, were analyzed with respect to the degree of MPyr-alkylation by two independent methods, amino acid analysis and HPLC-UV; similar results were obtained using these methods. A method for measurement of Hb adducts as modified peptides, used earlier to measure a similar adduct to N-terminal valines in Hb from the diepoxide of 1,3-butadiene, has in the present work been tested for application to isoprene diepoxide. The method is based on tryptic degradation of globin and LC/ESI-MS analysis of N-terminal Pyr-heptapeptides of the Hb α-chain enriched by HPLC. MPyr-adduct levels in isoprene diepoxide alkylated hemolysate from mouse erythrocytes incubated with different concentrations of isoprene diepoxide (2 and 10 mM) for 1 h were quantified. The adduct level was about 50 nmol/g α-chain Hb per mM × h. From the adduct levels the rate constant of isoprene diepoxide for reaction with N-terminal valine was calculated to be about 1.6 times faster than for diepoxybutane
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39.
  • Glykou, Aikaterini, et al. (author)
  • Intra- and inter-tooth variation in strontium isotope ratios from prehistoric seals by laser ablation multi-collector inductively coupled plasma mass spectrometry
  • 2018
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 32, s. 1215-1224
  • Journal article (peer-reviewed)abstract
    • RationaleStrontium isotope ratios (87Sr/86Sr) in modern‐day marine environments are considered to be homogeneous (~0.7092). However, in the Baltic Sea, the Sr ratios are controlled by mixing seawater and continental drainage from major rivers discharging into the Baltic. This pilot study explores if variations in Sr can be detected in marine mammals from archaeological sites in the Baltic Sea.               Methods87Sr/86Sr ratios were measured in tooth enamel from three seal species by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS). The method enables micro‐sampling of solid materials. This is the first time that the method has been applied to marine samples from archaeological collections.               ResultsThe analyses showed inter‐tooth 87Sr/86Sr variation suggesting that different ratios can be detected in different regions of the Baltic Sea. Furthermore, the intra‐tooth variation suggests possible different geographic origin or seasonal movement of seals within different regions in the Baltic Sea through their lifetime.               ConclusionsThe method was successfully applied to archaeological marine samples showing that: (1) the 87Sr/86Sr ratio in marine environments is not uniform, (2) 87Sr/86Sr differences might reflect differences in ecology and life history of different seal species, and (3) archaeological mobility studies based on 87Sr/86Sr ratios in humans should therefore be evaluated together with diet reconstruction.
  •  
40.
  • Goloborodko, Anton A., et al. (author)
  • Empirical approach to false discovery rate estimation in shotgun proteomics
  • 2010
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 24:4, s. 454-462
  • Journal article (peer-reviewed)abstract
    • Estimation of false discovery rate (FDR) for identified peptides is an important step in large-scale proteomic studies. We introduced an empirical approach to the problem that is based on the FDR-like functions of sets of peptide spectral matches (PSMs). These functions have close values for equal-sized sets with the same FDR and depend monotonically on the FDR of a set. We have found three of them, based on three complementary sources of data: chromatography, mass spectrometry, and sequences of identified peptides. Using a calibration on a set of putative correct PSMs these functions were converted into the FDR scale. The approach was tested on a set of similar to 2800 PSMs obtained from rat kidney tissue. The estimates based on all three data sources were rather consistent with each other as well as with one made using the target-decoy strategy.
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41.
  • Goodwin, Richard JA, et al. (author)
  • The significance of ambient-temperature on pharmaceutical and endogenous compound abundance and distribution in tissues sections when analyzed by matrix-assisted laser desorption/ionization mass spectrometry imaging
  • 2012
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 26:5, s. 494-498
  • Journal article (peer-reviewed)abstract
    • RATIONALE: Mass spectrometry imaging has proven to be a complementary assay to the traditional labeled-compound studies employed in drug research and development. However, there has been limited examination of the technical limitations of the technique with respect to small molecule stability in samples. METHODS: Raclopride dosed rat brain tissue sections (single dose i.v. 2 mg/kg) were allowed to warm to room temperature for 0 to 5 min prior to either a solvent-based wet matrix-assisted laser desorption/ionization (MALDI) matrix or a solvent-free dry MALDI matrix being applied. Subsequent MS imaging analysis was at a spatial resolution of 200 mm, performed using a MALDI TOF/TOF (Ultraflex II, Bruker Daltonics). RESULTS: MALDI-MS has been used to monitor the time-dependent appearance and loss of small molecule abundance in tissue sections brought rapidly to room temperature for short periods of time. The abundances of a range of markers were seen to vary across the time course, both increasing and decreasing. The intensity of some markers changed significantly within 1 min. Importantly, the abundance of raclopride was seen to decrease over the 5-min time period examined. CONCLUSIONS: The results strongly indicate that considerable care is required to allow comparison of both pharmaceutical and endogenous compounds between MALDI-MSI experiments and also has implications for the standard practice of thaw-mounting multiple tissue sections onto MALDI-MS targets during MSI experiments.
  •  
42.
  •  
43.
  • Green, Henrik, et al. (author)
  • Measurement of paclitaxel and its metabolites in human plasma using liquid chromatography/ion trap mass spectrometry with a sonic spray ionization interface
  • 2006
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 1097-0231 .- 0951-4198. ; 20:14, s. 2183-2189
  • Journal article (peer-reviewed)abstract
    • A quantitative liquid chromatography/ion trap mass spectrometry method for the simultaneous determination of paclitaxel, 6α-hydroxypaclitaxel and p-3'-hydroxypaclitaxel in human plasma has been developed and validated. 6α-,p-3'-Dihydroxypaclitaxel was also quantified using paclitaxel as a reference and docetaxel as an internal standard. The substances were extracted from 0.500 mL plasma using solid-phase extraction. The elution was performed with acetonitrile and the samples were reconstituted in the mobile phase. Isocratic high-performance liquid chromatography analysis was performed by injecting 50 µL of reconstituted material onto a 100 × 3.00 mm C12 column with a methanol:1% trifluoroacetic acid/ammonium trifluoroacetate in H2O 70:30 mobile phase at 350 µL/min. The [M+H]+ ions generated in the sonic spray ionization interface were isolated and fragmented using two serial mass spectrometric methods: one for paclitaxel (transition 854 → 569 & 551) and the dihydroxymetabolite (transition 886 → 585 & 567) and one for the hydroxy metabolites (transition 870 → 585 & 567; transition 870 → 569 & 551) and docetaxel ([M+Na]+, transition 830 → 550). Calibration curves were created ranging between 0.5 and 7500 ng/mL for paclitaxel, 0.5 and 750 ng/mL for 6α-hydroxypaclitaxel, and 0.5 and 400 ng/mL for p-3'-hydroxypaclitaxel. Adduct ion formation was noted and investigated during method development and controlled by mobile phase optimization. In conclusion, a sensitive method for simultaneous quantification of paclitaxel and its metabolites suitable for analysis in clinical studies was obtained.
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44.
  •  
45.
  • Gupta, Anubha, et al. (author)
  • Quantitative determination of cetirizine enantiomers in guinea pig plasma, brain tissue and microdialysis samples using liquid chromatography/tandem mass spectrometry
  • 2005
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 19:12, s. 1749-1757
  • Journal article (peer-reviewed)abstract
    • Sensitive enantioselective liquid chromatographic assays using tandem mass spectrometric detection were developed and validated for the determination of S-cetirizine (S-CZE) and R-cetirizine (R-CZE) in guinea pig plasma, brain tissue, and microdialysis samples. Enantioselective separation was achieved on an alpha1-acid glycoprotein column within 14 min for all methods. A cetirizine analog, ucb 20028, was used as internal standard. Cetirizine and the internal standard were detected by multiple reaction monitoring using transitions m/z 389.1 --> 200.9 and 396.1 --> 276.1, respectively. The samples were prepared using protein precipitation with acetonitrile. For guinea pig plasma, the assay was linear over the range 0.25-5000 ng/mL for both S-CZE and R-CZE, with a lower limit of quantification (LLOQ) of 0.25 ng/mL. For the brain tissue and microdialysis samples, the assays were linear over the range 2.5-250 ng/g and 0.25-50 ng/mL, respectively, and the LLOQ values were 2.5 ng/g and 0.25 ng/mL, respectively. The intra- and inter-day precision values were < or =7.1% and < or =12.6%, respectively, and the intra- and inter-day accuracy varied by less than +/-8.0% and +/-6.0% of the nominal value, respectively, for both enantiomers in all the matrices investigated.
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46.
  • Göttlicher, Sabine (author)
  • Preparation of starch and soluble sugars of plant material for the analysis of carbon isotope composition: a comparison of methods
  • 2009
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 23, s. 2476-2488
  • Journal article (peer-reviewed)abstract
    • Starch and soluble sugars are the major photosynthetic products, and their carbon isotope signatures reflect external versus internal limitations of CO(2) fixation. There has been recent renewed interest in the isotope composition of carbohydrates, mainly for use in CO(2) flux partitioning studies at the ecosystem level. The major obstacle to the use of carbohydrates in such studies has been the lack of an acknowledged method to isolate starch and soluble sugars for isotopic measurements. We here report on the comparison and evaluation of existing methods (acid and enzymatic hydrolysis for starch; ion-exchange purification and compound-specific analysis for sugars). The selectivity and reproducibility of the methods were tested using three approaches: (i) an artificial leaf composed of a mixture of isotopically defined compounds, (ii) a C(4) leaf spiked with C(3) starch, and (iii) two natural plant samples (root, leaf). Starch preparation methods based on enzymatic or acid hydrolysis did not yield similar results and exhibited contaminations by non-starch compounds. The specificity of the acidic hydrolysis method was especially low, and we therefore suggest terming these preparations as HCl-hydrolysable carbon, rather than starch. Despite being more specific, enzyme-based methods to isolate starch also need to be further optimized to increase specificity. The analysis of sugars by ion-exchange methods (bulk preparations) was fast but produced more variable isotope compositions than compound-specific methods. Compound-specific approaches did not in all cases correctly reproduce the target values, mainly due to unsatisfactory separation of sugars and background contamination. Our study demonstrates that, despite their wide application, methods for the preparation of starch and soluble sugars for the analysis of carbon isotope composition are not (yet) reliable enough to be routinely applied and further research is urgently needed to resolve the identified problems. Copyright (C) 2009 John Wiley & Sons, Ltd.
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47.
  • Hansson, Annelie, et al. (author)
  • Investigation of the selective androgen receptor modulators S1, S4 and S22 and their metabolites in equine plasma using high-resolution mass spectrometry
  • 2016
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 30:7, s. 833-842
  • Journal article (peer-reviewed)abstract
    • RationaleSelective androgen receptor modulators (SARMs) are prohibited in sports due to their performance enhancing ability. It is important to investigate the metabolism to determine appropriate targets for doping control. This is the first study where the equine metabolites of SARMs S1, S4 (Andarine) and S22 (Ostarine) have been studied in plasma. MethodsEach SARM was administered to three horses as an intravenous bolus dose and plasma samples were collected. The samples were pretreated with protein precipitation using cold acetonitrile before separation by liquid chromatography. The mass spectrometric analysis was performed using negative electrospray, quadrupole time-of-flight mass spectrometry operated in MSE mode and triple-quadrupole mass spectrometry operated in selected reaction monitoring mode. For the quantification of SARM S1, a deuterated analogue was used as internal standard. ResultsThe numbers of observed metabolites were eight, nine and four for the SARMs S1, S4 and S22, respectively. The major metabolite was formed by the same metabolic reactions for all three SARMs, namely amide hydrolysis, hydroxylation and sulfonation. The values of the determined maximum plasma concentrations were in the range of 97-170 ng/mL for SARM S1, 95-115 ng/mL for SARM S4 and 92-147 ng/mL for SARM S22 and the compounds could be detected for 96 h, 12 h and 18 h, respectively. ConclusionsThe maximum plasma concentration of SARMs S1, S4 and S22 was measured in the first sample (5 min) after administration and they were eliminated fast from plasma. The proposed targets to be used in equine doping control are the parent compounds for all three SARMs, but with the metabolite yielding the highest response as a complementary target. 
  •  
48.
  • Heim, C, et al. (author)
  • Spectral characterisation of eight glycerolipid standards and detection in natural samples using time-of-flight secondary iion mass spectrometry
  • 2009
  • In: Rapid Communications in Mass Spectrometry. - 0951-4198 .- 1097-0231. ; 23:17, s. 2741-2753
  • Journal article (peer-reviewed)abstract
    • In recent years, time-of-flight secondary ion mass spectrometry (ToF-SIMS) with cluster ion sources has opened new perspectives for the analysis of lipid biomarkers in geobiology and organic geochemistry. However, published ToF-SIMS reference spectra of relevant compounds are still sparse, and the influence of the chemical environment (matrix) on the ionisation of molecules and their fragmentation is still not well explored. This study presents ToF-SIMS spectra of eight glycerolipids as common target compounds in biomarker studies, namely ester- and ether-bound phosphatidylethanolamine, ester- and ether-bound phosphatidylcholine, ester-bound phosphatidylcholine, ester- and ether-bound diglycerides and archaeol, obtained with a Bi 3 + cluster ion source. For all of these compounds, the spectra obtained in positive and negative analytical modes showed characteristic fragments that could clearly be assigned to e.g. molecular ions, functional groups and alkyl chains. By comparison with the reference spectra, it was possible to track some of these lipids in a pre-characterised organic extract and in cryosections of microbial mats. The results highlight the potential of ToF-SIMS for the laterally resolved analysis of organic biomarkers in environmental materials. The identification of the target compounds, however, may be hampered by matrix effects (e.g. adduct formation) and often require careful consideration of all spectral features and taking advantage of the molecular imaging capability of ToF-SIMS.
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49.
  •  
50.
  • Hellman, Ulf, et al. (author)
  • Easy amino acid sequencing of sulfonated peptides using post-source decay on a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer equipped with a variable voltage reflector
  • 2002
  • In: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 16:19, s. 1851-1859
  • Journal article (peer-reviewed)abstract
    • Tryptic peptides were labeled with sulfonic acid groups at the N-termini using an improved chemistry. The derivatization was performed in common aqueous buffers on peptides adsorbed onto a ZipTip trade mark C(18), thus allowing simultaneous desalting/concentration of the sample. When only Arg-terminating peptides were considered, the procedure from adsorption onto the ZipTip until analysis by MALDI-PSD took about 10 min and several samples could be worked on in parallel. The resulting improved post-source decay (PSD) fragmentation produced spectra containing only y-ions. PSD amino acid sequencing of underivatized and derivatized synthetic peptides was compared. From the sequence information obtained from derivatized peptides isolated by ion selection from tryptic in-gel digests, a protein was correctly identified which was difficult to analyze from an unclear peptide mass fingerprint analysis. The method was also applied to the identification and localization of phosphorylated Ser and Tyr residues in native and synthetic peptides.
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