Colorimetric Determination of Indole using p-hydroxybenzaldehyde

Wafaa M. Yousef, Saad A.Al-Tamrah, Basmah H. Al-Shammari

Indoles are very important compounds and found in many alkaloids of physiological importance. They are also found in seeds and plants such as orange and lemon. Para-hydroxybenzaldehyde dehydrogenase is an enzyme found in carrots, it can be found in the orchid. Indole reacts with p-hydroxybenzaldehyde in the presence of concentrated hydrochloric acid to form an orange color complex which has a maximum absorbance at 475 nm. The parameters affecting this reaction were studied in order to find the suitable conditions for the reaction to complete. The effect of acid concentration, reaction temperature and the amount of the reagent on the determination of indole- p-hydroxybenzaldehyde complex were investigated. The system requirements and the best conditions for complete determination are sequently studied. At the optimal conditions, 0.02% w/v p-hydroxybenzaldehyde, 3MHCl at30oC, was used for the determination of indole. Calibration graph was over the range from 0.5-5.00 μg ml-1. The detection limit was 0.08 µg ml-1 and the correlation coefficient was 0.999. Linearity was obtained with slope equals 0.119 and the intercept equals zero.