Determination of glyphosate herbicide and aminomethylphosphonic acid in natural waters by liquid chromatography using pre-column fluorogenic labeling. Part I: Direct determination at the 0.1 μg/L level using FMOC

Abstract

A substantial number of pesticides are still very difficult to analyse in water at the 0.10 µg/L level, the maximum allowable concentration for the quality of water intended for human consumption set by the European Union. Among them are the widely used polar non-selective glyphosate herbicide and its major degradation product AMPA.Several chromatographic methods have been developed for the analysis of glyphosate and AMPA. Methods involving liquid chromatography seem to give better results since glyphosate and AMPA are very polar compounds. The nature of chromatographic phase depends on the detection mode selected. For instance, ionic phases are combined with conductimetric detection [1], mass spectrometry detection [2,3], UV or fluorescence after post-column derivatization with OPA [4], ninhydrin [5,6,7] or Al 3+ -morin reagent [8]. With a precolumn derivatization with 9-fluorenylmethylchloroformate (FMOC-Cl) for instance, reversed phase column may be used before fluorescence or UV detection.A pre-concentration of sample is necessary to reach the limit of quantification of 0.10 µg/L. Without any pre-concentration, the best performances were obtained by LC-MS analysis with a limit of detection (L. The aim of this study was to reach a limit of quantification lower than 0.10 µg/L without any pre-concentration or purification of samples before analysis. The work was oriented along two ways:1. Improvement of a published method involving LCFluorescence analysis after pre-column FMOC derivatization for direct determination of glyphosate and AMPA in water samples at the 0.10 µg/L level that is suitable for monitoring purposes (part I). This choice is explained below.2. Development of a new method based on derivatization of glyphosate and AMPA with fluorogenic reagents. The first results of this work are presented in part II with 4-chloro-7-nitrobenzofurazan reagent.Among the methods described in literature for the analysis of glyphosate and AMPA in water by liquid chromatography, the way of pre-column derivatization along with fluorescence detection was selected because its easy use. Few coupling reagents have been tested: dansyl chloride [10], ptoluenesulfonyl chloride [11,12] Abstract. An analytical method has been developed for the determination of glyphosate herbicide and its metabolite aminomethylphosphonic acid (AMPA) in natural waters to a level of 0.10 µg/L with a good linearity in the range 0.10-2.00 µg/L and coefficients of variation under 20 % for each spiked level. The procedure involves a precolumn derivatization step with 9-fluorenylmethylchloroformate (FMOC-Cl) yielding highly fluorescent derivatives of the analytes which then can be determined by HPLC with fluorescence detection. The method is used for analysis of natural (surface and ground) and treated waters. Matrice effects have been pointed out, particularly the effects of hard ionic content and the effects of chlorine residues into treated waters.

Analysis of glyphosate and aminomethylphosphonic acid in water, plant materials and soil

“…For instance, the length of a C‐18 column had to be increased from 25 to 300 mm for separation of glyphosate and AMPA in soil extracts as compared with other matrices . In one case, in spite of the instability and rapid deterioration of the stationary phase, an NH 2 column was used because of problems using a C18 column . Using MS/MS detection eliminates some of the potential problems; adequate separation of glyphosate and AMPA has been obtained using only a 30–50 mm guard column, as compared with 150–300 mm length columns used with other detectors.…”

Novel Analytical Methodologies for the Monitoring of Traditional and Non-traditional Pollutants in different Environmental Compartments of South Florida

“…As presented in figure 2.11, the reaction was completed in 30 min and derivates were stable up to 480 min (8 h). These results are in agreement with observations from a previous work which found that complete derivatization occurred in 30 min and that the obtained derivates were stable for up to 2 days (Le Bot et al, 2002;Le Fur et al, 2000). Samples were injected between 2 to 4 hours after derivatization in the course of the present research.…”

“…The addition of the large size, non-polar FMOC moiety to glyphosate and AMPA makes the retention of these compounds in reverse-phase columns possible, using stationary phases such as C8 and C18. These are more resistant to hydrolysis and therefore last much longer than columns with amino moieties traditionally used in ion-exchange chromatography (Ibanez et al, 2005;Le Fur et al, 2000). These advantages have made FMOC-Cl the most frequently used reagent for derivatization of glyphosate and AMPA, despite some drawbacks such as the very favorable side reaction with water to produce a large excess of FMOC-OH.…”

“…Figure 2.8 Structure of aspartic acid and pK a values (Bastug et al, 2011 The problem was first recognized by Le Fur et al (2000), who reported significant signal degradation upon analyzing drinking waters with conductivities above 0.580 mS/cm. In a round robin study, Ibanez et al (2006) also reported that results were satisfactory except for laboratories dealing with groundwater analysis, where 15% was the best recovery reported, and attributed these results to impediment of the FMOC-Cl reaction caused by the formation of complexes with divalent cations.…”

“…However, the large quantity of the FMOC-OH reaction byproduct is retained by reverse phase columns and represents a potential source of interference for non-selective detectors such as the FLD. To resolve this challenge, some authors have used liquid-liquid extraction steps with diethyl ether to extract the byproduct before injection into the LC system (Le Bot et al, 2002;Le Fur et al, 2000). A more sophisticated approach was used by Hanke et al (2008), who used a SPE cartridge that combines a high affinity for polar compounds and the ability to withstand cleanup steps with dichloromethane, selectively removing the non-polar FMOC-OH before eluting the derivatized analytes with methanol.…”