GC-MS Selected Ion Monitoring Research Articles

Triaromatic dinosteroids – Isomeric distributions and their geochemical significance

The distribution of triaromatic dinosteroids in a range of oils and some source rock bitumens was determined by GC–MS selected ion monitoring and GC–MS-MS in order to investigate possible ambiguity in the observed distribution of isomers, including those related to maturation and alteration processes commonly affecting oil accumulations. The results confirm that the eight possible isomers for the triaromatic dinosteroids and their 28-nor equivalents (triaromatic 23,24-dimethylcholesteroids) in post-Paleozoic samples are consistently represented by six peaks on commonly used GC stationary phases, although the fifth eluting is broadened and probably represents a pair of isomers. The presence of a seventh, early eluting, triaromatic dinosteroid isomer occasionally encountered in m/z 245 mass chromatograms in the literature was not substantiated. Closely co-eluting compounds can give the seemingly misleading impression that one or two triaromatic dinosteroid isomers (including the last eluting) are present at low levels in pre-Mesozoic samples and in younger oils from dominantly higher plant sources, so care is required in inferring source age for such samples. The relative abundance and retention time pattern observed for the triaromatic dinosteroids is duplicated by their 28-nor analogues. Triaromatic dinosteroid isomer distributions vary little throughout the oil window, based on data from Norwegian North Sea oils representing a range of mean maturities. Overall abundance of the series seems to decline in a similar way to other biomarkers towards the end of the oil window. In source rock bitumen corresponding to maturities of ≤0.5% vitrinite reflectance, when diasterenes are still abundant, the second eluting triaromatic dinosteroid peak was enhanced and the fifth depleted in the limited set of samples studied (Late Jurassic marine shales from the Norwegian continental shelf). Both dinosteroid series appear particularly resistant towards biodegradation and metamorphism, with no obvious change in isomeric distributions compared to unaltered oil. As a consequence, their relative abundances, as represented by age parameters that ratio each series to their 24-ethyl counterparts, increase when alteration is severe. Lacustrine oils can be difficult to date because post-Paleozoic samples do not always contain detectable dinosteroids and, when they are present, they can vary significantly in abundance. Unambiguous age resolution at the Period level was not possible for the Triassic-Tertiary oils studied, neither could depositional environments be distinguished with confidence.

Simultaneous analysis of ten drugs of abuse in blood and urine matrix by gas chromatography–mass spectrometry: Implications for air crash investigation

Introduction: Many of abuse drugs can alter a person’s thinking and judgment, leading to health risks, including addiction, drugged driving and infectious disease. Use of illicit drugs by aviation employees is associated with a significantly increased risk of accidents. The detection and quantitation of drugs of abuse in blood is of growing interest in forensic and clinical toxicology. Generally, the screening for drugs of abuse is carried out by using commercially available immunoassay based urine cassettes; however, such results needs to be confirmed by advanced analytical tools like HPLC, GCMS and LCMS. There have been several attempts to develop confirmatory methods for drugs of abuse in blood and urine. Material and Methods: In the present study in our laboratory, a single method was attempted for simultaneous detection and quantification of 10 drugs of abuse in whole blood and urine matrix by GC-MS Selective Ion Monitoring (SIM) method. Results: Chromatographic separation was optimized and achieved for separation of all 10 compounds using Agilent DB-5MS column. Retention time (Rt), selectivity and sensitivity were achieved by measuring each analyte in Selective Ion Monitoring (SIM) mode. A simple sample preparation method was standardized for extraction of all 10 compounds from blood and urine. Conclusion: The developed method in the study permits identification of these analytes from same biological specimen in small quantities and the method is tested on blood and urine matrix spiked with known concentration of pure compounds.

Simultaneous quantification of epoxy and hydroxy fatty acids as oxidation products of triacylglycerols in edible oils

Epoxy and hydroxy fatty acids are important intermediates during lipid oxidation; quantification of both structures may help evaluate the extent of competition among various lipid oxidation pathways. This article describes a method to simultaneously determine saturated- and unsaturated- epoxy and hydroxy fatty acids derived from oxidation of vegetable oils. The experimental procedures employed transesterification with sodium methoxide, separation of epoxy and hydroxy fatty acid methyl esters (FAME) using solid-phase extraction (SPE), and trimethylsilyl (TMS) derivatization of hydroxy groups. GC–MS was used to identify the epoxy and hydroxy FAME in two different SPE fractions, while GC-flame ionization detection (GC-FID) was used to determine their quantities. Epoxy-octadecanoate/octadecenoate and hydroxy-octadecanoate/octadecenoate/octadecadienoate were determined as lipid oxidation products generated from oxidation of sunflower and canola oils. An isomer of methyl 13-hydroxyoctadeca-9,11-dienoate (13-HODE) TMS ether co-eluted with methyl 15-hydroxyoctadeca-9,12-dienoate TMS ether, which was only present in canola oil; thus, GC–MS-selected ion monitoring (GC–MS–SIM) was used to determine the concentration of 13-HODE. The proposed method has been successfully applied to monitor epoxy and hydroxy fatty acids in sunflower oil and canola oil oxidized at 40 °C.

Validation of a GC–MS method for the estimation of dithiocarbamate fungicide residues and safety evaluation of mancozeb in fruits and vegetables

A sensitive and rugged residue analysis method was validated for the estimation of dithiocarbamate fungicides in a variety of fruit and vegetable matrices. The sample preparation method involved reaction of dithiocarbamates with Tin(II) chloride in aqueous HCl. The CS2 produced was absorbed into an isooctane layer and estimated by GC–MS selected ion monitoring. Limit of quantification (LOQ) was ⩽40μgkg−1 for grape, green chilli, tomato, potato, brinjal, pineapple and chayote and the recoveries were within 75–104% (RSD<15% at LOQ). The method could be satisfactorily applied for analysis of real world samples. Dissipation of mancozeb, the most-used dithiocarbamate fungicide, in field followed first+first order kinetics with pre-harvest intervals of 2 and 4days in brinjal, 7 and 10days in grapes and 0day in chilli at single and double dose of agricultural applications. Cooking practices were effective for removal of mancozeb residues from vegetables.

Ion-Pair Single-Drop Microextraction Determinations of Degradation Products of Chemical Warfare Agents in Water

Ion-pair single-drop microextraction (SDME) coupled to gas chromatography–mass spectroscopy (GC–MS) methods for the determination of four degradation products of chemical warfare agents were investigated in water. Acidic analytes were converted into their ion-pair complexes with cation surfactants in aqueous sample and then extracted into the organic single drop containing the derivatising agent. Upon injection, the analytes were derivatised in the GC injection hot port. Parameters, such as type of extraction solvent, ion-pairing (IP) reagent, reagent concentration, salt concentration, stirring speed and pH, were all optimized. This method is reproducible for spiked water sample for four different analytes (RSDs < 9.33 %, n = 5) and linear (r 2 > 0.9945). The limit of detection (LOD) is in the range of 0.08–0.01 ng mL−1 (S/N = 5) under GC–MS selected ion monitoring mode. The method was successfully applied to the proficiency test samples from the Organization for Prohibition of Chemical Weapons (OPCW).

GC–MS quantification and sensory thresholds of guaiacol in orange juice and its correlation with Alicyclobacillus spp.

Guaiacol is a profoundly negative taint/off-flavour produced by the increasingly common microbial contamination of fruit juices with Alicyclobacillus spp. The objectives of this study included: determining sensory thresholds for guaiacol in orange juice (OJ), developing an analytical method whose detection limits were equivalent to sensory thresholds and determining levels of Alicyclobacillus spp. that would produce detectable levels of guaiacol. A 12 member trained panel was used to establish guaiacol detection and recognition thresholds. Guaiacol ortho and retro nasal detection thresholds in OJ were 0.70 and 0.53 μg/l respectively. Odour recognition threshold was 2.0 μg/l. A SPME GC–MS Selected Ion Monitoring (SIM) procedure was optimised to achieve analytical detection limits of 0.5 μg/l. Optimum guaiacol detection limit was achieved using only responses from m/ z 109 and 124. Ion ratios ( m/ z 109/124) and linear retention index value matching were used to confirm the identification of guaiacol. Quantification was achieved using peak areas from standard guaiacol additions in orange juice between 0.5 and 100 μg/l. Alicyclobacillus growth of 2.2 log CFU/ml in OJ produced just detectable levels (0.7 μg/l) of guaiacol.

Simultaneous Determination of C22-C26 Very Long - Chain Fatty Acids Following tert-Butyldimethylsilyl Derivatization by Stable Isotope GC- MS for the Screening of Adrenoleucodystrophy

A rapid analytical method was developed to quantify very long-chain fatty acids (VLCFAs, C22:0, C24:0, C26:0) in human plasma with good sensitivity and specificity using tert-butyldimethylsilyl (TBDMS) derivatization and stable isotope GC-MS selective ion monitoring (GC-MS/SIM). Two-hundred and fifty <TEX>${\mu}L$</TEX> of plasma was fortified with deuterated stable isotope internal standards (d3-C22:0, d3-C24:0, d3-C26:0) and standard mixtures of chloroform and methanol, and then extracted with hexane and acetonitrile. To upper layer of liquid-liquid-extraction, N-(t-Butyldimethylsilyl)-N-methyltrifluoroacetamide was added and then heated to <TEX>$60^{\circ}C$</TEX> for 30 min to produce the TBDMS derivatives. Derivatives of VLCFAs were analyzed by GC-MS/SIM. Calibration curves showed a linear relationship for the target compounds in the concentration range of <TEX>$10^{-4}{\sim}2{\times}10^3\;{\mu}g/mL$</TEX> with the correlation coefficient ranging from 0.996 to 0.999. The limit of quantification for the plasma was <TEX>$10^{-4}{\sim}2{\times}10^{-4}\;{\mu}g/mL$</TEX> (S/N=3). When applied to the plasma specimens of patients with peroxisomal disorder, X-linked adrenoleucodystropy (ALD, Mckusick 202370), the method clearly differentiated normal subjects from ALD patients. The C24:0/C22:0 and C26:0/C22:0 ratios were significantly elevated in the plasma of patients with X-linked ALD compared to normal subjects. The new developed method might be useful for a rapid and sensitive diagnosis of X-linked ALD and other peroxisomal disorders.

Female Sex Pheromone of the Yunnan Pine Caterpillar Moth Dendrolimus Houi: First (E,Z)-Isomers in Pheromone Components of Dendrolimus spp

The Yunnan pine caterpillar Dendrolimus houi Lajonquière is a serious defoliator of coniferous forests in southwestern China. Gas chromatography-electroantennography (GC-EAG) analyses of extracts of female sex pheromone glands of D. houi moths revealed the presence of three compounds eliciting antennal responses. These were identified as (5E,7Z)-5,7-dodecadien-1-ol (E5,Z7-12:OH), (5E,7Z)-5,7-dodecadien-1-yl acetate (E5,Z7-12:OAc), and (5E,7Z)-5,7-dodecadienal (E5,Z7-12:Ald) by comparison of their GC retention indices, mass spectra, and EAG activities with those of synthetic standards. Average amounts of E5,Z7-12:OH, E5,Z7-12:OAc, and E5,Z7-12:Ald per calling virgin D. houi female were 14.7 +/- 12.9 ng (+/- SD), 5.8 +/- 5.4 ng, and 0.8+1.4 ng, respectively, in a ratio of 100:39.7:5.6. These three components were also collected from the headspace of calling virgin female moths by solid-phase microextraction (SPME). In addition, trace quantities of (Z)-5-dodecen-1-ol (Z5-12:OH), (5Z,7E)-5,7-dodecadien-1-ol (Z5,E7-12:OH), (5E,7E)-5, 7-dodecadien-1-ol (E5,E7-12:OH), (5Z,7E)-5,7-dodecadien-1-yl acetate (Z5,E7-12:OAc), (5Z,7Z)-5,7-dodecadien-1-yl acetate (Z5,Z7-12:OAc), and (5E,7E)-5,7-dodecadien-1-yl acetate (E5,E7-12:OAc) were tentatively identified in female pheromone gland extracts by selected ion monitoring GC-MS. Field trapping experiments showed that E5,Z7-12:OH, E5,Z7-12:OAc, and E5,Z7-12:Ald were essential for attraction of male D. houi moths. Traps baited with a 20:1:1 blend (alcohol/acetate/aldehyde) loaded on gray rubber septa were as effective as traps baited with virgin female moths. The optimum ratio of acetate to aldehyde was 1:1, and this ratio was more critical than the ratio of either compound to the alcohol. This represents the first example of (E,Z)-isomers in pheromone blends of Dendrolimus species.

Two Step Derivatization for the Analyses of Organic, Amino Acids and Glycines on Filter Paper Plasma by GC-MS/SIM

A rapid dried-filter paper plasma-spot analytical method was developed to quantify organic acids, amino acids, and glycines simultaneously in a two-step derivatization procedure with good sensitivity and specificity. The new method involves a two-step trimethylsilyl (TMS) - trifluoroacyl (TFA) derivatization procedure using GC-MS/ selective ion monitoring (GC-MS/SIM). The dried-filter paper plasma was fortified with an internal standard (tropate) as well as a standard mixture of distilled water and methanol. Methyl orange was added to the residue as an indicator. N-methyl-N-(trimethylsilyl-trifluoroacetamide) and N-methyl-bis-trifluoroacetamide were then added and heated to 60 degrees C for 10 and 15 min to produce the TMS and TFA derivatives, respectively. Using this method, the silylation of carboxylic functional groups was carried out, which was followed by the trifluoroacyl derivatization of the amino functional group. The derivatives were analyzed by GC-MS/SIM. A calibration cure showed a linear relationship for the target compounds between concentrations of 10-500 ng/mL. The limit of detection and quantification on a plasma spot were 10-90 ng/mL (S/N=9) and 80-500 ng/ mL, respectively. The correlation coefficient ranged from 0.938 and 0.999. When applied to the samples from positive patients, the method clearly differentiated normal subjects from the patients with various metabolic disorders such as PKU, MSUD, OTC and a Propionic Aciduria. The new developed method might be useful for making a rapid, sensitive and simultaneous diagnosis of inherited organic and amino acid disorders. In addition, this method is expected to be an alternative method for screening newborns for metabolic disorders in laboratories where expensive MS/MS is unavailable.

Simultaneous determination of endogenous and 13C-labelled thyroid hormones in plasma by stable isotope dilution mass spectrometry

This study describes a capillary gas chromatography–mass spectrometry (GC–MS) method for the simultaneous determination of endogenous thyroid hormone (thyroxine, T 4) and its 13 C -labelled analogue ( 13 C 6 -thyroxine) in plasma. 13 C 9 -thyroxine was used as analytical internal standard. A double derivatization (CH 3OH/HCl and HFBA) inducing good GC mobility was used for the GC–MS analysis of the thyroid hormones. Quantification was carried out by selected ion monitoring (SIM) of specific ions of the fragment ions ( m/ z 970/976/979). The detection limit of the present GC–MS–SIM method was found to be 100 pg per injection for thyroxine (S/N=3.0). A first implementation in in vivo tests of 13 C 6 -T 4 like metabolic tracer was carried out under veterinary control on one cat and one rabbit. The thyroxine follow-up was done by GC–MS and based on double isotopic dilution with two different regio-selective 13 C -labelled molecules of the same hormone. The present paper discusses the possibilities and limitations of this methodology. The in vivo experiment demonstrated that the use of stable isotopes and mass spectrometry provide a reliable methodology for hormonal monitoring.

Simultaneous determination of endogenous and 13C-labelled thyroid hormones in plasma by stable isotope dilution mass spectrometry

This study describes a capillary gas chromatography–mass spectrometry (GC–MS) method for the simultaneous determination of endogenous thyroid hormone (thyroxine, T4) and its 13C-labelled analogue (13C6-thyroxine) in plasma. 13C9-thyroxine was used as analytical internal standard. A double derivatization (CH3OH/HCl and HFBA) inducing good GC mobility was used for the GC–MS analysis of the thyroid hormones. Quantification was carried out by selected ion monitoring (SIM) of specific ions of the fragment ions (m/z 970/976/979). The detection limit of the present GC–MS–SIM method was found to be 100 pg per injection for thyroxine (S/N=3.0). A first implementation in in vivo tests of 13C6-T4 like metabolic tracer was carried out under veterinary control on one cat and one rabbit. The thyroxine follow-up was done by GC–MS and based on double isotopic dilution with two different regio-selective 13C-labelled molecules of the same hormone. The present paper discusses the possibilities and limitations of this methodology. The in vivo experiment demonstrated that the use of stable isotopes and mass spectrometry provide a reliable methodology for hormonal monitoring.

New technique using solid-phase extraction for the analysis of aromatic amines in mainstream cigarette smoke

A new procedure has been developed for the quantitation of aromatic amines in mainstream cigarette smoke. Two solid-phase extraction (SPE) cleanup steps using different retention mechanisms are required to process the samples. The first step uses a cation-exchange cartridge, followed by a second step that uses a cartridge with a hydrophobic retention character. The aromatic amines eluted from the second SPE cartridge are derivatized with heptafluorobutyric anhydride and analyzed with GC–MS selected ion monitoring in the negative chemical ionization mode. This new method has several advantages over other reported techniques, being sensitive, robust, and easily automated. The detection limits ranged from 0.02 ng/cigarette for tolidine to 1.41 ng/cigarette for aniline and the recoveries were from 79 to 109%.

Automated hollow fiber-protected dynamic liquid-phase microextraction of pesticides for gas chromatography–mass spectrometric analysis

Dynamic liquid-phase microextraction (LPME) controlled by a programmable syringe pump was evaluated for extracting pesticides in water prior to GC–MS analysis. A conventional microsyringe with a 1.3-cm length of hollow fiber attached to its needle was connected to a syringe pump to perform the extraction. The microsyringe was used as both the microextraction device as well as the sample introduction device for GC–MS analysis. The attached hollow fiber served as the “holder” and “protector” of 3 μl of organic solvent. The solvent was repeatedly withdrawn into and discharged from the hollow fiber by the syringe pump. Pesticides were extracted from 4-ml water samples into the organic solvent impregnated in the hollow fiber. The effects of organic solvents, plunger movement pattern, agitation and extraction time were investigated. Good repeatabilities of extraction performance were obtained, with the RSD values ranging from 3.0% (alachlor) to 9.8% (4-chlorophenol) for the 14 pesticides; most RSD values were under 5.0%. The method provided a 490-fold preconcentration of the target pesticides. The limits of detection were in the range of 0.01–5.1 μg/l ( S/ N=3) in the GC–MS selected ion monitoring mode. In addition, sample clean-up was achieved during LPME because of the selectivity of the hollow fiber, which prevented undesirable large molecules from being extracted. A slurry sample (mixture of 40 mg soil/ml of water) containing seven pesticides was extracted using this method which also gave good linearity and precision (most RSDs<7.0%, n=3).

Chitin in the fossil record: identification and quantification of d-glucosamine

Although a labile molecule, chitin is resistant to decay when complexed with protein. Currently, qualitative evidence for the preservation of chitin rests upon characteristic marker compounds derived through pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) of fossil arthropod cuticles, supported by a non-specific carbohydrate assay. However, unambiguous confirmation of the survival of chitin polymer requires detection of its hydrolysate monomer, d-glucosamine. We have now developed a GC–MS selected ion monitoring (SIM) method for the identification and quantification of d-glucosamine in fossil materials. Fossils of various ages and depositional settings were investigated and the results compared with those obtained by the Py–GC–MS approach. Specimens from the Rancho La Brea Tar Pits (USA, Pleistocene), showed the greatest degree of preservation: ∼10% (w/w), while fossil insects from Willershausen (Germany, Pliocene) and St Bauzile (France, Miocene) showed chitin to be present in ∼5% (w/w). Fossils from the Oligocene at Enspel, Germany, revealed that more than 0.5% is preserved for 25 million years. The GC–MS–SIM technique confirms the survival of chitin in the fossil record through the explicit identification of the polysaccharide monomer, and supports earlier Py–GC–MS and colorimetric analyses. The presence of other amino sugars of either exogenous (microbial) or diagenetic origin in more ancient specimens was also readily revealed using the GC–MS–SIM approach. This study illustrates the value of using a high-specificity quantitative ‘wet’ chemical approach in combination with Py–GC–MS to further advance the investigation of chitin in the fossil record.

Gas chromatographic–mass spectrometric determination of sulfolane in wetland vegetation exposed to sour gas-contaminated groundwater

Described is a GC–MS method for the determination of the levels of sulfolane (tetrahydrothiophene 1,1-dioxide, C 4H 8O 2S; a water miscible chemical used in the sweetening of sour gas) in wetland vegetation (roots, shoots, berries, seeds, grasses, and leaves). The technique was developed to provide positive detection of sulfolane in a variety of wetland vegetation and to determine the extent to which sulfolane may translocate within the plants. Vegetation samples collected at a sour gas processing facility were extracted using a two-stage process which utilized a back extraction of a water extract with toluene. The main advantages of this procedure were: good extraction efficiency (recovery of 80±12%), exclusion of most of the highly polar co-extractives during the toluene back extraction step, and a final extract well suited to routine GC–MS selected ion monitoring of sulfolane with a detection limit of 90 ng g −1 (wet mass). In general, the method was rugged, based on a study period of 18 months in which over 175 runs were conducted.

4-chloroindole-3-acetic and indole-3-acetic acids in Pisum sativum

Endogenous IAA and 4-chloroindole-3-acetic acid (4-C1-IAA) were analysed in vegetative and reproductive tissues of the garden pea ( Pisum sativum) using GC-MS selected ion monitoring in the presence of stable-isotope labelled internal standards. In fruit collected 3–8 days after anthesis (DAA) conjugates of both auxins were more abundant than the free hormones. Auxin levels (ng g −1 fr. wt) in the seeds were higher by 1–2 orders of magnitude than in the pericarps. However, as seeds are small at this stage, the pericarp nevertheless contains a substantial fraction of the overall quantity of IAA and 4-C1-IAA. While, in young fruit tissues, IAA was more abundant than 4-C1-IAA, the opposite was true for seeds at the ‘table-ready’ stage and for roots of nine-day-old seedlings. Our data suggest that both IAA and 4-C1-IAA are required to coordinate the vegetative and reproductive growth of pea plants. © 1997 Elsevier Science Ltd

GC/MS (SIM) Determination of 14 Pesticides Including Cyhexatin and 2, 4, 5-T in Nuts

GC/MS with selected ion monitoring (GC/MS (SIM)) has been developed as a screening method for the determination of 14 pesticides residues including cyhexatin and 2, 4, 5-T in nuts. The pesticides were extracted with acetone from nuts, and then partitioned between n-hexane and acetonitrile. Clean-up was conducted by solid-phase extraction (SPE) with a Bond Elut Florisil column. Most of the pesticides were eluted in a mixture of n-hexane and acetone (17:3) from the column, and the eluate was examined by GC/MS (SIM). Cyhexatin and 2, 4, 5-T were analyzed after derivatization and SPE clean-up. Recoveries of 14 pesticides from 6 kinds of nuts were mostly over 80%. This method is effective for multi-residue analysis of pesticides in nuts.

Quantification of GA1, GA3, GA4, GA7, GA8, GA9, GA19 and GA20 ; and GA20 metabolism in dormant and non-dormant beechnuts

The endogenous levels of GA1, GA3, GA4, GA7, GA8, GA9, GA19 and GA20 were determined in beech seeds (Fagus sylvatica L.) treated with different dormancy breaking treatments. Gibberellins were analysed separately in cotyledons and embryo axes. After purification of the extracts, GAs were quantified by GC-MS-selected ion monitoring (GC-MS-SIM) with deuterated GAs as internal standards. The results showed that GAs corresponding to the 13-OH pathway seemed to be involved in dormancy breaking. Strong differences in GA1, GA3, GA8, GA19 and GA20 levels between embryo axes and cotyledons of dormant and non-dormant beechnuts were detected with less pronounced differences for GA4, GA7 and GA9 levels. Both the quantitative differences between dormant and non-dormant seeds in the analysed GAs corresponding to the 13-OH pathway, and the capacity of non-dormant seeds to carry out metabolic conversions when labelled GA20 was injected into the seeds, reveal a dynamic role of GAs in dormancy release.

Method development for trace analysis of heteroaromatic compounds in contaminated groundwater

An analytical method providing high sensitivity (limit of quantitation of 50 ng/l) with acceptable reproducibility (mean R.S.D. 19%) has been developed for determining heteroaromatic compounds in creosote-contaminated groundwater. The best technique (highest recovery and reproducibility) found between liquid-liquid extraction using either dichloromethane, diethyl ether or pentane and solid-phase extraction with reversed-phase bonded columns, was the classical liquid extraction with dichloromethane from weak basic solutions and GC-MS (selective ion monitoring) analysis of concentrated extracts.

The Braer oil spill—Hydrocarbon concentrations in intertidal organisms

The concentrations of non-specific narcotic toxins such as the aromatic hydrocarbons toluene, naphthalene and phenanthrene were determined in specimens of limpets ( Patella vulgata) and razor shells ( Ensis spp.) collected from Shetland at the time of the Braer oil spill (84 000 t of Gullfaks production crude) and 3, 6 and 15 months after the spill. The analytical methods involved the use of deuterated analogues of the toxins to account for losses of analytes during recovery by steam distillation and determination by cryogenic GC-MS selected ion monitoring of molecular ions. Although the organisms were impacted by oil, the concentrations of total determinants in dead razor shells collected just after the oil spill were below the tissue effective concentrations for 50% reduction in filtering activity (TEC 50) for mussels (the most valid toxicological data available for comparative purposes). A portion of the unresolved monoaromatic hydrocarbons of Gullfaks crude would probably add to the burden of toxins, but this was not measured in this study. The distribution of aromatic hydrocarbons in the organisms (phenanthrenes > naphthalenes > toluene) was the reverse of that in the oil and correlates with the expected bioconcentration behaviour of hydrophobic organics whereby less water soluble compounds with higher octanol-water partition coefficients are concentrated. Concentrations of naphthalene to methylphenanthrenes in limpets collected in January at the time of the spill from sites close to the wreck were well below the TEC 50 values for mussels but comparison with the lower concentrations in limpets from a more remote site in Shetland indicated that the oil had impacted organisms near to the spill, consistent with intertidal survey data. Comparison with limited literature data for limpets and more extensive data for mussels also supported this conclusion, as did the identification of the oil residues in the limpets by biomarker fingerprinting. As with the razor shells, bioconcentration of the more hydrophobic compounds was observed. Concentrations in Shetland limpets generally decreased with increasing distance from the spill site. Concentrations of aromatic hydrocarbons decreased with time after the spill, such that by July concentrations were at what can reasonably be assumed to be background levels, comparable to the concentrations found at all times in the more remote site. Concentrations in a limited number of samples collected 15 months after the spill, following a further winter of storms in which sediment-sorbed oil could have been reintroduced to the limpets, showed no increase.