Analytical Sciences

Spectrophotometric Determination of Urea in Dermatologic Formulations and Cosmetics

Jorgovanka BOJIC,* Blaga RADOVANOVIC,** and Jasmina DIMITRIJEVIC***

*High Polytechnic School, Kosanciceva 36, 37000 Krusevac, Serbia
**Department of Chemistry, Faculty of Natural Science, University of Nis, Visegradska 33, 18000 Nis, Serbia
***Pharmacy, Luke Ivanovica 34, 37000 Krusevac, Serbia

A rapid, relatively sensitive, and low-cost method for the determination of water-soluble urea content in dermatological therapy products and cosmetics is proposed using a new spectrophotometric assay with water as the only extraction solvent. Spectrophotometric methods involve addition of a known excess of bromate to urea in an acid medium, followed by the determination of residual bromine and chlorine reacting with methyl orange and measurement of absorbance at 505 nm. The absorbance increases linearly with urea concentration (r = 0.9998). The systems obey Beer's law for 6 - 90 µg ml^-1. The calculated apparent molar absorbance values are found to be 4.537 × 10³ dm³ mol^-1 cm^-1 and the Sandell's sensitivity is 0.013 µg cm^-2. The variables affecting the rate of the reaction were investigated. The relative standard deviation for five-replication determination of 60 µg ml^-1 urea was 2.1% and the detection limit of the method is 0.34 ng ml^-1.

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