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

Capillary electrophoresis-mass spectrometry often lacks sufficient limits of detection for trace substances in the environment due to its low loadability. To overcome this problem, we conducted a feasibility study for column-coupling isotachophoresis to capillary electrophoresis-mass spectrometry. The first dimension isotachophoresis preconcentrated the analytes. The column-coupling of both dimensions was achieved by a hybrid capillary microfluidic chip setup. Reliable analyte transfer by voltage switching was enabled by an in-chip capacitively coupled contactless conductivity detector placed around the channel of the common section between two T-shaped crossings in the chip connecting both dimensions. This eliminated the need to calculate the moment of analyte transfer. A commercial capillary electrophoresis-mass spectrometry instrument with easily installable adaptations operated the setup. Prior to coupling isotachophoresis with capillary zone electrophoresis-mass spectrometry, both dimensions were optimized individually by simulations and verified experimentally. Both dimensions were able to stack/separate all degradation products of glyphosate, the most important herbicide applied worldwide. The first dimension isotachophoresis also removed phosphate, which is a critical matrix component in many environmental samples. Enrichment and separation of glyphosate and its main degradation product aminomethylphosphonic acid by the two-dimensional setup provided an excellent limit of detection of 150 pM (25 ng/L) for glyphosate.

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 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.

Advancements in capacitance-to-digital converter-based C4 D technology for detection in capillary electrophoresis using amplified excitation voltages and comparison to classical and open-source C4 Ds.

This work introduces new hardware configurations for a capacitively coupled contactless conductivity detector (C4 D) based on capacitance-to-digital conversion (CDC) technology for CE. The aim was to improve sensitivity, handling, price, and portability of CDC-based C4 D detectors (CDCD) to reach LODs similar to classic C4 Ds with more sophisticated electric circuits. To achieve this, a systematic study on the CDCDs was carried out including a direct comparison to already established C4 D setups. Instrumental setups differing in electrode lengths, measurement modes, and amplification of excitation voltages were investigated to achieve LODs for alkali metal ions of 4 to 12 µM, similar to LODs obtained by classic C4 D setups. Lowest LODs were achieved for a setup with two 10 mm electrodes at a distance of 0.2 mm and an excitation voltage of 24 V. The detection head was exceptionally lightweight with only 2.6 g and covered only 20 mm of the capillary on total. This allowed the use of multiple detectors along the separation path to enable spatial tracking of analytes during separation. The entirely battery-powered detector assembly weighs less than 200 g, and the data are transmitted wirelessly for possible portable applications. The freely accessible hardware and software were optimized for fully automated measurements with real time data plotting and allowed handling multidetector setups. The new developments were applied to quantify the potassium salt of glyphosate in its herbicide formulation.