Extraction, preconcentration and spectrophotometric determination of trace levels of thiosulfate in environmental waters

Abstract

In the existing study, a new vortex-assisted cloud point extraction (VA-CPE) method was developed for determination of low levels of thiosulfate in environmental waters at 632 nm by spectrophotometry. The method is selectively based on charge-transfer-sensitive ion-pair complex formation of Ag(S2O3)2 3?, which is produced by the reaction of thiosulfate with excess Ag+ ions with toluidine blue (3-amino-7-dimethylamino-2-methylphenazathionium chloride, TB+) and then its extraction into micellar phase of polyethylene glycol 4-tert-octylphenyl ether (Triton X-45) in presence of Na2SO4 as salting-out agent at pH 7.0. All the factors affecting complex formation and VA-CPE efficiency were optimized in detail. Under the optimized conditions, the linear calibration curves for thiosulfate were in the range of 0.2–120 and 5–180 µg L?1 with sensitivity improvement of 81-folds and 15-folds, respectively, as a result of efficient mass transfer obtained by CPE with and without vortex, while it changed in the range of 260–3600 µg L?1 without preconcentration at 642 nm. The limits of detection and quantification of the method for VA-CPE were found to be 0.05 and 0.22 µg L?1, respectively. The precision (expressed as the percent relative standard deviation) was in range of 2.5–4.8% (5, 10 and 25 µg L?1, n: 5). The method accuracy was validated by comparing the results to those of an independent 5,5?-dithiobis(2-aminobenzoic acid) (DTNB) method as well as recovery studies from spiked samples. It has been observed that the results are statistically in a good agreement with those obtained by DTNB method. Finally, the method developed was successfully applied to the preconcentration and determination of trace thiosulfate from environmental waters. © 2017, The Author(s).