Semi-automatic analysis of mercury in pharmaceuticals by catalytic titration

Abstract

The high toxicity of mercury, even at low concentrations, requires its determination in a great variety of samples in areas such as food and environmental analysis or clinical and pharmaceutical chemistry, by simple, sensitive and selective analytical techniques. A number of analytical techniques such as spectrophotometry [l, 21, cold-vapour [3-61 or electrothermal-atomization [7] atomic absorption spectrometry, X-ray fluorescence [8], neutron activation analysis [9] and voltametry [lo]. Of these methods the spectrophotometric and atomic absorption techniques yield the best results in respect of sensitivity, precision and accuracy and have been used for the determination of mercury in pharmaceutical preparations. The present paper describes a simple, sensitive and accurate method for the determination of mercury in pharmaceutical preparations; the method involves a recently developed mode of catalytic titration based on substrate inactivation [ 111. In this catalytic titration mode the analyte-inhibitor interacts with the substrate instead of the catalyst. One of the reactants of the indicator reaction acts as titrant while the other and the catalyst are added to the titration vessel together with the analyte-inhibitor (mercury in this case). Few kinetic methods for the determination of mercury have been proposed [12]; only one catalytic titration procedure has been reported for the determination of mercury in pharmaceutical preparations [13]. That method was based on the inhibitory effect of mercury on the iodide-catalyzed cerium(IV)-arsenic(II1) reaction and involves monitoring the titration by potentiometry.