Multi-element compound-specific stable isotope analysis (2H, 13C, 15N, 33/34S) to characterize the mechanism of sulfate and hydroxyl radical reaction and photolysis of benzothiazole

Benzothiazole was taken as a simple emerging aromatic heterocyclic contaminant as model compounds for analyzing multi-element isotope (ME-CSIA) fractionation (²H, ¹³C, ¹⁵N and ^33/34S) for the first time, in order to obtain information on the reaction mechanism upon sulfate and hydroxyl radical reactions and photolysis. The sulfur isotope effects (³³/³⁴S) allow to explore reaction mechanisms with respect to mass dependent and independent kinetic isotope effects. For compound specific isotope analysis for ²H, ¹³C, and ¹⁵N using GC-pyrolysis and combustion IRMS techniques were applied and for ^33/34S isotope analysis a novel approach using GC- multi collector ICPMS were developed. The multi-element fractionation factors of the radical reactions were obtained to characterize the first irreversible degradation step in order explore their potential to analyze radical oxidation processes in technical and natural systems. The hydroxyl radical reactions yield small carbon (ε_C = -0.67 ± 0.06 ‰), large hydrogen (ε_H = -8.8 ± 0.9 ‰), and negligible nitrogen and sulfur isotope fractionations as cleavage of the C - H bond the benzene ring is the first irreversible step. The heat-activated persulphate oxidation at pH = 2, dominated by SO₄^•-radicals were associated with significant for C (ε_C = -1.56 ± 0.09 ‰), N (ε_N = 1.08 ± 0.05 ‰), and S (ε³³S = -0.6 ± 0.04 ‰, ε³⁴S = -1.1 ± 0.09 ‰), and negligible for H isotope fraction, indicating cleavage of the C-S bond.