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

Abstract

A gas chromatography-single quadrupole mass spectrometry method was developed and validated for compoundspecific 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 tenfold and bracketed with two calibration standards which covered a wide range of δ 37 Cl values and whose 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 δ 37 Cl 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 to 5 µg/L in water before extraction). Therefore, the combination of large-volume SPE and Cl-CSIA is a promising tool for assessing the transformation processes of these pollutants in the environment. fractionation associated with reaction mechanisms relevant for field studies. Hence, future studies are warranted to better understand how variable dual isotope slopes are for specific processes in order to identify them unequivocally in the field. ASSOCIATED CONTENT Supporting Information Further details on target analytes, analytical and extraction methods, GC-qMS method performance and results of the validation tests are available in Supporting Information. The Supporting Information is available free of charge on the ACS Publications Website.

Direct and indirect photodegradation of atrazine and S-metolachlor in agriculturally impacted surface water and associated C and N isotope fractionation

“…Finally, recent developments on Cl-CSIA offer promising insights to investigate pesticide degradation pathways in surface waters using multi-element CSIA. 57,58…”

Photodegradation of pesticides using compound-specific isotope analysis (CSIA): a review

“…Thus, it would be particularly useful for contaminant accumulation, 125 source detection, 126 and the development of regulatory and monitoring strategies. 127 As additional elements, such as 2 H, 37,128 37 Cl, 129 and 34 S, 130 are included in the isotopic analysis of atrazine and its metabolite desethylatrazine in a given transformation process, the opportunity to assess the underlying reaction mechanism(s) increases. 131 This is particularly important for the phototransformation processes of agrochemicals, where different functional groups or bonds of a molecule might be involved.…”

Toward Improved Accuracy in Chlorine Isotope Analysis: Synthesis Routes for In-House Standards and Characterization via Complementary Mass Spectrometry Methods

“…In addition, the synthesis of the working standards for acetochlor (Aceto1 and Aceto2) and S-metolachlor (Metola1 and Metola2) showed that organic synthesis can generate substance-specific isotope working standards also of more complex chlorinated organic compounds. These working standards become even more important as GC-qMS methods for stable chlorine isotope analysis of acetochlor and Smetolachlor were recently developed by Ponsin et al 45 However, two of the working standards show a chlorine isotope value larger than 0 ‰ (δ 37 Cl Aceto2 = 18.54 ± 0.20 ‰ and δ 37 Cl Metola2 = 5.12 ± 0.27 ‰). Therefore, future work has to strive for synthesis routes to generate AgCl in-house standards with a more positive chlorine isotope value that would optimize the characterization process of secondary inhouse working standards even further.…”