Challenges in direct determination of Glyphosate and aminomethylphosphonic acid in water by liquid chromatography-tandem mass spectrometry at modified reverse phase columns: Effect of matrix interferences in fresh and hard water systems.

This study validated two underivatized methods (M1 and M2) according to the Eurachem guidelines to analyze the herbicide Glyphosate and its major metabolite aminomethylphosphonic acid simultaneously by liquid chromatography-tandem mass spectrometry in both fresh and hard waters. Samples were analyzed directly after filtration through 0.22 μm syringe filters in M1, while samples were acidified with acetic acid before filtration in M2. Spike recoveries were greater than 80% for Glyphosate and aminomethylphosphonic acid in both methods. The limit of quantitation was 0.5 μg/L for M1, and 0.1 μg/L for M2 by using matrix-matched calibrations. The linear regression coefficient of both methods was greater than 0.995. The expanded uncertainty was found to be less than 25% for both. Moreover, M1 has an additional mass spectral confirmation ability, and the column and the mobile phase used in M2 can be used to analyze the inert surfactant used in Glyphosate formulations, Polyethoxylated tallow amine. The accuracy of the developed methods was assured by participating in a proficiency testing program against M2 and conducting the t-test for results generated by both M1 and M2. Both methods, therefore, can be used to determine Glyphosate and aminomethylphosphonic acid content concurrently in fresh and hard waters.