Responses of enantioselective characteristics of imidazolinone herbicides and Chiralcel OJ column to temperature variations

Temperature affects not only the chromatographic characteristics of solute but may also alter the conformation of the stationary phase. However, temperature influences on enantioseparation of solute and conformation of chiral stationary phase (CSP) are seldom considered simultaneously. In this study, three temperature programs, a conventional heating procedure, a cyclic van't Hoff program, and a step-temperature program, were employed to evaluate temperature effects on enantioseparation of five imidazolinone herbicides on Chiralcel OJ column and the conformational state of the stationary phase. The van't Hoff plots of retention factor (k'), distribution constant (K) and separation factor (alpha) for imazapyr (1), imazapic (2), imazethapyr (3), and imazamox (4) were linear within 15-50 degrees C. Nonlinear van't Hoff plots of alpha were observed for imazaquin (5) with mobile phase of n-hexane (0.1% TFA)-2-propanol at 70/30 or 60/40 (v/v). The large molecular size of imazaquin (5) and van't Hoff plots of alpha were therefore more sensitive at detecting conformational changes of the stationary phase. Small but irreversible conformational changes occurred at 5-10 degrees C with the solvent ratio of 60/40. During the cyclic van't Hoff program, reversible conformational changes were observed at >or=15 degrees C. A switch was even visible at about 25 degrees C with the solvent ratio of 60/40 during the re-cooling cycle. The cyclic van't Hoff temperature program showed that using OJ column may yield satisfactory results at 15-50 degrees C but not at 相似文献   

Hold-up volume and its application in estimating effective phase ratio and thermodynamic parameters on a polysaccharide-coated chiral stationary phase

As an "unretained" marker, 1,3,5-tri-tert-butylbenzene (TTBB) has been commonly used to measure the hold-up volume. Despite many racemates have been resolved on Chiralcel OJ column, the hold-up volume of the column is still not well characterized. The aim of this work was to evaluate the chromatographic behavior of TTBB on the OJ column, and its application in estimating the effective phase ratio and thermodynamic parameters. The hold-up volume was affected not only by the mobile phase composition but also the solvents used for dissolving TTBB. A higher concentration of TTBB (0.500 mg/mL) showed a better reproducibility than when used at a lower concentration. After correction for thermal expansion of the mobile phase, TTBB was found to have slight retention on the OJ phase. The effective phase ratio increased with an increase in the temperature and decrease in the strength of the mobile phase. The enthalpy and entropy of enantiomers of imidazolinone herbicides were independent of the temperature in a linear van't Hoff plot when the effective phase ratio was changed. This study shows that, based on the hold-up volume from TTBB, thermodynamic evaluation with parameters derived from the distribution constant is valuable for understanding chromatographic retention and enantioseparation mechanisms of chiral analytes.     

Improved extraction and clean-up of imidazolinone herbicides from soil solutions using different solid-phase sorbents

Extraction and quantification of herbicide residues from soil are important in understanding the behaviour of persistent herbicides. This research investigated extraction and clean-up methods for imidazolinone herbicides from soil and soil amended with organic material. A series of solvent mixes, pH conditions and sorbents was tested. Across three imidazolinone herbicides: imazapyr, imazethapyr and imazaquin, 0.5 M NaOH extraction gave greater than 90% recovery from soil samples; however, 0.5 M NaOH:MeOH (80:20) resulted in higher recovery for imazaquin, but not for the other two herbicides. Of the sorbents tested, the use of chromatographic mode sequencing using C₁₈ and SCX sorbents provided consistent high (>85%) recovery of all three herbicides from soil and separation of the herbicides from other soil components by high performance liquid chromatography (HPLC). These two methods will allow high recovery of these imidazolinone herbicides from soil and have the ability to detect these herbicides without interference from other soil components.     

Residue Analysis and Determination of IMI Herbicides in Sunflower and Soil by GC–MS

Sunflower agriculture is an important subsector that plays a key role in the economy of Turkey, contributing 1.38 million tonnes. The aim of this study is to investigate the levels of imidazolinone (IMI) group herbicides in Thrace Region, Turkey. In particular, we aimed to determine the residue levels of imazamox, a herbicide used in sunflower production in Thrace Region, in soil, different parts of plant, and seed. Five herbicides were identified in sunflower samples using solid–liquid extraction with gas chromatography–electrospray ionization mass spectrometry (GC–EI–MS) on single-quadruple instruments in selected ion monitoring (SIM) mode. The optimized conditions were found to be mobile-phase flow rate of 1 mL min^?1 and injection volume of 3 μL in programmed temperature vaporization (PTV) solvent vent mode. The recovery of imazamox, imazaquin, imazethapyr, imazapyr, and imazapic from sunflower plant and soil was 89 and 99, 104 and 105, 92 and 93, 96 and 92, and 99 and 96%, respectively.     

Enantiomeric separations of chiral polychlorinated biphenyls on three polysaccharide-type chiral stationary phases by supercritical fluid chromatography

Enantiomeric separations of 18 chiral polychlorinated biphenyls (PCBs) were investigated on three polysaccharide-type chiral stationary phases (CSPs; Sino-Chiral OJ, Chiralpak IB, and Chiralcel OD) by supercritical fluid chromatography (SFC). With these commonly used polysaccharide CSPs, 17 PCBs except PCB 135 (R(S) = 0.81) were well resolved (R(S) > 1.5) under appropriate mobile phases and temperatures. Using Sino-Chiral OJ, 14 PCBs could be baseline-separated, while only one and nine PCBs could be completely separated using Chiralpak IB and Chiralcel OD, respectively. The influence of column temperature was studied for the optimization of resolution, as well as for the type and percentage of organic modifier in the mobile phase. The resolution decreased as the temperature increased in the range of 26-40 °C in which the enantiomeric separations were an enthalpy-driven process. The addition of modifiers in the mobile phase decreased the resolution of the PCB enantiomers, but it clearly shortened their retention time. These separation results indicate that SFC is a promising chromatographic technique for chiral separation and enantiopure standard preparation.     

高效液相色谱法拆分硅氟唑对映体

在纤维素-三-(3,5-二甲基苯基氨基甲酸酯)(Chiralcel OD-H)手性柱上对硅氟唑对映体的分离进行了研究.考察了流动相中改性剂的种类和浓度、流速以及柱温对分离效果的影响,并对手性拆分机制进行了讨论.实验结果表明:5种醇改性剂中,异丙醇的改性效果最佳,当异丙醇含量为2%时,分离度(Rs)达最大值10.19;在...     

Direct chromatographic resolution of racemic aminoglutethimide and its acetylated metabolite using different cellulose based chiral stationary phases

Summary Two improved methods for the enantiomeric separation of racemic aminoglutethimide (±AG) and its acetylated metabolite (±AAG) have been developed. Direct liquid chromatographic resolution of the enantiomers of aminoglutethimide and its acetylated metabolite was accomplished using Chiralcel OD and Chiralcel OJ columns without any derivatization. Maximum resolution of 8.87 and 2.23 was obtained for the enantiomers of aminoglutethimide and its acetylated metabolite using a Chiralcel OD column, while maximum resolution of 10.34 and 7.01 was obtained for the enantiomers using a Chiralcel OJ column. Optimization of separation was obtained using different concentration of 2-propanol in hexane as a mobile phase.     

Isocratic high-performance liquid chromatographic resolution of glutethimide enantiomers and their 4-hydroxyglutethimide metabolites using cellulose tribenzoate chiral stationary phase

Glutethimide (2-ethyl-2-phenylglutarimide) enantiomers and their corresponding 4-hydroxyglutethimide metabolites (RS and RR) are separated using newly developed commercially available cellulose tris(4-methylphenyl benzoate) ester (Chiralcel OJ) chiral stationary phase and hexane-ethanol or hexane-2-propanol as the mobile phase. The effects of ethanol or 2-propanol concentration in the mobile phase and of column temperature on retention and enantioselectivity of glutethimide enantiomers are also demonstrated. Maximum resolutions of 14.23 and 7.09 are obtained for glutethimide and their 4-hydroxyglutethimide metabolites, respectively, with hexane-ethanol (60:40) at 23 degrees C and a flow rate of 1 mL/min.     

Chiral separation of organic phosphonate compounds on cellulose CSP (chiral stationary phase) under reversed phase mode.

The enantiomers of fourteen O,O-dialkyl-2-benzyloxycarbonyl-aminoarylmethyl-phosphonates are directly separated on the tris(3,5-dimethylphenylcarbamate) cellulose column (Chiralcel OD-R) under reversed phase mode. The results of the chiral separation are different from the results obtained in the normal phase mode. The mobile phase plays an essential role in chiral discrimination when using Chiralcel OD-R. The influences of the mobile phase composition on the retention and the enantioselectivity are investigated. The influences on chiral separation of the length and steric hindrance of alkoxy groups of the phosphonate ester and of the nature of the substituent on the benzene ring that is attached to the chiral carbon atom are also discussed.     

Determination of imazethapyr and imazapyr residues in soil by coupled-column liquid chromatography

Summary A column-switching method using two separation columns combined with UV detection at 260 or 236 nm has been used to determine the imidazolinone herbicides imazethapyr and imazapyr in soils. The residues were extracted from the soil with 0.1 M aqueous sodium carbonate solution and, after adjusting the pH to 2.0, the solution was partitioned with dichloromethane. Limits of determination for imazethapyr and imazapyr were 3 μg/kg. Recoveries were from 55 to 75% for both imidazolinone herbicides in the range 3–100 μg/kg in soil.     

Liquid chromatographic separation of the enantiomers of metoprolol and its alpha-hydroxy metabolite on Chiralcel OD for determination in plasma and urine.

The two enantiomers of metoprolol and the four enantiomeric forms of alpha-hydroxymetoprolol were separated by liquid chromatography on a Chiralcel OD column containing a cellulose tris(3,5-dimethyl-phenylcarbamate) chiral stationary phase. The column efficiency was strongly dependent on the flow-rate and the enantioselectivity was influenced by temperature. Of utmost importance for the chiral separation was the water content of the mobile organic phase. The separation system was used for the separation and determination of the enantiomers in plasma and urine samples. The metoprolol enantiomers could be determined by fluorescence down to 10 nmol/l of each in plasma with a relative standard deviation of less than 15%.     

Enantiomeric separation of precursors of rho-kinase inhibitors by HPLC on polysaccharide-based chiral stationary phases

Summary The separation of enantiomers of substituted cyclohexanecarboxamides, benzamides and chemical precursors of Rho-kinase inhibitors was achieved using derivatized polysaccharide-based chiral stationary phases. Separations were by normal phase HPLC with a mobile phase ofn-hexane-alcohol (methanol, ethanol or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), tris-methylbenzoate (Chiralcel OJ), a silica-based amylose tris-(S)-1-phenylethylcarbamate (Chiralpak AS), or tris-3,5-dimethylphenylcarbamate (Chiralpak AD). The effects of cencentration of various aliphatic alcohols in the mobile phase were investigated. The effect of structural features on the discrimination between the enantiomers was examined. The isolation of milligram amounts of enantiomers of two derivatives was performed on an analytical column by multiple repetitive injections under overload conditions.     

氟环唑外消旋体在纤维素-三(3,5-二甲基苯基氨基甲酸酯)手性固定相上的高效液相色谱法拆分

在纤维素-三(3,5-二甲基苯基氨基甲酸酯)（CDMPC）手性固定相上,分别采用正相、反相及极性有机相色谱模式对氟环唑外消旋体进行了拆分,并考察了流动相组成在手性识别中对手性分离的影响。氟环唑在Chiralcel OD-H手性色谱柱（填充CDMPC手性固定相）上采用反相色谱模式,以甲醇-水(体积比为80∶20)为流动相,获得了最佳的拆分,其两对对映异构体的分离度Rs分别为1.64和6.50。     

Enantiomeric resolution of new aromatase inhibitors by liquid chromatography on cellulose chiral stationary phases

Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the direct enantioseparation of substituted [1-(imidazo-1-yl)-1-phenylmethyl)]-benzothiazolinone and benzoxazolinone derivatives with one chiral center. Those analogues of fadrozole constitute new potent nonsteroidal inhibitors of aromatase (P450 arom). The separations were made using normal phase methodology with a mobile phase consisting of n-hexane-alcohol (ethanol, 1-propanol, or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. A better separation was achieved on cellulose carbamate phase compared with the cellulose ester phase. The effects of structural features of the solutes along with the temperature of the column on the discrimination between the enantiomers were examined. Baseline separation (Rs > 1.5) was easily obtained in many cases.     

Determination of the Optical Purity of Fungicides of the Triazole Series

The influence of the nature of the chiral selector and the composition of the mobile phase on the enantioselectivity of the separation of two fungicides of the triazole series by high-performance liquid chromatography was studied. The optimum conditions were selected for the separation of enantiomers with the use of cellulose tris-(3,5-dimethylphenylcarbamate) as the chiral selector (Chiralcel OD column) and hexane–isopropanol mixtures as the mobile phase. Samples of technical diniconazole (China) were analyzed.     

用L-脯氨酸衍生物作为手性流动相添加剂拆分对映异构体

用自制的N-十二酰基-L-脯氨酸和N-十二酰基-L-脯氨酸-3，5-二甲基苯胺两种L-脯氨酸衍生物作手性流动相添加剂，在氨丙基硅烷化硅胶柱上，用正己烷／异丙醇作流动相，对多种手性化合物进行了高效液相色谱拆分。实验结果表明：用N-十二酰基-L-脯氨酸作添加剂拆分的12种手性化合物，有8种手性化合物能得到拆分，具有较好的手性选择性。虽然用N-十二酰基-L-脯氨酸-3，5-二甲基苯胺作添加剂，手性选择性也较好，但由于含有苯环，紫外吸收增强，基线波动严重。     

Molecularly imprinted polymer as a novel solid‐phase microextraction coating for the selective enrichment of trace imidazolinones in rice,peanut, and soil

The development and application of an imazethapyr molecularly imprinted polymer‐based solid‐phase microextraction coating were investigated. A novel molecularly imprinted polymer coating with imazethapyr as template was firstly prepared by a one‐step in situ polymerization method, and demonstrated specific selectivity to imidazolinone herbicides in complicated samples. The structural characteristics and extraction performance of the imazethapyr molecularly imprinted polymer coating were studied. The molecularly imprinted polymer coating was homogeneous, dense, and heat and solvent resistant. Adsorption capacity experiments showed that the molecularly imprinted polymer coating could selectively extract imazethapyr and its structural analogs, and the maximum adsorption capacity was 2.5 times as much as that of the nonimprinted polymer coating. A method for the determination of five imidazolinones by imazethapyr molecularly imprinted polymer solid‐phase microextraction coupled with high‐performance liquid chromatography was developed. The linear range was 0.50–50 μg/L for imazameth, imazamox, imazapyr acid, and imazethapyr, and 1.0–100 μg/L for imazaquin acid, and the detection limits were within the range of 0.070–0.29 μg/L. The method was applied to simultaneous and multiresidual determinations of trace imidazolinones in rice, peanut, and soil samples with satisfactory recoveries of 60.6–99.5, 79.1–123, and 61.3–116%, respectively, and relative standard deviations of 0.40–10%, which indicated that this method was suitable for the trace analysis of imidazolinones in complex food and environmental samples.     

Development of a high‐performance liquid chromatography method for the simultaneous determination of chiral impurities and assay of (S)‐clopidogrel using a cellulose‐based chiral stationary phase in methanol/water mode

A simple reversed‐phase high‐performance liquid chromatography method for the chiral separation of the active pharmaceutical ingredient (S)‐clopidogrel has been developed on the cellulose‐based Chiralcel OJ‐RH chiral stationary phase. The S enantiomer was baseline resolved from its R impurity (impurity C) with a mobile phase consisting of methanol/water (100:15) without any interference coming from the other two potential chiral impurities A and B. The enantio‐ and chemoselective method was partially validated and compared with that reported in the United States Pharmacopoeia for the drug product. The versatility of the Chiralcel OJ‐RH allowed separating the enantiomers of the impurity B also under normal phase and setting up an efficient strategy to convert the racemic sample into the enantiomeric S form on a semipreparative scale.     

High-performance liquid chromatographic separation of the enantiomers of organophosphorus pesticides on polysaccharide chiral stationary phases.

High-performance liquid chromatographic separation of the individual enantiomers of 12 organophosphorus pesticides (OPs) was obtained on polysaccharide enantioselective HPLC columns using alkane-alcohol mobile phase. The OP pesticides were crotoxyphos, dialifor, fonofos, fenamiphos, fensulfothion, isofenphos, malathion, methamidophos, profenofos, crufomate, prothiophos and trichloronate. The enantiomers of fenamiphos, fensulfothion, profenofos and crufomate were separated on CHIRALPAK AD; the enantiomers of fenamiphos were also separated on CHIRALPAK AS; the enantiomers of methamidophos, crufomate and trichloronate were separated on CHIRALCEL OD; the enantiomers of crotoxyphos, dialifor, fonofos, malathion, prothiophos and trichloronate were separated on CHIRALCEL OJ; and the enantiomers of isofenphos were separated on CHIRALCEL OG. Baseline or partial separation of the enantiomers of six of these OP pesticides was obtained on CHIRALCEL OJ. In continued method development, the separation of the enantiomers of the 12 OPs was investigated more extensively on CHIRALCEL OJ to determine whether the mobile phase composition, flow-rate and column temperature could be optimized to yield at least partial separation of the enantiomers. Chromatographic conditions were found that gave either baseline or near baseline separations of the enantiomers of the 12 OPs on the CHIRALCEL OJ column.     

LC Using Two Different Cellulose Chiral Stationary Phases for Direct Enantioseparation of Benzoxazolinone Aminoalcohols and Aminoketones

A series of six benzoxazolinone aminoketones and height aminoalcohols has been synthetized as agonist and antagonist ligands for adrenergic receptors. For those benzoxazolinone derivatives which contain one or two chiral carbons, a stereoselective liquid chromatographic method, using silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H) or tris-4-methylbenzoate (Chiralcel OJ) as chiral stationary phase, has been developed. A better separation was achieved on cellulose carbamate phase compared to the cellulose ester phase. The effects of concentration of various aliphatic alcohols in the mobile phase were studied. The effects of structural features of the solutes on the discrimination between the enantiomers were examined.