MERCURY FILM AND GLASSY CARBON THIN-LAYER ELECTROCHEMICAL TRANSDUCERS FOR TRACE DETERMINATION OF EASILY REDUCED COMPOUNDS

The marriage of liquid chromatography and electrochemical techniques (LCEC) has resulted in many useful applications in the last ten years, primarily with regard to easily oxidized compounds. The promise of LCEC for reductive substances has been slower to achieve due to problems with dissolved oxygen, trace metal ions, and the lack of reliable transducers. The goal of this work was to develop a solid electrode reductive transducer suitable for detection of trace amounts of easily reducible analytes of interest in environmental and pharmaceutical chemistry. A LCEC detector is described based on the use of a mercury film electrode (Au/Hg) in a thin-layer cell with the auxiliary electrode placed across the channel from the working electrode. The placement of the auxiliary electrode has provided a transducer with a linear range over five orders of magnitude while maintaining subpicomole detection limits for easily reduced analytes. Compounds undergoing specific surface surface reactions with mercury (e.g. thiols) can also be detected. While the Au/Hg transducer has a higher negative potential limit (by approximately 250 mV) and shorter equilibration times, the glassy carbon transducer is more convenient to use. Reductive and oxidative mode LCEC has been applied to the determination of nitro aromatics, nitrate esters, nitramines, and diphenylamines in military explosives and single and double base smokeless gunpowders. A sensitive and highly specific method is presented for the detection of organic "gunshot residue" on the hand of individuals who have discharged a weapon. The detection limits at S/N = 3 were on the order of 0.5, 1, 2, and 0.3 picomoles for nitro aromatic, nitramine and nitrate ester explosive compounds, and diphenylamines, respectively. The static solution and hydrodynamic electrochemical behavior of nifedipine and its photodecomposition products was investigated by cyclic voltammetry and series dual-electrode LCEC. The series dual-electrode transducer with quantitation at the downstream electrode minimized interference caused by reduction of dissolved oxygen, thus simplifying sample handling. Other applications include the determination of chloramphenicol and adriamycin in plasma as well as the agricultural products parathion, methyl parathion, cyolane and cytrolane in runoff water.