Spectrophotometric Assay of Thymol in Various Samples by Coupling with Diazotized p-Nitroaniline

A simple and rapid spectrophotometric method for the trace determination of trace amount of thymol in various samples has been established. The method is based on the coupling reaction of thymol with diazotized p-nitroaniline in basic medium to form an intense pinkish-red, water-soluble and stable mono azo dye which shows maximum absorption at 513nm. A plot of absorbance with thymol concentration gives a straight line indicating that Beers law has been obeyed over the range 1-300 g/25ml, i.e., 0.04-12 ppm with a molar absorptivity of 2.48104 l mol-1 cm-1, and Sandell sensitivity index of 0.006 g/cm2. The method does not resort to neither temperature control nor to solvent extraction. The effect of organic solvents on the spectrophotometric properties of the azo dye, the composition and stability constant and interference due to foreign compounds have been worked out. The method has been applied to the determination of thymol in pharmaceutical, oil and waters.