TLC determination of mebendazol and pentoxifylline as residues on pharmaceutical equipment surfaces

This paper presents the applicability of thin-layer chromatographic methods with a subsequent densitometric or video densitometric quantitation for de termination of residues in controlling pharmaceutical equipment cleanliness . Analytical methods were developed for monitoring residues of pentoxifylli ne at 10 mg/m(2) and mebendazol at 1 mg/m(2) on stainless steel surfaces. S imulated samples were prepared by addition of a calculated amount of pharma ceutical (as a solution) on a 35 x 35 cm stainless steel surface. After eva poration of solvent, the residues were wiped with wetted cotton. The cotton was extracted with dichloromethan-methanol (1 + 1). Filtered extract was c oncentrated by vacuum evaporation and an aliquot applied to the plate, wher e standards were also applied. In the narrow concentration range near the a cceptable residue limits, linear calibration curve could be obtained for bo th substances. The mean recovery (n = 4) obtained by densitometric quantita tion was 93.4% for pentoxifylline and 85.6% for mebendazol, with coefficien ts of variation of 3.5 and 8.3%, respectively. Results of video densitometr ic quantitation did not differ significantly. However, data acquisition and evaluation is faster compared with densitometry and allows better archivin g possibilities as required by the regulatory authorities. Both quantitatio n modes can be applied to routine control of pharmaceutical equipment clean liness.