| 1. |
- Bergström, Sara K., et al.
(författare)
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A simplified multidimensional approach for analysis of complex biological samples : on-line LC-CE-MS
- 2006
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 131:7, s. 791-798
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Tidskriftsartikel (refereegranskat)abstract
- Information on protein expression, disease biomarkers or surrogate markers and genetic disorders can nowadays be achieved from analysis of complex biological samples by liquid separation coupled to mass spectrometric (MS) detection. This paper describes fast multidimensional separation by on-line liquid chromatography (LC) and capillary electrophoresis (CE), followed by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) MS detection. This detector provides ultrahigh resolution of the detected ions, mass accuracy at the ppm-level and high sensitivity. Most of the challenge of this system lies in the development of a new interface for the on-line coupling of LC to CE. The interface developed in poly(dimethylsiloxane) provides a RSD for injection repeatability of <3.5% and surface control for unspecific binding by deactivation with a cationic polymer, PolyE-323. We have evaluated the interface, as well as the overall system, with respect to robustness and deconvolution ability. Sequence coverage for bovine serum albumin (BSA) of 93% showed a high recovery of sample in the different transfer steps through the system. The detection limit for identification is 277 ng mL−1 (or 280 nM) on average for peptides. In the future, we expect LC-CE-MS to be a novel strategy for elucidating the chemistry of biological matrices.
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| 2. |
- Candefjord, Stefan, et al.
(författare)
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Effects of snap-freezing and near-infrared laser illumination on porcine prostate tissue as measured by Raman spectroscopy
- 2009
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 134:9, s. 1815-1821
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Tidskriftsartikel (refereegranskat)abstract
- Most Raman spectroscopic studies on tissue are performed in vitro. To assure that the results are applicable to in vivo examinations, preparation protocols and measurement procedures of tissue for in vitro studies should preserve tissue characteristics close to the native state. This study had two aims. The first was to elucidate if photoinduced effects arise during 5 minutes' continuous illumination of tissue with an 830 nm laser at an irradiance of 3 × 1010 W/m2. The second was to investigate the effects of snap-freezing of porcine prostate tissue in liquid nitrogen and subsequent storage at -80 °C, by means of multivariate analysis. 830 nm laser illumination of the specified irradiance did not affect the Raman spectra. A decrease of the spectral background was observed, likely due to photobleaching of tissue fluorophores. Snap-freezing and subsequent storage at -80 °C gave rise to subtle but significant alterations in Raman spectra, most likely related to changes in the protein conformations
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| 3. |
- Edvardsson, Malin, 1973, et al.
(författare)
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Investigation of binding event perturbations caused by elevated QCM-D oscillation amplitude
- 2006
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Ingår i: Analyst. - : Royal Society of Chemistry (RSC). - 1364-5528. ; 131:7, s. 822-828
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Tidskriftsartikel (refereegranskat)abstract
- We report measurements with the quartz crystal microbalance with dissipation monitoring (QCM-D) technique, with focus on how the shear oscillation amplitude of the sensor surface influences biorecognition binding events. Technically, this is made as reported recently ( M. Edvardsson, M. Rodahl, B. Kasemo, F. Hook, Anal. Chem., 2005, 77( 15), 4918-4926) by operating the QCM in dual frequency mode; one harmonic (n = n(1)) is utilized for continuous excitation of the QCM-D sensor at resonance at variable driving amplitudes (1-10 V), while the second harmonic (n not equal n(1)) is used for combined f and D measurements. By using one harmonic as a "probe" and the other one as an "actuator", elevated amplitudes can be used to perturb - or activate - binding reactions in a controlled way, while simultaneously maintaining the possibility of probing the adsorption and/or desorption events in a non-perturbative manner using combined f and D measurements. In this work we investigate the influence of oscillation amplitude variations on the binding of NeutrAvidin-modified polystyrene beads (O similar to 200 nm) to a planar biotin-modified lipid bilayer supported on an SiO2-modified QCM-D sensor. These results are further compared with data on an identical system, except that the NeutrAvidin-biotin recognition was replaced by fully complementary DNA hybridization. Supported by micrographs of the binding pattern, the results demonstrate that there exists, for both systems, a unique critical oscillation amplitude, A(c), below which binding is unaffected by the oscillation, and above which binding is efficiently prevented. Associated with A(c), there is a critical crystal radius, r(c), defining the central part of the crystal where binding is prevented. From QCM-D data, A(c) for the present system was estimated to be similar to 6.5 nm, yielding a value of r(c) of similar to 3 mm - the latter number was nicely confirmed by fluorescent- and dark-field micrographs of the crystal. Furthermore, the fact that A(c) is observed to be identical for the two types of biorecognition reactions suggests that it is neither the strength, nor the number of contact points, that determine the amplitude at which binding is prevented. Rather, particle size seems to be the determining parameter.
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| 4. |
- Filippini, Daniel, 1968-, et al.
(författare)
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Effect of fingerprint conformation and spectral scaling on the performance of computer screen photo-assisted experiments
- 2006
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 131:1, s. 118-125
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Tidskriftsartikel (refereegranskat)abstract
- The use of computer screens as controlled light sources and web cameras as image detectors (the so-called computer screen photo-assisted technique, CSPT) is an ubiquitous alternative for the evaluation of colorimetric quick tests at homes or in primary care units. The performance of CSPT for such evaluations depends on several factors, from which the most relevant are the composition of illuminating sequences and the conformation of CSPT substance signatures. In this work, with the aid of a CSPT model, the effect of the construction of the substance signatures on the classification performance of different representative substance sets is studied. The correlation of illuminating colors with such classification is investigated, allowing one to determine redundancy and limitations with respect to visible spectroscopy. The concept of spectral scaling is introduced and its properties compared with standard procedures. © The Royal Society of Chemistry 2006.
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| 5. |
- Filippini, Daniel, 1968-, et al.
(författare)
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Measurement strategy and instrumental performance of a computer screen photo-assisted technique for the evaluation of a multi-parameter colorimetric test strip
- 2006
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 131:1, s. 111-117
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Tidskriftsartikel (refereegranskat)abstract
- A measuring strategy for the evaluation of a seven parameters colorimetric test using a computer screen photo-assisted technique (CSPT) is demonstrated. CSPT is a versatile approach aimed at point of care or home tests that uses regular computer sets and web cameras as the whole instrument. Issues such as the stability and the equivalency on different platforms of the determinations have been addressed in the present work. The method uses an embedded local reference simultaneously measured with the tests and solves the evaluation as a classification problem. The achieved performance tested along 580 classifications covering all the ranges of the assay, using synthetic samples, yielded 97.2% correct determinations compared with 89.7% for the case of colorimetric determinations. The errors were concentrated in only two parameters that show a significant correlation with a set of quality indices used to assess the performance of the classification. © The Royal Society of Chemistry 2006.
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| 6. |
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| 7. |
- Isetun, Sindra, et al.
(författare)
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Dynamic field sampling of airborne organophosphate triesters using solid-phase microextraction under equilibrium and non-equilibrium conditions
- 2005
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Ingår i: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 30, s. 94-98
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Tidskriftsartikel (refereegranskat)abstract
- A simple setup for dynamic air sampling using a solid-phase microextraction (SPME) device designed for use in the field was evaluated for organophosphate triester vapour under both equilibrium and non-equilibrium conditions. The effects of varying the applied airflows in the sampling device were evaluated in order to optimise the system with respect to the Reynolds number and magnitude of the boundary layer that developed near the surface. Further, the storage stability of the analytes was studied for both capped and uncapped 100- m m PDMS fibres. Organophosphate triesters are utilized on large scales as flame-retardants and/or plasticizers, for instance in upholstered furniture. In indoor working environments these compounds have become common components in the surrounding air. Measurements were performed in a recently furnished working environment and the concentration of tris(2-choropropyl) phosphate was found to be 7 mg m23 .
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| 8. |
- Jonsson, Pär, et al.
(författare)
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Extraction, interpretation and validation of information for comparing samples in metabolic LC/MS data sets
- 2005
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 130:5, s. 701-707
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- LC/MS is an analytical technique that, due to its high sensitivity, has become increasingly popular for the generation of metabolic signatures in biological samples and for the building of metabolic data bases. However, to be able to create robust and interpretable ( transparent) multivariate models for the comparison of many samples, the data must fulfil certain specific criteria: (i) that each sample is characterized by the same number of variables, (ii) that each of these variables is represented across all observations, and (iii) that a variable in one sample has the same biological meaning or represents the same metabolite in all other samples. In addition, the obtained models must have the ability to make predictions of, e. g. related and independent samples characterized accordingly to the model samples. This method involves the construction of a representative data set, including automatic peak detection, alignment, setting of retention time windows, summing in the chromatographic dimension and data compression by means of alternating regression, where the relevant metabolic variation is retained for further modelling using multivariate analysis. This approach has the advantage of allowing the comparison of large numbers of samples based on their LC/MS metabolic profiles, but also of creating a means for the interpretation of the investigated biological system. This includes finding relevant systematic patterns among samples, identifying influential variables, verifying the findings in the raw data, and finally using the models for predictions. The presented strategy was here applied to a population study using urine samples from two cohorts, Shanxi (People's Republic of China) and Honolulu ( USA). The results showed that the evaluation of the extracted information data using partial least square discriminant analysis (PLS-DA) provided a robust, predictive and transparent model for the metabolic differences between the two populations. The presented findings suggest that this is a general approach for data handling, analysis, and evaluation of large metabolic LC/MS data sets.
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| 9. |
- Kjeldsen, Frank, et al.
(författare)
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On studying protein phosphorylation patterns using bottom-up LC-MS/MS : the case of human alpha-casein
- 2007
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 132:8, s. 768-776
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Tidskriftsartikel (refereegranskat)abstract
- Most proteomics studies involving mapping post-translational modifications, such as the phosphorylation of serine and threonine, are performed today using the 'bottom-up' approach. This approach involves enzymatic cleavage of proteins, most often by trypsin, with subsequent nano-LC-MS/MS. The occupancy rates of phosphosites in proteins may differ by orders of magnitude, and thus the occupancy rate must be reported for each occupied phosphosite. To highlight potential pitfalls in quantifying the occupancy rates, αs1- casein from human milk was selected as a model molecule representing moderately phosphorylated proteins. For this purpose, human milk from one Caucasian woman in the eighth month of lactation was used. The phosphorylation level of caseins is believed to have major implications for the formation of micelles that are involved in delivering valuable calcium phosphate and other minerals to the new-born. Human αs1-casein has been reported to be much less phosphorylated than ruminant caseins, which may indicate a different function of caseins in humans. Revealing the phosphorylation pattern in human casein can thus shed light on its function. The current study found that the sequence region between the residues Ser70 and Ser76 in human αs1-casein is in fact phosphorylated, contrary to previous knowledge. The site of the most abundant phosphorylation is Ser75, in agreement with the known action of the mammary gland casein kinase. There is evidence for the second phosphorylation in that region, possibly at Ser73. Earlier reported positions of phosphorylations at Ser18 and Ser26 are also confirmed, but not the dominance of Ser18 phosphorylation. The occupancy rates at Ser18, Ser26 and Ser75 are estimated to be (7 ± 2), (20 ± 6) and (27 ± 9)%, respectively. Owing to differences in the ionization efficiency between phosphorylated and unphosphorylated peptides a 30% error margin is added to the occupancy rates. The highlighted pitfalls of the bottom-up strategy include the sensitivity of enzymes to proximal acidic and phosphorylated residues and the presence of multiple isoforms, including unexpected ones, of the tryptic peptides. The utility of the earlier introduced PhosTS_hunter and ModifiComb approaches for evading the latter pitfall is demonstrated.
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| 10. |
- Larsson, Tom, et al.
(författare)
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Studies of transport and collection characteristics of gaseous mercury in natural gases using amalgamation and isotope dilution analysis
- 2007
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Ingår i: The Analyst. - : RSC Publishing. - 0003-2654 .- 1364-5528. ; 132:6, s. 579-586
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Tidskriftsartikel (refereegranskat)abstract
- Transport and collection characteristics were studied for gaseous elemental mercury (Hg0(g)) in natural gases using newly developed methodology based on amalgamation, isotope dilution with permeation tubes and inductively coupled plasma mass spectrometry. The study involved different Au–Pt collection tube designs, tubing materials and gaseous matrices, including air, natural and sales gas, as well as methane and sales gas to which hydrogen sulfide (H2S) had been added. The Hg0(g) capacity of the Au–Pt tubes was determined to 3.5 ± 0.1 µg. Blanks and detection limits of gaseous mercury (Hg(g)) were 58 ± 17 pg m–3 and 50 pg m–3, respectively, for a 60 L sample volume. For the gases tested, added Hg0(g) tracers could be collected with 90% or higher efficiency at flow rates and volumes of up to 10 L min–1 and 100 L, respectively. The collection efficiency was found to be independent of the type of gas tested, even in the presence of H2S. However, for the gases containing H2S, the apparent transport efficiency of added Hg0(g) tracers through stainless steel tubing varied from 50 to 150% upon changing the temperature from 25 to 100 °C. The interaction of stainless steel with Hg0(g) leading to either a sink, or source of Hg, was not observed in the absence of H2S, nor was it observed for PTFE tubing in the presence of H2S. These observations raise questions about the applicability of currently used sampling procedures for determination of Hg(g) in H2S rich natural gases, including the 6978-2 ISO standard method, in which stainless steel is a prescribed material for tubing and valves of the sampling apparatus.
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