Quantification of glyphosate and AMPA by HPLC-ICP-MS/MS

Figure: glyphosate

Glyphosate (N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. For many years it was considered toxicologically and environmentally safe, which resulted in a considerable increase in agricultural applications, becoming the most widely adopted herbicide in the world. However, in recent years, this increase has raised doubts and concerns about its increasing use, which in the long run may lead to undesirable impacts on the environment and human health. In 2015, the International Agency for Research on Cancer (IARC) classified glyphosate as a probable carcinogen to humans.

This situation has fuelled many studies with glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), to investigate and develop simple, sensitive and efficient methods for extraction and detection of these compounds in several environmental and biological matrices such as water, soil, fruits, vegetables or body fluids. Unfortunately, chemical properties of glyphosate and AMPA such as high polarity, low solubility in organic solvents, absence of chromophore groups and low volatility make their separation and detection processes laborious. To increase the selectivity and sensitivity, an additional derivatization step is necessary to detect these compounds through spectroscopic techniques (conventional methods).

A group of Brazilian researchers have compared the conventional method of analysis (HPLC-DAD including derivatization) with detection by ICP-MS/MS. The ICP-MS/MS has been used to determine the phosphorus in the glyphosate and AMPA molecules, whereby the MS/MS mode eliminates interferences from the matrix, thereby increasing the technique’s detection power. The detection is based on oxygen-induced mass shift to ³¹O¹⁶O⁺. HPLC separation was based on a ZORBAX SB-C8 column (4.6 × 150 mm, 5 μm) and a mobile phase of 50 mM acetic acid/ammonium acetate + 5 mM tetrabutylammonium + 1% methanol, pH = 4.7. The HPLC-ICP-MS/MS methodology was applied to determine glyphosate and AMPA in water samples from Turmalina city, Minas Gerais, Brazil and included samples from artesian wells, dams, water springs and cisterns.

Both methods demonstrated adequate selectivity, but the chromatographic analysis using ICP-MS/MS as detector was four times faster than DAD. Detection by ICP-MS/MS was linear from 27 to 218 μg L-1, while by the conventional DAD method it was 1 to 8 mg L-1. Detection limits of the glyphosate achieved with the HPLC-ICP-MS/MS and HPLC-DAD methods were 8.2 and 300 μg L-1, respectively. The direct determination using ICP-MS/MS as detector showed a lower number of stages in sample preparation because it did not need the derivatization step. Seven real samples were analysed by HPLC‑ICP‑MS/MS and despite the improved detection power, the results showed that these analytes were not detected. Unfortunately, the obtained detection power was not adequate for real water samples and also did not reach the level obtained by other researchers using similar techniques (see Lajin and Goessler) by exploiting the carbon enhancement effect.

Emanuella M. Pimenta, Fabio F. da Silva, Érica S. Barbosa, Ane P. Cacique, Douglas L. Cassimiro, Gevany P. de Pinhoa, Flaviano O. Silvério, Quantification of Glyphosate and AMPA by HPLC-ICP-MS/MS and HPLC-DAD: A Comparative Study, J. Braz. Chem. Soc., 31/2 (2020) 298-304. DOI: 10.21577/0103-5053.20190175

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