A novel indirect colorimetric method for the quantification of Elaidic acid in vegetable oils via digital image...

A simple, sensitive, and rapid colorimetric method was developed for the quantitative determination of Elaidic acid in vegetable oil samples through the indirect measurement of a benzidine oxidation product using image analysis. The method is based on the ability of Elaidic acid to form a weak complex with silver ions in the presence of excess silver nitrate, which oxidizes the benzidine producing a blue-colored product whose intensity is inversely proportional to the concentration of bound Elaidic acid. Quantification was carried out using image analysis after optimizing experimental conditions, including pH and reaction time, enabling accurate determination of Elaidic acid concentration. The method incorporates a thin-layer chromatography (TLC) pre-separation step to ensure the selective isolation of Elaidic acid from its cis-isomer (Oleic acid) and other fatty acid constituents before colorimetric development.

The calibration curve for (Elaidic acid - Ag+) complex was linear up to 8.8 mg/10 mL, with correlation coefficient R² = 0.9941 and a detection limit of 0.6 mg/10 mL. Statistical analysis showed good precision, sensitivity, and repeatability, with an average recovery of 97% and an acceptable relative standard deviation (RSD = 1.44%). Furthermore, the results obtained for vegetable oil samples demonstrated high correlation with the standard GC-MS method, confirming the reliability of the proposed approach.

This hybrid TLC-DIA platform provides a rapid, cost-effective, and accurate alternative for monitoring trans-fatty acid levels without the need for expensive instrumentation, making it highly suitable for routine food quality control, particularly in resource-limited analytical settings.