Simultaneous ultrasound-assisted iodide oxidation and liquid-liquid microextraction for rapid quality control of iodized salts by UV–vis micro-spectrophotometry

Abstract

In this work, a rapid and simple analytical method for the quality control of iodized salt based on simultaneous ultrasound-assisted iodide oxidation and liquid-liquid microextraction, with the subsequent measurement of the organic phase by UV–vis micro-spectrophotometry is described. An aqueous sample solution along with 50μL of carbon tetrachloride are sonicated with a probe for 2min. CCl4 is used both for intensifying the oxidation capacity of ultrasound and as an extractant, which enables the determination of iodide at trace levels. Chlorine radicals and molecules arising upon sonication react quickly with iodide leading to the formation of iodine, which is simultaneously extracted to yield a purple solution. Relevant variables such as the volume of carbon tetrachloride, sample volume, sample temperature, type of sample vial, sonication parameters (amplitude and time) and pH were studied. The presence of high amounts of NaCl influences the ultrasonic oxidation of iodide, and hence, the use of matrix-matched standard solutions with NaCl was recommended. Under these conditions, the calibration curve was linear up to 20μgmL−1 of iodide. The LOD and LOQ, calculated following the 3σ criteria and 10σ criteria, respectively, were 0.2 and 0.6μgg−1. The repeatability, expressed as relative standard deviation, was 1.9%. The proposed methodology was successfully applied to different salt samples. Quantitative recoveries in the range 95–104% were obtained.