Trimethylation enhancement using diazomethane (TrEnDi) enables enhanced detection of glufosinate and 3-(methylphosphinico)propionic acid from complex canola samples

Over the past century, agriculture practices have transitioned from manual cultivation to the use of chemical herbicides for improved crop yields. The most common weedkiller glyphosate (GLY) has been used exponentially worldwide, leading to the emergence of GLY-resistant weeds. This has prompted a need for effective alternatives, leading to the development and increasing use of phosphinothricin, also known as glufosinate (GLUF). As the agricultural application of GLUF rises, the potential for long-term residual exposure in the food chain increases, highlighting the need for improved analytical strategies for its detection, as well as its main breakdown product 3-(methylphosphinico)propionic acid (MPPA). Chemical derivatization strategies have been developed to improve the detection of GLUF and MPPA via liquid chromatography tandem mass spectrometry (LCMS) analyses. In this article, we expand the use of trimethylation enhancement using diazomethane (TrEnDi) to quantitatively derivatize these analytes into permethylated GLUF ([GLUFTr]+) and MPPA ([MPPATr+H]+). Comparing [GLUFTr]+ and [MPPATr+H]+ to underivatized counterparts, TrEnDi yields 2.8-fold and 1.7-fold improvements in reversed-phase chromatographic retention, respectively, while MS-based sensitivity is enhanced 4.1-fold and 11.0-fold, respectively. Initial analytical improvements were performed on commercial standards; however, successful analyte derivatization (with >99% yields) was also demonstrated on a commercial herbicide solution imparting consistent analytical enhancements. To investigate the benefits of TrEnDi in a bona fide agricultural scenario, the quantities of GLUF and MPPA were determined in aqueous extracts from field-grown canola plants before and after TrEnDi derivatization. In their underivatized forms, GLUF and MPPA were undetectable in all field samples whereas [GLUFTr]+ and [MPPATr+H]+ were readily quantifiable using the same analysis conditions. Our results demonstrate that TrEnDi continues to be a useful tool to enhance the analytical characteristics of organic molecules that are traditionally difficult to detect.