Enantiomeric separation of six chiral pesticides that contain chiral sulfur/phosphorus atoms by supercritical fluid chromatography

Six chiral pesticides containing chiral sulfur/phosphorus atoms were separated by supercritical fluid chromatography with supercritical CO₂ as the main mobile phase component. The effect of the chiral stationary phase, different type and concentration of modifiers, column temperature, and backpressure on the separation efficiency was investigated to obtain the appropriate separation condition. Five chiral pesticides (isofenphos‐methyl, isocarbophos, flufiprole, fipronil, and ethiprole) were baseline separated under experimental conditions, while isofenphos only obtained partial separation. The Chiralpak AD‐3 column showed a better chiral separation ability than others for chiral pesticides containing chiral sulfur/phosphorus atoms. When different modifiers at the same concentration were used, the retention factor of pesticides except flufiprole decreased in the order of isopropanol, ethanol, methanol; meanwhile, the retention factor of flufiprole increased in the order of isopropanol, ethanol, methanol. For a given modifier, the retention factor and resolution decreased on the whole with the increase of its concentration. The enantiomer separation of five chiral pesticides was an “enthalpy‐driven” process, and the separation factor decreased as the temperature increased. The backpressure of the mobile phase had little effect on the separation factor and resolution.     

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.     

Influence of the kind of the Alcoholic Modifier on Chiral Separation of 4-Substituted-Pyrrolidin-2-Ones Using Amylose Based Chiral Stationary Phase

ABSTRACT

The enantioselective separation of 4-substituted-pyrrolidin-2-ones was investigated on a silica-based amylose tris (3, 5-dimetliylphenylcarbamate) (Chiralpak AD) using, normal phase methodology with a mobile phase consisting of H-hexane-alcohol (ethanol, 1-propanol or 2-propanol) in various percentage. Effects of variation of concentration of alcohol and the nature of aliphatic alcohols in the mobile phase were studied. In a general manner, for the ten compounds analysed, the retention times increased and the separations factors were improved on changing the alcohol modifier from 2-propanol to ethanol. The effects of substitution were analysed. Baseline separation was easily obtained in many cases with a maximum resolution factor of 11.     

Chiral separation of some triazole pesticides by supercritical fluid chromatography

The enantiomeric separation of six triazole pesticides: cyproconazole, propiconazole, diniconazole, hexaconazole, tebuconazole and tetraconazole, using supercritical fluid chromatography and the Chiralpak AD column, is presented in this work. The effect of different organic modifiers such as methanol, ethanol and 2-propanol on the retention and resolution was studied as well as the presence of additives in the mobile phase. The results obtained were highly successful, all the compounds were enantiomerically separated and in most of the cases the analysis time was close to 10 min. The type of organic modifier that provided the best results depended on the compound.     

Rapid Supercritical Fluid Chromatography Method for Separation of Chlorthalidone Enantiomers

Supercritical fluid chromatography employing chiral stationary phases is a popular separation technique to perform enantioselective separations. The main advantages of supercritical fluid chromatography are low analysis time, low consumption of organic modifiers, and therefore lower costs and higher environmental friendliness. A novel method for the separation of chlorthalidone enantiomers, widely used diuretic drug, is reported that clearly demonstrates the advantages of supercritical fluid chromatography. The effects of the amount and type of organic modifiers, temperature, and back pressure on enantioselectivity and resolution of the enantiomers were evaluated. The baseline separation was achieved in less than 2.5 min in the optimized system composed of Chiralpak AD column, mobile phase CO₂/MeOH 50/50 (v/v), temperature 40°C, a flow rate of 4.0 mL/min, and 120 bar back pressure. Moreover, enantiomers of chlorthalidone were determined in two commercially available pharmaceuticals. The proposed method may be easily transferred to a semi-preparative scale.     

Stereoselective effects in the separation of enantiomers of omeprazole and other substituted benzimidazoles on different chiral stationary phases

The enantioselective separation of omeprazole on different chiral stationary phases was investigated. The two enantiomers could be resolved on three different phases with immobilized protein, Chiral-AGP, Ultron ES-OVM and BSA-DSC, employing aqueous mobile phases with 2-propanol as organic modifier. On Chiralpak AD, an amylose-based chiral stationary phase, the enantiomers of omeprazole and three analogues could be separated using a non-polar hexane-ethanol mobile phase. For omeprazole the retention order was reversed when 2-propanol was replaced with ethanol or methanol as the modifier of hexane in the mobile phase.     

Evaluation of polysaccharide-based chiral stationary phases in quality control of (S)-mirtazapine

High-performance liquid chromatographic methods were developed for separation of the enantiomers of mirtazapine and its four process-related substances. The direct separations were achieved on chiral stationary phases containing amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD-H), cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD-H) and cellulose tris(4-methylbenzoate) (Chiralcel OJ-H ). The experimental data were utilized to discuss the effects of the mobile phase composition, the nature of the alcoholic modifier and the specific structural features of the analytes on retention and separation. The elution sequence was determined under the optimized separation conditions.     

A comparative study of chiral separation of proton pump inhibitors by supercritical fluid chromatography and high-performance liquid chromatography

A comparative study of chiral separation of pantoprazole and rabeprazole is carried out using supercritical fluid chromatography and high-performance liquid chromatography. The columns used were Chiralpak IA and Chiralpak IE. The best mobile phase in supercritical fluid chromatography was carbon dioxide-0.2% triethylamine in methanol (60:40) and 0.1% triethylamine in n-hexane-ethanol (50:50) in high-performance liquid chromatography. For supercritical fluid chromatography, values of the retention factor of pantoprazole enantiomers were 3.97 and 4.88. These values for rabeprazole enantiomers were 6.10 and 7.52. The values of separation and resolution factor for pantoprazole and rabeprazole were 1.23 and 1.23 and 2.20 and 3.36, respectively. Similarly, for high-performance liquid chromatography, the values of retention factor for enantiomers of pantoprazole were 4.02 and 7.32. These values for rabeprazole enantiomers were 5.32 and 7.88, respectively. The values of separation and resolution factor for pantoprazole and rabeprazole were 1.82 and 1.48 and 9.22 and 6.58, respectively. A comparison was carried out, which confirmed supercritical fluid chromatography as the best method due to its fastness, eco-friendly, and inexpensiveness. The reported methods are effective, efficient, and reproducible and may be used to separate and identify pantoprazole and rabeprazole in any unknown samples.     

Enantiomeric separation of several antimycotic azole drugs using supercritical fluid chromatography

The chiral resolution of four antifungal compounds, three imidazoles (miconazole, econazole and sulconazole) and one triazole (itraconazole) using supercritical fluid chromatography on the amylose-based chiral stationary phase Chiralpak AD, is presented in this work. The influence of pressure, type and percentage of organic modifier and temperature on retention times and resolution was studied. The enantiomeric separation of the three imidazoles was achieved with resolutions higher than two and analysis times lower than 10 min, obtaining the best results using methanol as modifier. However, the analysis time of the triazole was higher than 80 min due to the existence of a high number of functional groups that were able to interact with the chiral stationary phase. In this case, the resolution of the four stereoisomers was achieved only partially with mixtures of ethanol and 2-propanol as modifier. The isoenantioselective temperatures were obtained from the study of the influence of the temperature, they were above the range of temperatures assayed, except for sulconazole using 2-propanol.     

Enantioseparation of racemic paroxol on an amylose‐based chiral stationary phase by supercritical fluid chromatography

The separation of racemic paroxol, a key precursor of trans‐(?)‐paroxetine, on Chiralpak AD‐H, an amylose‐based chiral stationary phase, by supercritical fluid chromatography was studied. Pulse experiments were investigated using supercritical carbon dioxide modified with methanol (MeOH), ethanol and 2‐propanol at 35°C and 15 MPa. Retention and separation factors were determined under analytical conditions for different mobile phase compositions. Among the modifiers used, MeOH was shown to be the best additive, and 5% v/v of MeOH was the preferable concentration at which selectivity of 1.14 and resolution of 3.0 was obtained. In order to evaluate the potential with respect to preparative separations, the adsorption isotherms of individual enantiomers of paroxol were estimated using the elution by characteristic point method. Isotherm parameters were determined from the overloaded elution profiles that were collected at pressure ranging from 15 to 24 MPa. The isotherms obtained were further validated by comparing experimentally recorded elution profiles with the predictions based on the equilibrium‐dispersive model. The results are important to the process design and optimization of preparative supercritical fluid chromatography application.     

Possibility of predicting separations in supercritical fluid chromatography with the solvation parameter model

In order to obtain a selection of optimal chromatographic columns for the separation of chlorotriazine pesticides in packed column supercritical fluid chromatography (pSFC), a multi-criteria approach is applied. For this purpose, prediction of the separations is carried out, based on quantitative structure–retention relationships, then Derringer's desirability function is proposed to determine the stationary phase that will result in the most desirable separation. The best SFC separation obtained was then optimized using a mobile phase gradient. Besides, the accuracy of the solvation parameter model as SFC retention predictive model is assessed.     

CDMPC手性固定相对新型金属簇化合物的手性拆分

应用纤维素三（3,5-二甲基苯基氨基甲酸酯）（cellulose tris (3, 5- dimethylphenylcarbamate,CDMPC）手性固定相对两种新型金属簇合物进行了拆分,通过流动相组成、流速和样品溶剂等条件对拆分影响的考察进行了拆分条件的优化。实验结果表明,簇合物1和簇合物2分别在含乙醇V(hexane)∶V(ethanol)=95∶5)和异丙醇(V(hexane)∶V(2-propanol)=90∶10)的流动相中得到了较好的拆分,将样品溶解在和流动相组成相近的溶剂中更利于簇合物拆分,簇合物配体结构对簇合物在固定相上的保留和拆分有重要的影响。 在优化条件下,2种金属簇合物分离度均达到1.5以上。     

Separation of the enantiomers of 4-aryl-7,7-dimethyl- and 1,7,7-trimethyl-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-diones by chiral HPLC

Summary Analytical HPLC methods using derivatized cellulose chiral stationary phases have been developed for separation of the enantiomers of 25 racemic 4-aryl-7,7-dimethyl- or 1,77-trimethyl-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-diones, condensed derivatives of dihydropyrimidines. The enantiomers of the compounds were resolved by normal-phase chromatography on silica-based cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) and amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD) columns with mobile phases consisting of mixtures ofn-hexane and an alcohol (2-propanol, ethanol, or methanol) in different proportions. The mobile phase and the chiral stationary phase were varied to achieve the best resolution. The effect of the concentration of alcohol in the mobile phase was studied. The resolution obtained on the two columns was complementary.     

Supercritical fluid chromatography tandem-column method development in pharmaceutical sciences for a mixture of four stereoisomers

A tandem-column method using Chiralpak AD-H and Chiralcel OD-H columns was achieved for baseline separation of a mixture of chiral pharmaceutical compounds (i.e., four stereoisomers) via supercritical fluid chromatography (SFC) with a mobile phase consisting of 90% liquid carbon dioxide and 10% ethanol:isopropanol (50:50 v/v). On the contrary, this mixture (mixture A) could not be baseline separated by SFC conditions explored with individual Chiralpak AD-H and Chiralcel OD-H columns. The effects of various mobile phases on elution order, capacity factor, selectivity, and resolution were determined with mixture A on the individual aforementioned columns to develop the tandem-column method.     

Diastereomeric resolution of nucleoside analogues, new potential antiviral agents, using high-performance liquid chromatography on polysaccharide-type chiral stationary phases

This paper describes the separation of the four sets of stereoisomers of nucleoside analogs, new potential antiviral agents by direct analytical HPLC methods using derivatized cellulose and amylose chiral stationary phases. The resolution was made using normal-phase methodology with a mobile phase consisting of n-hexane-alcohol (ethanol or 2-propanol) in various percentages, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ) and a silica-based amylose tris-3,5-dimethylphenylcarbamate (Chiralpak AD) or tris-(S)-1-phenylethylcarbamate (Chiralpak AS). The effects of structural features on the extent of discrimination between the stereoisomers were examined through the retention, the selectivity and the resolution factors as well as the elution order. Baseline separation (Rs>1.5) was easily obtained in many cases. The resolution results were complementary between the different columns.     

Exploring solvent versatility in immobilized cellulose-based chiral stationary phase for the enantioselective liquid chromatographic resolution of racemates

Chiralpak IB, a new chiral stationary phase (CSP) containing cellulose tris(3,5-dimethylphenylcarabamate) immobilized onto silica gel, is investigated for the direct enantioselective separation of a set of racemic N-alkylated barbiturates and analogs of thalidomide alkylated in position 3 of the piperidin-2,6-dione ring using different nonstandard solvents such as dichloromethane (DCM), ethyl acetate, THF, methyl tert-butyl ether as an eluent and diluent, respectively, in HPLC. The separation, resolution, and elution order of the investigated compounds were compared on both immobilized and coated cellulose tris(3,5-dimethylphenylcarbamate) CSPs (Chiralpak IB and Chiralcel OD, respectively) using a mixture of n-hexane/2-propanol (90:10 v/v) as mobile phase with different flow-rates and fixed UV detection at 254 nm. The effect of the immobilization of the cellulose tris-(3,5-dimethylphenylcarbamate) CSP on silica (Chiralpak IB) on the chiral recognition ability was noted as the coated phase (Chiralcel OD) possesses a higher resolving power in some cases than the immobilized one (Chiralpak IB). However, a few racemates, which were not or poorly resolved on the immobilized Chiralpak IB or the coated Chiralcel OD when using standard solvents were most efficiently resolved on the immobilized Chiralpak IB upon using nonstandard solvents. Furthermore, the immobilized phase withstands the nonstandard (prohibited) HPLC solvents mentioned previously when used as eluents or as a dissolving agent for the analyte itself. An example of inversion or apparent inversion of elution order on Chiralpak IB is reported. The direct analysis of a spiked plasma sample extracted using DCM on Chiralpak IB is also shown.     

Application and comparison of derivatized cellulose and amylose chiral stationary phases for the separation of enantiomers of pharmaceutical compounds by high-performance liquid chromatography.

The direct high-performance liquid chromatographic separation of three pairs of structurally related enantiomers on derivatized cellulose and amylose chiral stationary phases (Chiralcel OD, Chiralpak AD and Chiralpak AS) was studied using hexane as the mobile phase with 2-propanol or ethanol as modifiers. The separation, retention and elution order of the enantiomers on the different columns using different alcohol modifiers were compared. The effect of structural variation of the solutes on their k' was noted. A reversal of elution order of one enantiomeric pair upon changing the mobile-phase modifier was observed. Chiralcel OD and Chiralpak AD columns provided different elution orders of the enantiomers, including a fourth pair of enantiomers that were not structurally related to the other three pairs.     

Enantiomeric separation of some pharmaceutical intermediates and reversal of elution orders by high-performance liquid chromatography using cellulose and amylose tris(3,5-dimethylphenylcarbamate) derivatives as stationary phases

Several pairs of enantiomers of pharmaceutical intermediates were separated by HPLC directly on cellulose and amylose tris(3,5-dimethylphenylcarbamate) derivatives (Chiralcel OD and Chiralpak AD) using hexane as mobile phase with 2-propanol or ethanol as modifier. The separation and elution order of the enantiomers on the two columns using different alcohol modifiers were compared. Reversal of the elution order of some enantiomeric pairs associated with increased retention of many of these solutes upon changing the mobile phase modifier from 2-propanol to ethanol was observed. The effect of structural variation of two pairs of enantiomers on their k' and separation factor alpha was noted. Chiralcel OD and Chiralpak AD columns provided different retention, separation and elution order of some of the enantiomeric pairs.     

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.     

An insight into the use of dimethylphenyl carbamate cyclofructan 7 chiral stationary phase in supercritical fluid chromatography: The basic comparison with HPLC

Cyclofructan‐based chiral stationary phases were previously shown as a promising possibility for separation of chiral compounds in high performance liquid chromatography. In this work retention and enantiodiscrimination properties of the 3,5‐dimethylphenyl carbamate cyclofructan 7 chiral stationary phase are described in supercritical fluid chromatography. The results obtained in both of the separation methods were compared. A set of compounds with axial or central chirality was used as analytes. The effect of mobile phase composition, that is, addition of different alcohol modifiers and/or trifluoroacetic acid to carbon dioxide, was examined in the supercritical system. Similarly, mobile phases composed of hexane modified with propan‐2‐ol and/or trifluoracetic acid were used in liquid chromatography. A linear free energy relationship model was utilized for characterization of interactions that are decisive for retention and separation in both techniques. Dispersion interactions showed similar negative values using both methods. The main contribution of hydrogen bond acidity was also comparable for both methods. The propensity to interact with n‐ and/or π‐electron pairs of solutes was significant only in the supercritical system.