Selective conversion of plasma glucose into CO2 by Saccharomyces cerevisiae for the measurement of 13C abundance by isotope ratio mass spectrometry: proof of principle

To study carbohydrate digestion and glucose absorption, time-dependent (13)C enrichment in plasma glucose is measured after oral administration of naturally occurring (13)C-enriched carbohydrates. The isotope enrichment of the administered carbohydrate is low (APE <0.1%) and plasma (13)C glucose measurements are routinely determined with gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) or liquid chromatography/combustion/isotope ratio mass spectrometry (LC/C/IRMS). In this study, plasma glucose was converted into CO(2) by an in-tube reaction with yeast permitting direct measurement of (13)CO(2) in the headspace. Saccharomyces cerevisiae incubated under anaerobic conditions was able to convert sufficient glucose into CO(2) to produce a consistent CO(2) peak in IRMS with little variation in peak area and precise delta(13)C(PDB) values for corn glucose: -11.40 +/- 0.16 per thousand, potato glucose: -25.17 +/- 0.13 per thousand, and plasma glucose: -26.29 +/- 0.05 per thousand. The measurement showed high linearity (R(2) = 0.999) and selectivity and was not affected by the glucose concentration in the tested range of 5-15 mM. Comparison with GC/C/IRMS showed a good correlation of enrichment data: R(2) > 0.98 for both sources of glucose and plasma samples. Commercially available, instant dried baker's yeast was qualitatively and quantitatively comparable with freshly prepared yeast: R(2) > 0.96, slope 1.03 and 1.08 for glucose solutions and plasma, respectively. Thus, yeast conversion of plasma glucose into CO(2) and (13)C measurement applying a breath (13)CO(2) analyzer is an inexpensive, simple and equally accurate alternative to the more expensive and laborious GC/C/IRMS and LC/C/IRMS measurements.     

Novel method for measurement of glutathione kinetics in neonates using liquid chromatography coupled to isotope ratio mass spectrometry

A novel analytical method using liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS) was developed for measuring the fractional synthesis rate (FSR) of glutathione (GSH) in neonates after infusion of [1-(13)C]-glycine as a tracer. After transformation of GSH into GSSG, its dimeric form, the intra-erythrocytic concentration and (13)C-isotopic enrichment of GSH were determined using 200 microL of blood. The results showed that, using LC/IRMS, the concentration (range of micromol/mL) was reliably measured using norvaline as internal standard with precision better than 0.1 micromol/mL. In addition, the (13)C-isotopic enrichment measured in the same run gave reliable values with excellent precision (with standard deviation (sd) lower than 0.3 per thousand) and accuracy (measured between 0 and 2 Atom % Excess (APE)). The inter-assay repeatability of delta(13)C of norvaline used as internal standard with in vivo samples was assessed at -26.07 +/- 0.28 per thousand with coefficient of variance (CV) at 1.1%. The FSR calculated either with GSH or GSSG showed similar results with slightly higher values for GSSG (41.6 +/- 4.7 and 46.5 +/- 4.4, respectively). The slightly lower FSR of GSH is probably due to interfering compounds in the biological matrix. Successfully used in a clinical study, this rapid and reliable method opens up a variety of kinetic studies with relatively low administration of tracer infusates, reducing the total cost of the study design. The small volume of blood needed enables studies even in extremely small subjects, such as premature infants, as reported in this study.     

Minimization of carbon addition during derivatization of monosaccharides for compound-specific delta13C analysis in environmental research

Little is known about the delta13C composition of monosaccharides representing the largest carbon reservoir in the biosphere. The main reason for this might be that monosaccharides have to be derivatized prior to gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analyses and that a large isotopic correction is necessary for the carbon that has to be added to the original molecule during derivatization, resulting in large uncertainty of the calculated delta13C values of individual monosaccharides. The amount of added derivatization carbon is twice (alditol acetates) or even three times (trimethylsilyl (TMS) derivatives) as high as the amount of the original monosaccharide carbon. In addition, isotope fractionation occurs during acetylation. Therefore, the objectives of this study were (i) to minimize carbon addition during derivatization for GC/C/IRMS measurements of monosaccharides in soil and sediment samples and (ii) to quantify improvements in accuracy and precision of the final results. Minimization of carbon addition was accomplished by derivatization with methylboronic acid (MBA) and TMS thereafter (MBA method). Monosaccharides derivatized with the MBA method instead of TMS reduced the number of added carbon atoms from 2.2-2.7 to 0.3-0.8 per sugar carbon atom. Although the precision of GC/C/IRMS measurements with both methods is comparable (about 0.3 per thousand), delta13C values of an internal standard indicated that the newly developed MBA method is about 2 per thousand more accurate than the TMS method. delta13C comparison between soil samples that differed only slightly in their bulk carbon isotope signature showed that the MBA method is better in proving these small differences on a significant level. Total precision of the whole MBA method including all analytical and calculation steps is better by a factor of almost three than the TMS method.     

Improved isotope ratio measurement performance in liquid chromatography/isotope ratio mass spectrometry by removing excess oxygen

A low dead volume oxygen scrubbing system was introduced in a commercially available liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) interface to enhance the analytical capability of the system. In the LC/IRMS interface carbon from organic samples is converted into CO(2) inside the mobile phase by wet chemical oxidation using peroxodisulfate (Na(2)S(2)O(8)). After passing the hot reaction zone, surplus oxygen (O(2)) remains dissolved in the liquid phase. Both CO(2) and O(2) diffuse through a transfer membrane into the helium carrier and are transferred to the mass spectrometer. The presence of O(2) in the ion source may have detrimental effects on measurement accuracy and precision as well as on filament lifetime. As a remedy, a new on-line O(2)-removing device has been incorporated into the system.The new O(2) scrubber consists of two parallel hot copper reduction reactors (0.8 mm i.d., active length 120 mm) and a switch-over valve between them. One reactor is regenerated using He/H(2) while the other is actively scavenging O(2) from the gas stream. The capacity of each reduction reactor, expressed as usage time, is between 40 and 50 min. This is sufficient for a single LC run for sugars and organic acids. A further increase of the reduction capacity is accompanied by a peak broadening of about 100%. After switching to a freshly reduced reactor the oxygen background and the delta(13)C values of the reference gas need up to 500 s to stabilize. For repeated injections the delta(13)C values of sucrose remain constant (+/-0.1 per thousand) for about 3000 s. The long-term stability for measurements of sucrose was 0.11 per thousand without the reduction oven and improved slightly to 0.08 per thousand with the reduction oven. The filament lifetime improved by more than 600%, thereby improving the long-term system stability and analytical efficiency. In addition the costs per analysis were reduced considerably.     

Optimization of automated gas sample collection and isotope ratio mass spectrometric analysis of delta(13)C of CO(2) in air

The application of (13)C/(12)C in ecosystem-scale tracer models for CO(2) in air requires accurate measurements of the mixing ratios and stable isotope ratios of CO(2). To increase measurement reliability and data intercomparability, as well as to shorten analysis times, we have improved an existing field sampling setup with portable air sampling units and developed a laboratory setup for the analysis of the delta(13)C of CO(2) in air by isotope ratio mass spectrometry (IRMS). The changes consist of (a) optimization of sample and standard gas flow paths, (b) additional software configuration, and (c) automation of liquid nitrogen refilling for the cryogenic trap. We achieved a precision better than 0.1 per thousand and an accuracy of 0.11 +/- 0.04 per thousand for the measurement of delta(13)C of CO(2) in air and unattended operation of measurement sequences up to 12 h.     

A selective unsaturated hydrocarbon subtraction technique for stable carbon isotopic analysis of atmospheric methyl chloride, methyl bromide, and C2-C5 saturated hydrocarbons using continuous-flow isotope ratio mass spectrometry

Using continuous-flow isotope ratio mass spectrometry, we have developed a new analytical system which enables us to determine the stable carbon isotopic composition of CH3Cl, CH3Br, and C2-C5 saturated hydrocarbons in gas samples even if they contain substantial amounts of unsaturated hydrocarbons, using an I2O5 reagent for their selective subtraction. The analytical precision of the delta13C determinations is better than 0.5 per thousand for >300 pmolC injections and better than 5 per thousand for 20 pmolC injections. Using the system, delta13C values for CH3Cl and CH3Br were found in burning exhaust that contain a substantial quantity of unsaturated hydrocarbons. CH3Cl and CH3Br measured in exhaust from burning rice plants exhibit highly 13C-depleted values of -56.6 +/- 1.3 per thousand and -48.6 +/- 3.9 per thousand, respectively, while saturated hydrocarbons exhibit delta13C values (-26.4 to -28.9 per thousand) that are comparable with the total delta13C value of the parent material (rice plant; -28.0 per thousand). Using the system, we can determine the delta13C values of methyl halides and hydrocarbons in many kinds of gas samples.     

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.     

GasBench/isotope ratio mass spectrometry: a carbon isotope approach to detect exogenous CO(2) in sparkling drinks

A new procedure for the determination of carbon dioxide (CO(2)) (13)C/(12)C isotope ratios, using direct injection into a GasBench/isotope ratio mass spectrometry (GasBench/IRMS) system, has been developed to improve isotopic methods devoted to the study of the authenticity of sparkling drinks. Thirty-nine commercial sparkling drink samples from various origins were analyzed. Values of delta(13)C(cava) ranged from -20.30 per thousand to -23.63 per thousand, when C3 sugar addition was performed for a second alcoholic fermentation. Values of delta(13)C(water) ranged from -5.59 per thousand to -6.87 per thousand in the case of naturally carbonated water or water fortified with gas from the spring, and delta(13)C(water) ranged from -29.36 per thousand to -42.09 per thousand when industrial CO(2) was added. It has been demonstrated that the addition of C4 sugar to semi-sparkling wine (aguja) and industrial CO(2) addition to sparkling wine (cava) or water can be detected. The new procedure has advantages over existing methods in terms of analysis time and sample treatment. In addition, it is the first isotopic method developed that allows (13)C/(12)C determination directly from a liquid sample without previous CO(2) extraction. No significant isotopic fractionation was observed nor any influence by secondary compounds present in the liquid phase.     

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.     

A rapid screening assay for measuring urinary androsterone and etiocholanolone delta(13)C ( per thousand) values by gas chromatography/combustion/isotope ratio mass spectrometry

A gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) method is described and validated for measurement of delta(13)C values of the acetate derivatives of urinary etiocholanolone and androsterone. The analysis was performed with only 2 mL of urine. The sample preparation consisted of deconjugation with beta-glucuronidase, solid phase extraction, and derivatization with acetic anhydride and pyridine. The within-assay precision of two quality control (QC) urine samples ranged from 0.5 to 2.1 CV%. The between-assay precision in the same QC urines ranged from 1.7 to 3.4 CV%. Administration of testosterone enanthate to a subject resulted in a 6 per thousand decrease in delta(13)C values from -25 per thousand (baseline) to -31 per thousand. Two weeks after testosterone administration was discontinued, the delta(13)C values remained abnormally low while the urine testosterone/epitestosterone (T/E) ratio returned to less than 6. This relatively simple method is useful for rapidly screening a large number of urine samples, including those with T/E <6.     

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.     

Methods to adjust for the interference of N2O on delta13C and delta18O measurements of CO2 from soil mineralization

In this paper we present an overview of the present knowledge relating to methods that avoid interference of N2O on delta13C and delta18O measurements of CO2. The main focus of research to date has been on atmospheric samples. However, N2O is predominantly generated by soil processes. Isotope analyses related to soil trace gas emissions are often performed with continuous flow isotope ratio mass spectrometers, which do not necessarily have the high precision needed for atmospheric research. However, it was shown by using laboratory and field samples that a correction to obtain reliable delta13C and delta18O values is also required for a commercial continuous flow isotope ratio mass spectrometer. The capillary gas chromatography column of the original equipment was changed to a packed Porapak Q column. This adaptation resulted in an improved accuracy and precision of delta13C (standard deviation(Ghent): from 0.2 to 0.08 per thousand; standard deviation(Lincoln): from 0.2 to 0.13 per thousand) of CO2 for N2O/CO2 ratios up to 0.1. For delta18O there was an improvement for the standard deviation measured at Ghent University (0.13 to 0.08 per thousand) but not for the measurements at Lincoln University (0.08 to 0.23 per thousand). The benefits of using the packed Porapak Q column compared with the theoretical correction method meant that samples were not limited to small N(2)O concentrations, they did not require an extra N2O concentration measurement, and measurements were independent of the variable isotopic composition of N2O from soil.     

Isotopic composition of inorganic carbon as an indicator of benzoate degradation by pseudomonas putida: temperature, growth rate and pH effects

Degradation experiments of benzoate by Pseudomonas putida resulted in enzymatic carbon isotope fractionations. However, isotopic temperature effects between experiments at 20 and 30 degrees C were minor. Averages of the last three values of the CO(2) isotopic composition (delta(13)C(CO2(g))) were more negative than the initial benzoate delta(13)C value (-26.2 per thousand Vienna Pee Dee Belenite (VPDB)) by 3.8, 3.4 and 3.2 per thousand at 20, 25 and 30 degrees C, respectively. Although the maximum isotopic temperature difference found was only 0.6 per thousand, more extreme temperature variations may cause larger isotope effects. In order to understand the isotope effects on the total inorganic carbon (TIC), a better measure is to calculate the proportions of the inorganic carbon species (CO(2)(g), CO(2)(aq) and HCO(3)(-)) and to determine their cumulative delta(13)C(TIC). In all three experiments delta(13)C(TIC) was more positive than the initial isotopic composition of the benzoate at a pH of 7. This suggests an uptake of (12)C in the biomass in order to match the carbon balance of these closed system experiments.     

Analysis of amino acid 13C abundance from human and faunal bone collagen using liquid chromatography/isotope ratio mass spectrometry

The scope of compound-specific stable isotope analysis has recently been increased with the development of the LC IsoLink which interfaces high-performance liquid chromatography (HPLC) and isotope ratio mass spectrometry (IRMS) to provide online LC/IRMS. This enables isotopic measurement of non-volatile compounds previously not amenable to compound-specific analysis or requiring substantial modification for gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), which results in reduced precision. Amino acids are an example of such compounds.We present a new chromatographic method for the HPLC separation of underivatized amino acids using an acidic, aqueous mobile phase in conjunction with a mixed-mode stationary phase that can be interfaced with the LC IsoLink for compound-specific delta13C analysis. The method utilizes a reversed-phase Primesep-A column with embedded, ionizable, functional groups providing the capability for ion-exchange and hydrophobic interactions. Baseline separation of 15 amino acids and their carbon isotope values are reported with an average standard deviation of 0.18 per thousand (n = 6). In addition delta13C values of 18 amino acids are determined from modern protein and archaeological bone collagen hydrolysates, demonstrating the potential of this method for compound-specific applications in a number of fields including metabolic, ecological and palaeodietary studies.     

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.     

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.     

Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry delta(13)C analysis of small polyfunctional compounds

Carbohydrates and proteins are among the most abundant naturally occurring biomolecules and so suitable methods for their reliable stable isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) are required. Due to the non-volatile nature of these compounds they require hydrolytic cleavage to their lower molecular weight subunits and derivatisation prior to GC/C/IRMS analysis. The addition of carbon to the molecules and any kinetic isotopic fractionation associated with derivatisation must be accounted for in order to provide meaningful stable isotope values and estimates of propagated errors. To illustrate these points amino acid trifluoroacetate/isopropyl esters and alditol acetates were prepared from authentic amino acids and monosaccharides, respectively. As predicted from the derivatisation reaction mechanisms, a kinetic isotope effect was observed which precludes direct calculation of delta(13)C values of the amino acids and monosaccharides by simple mass balance equations. This study shows that the kinetic isotope effect associated with derivatisation is both reproducible and robust, thereby allowing the use of correction factors. We show how correction factors can be determined and accurately account for the addition of derivative carbon. As a consequence of the addition of a molar excess of carbon and the existence of a kinetic isotope effect during derivatisation, errors associated with determined delta(13)C values must be assessed. We illustrate how such errors can be quantified (for monosaccharides +/-1.3 per thousand and for amino acids between +/-0.8 per thousand and +/-1.4 per thousand). With the magnitude of the errors for a given delta(13)C value of a monosaccharide or amino acid quantified, it is possible to make reliable interpretations of delta(13)C values, thereby validating the determination of delta(13)C values of amino acids as TFA/IP esters and monosaccharides as alditol acetates.     

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.     

Simplified method for microlitre deuterium measurements in water and urine by gas chromatography-high-temperature conversion-isotope ratio mass spectrometry

Deuterium (2H) in water and urine can be measured by off-line and, more recently, on-line techniques using isotope ratio mass spectrometry (IRMS). We describe a new simple on-line pyrolysis method for the analysis of 2H/1H in water and urine samples by continuous flow IRMS, normally used for 2H/1H measurements in organic compounds. A deactivated column connected the split injector to a high-temperature conversion reactor (TC HD), and 0.5 microL of sample was injected. Accuracy and precision were determined with Vienna Standard Mean Ocean Water (VSMOW), Standard Light Antarctic Precipitation (SLAP), and Greenland Ice Sheet Precipitation (GISP). The range of linearity was measured with a calibration curve of enriched water from 0 up to 0.1 atom percent excess (APE) (i.e. -72 up to 6323 delta per mil (deltaD per thousand)) with a precision of <5 per thousand and accuracy ranging between 1 and 55 per thousand. Blinded reanalysis of urine samples by an equilibration device (Gas Bench) and by a dedicated pyrolysis system (TC/EA) was performed and results compared by the Bland-Altman test. Enrichments ranged between 600 and 2400 per thousand deltaD(VSMOW) with a precision of +/-5 per thousand. Urine enrichments described by our method were strongly correlated with values obtained by Gas Bench and TC/EA (p < 0.0001). There was a significant memory effect that was reduced by injecting the sample 15 times and discarding the first 10 injections, together with accurate furnace conditioning and appropriate cleaning of the syringe. Data indicate that the method is accurate, and that it can be used for water and urine deuterium determination when a Gas Bench or TC/EA instrument is not available and the amount of sample is limited.     

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‰