Fluorescent labeling of drugs and simple organic compounds containing amine functional groups, utilizing dansyl chloride in Na 2CO 3 buffer

Abstract

Fluorescent labeling of amine functional groups using dansyl chloride (DNS-Cl), and in sodium carbonate buffer, allowed the detection of 1 μg amounts of analytes. The methodology presented allows dansylation of primary, secondary, and tertiary amine groups at a temperature of 25° 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 Na 2CO 3 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 25°, 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.