First Time Determination of Important Catalyst Sodium Methoxide Used in Biodiesel by Colorimetric Method.

A simple and selective spectrophotometric method has been developed for the first time for the determination of sodium methoxide in methanol solution in the presence of sodium hydroxide. The developed method involves the formation of a pink species by the reaction between sodium methoxide and α-santonin. The pink compound formed shows absorbance maximum at 513 nm. N, N-Dimethylformamide and methanol were used as solvents, and the reaction was performed at different temperatures and 25 °C was selected for further experiments. The pink compound formed was dried and then was studied using FTIR and mass spectrometry. The calibration curve was constructed from 0.10 to 0.30% (m/v) sodium methoxide in methanol, and the standard deviation is 0.010%. Similarly, the relative standard deviations of 28%, 26%, and 24% solutions of sodium methoxide were obtained in the range of 0.4 to 1.9%. The correlation coefficient of the analytical curve r = 0.9997; the limit of detection, LOD, is ca. 1.1 × 10 % w/w; and the limit of quantification, LOQ, is ca. 3.2 × 10 % w/w. The results of analysis were validated statistically.