Advancements in capacitance‐to‐digital converter‐based C⁴D technology for detection in capillary electrophoresis using amplified excitation voltages and comparison to classical and open‐source C⁴Ds

Abstract

This work introduces new hardware configurations for a capacitively coupled contactless conductivity detector (C 4 D) based on capacitance-to-digital conversion (CDC) technology for CE. The aim was to improve sensitivity, handling, price, and portability of CDC-based C 4 D detectors (CDCD) to reach LODs similar to classic C 4 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 C 4 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 C 4 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.

A compact and high-performance setup of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D)

“…eDAQ, TraceDec and Admet) can be installed in instruments, including CE devices from different manufacturers. 27 In addition, some compact versions of the C 4 D cell, 26 even those that integrate an oscillator, detection cell, and detection circuitry on a printed circuit board (PCB), [42][43][44][45][46][47] have been reported.…”

“…Many methods for CE-C 4 D instrument development have been proposed, such as high-voltage excitation, 10,48 rectifiercircuit-based detection, 1,47,49,50 RMS-to-DC (root mean square AC voltage signal to DC voltage signal) detection, 10,51 lock-in detection, 48,52 differential detection, 43,[53][54][55][56][57][58][59] high-resolution analog-to-digital converter (ADC) acquisition, 47,51,60 resonant C 4 D design, 55,61,62 and capacitance-to-digital converter (CDC) detection. [42][43][44][45] While these initiatives provide valuable reference points, typical limits of detection (LODs) for common inorganic ions currently range from 0.3 to 1 μM without preconcentration, 45,47,[63][64][65] and this sensitivity is often insufficient for the analysis of analytes at trace levels (e.g. 1 ppb or 20 nM level).…”

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

“…The in‐chip C 4 D used the electronics and software developed by Graf et al. [54] in the configuration with a preamplifier. The display data were smoothed by a ten‐point moving average function.…”

“…The optimization of the CZE and ITP was performed by simulations with the software PeakMaster [55] and Spresso [56] using the p K A and mobility data we published previously [54]. The EOF in CZE simulations was estimated from the EOF mobility in bare fused silica capillaries.…”

Pushing the Limits of Capacitively Coupled Contactless Conductivity Detection for Capillary Electrophoresis

“…While several articles elucidate the fundamental principles of C 4 D − , and numerous reviews highlight the applications of CE-C 4 D primarily in pharmaceutical, clinical, food, and environmental analyses, − CE-C 4 D offers several advantages, including cost-effectiveness, nanoliter injection volume, short analysis time, good separation efficiency, suitability for miniaturization, and portability. Commercial C 4 D products, such as eDAQ, TraceDec and Admet, have been integrated into a couple of CE apparatuses, while some specially designed compact CE-C 4 D devices accommodate the self-built circuitry of C 4 D in their detection cells. − Various ways for improving the performance of CE-C 4 D have been proposed, typical examples include high voltage excitation, , rectifier, − the root-mean-square of an AC signal to DC signal (RMS-to-DC) conversion, , lock-in, , differential, − high resolution analog-to-digital conversion (ADC), ,, resonance, ,, and capacitance to digital conversion (CDC) based detections. ,− These initiatives are effective, while for common inorganic ions, the typical limits of detection (LODs) are currently range from 0.3 to 1 μM without preconcentration. ,,− For analyzing trace analytes (e.g., 1 ppb or 20 nM level), this sensitivity is not enough. Therefore, there exists a high desire to further improve the detection limits of the CE-C 4 D method.…”