A Rapid, Novel Colorimetric Method for Assessing Contamination of Glycerol with Toxic Diethylene Glycol

Despite the stringency of the specifications of pharmaceutical glycerol to be used in oral syrups, diethylene glycol (DEG) contamination has been observed, leading to fatalities in young consumers. Formulations and glycerol raw materials in generic companies are not adequately tested due to the lack of sophisticated instrumentation and skilled manpower. The tests to determine glycerol purity according to recommended guidelines involve gas chromatographic techniques, which require expensive instruments and high technical skills. A rapid novel method for assessing glycerol purity is proposed, which can be used for screening glycerol raw material for DEG contamination. The colorimetric assay relies on the rapid reduction of chromium(VI) to chromium(III) by glycerol in the presence of excess sulfuric acid. The conversion of chromium(VI) to chromium(III) by DEG is much slower as compared to glycerol. Comparing both the analytes, a differential in the rate of reduction of chromium(VI) to chromium(III) was observed, which is exploited in the assay. The formation of chromium(III) product could be assessed by spectrophotometric analysis at 574 nm. The method is linearly sensitive to glycerol concentrations. The assay is simple, rapid, and can be used to screen glycerol consignments by comparing them with the readings obtained from standard pure pharmaceutical glycerol. DEG contamination greater than or equal to 5% (v/v) (~4.4%, m/m) can be indicated. However, confirmed analysis must be performed as per the recommended guidelines.