Compound-Specific Chlorine Isotope Analysis of the Herbicides Atrazine, Acetochlor, and Metolachlor

A gas chromatography−single quadrupole mass
spectrometry method was developed and validated for
compound-specific chlorine isotope analysis (Cl-CSIA) of
three chlorinated herbicides, atrazine, acetochlor, and
metolachlor, which are widespread contaminants in the
environment. For each compound, the two most abundant
ions containing chlorine (202/200 for atrazine, 225/223 for
acetochlor, and 240/238 for metolachlor) and a dwell time of
30 ms were determined as optimized MS parameters. A limit
of precise isotope analysis for ethyl acetate solutions of 10 mg/
L atrazine, 10 mg/L acetochlor, and 5 mg/L metolachlor
could be reached with an associated uncertainty between 0.5
and 1‰. To this end, samples were measured 10-fold and
bracketed with two calibration standards that covered a wide range of δ37Cl values and for which amplitudes matched those of
the samples within 20% tolerance. The method was applied to investigate chlorine isotope fractionation during alkaline
hydrolysis of metolachlor, which showed a shift in δ37Cl of +46‰ after 98% degradation, demonstrating that chlorine isotope
fractionation could be a sensitive indicator of transformation processes even when limited degradation occurs. This method,
combined with large-volume solid-phase extraction (SPE), allowed application of Cl-CSIA to environmentally relevant
concentrations of widespread herbicides (i.e., 0.5−5 μg/L in water before extraction). Therefore, the combination of largevolume SPE and Cl-CSIA is a promising tool for assessing the transformation processes of these pollutants in the environment.