Development of two-dimensional gas chromatography/isotope ratio mass spectrometry for the stable carbon isotopic analysis of C(2)-C(5) non-methane hydrocarbons emitted from biomass burning

A two-dimensional gas chromatography/combustion/isotope ratio mass spectrometry (2D-GC/C/IRMS) system was developed for stable carbon isotopic measurements of C(2)-C(5) non-methane hydrocarbons (NMHCs) in biomass burning smoke. The 2D-GC/C/IRMS system successfully improved the accuracy and precision for the measurements of C(4) and C(5) saturated compounds in a smoke sample by selective injection of target compounds into a combustion furnace and consequently allowed us to provide complete baseline separation for all individual NMHCs. The analytical precision of the delta(13)C of each compound was better than 0.5 per thousand for more than 500 pmolC injections and 2.1 per thousand for 30 pmolC injections, which was estimated from replicate analysis of standard gases. This system was applied to the analysis of NMHCs in smoke samples collected from laboratory biomass burning experiments. From the combustion of three fuel materials (rice straw, pine wood, and maize), we found that the isotopic fractionation between fuel material and individual NMHCs is almost independent of the fuel material and thus the delta(13)C values of the fuel materials are reflected in delta(13)C values of most of NMHCs. However, only i-butane emitted from maize combustion showed anomalous (13)C-depletion of -11.6 per thousand relative to the delta(13)C value of maize. Such a large (13)C depletion suggests the specific isotopic fractionation process which is attributed to the maize combustion itself or the chemical properties of i-butane during production from a radical recombination reaction.     

Continuous flow stable isotope methods for study of delta(13)C fractionation during halomethane production and degradation

Gas chromatography/mass spectrometry/isotope ratio mass spectrometry (GC/MS/IRMS) methods for delta(13)C measurement of the halomethanes CH(3)Cl, CH(3)Br, CH(3)I and methanethiol (CH(3)SH) during studies of their biological production, biological degradation, and abiotic reactions are presented. Optimisation of gas chromatographic parameters allowed the identification and quantification of CO(2), O(2), CH(3)Cl, CH(3)Br, CH(3)I and CH(3)SH from a single sample, and also the concurrent measurement of delta(13)C for each of the halomethanes and methanethiol. Precision of delta(13)C measurements for halomethane standards decreased (+/-0.3, +/-0.5 and +/-1.3 per thousand) with increasing mass (CH(3)Cl, CH(3)Br, CH(3)I, respectively). Given that carbon isotope effects during biological production, biological degradation and some chemical (abiotic) reactions can be as much as 100 per thousand, stable isotope analysis offers a precise method to study the global sources and sinks of these halogenated compounds that are of considerable importance to our understanding of stratospheric ozone destruction.     

Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.     

Enhancing the understanding of earthworm feeding behaviour via the use of fatty acid delta13C values determined by gas chromatography-combustion-isotope ratio mass spectrometry

Litter-dwelling (epigeic) Lumbricus rubellus and soil-dwelling (endogeic) Allolobophora chlorotica earthworms were observed aggregating under C(3) (delta(13)C = -31.3 per thousand; delta(15)N = 10.7 per thousand) and C(4) (delta(13)C = -12.6 per thousand; delta(15)N = 7.5 per thousand) synthetic dung pats applied to a temperate grassland (delta(13)C = -30.3 per thousand; delta(15)N = 5.7 per thousand) in an experiment carried out for 372 days. Bulk delta(13)C values of earthworms collected from beneath either C(3) or C(4) dung after 28, 56, 112 and 372 days demonstrated that (i) L. rubellus beneath C(4) dung were significantly (13)C-enriched after 56 days (delta(13)C = -23.8 per thousand) and 112 days (delta(13)C = -22.4 per thousand) compared with those from C(3) dung treatments (56 days, delta(13)C = -26.5 per thousand; 112 days, delta(13)C = -27.0 per thousand), and (ii) A. chlorotica were 2.1 per thousand (13)C-enriched (delta(13)C = -24.2 per thousand) relative to those from C(3) dung (delta(13)C = -26.3 per thousand) treatments after 372 days. Bulk delta(15)N values did not suggest significant uptake of dung N by either species beneath C(3) or C(4) dung, but showed that the endogeic species (total mean delta(15)N = 3.3 per thousand) had higher delta(15)N values than the epigeic species (total mean delta(15)N = 5.4 per thousand). Although the two species exhibited similar fatty acid profiles, individual fatty acid delta(13)C values revealed extensive routing of dietary C into body tissue of L. rubellus, but minor incorporation into A. chlorotica. In particular, the direct incorporation of microbial biomarker fatty acids (iC(17:0), aC(17:0)) from (13)C-labelled dung in situ, the routing of dung C into de novo synthesised compounds (iC(20:4)(omega)(6),C(20:5)(omega)(3), and the assimilation of essential fatty acids ((C(18:1)(omega)(9), C(18:1)(omega(7), C(18:2)(omega(6), C(18:3)(omega)(3)) derived from dung, were determined.     

Development of a compound-specific isotope analysis method for acetone via 2,4-dinitrophenylhydrazine derivatization

A novel method has been developed for compound-specific isotope analysis for acetone via DNPH (2,4-dinitrophenylhydrazine) derivatization together with combined gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Acetone reagents were used to assess delta13C fractionation during the DNPH derivatization process. Reduplicate delta13C analyses were designed to evaluate the reproducibility of the derivatization, with an average error (1 standard deviation) of 0.17 +/- 0.05 per thousand, and average analytical error of 0.28 +/- 0.09 per thousand. The derivatization process introduces no isotopic fractionation for acetone (the average difference between the predicted and analytical delta13C values was 0.09 +/- 0.20 per thousand, within the precision limits of the GC/C/IRMS measurements), which permits computation of the delta13C values for the original underivatized acetone through a mass balance equation. Together with further studies of the carbon isotopic effect during the atmospheric acetone-sampling procedure, it will be possible to use DNPH derivatization for carbon isotope analysis of atmospheric acetone.     

A new method for determining delta13C and deltaD simultaneously for CH4 by gas chromatography/continuous-flow isotope-ratio mass spectrometry

A continuous-flow technique has been developed to analyse the deltaD and delta(13)C values for CH(4) from gas samples, in a single run. This is achieved by splitting the sample gas stream and directing the streams simultaneously through a CuNiPt combustion reactor and an alumina pyrolysis reactor. The CO(2) from CH(4) combustion is trapped in a liquid nitrogen trap while the H(2) exiting the pyrolysis reactor is directed to the mass spectrometer for deltaD(CH4) determination. The CO(2) is then sublimed and directed to the mass spectrometer for delta(13)C(CH4) determination. Sample runs take approximately 10 minutes. This technique gives accurate delta(13)C(CH4) results to within +/-0.3-0.5 per thousand and deltaD(CH4) results to within +/-2-5 per thousand. Injection volumes between 0.5 and 2.5 microL of CH(4), equivalent to between 20 and 100 nmol CH(4), are required for accurate delta(13)C and deltaD analyses, respectively, using sample injection into a split flow with a split ratio of 10. This method provides rapid, accurate and reproducible results on multiple sample runs and is, therefore, an ideal method for analysing natural gas samples from a variety of sources.     

Measurements of the 12C/13C kinetic isotope effects in the gas-phase reactions of light alkanes with chlorine atoms

The carbon kinetic isotope effects (KIEs) of the reactions of several light non-methane hydrocarbons (NMHC) with Cl atoms were determined at room temperature and ambient pressure. All measured KIEs, defined as the ratio of the Cl reaction rate constants of the light isotopologue over that of the heavy isotopologue (Clk12/Clk13) are greater than unity or normal KIEs. For simplicity, measured KIEs are reported in per mil according to Clepsilon=(Clk12/Clk13 -1)x1000 per thousand unless noted otherwise. The following average KIEs were obtained (all in per thousand): 10.73+/-0.20 (ethane), 6.44+/-0.14 (propane), 6.18+/-0.18 (methylpropane), 3.94+/-0.01 (n-butane), 1.79+/-0.42 (methylbutane), 3.22+/-0.17 (n-pentane), 2.02+/-0.40 (n-hexane), 2.06+/-0.19 (n-heptane), 1.54+/-0.15 (n-octane), 3.04+/-0.09 (cyclopentane), 2.30+/-0.09 (cyclohexane), and 2.56+/-0.25 (methylcyclopentane). Measurements of the 12C/13C KIEs for the Cl atom reactions of the C2-C8 n-alkanes were also made at 348 K, and no significant temperature dependence was observed. To our knowledge, these 12C/13C KIE measurements for alkanes+Cl reactions are the first of their kind. Simultaneous to the KIE measurement, the rate constant for the reaction of each alkane with Cl atoms was measured using a relative rate method. Our measurements agree with published values within+/-20%. The measured rate constant for methylcyclopentane, for which no literature value is available, is (2.83+/-0.11)x10-10 cm3 molecule-1 s-1, 1sigma standard error. The Clepsilon values presented here for the C2-C8 alkanes are an order of magnitude smaller than reported methane Clepsilon values (Geophys. Res. Lett., 2000, 27, 1715), in contrast to reported OHepsilon values for methane (J. Geophys. Res. (Atmos.), 2001, 106, 23, 127) and C2-C8 alkanes (J. Phys. Chem. A, 2004, 108, 11537), which are all smaller than 10 per thousand. This has important implications for atmospheric modeling of saturated NMHC stable carbon isotope ratios. 13C-structure reactivity relationship values (13C-SRR) for alkane-Cl reactions have been determined and are similar to previously reported values for alkane-OH reactions.     

A field and laboratory method for monitoring the concentration and isotopic composition of soil CO2

The stable isotope composition of nmol size gas samples can be determined accurately and precisely using continuous flow isotope ratio mass spectrometry (IRMS). We have developed a technique that exploits this capability in order to measure delta13C and delta18O values and, simultaneously, the concentration of CO2 in sub-mL volume soil air samples. A sampling strategy designed for monitoring CO2 profiles at particular locations of interest is also described. This combined field and laboratory technique provides several advantages over those previously reported: (1) the small sample size required allows soil air to be sampled at a high spatial resolution, (2) the field setup minimizes sampling times and does not require powered equipment, (3) the analytical method avoids the introduction of air (including O2) into the mass spectrometer thereby extending filament life, and (4) pCO2, delta13C and delta18O are determined simultaneously. The reproducibility of measurements of CO2 in synthetic tank air using this technique is: +/-0.08 per thousand (delta13C), +/-0.10 per thousand (delta18O), and +/-0.7% (pCO2) at 5550 ppm. The reproducibility for CO2 in soil air is estimated as: +/-0.06 per thousand (delta13C), +/-0.06 per thousand (delta18O), and +/-1.6% (pCO2). Monitoring soil CO2 using this technique is applicable to studies concerning soil respiration and ecosystem gas exchange, the effect of elevated atmospheric CO2 (e.g. free air carbon dioxide enrichment) on soil processes, soil water budgets including partitioning evaporation from transpiration, pedogenesis and weathering, diffuse solid-earth degassing, and the calibration of speleothem and pedogenic carbonate delta13C values as paleoenvironmental proxies.     

delta(13)C- and delta(18)O-values of glycerol of food fats

The average values of carbon and oxygen isotopic contents (delta(13)C and delta(18)O) of 36 glycerol samples from fats have been determined. The examined samples arise from many fats of animal and plant origin, as well as from the three Italian hard cheeses Parmigiano-Reggiano, Grana Padano and Trentingrana. The total (13)C content allows one to distinguish between glycerol from plants with the C-4 carbon fixation pathway (maize, mean delta(13)C = -14.4 per thousand) and that from plants with the C-3 pathway (mean delta(13)C = -30.7 per thousand). The delta(13)C-values of glycerols of animal origin seem to depend on the diet of the animal, as suggested by the mean values -29.6, -29.0 and -25.1 per thousand, respectively, observed for Parmigiano-Reggiano, Trentingrana and Grana Padano. Additionally, the mean total (18)O content of glycerol samples of vegetable origin is approximately 23.8 per thousand, while that from animal fat is 15.1 per thousand. However, the delta(18)O mean values relative to Parmigiano-Reggiano, Grana Padano and Trentingrana are 11.8, 16.0 and 13.8 per thousand, respectively. The combination of the (13)C and (18)O measurements relative to the fat glycerol of the three cheeses might be considered a potential criterion of authentication.     

Use of compound-specific delta13C and deltaD stable isotope measurements as an aid in the source apportionment of polyaromatic hydrocarbons

The potential of using compound-specific stable carbon isotopic analysis for the source apportionment of environmental polycyclic aromatic hydrocarbons (PAHs) has already been demonstrated by the authors, and other researchers. PAHs arising from wood burning and vehicle emissions have been shown to exhibit different isotopic signatures, and the isotopic compositions of n-alkanes and PAHs produced from combustion of C3 and C4 plant species have been reported. 13C/12C isotopic ratios for PAHs derived from coal and wood pyrolysis and from diesel particulates have been noted to vary over a range by ca. 8 per thousand, which may provide a basis for source apportionment. In order to further improve the ability of stable isotope measurements to source apportion environmental PAHs, hydrogen stable isotopes (deltaD) of PAHs from a number of processes have been measured. The wide range of deltaD values, in conjunction with the delta13C values obtained, provide a much greater degree of differentiation between petrol and jet fuel derived PAHs, and between PAHs from different coal conversion processes, than the delta13C values alone.     

Delta13C analyses of calcium carbonate: Comparison between the GasBench and elemental analyzer techniques

Measurements of stable carbon isotopic composition (delta13C) of carbonates or carbonate-rich soils are seldom performed in a continuous-flow isotope ratio mass spectrometer (IRMS) using an elemental analyzer (EA) as an online sample preparation device. Such analyses are routinely carried out with an external precision better than 0.1 per thousand using a GasBench II (GB) sample preparation device coupled online with a continuous-flow IRMS. In this paper, we report and compare delta13C analyses (86 total analyses) of calcium carbonates obtained by using both the GB and the EA. Using both techniques, the delta13C compositions of two in-house carbonate standards (MERCK carbonate and NR calcite) and ten selected carbonate-rich paleosol samples (of variable CaCO3 content) were analyzed, and data are reported in the VPDB scale calibrated against international standards, NBS 18 and 19. For the in-house standards analyzed by both techniques, a precision better than 0.08 per thousand is achieved. The analytical errors (1sigma) computed from multiple analyses of the delta13C of both the MERCK and NR obtained by the above two techniques are nearly identical. In general, the 1sigma (internal error) of paleosol analyses obtained in the GB is better than 0.06 per thousand, whereas that for the analyses in the EA (three repetitive analyses of the same sample) varies in the range 0.05-0.21 per thousand. However, for paleosols having more than 85% CaCO3, 1sigma is better than 0.15 per thousand (similar to the instrument precision), and in this case the delta13C(VPDB) of samples obtained by the GB is similar to that obtained by the EA. Our results suggest that the delta13C of pure calcium carbonate samples can also be analyzed using the EA technique.     

Grain-scale heterogeneities in the stable carbon and oxygen isotopic compositions of the international standard calcite materials (NBS 19, NBS 18, IAEA-CO-1, and IAEA-CO-8)

We determined grain-scale heterogeneities (from 6 to 88 microg) in the stable carbon and oxygen isotopic compositions (delta(13)C and delta(18)O) of the international standard calcite materials (NBS 19, NBS 18, IAEA-CO-1, and IAEA-CO-8) using a continuous-flow isotope ratio mass spectrometry (CF-IRMS) system that realizes a simultaneous determination of the delta(13)C and the delta(18)O values with standard deviations (S.D.) of less than 0.05 per thousand for CO(2) gas. Based on the S.D. of the delta(13)C and delta(18)O values determined for CO(2) gases evolved from the different grains of the same calcite material, we found that NBS 19, IAEA-CO-1, and IEAE-CO-8 were homogeneous for delta(13)C (less than 0.10 per thousand S.D.), and that only NBS 19 was homogeneous for delta(18)O (less than 0.14 per thousand S.D.). On the level of single grains, we found that both IAEA-CO-1 and IAEA-CO-8 were heterogeneous for delta(18)O (1.46 per thousand and 0.76 per thousand S.D., respectively), and that NBS 18 was heterogeneous for both delta(13)C and delta(18)O (0.34 per thousand and 0.54 per thousand S.D., respectively). Closer inspection of NBS 18 grains revealed that the highly deviated isotopic compositions were limited to the colored grains. By excluding such colored grains, we could also obtain the homogeneous delta(13)C and delta(18)O values (less than 0.18 per thousand and less than 0.16 per thousand S.D., respectively) for NBS 18. We conclude that NBS 19, IAEA-CO-1, or pure grains in NBS 18 are suitable to be used as the standard reference material for delta(13)C, and that either NBS 19 or pure grains in NBS 18 are suitable to be used as the reference material for delta(18)O during the grain-scale isotopic analyses of calcite.     

Olefin metatheses in metal coordination spheres: versatile new strategies for the construction of novel monohapto or polyhapto cyclic, macrocyclic, polymacrocyclic, and bridging ligands

The broad applicability of the title reaction is established through studies of neutral and charged, coordinatively saturated and unsaturated, octahedral and square planar rhenium, platinum, rhodium, and tungsten complexes with cyclopentadienyl, phosphine, and thioether ligands which contain terminal olefins. Grubbs' catalyst, [Ru(=CHPh)(PCy3)2(Cl)2], is used at 2-9 mol% levels (0.0095-0.00042 M, CH2-Cl2). Key data are as follows: [(eta5-C5H4(CH2)6CH=CH2)Re(NO)(PPh3)-(CH3)], intermolecular metathesis (95 %); [(eta5-C5H5)Re(NO)(PPh3)(E(CH2CH=CH2)2)]+ TfO (E=S, PMe, PPh), formation of five-membered heterocycles (96-64%; crystal structure E = PMe); [(eta5-C5Me5)Re(NO)(PPh((CH2)6CH=CH2)2)(L)]n+ nBF4-(L/n = CO/1, Cl/0), intramolecular macrocyclization (94-89%; crystal structure L= Cl); fac-[(CO)3Re(Br)(PPh2(CH2)6CH=CH2)2] and cis-[(Cl)2Pt(PPh2(CH2)6CH=CH2)2], intramolecular macrocyclizations (80-71%; crystal structures of each and a hydrogenation product); cis-[(Cl)2Pt(S(R)(CH2)6CH= CH2)2], intra-/intermolecular macrocyclization (R=Et, 55%/24%; tBu, 72%/ <4%); trans-[(Cl)(L)M(PPh2(CH2)6CH=CH2)2] (M/L = Rh/CO, Pt/C6F5) intramolecular macrocyclization (90-83%; crystal structure of hydrogenation product, M=Pt); fac-[W(CO)3(PPh((CH2)6CH=CH2)2)3], intramolecular trimacrocyclization (83 %) to a complex mixture of triphosphine, diphosphine/ monophosphine, and tris(monophosphine) complexes, from which two isomers of the first type are crystallized. The macrocycle conformations, and basis for the high yields, are analyzed.     

Application of stable carbon isotope analysis to the detection of 17beta-estradiol administration to cattle

The use of anabolic agents in food producing animals is prohibited within the EU since 1988 (96/22/EC directive). The control of the illegal use of natural steroid hormones in cattle is still an exciting analytical challenge as far as no definitive method and non-ambiguous analytical criteria are available. The ability of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) to demonstrate the administration of 17beta-estradiol to bovine has been investigated in this paper. By comparison of 13C/12C isotopic ratio of main urinary estradiol metabolite, i.e. 17alpha-estradiol, with two endogenous reference compounds (ERCs), i.e. dehydroepiandrosterone (DHEA) and 5-androstene-3beta,17alpha-diol, the differentiation of estradiol metabolite origin, either endogenous or exogenous, has been proved to be achievable. After treatment, the delta(13)C(VPDB)-values of 17alpha-estradiol reached -27 per thousand to -29 per thousand, whereas delta13CVPDB-values of DHEA remained between -13 per thousand and -20 per thousand depending on the diet, maize and grass, respectively. A significant difference of delta13CVPDB between ERCs and 17alpha-estradiol was measurable over a period of 2 weeks after estradiol ester administration to the animal.     

A portable automated system for trace gas sampling in the field and stable isotope analysis in the laboratory

A computer-controllable mobile system is presented which enables the automatic collection of 33 air samples in the field and the subsequent analysis for delta13C and delta18O stable isotope ratios of a carbon-containing trace gas in the laboratory, e.g. CO2, CO or CH4. The system includes a manifold gas source input for profile sampling and an infrared gas analyzer for in situ CO2 concentration measurements. Measurements of delta13C and delta18O of all 33 samples can run unattended and take less than six hours for CO2. Laboratory tests with three gases (compressed air with different pCO2 and stable isotope compositions) showed a measurement precision of 0.03 per thousand for delta13C and 0.02 per thousand for delta18O of CO2 (standard error (SE), n = 11). A field test of our system, in which 66 air samples were collected within a 24-hour period above grassland, showed a correlation of 0.99 (r2) between the inverse of pCO2 and delta13C of CO2. Storage of samples until analysis is possible for about 1 week; this can be an important factor for sampling in remote areas. A wider range of applications in the field is open with our system, since sampling and analysis of CO and CH4 for stable isotope composition is also possible. Samples of compressed air had a measurement precision (SE, n = 33) of 0.03 per thousand for delta13C and of 0.04 per thousand for delta18O on CO and of 0.07 per thousand for delta13C on CH4. Our system should therefore further facilitate research of trace gases in the context of the carbon cycle in the field, and opens many other possible applications with carbon- and possibly non-carbon-containing trace gases.     

Influence of dietary composition on the carbon, nitrogen, oxygen and hydrogen stable isotope ratios of milk

The stable isotope ratios ((13)C/(12)C, (15)N/(14)N, (18)O/(16)O, D/H) of animal feed and milk were investigated, considering cows stabled in two farms and fed with diets made up of different kinds of C(3) plants and different amounts of maize. Maize was characterised by delta(13)C, delta(18)O and deltaD values significantly higher than those of the C(3) plants, while, for the C(3) plants, Festuca arudinacea had significantly higher content of (13)C and (15)N. The delta(13)C and delta(18)O values of the overall diet and the delta(13)C of milk casein and lipids were shown to be significantly correlated with the percentage of maize in the animal diet. On the other hand, the delta(18)O values of milk water and the delta(18)O, deltaD and delta(15)N values of casein were shown to be only slightly influenced by the amount of maize in the feed, being probably more closely correlated with the geo-climatic and pedological characteristics of the area of origin and with the presence of fresh plant or silage in the ration. The delta(13)C value of casein was shown to be a suitable parameter for evaluating the amount of maize in the diet: each 10% increase in the maize content corresponded to a shift of 0.7 per thousand to 1.0 per thousand in the delta(13)C of casein. A threshold value of -23.5 per thousand for delta(13)C in milk casein, above which it is not possible to exclude the presence of maize in the diet, was suggested. The results obtained could be useful for determining mislabelling of dairy products declared to have been produced by pastured animals or of PDO cheeses with an established amount of maize in the diet and for verifying the unpermitted addition of exogenous components to milk.     

水体中痕量挥发性有机物单体碳同位素组成分析

将固相微萃取(SPME)技术与冷阱富集系统相结合,对水体中痕量挥发性有机物进行了单体碳同位素分析,方法检测限较常规SPME提高了一个数量级。在优化的条件下,对20 μg/L的三氯乙烯/四氯乙烯和10 μg/L的苯/甲苯水溶液进行了单体碳同位素分析,相比于纯溶剂(液相)碳同位素值,顶空(气相)同位素分析误差不超过0.5‰,而样本标准偏差为0.3‰。对某受四氯乙烯污染的北京地下水进行了同位素测定,近污染源点(B408)与远污染源点(B230)四氯乙烯的碳同位素值(δ13C)分别为 -37.8‰和-34.45‰     

A method for carbon stable isotope analysis of methyl halides and chlorofluorocarbons at pptv concentrations

A pre-concentration system has been validated for use with a gas chromatography/mass spectrometry/isotope ratio mass spectrometer (GC/MS/IRMS) to determine ambient air (13)C/(12)C ratios for methyl halides (MeCl and MeBr) and chlorofluorocarbons (CFCs). The isotopic composition of specific compounds can provide useful information on their atmospheric budgets and biogeochemistry that cannot be ascertained from abundance measurements alone. Although pre-concentration systems have been previously used with a GC/MS/IRMS for atmospheric trace gas analysis, this is the first study also to report system validation tests. Validation results indicate that the pre-concentration system and subsequent separation technologies do not significantly alter the stable isotopic ratios of the target methyl halides, CFC-12 (CCl(2)F(2)) and CFC-113 (C(2)Cl(3)F(3)). Significant, but consistent, isotopic shifts of -27.5 per thousand to -25.6 per thousand do occur within the system for CFC-11 (CCl(3)F), although the shift is correctible. The method presented has the capacity to separate these target halocarbons from more than 50 other compounds in ambient air samples. Separation allows for the determination of stable carbon isotope ratios of five of these six target trace atmospheric constituents within ambient air for large volume samples (相似文献   

Compound-specific stable carbon isotope ratios (delta13C values) of the halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1)

Compound-specific isotope analysis using gas chromatography interfaced to isotope ratio mass spectrometry (GC/IRMS) was applied for the determination of delta13C values of the marine halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1). The delta13C value of a lab-made Q1 standard (-34.20 +/- 0.27 per thousand) was depleted in 13C by more than 11 per thousand relative to the residues of Q1 in dolphin blubber from Australia and skua liver from Antarctica. This clarified that the synthesized Q1 was not the source for Q1 in the biota samples. However, two Australian marine mammals showed a large variation in the delta13C value, which, in our experience, was implausible. Since the GC/IRMS system was connected to a conventional ion trap mass spectrometer by a post-column splitter, we were able to closely inspect the peak purity of Q1 in the respective samples. While the mass spectra of Q1 did not indicate any impurity, a fronting peak of PCB 101 was identified in one sample. This interference falsified the delta13C value of the respective sample. Once this sample was excluded, we found that the delta13C values of the remaining samples, i.e. liver of Antarctic brown skua (-21.47 +/- 1.47 per thousand) and blubber of Australian melon-headed whale (-22.80 +/- 0.33 per thousand), were in the same order. The standard deviation for Q1 was larger in the skua samples than in the standard and the whale blubber sample. This was due to lower amounts of skua sample available. It remained unclear if the Q1 residues originate from the same producer and location.     

Detection of royal jelly adulteration using carbon and nitrogen stable isotope ratio analysis

Stable isotope ratios ((13)C/(12)C and (15)N/(14)N) were measured in royal jelly (RJ) samples by isotope ratio mass spectrometry (IRMS) to evaluate authenticity and adulteration. Carbon and nitrogen isotope contents (given as delta values relative to a standard, delta(13)C, delta(15)N) of RJ samples from various European origins and samples from commercial sources were analyzed. Uniform delta(13)C values from -26.7 to -24.9 per thousand were observed for authentic RJ from European origins. Values of delta(15)N ranged from -1.1 to 5.8 per thousand depending on the plant sources of nectars and pollen. High delta(13)C values of several commercial RJ samples from -20.8 to -13.3 per thousand indicated adulteration with high fructose corn syrup (HFCS) as a sugar source. Use of biotechnologically produced yeast powder as protein source for the adulterated samples was assumed as delta(15)N values were lower, as described for C(4) or CAM plant sources. RJ samples from authentic and from adulterated production were distinguished. The rapid and reliable method is suitable for urgent actual requirements in food monitoring.