Extraction and determination of Glyphosate, Glufosinate and their major metabolites in soil and water

Abstract

Introduction: A new method for separation and determination of Glyphosate and Glufosinate alongside their respective major metabolites aminomethylphosphonic acid and 3-(methylphosphinico)propionic acid was found then tested in spiked soil and surface water.

Background: Most methods today require derivatization for determination and separation of these compounds. Methods without derivatization rely on expensive mass spectrometers for determination.

Aim(s): Use a hydrophilic interaction column for achieving separation without derivatization and test an evaporative light scattering detector for determination. Pre-concentration also tested and optimized.

Methods: Traditional one variable at a time approach was used for optimizing the pre-concentration and detector, while design of experiments software was used for optimizing the separation (using UPLC). The traditional method was used for maximizing (in most cases) peak areas and recoveries. The software design was used for checking interactions between mobile phase pH, buffer concentration and water percentage, in addition to optimization of these parameters. For this two responses was used with one being the number of peaks and the other being the retention time of the second analyte.

Results: Optimization was done and interactions (and lack of) between variables found. Lack of proper clean-up for the real-world samples resulted in aminomethylphosphonic acid being impossible to detect in either matrix. These impurites were likely non-charged compounds. Glyphosate was only detected in the surface water sample with a LOQ close to legal limits. 3-(methylphosphinico)propionic acid and Glufosinate were well separated and detectable in both matrixes.

Conclusion: The evaporative light scattering detector can detect all the analytes. For real samples there needs to be better clean-up. An interaction that was ignored in the DoE model between formic acid and the buffer ammonium formate needs to be studied in future work.

Popular Abstract

Glyphosate, aminomethylphosphonic acid (AMPA), Glufosinate and 3-(methylphosphinico)propionic acid (3-MPPA) are substances that accumulate in soil as a result of using certain herbicides containing Glyphosate and Glufosinate (the other two are their respective breakdown products). Not only that but these are also amongst the most used herbicides globally. Modifying and improving already existing methods is a staple of analytical chemistry and its partly what i’m doing here alongside some novel studies. Although there are studies for some combinations of the four analytes in soil using similar methods to mine, there are none with all four simply because it has not been done yet.

In this study a less typically used way of detecting them was used. These Evaporative Light Scattering Detectors (ELSD) are a good choise for analytes like mine that do not respond to much more common methods of detection. They are also very inexpensive compared to the mass spectrometry detectors commonly used in methods similar to the one in this study. To separate the compounds and thus be able to individually detect them a special technique (column) intended for very water-soluble compounds was used. These hydrophilic interaction liquid chromatography (HILIC) columns have additional benefits.

An additional goal was to achieve this method without chemically modifying the analytes during analysis (derivatization) as it saves time, money and is more environmentally sustainable. It also has the benefit of reducing errors as is allways the case when reducing steps in any method. Usually, derivatization is required for these substances due to their properties making analysis difficult, particularly at the usual very low amounts they are found in contaminated soil and water. While underivatized separation is difficult with common columns like C18 and these derivatizations are primarily done to enhance detection, it also makes separation possible on those common columns. One benefit of HILIC columns is that derivatization can be skipped. ELSD should in theory (and as found in the study) respond to all the analytes.

The results were that this method can be used for Glufosinate and 3-MPPA, with difficulties for Glyphosate. For AMPA its currently unusable until a method of removing certain impurities is found in future work.

• author: Shahne, Daniel
• supervisor: Mahdi Khataei
• organization: Department of Chemistry
• course: KEML10 20211
• year: 2021
• type: M2 - Bachelor Degree
• subject: Chemistry
• keywords: Glyphosate, herbicides, extraction, zwitterionic, hydrophilic interaction liquid chromatography, analytical chemistry
• language: English
• id: 9057947
• date added to LUP: 2021-06-28 15:59:25
• date last changed: 2021-06-28 15:59:25