FLOW CHARACTERISTICS OF A VERSATILE WALL-JET OR RADIAL-FLOW THIN-LAYER LARGE-VOLUME CELL FOR ELECTROCHEMICAL DETECTION IN FLOW-THROUGH ANALYTICAL SYSTEMS

Flow characteristics of a versatile large-volume flow-through electroc hemical cell, which features exchangeable disk, ring-disk or microdisk working electrodes, are presented. The cell operates in a radial-flow thin-layer, wall-jet or wall-tube mode, under amperometric or voltamm etric conditions, being therefore suitable for flow analytical techniq ues, such as high performance liquid chromatography (HPLC) and flow in jection analysis (FIA). The operation mode is selected by using the in let capillary either of a Rat or conical nozzle and by suitably adjust ing the nozzle-to-electrode distance. The cell is equipped with a micr ometer screw which allows for adjusting of this distance to be as smal l as 10 +/- 5 mu m. The inlet solution stream is centered axially agai nst the working electrode surface. Under radial-flow thin-layer condit ions, flow-through detection at a ring-disk electrode benefits from sh ielding and collecting properties which are enhanced as compared to th ose for the rotating ring-disk electrode conditions. The HPLC extracol umn effects due to detection were determined by the peak variance anal ysis of a mixture of regio isomers of nitrobenzene derivatives. Despit e the large (35 mL) geometric cell volume, the effective detection vol ume of the cell is of the microliter order. Therefore, the cell is sui table for detection both in the analytical and microbore-column HPLC. Due to the large geometric cell volume, solution composition can be di fferent, under wall-jet conditions, for detection than that for HPLC s eparation. Hence, in situ postcolumn modification of the mobile phase or analyte is feasible.