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

Ramazan Gürkan,Nimet Gürkan,Nail Altunay

doi:10.1007/s13738-017-1053-9

Ramazan Gürkan, Nimet Gürkan + Show 1 more

Open Access

https://doi.org/10.1007/s13738-017-1053-9

Copy DOI

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)23−, 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.

Highlights

Thiosulfate is a common product of the inorganic oxidation of sulfide ions and iron sulfides, as well as the disproportionation of bisulfite and sulfite ions [1]
The method is based on the selective charge-transfer-sensitive ion-association of anionic Ag(S2O3)− or Ag(S2O3)23− complex, which is produced depending on concentration of thiosulfate in presence of excess Ag+ ions with ion-pairing reagent, TB+ as pH sensitive redox species at pH 7.0, and extraction of ternary complex to micellar phase of Triton X-45 as extracting agent
At lower concentrations than 10 μg L−1, the calibration sensitivity was much higher because of the fast and efficient mass transfer provided by mixing with the vortex at the micellar interface

Summary

Introduction

Thiosulfate is a common product of the inorganic oxidation of sulfide ions and iron sulfides, as well as the disproportionation of bisulfite and sulfite ions [1]. There is still a great need to develop a simple, sensitive, selective and inexpensive method for the determination of trace levels of thiosulfate in different waters requiring novel methods in terms of water quality and human health In this sense, the UV–Vis spectrophotometry is still widely used in analytical chemistry and successfully can be able to couple to cloud point extraction (CPE) in order to enhance the detection limit and selectivity of the method in trace analysis. The absorbance was measured at 412 nm against analyte blank after a reaction time of 15 min at 20 °C

Results and Discussion

Conclusions

Compliance with ethical standards