Densitometric thin layer chromatographic analysis of tretinoin and erythromycin in lotions for topical use in acne treatment.

A TLC-method was developed to analyse tretinoin and erythromycin in a lotion in the presence of several excipients. Erythromycin was separated on a silica gel plate and a mobile phase with dichloromethane, methanol and ammonia 25% (60:6:1 (v/v/v)), tretinoin on a C(18) RP plate with acetonitrile and water (50:25 (v/v)) as mobile phase, adding 1 ml acetic acid for the separation of the excipients and erythromycin. The derivatization for both was done with a dipping reagent, consisting of anisaldehyde, sulphuric acid and acetic acid (respectively 1, 2 and 10% (v/v/v)) and dissolved in chloroform/alcohol 94% v/v (60:30 (v/v)) for erythromycin and alcohol 94%/water (50:40 (v/v)) for tretinoin. These TLC-systems were quantitatively evaluated in terms of stability of the colour, precision, accuracy and calibration, proving the utility in the analysis of the lotion.