Differential-pulse polarographic determination of cholic acids

Abstract

A differential-pulse polarographic technique is described for the determination of the concentration of cholic acids in pharmaceutical products and in human bile. The procedure is carried out at a temperature of 25 °C, an ionic strength of 0.4 mol l^–1 and a pH of 5.25. The similar polarographic behaviour of the peak height versus the concentration of the unconjugated and conjugated acids allows the evaluation of the total cholic acids content by summing the independent forms in which they are present in the sample. The method is particularly good for the determination of cholic acids in human bile because it is cheap, very fast and sufficiently acurate and precise results are obtained without pre-treatment of the sample.

The results are comparable to those obtained by the enzymatic-spectrophotometric method. The linearity range in the solution to be polarographed lies between 2 × 10^–6 and 1 × 10^–4 mol l^–1, depending on the nature of the acid; the relative standard deviation of a single measurement on five different samples is less than 1% for pure cholic acid solutions, between 3.3 and 9.2% for pharmaceuticals and 2.4 and 8.9% for human bile.