β-Naphthoquinone sulfonate as electrochemical labelling reagent for high-sensitivity LC analysis of drugs in biological fluids

Summary A new sensitive, high-performance liquid chromatography (HPLC) method using electrochemical detection (ECD) is reported for the determination of 21 amphetamine-like compounds such as amphetamine, methamphetamine, methoxyphenamine, phentermine, ephedrine, mescaline, STP and methylenedioxyamphetamine, in biological fluids. Primary and secondary amines in biological specimens were easily labelled with -naphtho-quinone-4-sulfonate (BNQS) at 60°C for 30 min. Hydrodynamic voltamograms of BNQ-derivatives showed a maximum response at an applied potential of around zero V (against Ag/AgCl) in reducing model. BNQ derivatives of amines were analyzed by HPLC using a reducing ECD at zero V (Ag/AgCl). Separation was on a Bondasphere C18 with mobile phase: acetonitrile-methanol-0.01 M H₂SO₄. Good separations of twenty one amphetamine-analogs were obtained. Only 50 l of biological fluid containing those drugs at a concentration of over 1 g ml^–1 were needed direct for determination with good accuracy. When extraction was carried out prior to the labelling reaction, the detection limits were much improved to less than 10 ng ml^–1.This method was successfully applied to determination of methamphetamine in hair.