Facilitation of thin-layer chromatographic identification of opiates by derivatization with acetic anhydride or methoxyamine.

Qualitative identification of opiates in urine is commonly achieved in two stages, the first involving immunoassay screening and the second involving chromatographic confirmation. Identification of specific opiates is often requested to determine whether the source of opiates is from diet, prescription pharmaceuticals, or illicit drugs. During evaluation of the Toxi-Lab thin-layer chromatographic system as a confirmatory technique for urinary opiates, we encountered difficulty distinguishing opiates with similar retention factor values and colorimetric behavior. By exploiting chemical differences of the comigrating opiates through preparation of acetate or methoxime derivatives, followed by chromatography of the underivatized and derivatized samples in adjacent lanes, we were able to more easily distinguish codeine from hydrocodone, 6-acetylmorphine from oxymorphone, and dihydrocodeine from hydromorphone.