Chromatographic enrichment and enantiomer separation of axially chiral polybrominated biphenyls in a technical mixture

The separation properties of different chromatographic methods regarding the enantioselective separation of axially chiral (atropisomeric) polybrominated biphenyls (PBB) were studied. For this purpose, the technical hexabromobiphenyl product Firemaster BP-6 was characterised by gas-chromatography coupled to electron capture detection (GC/ECD) and electron-capture negative ion mass spectrometry (GC/ECNI-MS) as well as by liquid chromatographic fractionating on active carbon and celite. Twelve individual PBBs including potential atropisomeric PBBs were isolated from Firemaster BP-6 by reversed-phase high-performance liquid chromatography (HPLC) on three serially coupled octadecylsilane columns. Six of the 12 isolated PBBs (three tri-ortho and di-ortho substituted PBBs, respectively) were separated into atropisomers on a HPLC column containing permethylated beta-cyclodextrin on silica. Moreover, the temperature dependency of the enantiomer separations is discussed. Gas chromatographic enantiomer separation of PBBs is a very demanding task due to high elution temperatures. However, the atropisomers of one tri-ortho substituted PBB congener (PBB 149) could be resolved on a column coated with randomly modified heptakis(6-O-tert.-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyclodextrin in OV 1701.     

Analytical strategies for successful enantioselective separation of atropisomeric polybrominated biphenyls 132 and 149 in environmental samples

Some of the polybrominated biphenyls (PBBs) found in the environment are axially chiral, due to hindered rotation about the interannular phenyl-phenyl bond. This applies for PBB congeners having two or more bromine substituents in ortho-position to this bond. In this study analytical methods were developed that allow determining the enantiomer fraction (EF) of axially chiral (atropisomeric) PBBs in environmental samples. A white-tailed sea eagle egg was used as test sample. The egg extract was purified and further fractionated by normal phase (NP) high performance liquid chromatography (HPLC), yielding enriched fractions of axially chiral PBB 132 and PBB 149. Gas chromatographic (GC) enantioseparation of the atropisomers of PBB 149 was achieved on one of nine tested modified cyclodextrin phases. Due to coelution with an unknown brominated compound, conventional GC/ECNI-MS, which is based on the detection of the bromide ion, did not allow for the establishment of the EF. However, by means of GC/EI-MS-MS it was possible to verify an EF of 0.42-0.43, i.e. a significant enantiomeric enrichment of the second eluting atropisomer of PBB 149 in the white-tailed sea eagle egg. This is the first proof of non-racemic proportions of a chiral PBB in environmental samples. Despite the testing of nine different chiral stationary phases, GC enantioseparation of PBB 132 or other atropisomeric PBB congeners failed. For this reason, an enantioselective reversed-phase HPLC method was developed. This method proved to be a powerful tool for the separation of PBB atropisomers. It was found that even a standard of the di-ortho substituted PBB 153 could be partially separated into atropisomers at 0 degrees C but already enantiomerized at 5 degrees C. For establishing the EF of PBB 132 in the bird egg sample a combination of enantioselective HPLC followed by non-chiral gas chromatography was employed. Using enantioselective HPLC, the atropisomers of PBB 132 were quantitatively targeted into two separate fractions at room temperature (20 degrees C). After addition of internal standards for volume adjustment the relative amounts of the atropisomers in the isolated fractions were quantified by using non-chiral GC/EI-MS analysis. A deviation from the racemic mixture of the atropisomers of PBB 132 in the egg extract could not be statistically proven.     

Highly selective and sensitive gas chromatography-electron-capture negative-ion mass spectrometry method for the indirect enantioselective identification of 2- and 3-hydroxy fatty acids in food and biological samples

A gas chromatographic (GC) method is described for the indirect enantioresolution of 2- and 3-hydroxy fatty acids (OH-FAs). It combines the derivatization of each alkylated enantiomer and the subsequent transfer with (R)-(-)-alpha-methoxy-alpha-trifluoromethylphenylacetyl chloride [(R)-(-)-MTPA-Cl, Mosher's reagent] into a diastereomeric (S)-MTPA derivative. The enantiomers of each derivatized OH-FA were well separated on three non-chiral GC-columns (CP-Sil 2, CP-Sil 8/20% C18 and VF-5ms). The derivatives were detected with high sensitivity by GC with electron-capture detection (GC/ECD) and electron-capture negative-ion mass spectrometry (GC/ECNI-MS) because of their enhanced electron-capturing properties. When applied to sunflower oil spiked with a small amount of a racemic 2-OH-FA, the present method allowed for a highly selective identification without influence from the sample matrix. For more complex samples such as wool wax, GC/ECNI-MS was superior to GC/ECD, since the high sensitivity of this method was linked with high selectivity. Using GC/ECNI-MS in the selected ion monitoring (SIM) mode, 16 enantiopure 2-OH-FAs were detected in a wool wax sample.     

Determination of polybrominated biphenyls in Tasmanian devils (Sarcophilus harrisii) by gas chromatography coupled to electron capture negative ion tandem mass spectrometry or electron ionization high‐resolution mass spectrometry

Two gas chromatography/mass spectrometry (GC/MS) methods for the determination of polybrominated biphenyls (PBBs) by isotope dilution analysis (IDA) using ¹³C₁₂‐PBB 153 in the presence of polybrominated diphenyl ethers (PBDEs) were compared. Recovery of ¹³C₁₂‐PBB 153 which was added to the extracted lipids before sample purification was commenced ranged from 88–117% (mean value 98.2 ± 8.9%). Nevertheless, IDA analysis of PBBs using ¹³C₁₂‐labelled congeners is limited by the potential co‐elution of PBBs with polybrominated diphenyl ethers (PBDEs). The pair PBB 153 and BDE 154 was inspected since M⁺ and [M–2Br]⁺ ions of ¹³C₁₂‐PBB 153 and BDE 154 were only separated by 4 u. Gas chromatography/electron ionization high‐resolution mass spectrometry with selected ion monitoring (GC/EI‐HRMS‐SIM) was suitable when m/z 475.7449 and m/z 477.7429 were used for ¹³C₁₂‐PBB 153 because they are below the monoisotopic peak of the [M–2Br]⁺ fragment ion of hexaBDEs at m/z 479.7. Gas chromatography/electron capture negative ion tandem mass spectrometry selected reaction monitoring (GC/ECNI‐MS/MS‐SRM) measurements could be applied because ¹³C₁₂‐PBB 153 and BDE 154 were separated by GC on a 25‐m Factor Four CP‐Sil 8MS column. Comparative measurements with GC/EI‐HRMS‐SIM and GC/ECNI‐MSMS‐SRM were carried out with samples of Tasmanian devils from Tasmania (Australia), an endangered species due to a virus epidemy which has already proved fatal for half of the population. Both techniques verified concentrations of PBB 153 in the range 0.3–11 ng/g lipids with excellent agreement of the levels in all but two samples. The PBB residue pattern demonstrated that PBB pollution originated from the previous discharge with technical hexabromobiphenyl which is dominated by PBB 153. Other congeners such as PBB 132 and PBB 138 were detected in the Tasmanian devils but the proportions relative to PBB 153 were lower than in the technical product. Samples of healthy and affected Tasmanian devils showed no significant difference in the PBB pollution level. The PBB concentrations in the Tasmanian devils were significantly below those causing toxic effects. On the other hand, PBB concentrations were one level or even higher than PBDEs. Copyright © 2008 John Wiley & Sons, Ltd.     

Offline coupling of high-speed counter-current chromatography and gas chromatography/mass spectrometry generates a two-dimensional plot of toxaphene components

High-speed counter-current chromatography (HSCCC), a separation technique based solely on the partitioning of solutes between two immiscible liquid phases, was applied for the fractionation of technical toxaphene, an organochlorine pesticide which consists of a complex mixture of structurally closely related compounds. A solvent system (n-hexane/methanol/water 34:24:1, v/v/v) was developed which allowed to separate compounds of technical toxaphene (CTTs) with excellent retention of the stationary phase (S_f = 88%). Subsequent analysis of all HSCCC fractions by gas chromatography coupled to electron-capture negative ion mass spectrometry (GC/ECNI-MS) provided a wealth of information regarding separation characteristics of HSCCC and the composition of technical toxaphene. The visualization of the large amount of data obtained from the offline two-dimensional HSCCC–GC/ECNI-MS experiment was facilitated by the creation of a two-dimensional (2D) contour plot. The contour plot not only provided an excellent overview of the HSCCC separation progress, it also illustrated the differences in selectivity between HSCCC and GC. The results of this proof-of-concept study showed that the 2D chromatographic approach involving HSCCC facilitated the separation of CTTs that coelute in unidimensional GC. Furthermore, the creation of 2D contour plots may provide a useful means of enhancing data visualization for other offline two-dimensional separations.     

Development of a gas chromatography/ion trap mass spectrometry based method for the quantification of polybrominated diphenyl ethers and polychlorinated biphenyls in adipose tissue

A combined gas chromatographic mass spectrometric (GC/MS/MS) method for the determination of seven polybrominated diphenyl ethers (PBDEs) and seven marker polychlorinated biphenyls (PCBs) in adipose tissue has been developed. Adipose tissue was melted and filtered through anhydrous sodium sulphate to obtain pure fat. Clean-up was performed using a glass column containing acidified silica, deactivated alumina and anhydrous sodium sulphate. Polybrominated biphenyl (PBB) 155 and Mirex were added as internal standards for PBDEs and PCBs, respectively. Injection standards, PBB 103 and PCB 143, for PBDEs and PCBs, respectively, were added before analysis with GC/MS/MS. The developed GC/MS/MS method has the advantage of being more selective than single MS methods because matrix effects are largely eliminated. Validation of this method was conducted according to Commission Decision 2002/657/EC. Decision limits for PBDEs and PCBs ranged from 0.06-0.15 ng g(-1) and from 0.35-1.22 ng g(-1), respectively. Detection capabilities were all between 0.23-0.55 ng g(-1) for PBDEs and between 0.98-2.29 ng g(-1) for PCBs. Precision, recovery, bias and selectivity were tested, with satisfactory results.     

Chiral comprehensive two-dimensional gas chromatography with electron-capture detection applied to the analysis of chiral polychlorinated biphenyls in food samples

The feasibility of comprehensive two-dimensional gas chromatography with electron-capture detection (GC x GC-ECD) for the enantioseparation of chiral PCBs from other possible interfering compounds has been evaluated. Three commercially available enantioselective beta-cyclodextrin-based capillary columns (Chirasil-Dex, BGB-172 and BGB-176SE) have been tested as first-dimension columns. Three non-enantioselective stationary phases (HT-8, BPX-50 and Supelcowax-10) were combined with the enantioselective columns to allow the unambiguous determination of the enantiomers of the target chiral PCBs. Each enantioselective first-dimension column tested was able to separate into enantiomers different PCB congeners, but in all cases, the use of Supelcowax-10 as second-dimension column provided the most satisfactory results. The Chirasil-Dex x Supelcowax-10 column combination allowed the determination of the enantiomeric fraction (EF) of PCBs 84, 91, 95, 132, 136, 149, 174 and 176 in the working standard solution, while that of congener 135 was hindered. The BGB-172 x Supelcowax-10 column set allowed a proper EF determination of congeners 45, 84, 131, 132, 135, 171, 174 and 183, while that of PCB 91 was interfered with co-elutants. The column combination BGB-176SE x Supelcowax-10 allowed the determination of all congeners that this enantioselective stationary phase was able to separate into enantiomers, i.e. PCBs 45, 91, 95, 136, 149 and 176. These column combinations have also been evaluated for the simultaneous determination of the 12 congeners with a toxic equivalency factor assigned by the WHO (PCBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, 189) and the seven indicator congeners (PCBs 28, 52, 101, 118, 138, 153 and 180), and evaluated for the analysis of food samples.     

Stereoselective determination of famoxadone enantiomers with HPLC-MS/MS and evaluation of their dissipation process in spinach

A simple and enantioselective method for the determination of famoxadone enantiomers in spinach using reversed-phase HPLC-MS/MS is presented. Famoxadone residues in spinach were extracted with acetonitrile and an aliquot was cleaned up with PSA (primary and secondary amine, Si-(CH(2))(3)-NH-(CH(2))(2)-NH(2)) and C(18) sorbent, which were powder material. Chiral stationary phase (CSP), cellulose tris(3,5-dimethylphenylcarbamate), was successfully applied to separate two enantiomers using methanol/formic acid-ammonium acetate buffer as mobile phase. The MS/MS fragmentation pathway of ammonium adduct famoxadone molecules ion at m/z 392 was analyzed and an odd electron fragment ion at m/z 238 was observed. Excellent linearity was achieved for each enantiomer over a range of concentrations from 0.5 to 1500 μg/L with coefficients more than 0.99. Average recoveries at five different levels (1, 2.5, 12.5, 250 and 1250 μg/kg, for each enantiomer) ranged from 80.8 to 96.5% with RSD of 4.8-13.4%. The famoxadone enantiomers LODs in spinach were determined to be both 0.3 μg/kg with LOQs of 1 μg/kg. Based on this method, the dissipation process of famoxadone enantiomers in spinach under open field and greenhouse conditions was characterized, providing guidance to the proper and safe use of this fungicide in agriculture.     

Enantiomer identification in the flavour and fragrance fields by "interactive" combination of linear retention indices from enantioselective gas chromatography and mass spectrometry

This study describes the development of a gas chromatography-mass spectrometry (GC-MS) library to identify optically active compounds in the flavour and fragrance field using enantioselective GC with cyclodextrin derivatives (CDs) as chiral selectors in combination with MS. The library operates on the "interactive" combination of linear retention indices (I(T) values) in parallel to MS spectra, so as to identify enantiomers reliably and to measure EE and/or ER unequivocally. Since MS is not a selective probe to discriminate optical isomers, mass spectra (or diagnostic ions in SIM mode) are used to locate the enantiomer(s) in the chromatogram, and I(T) values to identify it(them) safely and reliably in particular in complex mixtures. The library has been built up through the following steps: Some applications of the library are also reported. (a) Selection of CD derivatives able to cover a wide range of racemate separations. Four cyclodextrin derivatives were used: 2,6-di-O-methyl-3-O-pentyl-beta-CD, 2,3-di-O-methyl-6-O-tert-butyldimethylsilyl-beta-CD, 2,3-di-O-ethyl-6-AO-tert-butyldimethylsilyl-beta-CD, and 2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-beta-CD. (b) Determination of the analytes' I(T) values and evaluation of their stability and reliability at both intra- and inter-laboratory level. (c) Determination of the range within which the I(T) of an enantiomer has to be correctly identified, i.e. determination of a common retention index allowance (RIA). (d) Construction of the library, at the moment comprising the enantiomers of 134 racemates. A record has been attributed to each enantiomer including I(T) values determined on the four CD coated columns, mass spectrum, IUPAC chemical names, CAS numbers, molecular weight, and, when separated, racemate enantiomer resolution on the CD investigated. Some applications of the library are also reported.     

Environmental fate processes and biochemical transformations of chiral emerging organic pollutants

This review highlights the analytical chemistry, environmental occurrence, and environmental fate of individual stereoisomers of chiral emerging pollutants, which are modern current-use chemicals of growing environmental concern due to their presence in the environment and potential for deleterious effects. Comparatively little is known about individual stereoisomers of pollutants, which can have differential toxicological effects and can be tracers of biochemical weathering in the environment. Stereoisomers are resolved by gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE). Separation techniques in environmental analysis are typically coupled to mass spectrometry (MS) and tandem mass spectrometry (MS/MS), as these provide the sensitivity and selectivity needed. The enantiomer composition of phenoxyalkanoic and acetamide herbicides, organophosphorus and pyrethroid pesticides, chiral polychlorinated biphenyl metabolites, synthetic musks, hexabromocyclododecane, and pharmaceuticals in the environment show species-dependent enantioselectivity from biotransformation and other biologically mediated processes affecting enantiomers differentially. These enantiomer compositions are useful in detecting biologically mediated environmental reactions, apportioning sources of pollutants, and gaining insight into the biochemical fate of chiral pollutants in the environment, which are needed for accurate risk assessment of such chemicals.     

Development of a new method for the enantiomer specific determination of HBCD using an ion trap mass spectrometer

An alternative method for the enantiomer specific determination of hexabromocyclododecanes (HBCD) by LC-ESI-MS/MS using an ion trap analyser is proposed. The method is based on the formation of a chlorine adduct (m/z 676.6) of the (±)α-, (±)β-, and (±)γ-HBCD enantiomers and their further fragmentation into their stable quasi-molecular ion (m/z 640.6). In this way, problems related to the ion trap low mass cutoff and variable amounts of other adduct peaks in the samples are solved. Parameters affecting separation, ionisation and MS/MS detection were studied. Method performance was also evaluated: calibration curves were found linear from 20 to 400 pg μL⁻¹ for each enantiomer; detection limits ranged between 1.5 and 4.3 pg μL⁻¹; repeatability and reproducibility, expressed as relative standard deviation, were lower than 6% and 13%, respectively. The application to different types of spiked samples (pork meat, lean fish, and butter) pointed out the occurrence of matrix effects that could be solved by using labelled standards.     

Development and validation of an enantioselective LC‐MS/MS method to quantify enantiomers of (±)‐TAK‐700 in rat plasma: lack of in vivo inversion of (+)‐TAK‐700 (Orteronel) to its antipode

A highly sensitive, specific and enantioselective assay has been developed and validated for the estimation of TAK‐700 enantiomers [(+)‐TAK‐700 and (?)‐TAK‐700] in rat plasma on LC‐MS/MS‐ESI in the positive‐ion mode. Liquid–liquid extraction was used to extract (±)‐TAK‐700 enantiomers and IS (phenacetin) from rat plasma. TAK‐700 enantiomers were separated using methanol and 5 mm ammonium acetate (80:20, v/v) at a flow rate of 0.7 mL/min on a Chiralcel OJ‐RH column. The total run time was 7.0 min and the elution of (+)‐TAK‐700, (?)‐TAK‐700 and IS occurred at 3.71, 4.45 and 4.33 min, respectively. The MS/MS ion transitions monitored were m/z 308.2 → 95.0 for TAK‐700 and m/z 180.2 → 110.1 for IS. The standard curves for TAK‐700 enantiomers were linear (r² > 0.998) in the concentration range 2.01–2015 ng/mL for each enantiomer. The inter‐ and intra‐day precisions were in the ranges 3.74–7.61 and 2.06–8.71% and 3.59–9.00 and 2.32–11.0% for (+)‐TAK‐700 and (?)‐TAK‐700, respectively. Both the enantiomers were found to be stable in a battery of stability studies. This novel method was applied to the study of stereoselective oral pharmacokinetics of (+)‐TAK‐700 and it was unequivocally demonstrated that (+)‐TAK‐700 does not undergo chiral inversion to its antipode in vivo. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of three ionisation modes for the analysis of chlorinated paraffins by gas chromatography/ion-trap mass spectrometry

The applicability of three ionisation modes to the analysis of short-chain chlorinated paraffins (SCCPs) using gas chromatography coupled with mass spectrometry (GC/MS) was evaluated. MS conditions for electron ionisation (EI), positive chemical ionisation (PCI) and electron-capture negative ionisation (ECNI) were optimised using commercially available individual tetra-, penta- and hexachlorodecanes. In addition, mass spectra were studied and fragmentation pathways were proposed for each individual congener. Different fragment ions were evaluated for quantification, and ECNI-MS using [HCl2](-) and [Cl2](-*) ions was selected for the determination of SCCPs. Quality parameters (repeatability, limits of detection and calibration range) were established for the proposed method, which was then applied to the analysis of SCCPs in river sediments.     

Quantification of fg-pg amounts by electron capture negative ion mass spectrometry — Parameter optimisation and practical advices

Electron capture negative ion mass spectrometry (ECNI-MS) is a very suitable and popular technique for the identification and quantification of fg-pg amounts of compounds with a sufficiently high electron affinity. Many users of the ECNI mode have faced a lot of frustrating problems due to instrument contamination and wrong recommendations concerning instrument optimisation. This article summarises 14 years of experience with ECNI-MS using a large number of different instruments. Recommendations are given concerning optimisation procedures of important parameters such as ion source pressure and temperature as well as electron energy. An ion pressure optimisation method is proposed using a gas chromatograph. ECNI-MS is very sensitive against trace amounts of contaminants in the mass spectrometer and requires very clean components in the reagent gas line. Recommendations are given concerning suitable parts. Different other contamination sources are also discussed. The construction of a simple and clean gas inlet system is presented. Furthermore, contamination-free cleaning methods for the ion source are suggested. A test method based on the detection of hexachlorobenzene in the full scan mode (m/z 34–300) is proposed. It allows to evaluate both the background level in the mass spectrometer and the overall system performance. Clean instruments should show a signal-to-noise ratio of the total ion current GC signal of at least 20:1 without applying any mass signal area reject threshold. A linearity test procedure is also suggested. It shows that the linear range of a clean and optimised instrument is at least 3 orders of magnitude in the ECNI mode.     

Improved GC/ECNI-MS sensitivity of decabromodiphenyl ether determination on 30 m columns by increasing the carrier gas flow after a modified gel permeation chromatographic cleanup protocol employing cyclohexane/ethyl acetate as eluent

BDE-209 is the predominant constituent of the commercial mixture decabromodiphenyl ether which is used as brominated flame retardant (BFR). Owing to difficulties associated with the high mass (thermal instability and low vapour pressure), short GC columns (≤15?m) have been suggested for its analysis while longer columns (30–50?m) are suggested for other polybrominated diphenyl ether (PBDE) congeners. To overcome this considerable expenditure in the analysis of PBDEs, we aimed at increasing the sensitivity of BDE-209 analysis by gas chromatography coupled with electron-capture negative ion mass spectrometry (GC/ECNI-MS) on a 30?m column. The chromatographic performance of BDE-209 on the 30?m GC column was improved by increasing the carrier gas flow from initially 1.2?mL?min^?1 to 5 or 10?mL?min^?1 after the last octabromo diphenyl ether (Br₈DE) congener was eluted. With this high carrier gas flow, the column residence time of BDE-209 was shortened by ～25%, the peak height was increased and, consequently, the limit of detection by GC/ECNI-MS in selected ion monitoring (SIM) mode was improved. When this high-flow GC/ECNI-MS-SIM method was applied to a sediment sample, we realized that gel permeation chromatography (GPC) – used for the removal of lipids and/or sulphur – provided low recovery rates for BDE-209. The large molecule BDE-209 eluted late and only 50% was recovered by our previous standard protocol for polyhalogenated compounds. Application of a modified GPC procedure with a longer collection time increased the recovery of BDE-209 in the GPC step to ～90%.     

Analysis of N7-(benzo[a]pyrene-6-yl)guanine in urine using two-step solid-phase extraction and isotope dilution with liquid chromatography/tandem mass spectrometry

Analysis of urinary N7-(benzo[a]pyren-6-yl)guanine (BP-6-N7Gua), a DNA adduct induced by benzo[a]pyrene, may serve as a risk-associated biomarker for exposure to polyaromatic hydrocarbons (PAHs). In this study a highly sensitive and specific analytical method, incorporating on-line sample preparation coupled with isotope-dilution liquid chromatography and tandem mass spectrometry (LC/MS/MS), was developed to quantitate this adduct in human urine. In order to achieve accurate quantitation, 15N5-labeled BP-6-N7Gua was synthesized to serve as the internal standard, and a two-step solid-phase extraction (SPE) procedure using C8 and SCX cartridges was used for sample cleanup. BP-6-7-N7Gua was analyzed using positive ion LC/MS/MS operated in multiple reaction monitoring (MRM) mode. The [M+H]+ ions at m/z 402 and 407 and the common fragment ion of [M+H]+ at m/z 252 were monitored for quantification. The recovery of this analyte after two-step SPE was 90%, and the limit of detection was 2.5 fmol/mL in 10 mL of urine. This highly specific and sensitive method for BP-6-N7Gua in urine may be applied to assess exposure to PAHs in coke-oven workers for future molecular epidemiology studies on health effects of PAHs.     

Fast gas chromatographic/mass spectrometric determination of diuretics and masking agents in human urine: Development and validation of a productive screening protocol for antidoping analysis

An analytical procedure was developed for the fast screening of 16 diuretics (acetazolamide, althiazide, amiloride, bendroflumethiazide, bumetanide, canrenoic acid, chlorthalidone, chlorthiazide, clopamide, ethacrynic acid, furosemide, hydrochlorthiazide, hydroflumethiazide, indapamide, triamterene, trichlormethiazide) and a masking agent (probenecid) in human urine. The whole method involves three analytical steps, including (1) liquid/liquid extraction of the analytes from the matrix, (2) their reaction with methyl iodide at 70 degrees C for 2 h to form methyl derivatives, (3) analysis of the resulting mixture by fast gas chromatography/electron impact mass spectrometry (fast GC/EI-MS). The analytical method was validated by determining selectivity, linearity, accuracy, intra and inter assay precision, extraction efficiencies and signal to noise ratio (S/N) at the lowest calibration level (LCL) for all candidate analytes. The analytical performances of three extraction procedures and five combination of derivatization parameters were compared in order to probe the conditions for speeding up the sample preparation step. Limits of detection (LOD) were evaluated in both EI-MS and ECNI-MS (electron capture negative ionization mass spectrometry) modes, indicating better sensitivity for most of the analytes using the latter ionization technique. The use of short columns and high carrier gas velocity in fast GC/MS produced efficient separation of the analytes in less than 4 min, resulting in a drastic reduction of the analysis time, while a resolution comparable to that obtained from classic GC conditions is maintained. Fast quadrupole MS electronics allows high scan rates and effective data acquisition both in scan and selected ion monitoring modes.     

Structural elucidation of disinfection by-products in treated drinking water

Two unusual disinfection by-products have been detected periodically in the gas chromatography/mass spectrometry (GC/MS) characterization analyses of semi-volatile organics in treated drinking water. The electron ionization (EI) mass spectra contained mono-chlorinated and mono-brominated ions at m/z 107/109 and 151/153, respectively. Library searching techniques suggested mono-halogenated butanol structures but no matches could be found. Positive ion chemical ionization (CI) spectra contained mono-chlorinated and mono-brominated ions at m/z 105/107 and 149/151, respectively. No [M + H]+ ions were initially observed. Accurate mass measurements confirmed the empirical formulae for the significant ions in the EI spectra and the mono-halogenated butanol structures. Further CI experiments with other reagent gases and instruments revealed possible molecular weights of 139 and 183 Da, respectively. Tandem mass spectrometry (MS/MS) experiments in EI and CI were used to elucidate the fragmentation schemes. The two compounds have been tentatively identified as 1-aminoxy-1-chlorobutan-2-ol and 1-aminoxy-1-bromobutan-2-ol, respectively.     

Enantioselective determination of the organochlorine pesticide bromocyclen in spiked fish tissue using solid-phase microextraction coupled to gas chromatography with ECD and ICP-MS detection

A method for enantioselective determination of bromocyclen enantiomers in fish tissue has been developed. The enantiomers were resolved by capillary gas chromatography (GC) using a commercial chiral column (CP-Chirasil-Dex CB) and a temperature program from 50 degrees C (held for 1 min), raised to 140 degrees C at 40 degrees C min(-1) and then raised at 0.2 degrees C min(-1) to 155 degrees C. This enantioselective gas chromatographic separation was combined with a clean-up/enrichment procedure based on solid-phase microextraction (SPME). Under SPME optimized conditions, precision, linearity range and detection limits of the developed SPME-enantioselective GC procedure were evaluated and compared using two different detection systems: a classical electron-capture detection (ECD) and an element specific detection using inductively coupled plasma mass spectrometry (ICP-MS). The SPME-GC-ECD method exhibited an excellent sensitivity, with detection limits of 0.2 ng L(-1) for each enantiomer of bromocyclen. Although ICP-MS offered poorer detection limits (7 ng L(-1) as Br, equivalent to 36 ng L(-1) of each enantiomer) than conventional ECD detector, it proved to be clearly superior in terms of selectivity. The relative potential and performance of the two compared methods for real-life analysis has been illustrated by the determination of enantiomers of bromocyclen in spiked tissue extracts of trout.     

Silver (Ι)‐assisted enantiomeric analysis of ginsenosides using electrospray ionization tandem mass spectrometry

For identification of ginsenoside enantiomers, electrospray ionization mass spectrometry (ESI‐MS) was used to generate silver complexes of the type [ginsenoside + Ag]⁺. Collision induced dissociation of the silver‐ginsenoside complexes produced fragment ions by dehydration, allowing differentiation of ginsenoside enantiomers by the intensity of [M + Ag ? H₂O]⁺ ion. In the meanwhile, an approach based on the distinct profiles of enantiomer‐selective fragment ion intensity varied with collision energy was introduced to refine the identification and quantitation of ginsenoside enantiomers. Five pairs of enantiomeric ginsenosides were distinguished and quantified on the basis of the distribution of fragment ion [M + Ag ? H₂O]⁺. This method was also extended to the identification of other type of ginsenoside isomers such as ginsenoside Rb2 and Rb3. For demonstrating the practicability of this novel approach, it was utilized to analyze the molar ratio of 20‐(S) and 20‐(R) type enantiomeric ginsenosides in enantiomer mixture in red ginseng extract. The generation of characteristic fragment ion [M + Ag ? H₂O]⁺ likely results from the reduction of potential energy barrier of dehydration because of the catalysis of silver ion. The mechanism of enantiomer identification of ginsenosides was discussed from the aspects of computational modeling and internal energy. Copyright © 2012 John Wiley & Sons, Ltd.