Spectrophotometric Determination of Barbituric Acid by Coupling with Diazotized Nitroanilines


A simple spectrophotometric method for the trace determination of barbituric acid (BA) has been established. The method is based on the coupling reaction of barbituric acid with diazotized nitroaniline in basic medium to form an intense yellow-water soluble and stable mono azodyes which shows maximum absorption at 418, 380, and 370 nm with diazotized o-, m- and p-nitroanilines, (DONA, DMNA, and DPNA), respectively. A plot of absorbance versus BA concentration was linear to a certain limit, indicating that Beer's law was adhered to over the range 5-300 g of BA/25 ml final volume (i.e., 0.2-12 ppm) with a molar absorptivity of 1.998×104, 2.328×104, and 2.184×104 l mol–1 cm–1 for DONA, DMNA, and DPNA, respectively. Sandell sensitivity indexes were 0.0064, 0.0055, and 0.0059 µg cm–2, while the relative errors were -3.365 to 0.904%, -3.325 to 0.138%, and -2.053 to 2.679% for DONA, DMNA, and DPNA, respectively. The relative standard deviation (RSD) were 0.489 to 3.330, 0.897 to 2.209 and 0.059 to 3.689 for DONA, DMNA and DPNA, respectively. The optimum conditions for the color reaction, nature of dye, stability constant and the interference of variety of organic compounds had been investigated. The method has been successfully applied to the determination of barbituric acid in Tigris water river. The proposed method for the determination of barbituric acid is simple, sensitive, very low cost, has a wide analytical range and without the need for heating or solvent extraction techniques.