Chiral Liquid Chromatography-tandem Mass Spectrometry Research Articles

Urinary D-amino acid profiles in cats with chronic kidney disease.

Chronic kidney disease (CKD) is highly prevalent in domestic cats. This study aimed to compare urinary D-amino acid levels between control and CKD-afflicted cats as a novel noninvasive method for assessing CKD. Cats were divided into control and CKD stage II groups in accordance with the International Renal Interest Society guidelines. The urinary DL-amino acid levels of the cats were analyzed using chiral tandem liquid chromatography-tandem mass spectrometry, and their medical records were investigated. The CKD group had considerably lower urinary D-amino acid concentrations and enantiomeric ratios than the control group. The total urinary D-amino acid contents significantly correlated with blood parameters (creatinine and urea nitrogen). These findings may contribute towards the detection of CKD stage II in domestic cats.

Chiral liquid chromatography-tandem mass spectrometry for enantiomeric profiling of ten alkaloids in tobacco: Assessing interconversion in precursor materials and aerosol

Multiple chiral enantiomer separation poses challenges in analyzing complex matrices like natural plant materials. Currently, there is no straightforward method for simultaneous separation and analysis of ten alkaloids and enantiomers, mainly due to most of their low levels. Here, we present an improved chiral liquid chromatography-tandem mass spectrometry method for accurate quantification of ten alkaloids and enantiomers. This method exhibits recoveries of 92.3 to 118.1 %, intra-day precisions of 0.6 to 4.7 %, and inter-day precisions of 1.2 to 4.5 %, with detection limits ranging from 0.03 to 3.0 ng/mL. Successfully applied to the ten alkaloids and enantiomers quantification in precursor tobacco materials and aerosols from traditional cigarettes and heated tobacco products, our results show higher concentrations of ten alkaloids in traditional cigarette aerosol compared to heated tobacco products aerosol. During aerosol formation, (R)-cotinine, N-methylanabasine, and β-nornicotyrine were produced. Notably, high temperatures during aerosol formation favored the (R)-enantiomer of several chiral alkaloids, and lead to the formation of new secondary alkaloids. This proposed mechanism represents the first attempt to elucidate the interconversion of alkaloids during aerosol formation.

Improved quantitative determination of (R)- and (S)‐rabeprazole sodium and its metabolites in rat plasma by LC-MS/MS and its application to a toxicokinetic study

There exist two enantiomers: (R)‐ and (S)‐rabeprazole. (R)‐rabeprazole offers specific pharmacokinetic advantages and enhanced therapeutic efficacy, warranting further investigation and development. Here, we developed a simple and rapid chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to simultaneously quantify rabeprazole enantiomers and their metabolites (rabeprazole sulfoxide and desmethyl rabeprazole enantiomers) and a LC-MS to quantify rabeprazole thioether. As for the chiral LC-MS/MS method, Chiral-AGP column (150 × 4 mm, 5 μm) was used and its mobile phase was acetonitrile (mobile phase A) and 10 mmol/L ammonium acetate (mobile phase B) (linear gradient profile: 0 min, 10 % B; 5 min, 15 % B; 9 min, 15 % B; 9.01 min, 10 % B; 13 min, 10 % B). The multiple reactions monitoring transitions of m/z 360.3 → 242.1, 376.2 → 240.1, 346.2 → 228.2 and 368.2 → 190.2 were opted for quantifying rabeprazole enantiomers, rabeprazole sulfoxide, desmethyl rabeprazole enantiomers and internal standard omeprazole. The analyte samples were prepared by a simple liquid–liquid extraction method. As for the LC-MS method, analytes were separated on a Inertsil® ODS-3 column (4.6 × 150 mm, 5 μm). The mobile phase was acetonitrile-5 mmol/L ammonium acetate water solution (65:35, v/v). ESI+ was used and ion peaks with m/z 344.2 (rabeprazole thioether) and 285.1 (internal standard diazepam) were monitored. Both these 2 methods were validated for specificity, linearity, precision, accuracy, matrix effect and extraction recovery, and, particularly, the stability of analytes under various conditions. We successfully applied these methods to a 13-week toxicokinetic study of rabeprazole in rats after intravenous administration of (R)- (80, 20, 5 mg/kg/d) and racemic (80 mg/kg/d) rabeprazole sodium. The results showed that rabeprazole and its metabolites did not accumulate in rats. However, desmethyl rabeprazole and rabeprazole thioether showed higher exposure and lower clearance rate in the last administration than in the first one. (R)-rabeprazole showed a higher exposure and a slower elimination rate than (S)-rabeprazole in rats. These findings offer experimental evidence and a theoretical foundation for further preclinical investigations and clinical applications of (R)-rabeprazole.

Simultaneous determination of enantiomer residues of metalaxyl and its metabolite metalaxyl acid in animal muscle tissues by chiral liquid chromatography-tandem mass spectrometry

The toxicity of the two enantiomers of metalaxyl is significantly different and, for food safety concerns, stereoselective analysis of its residues is extremely important in animal muscle tissues. Herein, a simple, sensitive and reproducible method for the simultaneous stereoselective analysis of metalaxyl and its metabolite metalaxyl acid in animal-derived foods has been established based on mixed-mode anion exchange solid phase extraction and chiral liquid chromatography-tandem mass spectrometry. Under the optimized separation and sample pretreatment conditions, good linearity (r > 0.99) was obtained for four target analytes in four animal muscle tissues including bovine, chicken, swine and fish. Mean recoveries of all enantiomers in muscle tissue samples were 89.5–110.3 % with relative standard deviations below 12.4 %. The limits of quantification of the analytes were 0.3–1.0 µg/kg. The proposed method provides an effective means to monitor the enantiomer residues in real samples whether using highly active R-metalaxyl or racemic mixture drugs.

Simultaneous stereoisomeric separation of loxoprofen sodium and its alcohol metabolites. Application to a stereoselective pharmacokinetic study

Loxoprofen sodium (LOX) is a propionic acid derivative non-steroidal anti-inflammatory drug (NSAID), existing in the form of four stereoisomers. The main metabolites of LOX in vivo were trans- and cis-alcohol, each consisting of four stereoisomers. The objectives of the present study were to examine the selective pharmacokinetic behavior of LOX stereoisomers and stereoselective formation of its alcohol metabolites in rats based on a chiral liquid chromatographytandem mass spectrometry (LC-MS/MS) method by using an FLM Chiral NQ-RH column, which was reported for the first time. The significant difference in pharmacokinetic parameters of four stereoisomers indicated that stereoselective behavior has occurred in rats after oral administration of LOX. (1′S,2S)-LOX showed the highest concentration among the four stereoisomers in both plasma and urine samples. Trans- and cis-alcohol metabolites of LOX were also detected in plasma and urine, and trans-alcohol was found to be primary and the stereoisomeric fractions (SFs) of its four stereoisomers at different times were calculated. Examination of the stereoisomeric composition indicated a stereo preference for (2S)-configuration with respect to trans-alcohol formation. The overall results of the present study revealed the enantioselective pharmacokinetic properties of LOX stereoisomers in rats, which provided a means to advance understanding of the complex pharmacokinetic of LOX.

Simultaneous determination of all aminobutyric acids by chiral derivatization and liquid chromatography-tandem mass spectrometry.

Aminobutyric acids include eight structural or stereoisomers that exhibit a wide range of biological activities. Recent evidence on some low abundant isomers have increased the demand for highly selective analysis of all the isomers; however, simultaneous separation of all the aminobutyric acid isomers has not been successful yet, except for a specialized method that uses multiple separation columns and a split of samples. In this study, we developed a new analytical method using chiral derivatization and liquid chromatography-tandem mass spectrometry to separate all the aminobutyric acid isomers in a single separation column. All the diastereomeric derivatives were resolved in a C18 column, and the derivatives showed characteristic fragmentation patterns in tandem mass spectrometry. By using the method, we analyzed the isomers in the Arabidopsis thaliana seeds and revealed the existence of three low abundant isomers, i.e., D-, L-β-aminoisobutyric acid, and D-β-aminobutyric acid. The proposed method uses a commercially available chiral derivatizing reagent and a broadly used column; therefore, it can be widely used in biological and food analyses.

Pharmacokinetics and residue elimination of metalaxyl enantiomers in snakehead (Channa argus)

Metalaxyl is widely used as a racemic mixture to control various plant and aquatic animal diseases caused by fungal infection. It has been proved that the two enantiomers of metalaxyl have significant differences in activity and toxicity, while little is known about the pharmacokinetics and residual elimination of the individual enantiomers of metalaxyl in aquatic animals. In this study, a simple, sensitive and reliable chiral liquid chromatography-tandem mass spectrometry method was established for the determination of metalaxyl and its metabolite metalaxyl acid enantiomers, which was applied to study the stereoselective pharmacokinetics and residue elimination of individual enantiomers in snakehead (Channa argus). The snakehead was bath administered with the racemic metalaxyl and the highly active enantiomeric R-metalaxyl, respectively. The results showed that the elimination of metalaxyl in the plasma and tissues of snakehead was enantioselective. The concentration of metalaxyl in tissues was kidney > liver > muscle, and preferential degradation of the R-metalaxyl enantiomer was observed in three tissues. However, no transformation between metalaxyl enantiomers was observed in snakehead plasma and tissues when R-metalaxyl enantiomer was administered. In addition, the distribution of metalaxyl acid enantiomers in tissues is closely related to the parent compound metalaxyl, and S-metalaxyl acid was only observed in the kidney and slowly eliminated. The highest concentrations of both metalaxyl and metalaxyl acid were observed in the kidney, suggesting that kidney is the major site of metalaxyl metabolism in snakehead. Given that the highly active R-metalaxyl has a shorter half-life and does not undergo transformation between enantiomers in snakehead, it may be a better choice to use R-metalaxyl instead of racemic metalaxyl in clinical practice. The results are helpful to understand the detailed fate of metalaxyl enantiomers and should be considered in future aquaculture, environmental pollution risk and food safety evaluations.

Simultaneous Characterization and Determination of Warfarin and Its Hydroxylation Metabolites in Rat Plasma by Chiral Liquid Chromatography-Tandem Mass Spectrometry.

Warfarin is extensively used for venous thromboembolism and other coagulopathies. In clinical settings, warfarin is administered as a mixture of S- and R-warfarin, and both enantiomers are metabolized by multiple cytochrome P450 enzymes into many hydroxylation metabolites. Due to the high degree of structural similarity of hydroxylation metabolites, their profile possesses significant challenges. The previous methods generally suffer from lacking baseline resolution and/or involving complex analysis processes. To overcome this limitation, a sensitive and specific chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to simultaneously identify warfarin and hydroxywarfarins enantiomers. Chromatographic separation was achieved on a HYPERSIL CHIRAL-OT column. The mass spectrometric detection was carried out in negative ion MRM mode with electrospray ionization source. The optimized method exhibited satisfactory within-run and between-run accuracy and precision with lower limit of quantification (LLOQ) of 10.0 ng/mL and 1.0 ng/mL for warfarin and 7-, 10(R)-OH-warfarin enantiomers, respectively. Linear responses of warfarin enantiomers and 7-, and 10(R)-OH-warfarin enantiomers in rat plasma were observed over the range of 10.0–8000 ng/mL, and 1.00–800 ng/mL, respectively. The analytes were shown to be stable in various experimental conditions in rat plasma. Protein precipitation was used in sample preparation without a matrix effect. This method was successfully applied to pharmacokinetic study for quantitating the concentrations of S/R-warfarin, S/R-7-OH-warfarin, and S/R-10(R)-OH-warfarin and relatively quantitating 3′-, 4-, 6-, and 8-OH warfarin enantiomers in rat plasma.

Enantioselective analyses of chloroquine and hydroxychloroquine in rat liver microsomes through chiral liquid chromatography-tandem mass spectrometry.

An efficient, sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) chiral analysis method was established for determination of chloroquine and hydroxychloroquine enantiomers in rat liver microsomes. Effects of polysaccharide chiral stationary phases and basic additives on chiral separations of two analytes were discussed in detail. Amylose tris(3, 5-dimethylphenylcarbamate)-coated chiral stationary phase showed the best separation performance for them with acetonitrile-diethylamine-ethanol-diethylamine mixture (90:0.1:10:0.1, v/v/v/v) among four chiral stationary phases. Then, multiple reaction monitoring mode was selected as the data acquisition for determination of two pairs of enantiomers. The proposed LC-MS/MS chiral analysis method was validated in terms of linearity, accuracy, precision, and specificity. Good linearity with correlation coefficient over 0.998 was obtained in the concentration range of 0.05-5 μM. Limits of quantification for chloroquine and hydroxychloroquine enantiomers were 5.0 and 1.0 nM, respectively. The recoveries ranged from 81.14% to 111.09%. The intra-day and inter-day relative standard deviation were less than 6.5%. Moreover, concentrations of chloroquine and hydroxychloroquine enantiomers in rat liver microsomes were determined through the proposed LC-MS/MS analysis method. After incubated with rat liver microsomes for 10 min, the enantiomeric factor of hydroxychloroquine decreased from 0.50 to 0.45 (p < 0.001). In brief, our developed determination method for chloroquine and hydroxychloroquine enantiomers through LC-MS/MS spectrometry showed the characteristics of high-efficiency, fast speed, and very low detection limit, and would be greatly beneficial for screening and quantitation of them in biological matrices.

Evaluating the reliability of hair analysis in monitoring the compliance of ADHD patients under treatment with Lisdexamphetamine.

Considering the high clinical and forensic relevance of pharmaco-adherence during lisdexamphetamine (LDX) treatment for attention-deficit/hyperactivity disorder (ADHD), the aim here was to evaluate hair analysis as a tool for monitoring compliance in patients currently undergoing long term treatment with LDX, by detecting possible interruptions of medication intake or changes in dosage. For this purpose, a total of 24 patients from an outpatient clinic for ADHD were recruited. Hair and urine samples were taken after three consecutive therapy sessions over a 7-month period and analyzed for amphetamine (AMP) enantiomers and other drugs, using chiral and achiral liquid chromatography-tandem mass spectrometry (LC-MS/MS). Participants also provided information on the condition of their hair, the consumption of illegal psychotropic substances and the regularity of taking LDX. Two participants withdrew from the study early. Urine analyses were positive for D-AMP in all urine samples and therapy sessions, except in two patients who did not take LDX on a daily basis. D-AMP was detected in all hair samples; however, no correlation was found between prescribed dose/day and D-AMP concentrations in proximal hair segments. Qualitative interpretation of hair analysis showed that 18 of the 22 study completers were compliant concerning the intake of LDX without additional consumption of illegal D,L-AMP. Analysis of urine taken during the therapy sessions showed no correlation between D-AMP concentrations and prescribed dosage, with or without normalization for creatinine. In conclusion, chiral LC-MS/MS hair analysis might represent a non-invasive way to confirm LDX use within the approximate period covered by the hair segment tested, but it does not allow for quantitative therapeutic drug monitoring because of interindividual variability of concentrations in hair. Drug concentrations in hair at different stages of long-term treatment should thus be interpreted with caution by clinicians and forensic experts alike when making assessments of treatment adherence.

Development and validation of a LC-MS/MS method for the enantioseparation and determination of clopidogrel bisulfate in beagle plasma and its application to a stereoselective pharmacokinetic study

A rapid and sensitive chiral liquid chromatography-tandem mass spectrometry (LC–MS/MS) method for the enantioseparation and determination of clopidogrel bisulfate enantiomers in beagle plasma was established and successfully applied to a stereoselective pharmacokinetic study. The chromatographic separation was achieved on an Ultron ES-OVM column (150 × 2.0 mm, 5 μm) with acetonitrile-ammonium acetate (10 mM, pH 4.5) (22:78, v/v) at a flow rate of 0.3 mL/min. The mass detection was conducted using multiple reaction monitoring mode with the transition of the m/z 322.00→212.00 for clopidogrel and m/z 285.00→193.00 for diazepam (IS), respectively. The calibration curve was linear at the range of 1−800 ng/mL (r2>0.997) for each enantiomer. The intra- and inter-day precision (CV%) was within 10.9 % and the accuracy was at the range of 88.5 %–101.3 % for both enantiomers. The extraction recovery was >90.2 % and no obvious matrix effect was observed. The pharmacokinetic results showed that the R-CB have higher Cmax and AUC than that of S-CB. It is first time to find the chiral inversion between S-CB and R-CB in beagle.

Enantioselective Analysis and Degradation Studies of Four Stereoisomers of Difenoconazole in Citrus by Chiral Liquid Chromatography-Tandem Mass Spectrometry.

Four difenoconazole stereoisomers were well separated on a Superchiral S-OX column. The absolute configurations of the four stereoisomers of difenoconazole eluted in an orderly fashion with the chiral column were confirmed as (2S,4S), (2S,4R), (2R,4R), and (2R,4S)-difenoconazole, respectively, by single-crystal X-ray diffraction. For the first time, a simple and efficient trace detection method for the determination of residues of the four stereoisomers of difenoconazole in a plant sample by HPLC-MS/MS was developed. The mean recoveries were 78.23-104.38% with RSDs of 0.33-9.95%. The limits of detection for the four difenoconazole enantiomers were 0.0002-0.0004 mg/kg, and the limits of quantitation were 0.0044-0.011 mg/kg in citrus leaves and whole fruits. There was no obvious enantioselectivity upon degradation of the four stereoisomers in citrus leaves and whole fruits in Hunan and Guizhou. In Guangzhou, the rate of degradation of (2R,4R)-difenoconazole was the slowest among the four stereoisomers of difenoconazole.

Simultaneous enantiomeric analysis of five proton-pump inhibitors in soil and sediment using a modified QuEChERS method and chiral high performance liquid chromatography coupled with tandem mass spectrometry

This study presents a simple, sensitive, rapid, cheap and reliable method for the simultaneous quantification of five proton pump inhibitors (omeprazole, rabeprazole, lansoprazole, pantoprazole, and ilaprazole) at enantiomeric levels in environmental soil and river sediment by chiral high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The modified QuEChERS procedure, a very simple and efficient sample preparation method, was employed for the extraction and purification of the target analytes. To obtain satisfactory chromatographic performance and high extraction efficiency, several experimental variable parameters including the type and content of the organic modifier, the content of the additive, temperature and mobile phase flow rate, the type and volume of extraction solvent, and the type and content of clean-up sorbent were systematically optimized. Under the optimum condition, the simultaneous baseline separation of five chiral drugs was achieved on a Chiralpak IH column within 13 min. The method detection limits and quantification limits of the enantiomers were below 0.17 ng/g and 0.69 ng/g, respectively. Correlation coefficients (R2) ≥ 0.9905 were obtained for all enantiomers within the linearity range of 1–200 ng/g. The mean recoveries for all enantiomers ranged from 83.6% to 108.5% with intra-day RSD less than 11.6% and inter-day RSD less than 12.9%. Finally, the proposed method was successfully applied to authentic samples (green belt soil, agricultural soil, and river sediment) to analyze the enantiomeric composition of target chiral analytes, indicating its applicability and reliability for the enantioselective determination of proton pump inhibitors in environmental matrices. This research will help better elucidate the behavior of individual enantiomer and make an excellent risk assessment on the environment.

Enantioseparation and determination of alminoprofen in rat plasma and its application to a stereoselective pharmacokinetic study

An enantioselective study of alminoprofen (AMF) in rat plasma was performed by a rapid, specific and sensitive chiral liquid chromatography–tandem mass spectrometry (LCMS/MS) method. A homemade β-cyclodextrin (β-CD) derivatized based chiral column and a commercial polysaccharide type chiral column were selected and evaluated. The former one per-4-chlorophenylcarbamate-β-CD bonded chiral stationary phase (CSP) which was synthesized in our lab produced the enhanced enantioselective separation. The dextro-ketoprofen (d-KTF) was selected as the internal standard (IS). The approach was linear in the concentration ranges of 1.00–20000.0 ng mL−1 (r2≥0.99) for each enantiomer. The mean recoveries of R‐(−)‐ and S‐(+)‐AMF at three spiked levels of 2.00, 1000.0 and 16000.0 ng mL−1 ranged from 92.0 %–96.1 %, and the intra-day and inter-day relative standard deviations (RSDs) were within 8.9 %. The lower limit of quantification (LLOQ) values of R‐(−)‐ and S‐(+)‐AMF in rat plasma matrices were both 1.00 ng mL−1. The established method was successfully applied to a stereoselective pharmacokinetic study of AMF enantiomers in rat plasma following oral administration. The pharmacokinetic results revealed that S‐(+)‐AMF displayed prominently higher Cmax and AUC values than R‐(−)‐enantiomer.

Application of a chiral high-performance liquid chromatography-tandem mass spectrometry method for the determination of 13 related amphetamine-type stimulants to forensic samples: Interpretative hypotheses.

Interpretation of amphetamine-type stimulant (ATS) findings in urine samples can be challenging without chiral information. We present a sensitive enantioselective high-performance liquid chromatography-tandem mass spectrometry method for the quantification of (R)-amphetamine, (S)-amphetamine, (R)-methamphetamine, (S)-methamphetamine, (1R,2R)-pseudoephedrine, (1S,2S)-pseudoephedrine, (1R,2S)-ephedrine, (1S,2R)-ephedrine, (1R,2S)-norephedrine, (1S,2R)-norephedrine, (R)-cathinone, (S)-cathinone, and (1S,2S)-norpseudoephedrine (cathine) in urine. The method was successfully applied to more than 100 authentic urine samples from forensic casework. In addition, samples from a controlled self-administration of (1S,2S)-pseudoephedrine (Rinoral, 1200 mg within 6 days) were analyzed. The results strengthen the hypothesis that (1R,2S)-norephedrine is a minor metabolite of amphetamine and methamphetamine. We suggest cathine and (1S,2R)-norephedrine as minor metabolites of amphetamine racemate in humans. Small methamphetamine concentrations detected in samples with high concentrations of amphetamine could result from a metabolic formation by methylation of amphetamine although in samples with an (R)/(S) ratio for methamphetamine < 1 an additional (previous) (S)-methamphetamine consumption seems likely. Our data suggest that even amphetamine concentrations exceeding methamphetamine concentrations in urine can be caused by the biotransformation of methamphetamine to amphetamine as long as no (R)-amphetamine is detected. However, without chiral information, such findings might be (falsely) assumed as a co-consumption of both substances. Cathinone enantiomers detected in urine samples with high amphetamine concentrations can be interpreted as metabolites of amphetamine. In addition, the results of the self-administration study revealed that both cathinone enantiomers are minor metabolites of (1S,2S)-pseudoephedrine, which is the active ingredient of various medicines used for cold. The enantioselective analysis is a powerful tool to avoid the misinterpretation of ATS findings in urine samples.

Simultaneous enantioselective determination of omeprazole, rabeprazole, lansoprazole, and pantoprazole enantiomers in human plasma by chiral liquid chromatography-tandem mass spectrometry.

Proton pump inhibitors, including omeprazole, rabeprazole, lansoprazole, and pantoprazole, achieved simultaneous enantioselective determination in the human plasma by chiral liquid chromatography-tandem mass spectrometry. The four corresponding stable isotope-labeled proton pump inhibitors were adopted as the internal standards. Each enantiomer and the internal standards were extracted with acetonitrile containing 0.1% ammonia, then separated with a Chiralpak IC column (5 µm, 4.6mm × 150mm) within 10 min. The mobile phase was composed of acetonitrile-ammonium acetate (10mM) containing 0.2% acetic acid (50:50, v/v). To quantify all enantiomers, an API 4000 tandem mass spectrometer was used, and multiple reaction monitoring transitions were performed on m/z 360.1→242.1, 384.1→200.1, 370.1→252.1, and 346.1→198.1, respectively. No significant matrix effect was observed for all analytes. The calibration curve for all enantiomers were linear from 1.25 to 2500ng/mL. The precisions for intra- and inter-run were<14.2%, and the accuracy fell in the interval of -5.3 to 8.1%. Stability of samples was confirmed under the storage and processing conditions. The developed method was also suitable for separation and determination of ilaprazole enantiomers. The validated method combining the equilibrium dialysis method was applied to the protein binding ratio studies of four pairs proton pump inhibitor enantiomers in human plasma.

Development of a cognitive function marker based on D-amino acid proportions using new chiral tandem LC-MS/MS systems

The incidence of dementia, a clinical symptom characterized by severe cognitive decline, is increasing worldwide. Predictive biomarkers are therefore required for early identification and management. D-amino acids in the brain contribute to cognitive function and are suggested as useful biomarkers for diagnosing dementia risk. To clarify their relationship with human cognitive decline, we developed an identification method of chiral metabolomics for detecting slight differences in chiral amino acid amounts. Chiral tandem liquid chromatography-tandem mass spectrometry systems were applied for sensitive and selective amino acid species along with chiral species determination based on anion and zwitterion exchange mechanisms. In a comprehensive health cohort (cross-sectional study), we measured blood chiral amino acid levels from 305 women (65–80 years old) classified into Control, Mild-cognitive-Impairment (MCI), and Dementia groups using the Mini-Mental State Examination. MCI exhibited higher D-Pro (D-Pro/(D-Pro + L-Pro)) proportion vs the Control group, suggesting this proportion as a useful biomarker for MCI. Biomarker accuracy was improved in combination with D-Ser proportion. Receiver operating characteristics analysis of the Control vs. MCI proportion obtained area under the curve (0.80) with 70% sensitivity and 84% specificity at the optimal cutoff value (0.30). Thus, dementia monitoring can be improved by including trace D-amino acids measurements.

Identification, Quantification, and Stereoselective Degradation of Triazole Fungicide Cyproconazole in Two Matrixes through Chiral Liquid Chromatography-Tandem Mass Spectrometry.

Systematic investigation of cyproconazole, including absolute stereochemistry, fungicidal activity, quantification in two matrixes, and stereoselective degradation in cucumber, are conducted in this study. By virtue of vibrational circular dichroism (VCD) spectroscopy, absolute configurations of four stereoisomers were identified to be (2R,3R)-(+)-, (2R,3S)-(+)-, (2S,3S)-(-)-, and (2S,3R)-(-)-cyproconazoles. Then four stereoisomers exhibited stereoselective fungicidal activities against Fusarium graminearum Schw and Magnaporthe oryzae, and the order of fungicidal activity was (2S,3S)-(-)-stereoisomer > the stereoisomer mixture > (2S,3R)-(-)-stereoisomer > (2R,3R)-(+)-stereoisomer > (2R,3S)-(+)-stereoisomer. Moreover, chiral liquid chromatography-tandem mass spectrometry was used to identify and quantify cyproconazole stereoisomers in soil and cucumber matrixes. Good linearity (R2 ≥ 0.99) and recoveries (86.79-92.47%, RSD ≤ 3.94%) for them were achieved, individually. Furthermore, stereoselective degradation of four cyproconazole stereoisomers was observed in cucumber and the order of degradation rate was (2R,3R)-(+)-cyproconazole > (2S,3S)-(-)-cyproconazole > (2R,3S)-(+)-cyproconazole > (2S,3R)-(-)-cyproconazole. We envision that such systematic assessments of chiral fungicides at an enantiomeric level would provide valuable information in future studies involving enantioselective physiological, metabolic, and toxicological activities.

Enantioseparation and determination of flumequine enantiomers in multiple food matrices with chiral liquid chromatography coupled with tandem mass spectrometry.

The present work firstly described the enantioseparation and determination of flumequine enantiomers in milk, yogurt, chicken, beef, egg, and honey samples by chiral liquid chromatography-tandem mass spectrometry. The enantioseparation was performed under reversed-phase conditions on a Chiralpak IC column at 20°C. The effects of chiral stationary phase, mobile phase components, and column temperature on the separation of flumequine enantiomers have been studied in detail. Target compounds were extracted from six different matrices with individual extraction procedure followed by cleanup using Cleanert C18 solid phase extraction cartridge. Good linearity (R2 >0.9913) was obtained over the concentration range of 0.125 to 12.5 ng g-1 for each enantiomer in matrix-matched standard calibration curves. The limits of detection and limits of quantification of two flumequine enantiomers were 0.015-0.024 and 0.045-0.063 ng g-1 , respectively. The average recoveries of the targeted compounds varied from 82.3 to 110.5%, with relative standard deviation less than 11.7%. The method was successfully applied to the determination of flumequine enantiomers in multiple food matrices, providing a reliable method for evaluating the potential risk in animal productions.

Enantioselective determination of ketamine in dog plasma by chiral liquid chromatography-tandem mass spectrometry.

Ketamine is an N-methyl-d-aspartate receptor antagonist that is usually used clinically as a racemic mixture. Its two enantiomers exhibit different pharmacological activities. To determine whether the enantiomers have different pharmacokinetic profiles, a chiral liquid chromatography-tandem mass spectrometry method was developed and validated for the determination of ketamine enantiomers in dog plasma. The enantiomers of ketamine were extracted from 50 μL of plasma by methyl tert-butyl ether. Adequate chromatographic retention and baseline resolution of the enantiomers were achieved within a runtime of 5 min on a chiral column coated with polysaccharide derivatives, using a gradient mobile phase of acetonitrile and 10 mm ammonium bicarbonate aqueous solution. Ketamine enantiomers were detected by mass spectrometry with multiple reaction monitoring mode using the transitions of m/z 238.3 → 125.9 for the analytes and m/z 237.1 → 194.1 for carbamazepine (internal standard). The method was linear over the concentration range from 0.5 to 500 ng/mL for each enantiomer. The lower limit of quantification (LLOQ) for each enantiomer was 0.5 ng/mL. The intra- and inter-day precision was <7.3% and 8.5% for R- and S-ketamine, respectively. The accuracy was 92.9-110.4% for R-ketamine and 99.8-102.4% for S-ketamine. The method was successfully applied to characterize the stereoselective pharmacokinetic profiles of ketamine in beagle dogs.