Deep Eutectic Solvent Liquid-Liquid Microextraction Prior to Smartphone Digital Image Colorimetry for the Determination of Iodate in Table Salt

The development of affordable, easy-to-use methods holds promise to broaden access to food analysis in resource-limited settings that will enhance food safety monitoring and the assessment of public health interventions. In this study, we propose a green extraction method called deep eutectic solvent liquid-liquid microextraction (DES-LLME), coupled with a simple detection technique referred to as the smartphone digital image colorimetry (SDIC), for the quantification of iodate in table salt. Optimization of the DES-LLME-SDIC method was conducted to enhance performance. At the optimum conditions, the proposed method achieved an enrichment factor between 6.1 and 27.8, with a limit of detection (LOD) between 0.52 and 0.84 µmol L−1, and a limit of quantitation (LOQ) between 1.73 and 2.81 µmol L−1. The concentration of iodate exhibited a satisfactory linear correlation with absorbance, as demonstrated by a well-fit regression model as verified by lack of fit test (p > 0.05), within a linear dynamic range from 1.73 to 25.00 µmol L−1. The precision of the method was validated through the relative standard deviation (%RSD) for intraday (3.6%) and interday (6.3%) precision. The developed method was applied for the determination of iodate in various salt samples. Additionally, the accuracy of the proposed SDIC method was evaluated with a separate ultraviolet-visible spectrometry method. Both methods exhibited statistical agreement.