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.     

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 novel online approach to the determination of isotopic ratios for organically bound chlorine, bromine and sulphur

A novel approach for the measurement of (37)Cl, (81)Br and (34)S in organic compounds containing chlorine, bromine, and sulphur is presented to overcome some of the major drawbacks of existing methods. Contemporary methods either require reference materials with the exact molecular compositions of the substances to be tested, or necessitate several laborious offline procedures prior to isotope analysis. In our online setup, organic compounds are separated by gas chromatography (GC) coupled to a high-temperature reactor. Using hydrogen as a makeup gas, the reactor achieves quantitative conversion of chlorinated, brominated and sulphurated organic compounds into gaseous hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen sulphide (H(2)S), respectively. In this study, the GC interface was coupled to a quadrupole mass spectrometer operated in single-ion mode. The ion traces of either H(35)Cl (m/z 36) and H(37)Cl (m/z 38), H(79)Br (m/z 80) and H(81)Br (m/z 82), or H(2)(32)S (m/z 34) and H(2)(34)S (m/z 36), were recorded to determine the isotopic ratios of chlorine, bromine, and sulphur isotopes. The conversion interface presented here provides a basis for a novel method for compound-specific isotope analysis of halogenated and sulphur-containing compounds. Rapid online measurements of organic chlorine-, bromine- and sulphur-containing mixtures will facilitate the isotopic analysis of compounds containing these elements, and broaden their usage in fields of environmental forensics employing isotopic concepts.     

Assessing transformation processes of organic contaminants by compound-specific stable isotope analysis

The analysis of variations in stable isotope composition is becoming an essential approach for evaluating enzymatic and abiotic reactions of organic contaminants in soils and aquatic systems. Different, sometimes complementary analytical techniques are currently used and developed to determine stable isotope ratios in individual organic compounds. Anticipating an increasing demand for compound-specific isotope analysis, this survey compiles information for choosing the most promising analytical approach to an isotope-related problem. To this end, we review the principles of instrumentation for compound-specific isotope analysis and show how they can be exploited to assess contaminant transformation processes. Using chlorinated solvents and triazine herbicides as illustrative examples, we discuss how the isotope-sensitive techniques impact the investigation of stable isotope fractionation in environmental chemistry and microbiology.     

Compound-specific stable isotope analysis of organic contaminants in natural environments: a critical review of the state of the art,prospects, and future challenges

Compound-specific stable isotope analysis (CSIA) using gas chromatography-isotope ratio mass spectrometry (GC/IRMS) has developed into a mature analytical method in many application areas over the last decade. This is in particular true for carbon isotope analysis, whereas measurements of the other elements amenable to CSIA (hydrogen, nitrogen, oxygen) are much less routine. In environmental sciences, successful applications to date include (i) the allocation of contaminant sources on a local, regional, and global scale, (ii) the identification and quantification of (bio)transformation reactions on scales ranging from batch experiments to contaminated field sites, and (iii) the characterization of elementary reaction mechanisms that govern product formation. These three application areas are discussed in detail. The investigated spectrum of compounds comprises mainly n-alkanes, monoaromatics such as benzene and toluene, methyl tert-butyl ether (MTBE), polycyclic aromatic hydrocarbons (PAHs), and chlorinated hydrocarbons such as tetrachloromethane, trichloroethylene, and polychlorinated biphenyls (PCBs). Future research directions are primarily set by the state of the art in analytical instrumentation and method development. Approaches to utilize HPLC separation in CSIA, the enhancement of sensitivity of CSIA to allow field investigations in the µg L^–1 range, and the development of methods for CSIA of other elements are reviewed. Furthermore, an alternative scheme to evaluate isotope data is outlined that would enable estimates of position-specific kinetic isotope effects and, thus, allow one to extract mechanistic chemical and biochemical information.Abbreviations BTEX benzene, toluene, ethylbenzene, xylenes - MTBE methyl tert-butyl ether - PAHs polycyclic aromatic hydrocarbons - VOCs volatile compounds - PCBs polychlorinated biphenyls - CSIA compound-specific (stable) isotope (ratio) analysis - GC-IRMS, GC/IRMS or GCIRMS gas chromatography-isotope ratio mass spectrometry - GC-C-IRMS, GC/C/IRMS or GCC-IRMS gas chromatography-combustion-isotope ratio mass spectrometry - irmGC/MS isotope ratio monitoring gas chromatograph-mass spectrometry - GC/P/IRMS gas chromatography-pyrolysis-isotope ratio mass spectrometry (used for D/H) - KIE kinetic isotope effect - PSIA position-specific isotope analysis (for intramolecular isotope distribution) - SNIF-NMR site-specific natural isotopic fractionation by nuclear magnetic resonance spectroscopy     

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.     

Determination of inorganic chlorine stable isotopes by continuous flow isotope ratio mass spectrometry

Chlorine stable isotope analyses of inorganic samples were conducted using continuous flow isotope ratio mass spectrometry (CF-IRMS) coupled with gas chromatography (GC). Inorganic chloride was precipitated in the form of silver chloride (AgCl) by using silver nitrate in a standard methodology. Chlorine stable isotope analysis was carried out on methyl chloride (CH3Cl) after converting AgCl into CH3Cl by reacting it with methyl iodide (CH3I). The reaction between AgCl and CH3I took place in 20 mL size vials. Addition of CH3I was performed in a glove bag under helium flow. An Agilent 6890 gas chromatograph equipped with a CTC Analytics CombiPAL autosampler and a DB-5MS 60 m column was used to separate CH3Cl from CH3I. This new technique uses samples as small as 0.2 mg of AgCl (1.4 micromol of Cl-). The chlorine stable isotope analysis using continuous flow technology showed excellent precision and accuracy. The internal precision using pure CH3Cl gas is better than +/-0.04 per thousand (+/-STDV). The external precision using seawater standard is better than +/-0.07 per thousand (+/-STDV) for n=12. Moreover, the sample analysis time is much shorter and many more samples can be analyzed in one day than by using the conventional off-line techniques.     

干洗织物中氯代烃溶剂残留的气相-质谱测定

 采用固相微萃取和气 质联用技术(GC MS)对干洗衣物中氯代烯烃的残留和释放进行了分析测定。干洗过程使用的有害物质包括四氯乙烯(PCE)、三氯乙烯(TCE)及少量的三氯乙烷,这些挥发性有机物已列入许多国家和地区优先控制的污染物指标。该方法参照欧洲生态纺织品标准100对目标化合物的限量控制,以加标的标准贴衬为样品基质,将样品浸渍在含5%(体积分数)甲醇的饱和NaCl溶液中,于(40±1)℃水浴中超声处理10min后,再将样液用100μmPDMS固相微萃取纤维顶空提取,然后进行GC MS测定。     

Chlorine isotope fractionation of a semi-volatile organochlorine compound during preparative megabore-column capillary gas chromatography

Chlorine isotope fractionation during preparative capillary gas chromatography (pcGC) was investigated using 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) as a model compound for semi-volatile organochlorine (OCl) molecules. Chlorine isotope analysis by thermal ionization mass spectrometry revealed no significant alteration of the chlorine isotope composition when the whole peaks were collected in pcGC (delta37Cl -3.2 per thousand versus -3.6 per thousand for the unprocessed DDT, +/-0.5 per thousand SD). However, distinct isotope fractionations were measured for the front (delta37Cl -5.1 per thousand) and tail (delta37Cl -1.8 per thousand) segments of partially collected samples. Isolation of individual OCls by pcGC enables accurate off-line chlorine isotope analysis, and thus facilitates the investigation of naturally occurring OCls.     

A gas chromatography/combustion/isotope ratio mass spectrometry system for high-precision delta13C measurements of atmospheric methane extracted from ice core samples

Past atmospheric composition can be reconstructed by the analysis of air enclosures in polar ice cores which archive ancient air in decadal to centennial resolution. Due to the different carbon isotopic signatures of different methane sources high-precision measurements of delta13CH4 in ice cores provide clues about the global methane cycle in the past. We developed a highly automated (continuous-flow) gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique for ice core samples of approximately 200 g. The methane is melt-extracted using a purge-and-trap method, then separated from the main air constituents, combusted and measured as CO2 by a conventional isotope ratio mass spectrometer. One CO2 working standard, one CH4 and two air reference gases are used to identify potential sources of isotope fractionation within the entire sample preparation process and to enhance the stability, reproducibility and accuracy of the measurement. After correction for gravitational fractionation, pre-industrial air samples from Greenland ice (1831 +/- 40 years) show a delta13C(VPDB) of -49.54 +/- 0.13 per thousand and Antarctic samples (1530 +/- 25 years) show a delta13C(VPDB) of -48.00 +/- 0.12 per thousand in good agreement with published data.     

Isotope fractionation factors of N2O diffusion

Isotopic signatures of N2O are increasingly used to constrain the total global flux and the relative contribution of nitrification and denitrification to N2O emissions. Interpretation of isotopic signatures of soil-emitted N2O can be complicated by the isotopic effects of gas diffusion. The aim of our study was to measure the isotopic fractionation factors of diffusion for the isotopologues of N2O and to estimate the potential effect of diffusive fractionation during N2O fluxes from soils using simple simulations. Diffusion experiments were conducted to monitor isotopic signatures of N2O in reservoirs that lost N2O by defined diffusive fluxes. Two different mathematical approaches were used to derive diffusive isotope fractionation factors for 18O (epsilon18O), average 15N (epsilonbulk) and 15N of the central (alpha(-)) and peripheral (beta(-)) position within the linear N2O molecule (epsilon15Nalpha, epsilon15Nbeta). The measured epsilon18O was -7.79 +/- 0.27 per thousand and thus higher than the theoretical value of -8.7 per thousand. Conversely, the measured epsilonbulk (-5.23 +/- 0.27 per thousand) was lower than the theoretical value (-4.4 per thousand). The measured site-specific 15N fractionation factors were not equal, giving a difference between epsilon15Nalpha and epsilon15Nbeta (epsilonSP) of 1.55 +/- 0.28 per thousand. Diffusive fluxes of the N2O isotopologues from the soil pore space to the atmosphere were simulated, showing that isotopic signatures of N2O source pools and emitted N2O can be substantially different during periods of non-steady state fluxes. Our results show that diffusive isotope fractionation should be taken into account when interpreting natural abundance isotopic signatures of N2O fluxes from soils.     

Analysis of dichloroacetic acid in rat blood and tissues by hydrophilic interaction liquid chromatography with tandem mass spectrometry

Dichloroacetic acid (DCA) is a compound found in chlorinated drinking water. In addition, the compound is a metabolite of several halogenated solvents, including trichloroethylene (TCE) and perchloroethylene (PCE). Exposure to DCA is of concern because high doses of the compound have been shown to cause cancer in laboratory animals. Dosages of TCE administered to animals in cancer studies are designed to elicit maximal DCA formation in vivo, whereas levels of DCA to which individuals are exposed in drinking water are very low. Analysis of DCA in biological samples has been quite challenging. Derivatizing reagents commonly used to convert DCA into a more volatile form for analysis by gas chromatography (GC) have been found to convert trichloroacetic acid (TCA), a major metabolite of TCE and PCE, into DCA. High-performance liquid chromatography (HPLC) analysis does not require derivatization of DCA and can thus avoid this problem. However, the most popular stationary phases in HPLC columns do not retain small, polar compounds such as DCA well. The liquid chromatography/tandem mass spectrometry (LC/MS/MS) method described in this paper uses hydrophilic interaction liquid chromatography (HILIC), a type of chromatography that is able to retain these small, polar compounds. Method validation was performed using the United States Food and Drug Administration (USFDA) and International Conference on Harmonziation (ICH) Guidance for Industry: Bioanalytical Method Validation as a guide. Levels of DCA found in rats dosed with 2 g/kg TCE were 17.2 ng/mL (liver), 262.4 ng/mL (kidney), 175.1 ng/mL (lung), and 39.5 ng/mL (blood).     

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.     

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   

Reaction orders of radiation-induced dechlorinations of some aliphatic chlorinated hydrocarbons in aqueous solutions

Previously obtained data regarding radiation-induced dechlorination of some aliphatic chlorinated hydrocarbons tetrachloroethene (PCE), trichloroethene (TCE), chloroform (CHCl₃) and tetrachloromethane (CCl₄) in aqueous solutions were used for determination of formal reaction order of dechlorination. The influence of various factors on this process was investigated. It was found that the formal reaction order changes in the course of reaction and may depend on the initial concentration of chlorinated hydrocarbons.     

Dynamic headspace: a single-step extraction for isotopic analysis of microg/L concentrations of dissolved chlorinated ethenes

In this study a dynamic headspace method was developed to measure the carbon isotope values of dissolved chlorinated ethenes at microg/L concentrations. A gas chromatograph/combustion/isotope ratio mass spectrometer (GC/C/IRMS) was modified to include a headspace extraction system followed by a cryogenic trap. Extracting headspace from a 160 mL vial with 80 mL of aqueous solution and 40 g of NaCl for 8-12 min resulted in accurate and reproducible delta13C values for trichloroethene (TCE) and cis-1,2-dichloroethene (cDCE) at concentrations of 50-75 microg/L. Based on these results a conservative lower limit of quantitation of 38 microg/L can be calculated for these compounds. For more volatile compounds such as tetrachloroethene (PCE) and vinyl chloride (VC), field data analyzed using this method indicate a lower limit of quantitation in the tens of microg /L range.     

Deuterium and oxygen-18 determination of microliter quantities of a water sample using an automated equilibrator

We describe a modified version of the equilibration method and a correction algorithm for isotope ratio measurements of small quantities of water samples. The deltaD and the delta(18)O of the same water sample can both be analyzed using an automated equilibrator with sample sizes as small as 50 microL. Conventional equilibration techniques generally require water samples of several microL. That limitation is attributable mainly to changes in the isotope ratio ((18)O/(16)O or D/H) of water samples during isotopic exchange between the equilibration gas (CO(2) or H(2)) and water, and therefore the technique for microL quantities of water requires mass-balance correction using the water/gas (CO(2) or H(2)) mole ratio to correct this isotopic effect. We quantitatively evaluate factors controlling the variability of the isotopic effect due to sample size. Theoretical consideration shows that a simple linear equation corrects for the effects without determining parameters such as isotope fractionation factors and water/gas mole ratios. Precisions (1-sigma) of 50-microL meteoric water samples whose isotopic compositions of -1.4 to -396.2 per thousand for deltaD are +/-0.5 to +/-0.6 per thousand, and of -0.37 to -51.37 per thousand for delta(18)O are +/-0.01 to +/-0.11 per thousand.     

Aqueous reductive dechlorination of chlorinated ethylenes with tetrakis(4-carboxyphenyl)porphyrin cobalt

The catalytic dechlorination of chlorinated ethylenes by 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin cobalt ((TCPP)Co), a cobalt complex structurally similar to vitamin B12, was studied. It was found to have superior aqueous-phase dechlorination activity on chlorinated ethylenes (CEs) relative to vitamin B12. Bimolecular rate constants for the degradation of CEs by (TCPP)Co of 250, 24, 0.24, and 1.5 M(-1) s(-1) were found for perchloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cDCE), and trans-dichloroethylene (tDCE), respectively. Through kinetic analysis, the rate laws for PCE and TCE were determined to be first order in substrate and catalyst, and PCE degradation was shown to be sensitive to the concentration of the titanium citrate bulk reductant and pH. The importance of the Co(I) oxidation state on dehalogenation was studied with UV-vis absorbance spectroscopy, a variety of reducing agents, and cyclic voltammetry. Evidence of chlorovinyl complexes as potential catalytic cycle intermediates was obtained through the preparation of (TPP)Co(trans-C2H2Cl) and the observation of (TPP)Co(C2HCl2) and (TCPP)Co(C2HCl2) by mass spectrometry. The X-ray crystal structure of (TPP)Co(trans-C2H2Cl) is reported.     

Determination of 13C/12C-ratios of anthropogenic organic contaminants in river water samples by GC-irmMS

This study describes the application of a common analytical procedure adapted for compound-specific stable carbon isotope analyses of riverine contaminants. To evaluate the sensitivity of the analytical method and the precision of the isotopic data obtained, a set of numerous substances at different concentration levels were measured. For most of the anthropogenic contaminants investigated (including chlorinated aliphatics and aromatics, musk fragrances, phthalate-based plasticizers and tetrabutyl tin) acceptable carbon isotope analyses could be obtained down to amounts of approximately 5?ng absolutely applied to the gas chromatograph. These amounts correspond to concentrations in water samples at a natural abundance level of approximately 50–200?ng?L^?1 (low to medium contaminated river systems). However, it has to be considered that the precision and the sensitivity of the analytical method depend partially on the chemical properties of the substances measured. Five recovery experiments were conducted to assess changes in carbon isotope ratios during sample preparation and measurement. The compounds selected for these experiments are known riverine contaminants. Isotopic shifts or higher variations of the isotope ratios as a result of the analytical procedures applied were observed only for a couple of contaminants. Furthermore, compound-specific carbon isotope analyses were performed on eight water extracts of the Rhine river. By comparing the variation of the data of several individual compounds with the deviations obtained from the recovery experiments, it was possible to differentiate contaminants with unaffected isotope ratios and substances with significant alterations of the δ¹³C-values.     

Determination of stable carbon isotopes of organic acids and carbonaceous aerosols in the atmosphere

A wet oxidation method for the compound-specific determination of stable carbon isotopes (delta(13)C) of organic acids in the gas and aerosol phase, as well as of water-soluble organic carbon (WSOC), is presented. Sampling of the organic acids was done using a wet effluent diffusion denuder/aerosol collector (WEDD/AC) coupled to an ion chromatography (IC) system. The method allows for compound-specific stable carbon isotope analysis by collecting different fractions of organic acids at the end of the IC system using a fraction collector. delta(13)C analyses of organic acids were conducted by oxidizing the organic acids with sodium persulfate at a temperature of 100 degrees C and determining the delta(13)C value of the resulting carbon dioxide (CO(2)) with an isotope ratio mass spectrometer. In addition, analysis of delta(13)C of the WSOC was performed for particulate carbon collected on aerosol filters. The WSOC was extracted from the filters using ultrapure water (MQ water), and the dissolved organic carbon was oxidized to CO(2) using the oxidation method. The wet oxidation method has an accuracy of 0.5 per thousand with a precision of +/-0.4 per thousand and provides a quantitative result for organic carbon with a detection limit of 150 ng of carbon.