Colorimetric Determination of Indole using 2,4,6-trimethoxybenzaldehyde

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

Indole is an aromatic heterocyclic organic compound. The indole nucleus is very important for many natural and synthetic molecules with significant biological activity. Compounds that contain an indole ring are called indoles. Indoles are an important class of heterocycles not only because they are among the most ubiquitous compounds in nature, but also because they have a wide range of biological activities. 2,4,6-Trimethoxybenzaldehyde can be used as antibacterial synergist.  When indole was mixed with 2,4,6-trimethoxybenzaldehyde at room temperature, no color was observed. However in the presence of concentrated hydrochloric acid, a brown red complex is formed which has a maximum absorbance at 488 nm. The parameters affecting this reaction were studied in order to find the suitable conditions for the reaction to complete. The effect of the acid concentration, the reaction temperature and the amount of the reagent on the determination of indole- 2,4,6-trimethoxybenzaldehyde complex were investigated. The system requirements and the best conditions for complete determination are sequently studied. At the optimal conditions, 0.02% w/v 2,4,6-trimethoxybenzaldehyde, 4M HCl at 60^oC, were used for the determination of indole , At these conditions, it was found that the absorbance is directly related to the concentration of indole. Different concentrations of indole over the range from 0.25-1 μg ml-1 were reacted with the reagent. The detection limit (signal : noise 3:1) was 0.02 µg ml-1 and the correlation coefficient was 0.995, Linearity was obtained with slope equals 0.608and the intercept equals 0.000..