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.

Thermodynamic acidity constants and limiting ionic mobilities were determined for polyprotic non-chromophore analytes using CE 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 CE 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 (aminomethylphosphonic acid, glyoxylic acid, sarcosine, glycine, N-acetyl glyphosate, N-acetyl aminomethylphosphonic acid, hydroxymethyl phosphonic acid). The obtained data were used in simulations to optimize separations by CE. 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. This article is protected by copyright. All rights reserved.