Capillary electrophoresis applied for the determination of acidity constants and limiting electrophoretic mobilities of ionizable herbicides including glyphosate and its metabolites and for their simultaneous separation

Abstract

Thermodynamic acidity constants and limiting ionic mobilities were determined for polyprotic non‐chromophore analytes using capillary electrophoresis with capacitively coupled contactless conductivity detection. It was not necessary to work with buffers of identical ionic strength as ionic strength effects on effective electrophoretic mobilities were corrected by modeling during data evaluation (software AnglerFish). The mobility data from capillary electrophoresis coupled to conductivity detection were determined in the pH range from 1.25 to 12.02 with a high resolution (36 pH steps). With this strategy, thermodynamic acidity constants and limiting ionic mobilities for various acidic herbicides were determined, sometimes for the first time. The model analytes included glyphosate, its metabolites, and its acetylated derivates (aminomethyl phosphonic acid, glyoxylic acid, sarcosine, glycine, N‐acetyl glyphosate, N‐acetyl aminomethyl phosphonic acid, hydroxymethyl phosphonic acid). The obtained data were used in simulations to optimize separations by capillary electrophoresis. Simulations correlated very well to experimental results. With the new method, the separation of glyphosate from interfering components like phosphate in beer samples was possible.

Picomolar detection limits for glyphosate by two‐dimensional column‐coupled isotachophoresis/capillary zone electrophoresis‐mass spectrometry

“…As predicted by simulations, see Figure 2A, a BGE with a pH of 10.2 allowed a baseline separation of all analytes by CZE-MS, especially of GLP and its two main metabolites AMPA and SAR (see also discussion in [43]), compare Figure 2B. Due to insufficient ionization efficiency in the ESI process, glyoxylic acid was not detected.…”

“…Due to insufficient ionization efficiency in the ESI process, glyoxylic acid was not detected. Separations at lower pH values were discarded due to insufficient robustness to small pH changes, especially for SAR and glycine, see [43]. The relatively high effective electrophoretic mobility of the slowest target ion SAR also simplified the search for a suitable terminating ion in the first-dimension ITP.…”

“…To optimize the separation conditions, the pK A values and limiting electrophoretic mobilities for GLP and its metabolites were used to simulate optimal separation conditions for CZE-MS [43]. A focus was set on simultaneously removing phosphate as the most critical matrix component, which we intended to exclude from the ITP stack [49,50].…”

“…The lack of a chromophoric system and their high charge and polarity make them difficult to be analyzed by chromatographic methods. In addition to GLP, we also included its metabolites in this study (for analyte selection, see [43]) to demonstrate the broad applicability of the ITP method.…”

Determination of Glyphosate, Glufosinate, and Their Major Metabolites in Tea Infusions by Dual-Channel Capillary Electrophoresis following Solid-Phase Extraction

“…However, the analytical procedures in these works have only been illustrated for the relatively simple matrix of tap water and are difficult to apply to more complex samples. Another study used the software to determine thermodynamic acidity constants and limit ionic mobilities of glyphosate and its metabolites and application in the separation of glyphosate [41]. Regardless, GLUF and MPPA were not the targets of that work.…”