Partitioning of cocaine and its adulterants in aqueous two-phase systems: An alternative drug identification method

Abstract

The partitioning behaviors of cocaine freebase (CoF), cocaine hydrochloride (CoH), and a range of adulterants (procaine (PRO), phenacetin (PHE), caffeine (CAF), benzocaine (BEN), and lidocaine (LID)) in aqueous two-phase systems (ATPS) were evaluated, with the aim of developing a selective and efficient alternative technique for the identification of cocaine in samples confiscated by the police. The partition coefficients (KS) of all the solutes were obtained in ATPS formed using a macromolecule (PEO1500 or L35 copolymer), a salt (Na2SO4 or Li2SO4), and water. The KS values were consistently higher than 1 and increased with increase of the tie-line length. For the PEO1500 + Li2SO4 + water ATPS at pH 6.0, the KS values increased in the order: KLID < KPRO < KCAF < KCoF < KCoH < KPHE < KBEN. The greatest effect on the partitioning was shown by the polymer hydrophobicity, followed by the nature of the electrolyte and the pH of the ATPS. The ratio between two KS values for two different ATPS types was used as a strategic parameter for distinguishing between the two forms of cocaine, as well as between cocaine and the adulterants. The K12/K6 ratio, where K6 and K12 are the KS values for the PEO1500 + Li2SO4 + water ATPS at pH 6.0 and 12.0, respectively, enabled CoH to be distinguished from all the other solutes studied. In addition, the effect of the hydrophobicity of the polymer on the KS values was fundamental for distinguishing CoF from the other solutes.