j. Soc. Cosmet. Chem., 47, 325-336 (September/October 1996) Tretinoin assay in cosmetics andpharmaceuticals by carbon phase extraction G. RAGNO, M. VERONICO, R. MADDALENA,and C. VETUSCHI,Pharmaco Chemistry Department ofUniversity, Via E. Orabona 4, 70126 Bari, Italy. Accepted for publication September 30, 1996. Presented at IV CRSAAE Bologna, Italy, October 1991. Synopsis A tretinoin assay, useful to verifyits absence in cosmetics, where the drug is forbidden, was proposed. The method was based on a carbon phase extraction that allows oneto obtain the analyte free from interfering matrix components and in an enriched concentration in such a way as to attain a higher sensitivity. When the analyte was present, a quantitation was performed by UV-derivative spectrophotometry. In the presence of substances with a high absorptivity, like sunfilters,besides the carbon extraction step, a furthersepara- tion by HPTLC was required. The drug absence was validated over 0.1 mg/100g. Since theTRT amount in pharmaceuticals for topical use is 10 to 100 mg/100g, this revelation limit assures a sufficient warranty. A simplified procedure, by direct derivative spectrophotometry, maybe applied for tretinoin determination in pharmaceuticals. INTRODUCTION Tretinoin (TRT), all-trans retinoic acid, is usedfor the treatment of severe cystic acne (1-2) and other skin diseases (3), for its positiveactionon cell proliferation and kera- tinization of the skin, as well as for decreasing sebum secretion and inflammation (4). Research with retinoids and clinical observations in humans sometimes givesapparently contradictory results: while stimulating the proliferation of normal epidermal cells, retinoids may check the growthof psoriatic cells and neoplasms, but the side effects of these compounds are fairly unpleasant (3). Sun exposure during treatmentmust be stringently avoided. Teratogenicity for isotretinoin is well documented (5,6), and it is suspected as a potential effectof tretinoin. For thesereasons, the use of tretinoin in pregnancy is forbidden. On 27 July 1976 theEuropean Community promulgated Law76/768, actuated in Italy with Law 11 October 1986 no. 713, which forbids the use of TRT and several other chemicals in the cosmetic field. Furthermore, in Italy the Ministry of Health, with Cir- cular 18 October 1990 no. 27, hascommittedthe public laboratories to checkfor the absence of TRT in cosmetics. Analytical methods for TRT have been developed by usingHPLC on biological samples (7) and on anti-aging cosmetics (8,9); the U.S. Pharmacopeia 23rd Rev. (10) reportsa 325