Spectrophotometric quantification of trace levels of cyanide in water-insoluble drug substances and confirmation of specificity through an orthogonal comparison approach

Abstract

Some pharmaceutical ingredients use cyanide in their synthesis, and this impurity must be controlled as per ICH, FDA and EDQM regulatory compliance. Spectrophotometric approaches for measuring cyanide levels are confined to water or water-soluble compounds with poor solution stability and low sensitivity. No method is available for the cyanide in water-insoluble drug substances through spectrophotometry. To address this gap, our study proposed a spectrophotometric approach for measuring trace cyanide in water-insoluble drugs such as Primidone and Clobazam. This method utilizes chloramine-T, which reacts with cyanide to form cyanogen chloride (CNCl), consequently reacting with pyridine-barbituric acid to produce a coloured derivative (C13H10N4O6, MW: 318.06 g/mol). This protocol also involves the selection of a suitable solvent and optimizing the pH for sensitive/accurate quantification of cyanide impurity. Mass spectrometry confirms cyanide derivatization as part of the orthogonal procedure comparison of ICH Q2 (R2). Method validation follows ICH Q2 (R2) guidelines in determining specificity, LOD (0.396 ppm), LOQ (1.200 ppm), linearity (1.2-45 ppm), and recovery (91-99% with %RSD<10%) of the method. The stability of the pyridine-barbituric acid reagent and derivatized compound was also evaluated. This approach effectively measures cyanide in water-insoluble drugs, meeting essential regulatory standards.