ABSTRACT
Three simple, accurate and sensitive methods were developed for simultaneous determination of oxyclozanide and levamisole. Method (A) was depending on zero-order absorption spectrophotometry for measuring oxyclozanide at 300 nm and derivative ratio spectrophotometry for levamisole using oxyclozanide as a divisor, then measuring the peak amplitude at 246 nm. Method (B) was TLC method, using silica gel 60 F254 plates; the optimized mobile phase was ethyl acetate/ methanol/ ammonium hydroxide 33% (8:2:0.2 by volume). The spots were scanned densitometrically at 300 nm for oxyclozanide and 220 nm for levamisole. Method (C) was an HPLC method, performed on C18 column using acetonitrile/ methanol/ 0.05M potassium dihydrogen phosphate (60:20:20 by volume), the pH was adjusted to 3.5±0.2 with ortho-phosphoric acid as a mobile phase with a flow rate of 1 ml/min. Detection was performed at 220 nm. Linearity ranges were 5 – 40 μg/ml of oxyclozanide and levamisole for method (A), 1 – 6 μg/band of oxyclozanide and 2 - 10 μg/ band of levamisole for method (B) and 0.5 – 10 μg/ml of both drugs for method (C), the mean percentage recoveries were 100.21±0.844% for oxyclozanide and 99.53±0.920% for levamisole in case of method (A), 99.72±1.348% for oxyclozanide and 99.14±1.277% for levamisole in case of method (B) and 99.81±0.852% for oxyclozanide and 100.20±0.886% for levamisole in case of method (C). The proposed methods were found to be specific for both drugs in their binary mixture. Statistical comparison between the results obtained by these methods and the manufacturer’s method for oxyclozanide and the official method for levamisole was done, and no significance difference was observed.
ABSTRACT
This study was developed and validated for the determination of oxyclozanide residue concentrations in beef and commercial milk, using high-performance liquid chromatography system. Oxyclozanide was successfully separated on a reverse phase column (Xbridge-C18, 4.6x250 mm, 5 microm) with a mobile phase composed of acetonitrile and 0.1% phosphoric acid (60:40, v/v%). This analytical procedure involved a deproteinization process using acetonitrile for beef and 2% formic acid in acetonitrile for commercial milk, dehydration by adding sodium sulfate to the liquid analytical sample, and a defatting process using n-hexane; after these steps, the extract was exposed to a stream of nitrogen dryness. The final extracted sample was dissolved in the mobile phase and filtered using a 0.45 microm syringe filter. This method had good selectivity and recovery (70.70+/-7.90-110.79+/-14.95%) from the matrices. The LOQs ranged from 9.7 to 9.8 microg/kg for beef and commercial milk. The recoveries met the standards set by the CODEX guideline.