Christophe Devos

Cellular energy allocation in the estuarine mysid shrimp Neomysis integer (Crustacea: Mysidacea) following tributyltin exposure

Recently, we described the cellular energy allocation (CEA) methodology to asses the effects of abiotic stress on the energy metabolism of the estuarine crustacean Neomysis integer (Crustacea: Mysidacea) [J. Exp. Mar. Biol. Ecol. 279 (2002) 61]. This short-term assay is based on the biochemical assessment of changes in the energy reserves (total carbohydrate, protein and lipid content) and the energy consumption (electron transport activity), and has been shown to be predictive of effects at the population level in daphnids [J. Aquat. Ecosyst. Stress Recovery 6 (1997) 43]. In the present study, the CEA methodology was evaluated using adult N. integer exposed for 96 h to the antifoulant tributyltinchloride (TBTCl). From a range-finding experiment with juvenile N. integer, a 96-h LC50 of 164 ng TBTCl/l was calculated. The energy metabolism of N. integer, as summarized by the CEA, was significantly altered by TBTCl exposure. Mysids exposed to 10, 100 and 1000 ng TBTCl/l consumed less energy and had lower respiration rates (in 10 and 1000 ng TBTCl/l treatments) than the control, resulting in a lower CEA. These changes at the cellular level occurred at environmentally relevant concentrations of the toxicant TBTCl which were an order of magnitude lower than reported effect concentrations for scope for growth in other marine invertebrates.

Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICPMS) for the enantiomeric analysis of d,l-selenomethionine in food supplements and urine

Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICPMS) was applied to the determination of D- and L-selenomethionine in food supplements and in urine. Derivatization was performed with ethylchloroformate (ECF) offering the advantage that the reaction can be carried out in aqueous medium i.e. urine. The derivatives were separated on the chiral stationary phase (CSP) Chiralsil-L-Val. The method was validated with D- and L-seleno-ethionine as internal standard (IS) and the linearity for a seven point calibration from 12.5 pg to 2.5 ng per enantiomer was excellent (R(2) 0.9997). Repeatability of injection (n=3) was <1.8%. The limit of detection (LOD) and quantification (LOQ) were 4 and 12 pg, respectively. Food supplements presently on the market contain L-selenomethionine for at least 90%. Repeatability of the whole procedure (n=6) was tested on one L-selenomethionine formulation and was 3.8 (R.S.D.%). Data for urine samples after a daily intake of L-selenomethionine or the racemate D,L-selenomethionine corresponding to 100 microg selenium indicate that the D-enantiomer is not metabolized.

Improved accuracy in the determination of polycyclic aromatic hydrocarbons in air using 24 h sampling on a mixed bed followed by thermal desorption capillary gas chromatography–mass spectrometry

A new sampling method for the determination of polycyclic aromatic hydrocarbons (PAHs) in ambient air is described. The method is based on active sampling on sorption tubes consisting of polydimethylsiloxane (PDMS) foam, PDMS particles and a TENAX TA bed. After sampling, the solutes are quantitatively recovered by thermal desorption and analysed by capillary GC-MS. The new sampling method has been compared to the classical method using high-volume sampling on a glass fiber filter followed by polyurethane foam for 24h sampling of ambient air. Volumes enriched were 144 l on the mixed bed and 1296 m3 with the classical method. The concentrations measured using the new method were significantly higher that the values obtained using the classical method, i.e. a factor 1.2-3 for the high molecular weight PAHs and up to 35 times for naphthalene and 23 times for acenaphthene. The total toxicity equivalence value (TEQ) for PAHs was ca. two times higher compared to the conventional method, illustrating that the concentrations of PAHs in ambient air have been underestimated until now. Some figures of merit (mean value for 17 PAHs) of the method are repeatability 7.4%, detection limit 13 pg/m3, accuracy 105.6% and linearity 0.996. The method also opens interesting perspectives for the determination of other semi-volatile persistent organic pollutants (POPs) in air as illustrated with the analysis of polychlorinated biphenyls (PCBs) at a workplace during removal of transformer oil.

Full evaporation dynamic headspace in combination with selectable one-dimensional/two-dimensional gas chromatography-mass spectrometry for the determination of suspected fragrance allergens in cosmetic products.

Suspected fragrance allergens were determined in cosmetic products using a combination of full evaporation-dynamic headspace (FEDHS) with selectable one-dimensional/two-dimensional GC-MS. The full evaporation dynamic headspace approach allows the non-discriminating extraction and injection of both apolar and polar fragrance compounds, without contamination of the analytical system by high molecular weight non-volatile matrix compounds. The method can be applied to all classes of cosmetic samples, including water containing matrices such as shower gels or body creams. In combination with selectable (1)D/(2)D GC-MS, consisting of a dedicated heart-cutting GC-MS configuration using capillary flow technology (CFT) and low thermal mass GC (LTM-GC), a highly flexible and easy-to-use analytical solution is offered. Depending on the complexity of the perfume fraction, analyses can be performed in one-dimensional GC-MS mode or in heart-cutting two-dimensional GC-MS mode, without the need of hardware reconfiguration. The two-dimensional mode with independent temperature control of the first and second dimension column is especially useful to confirm the presence of detected allergen compounds when mass spectral deconvolution is not possible.

Automated capillary gas chromatographic system to monitor ethylene emitted from biological materials

An automated capillary gas chromatographic system to measure ethylene emitted from biological materials is presented. The system consists of an on-line sampling device, a thermodesorption preconcentration apparatus and a capillary gas chromatograph with a flame ionization detection system. The limit of detection achievable on the GC system alone is 5 pg ethylene. The use of the strong Carboxen 1000 adsorbent at a sampling temperature as low as -50 degrees C allows sampling of volumes up to a few liters. Ethylene concentrations at low ppt levels can be accurately and reproducibly determined.

A new validated analytical method for the determination of tributyltin in water samples at the quantification level set by the European Union

According to recent directives of the European Union (EU), limits of quantification (LOQ) for the determination of tributyltin (TBT) in surface waters should be ca. 60 pg/L (ppq). This put very stringent requirements on analytical methodologies; definitely when they have to be applied in a routine environment. Stir bar sorptive extraction (SBSE), followed by thermal desorption (TD) and capillary gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) can provide accurate and precise data at the 2 ng/L level (ppt). For lower concentrations, matrix and reagent interferences together with contamination may provide too high TBT values. A two-dimensional heart-cut GC method was developed to fractionate TBT from interferences. The GC-GC-MS/MS method shows excellent linearity in the range 50 pg/L-4 ng/L, good repeatability (RSD<20% at 200 pg/L), and a limit of detection of 11 pg/L. The method performance is demonstrated with representative samples i.e. harbor water and waste water samples.

Determination of pesticides in fatty matrices using gel permeation clean-up followed by GC-MS/MS and LC-MS/MS analysis: A comparison of low- and high-pressure gel permeation columns

Two low-pressure columns (Bio-Beads SX-3) and three high-pressure GPC columns were compared for clean-up of a wide range of pesticides in fatty matrices of vegetable or animal origin. The GPC fractions were analyzed by GC-MS/MS and LC-MS/MS without additional clean-up. The performance of the GPC clean-up on the five column types was compared in terms of solvent consumption, lipid removal, pesticide recovery and repeatability. It was found that for fatty matrices, mainly consisting of high molecular weight triglycerides i.e. most vegetable oils and animal fats, good fractionation is obtained for the majority of the pesticides. On the other hand, for fats and oils containing relatively high amounts of low molecular weight triglycerides, i.e. butter fat and palm kernel oil, none of the columns provided sufficient clean-up and cause interferences and system contamination, especially in the case of GC-MS/MS analysis. For the latter case, best results in terms of lipid removal and pesticide recovery were obtained on a set (2×300mmlength) of narrow bore (7.5mm ID) columns packed with 5µm PL Gel material. Column loadability is, however, much lower on that set of columns compared the other evaluated GPC columns, impairing overall method sensitivity.

Increasing productivity for the analysis of trace contaminants in food by gas chromatography-mass spectrometry using automated liner exchange, backflushing and heart-cutting.

Laboratories focusing on residue analysis in food are continuously seeking to increase sample throughput by minimizing sample preparation. Generic sample extraction methods such as QuEChERS lack selectivity and consequently extracts are not free from non-volatile material that contaminates the analytical system. Co-extracted matrix constituents interfere with target analytes, even if highly sensitive and selective GC-MS/MS is used. A number of GC approaches are described that can be used to increase laboratory productivity. These techniques include automated inlet liner exchange and column backflushing for preservation of the performance of the analytical system and heart-cutting two-dimensional GC for increasing sensitivity and selectivity. The application of these tools is illustrated by the analysis of pesticides in vegetables and fruits, PCBs in milk powder and coplanar PCBs in fish. It is demonstrated that considerable increase in productivity can be achieved by decreasing instrument down-time, while analytical performance is equal or better compared to conventional trace contaminant analysis.