Flow-through polarographic cell for flow-injection analysis. Determination of nifedipine in pharmaceutical formulations

A simple design of a polarographic flow-through cell is proposed in which a conventional dropping mercury electrode (DME) is used as working electrode, and a mercury pool and a platinum wire are used as the reference and counter electrodes, respectively. The mercury droplets falling from the DME coalesce with the pool, and a fairly constant hold-up cell volume is achieved by controlled removal of the mercury from the pool at an equivalent flow rate than that of the DME. The analytical features of the cell are illustrated by flow-injection (FI) determination of the nitro derivative nifedipine in pharmaceuticals. The flow-through detector can be used either amperometrically, under continuous flow operation, or voltammetrically in quiet solution, under continuous flow-stopped flow mode. Under continuous flow operation of the cell, the sampling rate obtained was 120 h⁻¹. The repeatability of the analytical signals, expressed as RSD, was always lower than 2.1%. The recovery of nifedipine in synthetic tablet formulations was 99.8 ± 0.6%. © 1997 John Wiley & Sons, Inc. Lab Robotics and Automation 9: 255–262, 1997