A SOLID POLYMER ELECTROLYTE AMPEROMETRIC DETECTOR FOR FIA AND HPLC WITH MOBILE PHASES OF LOW CONDUCTIVITY

An amperometric cell with a small platinum wire working electrode, a submicroliter geometric volume, and a solid polymer electrolyte (Nafion) was constructed and tested. The cell permits sensitive and reliable detection even in mobile phases of negligible electric conductivity, (e.g., distilled water or nonpolar organic solvents). The sensitivity is substantially higher than that attained with similar cells containing large-area working electrodes; typical limits of detection amount to analyte concentrations between 10(-7) and 10(-6) mol/dm3, corresponding to subnanogram amounts in common HPLC sample volumes. The detector response exhibits satisfactory linearity, a linear dynamic range of at least three concentration decades, and a good precision, with relative standard deviations of 1 to 5%. This cell substantially widens the possibilities of amperometric detection, permitting direct application, for example, to normal- phase HPLC or to methods with programmed composition of the mobile phase (gradient elution).