Rapid determination of cinchocaine in skin by high-performance liquid chromatography.

A simple, rapid, accurate, precise and specific analytical method has been developed, validated and applied for determination of cinchocaine in guinea pig and albino rabbit dorsal skins, after in vivo application of cinchocaine formulations. Extraction was performed using a solvent mixture of ethanol and 0.1 M hydrochloric acid (90:10; v/v). Samples were chromatographed on Spheri-5, RP(18) column with a particle size of 5 microm and 220 mm x 4.6 mm i.d. The mobile phase was a mixture of acetonitrile and triethylamine phosphate buffer (pH 2.8; 0.04 M) (60:40, v/v). UV detection was carried out at 247 nm and the run time was 6 min with typical retention time of cinchocaine of 3.63 +/- 0.02 min. Specificity was demonstrated, showing that the cinchocaine peak was free of interference from skin endogenous components. The detector response was found to be linear in the concentration range 0.96-56.00 microg/mL with a coefficient of correlation r = 0.99996. The relative standard deviations of within- and between-day analyses were all below 5%. The drug extraction procedure was validated. Satisfactory recoveries with relative standard deviation values below 5% were obtained, indicating efficient quantitative reproducible extraction procedure.