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 determination of residues in controlling pharmaceutical equipment cleanliness. Analytical methods were developed for monitoring residues of pentoxifylline at 10 mg/M2 and mebendazol at 1 mg/M2 on stainless steel surfaces. Simulated samples were prepared by addition of a calculated amount of pharmaceutical (as a solution) on a 35 x 35 cm stainless steel surface. After evaporation of solvent, the residues were wiped with wetted cotton. The cotton was extracted with dichloromethan-methanol (1 + 1). Filtered extract was concentrated by vacuum evaporation and an aliquot applied to the plate, where standards were also applied. In the narrow concentration range near the acceptable residue limits, linear calibration curve could be obtained for both substances. The mean recovery (n = 4) obtained by densitometric quantitation was 93.4% for pentoxifylline and 85.6% for mebendazol, with coefficients of variation of 3.5 and 8.3%, respectively. Results of video densitometric quantitation did not differ significantly. However, data acquisition and evaluation is faster compared with densitometry and allows better archiving possibilities as required by the regulatory authorities. Both quantitation modes can be applied to routine control of pharmaceutical equipment cleanliness.