Enantioselective determination of (R)‐ and (S)‐lansoprazole in human plasma by chiral liquid chromatography with mass spectrometry and its application to a stereoselective pharmacokinetic study

A simple and enantioselective method was developed and validated for the simultaneous determination of (R)‐ and (S)‐lansoprazole in human plasma by chiral liquid chromatography with tandem mass spectrometry. Lansoprazole enantiomers and internal standard (esomeprazole) were extracted from plasma using acetonitrile as protein precipitating agent. Baseline chiral separation was achieved within 9.0 min on a Chiralpak IC column (150 mm × 4.6 mm, 5 μm) with the column temperature of 30°C. The mobile phase consisted of 10 mM ammonium acetate solution containing 0.05% acetic acid/acetonitrile (50:50, v/v). The mass spectrometric analysis was performed using a QTrap 5500 mass spectrometer coupled with an electrospray ionization source in positive ion mode. The multiple reactions monitoring transitions of m/z 370.1→252.1 and 346.1→198.1 were used to quantify lansoprazole enantiomers and esomeprazole, respectively. For each enantiomer, no apparent matrix effect was found, the calibration curve was linear over 5.00–3000 ng/mL, the intra‐ and inter‐day precisions were below 10.0%, and the accuracy was –3.8 to 3.3%. Analytes were stable during the study. No chiral inversion was observed during sample storage, preparation procedure and analysis. The method was applied to the stereoselective pharmacokinetic studies in human after intravenous administration of dexlansoprazole or racemic lansoprazole.     

Simultaneous stereoselective analysis of naftopidil and O‐desmethyl naftopidil enantiomers in rat feces using an online column‐switching high‐performance liquid chromatography method

A novel online column‐switching chiral high‐performance liquid chromatography method was developed and validated for the simultaneous determination of naftopidil (NAF) and its O‐desmethyl metabolites (DMN) enantiomers in rat feces. Direct and multiple injections of supernatant from rat feces homogenate were allowed through the column‐switching system. Analyte extraction was performed on the Capcell Pak mixed‐functional column by acetonitrile–phosphate buffer (pH 7.4; 10 mm ; 8:92, v/v) flowing at 1 mL/min. Separation of NAF and DMN enantiomers was achieved on the Chiralpak IA column by methanol–acetonitrile–acetate buffer (pH 5.3; 5 mm ; 45:33:22, v/v/v) flowing at 0.5 mL/min. The analytes were measured with a fluorescence detector at 290 nm (λ_ex) and 340 nm (λ_em). The validated method showed a good linearity [22.5–15,000 ng/mL for (+)‐/(?)‐NAF; 35–25,000 ng/mL for (+)‐/(?)‐DMN] and the lowest limits of quantification for NAF and DMN enantiomers were 22.5 and 35 ng/mL, respectively. Both intra‐ and inter‐day variations were <10%. The assay was successfully applied to the fecal excretion of NAF and DMN enantiomers in rat after single oral administration of (±)‐NAF. Nonstereoselective excretion of (+)‐ and (?)‐NAF was found in feces, while stereoselective excretion of (+)‐ and (?)‐DMN was observed with higher excretion levels of (+)‐DMN, indicating that there may exist stereoselective metabolism for NAF enantiomers. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of rabeprazole enantiomers in dog plasma by supercritical fluid chromatography tandem mass spectrometry and its application to a pharmacokinetic study

Rabeprazole is a novel benzimidazole proton pump inhibitor used for the treatment of gastrointestinal disorders. It is a chiral molecule that gives rise to the possibility of stereoselective pharmacokinetics. To investigate this phenomenon, a rapid and sensitive chiral assay based on supercritical fluid chromatography tandem mass spectrometry was developed and applied to the determination of (R )‐rabeprazole and (S )‐rabeprazole in dog plasma. Sample preparation involved protein precipitation with acetonitrile after the addition of (R )‐lansoprazole as internal standard. Baseline separation of enantiomers in 4.5 min was achieved on an Acquity UPC² system using an ACQUITY UPC² Trefoil CEL2 column maintained at 60°C and a mobile phase consisting of methanol/CO₂ (30:70, v/v) delivered at 2.5 mL/min. Detection was achieved by multiple reaction monitoring of the transitions at m/z 360.0→242.2 (rabeprazole) and 370.3→252.0 (internal standard) in the positive ion mode. The assay was linear in the range of 1–1000 ng/mL and free of matrix effects. Intra‐ and interday precisions were less than 10.0% with accuracy in the range of –2.6 to 3.1%. The method was successfully applied to a pharmacokinetic study of rabeprazole enantiomers after administration of a single oral dose of 10 mg racemate to beagle dogs.     

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, 4.6 mm × 150 mm) within 10 min. The mobile phase was composed of acetonitrile–ammonium acetate (10 mM) 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 2500 ng/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.     

A chiral LC‐MS/MS method for the enantioselective determination of R‐(+)‐ and S‐(–)‐pantoprazole in human plasma and its application to a pharmacokinetic study of S‐(–)‐pantoprazole sodium injection

Pantoprazole, a proton pump inhibitor, is clinically used for the treatment of peptic diseases. An enantioselective LC‐MS/MS method was developed and validated for the simultaneous determination of pantoprazole enantiomers in human plasma. Pantoprazole enantiomers and the internal standard were extracted from plasma using acetonitrile. Chiral separation was carried on a Chiralpak IE column using the mobile phase consisted of 10 mm ammonium acetate solution containing 0.1% acetic acid–acetonitrile (28 : 72, v /v). MS analysis was performed on an API 4000 mass spectrometer. Multiple reactions monitoring transitions of m /z 384.1→200.1 and 390.1→206.0 were used to quantify pantoprazole enantiomers and internal standard, respectively. For each enantiomer, no apparent matrix effect was found, the calibration curve was linear over 5.00–10,000 ng/mL, the intra‐ and inter‐day precisions were below 10.0%, and the accuracy was within the range of –5.6% to 0.6%. This method was applied to the stereoselective pharmacokinetic studies in human after intravenous administration of S ‐(–)‐pantoprazole sodium injections. No chiral inversion was observed during sample storage, preparation procedure and analysis. While R ‐(+)‐pantoprazole was detected in human plasma with a slightly high concentration, which implied that S ‐(–)‐pantoprazole may convert to R ‐(+)‐pantoprazole in some subjects.     

Green high‐performance liquid chromatography enantioseparation of lansoprazole using a cellulose‐based chiral stationary phase under ethanol/water mode

A simple and environmentally friendly reversed‐phase high‐performance liquid chromatography method for the separation of the enantiomers of lansoprazole has been developed. The chromatographic resolution was carried out on the cellulose‐based Chiralpak IC‐3 chiral stationary phase using a green and low‐toxicity ethanol‐aqueous mode. The effects of water content in the mobile phase and column temperature on the retention of the enantiomers of lansoprazole and its chiral and achiral related substances have been carefully investigated. A mixed‐mode hydrophilic interaction liquid chromatography and reversed‐phase retention mechanism operating on the IC‐3 chiral stationary phase allowed us to achieve simultaneous enantioselective and chemoselective separations in water‐rich conditions. The enantiomers of lansoprazole were baseline resolved with a mobile phase consisting of ethanol/water 50:50 without any interference coming from chiral and achiral impurities within 10 min.     

Chiral determination of a novel acaricide cyflumetofen enantiomers in cucumber,tomato, and apple by HPLC

A simple chiral analytical method was developed for the enantiomeric determination of cyflumetofen in cucumber, tomato, and apple by normal‐phase HPLC. The effects of mobile phase composition and column temperature on the enantioseparation were evaluated. Excellent separation was achieved at 25°C on a Chiralpak AD‐H column, with a mixture of n‐hexane and 2‐propanol (95:5, v/v) as mobile phase at a flow rate of 1.0 mL/min detecting at 234 nm. The resolution of cyflumetofen enantiomers was up to 5.5. The elution order of the enantiomers was determined by an online OR‐2090 detector, which was performed under the same chromatographic conditions. The first eluted enantiomer was (–)‐cyflumetofen and the second eluted one was (+)‐cyflumetofen. The method was validated for linearity, repeatability, accuracy, LOD, and LOQ. LOD ranged from 0.1 to 0.15 mg/kg, with the LOD varying from 0.33 to 0.5 mg/kg for each enantiomer, respectively. The average recoveries of the pesticide ranged from 71.4 to 102.0% at all fortification levels. The precision values associated with the analytical method, expressed as RSD values, were below 14.8% in all matrices. The method was then successfully applied to detect cyflumetofen enantiomers in real samples.     

Validation of an enantioselective LC–MS/MS method to quantify enantiomers of (±)‐OTX015 in mice plasma: Lack of in vivo inversion of (−)‐OTX015 to its antipode

A highly sensitive, specific and enantioselective assay has been validated for the quantitation of OTX015 enantiomers [(+)‐OTX015 and (−)‐OTX015] in mice plasma on LC–MS/MS‐electrospray ionization as per regulatory guidelines. Protein precipitation was used to extract (±)‐OTX015 enantiomers and internal standard (IS) from mice plasma. The active [(−)‐OTX015] and inactive [(+)‐OTX015] enantiomers were resolved on a Chiralpak‐IA column using an isocratic mobile phase (0.2% ammonia/acetonitrile 20 : 80, v /v) at a flow rate of 1.2 mL/min. The total run time was 6.0 min. (+)‐OTX015, (−)‐OTX015 and IS eluted at 3.34, 4.08 and 4.77 min, respectively. The MS/MS ion transitions monitored were m/z 492 → 383 for OTX015 and m/z 457 → 401 for IS. The standard curves for OTX015 enantiomers were linear (r ² > 0.998) in the concentration range 1.03–1030 ng/mL. The inter‐ and intraday precisions were in the range 2.20–13.3 and 8.03–12.1% and 3.80–14.4 and 8.97–13.6% for (+)‐OTX015 and (−)‐OTX015, respectively. Both the enantiomers were found to be stable in a battery of stability studies. This novel method has been applied to the study of stereoselective oral pharmacokinetics of (−)‐OTX015 and unequivocally demonstrated that (−)‐OTX015 does not undergo chiral inversion to its antipode in vivo in mice.     

High-throughput chiral analysis of albuterol enantiomers in dog plasma using on-line sample extraction/polar organic mode chiral liquid chromatography with tandem mass spectrometric detection

An automated chiral chromatography/tandem mass spectrometry bioanalytical method for the determination of albuterol in dog plasma was developed. The method employed on-line sample extraction using turbulent flow chromatography coupled to a Chirobiotic T column for chiral separation using a polar organic mobile phase consisting of methanol, 0.02% formic acid, and 0.1% ammonium formate. The analytes were detected by a tandem mass spectrometer operated in positive ion mode. The (S)- and (R)-isomers were resolved chromatographically with retention times of 5.1 and 5.6 min, respectively. The analytical run time was 8 min. The enantiomers did not interconvert either in mobile phase or in dog plasma at room temperature over the course of at least 2 h. The assay has a linear dynamic range from 2.5-2500 nM for both enantiomers. The lower limit of quantitation (LLOQ) was 2.5 nM for both enantiomers using 50 microL of plasma. The accuracy and precision of intraday validation were determined at five concentration levels of six replicates. The accuracy of the method for the (R)-isomer ranged from 94-103% of nominal concentrations, and the precision (%CV) ranged from 3.6-12%. The accuracy of the method for the (S)-isomer ranged from 94.5-108% of nominal concentrations, and the precision ranged from 3.2-9.3%. Interday accuracy and precision were evaluated for three days at five concentrations for one replicate. The accuracy of the method for the (R)-isomer ranged from 98-110% of nominal concentrations, and the precision ranged from 1.5-10.6%. The accuracy of the method for the (S)-isomer ranged from 96-104% of nominal concentrations, and the precision ranged from 1.5-8.7%. The combination of turbulent flow on-line sample extraction with polar organic mode chiral chromatography provided a specific, rugged, and high-throughput method for the chiral analysis of albuterol in biological fluids.     

Development and Validation of a Chiral Liquid Chromatographic Assay for Enantiomeric Separation and Quantification of Verapamil in Rat Plasma: Stereoselective Pharmacokinetic Application

A novel, fast and sensitive enantioselective HPLC assay with a new core–shell isopropyl carbamate cyclofructan 6 (superficially porous particle, SPP) chiral column (LarihcShell-P, LSP) was developed and validated for the enantiomeric separation and quantification of verapamil (VER) in rat plasma. The polar organic mobile phase composed of acetonitrile/methanol/trifluoroacetic acid/triethylamine (98:2:0.05: 0.025, v/v/v/v) and a flow rate of 0.5 mL/min was applied. Fluorescence detection set at excitation/emission wavelengths 280/313 nm was used and the whole analysis process was within 3.5 min, which is 10-fold lower than the previous reported HPLC methods in the literature. Propranolol was selected as the internal standard. The S-(−)- and R-(+)-VER enantiomers with the IS were extracted from rat plasma by utilizing Waters Oasis HLB C18 solid phase extraction cartridges without interference from endogenous compounds. The developed assay was validated following the US-FDA guidelines over the concentration range of 1–450 ng/mL (r² ≥ 0.997) for each enantiomer (plasma) and the lower limit of quantification was 1 ng/mL for both isomers. The intra- and inter-day precisions were not more than 11.6% and the recoveries of S-(−)- and R-(+)-VER at all quality control levels ranged from 92.3% to 98.2%. The developed approach was successfully applied to the stereoselective pharmacokinetic study of VER enantiomers after oral administration of 10 mg/kg racemic VER to Wistar rats. It was found that S-(−)-VER established higher C_max and area under the concentration-time curve (AUC) values than the R-(+)-enantiomer. The newly developed approach is the first chiral HPLC for the enantiomeric separation and quantification of verapamil utilizing a core–shell isopropyl carbamate cyclofructan 6 chiral column in rat plasma within 3.5 min after solid phase extraction (SPE).     

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.     

Development and validation of an enantioselective LC‐MS/MS method to quantify enantiomers of (±)‐TAK‐700 in rat plasma: lack of in vivo inversion of (+)‐TAK‐700 (Orteronel) to its antipode

A highly sensitive, specific and enantioselective assay has been developed and validated for the estimation of TAK‐700 enantiomers [(+)‐TAK‐700 and (?)‐TAK‐700] in rat plasma on LC‐MS/MS‐ESI in the positive‐ion mode. Liquid–liquid extraction was used to extract (±)‐TAK‐700 enantiomers and IS (phenacetin) from rat plasma. TAK‐700 enantiomers were separated using methanol and 5 mm ammonium acetate (80:20, v/v) at a flow rate of 0.7 mL/min on a Chiralcel OJ‐RH column. The total run time was 7.0 min and the elution of (+)‐TAK‐700, (?)‐TAK‐700 and IS occurred at 3.71, 4.45 and 4.33 min, respectively. The MS/MS ion transitions monitored were m/z 308.2 → 95.0 for TAK‐700 and m/z 180.2 → 110.1 for IS. The standard curves for TAK‐700 enantiomers were linear (r² > 0.998) in the concentration range 2.01–2015 ng/mL for each enantiomer. The inter‐ and intra‐day precisions were in the ranges 3.74–7.61 and 2.06–8.71% and 3.59–9.00 and 2.32–11.0% for (+)‐TAK‐700 and (?)‐TAK‐700, respectively. Both the enantiomers were found to be stable in a battery of stability studies. This novel method was applied to the study of stereoselective oral pharmacokinetics of (+)‐TAK‐700 and it was unequivocally demonstrated that (+)‐TAK‐700 does not undergo chiral inversion to its antipode in vivo. Copyright © 2012 John Wiley & Sons, Ltd.     

Separation of lansoprazole enantiomers in human serum by HPLC

Summary A new and simple HPLC method is described for the separation and quantitative determination of the (+)-and (−)-enantiomers of lansoprazole. The analytes were extracted from serum as previously described for whole lansoprazole [K. Borner, Chromatographia 45, 450–452 (1997)]. The enantiomers were separated by chromatography on a CHIRAL-AGP^R column which contained covalently bound acid α₁-glycoprotein as chiral selector. In the pure drug the (−)/(+) ratio was 0.99:1.01. In serum of twelve human volunteers the concentration of the (−)-enantiomer was 3 to 5 times higher than that of the (+)-enantiomer. Both enantiomers differ remarkably in their pharmacokinetics.     

Resolution and isolation of enantiomers of (±)‐isoxsuprine using thin silica gel layers impregnated with l‐glutamic acid,comparison of separation of its diastereomers prepared with chiral derivatizing reagents having l‐amino acids as chiral auxiliaries

Thin silica gel layers impregnated with optically pure l ‐glutamic acid were used for direct resolution of enantiomers of (±)‐isoxsuprine in their native form. Three chiral derivatizing reagents, based on DFDNB moiety, were synthesized having l ‐alanine, l ‐valine and S‐benzyl‐l ‐cysteine as chiral auxiliaries. These were used to prepare diastereomers under microwave irradiation and conventional heating. The diastereomers were separated by reversed‐phase high‐performance liquid chromatography on a C₁₈ column with detection at 340 nm using gradient elution with mobile phase containing aqueous trifluoroacetic acid and acetonitrile in different compositions and by thin‐layer chromatography (TLC) on reversed phase (RP) C₁₈ plates. Diastereomers prepared with enantiomerically pure (+)‐isoxsuprine were used as standards for the determination of the elution order of diastereomers of (±)‐isoxsuprine. The elution order in the experimental study of RP‐TLC and RP‐HPLC supported the developed optimized structures of diastereomers based on density functional theory. The limit of detection was 0.1–0.09 µg/mL in TLC while it was in the range of 22–23 pg/mL in HPLC and 11–13 ng/mL in RP‐TLC for each enantiomer. The conditions of derivatization and chromatographic separation were optimized. The method was validated for accuracy, precision, limit of detection and limit of quantification. Copyright © 2014 John Wiley & Sons, Ltd.     

Enantioselective separation and determination of the dinotefuran enantiomers in rice,tomato and apple by HPLC

An effective chiral analytical method was developed for the resolution and determination of dinotefuran enantiomers in rice, tomato and apple samples. Dinotefuran enantiomers were baseline‐separated and determined on a novel chiral column, ChromegaChiral CCA, with n‐hexane–ethanol–methanol (85:5:10, v/v/v) as the mobile phase at a flow rate of 1.0 mL/min with UV detection at 270 nm. The resolution of dinotefuran enantiomers was about 1.8. The first eluted enantiomer was (+)‐dinotefuran and the second eluted one was (?)‐dinotefuran. The effects of mobile‐phase composition and column temperature on the enantioseparation were evaluated. The method was validated for linearity, repeatability, accuracy, LOD and LOQ. LOD was 0.15 mg/kg in rice and tomato, 0.05 mg/kg in apple, with an LOQ of 0.5 mg/kg in rice and tomato, 0.2 mg/kg in apple. The average recoveries of the pesticide from all matrices ranged from 75.8 to 92.9% for all fortification levels The precision values associated with the analytical method, expressed as RSD values, were <16.5% for the pesticide in all matrices. The methodology was successfully applied for the enantioselective analysis of dinotefuran enantiomers in real samples, indicating its efficiency in investigating the environmental stereochemistry of dinotefuran in food matrix.     

Direct chiral resolution of cloquintocet-mexyl and its application to in vitro degradation combined with clodinafop-propargyl

A simple chiral high‐performance liquid chromatography (HPLC) method with ultraviolet (UV) detection was developed and validated for measuring Cloquintocet‐mexyl (ClM) enantiomers and clodinafop‐propargyl (CP) using cellulose tris‐(3,5‐dimethylphenylcarbamate) (CDMPC) as chiral stationary phase (CSP). The effects of mobile phase composition and column temperature on the ClM enantiomer separation were investigated. Good separation was achieved by using a mixture of n‐hexane and n‐propanol as mobile phase. Based on the chiral HPLC method, enantioselective quantitative determination analysis methods for this herbicide combined with CP in diluted plasma were developed and validated. The assay method was linear over a range of concentrations (0.5–100 µg/mL) in diluted plasma and the mean recovery was greater than 80% for both enantiomers and CP. The limits of quantification and detection for both ClM enantiomers and CP were 0.5 and 0.2 µg/mL, respectively. Intra‐ and interday relative standard deviations did not exceed 10% for three tested concentrations. The result suggested that the degradation of ClM enantiomers was stereoselective in rabbit plasma, and both rac‐ClM and CP degraded quickly in plasma, showing that the main existing forms with biological effect in animals are their metabolites. Copyright © 2011 John Wiley & Sons, Ltd.     

HPLC enantioseparation of alkaloid malacitanine using fluorimetric/polarimetric detection

This work reports two methods developed for the separation and determination of the enantiomers of the new alkaloid malacitanine (MLC) and the determination of the enantiomeric purity in mixtures. First, the isomers were separated using a Chirex 3020 (250 mm × 4.6 mm, 5 μm) chiral column with a mobile phase of cyclohexane–1,2‐dichloroethane–ethanol–trifluoroacetic acid (64:30:6:0.6, v/v/v/v) at a flow rate of 1 mL/min and fluorimetric detection. Obtained retention times were 12.4 and 15.9 min (+ and ?) with a resolution Rs of 1.13. Relative standard deviations (RSDs) were 2.5 and 2.4% at the 0.5‐μg level (four determinations). Second, a nonenantioselective procedure for the determination of enantiomeric purity of MLC using a Lichrospher ® Si‐60 (250 mm × 5 mm, 5 μm) normal phase with a mobile phase of 100% ethanol at a flow rate of 0.9 mL/min coupled to two detectors in series, fluorimetric and polarimetric. RSD of 3.3% was obtained. Calculated enantiomeric purity by chiral chromatography gave 48.6% (?)‐MLC in the near racemic product. Using polarimetric signal of the nonseparated enantiomers and comparing the slopes of the calibration curves (enantiomers) from the racemic product gave 47.8% (?)‐MLC content. A study of accuracy of (?)‐MLC gave recoveries from 98.3 to 100.7%.     

Enantioseparation of selected chiral sulfoxides in high‐performance liquid chromatography with polysaccharide‐based chiral selectors in polar organic mobile phases with emphasis on enantiomer elution order

The separation of the enantiomers of 17 chiral sulfoxides was studied on polysaccharide‐based chiral columns in polar organic mobile phases. Enantiomer elution order (EEO) was the primary objective in this study. Two of the six chiral columns, especially those based on amylose tris(3,5‐dimethylphenylcarbamate) and cellulose tris(4‐chloro‐3‐methylphenylcarbamate) (Lux Cellulose‐4) proved to be most successful in the separation of the enantiomers of the studied sulfoxides. Interesting examples of EEO reversal were observed depending on the chiral selector or the composition of the mobile phase. For instance, the R‐(+) enantiomer of lansoprazole eluted before the S‐(?) enantiomer on Lux Cellulose‐1 in both methanol or ethanol as the mobile phase, while the elution order was opposite in the same eluents on amylose tris(3,5‐dimethylphenylcarbamate) with the S‐(?) enantiomer eluting before the R‐(+) enantiomer. The R‐(+) enantiomer of omeprazole eluted first on Lux Amylose‐2 in methanol but it was second when acetonitrile was used as the mobile phase with the same chiral selector. Several other examples of reversal in EEO were observed in this study. An interesting example of the separation of four stereoisomers of phenaminophos sulfoxide containing chiral sulfur and phosphor atoms is also reported here.     

Use of chiral derivatization for the determination of dichlorprop in tea samples by ultra performance LC with fluorescence detection

Dichlorprop is available for agricultural use as a chiral pesticide. In this study, the stereoselective determination of dichlorprop enantiomers in tea samples such as green, black, jasmine, and oolong was developed by ultra performance LC with fluorescence spectrometry after covalent chiral derivatization. The separation was achieved on an Acquity BEH C18 column with the mobile phase consisting of 0.1% formic acid in acetonitrile/water at a flow rate of 0.4 mL/min. In the covalent chiral derivatization using (S)‐(+)‐4‐(N,N‐dimethylaminosulfonyl)‐7‐(3‐aminopyrrolidin‐1‐yl)‐2,1,3‐benzoxadiazole, the peak resolution between the S and R‐dichlorprop enantiomers was 2.6. LODs and LOQs values were 10 and 50 ng/mL standard solution. The linearity of the calibration curves yielded the coefficients (r² > 0.99, ranging from 0.05 to 5 μg/mL) of determination of each of the dichlorprop enantiomers. SPE extraction was used for the sample preparation of dichlorprop in various tea samples. Recoveries were in the range of 82.4–97.6% with associated precision values (within‐day: 82.4–95.8%, n = 6, and between‐day: 83.7–97.6% for 3 days) for repeatability and reproducibility. Based on this result, our method has been proven to be highly efficient and suitable for the routine assay of dichlorprop enantiomers in various tea samples. We propose that the ultra performance LC assay after covalent chiral derivatization would be the renewed tools in the era of chiral stationary platform for chiral pesticide residues in foods.     

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 × 150 mm i.d., 5 μm) 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 0.5 μg/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.