Development of electrokinetic capillary electrophoresis equipped with amperometric detection for analysis of explosive compounds

Cyclic voltammograms of trinitrotoluene (TNT) and other related explosive compounds obtained by using glassy carbon, platinum, nickel, gold, and silver electrodes revealed the applicability of gold and silver in capillary electrophoresis (CE) amperometric detection. The selected electrode, gold or silver, was inserted into a specially designed detection cell that was easily adapted to a commercial CE apparatus. The electrochemical reduction of TNT, octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triozine (RDX), and 10 other explosives could be reliably monitored at -700 mV vs Ag/AgCl. CE analyses were performed with a borate buffer (15 mM, pH 8.7) containing 25 mM sodium dodecyl surfate (SDS) to attain baseline resolution of the selected compounds. A bimetal electrode, prepared by depositing silver on gold, offered a superior performance by exploiting the sensitivity of gold while suppressing its response toward acetonitrile to achieve a 10-fold lower detection limit than UV measurement. The CE system equipped with amperometric detection was used to determine the explosive content of soil extracts and groundwater, yielding results in good agreement with those obtained by the liquid chromatographic method recommended by the U.S. Environmental Protection Agency.