Exploring the possibilities of capacitively coupled contactless conductivity detection in combination with liquid chromatography for the analysis of polar compounds using aminoglycosides as test case

A five-electrode capacitively coupled contactless conductivity detector with a low limit of detection

The conductivity detector is a broadly used device that allows for the highly efficient detection of analytes, and continuous efforts have been directed toward lowering the limit of detection. In this study, a five-electrode capacitively coupled contactless conductivity detector (TIC⁴D) is proposed, which uses copper mesh between the electrodes for a grounding shield to reduce the interference of stray capacitance and noise. After adding the copper mesh shield, the difference value between the response signal and baseline at low KCl concentration is effectively increased, achieving 33 mV for 10^-9 M KCl solution. Meanwhile, for the unshielded detector, the difference is only 18 mV for the KCl solution at the same concentration. The response signal shows a linear function of the logarithm at the range of 10^-4 M to 10^-5 M KCl solution, and the TIC⁴D detector displays a higher slope (0.8448) than the conventional single-input capacitively coupled contactless conductivity detector (C⁴D: 0.5579) and dual-input capacitively coupled contactless conductivity detectors (DIC⁴D: 0.6173). Moreover, two TIC⁴D detectors are combined to achieve a dual-channel six-input differential capacitively coupled contactless conductivity detector (SIDC⁴D), reducing the high baseline levels caused by the multi-signal input. By differentially amplifying the output signal, the high baseline levels and noise interference can be effectively reduced. For the 10^-3 M KCl solution, the ratio of the response signal to baseline for SIDC⁴D can reach 8.500, almost 7 times that of TIC⁴D, and a lower limit of detection (LOD) of 3 × 10^-10 M is also achieved. This work may open a new door based on coupled contactless conductivity for detection performance.

Thiol-ene Click Derivatization for the Determination of Acrylamide in Potato Products by Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

The development of analytical methods for acrylamide formed during food processing is of great significance for food safety, but limited by its inherent characteristics, the analysis of acrylamide is a continuing challenge. In this study, an efficient derivatization strategy for acrylamide based on thiol-ene click reaction with cysteine as derivatization reagent was proposed, and the resulting derivative was then analyzed by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D). After systematic investigation including catalyst dosage (0-20 mM), reaction temperature (30-90 °C) and time (1-60 min), and cysteine concentration (0.2-3.6 mM), acrylamide could be efficiently labeled by 2.0 mM cysteine at 70 °C for 10 min using 4 mM n-butylamine as catalyst. Application of 10 mM triethylamine as separation buffer, the labeled acrylamide was analyzed within 2.0 min, and the relative standard deviations of migration time and peak area were less than 0.84% and 5.6%, indicating good precision. The C⁴D signal of acrylamide derivative showed a good linear relationship with acrylamide concentration in the range of 7-200 μM with the correlation coefficient of 0.9991. The limit of detection and limit of quantification were calculated to be 0.16 μM and 0.52 μM, respectively. Assisted further by the QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample pretreatment, the developed derivatization strategy and subsequent CE-C⁴D method were successfully applied for the determination of acrylamide in potato products.

Rapid Detection of AGs using Microchip Capillary Electrophoresis Contactless Conductivity Detection

Background:

In order to realize current aminoglycosides supervision in food and environment, our team improved the sensitivity and separation efficiency of the portable ITO detector, based on the technology of microchip capillary electrophoresis and contactless conductivity detection.

Experiment:

Parameters (the separation voltage, buffer concentration, electrodes gap, elicitation frequency, elicitation voltage) were optimized for the detection of three aminoglycosides, gentamicin, kanamycin and streptomycin and the separation of their mixture in background electrolyte consists of 2-(N-Morpholino) ethanesulfonic acid (MES) and L-Histidine (His). The enhanced method was also applied to other types of aminoglycosides.

Results:

Under optimal conditions, the monitoring of three types of aminoglycosides obtained such a sensitive response that the limits of detection of gentamicin sulfate, kanamycin sulfate and streptomycin sulfate were calculated as 3.1 µg/ml, 0.89 µg/ml and 0.96 µg/ml, at signal-to-noise ratio 3, respectively. In addition they got separated completely from each other only in 40 s. The results of other varieties of aminoglycosides including tobramycin sulfate and amikacin sulfate also met the standard.

Conclusion:

We successfully proposed here an unprecedentedly portable, miniaturized and rapid microchip capillary electrophoresis contactless conductivity detection system to realize current aminoglycosides supervision in food and environment.