Fluorescent labeling of drugs and simple organic compounds containing amine functional groups, utilizing dansyl chloride in Na2CO3 buffer

Fluorescent labeling of amine functional groups using dansyl chloride (DNS-Cl), and in sodium carbonate buffer, allowed the detection of 1 mug amounts of analytes. The methodology presented allows dansylation of primary, secondary, and tertiary amine groups at a temperature of 25degrees C. The dansylation of tertiary amines involves a chemical reaction which removes one substituent (or branch) of the amine group. A one molar working concentration of Na2CO3 is used, and is at pH 11.0. Compounds such as isopropylamine, dipropylamine, diethylamine, triethylamine, triisooctylamine, and N,N-dimethylaniline were labeled by use of DNS-Cl from samples obtained from a complex mixture of alkanes. The compound p-chloroaniline contains a primary amine group and is a solid at 25degrees, quickly dissolves in the one molar sodium carbonate buffer and is dansylated in 15 min. Heroin, which contains a tertiary amine group, was extracted into ethyl acetate from an aqueous solution, then reacted with DNS-Cl. Benzocaine, a local anesthetic, was dansylated in 15 min. Tertiary amine groups incorporated in a rigid ring system, such as for caffeine, strychnine, and the ionic salt form of cocaine hydrochloride did not react with DNS-Cl under these conditions. The reaction time for tertiary amines was 2 h or less, and 15 min for compounds having primary and secondary amine groups. Separation of the dansylated compounds from unreacted DNS-Cl was accomplished by diethyl ether extraction of the aqueous reaction solution, followed by thin layer chromatography using various organic solvents such as acetone and methylene chloride. (C) 2002 Elsevier Science Inc. All rights reserved.