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 (epsilon C =-0.67 f 0.06 %o), large hydrogen (epsilon H =-8.8 f 0.9 %o), 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 center dot- radicals were associated with significant for C (epsilon C =-1.56 f 0.09 %o), N (epsilon N = 1.08 f 0.05 %o), and S (epsilon 33S =-0.6 f 0.04 %o, epsilon 34S =-1.1 f 0.09 %o), and negligible for H isotope fraction, indicating cleavage of the C-S bond.