Improved GC‐MS/MS Method for Determination of Atrazine and Its Chlorinated Metabolites in Forage Plants—Laboratory and Field Experiments

Abstract

Analytical procedures using gas chromatography–ion trap tandem mass spectrometry (GC‐MS/MS) were developed to analyze atrazine (ATR) and its dealkylated metabolites in four forage species (switchgrass, tall fescue, smooth bromegrass, and orchardgrass). Atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) were extracted with methanol (CH₃OH) followed by liquid–liquid extraction and partitioning into chloroform, with additional cleanup by C₁₈ solid‐phase extraction (SPE). Through the optimization of ionization conditions and ion storage voltages, the background noise of product ion spectra (MS/MS) was reduced dramatically, providing sub‐µg/kg detection limits. Mean recoveries of ATR, DEA, and DIA were 94.3, 105.6, and 113.1%, respectively. The estimated limit of detection (LOD) was 0.6 µg/kg for ATR, 1.3 µg/kg for DEA, and 0.3 µg/kg for DIA. These LODs were one to two orders of magnitude lower than those reported for other GC‐MS, GC‐MS/MS, high pressure liquid chromatography (HPLC)‐UV, or HPLC‐MS/MS procedures designed for food‐safety monitoring purposes. To validate the developed method, a field experiment was carried out utilizing three replications of four forage treatments (orchardgrass, tall fescue, smooth bromegrass, and switchgrass). Forage plants were sampled for analyses 25 days after atrazine application. DEA concentrations in C3 grasses ranged from 47 to 96 µg/kg, about 10‐fold higher than in switchgrass, a C4 species. The ATR and DIA concentrations were similar, ranging from 1.5 to 13.2 µg/kg. The developed method provided sufficient sensitivity to determine the fate of ATR and its chlorinated metabolites via plant uptake from soil or dealkylation within living forage grasses. It also represented significant improvements in sensitivity compared to previous GC methods.

Keywords:

• DEA
• DIA
• gas chromatography
• ion trap
• metabolites
• tandem mass spectrometry
• triazine herbicide

Acknowledgment

The authors thank Joe Absheer for his assistance throughout the study. The authors also thank the Center for Agroforestry at University of Missouri for funding this work. This work was funded through the University of Missouri Center for Agroforestry under cooperative agreement 58‐6227‐1‐004 with the ARS. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. Mention of specific companies, products, or trade names is made only to provide information to the reader and does not constitute endorsement by the USDA Agricultural Research Service.