Enantiomers In High-performance Liquid Chromatography Research Articles

Comparative Study of Cellulose Tris(3-chloro-5-methylphenylcarbamate) Coated or Covalently Immobilized on Silica for the Separation of Enantiomers in High-Performance Liquid Chromatography

Comparative Study of Cellulose Tris(3-chloro-5-methylphenylcarbamate) Coated or Covalently Immobilized on Silica for the Separation of Enantiomers in High-Performance Liquid Chromatography

Potential and current limitations of superficially porous silica as a carrier for polysaccharide-based chiral selectors in separation of enantiomers in high-performance liquid chromatography

In this study superficially porous silica particles with a nominal pore size of 450 Å and average particle size of 2.6 micrometers was compared to fully porous silica particles with nominal particle size 3 micrometers and nominal pore size 1000 A as carriers for a polysaccharide based chiral selector for the separation of enantiomers in high-performance liquid chromatography. In addition, the effects of chiral selector loading onto the silica support and of column internal dimeter in the case of both, superficially porous and totally porous silica, as well as of the pore size of superficially porous silica on column performance were studied. The dependence of plate height on mobile phase flow rate was also studied and attempts were made for shortening analysis time. The baseline separation of enantiomers of some chiral sulfoxides was obtained within 2.0–4.5 s.

Polysaccharide-Based Chiral Stationary Phases for Enantioseparations by High-Performance Liquid Chromatography: An Overview.

This chapter summarizes the application of polysaccharide-based chiral stationary phases (CSPs) for separation of enantiomers in high-performance liquid chromatography (HPLC). Since this book contains dedicated chapters on enantioseparations using supercritical fluid chromatography (SFC), or capillary electrochromatography (CEC), the application of polysaccharide-based materials in these modes of liquid-phase separation techniques is touched just superficially. Special emphasis is directed toward a discussion of the optimization of polysaccharide-based chiral selectors, their attachment onto the carrier, and the optimization of the support. The optimization of the separation of enantiomers based on various parameters such as mobile phase composition and temperature is discussed.

On our way to sub-second separations of enantiomers in high-performance liquid chromatography

In this study our preliminary attempt for obtaining fast and highly efficient separations of enantiomers in high-performance liquid chromatography with slightly modified state-of-the-art commercial instrumentation is described. In order to reach this goal after careful selection of chiral analytes, the preparation of chiral stationary phase (CSP), mobile phase composition and column dimensions were optimized. The concept of segmented chiral-achiral column was introduced. As the result of these optimizations baseline separation of enantiomers was achieved with the analysis time between 1–2 s.

Application of cellulose 3,5-dichlorophenylcarbamate covalently immobilized on superficially porous silica for the separation of enantiomers in high-performance liquid chromatography

Our earlier studies have demonstrated the applicability of polysaccharide-based chiral selectors in combination with superficially porous (or core-shell) silica (SPS) particles for the preparation of highly efficient chiral stationary phases (CSP). In earlier studies, CSPs were prepared by coating (adsorption) of the chiral selector onto the surface of silica. In this study we report for the first time the CSP obtained by covalent immobilization of a chiral selector onto the surface of SPS particles. The applicability of this CSP for the separation of enantiomers in pure methanol and acetonitrile, as well as in n-hexane/2-propanol mobile phases is shown. The effect of the injected sample amount, mobile phase flow rate and detection frequency on separation performance were studied, as well as high efficiency separation of enantiomers with the analysis time less than 30 s was attempted.

Effect of pore-size optimization on the performance of polysaccharide-based superficially porous chiral stationary phases for the separation of enantiomers in high-performance liquid chromatography

Our earlier studies on the preparation of chiral stationary phases (CSP) based on superficially porous (or core-shell) silica (SPS) particles for the separation of enantiomers in HPLC have provided proof to the advantages of such sorbents. In particular, higher enantioselectivity was observed with the columns packed with superficially porous CSP compared to the columns packed with fully-porous (FP) silica-based CSPs at comparable content of chiral selector (polysaccharide derivative) in CSP. Also, less dependence of plate height on mobile phase flow rate and higher plate numbers and resolution calculated per unit time (i.e. speed of separation) were observed with SPS-based CSPs. Thirty years of CSP development have demonstrated that wide-pore silica has to be used as a support for large molecular weight chiral selectors such as the ones based on polysaccharides. In this study the effect of pore size of the core-shell silica support and of other experimental factors on column performance is demonstrated. Reduced plate heights in the range 1.4–1.5 were obtained, as well as highly effective baseline separations of enantiomers were observed with analysis times of less than 15s.

Separation of enantiomers of chiral weak acids with polysaccharide-based chiral columns and aqueous-organic mobile phases in high-performance liquid chromatography: Typical reversed-phase behavior?

When polysaccharide-based chiral columns are used in combination with aqueous-organic mobile phases for the separation of enantiomers in high-performance liquid chromatography the separation mode is commonly called “reversed-phase” in analogy to achiral separations. In several earlier and recent studies on neutral and basic chiral analytes it was shown by our and other groups that due to multiple type of interactions involved in selector-selectand binding and enantioselective recognition with polysaccharide derivatives, the above mentioned separation system may not always behave like a reversed-phase system. In the present study additional examples of non-reversed-phase behavior are described for the first time for weak acidic chiral analytes. In addition, the reversal of enantiomer elution order was observed again for the first time for several analytes based on water-content in the mobile phase.

Further proof to the utility of polysaccharide-based chiral selectors in combination with superficially porous silica particles as effective chiral stationary phases for separation of enantiomers in high-performance liquid chromatography

The first ever report on the preparation of chiral stationary phases (CSP) based on superficially porous silica (SPS) particles for the separation of enantiomers in HPLC demonstrated clear advantages of such materials. Higher enantioselectivity at the comparable content of a chiral selector, limited dependence of plate height on the mobile phase flow rate and higher plate numbers and resolution calculated per unit time (i.e. higher speed of separation) were observed with columns made with superficially porous CSP in comparison to columns made with fully-porous silica-based CSP. However, later studies reported diverging conclusions. In this report further evidences are described supporting the findings of our first study about the superior performance of polysaccharide-based chiral selectors in combination with SPS when compared to traditional CSPs based on fully porous silica (FPS) particles.

Enantioseletive bioaccumulation of tebuconazole in earthworm Eisenia fetida

Methods of extraction and determination of tebuconazole enantiomers in earthworm (Eisenia fetida) were developed by capillary electrophoresis (CE) and high performance liquid chromatography (HPLC). Both CE and HPLC have excellent resolution and recovery. The linearity ranges were 2.9–102.4 mg/kg and 3.0–99.6 mg/kg for (+)-R-tebuconazole and (−)-S-tebuconazole respectively in CE, and from 0.56 to 1000 mg/kg for both enantiomers in HPLC. Enantioselective bioaccumulation in earthworms from soil was investigated under laboratory condition at concentrations of 10 and 50 mg/kg dw in soil. The uptake kinetics of (+)-R-tebuconazole fitted the first-order kinetics well with r2 0.97 and 0.94 under 10 and 50 mg/kg dw exposure condition, respectively, while (−)-S-tebuconazole with r20.75 and 0.22 did not show the same. Bioaccumulation of tebuconazole in earthworm tissues was enantioselective with a preferential accumulation of (+)-R-tebuconazole. The (+)-R-tebuconazole might also have biomagnifying effect potential in earthworm food chain with biota-sediment accumulation factor (BSAF) of 1.64 kg OC/kg lip in 10 mg/kg dw exposure group and 2.61 kg OC/kg lip in 50 mg/kg dw exposure group from soil to earthworm after 36 days. Although (−)-S-tebuconazole shares the same physicochemical properties with (+)-R-tebuconazole, it did not biomagnify. BSAFs of (−)-S-tebuconazole were 0.50 kg OC/kg lip (10 mg/kg dw tebuconazole exposure) and 0.28 kg OC/kg lip (50 mg/kg dw tebuconazole exposure) after 36 days, which was possibly owing to biotransformation or metabolism in earthworm tissues.

( S)-(+)-1-Methyl-2-(6,7,-dimethoxy-2,3-naphthalimido)ethyl trifluoromethanesulfonate as a fluorescence chiral derivatizing reagent for carboxylic acid enantiomers in high-performance liquid chromatography

A new triflate-type fluorescence chiral derivatizing reagent, ( S)-(+)-1-methyl-2-(6,7-dimethoxy-2,3-naphthalimido)ethyl trifluoromethanesulfonate, [ S-(+)-MDNE-OTf], has been developed for the determination of the enantiomers of carboxylic acids. By introducing the two methoxy groups on the naphthalimido ring moiety, the red shift in the fluorescence spectrum and a high resolution in reversed-mode separation of the diastereomers of chiral carboxylic acids have been achieved. The detection limits ( S/ N=3) with ultraviolet and fluorescence detection are 8 fmol ( λ max=283 nm) and 4 fmol ( λ ex=283 nm, λ em=467 nm), respectively.

Regioselectivity carbamoylated polysaccharides for the separation of enantiomers in high-performance liquid chromatography

The chromatographic behavior of new chiral stationary phases (CSPs) based on mixed substituted cellulose, amylose or amylopectin is reported. Most CSPs have a 3,5-dimethylphenylcarbamate at the 2 and 3 positions of the glucose unit and either an ( R)-, ( S)- or ( RS)-phenylethylcarbamate at the 6 position. This study shows that configuration of the phenylethylcarbamate at the 6 position largely influences the chiral recognition depending upon the polysaccharide studied. Some of the new CSPs exhibit a better enantioselective power for several racemates as compared to the corresponding symmetrical substituted polysaccharides CSPs. The resolution of some benzodiazepines is also reported.

Regioselective carbamoylated and benzoylated cellulose for the separation of enantiomers in high-performance liquid chromatography

The preparation of new chiral stationary phases (CSPs) based on mixed substituted cellulose is reported. The first type of CSP has a 3,5-dimethylphenylcarbamate at the 2 and 3 positions and a phenylethylcarbamate at the 6 position. The second one has a benzoate at the 2 and 3 positions and a meta-substituted phenylcarbamate at the 6 position. The last one has a 3,5-dimethylphenylcarbamate at the 2 and 3 positions and a para-substituted benzoate at the 6 position. This work shows that the substituent present at the 6 position is very important for chiral recognition. Some of the new CSPs exhibit a better enantioselective power for several racemates compared to the corresponding Chiralcel columns. The resolution of some β-adrenergic blockers and benzodiazepines is also reported.

Fluorescent chiral derivatization reagents for carboxylic acid enantiomers in high-performance liquid chromatography

Six chiral derivatization reagents, viz., (+)-4-(N,N-dimethylaminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (D-DBD-APy), (–)-4-(N,N-dimethylaminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (L-DBD-APy), (+)-4-nitro-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (D-NBD-APy), (–)-4-nitro-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (L-NBD-APy), (+)-4-(aminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (D-ABD-APy) and (–)-4-(aminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (L-ABD-APy), have been synthesized to permit separation of carboxylic acid enantiomers by high-performance liquid chromatography (HPLC). The reagents react with carboxylic acids at room temperature in the presence of activation agents (2,2′-dipyridyl disulfide and triphenylphosphine). The maximum emission wavelengths of the diastereomeric amide derivatives formed from D-naproxen (Nap) with D-DBD-APy, D-ABD-APy and D-NBD-APy were approximately 580 nm (excitation at 470 nm), 585 nm (excitation at 470 nm) and 540 nm (excitation at 470 nm), respectively. The emission wavelengths of the derivatives shifted towards the blue, and the fluorescence intensities increased with increasing acetonitrile concentration in the medium. The fluorescence intensities of three derivatives at pH 2–11 were higher in neutral than in acidic and alkaline solutions. The diastereomers derived from anti-inflammatory drugs and N-acetylamino acids were efficiently resolved by a reversed-phase column (5 µ Inertsil ODS-2) with a water-acetonitrile mixture as mobile phase. The detection limits (S/N = 2) of DBD-APy-Nap, NBD-APy-Nap and ABD-APy-Nap on HPLC chromatograms were 10, 15 and 30 fmol, respectively.

Chiral polymeric reagents for off-line and on-line derivatizations of enantiomers in high-performance liquid chromatography with ultraviolet and fluorescence detection: an enantiomer recognition approach.

Optically active and detector-sensitive polymeric reagents have been synthesized, loadings determined, derivatizations/separations/detection optimized, and applications to simple amines and amino alcohols described. Such reagents have been designed to contain different chiral centers, usually amino acids, leashed via an activated ester attachment to an insoluble, structurally rigid, organic polymer backbone. 9-Fluorenylmethyl (FMOC) moieties chemically bonded to the amino acids were used as ultraviolet (UV) and fluorescence (FL) sensitive detector probes to the final diastereomers of enantiomer substrates. Such diastereomers can be readily separated by isocratic or gradient elution normal-phase methods. The kinetics for diastereomer formation have been determined, and final UV/FL responses for known mixtures of enantiomers have been compared to demonstrate overall validity of the method. Minimum detection limits, linearity of calibration plots, dual detector responses, and linear diode array spectra and absorbance ratios have also been demonstrated. In some cases, authentic standards have been prepared to calculate absolute percent derivatizations for specific enantiomer pairs. The overall approach permits, for the very first time, off-line or on-line precolumn derivatization for the formation of diastereomers having unique detector properties. It has been proven that the rates and rate constants for such formations are identical for at least those pairs of enantiomers studied. Separations are base-line or near-base-line, permitting accurate and precise quantitative determinations, by both UV and FL, of enantiomer/optical purity and chemical purity.