Enantiomers In Soil Research Articles

Enantioseparation of β-receptor blockers and the enantioselective degradation of carvedilol in soil

Enantioseparation of seven β-receptor blockers, including carvedilol, metoprolol, atenolol, sotalol, propafenone, bisoprolol and arotinolol was investigated using HPLC coupled with pre-column derivatization in this work. The derivative conditions of the ratio of the analytes and the derivative reagent, (S)-N-(4-nitrophenoxycarbonyl) phenylalanine methoxyethyl ester, the amount of sodium tetraborate, the reaction temperature and reaction time were optimized. The effects of the types of chromatographic columns, the composition and ratio of the mobile phase and mobile phase additives on enantioseparation were also evaluated in HPLC analysis. The seven pairs of enantiomers showed a good baseline separation on an InfinityLab Poreshell 120 EC-C18 column (150 mm × 4.6 mm, 4 µm) using the mobile phase of methanol and 5 mM ammonium bicarbonate at a flow rate of 1.0 mL/min. In addition, a LC-MS/MS method coupled with QuEChERS extraction for the enantioselective quantitation of carvedilol in soil was developed. The method was fully validated in terms of selectivity, linearity, matrix effect, accuracy, precision, limit of detection and limit of quantification. The linear ranges of carvedilol enantiomers were both 0.5–100 ng/mL and the limits of quantification were 0.5 ng/mL. Extraction recoveries were more than 83.0% with the intra-day and inter-day precision less than 6.8%. The matrix effect values were in the range from 84.5% to 91.3%. The proposed method was successfully applied to determine carvedilol enantiomers in soil and their degradation process was investigated. The degradation of carvedilol enantiomers in soil at natural condition conformed to the first-order degradation kinetics (R2 > 0.9790). The half-lives of carvedilol enantiomers were 17.77 and 16.90 days, respectively and the enantiomer fraction (EF) values of carvedilol enantiomers ranged from 0.488 to 0.523 with time in soil, indicating the degradation behaviors, disposition and biotransformation of carvedilol enantiomers in soil showed no enantioselectivity (P > 0.05).

Assessment of the eco-toxicological effects in zoxamide polluted soil amended with fertilizers-An indoor evaluation

Zoxamide is a benzamide fungicide applied to control diseases caused by oomycete fungi. Fertilizers are important agricultural supplies to adjust soil properties and increase nutrition. To investigate the impact of zoxamide and seven fertilizers urea, phosphate fertilizer, potash fertilizer, compound fertilizer, organic fertilizer, vermicompost and soya bean cakes on the soil environment, the enantioselective dissipation characteristics of zoxamide, soil enzyme activities, pH and N, P nutrition changes were comprehensively analyzed in our present study. The enantioseparation method was successfully validated to quantify the zoxamide enantiomers in soil by HPLC using Chiral NQ (2)-RH column. Our results demonstrated that the R-(−)- and S-(+)-zoxamide half dissipated in the range of 10.88–17.81 and 8.05–14.41 days, respectively. S-(+)-zoxamide disappeared faster in soil. The vermicompost accelerated the dissipation rate of S-(+)-zoxamide, while urea, phosphate, organic and vermicompost fertilizer increased the dissipation selectivity. Zoxamide and fertilizers other than urea caused soil acidification during 80 days. Zoxamide was beneficial to soil catalase, instead inhibited soil urease, dehydrogenase activities and available phosphorus content. No significant effects on sucrase activity and available nitrogen content were found by zoxamide. Vermicompost and soya bean cakes had lasting and outstanding performance in efficiently improving soil enzyme activity and N, P nutrition. The comprehensive understanding of the ecological impact induced by chiral pesticide enantiomers and fertilizers on soil is vital to ensure the sustainable development and safety of agricultural production.

Enantiomeric separation of malathion and malaoxon and the chiral residue analysis in food and environmental matrix.

Malathion is a widely used chiral phosphorus insecticide, which has a more toxic chiral metabolite malaoxon. In this work, the enantiomers of malathion and malaoxon were separated by high-performance liquid chromatography-mass/mass (HPLC-MS/MS) with chiral columns using acetonitrile/water or methanol/water as mobile phase, and the chromatographic conditions were optimized. Based on the chiral separation, the chiral residue analysis methods for the enantiomers in soil, fruit, and vegetables were set up. Two pairs of the enantiomers were better separated on CHIRALPAK IC chiral column, and baseline simultaneous separations of malathion and malaoxon enantiomers were achieved with acetonitrile/water (40/60, v/v) as mobile phase at a flow rate of 0.5 mL/min. The elution orders were -/+ for both malathion and malaoxon measured by an optical rotation detector. The chiral residue analysis in soil, fruit, and vegetables was validated by linearity, recovery, precision, limit of detection (LOD), and limit of quantification (LOQ). The LODs and LOQs for the enantiomers of malathion were 1 μg/kg and 3-5 μg/kg and 0.08 μg/kg and 0.20-0.25 μg/kg for malaoxon enantiomers. Good linear calibration curves for each enantiomer in the matrices were obtained within the concentration range of 0.02-12 mg/L. The mean recoveries of the enantiomers of malathion and malaoxon ranged from 82.26% to 109.04%, with RSDs of 0.71-8.63%.The results confirmed that this method was capable of simultaneously determining the residue of malathion and malaoxon in food and environmental matrix on an enantiomeric level.

Determination of Four Chiral Pesticides in Soil by QuEChERS-Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

The enantiomer residues of metalaxyl, napropamide, triticonazole and metconazole were detected in soil by QuECh-ERS-ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The soil sample was extracted with acetonitrile containing 1% acetic acid and purified using QuEChERS method. Quantitative analysis for the enantiomers of these four chiral pesticides was performed in MS in multi-response monitoring (MRM) mode by external standard method. All enantiomers showed good linearity in the range of 0.5 to 50 μg/L. The average recoveries of enantiomers in soil were 81.74% to 105.79% with relative standard deviations (RSDs) from 3.69% to 7.86%. The method quantitative limit (MQL) was 5.3-30.3 ng/kg. The method can be used for rapid screening and determination of chiral pesticides in soil.

Enantiomeric separation of type I and type II pyrethroid insecticides with different chiral stationary phases by reversed‐phase high‐performance liquid chromatography

The enantiomeric separation of type I (bifenthrin, BF) and type II (lambda-cyhalothrin, LCT) pyrethroid insecticides on Lux Cellulose-1, Lux Cellulose-3, and Chiralpak IC chiral columns was investigated by reversed-phase high-performance liquid chromatography. Methanol/water or acetonitrile/water was used as mobile phase at a flow rate of 0.8mL/min. The effects of chiral stationary phase, mobile phase composition, column temperature, and thermodynamic parameters on enantiomer separation were carefully studied. Bifenthrin got a partial separation on Lux Cellulose-1 column and baseline separation on Lux Cellulose-3 column, while LCT enantiomers could be completely separated on both Lux Cellulose-1 and Lux Cellulose-3 columns. Chiralpak IC provided no separation ability for both BF and LCT. Retention factor (k) and selectivity factor (α) decreased with the column temperature increasing from 10°C to 40°C for both BF and LCT enantiomers. Thermodynamic parameters including ∆H and ∆S were also calculated, and the maximum Rs were not always obtained at lowest temperature. Furthermore, the quantitative analysis methods for BF and LCT enantiomers in soil and water were also established. Such results provide a new approach for pyrethroid separation under reversed-phase condition and contribute to environmental risk assessment of pyrethroids at enantiomer level.

Stereoselective determination of dufulin in watermelon under field conditions using chiral ultra high performance liquid chromatography with high-resolution mass spectrometry.

An effective and sensitive chiral analytical method was established to investigate the stereoselective dissipation of rac-dufulin in watermelon using ultra high performance liquid chromatography with a superchiral S-OD chiral column (4.6×150mm i.d., 5μm) coupled with high-resolution mass spectrometry. To optimize the pretreatment method for detecting rac-dufulin in the three matrixes, different extraction solvents, extractant volumes, extraction times, and absorbents were investigated to improve extraction efficiency. Moreover, analysis of variance was used to perform method validation for determination of the two dufulin enantiomers in the three matrixes. Using the optimized method, good linearity was obtained (determination coefficient>0.999). The limits of detection and quantification of the two dufulin enantiomers in soil, watermelon, and pulp were 0.15 and 0.5μg/kg, respectively. The average recoveries of the two enantiomers in the three matrixes at four spiked levels ranged from 75.0 to 107.8%, with intra- and inter-day relative standard deviations of 0.4-10.4%. In field trials, the R enantiomer was preferentially dissipated in watermelon. These method validation results confirmed that the developed method was convenient and reliable for the stereoselective determination of enantiomers of rac-dufulin in watermelon.

Evaluation of an organo-layered double hydroxide and two organic residues as amendments to immobilize metalaxyl enantiomers in soils: A comparative study

Many pollutants released into the environment as a result of human activities are chiral. Pollution control strategies generally consider chiral compounds as if they were achiral and rarely consider enantiomers separately. We compared the performance of three different materials, an organically-modified anionic clay (HT-ELA) and two organic agro-food residues (ALP and ALPc), as amendments to immobilize the chiral fungicide metalaxyl in two soils with different textures, addressing the effects of the amendments on the sorption, persistence, and leaching of each of the two enantiomers of metalaxyl (R-metalaxyl and S-metalaxyl) separately. The effects of the amendments were both soil- and amendment-dependent, as well as enantiomer-selective. The organo-clay (HT-ELA) was much more efficient in increasing the sorption capacity of the soils for the two enantiomers of metalaxyl than the agro-food residues (ALP and ALPc), even when applied at a reduced application rate. The enhanced sorption in HT-ELA-amended soils reduced the bioavailability of metalaxyl enantiomers and their leaching in the soils, mitigating the particularly high leaching potential of the more persistent S enantiomer. The immobilizing capacity of the agro-food residues was more variable, mainly because their addition did not greatly ameliorate the sorption capacity of the soils and had variable effects on the enantiomers degradation rates. HT-ELA showed potential to reduce the bioavailability and mobility of metalaxyl enantiomers in soil and to mitigate the contamination problems particularly associated with the higher leaching potential of the more persistent enantiomer.

Evidence for the effect of sorption enantioselectivity on the availability of chiral pesticide enantiomers in soil

Although enantioselective sorption to soil particles has been proposed as a mechanism that can potentially influence the availability of individual chiral pesticide enantiomers in the environment, environmental fate studies generally overlook this possibility and assume that only biotic processes can be enantioselective, whereas abiotic processes, such as sorption, are non-enantioselective. In this work, we present direct evidence for the effect of the enantioselective sorption of a chiral pesticide in a natural soil on the availability of the single pesticide enantiomers for transport. Batch sorption experiments, with direct determination of the sorbed amounts, combined with column leaching tests confirmed previous observations that from non-racemic aqueous solutions the sorption of the chiral fungicide metalaxyl on the soil appeared to be enantioselective, and further demonstrated that the enantiomer that was sorbed to a greater extent (R-metalaxyl, Kd = 1.73 L/kg) exhibited retarded leaching compared to its optical isomer (S-metalaxyl, Kd = 1.15 L/kg). Interconversion and degradation of the pesticide enantiomers, which are potential experimental artifacts that can lead to erroneous estimates of sorption and its enantioselectivity, were discarded as possible causes of the observed enantioselective behavior. The results presented here may have very important implications for a correct assessment of the environmental fate of chiral pesticides that are incorporated into the environment as non-racemic mixtures, and also of aged chiral pesticide residues that have been transformed from racemic to non-racemic by biologically-mediated processes.

Enantioselective separation and pharmacokinetic dissipation of cyflumetofen in field soil by ultra‐performance convergence chromatography with tandem mass spectrometry

Little data on the enantioselective separation of cyflumetofen exists, despite the fact that such data are essential to the assessment of the fate and potential toxic effects of cyflumetofen enantiomers. To address this issue, a simple and sensitive method for the enantioselective determination of cyflumetofen enantiomers in soil has been established using ultra performance convergence chromatography tandem triple quadrupole mass spectrometry. The effects of the chiral stationary phases, mobile phase, auto backpressure regulator pressure, column temperature, flow rate of the mobile phase, and compensation pump solvent were evaluated. The proposed method was applied to the study of the pharmacokinetic dissipation of cyflumetofen stereoisomers in soil under greenhouse conditions. The estimated half-life of cyflumetofen isomers ranged from 12.2 to 13.6 days, and statistically significant enantioselective degradation was observed. This study not only demonstrates that there is an efficient and sensitive method for cyflumetofen enantioseparation, but also provides the first experimental evidence of the pharmacokinetic dissipation of cyflumetofen stereoisomers in the environment.

Sorption, persistence and leaching of abscisic acid in agricultural soils: an enantiomer-selective study

Little is known about the enantioselectivity of the processes that determine the efficacy and environmental fate of natural compounds with potential to be used as environmentally-friendly agrochemicals. We conducted incubation and column leaching experiments to examine the extent and enantioselectivity of the sorption, persistence, and leaching of (RS)-abscisic acid (ABA) in three agricultural soils. Sorption of ABA enantiomers was a non-enantioselective process that occurred only in the soil with pH close to the pKa (4.8) of ABA enantiomers, but not in the two other (alkaline) soils. The degradation of (RS)-ABA was enantioselective for the three soils tested. (S)-ABA, the naturally-occurring enantiomer, was always degraded faster (DT50<4days), compared to (R)-ABA (DT50>8days). The movement of ABA enantiomers through the soil profile was enantioselective with column leachates being enriched in (R)-ABA enantiomer. Leaching was delayed in the soil that displayed sorption for both enantiomers. The results showed that the behavior of ABA enantiomers in soil was enantioselective and that the final fate of (R)-ABA and (S)-ABA depended on the soil type and appeared to be affected by their sorption on soil. The longer persistence of (R)-ABA should be considered when assessing the possibility of using this enantiomer or formulations containing enantiomer mixtures of ABA for crop management.

Environmental fate of the fungicide metalaxyl in soil amended with composted olive-mill waste and its biochar: An enantioselective study

A large number of pesticides are chiral and reach the environment as mixtures of optical isomers or enantiomers. Agricultural practices can affect differently the environmental fate of the individual enantiomers. We investigated how amending an agricultural soil with composted olive-mill waste (OMWc) or its biochar (BC) at 2% (w:w) affected the sorption, degradation, and leaching of each of the two enantiomers of the chiral fungicide metalaxyl. Sorption of metalaxyl enantiomers was higher on BC (Kd≈145Lkg−1) than on OMWc (Kd≈22Lkg−1) and was not enantioselective in either case, and followed the order BC-amended>OMWc-amended>unamended soil. Both enantiomers showed greater resistance to desorption from BC-amended soil compared to unamended and OMWc-amended soil. Dissipation studies revealed that the degradation of metalaxyl was more enantioselective (R>S) in unamended and OMWc-amended soil than in BC-amended soil. The leaching of both S- and R-metalaxyl from soil columns was almost completely suppressed after amending the soil with BC and metalaxyl residues remaining in the soil columns were more racemic than those in soil column leachates. Our findings show that addition of BC affected the final enantioselective behavior of metalaxyl in soil indirectly by reducing its bioavailability through sorption, and to a greater extent than OMWc. BC showed high sorption capacity to remove metalaxyl enantiomers from water, immobilize metalaxyl enantiomers in soil, and mitigate the groundwater contamination problems particularly associated with the high leaching potential of the more persistent enantiomer.

Environmental behavior of the chiral herbicide haloxyfop. 1. Rapid and preferential interconversion of the enantiomers in soil.

Haloxyfop-methyl is a chiral herbicide that was first introduced as racemate and later replaced by "haloxyfop-P-methyl", mainly consisting of the R-enantiomer, which carries the herbicidal activity. We studied the ester cleavage of haloxyfop-methyl and further degradation and chiral inversion of the acid enantiomers in three different soils using enantioselective gas chromatography-mass spectrometry. Our results confirm the rapid ester hydrolysis of haloxyfop-methyl with half-lives of a few hours and indicate that hydrolysis is weakly enantioselective. Further degradation of haloxyfop was slower with half-lives of several days. In all three soils, S-haloxyfop was rapidly converted to R-haloxyfop. In sterile soil, no degradation and no inversion were observed, indicating that both processes are biologically mediated. In soil where 50% of the water had been replaced by deuterium oxide, significant H-D exchange in haloxyfop was observed, pointing to a reaction mechanism involving abstraction of the proton at the chiral center of the molecule.

Mineralization of alanine enantiomers in soil treated with heavy metals and nutrients

This work deals with the determination of the effect of heavy metals and nutrients applied to the soil on alanine enatiomers mineralization with the main focus on evaluating the effect on L/D alanine respiration rate ratio. This study was initiated because previous research works revealed a change in L/D amino acid respiration under acid- or heavy metal-stress in soil. Generally, D-amino acids artificially supplied to soil are less utilized by microorganisms compared with their L-enantiomers. Stress of soil microorganisms cause decreased discrimination of D-amino acids utilization. Also, previous research showed that an application of fertilizers or combinations of fertilizers may affect the mineralization rate of L-amino acids differently, compared with their D-enantiomers. The results of this study show, that the effect of both heavy metals and nutrients on the L/D ratio was not clear, increasing or decreasing this ratio. Further research is necessary to broaden this study.

Chiral Separation and Enantioselective Degradation of Vinclozolin in Soils

Vinclozolin is a chiral fungicide with potential environmental problems. The chiral separation of the enantiomers and enantioselective degradation in soil were investigated in this work. The enantiomers were separated by high-performance liquid chromatography (HPLC) on Chiralpak IA, IB, and AZ-H chiral columns under normal phase and the influence of the mobile phase composition on the separation was also studied. Complete resolutions were obtained on all three chiral columns under optimized conditions with the same elution order of (+)/(-). The residual analysis of the enantiomers in soil was conducted using accelerate solvent extraction followed by HPLC determination. The recoveries of the enantiomers ranged from 85.7-105.7% with relative standard deviation (SD) of 0.12-3.83%, and the limit of detection (LOD) of the method was 0.013 µg/g. The results showed that the degradations of vinclozolin enantiomers in the soils followed first-order kinetics. Preferential degradation of the (-)-enantiomer was observed only in one soil with the largest |ES| value of 0.047, and no obvious enantioselective degradation was observed in other soils. It was found that the persistence of vinclozolin in soil was related to pH values based on the half-lives. The two enantiomers disappeared about 8 times faster in basic soils than that in neutral or acidic soils.

LC-MS/MS method for simultaneous determination of myclobutanil, hexaconazole, diniconazole, epoxiconazole and tetraconazole enantiomers in soil and earthworms

A new method using gel permeation chromatography (GPC) clean-up followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of myclobutanil, hexaconazole, diniconazole, epoxiconazole and tetraconazole enantiomers in soil and earthworms. The soil and earthworm samples were extracted with acetonitrile and then purified with a GPC procedure conducted on a CO785 column with cyclohexane and ethyl acetate (50:50, V/V) as the mobile phase at a flow rate of 4.7 mL/min. The eluent between 7.5 min and 15 min was collected for LC-MS/MS analysis. The LC mobile phase and MS/MS conditions were optimised. Formic acid (0.1%, V/V) was added to the water phase to enhance MS responses. The LODs of the enantiomers were between 0.001–0.003 mg/kg. At three fortification levels of 0.01–1.00 mg/kg, recoveries were between 81.2% and 100.2% in soil and earthworms. The relative standard deviation was below 14%. The results of earthworm experiment showed that hexaconzole and diniconazole might have the bioaccumulation potential, whereas tetraconazole, epoxiconazole and myclobutanil were most likely to undergo enantioselective biotransformation. On the contrary, the degradation of the triazoles in soil was achiral, and less than 10% of them were degraded after 21 days.

Enantiomer-specific toxicity and bioaccumulation of alpha-cypermethrin to earthworm Eisenia fetida

Alpha-cypermethrin, a synthetic pyrethroid, is highly effective against a wide range of chewing and sucking insects in crops, and it is a racemic mixture of two enantiomers ((+)- 1R- cis- αS + (−)- 1S- cis- αR). Studies about the toxicity of alpha-cypermethrin to non-target organisms are mainly focused on aquatic organisms, whereas information regarding terrestrial organisms is relatively much less. Very little report about its enantioselective toxicity is known, so the present study tested the enantiomer-specific acute toxicity to earthworm Eisenia fetida. Experiment about bioaccumulation of two enantiomers in soil was conducted, peak-shaped accumulation curves were observed for both enantiomers, and the calculated biota to soil accumulations factor (BSAF) have significant difference between the two enantiomers. It was obvious that earthworm can uptake alpha-cypermethrin enantioselectively, preferentially accumulating (−)-( 1S-cis-αR)-enantiomer. Great difference in toxicity to earthworm between two enantiomers was found, and the calculated LC 50 values for (+)-( 1R-cis-αS)-, (−)-( 1S-cis-αR)-, and rac-alpha-cypermethrin were 49.53, 1663.87 and 165.61 ng/cm 2, respectively. The acute toxicity of alpha-cypermethrin enantiomers was enantioselective.

Enantioselective bioaccumulation and toxic effects of metalaxyl in earthworm Eisenia foetida

Knowledge about the enantioselective bioavailability of chiral pesticides in soil invertebrates facilitates more accurate interpretation of their environmental behaviors. In this study, the acute toxicities of R-metalaxyl and rac-metalaxyl to earthworm ( Eisenia foetida) were assayed by filter paper contact test. After 48 h of exposure, the calculated LC 50 values for R- and rac-metalaxyl were 0.052 and 0.022 mg cm −2, respectively, resulting in a two fold difference in toxicity. For uptake experiment, earthworms were exposed in soil at two dose levels (10 and 50 mg kg dwt - 1 ). The concentrations of two enantiomers in soil and earthworm were determined by high-performance liquid chromatography based on cellulose tri-(3,5-dimethylphenyl-carbamate) chiral stationary phase. The results showed that metalaxyl was taken up by earthworm rapidly, and the bioaccumulation of metalaxyl in earthworm was enantioselective with preferential accumulation of S-enantiomer. In addition, biota to soil accumulation factor (BSAF) used to express the bioaccumulation of metalaxyl enantiomers was investigated, and significant difference was observed between rac-metalaxyl and R-metalaxyl.

Enantioselective separation of the carfentrazone‐ethyl enantiomers in soil, water and wheat by HPLC

A simple enantioselective HPLC method was developed for measuring carfentrazone-ethyl enantiomers. The separation and determination was accomplished on an amylose tris[(S)-alpha-methylbenzylcarbamate] (Chiralpak AS) column using n-hexane/ethanol (98:2, v/v) as mobile phase at a flow rate of 1.0 mL/min with UV detection at 248 nm. The effects of mobile-phase composition and column temperature on the enantioseparation were discussed. The accuracy, precision, linearity, LODs, and LOQ of the method were also investigated. LOD was 0.001 mg/kg in water, 0.015 mg/kg in soil and wheat, with an LOQ of 0.0025 mg/kg in water and 0.05 mg/kg in soil and wheat for each enantiomer of carfentrazone-ethyl. SPE was used for the enrichment and cleanup of soil, water, and wheat samples. Recoveries for two enantiomers were 88.4-106.7% with RSD(r) of 4.2-9.8% at 0.1, 0.5, and 1 mg/kg levels from soil, 85.8-99.5% with the RSD(r) of 4.4-9.6% at 0.005, 0.025, and 0.05 mg/kg levels from water, and from wheat the recoveries were 86.3-91.3% with RSD(r) below 5.0% at 0.2, 0.5, and 1 mg/kg levels. This method could be used to identify and quantify the carfentrazone-ethyl enantiomers in food and environment.

Stereoselective degradation of diclofop-methyl in soil and Chinese cabbage

The stereoselective degradation of the racemic diclofop-methyl in Chinese cabbage and several agricultural soils had been investigated. Both the enantiomers were analyzed by organic solvent extraction and validated by chiral high-performance liquid chromatography-diode array detector (DAD). Cellulose-tris-(3,5-dimethylphenylcarbamate)-based chiral column was used for the chiral separation of the two enantiomers applying a mixture of n-hexane and 2-propanol (90:10) as mobile phase at a flow rate of 1.0 mL/min. The elution order of the two enantiomers was distinguished by a JASCO 2000 HPLC-circular dichroism (CD) system and the first elution was (−)-enantiomer while the other was (+)-enantiomer. Racemic diclofop-methyl was fortified into 10 types of agricultural soils and foliar applied to Chinese cabbage. The assay method was linear over a range of concentrations (0.5–250 mg L −1) and the mean recovery was more than 80% for both enantiomers. The limit of detection for both enantiomers was 0.1 μg g −1 in soil and plant samples. The results of the stereoselectivity degradation of diclofop-methyl enantiomers in soil showed that the (−)-enantiomer was dissipated faster than the (+)-enantiomer in two typical soils and this enantioselectivity may be caused by microorganism, but no stereoselectivity was observed in other soils. In Chinese cabbage plant, (+)-enantiomer accumulated and eliminated faster than its antipode.

Determination of (13)C natural abundance of amino acid enantiomers in soil: methodological considerations and first results.

The application of a combined gas chromatography-combustion/isotope ratio mass spectrometry (GC-C/IRMS) method for stable carbon isotope analysis of amino acid enantiomers in soil samples is presented. Triplicate delta(13)C analyses of pentafluoropropionyl (PFP) isopropyl ester derivatives of 27 amino acid enantiomers revealed that discrimination of (13)C during derivatization is different for different amino acid enantiomers and different amounts. Injection of increasing amounts of amino acid derivatives showed that the isotopic signal varied up to 10 per thousand for D-aspartic acid. Correction for the delta(13)C signal of underivatized amino acid enantiomers is possible for all investigated amino acid enantiomers using logarithmic functions. Operating the GC-C/IRMS system in the split-mode (split ratio 1:12) is possible but resulted in a higher isotopic discrimination. The detection limit approached 3 ng for some amino acid enantiomers in the splitless mode, while the lower limit of routine determination exceeded 10 ng injection amount. The upper limit at which accurate stable isotope values were obtained was 200 ng injection amount. Compound-specific delta(13)C analysis of alanine, valine, aspartic and glutamic acid showed that the D-forms were enriched in (13)C relative to the L-forms, suggesting that microbes significantly contributed to the formation of the D-enantiomers in soil.