Heart-cut achiral-chiral LC-LC method development using factorial design: application to the chiral separation of ketoprofen.

A two-dimensional achiral-chiral LC-LC method in heart-cut mode for ketoprofen and its enantiomeric fraction determination was proposed. A C8 column was used in the first dimension, and the chiral column was an α1-acid glycoprotein. The mobile phase of the chiral system was optimized by a factorial design. The effect of temperature on retention and on enantiomeric resolution was studied. Particular attention was paid to mobile phase compatibility for the two columns and to transferring time, using ketoprofen standards. The R-(-) and S-(+)-ketoprofen retention times were 9 and 11 min, respectively; the resolution was higher than 1.1 and enantiomeric fraction close to 0.5. The method was applied to capsules and gels containing ketoprofen. Factorial design was also used to establish the best conditions for gel sample preparation. Recoveries were 84 and 105 % for capsules and gels, respectively. Graphical abstract Two-dimensional chromatogram for KPF and its enantiomers.

Determination of free cholesterol oxide products in food samples by gas chromatography and accelerated solvent extraction: influence of electron-beam irradiation on cholesterol oxide formation.

BACKGROUND: The aim of this study was to develop an efficient method for cholesterol oxide product (COP) determination in irradiated and non-irradiated ready-to-eat foods with high water content by gas chromatography-flame ionisation detector after accelerated solvent extraction (ASE), and derivatisation with a silylating reagent. RESULTS: The ASE solvent was an 85:15 v/v petroleum ether/chloroform mixture at 40 °C and 1500 psi followed by solid phase extraction. The ASE method was compared with the established lixiviation method, proving an advantageous alternative which reduces analysis time by a factor of 15 and solvent volume by 50%, and minimises the use of chlorinated solvents. COP derivative structures were identified by gas chromatography coupled with mass spectrometry. Analytical characteristics were determined from standards and recoveries were 63-95%, establishing the validity of the method. CONCLUSION: The results obtained and their analysis by chemometric techniques established COP formation in food samples after e-beam irradiation. Increase in COP concentration depended on both irradiation doses and food composition, mainly water and fat content, although linear correlations among variables were not found. © 2016 Society of Chemical Industry.

Determination of salbutamol by direct chiral reversed-phase HPLC using teicoplanin as stationary phase and its application to natural water analysis.

A direct chiral LC-UV method was optimized for the determination of salbutamol (SAL) ß2 -agonist in environmental water. Two commercially available columns were evaluated: teicoplanin Chirobiotic-T™ (150 × 2.1 mm i.d., 5 µm) and vancomycin Chirobiotic-V™ (150 × 2.1 mm i.d., 5 µm). Finally, teicoplanin chiral stationary phase was selected for SAL enantiomer resolution. In order to preserve its integrity and maintain the column performance for longer time, the use of additives such as triethylamine (TEA) in the mobile phase was avoided. Experimental design was applied to simultaneously evaluate the influence of several parameters involved in enantiomer separation and to establish the conditions for acceptable resolution and performance in short analysis time. Optimum mobile phase was methanol-20 mM ammonium acetate buffer at pH 4.5 (98:2, v/v). A solid-phase extraction procedure for sample pre-concentration and clean-up allowed the determination of chiral SAL residues in natural water samples spiked at low concentrations in the range 1.0-20 ng mL(-1) . Reproducible recoveries, between 77 and 98%, were obtained and matrix effect was negligible. Injection of sample solutions at low elution strength permitted the SAL enantioresolution in the natural water complex matrix with satisfactory sensitivity and precision.

Direct chiral determination of free amino acid enantiomers by two-dimensional liquid chromatography: application to control transformations in E-beam irradiated foodstuffs.

Changes in free amino acids content and its potential racemization in ready-to-eat foods treated with E-beam irradiation between 1 and 8 kGy for sanitation purposes were studied. A simple heart cut two-dimensional high performance liquid chromatographic method (LC-LC) for the simultaneous enantiomeric determination of three pairs of amino acids used as markers (tyrosine, phenylalanine, and tryptophan) is presented. The proposed method involves the use of two chromatographs in an LC-LC achiral-chiral coupling. Amino acids and their decomposition products were firstly separated in a primary column (C(18)) using a mixture of ammonium acetate buffer (20 mM, pH 6) (94%) and methanol (6%) as the mobile phase. Then, a portion of each peak was transferred by heart cutting through a switching valve to a teicoplanin-chiral column. Methanol (90%)/water (10%) was used as the mobile phase. Ultraviolet detection was at 260 nm. Detection limits were between 0.16 and 3 mg L(-1) for each enantiomer. Recoveries were in the range 79-98%. The LC-LC method combined with the proposed sample extraction procedure is suitable for complex samples; it involves an online cleanup, and it prevents degradation of protein, racemization of L-enantiomers, and degradation of tryptophan. Under these conditions, D-amino acids were not found in any of the analyzed samples at detection levels of the proposed method.

One- and two-dimensional direct chiral liquid chromatographic determination of mixtures of diclofop-Acid and diclofop-methyl herbicides.

Simple one- and two-dimensional high-performance liquid chromatography (HPLC) methods for the simultaneous enantiomeric determination of alkyloxyphenoxypropionic acid herbicides is presented. Compounds studied were ( R, S)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionic acid (diclofop-acid) and ( R, S)-2-[4-(2,4-dichlorophenoxy)]methyl propionate (diclofop-methyl). Mobile phases necessary to separate their enantiomers on an alpha1-acid glycoprotein chiral stationary phase are different; therefore, the simultaneous separation by an isocratic mode is not possible. The chiral separation method proposed involves a one-step gradient allowing for the simultaneous determination of both racemic enantiomers. Detection limits of the method were 0.03 mg/L for both diclofop-acid enantiomers and 0.14 and 0.15 mg/L for diclofop-methyl enantiomers, respectively. The two-dimensional method involves the use of two chromatographs in one achiral-chiral coupling. The LC-LC method is more suitable for complex samples because it involves an online cleanup effect. Detection limits were 1.25 and 1.87 mg/L for diclofop-acid and 2.70 and 3.02 mg/L for diclofop-methyl enantiomers, respectively. Accuracy, repeatability, and reproducibility have been studied in standard samples and a technical product.