Gas Chromatography Combustion Isotope Ratio Mass Spectrometry Research Articles

Prediction of feeding system in Iberian pigs with three analytical methods by means of discriminant analysis

Subcutaneous fat samples from Iberian pigs were analysed by means of three analytical methods developed to predict the feeding system during the last fattening period (bellota, recebo, campo and cebo). These three methods were: (1) quantification of palmitic, stearic, oleic and linoleic fatty acids methyl esters by gas chromatography, (2) quantification of alpha and gamma tocopherol by high-performance liquid chromatography and (3) quantification of 13C/12C ratio by gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS). The results obtained by these methods over three season’s samples were used to perform a discriminant analysis in order to predict the feeding system during the fourth season, considered as the problem data. The results showed the capacity of the discriminant analysis for distinguishing between the feeding regime based in the consumption of acorn and pastures and that based in mixed diets (90% of success rate). However, differentiation of feeding systems in the case of mixed diet and natural resources during any time of the fattening phase seems not to be feasible.

Final report on CCQM-K27.2: Second Subsequent study: determination of ethanol in aqueous media

Ethanol is important both forensically ('drunk driving' or driving while under the influence, 'DWI', regulations) and commercially (alcoholic beverages). Blood- and breath-alcohol testing can be imposed on individuals operating private vehicles such as cars, boats or snowmobiles, or operators of commercial vehicles like trucks, planes and ships. The various levels of blood alcohol that determine whether these operators are considered legally impaired vary depending on the circumstances and locality. Accurate calibration and validation of instrumentation is critical in areas of forensic testing where quantitative analysis directly affects the outcome of criminal prosecutions, as is the case with the determination of ethanol in blood and breath. Additionally, the accurate assessment of the alcoholic content of beverages is a commercially important commodity.In 2002, the CCQM conducted a key comparison (CCQM-K27) for the determination of ethanol in aqueous matrix with nine participants. A report on this project has been approved by the CCQM and can be found at the BIPM website. CCQM-K27 comprised three samples, one at low mass fraction of ethanol in water (nominal concentration of 0.8 mg/g), one at high level (nominal concentration of 120 mg/g) and one wine matrix (nominal concentration of 81 mg/g). Overall agreement among eight participants using gas chromatography with flame ionization detection (GC-FID), titrimetry, isotope dilution gas chromatography/mass spectrometry (GC-IDMS) and gas chromatography–combustion-isotope ratio mass spectrometry (ID-GC-C-IRMS) was good. The ninth participant used a headspace GC-FID method that had not been validated in an earlier pilot study (CCQM-P35).A follow-on key comparison, CCQM-K27-Subsequent, was initiated in 2003 to accommodate laboratories that had not been ready to benchmark their methods in the original CCQM-K27 study or that wished to benchmark a different method. Four levels of ethanol in water were used in the subsequent study (nominal concentrations of 0.2 mg/g, 1 mg/g, 3 mg/g and 60 mg/g). The three participants in the CCQM-K27-Subsequent key comparison demonstrated their ability to measure ethanol in aqueous matrix in the concentration range of 0.2 mg/g to 60 mg/g. A report on this project has been approved by the CCQM and can be found at the BIPM website.A second follow-on key comparison, CCQM-K27.2 Second Subsequent, was initiated in 2006 to accommodate laboratories that had not been ready to benchmark their methods in the previous two CCQM-K27 studies. Two levels of ethanol in water were used in the second subsequent study ranging in concentration between 0.5 mg/g and 4 mg/g. Four of the five participants in the CCQM-K27.2 Second Subsequent key comparison demonstrated their ability to measure ethanol in aqueous matrix in that concentration range.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Pots and lipids: molecular and isotope evidence of the food processing at Maharski prekop

The pottery assemblage from the Maharski prekop site was analysed to obtain insights into vessel use and husbandry practices. Total lipid extracts of pottery samples were subjected to gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS) and soft ionisation electrospray mass spectrometric techniques ESI Q–TOF MS and ESI Q–TOF MS/MS. The charred organic deposits on vessels were AMS 14C dated. The results show that some vessels were used for cooking ruminant meat, while in other traces of mixed non–ruminant and ruminant meat or plants and animal meat cooking were identified. Some vessels were used for milk processing.

Can the labile carbon contribute to carbon immobilization in semiarid soils? Priming effects and microbial community dynamics

Tracer experiments with isotopic-enriched carbon compounds can provide information regarding the carbon cycling in semiarid soils. We studied priming effects and microbial utilization of glucose as an example of bioavailable labile molecule in the carbon cycle of a semiarid soil. The soil, which has low content of total organic carbon (5.0 g kg−1), was amended with U13C-glucose (99 atom %) at concentration of 75 μg C g−1 soil (LD) or 300 μg C g−1 soil (HD). Glucose-derived carbon remained in soil after two months of incubation. The percentage of residual carbon stabilized was greater in LD with 40% of the initial 13C added compared to 30% of the initial 13C added in the HD. Comparison of 13C content in water- and sodium-pyrophosphate extracts pointed to a significant humification of up to 2.4% of the initial 13C-glucose. Glucose was subjected to an intense mineralization in the first 17-days of 22.8% and 40.94% for the LD and HD, respectively. The stable isotope probing (SIP) of phospholipid fatty acids (PLFAs) by gas-chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) showed that bacteria dominated glucose metabolism in comparison to fungi. Gram-negative populations were initially more involved in glucose assimilation than Gram-positive bacteria. In the fatty acids fraction, up to 95% of the 13C was predominantly found in fatty acids typical for Gram-negative bacteria. However, after 4 and 17 days the 13C-enrichment in Gram-positive biomarkers increased. The mineralization of soil organic matter triggered by glucose additions was more intense in HD (3.6% of soil TOC) than LD (1.0% of soil TOC) and reached the highest level after 4 days in HD. Priming was controlled by Gram-negative populations but fungi and, particularly actinobacteria played an important role in latter steps. Our data indicated that the intense metabolism of SOM due to priming phenomena compromises the potential carbon sequestration in this semiarid soil amended with glucose.

Evaluation of Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometry (GC-C-IRMS) for the Quality Assessment of Citrus Liqueurs

Citrus liqueurs are alcoholic beverages obtained by maceration. The European Parliament protects these alcoholic beverages, forbidding the addition of nature-identical flavoring substances. However, for economical and technological reasons, producers often add natural and/or synthetic flavors to the alcoholic syrup, obtaining artificial spirit drinks. The aim of this study is to investigate the authenticity of Italian liqueurs, of lemon, bergamot, and mandarin (locally known as "limoncello", "bargamino", and "mandarinetto"), comparing the carbon isotope ratios with values determined in genuine cold-pressed peel oils. Authenticity assessment was performed using headspace-solid phase microextraction coupled to gas chromatography-combustion-isotope ratio mass spectrometry. Additional analyses were performed by direct enantioselective gas chromatography to determine the enantiomeric distribution of selected chiral volatiles and by gas chromatography-mass spectrometry for the qualitative analyses of the samples. The method allowed confirmation of genuineness. Enantioselective gas chromatography analyses confirmed the results, demonstrating the reliability of the method.

Evaluation of the organic matter sources using the δ13C composition of individual n-alkanes in sediments from Brazilian estuarine systems by GC/C/IRMS

The δ13C composition of individual n-alkanes (from C16 to C34) was measured from surface sediments of five Brazilian estuarine systems affected by different organic matter sources, such as harbor area, industries, urban centers and sugar cane crops, in order to determine the origins of the organic matter. The aliphatic hydrocarbon fraction was analyzed by gas chromatography–combustion–isotope ratio mass spectrometry (GC/C/IRMS). The levels of n-alkanes in the studied areas ranged from 0.34 to 18.14 μg kg−1, being relatively low in comparison to high polluted environments. The Carbon Preference Index (CPI) calculated in the C23–C34 range indicates that n-alkanes are mainly inherited from cuticular waxes of higher plants. The δ13C composition of all n-alkanes detected in the sediment samples ranged from −39.6 to −18.3‰ showing different sources for the studied estuarine systems. Through Principal Component Analysis (PCA) it was possible to verify the petrogenic influence in the n-alkane sources, especially in the Paraíba do Sul sediment samples. Differences up to 15‰ of the δ13C values between n-alkanes of odd and even carbon number (C26 and C27) also indicated mixture of petrogenic and biogenic sources in Paraíba do Sul River. High (less negative) δ13C n-alkane values of odd carbon number were obtained from two sampling sites located close to an ethanol plant, indicating residues discharge of sugar cane (C4 plant). Influence of C3 plants that are the main components of dense ombrophile forest was observed in the Itajaí-Açu sediments by the decrease of δ13C (about 10‰ compared to the Paraíba do Sul River δ13C).

Soil Fertilization Leads to a Decline in Between-Samples Variability of Microbial Community δ13C Profiles in a Grassland Fertilization Experiment

Gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) was used to measure the 13C/12C ratios of PLFAs at natural abundance levels from a temperate grassland nitrogen (N) and phosphorus (P) factorial fertilization experiment in northern Greece. In each plot two rhizosphere samples were derived centred around individual Agrostis capillaris and Prunella vulgaris plants. It was hypothesized that the isotopic signal of microbes that preferentially feed on recalcitrant litter such as fungi would be modified by fertilization more strongly than that of opportunistic microbes using labile C. Microbial community δ13C was affected by both P and N fertilization regime and plant species identity. However, we have been unable to detect significant nutrient effects on individual groups of microbes when analyzed separately in contrast to our original hypothesis. Intra-treatment variability, as evaluated from Hartley’s F max tests in the five first PCA components axes as well as the size of the convex hulls in PCA scoreplots and Mahalanobis distances, was considerably higher in the non-fertilized controls. Moreover, a significant relationship was established between the change in PLFA abundances and their respective changes in δ13C for the aggregate of samples and those simultaneously fertilized with N and P. We conclude that use of compound specific isotope analysis in the absence of labelling represents a valuable and overlooked tool in obtaining an insight of microbial community functioning.

Two‐dimensional gas chromatography with heart‐cutting for isotope ratio mass spectrometry analysis of steroids in doping control

The accuracy and precision of gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) measurements are highly dependent on analyte purity. Reliable analysis of urinary steroids for doping control therefore requires extensive and time-consuming sample preparation (i.e. liquid chromatography fraction collection) prior to GC-C-IRMS analysis. The use of two-dimensional GC (GC-GC) with heart-cutting (Deans Switch) as a possible approach to reduce the sample purification required for IRMS analysis is described herein. The system uses a low thermal mass oven (LTM) incorporated into an existing GC-C-IRMS system. GC-GC allowed the use of a cyanopropyl/phenyl column in the first dimension to optimize the separation of underivatized steroids, while a phenyl-methylpolysiloxane column in the second dimension focuses the selectively cut analytes into narrower peaks for more sensitive and reliable MS analysis. In addition, to confirm analyte identity, eluent from the second GC was split, with 20 % entering a scanning MS, and 80 % flowing to the IRMS. As a proof concept, the developed method was then used to analyze a single spot urine (5 ml) from an individual receiving T therapy (2 × 50 mg sachets of Testogel(®)). The T delta value (-27.8 ‰, [T] = 38 ng/ml) was clearly distinct from 11-ketoetiocholanolone (-22.5 ‰) (used as an endogenous reference compound (ERC)), indicating T as being of exogenous origin. The simultaneous analysis by the scanning MS yielded a full scan mass spectrum of the same chromatographic peak, thus confirming the peak to be T.

Calibration and data processing in gas chromatography combustion isotope ratio mass spectrometry

Compound-specific isotope analysis (CSIA) by gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) is a powerful technique for the sourcing of substances, such as determination of the geographic or chemical origin of drugs and food adulteration, and it is especially invaluable as a confirmatory tool for detection of the use of synthetic steroids in competitive sport. We review here principles and practices for data processing and calibration of GCC-IRMS data with consideration to anti-doping analyses, with a focus on carbon isotopic analysis ((13)C/(12)C). After a brief review of peak definition, the isotopologue signal reduction methods of summation, curve-fitting, and linear regression are described and reviewed. Principles for isotopic calibration are considered in the context of the Δ(13)C = δ(13)C(M) - δ(13)C(E) difference measurements required for establishing adverse analytical findings for metabolites (M) relative to endogenous (E) reference compounds. Considerations for the anti-doping analyst are reviewed.

Geo-microbial and light gaseous hydrocarbon anomalies in the near surface soils of Deccan Syneclise Basin, India: Implications to hydrocarbon resource potential

Deccan Syneclise Basin is considered geologically prospective for oil and gas reserves; however, a major part of the basin is covered by the Deccan Traps, hindering the exploration of Mesozoic hydrocarbon targets. Surface geochemical prospecting, based on micro-seepage of hydrocarbons from subsurface accumulations, could be advantageous in such areas. Surface geochemical prospecting method was applied in Deccan Syneclise for evaluation of hydrocarbon resource potential of the basin. The gas chromatographic analyses of adsorbed soil gasses showed the presence of C1 to C4 hydrocarbons. The concentrations of adsorbed soil gasses ranged for methane (C1)=1 to 483ppb, ethane (C2)=1 to 83ppb, propane (C3)=1 to 38ppb, butane (nC4)=1 to 60ppb and ΣC2+=1 to 129ppb, respectively. The scatter plots between C1 and C4 components depict linear trend indicating that all the gasses are derived from the same source.The carbon isotope composition of adsorbed methane was measured using Gas Chromatography–Combustion-Isotope Ratio Mass Spectrometry (GC–C-IRMS). The values for methane δ13C1 varied from −39.9 to −19.9‰ versus the Vienna PeeDee Belemnite (VPDB). The carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gasses derived from thermogenic sources. The propane oxidizing bacteria (POB) ranged between 1.0×102 and 12.8×105cfu/g of soil. The adsorbed light gaseous hydrocarbons and propane oxidizing bacterial anomalies found in and around Aurangabad, Ahmednagar, Shirdi, Akola, Bhusawal and Indore areas are considered to be promising for future hydrocarbon research and exploration.

Authenticity control on lemon essential oils employing Gas Chromatography–Combustion-Isotope Ratio Mass Spectrometry (GC–C-IRMS)

Gas Chromatography–Combustion-Isotope Ratio Mass Spectrometry (GC–C-IRMS) can provide information useful to discriminate among essential oils of different geographical origin and to reveal frauds on essential oils by addition of synthetic or natural compounds from different botanical origin. The present work reports the combination of information obtained by GC–C-IRMS, Enantioselective Gas Chromatography (Es-GC), high resolution Gas Chromatography (GC-FID) and spectrophotometry (CD values). All these techniques represent useful tools to evaluate the authenticity control on lemon essential oils. The GC–C-IRMS was applied to determine the authenticity range of carbon stable isotope ratios in genuine Italian lemon essential oils industrially cold-pressed. Several commercial samples were evaluated to assess their genuineness. The IRMS results are discussed in function of the values also obtained by GC-FID, es-GC and CD values. Stable isotope ratio analysis, by GC–C-IRMS, proved to be useful to detect the presence of sophistications in lemon essential oils, even when other techniques of analysis fail. However for subtle sophistications (e.g. addition of distilled lemon oil) quality assessment must be performed by the auxiliary of more than one technique.

Comparison of liquid chromatography–isotope ratio mass spectrometry (LC/IRMS) and gas chromatography–combustion–isotope ratio mass spectrometry (GC/C/IRMS) for the determination of collagen amino acid δ13C values for palaeodietary and palaeoecological reconstruction

Results are presented of a comparison of the amino acid (AA) δ(13)C values obtained by gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS) and liquid chromatography-isotope ratio mass spectrometry (LC/IRMS). Although the primary focus was the compound-specific stable carbon isotope analysis of bone collagen AAs, because of its growing application for palaeodietary and palaeoecological reconstruction, the results are relevant to any field where AA δ(13)C values are required. We compare LC/IRMS with the most up-to-date GC/C/IRMS method using N-acetyl methyl ester (NACME) AA derivatives. This comparison involves the analysis of standard AAs and hydrolysates of archaeological human bone collagen, which have been previously investigated as N-trifluoroacetyl isopropyl esters (TFA/IP). It was observed that, although GC/C/IRMS analyses required less sample, LC/IRMS permitted the analysis of a wider range of AAs, particularly those not amenable to GC analysis (e.g. arginine). Accordingly, reconstructed bulk δ(13)C values based on LC/IRMS-derived δ(13)C values were closer to the EA/IRMS-derived δ(13)C values than those based on GC/C/IRMS values. The analytical errors for LC/IRMS AA δ(13)C values were lower than GC/C/IRMS determinations. Inconsistencies in the δ(13)C values of the TFA/IP derivatives compared with the NACME- and LC/IRMS-derived δ(13)C values suggest inherent problems with the use of TFA/IP derivatives, resulting from: (i) inefficient sample combustion, and/or (ii) differences in the intra-molecular distribution of δ(13)C values between AAs, which are manifested by incomplete combustion. Close similarities between the NACME AA δ(13)C values and the LC/IRMS-derived δ(13)C values suggest that the TFA/IP derivatives should be abandoned for the natural abundance determinations of AA δ(13)C values.

Headspace-solid phase microextraction coupled to gas chromatography–combustion-isotope ratio mass spectrometer and to enantioselective gas chromatography for strawberry flavoured food quality control

Authenticity assessment of flavoured strawberry foods was performed using headspace-solid phase microextraction (HS-SPME) coupled to gas chromatography–combustion-isotope ratio mass spectrometry (GC–C-IRMS). An authenticity range was achieved, investigating on the carbon isotope ratio of numerous selected aroma active volatile components (methyl butanoate, ethyl butanoate, hex-(2E)-enal, methyl hexanoate, buthyl butanoate, ethyl hexanoate, hexyl acetate, linalool, hexyl butanoate, octyl isovalerate, γ-decalactone and octyl hexanoate) of organic Italian fresh strawberries. To the author's knowledge, this is the first time that all these components were investigated simultaneously by GC–C-IRMS on the same sample. The results were compared, when applicable, with those obtained by analyzing the HS-SPME extracts of commercial flavoured food matrices. In addition, one Kenyan pineapple and one fresh Italian peach were analyzed to determine the δ 13C VPDB of the volatile components common to strawberry. The δ 13C VPDB values are allowed to differentiate between different biogenetic pathways (C 3 and CAM plants) and more interestingly between plants of the same CO 2 fixation group (C 3 plants). Additional analyses were performed on all the samples by means of Enantioselective Gas Chromatography (Es-GC), measuring the enantiomeric distribution of linalool and γ-decalactone. It was found that GC–C-IRMS and Es-GC measurements were in agreement to detect the presence of non-natural strawberry aromas in the food matrices studied.

External calibration in Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometry measurements of endogenous androgenic anabolic steroids in sports doping control

An alternative calibration procedure for the Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometry (GC–C–IRMS) measurements of the World Antidoping Agency (WADA) Accredited Laboratories is presented. To alleviate the need for externally calibrated CO 2 gas for GC–C–IRMS analysis of urinary steroid metabolites, calibration using an external standard mixture solution of steroids with certified isotopic composition was investigated. The reference steroids of the calibration mixture and routine samples underwent identical instrumental processes. The calibration standards bracketed the entire range of the relevant δ 13C values for the endogenous and exogenous steroids as well as their chromatographic retention times. The certified δ 13C values of the reference calibrators were plotted in relation to measured m/ z 13CO 2/ 12CO 2 (i.e. R(45/44)) mass spectrometric signals of each calibrator. δ 13C values of the sample steroids were calculated from the least squares fit through the calibration curve. The effect of the external calibration on δ 13C values, using the same calibration standards and set of urine samples but different brands of GC–C–IRMS instruments, was assessed by an interlaboratory study in the WADA Accredited Laboratories of Sydney, Australia and Athens, Greece. Relative correspondence between the laboratories for determination of androsterone, etiocholanolone, 5β-androstane-3α,17β-diacetate, and pregnanediacetate means were SD( δ 13C) = 0.12‰, 0.58‰, −0.34‰, and −0.40‰, respectively. These data demonstrate that accurate intralaboratory external calibration with certified steroids provided by United States Antidoping Agency (USADA) and without external CO 2 calibration is feasible and directly applicable to the WADA Accredited Laboratories for the harmonization of the GC–C–IRMS measurements.

Stable carbon isotope geochemistry of adsorbed alkane gases in near-surface soils of the Saurashtra Basin, India

The stable carbon isotopic compositions of light hydrocarbon gases adsorbed in near-surface soil and sediments from the Saurashtra basin were characterized for their origin and maturity. Saurashtra is considered geologically prospective for oil and gas reserves; however, a major part of the basin is covered by the Deccan Traps, hindering the exploration of Mesozoic hydrocarbon targets. Surface geochemical prospecting, based on micro-seepage of hydrocarbons from subsurface accumulations, could be advantageous in such areas. In light of this, 150 soil samples were collected from the northwestern part of Saurashtra, around the Jamnagar area, where a thick sedimentary sequence of about 2–3 km exists under 1–1.5 km of Deccan basalt. The concentration of acid desorbed alkane gases from soil samples was found to vary (in ppb) as: methane (C 1) = 3–518; ethane (C 2) = 0–430; propane (C 3) = 0–331; i-butane (iC 4) = 0–297; n-butane (nC 4) = 2–116; i-pentane (iC 5) = 0–31 and n-pentane (nC 5) = 0–23, respectively. Fifteen samples with high concentrations of alkane gases were measured for their δ 13C 1; δ 13C 2 and δ 13C 3 compositions using gas chromatography–combustion-isotope ratio mass spectrometry (GC–C-IRMS). The values for methane varied from − 27 to − 45.4‰, ethane from − 20.9 to − 27.6‰, and propane from − 20.4 to − 29.1‰ versus the Vienna PeeDee Belemnite (VPDB). The carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources. Comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter, likely to be mainly a terrestrial source rock with a partial contribution from a marine source. These gases may have migrated to the near-surface environment, where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity. The maturity scale (δ 13C versus Log Ro %) applied to the surface sediment samples of the Jamnagar area indicated the source material to be capable of generating oil and gas. The detection of thermogenic alkane gases in near-surface sediments offers the possibility of hydrocarbons at depth in Saurashtra.

Stable carbon kinetic isotope effects for the production of methacrolein and methyl vinyl ketone from the gas-phase reactions of isoprene with ozone and hydroxyl radicals

The stable-carbon kinetic isotope effects (KIEs) associated with the production of methacrolein (MACR) and methyl vinyl ketone (MVK) from the reactions of isoprene with ozone and OH radicals were studied in a 25 L reaction chamber at (298±2) K and ambient pressure. The time dependence of both the stable-carbon isotope ratios and the concentrations was determined using a gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) system. The average yields of 13C-containing MACR and MVK generated from the ozone reaction of 13C-containing isoprene differed by −3.6‰ and −4.5‰, respectively, from the yields for MACR and MVK containing only 12C. For MACR and MVK generated from the OH-radical oxidation of isoprene the corresponding values were −3.8‰ and −2.2‰, respectively. These values indicate a significant depletion in the 13C abundance of MACR and MVK upon their formation relative to isoprene’s pre-reaction 13C/ 12C ratio, which is supported by theoretical interpretations of the oxidation mechanism of isoprene and its 13C-substituted isotopomers. Numerical model calculations of the isoprene + O 3 reaction predicted a similar depletion in 13C for both reaction products upon production. Furthermore, the model predicts mixing ratios and stable carbon delta values for isoprene, MACR, and MVK that were in agreement with the experimental results. The combined knowledge of isotope enrichment values with KIEs will reduce uncertainties in determinations of the photochemical histories of isoprene, MACR, and MVK in the troposphere. The studies presented here were conducted with using isoprene without any artificial isotope enrichment or depletion and it is therefore very likely that these results are directly applicable to the interpretation of studies of isoprene oxidation using stable carbon isotope ratio measurements.

Characterization of Rapeseed (Brassica napus) Oils by Bulk C, O, H, and Fatty Acid C Stable Isotope Analyses

Rapeseed ( Brassica napus ) oils differing in cultivar, sites of growth, and harvest year were characterized by fatty acid concentrations and carbon, hydrogen, and oxygen stable isotope analyses of bulk oils (delta(13)C(bulk), delta(2)H(bulk), delta(18)O(bulk) values) and individual fatty acids (delta(13)C(FA)). The delta(13)C(bulk), delta(2)H(bulk), and delta(18)O(bulk) values were determined by continuous flow combustion and high-temperature conversion elemental analyzer-isotope ratio mass spectrometry (EA/IRMS, TC-EA/IRMS). The delta(13)C(FA) values were determined using gas chromatography--combustion-isotope ratio mass spectrometry (GC/C/IRMS). For comparison, other C(3) vegetable oils rich in linolenic acid (flax and false flax oils) and rich in linoleic acid (poppy, sunflower, and safflower oils) were submitted to the same chemical and isotopic analyses. The bulk and molecular delta(13)C values were typical for C(3) plants. The delta(13)C value of palmitic acid (delta(13)C(16:0)) and n-3 alpha-linolenic acid (delta(13)C(18:3n-3)) differed (p < 0.001) between rape, flax, and poppy oils. Also within species, significant differences of delta(13)C(FA) were observed (p < 0.01). The hydrogen and oxygen isotope compositions of rape oil differed between cultivars (p < 0.05). Major differences in the individual delta(13)C(FA) values were found. A plant-specific carbon isotope fractionation occurs during the biosynthesis of the fatty acids and particularly during desaturation of C(18) acids in rape and flax. Bulk oil and specific fatty acid stable isotope analysis might be useful in tracing dietary lipids differing in their origin.

Analysis of polycyclic aromatic hydrocarbons extracted from air particulate matter using a temperature programmable injector coupled to GC–C–IRMS†

Compound specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds – in this case, polycyclic aromatic hydrocarbons (PAHs). In the study, PAHs were extracted from three dust samples: winter and summer filter dust and tunnel dust. The measurement was performed using the method validated in our laboratory using pure, solid compounds and EPA 610 reference assortment. CSIA required an appropriate clean-up method to avoid an unresolved complex in the gas chromatographic analysis usually found in the chromatography of PAHs. Extensive sample clean-up for this particular matrix was found to be necessary to obtain good gas chromatography–combustion–isotope ratio mass spectrometry analysis results. The sample purification method included two steps in which the sample is cleaned up and the aliphatic and aromatic hydrocarbons are separated. The concentration of PAHs in the measured samples was low; so a large volume injection technique (100 μl) was applied. The δVPDB 13C was measured with a final uncertainty smaller than 1 ‰. Comparison of the δVPDB 13C signatures of PAHs extracted from different dust samples was feasible with this method and, doing so, significant differences were observed.

Quantification of 15N-Nitrate in Urine with Gas Chromatography Combustion Isotope Ratio Mass Spectrometry to Estimate Endogenous NO Production

The use of stable isotope labeled substrates and subsequent analysis of urinary nitrate, forms a noninvasive test for evaluation of the in vivo NO metabolism. The present paper describes a new method for simultaneous quantification of (15)N-nitrate and total nitrate with gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS). Nitrate, isolated from urine with a nitrate selective resin, was reduced to nitrite using copperized cadmium. Subsequently, Sudan I was formed by diazotation. Sudan II was added as internal standard, and both molecules were analyzed with GC-C-IRMS as tert-butyldimethylsilyl derivatives. The accuracy was determined during a recovery study of two different known nitrate concentrations and two (15)N-enrichments. A recovery of 101.6% and 103.9% for total nitrate and 107.6% and 91.2% for (15)N-nitrate was obtained, respectively. The validated method was applied on complete 72 h urine collections after intravenous administration of (15)N-nitrate and (15)N-arginine in humans. On average, 51.8% (47.0-71.0%) of administered (15)N-nitrate was excreted, while 0.68% (0.44-1.17%) of (15)N-arginine was metabolized to nitrate. In conclusion, this method can be used for accurate simultaneous determination of (15)N-nitrate and total nitrate concentrations in urine and can be applied in clinical studies for noninvasive evaluation of NO metabolism in vivo.

Use of a temperature‐programmable injector coupled to gas chromatography–combustion–isotope ratio mass spectrometry for compound‐specific carbon isotopic analysis of polycyclic aromatic hydrocarbons

Compound-specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds; for instance, polycyclic aromatic hydrocarbons (PAHs) in aerosols. This could be a valuable tool in source apportionment of particulate matter (PM) air pollution. Because gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) analysis requires an amount of at least 10 ng of an individual PAH, a high concentration of PAHs in the injected extract is needed. When the concentration is low a large volume injector creates the possibility of introducing a satisfactory amount of individual PAHs. In this study a temperature-programmable injector was coupled to GC-C-IRMS and injection parameters (solvent level, transfer column flow, transfers time) were optimised using six solid aromatic compounds (anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene) dissolved in n-pentane and EPA 610 reference mixture. CSIA results for solid PAHs were compared with results obtained for the single components analysed by elemental analysis-isotope ratio mass spectrometry. The injection method was validated for two sample injection volumes, 50 and 100 microL. This method was also compared with commonly used splitless injection. To be included in the study, measurements had to have an uncertainty lower than 0.5 per thousand for delta(VPDB)13C and a minimum peak height of 200 mV. The lower concentration limits at which these criteria were fulfilled for PAHs were 30 mg/L for 1 microL in splitless injection and 0.3 and 0.2 mg/L for 50 and 100 microL, respectively, in large volume injection.