Abstract
A novel chromatographic application in chiral separation by using the nano-LC technique is here reported. The chiral recognition of 12 antifungal drugs was obtained through a 75 µm I.D. fused-silica capillary, which was packed with a CSP-cellulose 3,5-dichlorophenylcarbamate (CDCPC), by means of a lab-made slurry packing procedure. The mobile phase composition and the experimental conditions were optimized in order to find the optimum chiral separation for some selected racemic mixtures of imidazole and triazole derivatives. Some important parameters, such as retention faction, enantioresolution, peak efficiency, and peak shape, were investigated as a function of the mobile phase (pH, water content, type and concentration of both the buffer and the organic modifier, and solvent dilution composition). Within one run lasting 25 min, at a flow rate of approximately 400 nL min−1, eight couples of enantiomers were baseline-resolved and four of them were separated in less than 25 min. The method was then applied to milk samples, which were pretreated using a classical dispersive liquid–liquid microextraction technique preceded by protein precipitation. Finally, the DLLME-nano-LC–UV method was validated in a matrix following the main FDA guidelines for bioanalytical methods.
Highlights
One of the most important categories of pharmaceuticals is that of chiral drugs
3,5-dichlorophenylcarbamate (CDCPC), covalently bonded to 5 μm silica particles) for the chiral separation of eight imidazole derivates and four triazole derivates. Their nano-liquid chromatography coupled with ultraviolet detection (LC–UV) analysis was preceded by dispersive liquid–liquid microextraction (DLLME), a procedure that is usually applied to treat water samples and is here combined with a previous clean-up to process milk samples
The analytes selected in this study exhibit different values of hydrophobicity (see logP and hydrophilic–lipophilic balance (HLB) in Table 1) and acidity; in particular, imidazoles are weak dibasic agents whose nature has to be considered in order to achieve their chiral separation
Summary
One of the most important categories of pharmaceuticals is that of chiral drugs. Due to the difficulty and cost of synthesis, most of them are still marketed as a racemic mixture, the pharmacological activity is often associated with only one enantiomer, with the other one being inactive or even harmful. Yahaya et al isolated three azole antifungals from milk by ultrasound-assisted emulsification microextraction combined with dispersive micro-solid-phase extraction (USAED-μ-SPE), followed by the use of an LC diode array detector (DAD) [9] In both cases, antifungal drugs were analyzed by achiral methods and determined as racemic mixtures. 3,5-dichlorophenylcarbamate (CDCPC), covalently bonded to 5 μm silica particles) for the chiral separation of eight imidazole derivates (miconazole, bifonazole, butoconazole, econazole, isoconazole, ketaconazole, sertaconazole, fenticonazole) and four triazole derivates (fluconazole, posaconazole, terconazole, voriconazole) Their nano-LC–UV analysis was preceded by dispersive liquid–liquid microextraction (DLLME), a procedure that is usually applied to treat water samples and is here combined with a previous clean-up to process milk samples. The whole method, based on miniaturized extractive and separative techniques, responds to the criteria of sustainability as regards Green Analytical Chemistry
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