Sulfate radical formation by Cr(III) activation of peroxydisulfate - Diphenylcarbazide spectrophotometric determination of sulfate radical and its scavenging activity

Seda Uzunboy; Özge Karakaş; Sema Demirci-Çekiç; Reşat Apak

doi:10.1016/j.saa.2021.119941

Sulfate radical formation by Cr(III) activation of peroxydisulfate - Diphenylcarbazide spectrophotometric determination of sulfate radical and its scavenging activity

Spectrochim Acta A Mol Biomol Spectrosc. 2021 Nov 5:260:119941. doi: 10.1016/j.saa.2021.119941. Epub 2021 May 11.

Authors

Seda Uzunboy¹, Özge Karakaş¹, Sema Demirci-Çekiç², Reşat Apak³

Affiliations

¹ Department of Chemistry, Faculty of Engineering, Istanbul University-Cerrahpasa, 34320 Avcilar, Istanbul, Turkey; Department of Chemistry, Institute of Graduate Studies, Istanbul University-Cerrahpaşa, Turkey.
² Department of Chemistry, Faculty of Engineering, Istanbul University-Cerrahpasa, 34320 Avcilar, Istanbul, Turkey.
³ Department of Chemistry, Faculty of Engineering, Istanbul University-Cerrahpasa, 34320 Avcilar, Istanbul, Turkey; Turkish Academy of Sciences (TUBA), Vedat Dalokay St. No. 112, 06670 Cankaya, Ankara, Turkey. Electronic address: rapak@istanbul.edu.tr.

PMID: 34034074
DOI: 10.1016/j.saa.2021.119941

Abstract

Even though sulfate anion radical (SO₄^-) is a very reactive oxidant used in advanced oxidation processes, a reliably selective and simple colorimetric method for determining this radical can hardly be found. Peroxydisulfate (S₂O₈^2-) or peroxymonosulfate (HSO₅^-) can be activated with transition metal ions to produce SO₄^-. We have discovered that Cr(III) can be an activator for persulfate, generating Cr(VI) along with SO₄^-. By measuring the emerging chromate with diphenyl carbazide (DPC) spectrophotometry at 542 nm, we could measure both the formation of SO₄^- and its scavenging with antioxidant compounds. We could also investigate a number of UV-absorbing SO₄^- scavengers which could not be measured with other UV spectrometric methods. In addition to conventional antioxidants (phenolics such as quercetin, catechin, epicatechin, caffeic acid, thiols like cysteine and N-acetyl cysteine, and ascorbid acid), nitro-aromatics (represented by 2,4,6-trinitrophenol and 2,4-dinitrophenol) used in ammunition formulations could also be measured as scavengers. The presence of scavengers caused a reduction in the amount of Cr(VI) generated, where the difference in absorbance (ΔA) of chromate - with respect to the DPC method - in the absence and presence of scavengers was a linear function of SO₄^- scavenging capacity. Ethanol and tert-butanol were tested as solvents to show the selectivity of the method for SO₄^-. The method was statistically compared to a suitably modified ABTS/persulfate assay. The efficiency order of sulfate radical scavengers was determined and ranked (Spearman's test) using both the proposed method and modified ABTS/persulfate method to reveal a moderate correlation.

Keywords: Antioxidants; Nitro-aromatic compounds; Persulfate activation; Radical scavenging; Sulfate radical determination.