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| 4. |
- Arshadi, Mehrdad, et al.
(författare)
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Gas chromatography-mass spectrometry determination of the pentafluorobenzoyl derivative of methylhydrazine in false morel (Gyromitra esculenta) as a monitor for the content of the toxin gyromitrin
- 2006
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1125:2, s. 229-233
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Tidskriftsartikel (refereegranskat)abstract
- The main toxic compound found in false morel (Gyromitra esculenta) is acetaldehyde-N-methyl-N-formylhydrazone (gyromitrin). This paper describes a method of determining the total hydrazones content based on acid hydrolysis of gyromitrin and other related hydrazones in air-dried false morel followed by derivatisation of methylhydrazine with pentafluorobenzoyl chloride. The derivative, tris-pentafluorobenzoyl methylhydrazine (tris-PFB-MH) is analyzed by gas chromatography–mass spectrometry. The overall precision of the method is better than 10% (relative standard deviation) for 0.5 ng/μl methylhydrazine in solution. The minimum detectable concentration of methylhydrazine (tris-PFB-MH) by this method is estimated to be approximately 12 pg/μl, which is equal to 0.3 μg/g dry matter (DM) of false morel.
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- Bouchet, Sylvain, et al.
(författare)
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Analytical developments for the determination of monomethylmercury complexes with low molecular mass thiols by reverse phase liquid chromatography hyphenated to inductively coupled plasma mass spectrometry
- 2014
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1339, s. 50-58
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of monomethylmercury (MMHg) is markedly influenced by its distribution among complexes with low molecular mass (LMM) thiols but analytical methodologies dedicated to measure such complexes are very scarce up to date. In this work, we selected 15 LMM thiols often encountered in living organisms and/or in the environment and evaluated the separation of the 15 corresponding MMHg-thiol complexes by various high performance liquid chromatography (HPLC) columns. Two C18 (Phenomenex Synergi Hydro-RP and LunaC18(2)), two phenyl (Inertsil Ph 3 and 5 mu m) and one mixed-mode (Restek Ultra IBD) stationary phases were tested for their retention and resolution capacities of the various complexes. The objective was to find simple separation conditions with low organic contents in the mobile phase to provide optimal conditions for detection by inductively coupled plasma mass spectrometry (ICPMS). The 15 complexes were synthesized in solution and characterized by electrospray ionization-mass spectrometry (ESI-MS). The C18 columns tested were either not resolutive enough or too retentive. The 3 pm phenyl stationary phase was able to resolve 10 out of the 15 complexes in less than 25 min, under isocratic conditions. The mixed-mode column was especially effective at separating the most hydrophilic complexes (6 complexes out of the 15), corresponding to the main LMM thiols found in living organisms. The detection limits (DLs) for these two columns were in the low nanomolar range and overall slightly better for the phenyl column. The possibilities offered by such methodology were exemplified by monitoring the time-course concentrations of four MMHg-thiol complexes within a phytoplankton incubation containing MMHg in the presence of an excess of four added thiols.
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- Courtois, Julien, et al.
(författare)
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Molecularly imprinted polymers grafted to flow through poly(trimethylolpropane trimethacrylate) monoliths for capillary-based solid-phase extraction
- 2006
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1109:1, s. 92-99
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Tidskriftsartikel (refereegranskat)abstract
- Monolithic previous termmolecularly imprinted polymersnext term (mMIPs) have been synthesized in a novel way using a trimethylolpropane trimethacrylate core material photo-polymerized in situ in a 100 μm I.D. UV-transparent capillary and further photo-previous termgraftednext term to create specific cavities in the previous termgraftednext term layer. This polymerization technique allows the imprints to be directly created on the surface of the material using a minimum amount of template. Three different anaesthetics of similar structures (bupivacaine, mepivacaine and S-ropivacaine) were used as model target molecules to synthesize sample enrichment media. Hence, various mMIPs have been prepared and evaluated on a micro-system against each analyte in order to test the retention properties and cross-selectivities of the materials. The retention factors were determined and compared with the non-previous termimprintednext term reference column (mNIP), yielding high imprinting factors together with good selectivity factors between the three analytes. A study with a pure enantiomeric target was carried out to assess the degree of stereo-specific imprinting for injection of racemic mixtures. Finally, one column was previous termimprintednext term with an equimolar mixture of all three anaesthetics to provide further comprehension of the retention mechanism and accredit the possibility of using the material as a sample enrichment entity. Scanning electron microscopy (SEM), nitrogen absorption/desorption (BET) and mercury intrusion porosimetry were used to characterize the monolith and the mMIPs properties. Nuclear magnetic resonance (NMR) has been used to assess the similarities between the mMIP and mNIP.
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- Danielsson, Conny, et al.
(författare)
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Trace analysis of polychlorinated dibenzo-p-dioxins, dibenzofurans and WHO polychlorinated biphenyls in food using comprehensive two-dimensional gas chromatography with electron-capture detection
- 2005
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1086:1-2, s. 61-70
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Tidskriftsartikel (refereegranskat)abstract
- Trace analysis of 2,3,7,8-polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and the 12 WHO-PCBs (four non-ortho and eight mono-ortho congeners that have been assigned toxic equivalence factors, TEFs, by the World Health Organisation) was conducted by comprehensive two-dimensional gas chromatography with a micro electron-capture detector (GC x GC-mu ECD). Four food matrices (fish oil from herring, spiked cows' milk, vegetable oil and an eel extract) were analysed by two GC x GC laboratories, and four GC-HRMS laboratories generated reference values. The two GC x GC laboratories used different column combinations for separating the target analytes. For the first dimension, non-polar DB-XLB and VF-1 columns were used, and for the second dimension, an LC-50 liquid crystalline column with unique selectivity for planar compounds. The congener-specific and total toxic equivalence (TEQ) data obtained using DB-XLB x LC-50 were in good agreement with results obtained by the GC-HRMS laboratories. The WHO-PCB data obtained with the VF-1 x LC-50 combination was also good, but the PCDD/F concentrations were sometimes overestimated due to matrix interferences. GC x GC-mu ECD using DB-XLB x LC-50 seems to fulfil the European Community requirements of a screening method for PCDD/F and WHO-PCB TEQ in food.
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- Dinh, Ngoc Phuoc, et al.
(författare)
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Probing the interaction mode in hydrophilic interaction chromatography
- 2011
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1218:35, s. 5880-5891
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Tidskriftsartikel (refereegranskat)abstract
- This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. "Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole, π-π interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar.
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| 9. |
- Dinh, Ngoc Phuoc, 1985-, et al.
(författare)
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Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1320, s. 33-47
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In hydrophilic interaction chromatography, water is known to accumulate on the stationary phase to form a water enriched layer, which is believed to play an important role in the retention mechanism. To gain a better understanding retention mechanism in HILIC, we have determined the water uptake on twelve different HILIC stationary phases. Non-modified and monomerically functionalized silica phases followed a pattern of monolayer formation followed by multiple layer adsorption, while the water uptake on polymerically functionalized silica stationary phase showed the characteristics of formation and swelling of hydrogels. This difference in the nature of water accumulation was found to be related to different water uptake patterns when methanol and tetrahydrofuran were added to 80:20 % (v/v) acetonitrile/water by replacing 5 % of the acetonitrile as tertiary solvents, and also when ammonium acetate was added as buffering electrolyte. The relationship between water uptake and retention mechanism was investigated by looking at the correlation between retention factors of neutral analytes and phase ratios of HILIC columns, calculated either as surface area (adsorption) or volume of the water layer enriched from the acetonitrile/water eluent (partitioning). Regardless of the adsorption or partitioning mechanism, the interaction of neutral analytes and stationary phase could be mainly the hydrogen bonding between analytes and the accumulated water in the water enriched layer.
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| 10. |
- Do, Lan, et al.
(författare)
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Comprehensive profiling of 136 tetra- to octa-polychlorinated dibenzo-p-dioxins and dibenzofurans using ionic liquid columns and column combinations
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1311, s. 157-169
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Tidskriftsartikel (refereegranskat)abstract
- The orders of elution of all 136 tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were determined on six gas chromatography (GC) columns. Three of these columns had ionic liquid stationary phases (SLB-IL111, SLB-IL76 and SLB-IL61; Supelco), one a liquid crystal phase (LC-50; Restek), one a chiral phase (beta DEXcst; Restek) and one a low bleed non-polar phase (DB-XLB; J&W/Agilent). According to our results, the high polarity and multiple solvation interactions of the ionic liquid stationary phases offered superior resolving power to that achieved with previously evaluated columns. The SLB-IL61 and SLB-IL111 columns resolved or partially separated 106 and 100 congeners, respectively, of the 136 PCDD/Fs. The SLB-IL61 also resolved 15 and partially separated one of the seventeen 2,3,7,8-substituted PCDD/Fs. Additional congeners can be separated by complementary analyses using additional columns in a dual- or triple-column approach. For example, using a combination of the SLB-IL61 and SLB-IL111 columns all but 8 congeners would be separated, including all 2,3,7,8-substituted PCDD/Fs. Two more congeners would be separated using a combination of SLB-IL76 and a liquid crystal (SB-Smectic) column, but in this case the 2,3,7,8-TeCDF would not be resolved. Three-column combinations would give even better separation: the DB-17/Smectic/SLB-IL76 and DB-225/Smectic/SLB-IL111 combinations would separate all but 1 of the 136 PCDD/F congeners. Unfortunately, the smectic column is no longer in production. If only commercially available columns are considered, combinations of SLB-IL61 and SLB-IL111 with DB-XLB, LC-50, or DB-225 offer the best performance, with 4, 4, and 3 unresolved congeners, respectively. Moreover, in each of these cases, one of the congeners in each unresolved pair is resolved on at least one of the other columns and so a reasonable estimate of the unresolved congeners' concentrations can be obtained by subtraction. The profiling of all 136 PCDD/Fs is thus greatly facilitated by using ionic liquid columns or combinations including such columns. However, there is room for improvement in the technical performance of the evaluated ionic liquid columns: their long-term retention time stability was poor and some highly chlorinated and sterically hindered congeners underwent dehalogenation during separation.(C) 2013 Elsevier B.V. All rights reserved.
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