Indirect Determination of Free, Total, and Reversibly Bound Sulfite in Selected Beverages by Spectrophotometry Using Ultrasonic-Assisted Cloud Point Extraction as a Preconcentration Step

Abstract

A new indirect ultrasonic-assisted cloud point extraction (UA-CPE) method has been developed for the determination of trace sulfite species by means of spectrophotometry. The method is based on either directly imide–bisulfite adducts formation or ion-pairing complexation of enolate–bisulfite adducts produced by the oxidation of pyrogallol with sulfite at pH 10 with 3-amino-7-diethylamino-8,9-benzo-2-phenoxazine chloride (Nile blue A) and CPE of ion-pairing complex formed from aqueous solution using Triton X-114. Under the optimized conditions, the calibration graphs with and without bromide were highly linear in the ranges of 6–180 and 7.5–180 μg L−1 with changing sensitivity. The limits of detection and quantification (LOD and LOQ) (3σblank/m and 10σblank/m) with bromide was 1.75 and 5.83 μg L−1 (n = 6) and the precision, the relative standard deviations (RSDs), for determination of 25, 75, and 150 μg L−1 of sulfite was in range of 2.40–5.20 % (n = 10). The method showed good selectivity, and was successfully applied to the speciative determination of trace sulfite in selected beverages with and without alcohol. The results were compared with those of the standard 5,5′-dithio-bis(2-nitrobenzoic acid (DTNB) method, and the two paired t test was used to determine whether the results obtained by the two methods differ significantly.