Development and validation of a thin-layer chromatographic method for determination of chloramphenicol residues on...

A thin-layer chromatographic (TLC) method with densitometric quantitation using the absorption reflectance mode at 280 nm was developed and validated for the determination of chloramphenicol residues in controlling pharmaceutical equipment cleanliness. Simulated samples at residue levels 0.5, 1, and 1.2 mg/m2 were prepared by spreading the calculated amount of chloramphenicol solution on a 10 dm2 stainless steel surface. After evaporation of the solvent, the residue was removed by 2 methanol-wetted cotton swabs, which were then extracted with methanol. The extract was applied on a high-performance TLC (HPTLC) silica gel F254 plate together with standards ranging from 10 to 60 ng. Plates were developed in a horizontal developing chamber from both sides (36 applications per plate) by using n-hexane-ethyl acetate (35 + 65, v/v) as developing solvent. The mean recovery (n=6) at 1 mg/m2 was 95.8%, and the coefficient of variation was 5.8%. The absolute detection limit was 3 ng, and the quantitation limit 10 ng. The method detection limit was 0.3 mg/m2 by swabbing 2.5 dm2 and 0.075 mg/m2 by swabbing 10 dm2. Chloramphenicol was stable on the plate 2 h before and 24 h after development. Additionally, it was stable during 7 days storage on the cotton swabs in the solvent at room temperature and in diluted standard solution stored in darkness at 4 degrees C. The method can be applied to routine control of pharmaceutical equipment cleanliness by sampling from the stainless steel surface areas of 2.5 to 10 dm2, and an acceptable residue limit of 1 mg/m2.