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

A convenient HPTLC method is described for the quantification of cinchocain e hydrochloride (dibucaine) in a local anaesthetic ointment. Classical slit scanning densitometry is compared with video densitometry by evaluating th e plates by line scanning and then by image analysis. For the ointment dete rmination, detection and quantification limits in the lower nanogram range are attained, wi th 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 mixtu re of toluene, acetone, methanol and 25% ammonia as developing solvent. Cin chocaine hydrochloride shows blue fluorescent spots that were detected by v ideo densitometry at 366 nm and by scanning densitometry at 312 nm. Linear calibration in the working range of 50 - 350 ng cinchocaine hydrochloride w as demonstrated by integrating the area under the peaks. When compared to c lassical slit scanning densitometry, video densitometry - in combination wi th a rapid sample preparation - represents a fast alternative for quantifyi ng thin layer chromatograms in cinchocaine analysis.