Chromatography and electrochemistry are the two most widely used analytical tools which (a) are heterogeneous, and (b) require an understanding of the mass transport of molecules. Experimentally, the combination provides a powerful tool for trace determinations, and is the fastest growing electroanalytical technique. Figure 1 illustrates the components of a typical LC-EC system. Both chromatography and electrochemistry have long been used in clinical laboratories for specialized applications. With few exceptions (determination of blood oxygen by amperometry), both methodologies have continued to present too many reliability problems for use in smaller laboratories by less skilled personnel.