Fluorimetric determination of cinchocaine in a pharmaceutical drug by scanning and video densitometry

Abstract

A convenient HPTLC method is described for the quantification of cinchocaine hydrochloride (dibucaine) in a local anaesthetic ointment. Classical slit scanning densitometry is compared with video densitometry by avaluating the plates by line scanning and then by image analysis. For the ointment determination, detection and quantification limits in the lower nanogram range are attained, with very low coefficients of variation (about 0.06–0.2%). Whereas the results are average for scanning densitometry, the results for image analysis are very good. Cinchocaine hydrochloride was extracted from a commercial ointment with methanol. Separation from the other ingredients and excipients was accomplished by HPTLC on silica gel plates with a mixture of toluene, acetone, methanol and 25% ammonia as developing solvent. Cinchocaine hydrochloride shows blue fluorescent spots that were detected by video densitometry at 366 nm and by scanning densitometry at 312 nm. Linear calibration in the working range of 50–350 ng cinchocaine hydrochloride was demonstrated by integrating the area under the peaks. When compared to classical slit scanning densitometry, video densitometry —in combination with a rapid sample preparation-represents a fast alternative for quantifying thin layer chromatograms in cinchocaine analysis.