Capacitively Coupled Contactless Conductivity Detection Research Articles

Rapid Detection of Soil Available Phosphorus using Capacitively Coupled Contactless Conductivity Detection

Background: In China, the traditional method for analyzing soil available phospho-rus is inadequate for large-scale soil assessment and nationwide soil formulation demands. To address this, we propose a rapid and reliable method for soil-available phosphorus detection. The setup includes an on-site rapid pre-treatment device, a non-contact conductivity detection device, and a capillary electrophoresis buffer solution system composed of glacial acetic acid and hydroxypropyl-β-cyclodextrin. Methods: The on-site rapid pre-treatment process includes fresh soil moisture content detec-tion (moisture rapid detector), weighing (handheld weighing meter), stirring (handheld rapid stirrer), and filtration (soil rapid filter) to obtain the liquid sample, and direct injection (capil-lary electrophoresis detector). The phosphate ion detection parameters include capillary size, separation voltage, injection parameters, and electric injection. We used Liaoning brown soil, Henan yellow tidal soil, Heilongjiang black soil, and Anhui tidal soil as standard samples. Additionally, we used mathematical modeling methods and machine learning algorithms to analyze and process research data. Results and Conclusion: Following calibration with standard samples, the experimental blind test samples demonstrated conformity with the national standard method, exhibiting a relative standard deviation of less than 3%. The proposed pre-treatment device and non-contact con-ductivity detector are powered by lithium-ion batteries, rendering them ideal for extended field operations. The non-contact conductivity detector obviates the need for direct contact with test samples, mitigating environmental pollution. Furthermore, the neural network model exhibited the highest level of goodness of fit in chemical data analysis.

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

Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) has proven to be an efficient technique for the separation and detection of charged inorganic, organic, and biochemical analytes. It offers several advantages, including cost-effectiveness, nanoliter injection volume, short analysis time, good separation efficiency, suitability for miniaturization, and portability. However, the routine determination of common inorganic cations (NH4+, K+, Na+, Ca2+, Mg2+, and Li+) and inorganic anions (F-, Cl-, Br-, NO2-, NO3-, PO43-, and SO42-) in water quality monitoring typically exhibits limits of detection of about 0.3-1 μM without preconcentration. This sensitivity often proves insufficient for the applications of CE-C4D in trace analysis situations. Here, we explore methods to push the detection limits of CE-C4D through a comprehensive consideration of signal and noise sources. In particular, we (i) studied the model of C4D and its guiding roles in C4D and CE-C4D, (ii) optimized the bandwidth and noise performance of the current-to-voltage (I-V) converter, and (iii) reduced the noise level due to the strong background signal of the background electrolyte by adaptive differential detection. We characterized the system with Li+; the 3-fold signal-to-noise (S/N) detection limit for Li+ was determined at 20 nM, with a linear range spanning from 60 nM to 1.6 mM. Moreover, the optimized CE-C4D method was applied to the analysis of common mixed inorganic cations (K+, Na+, Ca2+, Mg2+, and Li+), anions (F-, Cl-, Br-, NO2-, NO3-, PO43-, and SO42-), toxic halides (BrO3-) and heavy metal ions (Pb2+, Cd2+, Cr3+, Co2+, Ni2+, Zn2+, and Cu2+) at trace concentrations of 200 nM. All electropherograms showed good S/N ratios, thus proving its applicability and accuracy. Our results have shown that the developed CE-C4D method is feasible for trace ion analysis in water quality control.

Numerical-Simulation-Based Buffer Design for Microchip Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

Numerical-Simulation-Based Buffer Design for Microchip Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

Compact contactless conductometric, ultraviolet photometric and dual-detection cells for capillary electrophoresis via additive manufacturing

The growing demand for tailored detectors in capillary electrophoresis (CE), addressing tasks like field deployment or dual-detection analysis, emphasizes the necessity for compact detection cells. In this work, we propose cost-effective and user-friendly additive manufacturing (3D-printing) approaches to produce such miniaturized detection cells suitable for a range of CE applications. Firstly, capacitively-coupled contactless conductivity detection (C4D) cells of different sizes are fabricated by casting low-melting-point alloy into 3D-printed molds. Various designs of Faraday shields are integrated within the cells and compared. A mini-C4D cell (9.5×7.0×7.5 mm3) is produced, with limits of detection for alkaline cations ranging from 8-12 μM in a short–capillary based CE application. Secondly, ultraviolet photometric (UV-PD) detection cells are fabricated using 3D printing. These cells feature two narrow slits with a width of 60 μm, which are positioned along the path of incident and transmission light to facilitate collimation. A deep UV-LED (235 nm or 255 nm) is employed as the light source, and black resin is determined to be the optimal material for 3D printing the UV-PD cell, owing to its superior UV light absorption capabilities. The UV-PD cell is connected to the LED and photodetector through two optical fibers, making it easy to switch the light source and detector. The effective pathlength and stray light percentage for detecting on a 75 μm id capillary are 74 μm and 0.5 %, respectively. Thirdly, a dual-detection cell that combined C4D and UV-PD at a single detection point is proposed. The performance of direct detection by C4D and indirect detection by UV-PD is compared for detecting organic acids. The strategies for developing cost-effective compact detection cells facilitate the versatile integration of multiple detection methods in CE analysis.

Green Analytical Method for Simultaneous Determination of Glucosamine and Calcium in Dietary Supplements by Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection.

The need for analytical methods that are fast, affordable, and ecologically friendly is expanding. Because of its low solvent consumption, minimal waste production, and speedy analysis, capillary electrophoresis is considered a "green" choice among analytical separation methods. With these "green" features, we have utilized the capillary electrophoresis method with capacitively coupled contactless conductivity detection (CE-C4D) to simultaneously determine glucosamine and Ca2+ in dietary supplements. The CE analysis was performed in fused silica capillaries (50 μm inner diameter, 40 cm total length, 30 cm effective length), and the analytical time was around 5 min. After optimization, the CE conditions for selective determination of glucosamine and Ca2+ were obtained, including a 10 mM tris (hydroxymethyl) aminomethane/acetic acid (Tris/Ace) buffer of pH 5.0 as the background electrolyte; separation voltage of 20 kV; and hydrodynamic injection (siphoning) at 25 cm height for 30 s. The method illustrated good linearity over the concentration range of 5.00 to 200 mg/L of for glucosamine (R 2 = 0.9994) and 1.00 to 100 mg/L for Ca2+ (R 2 = 0.9994). Under the optimum conditions, the detection limit of glucosamine was 1.00 mg/L, while that of Ca2+ was 0.05 mg/L. The validated method successfully analyzed glucosamine and Ca2+ in seven dietary supplement samples. The measured concentrations were generally in line with the values of label claims and with cross-checking data from reference methods (HPLC and ICP-OES).

Partition Management of Soil Nutrients Based on Capacitive Coupled Contactless Conductivity Detection

A method based on capacitively coupled contactless conductivity detection (C4D), which has been proven effective for the rapid detection of available soil potassium content, was firstly proposed to apply to soil nutrient detection. By combining a detection signal spectrum analysis, geographic information system (GIS) data, and a cluster analysis, a soil nutrient management system to match the detection device was developed. This system included six modules: soil sample information management, electrophoresis analysis, quantitative calculation, nutrient result viewing, cluster analysis, and nutrient distribution map generation. The soil samples, which were collected from an experimental field in Xuchang City of Henan Province, were analyzed using the C4D and flame photometer methods. The results showed that the detection results for the soil samples obtained via the two methods were in good agreement. C4D technology was feasible for the detection of the soil available nutrients and had the advantages of a high timeliness, low sample volume, and low pollution. The soil nutrient management system adopted the hierarchical clustering method to classify the grid cells of the experimental field according to the nutrient detection results. A soil nutrient distribution map displayed the spatial difference in nutrients. This paper provides a systematic solution for soil nutrient zone management that includes nutrient detection, signal analysis, data management for the nutrient zone, and field nutrient distribution map generation to support decision making in variable fertilization.

Fast and Environmentally Friendly Method for Simultaneous Determination of Hydrochlorothiazide, Losartan and Potassium by Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

Losartan potassium and hydrochlorothiazide are often combined in pharmaceutical formulations for the treatment of hypertension. Therefore, the determination of these compounds in a single run is highly desirable for rapid quality control applications. The present study describes an ultra-fast (ca. 85 injections h−1) and environmentally friendly method based on capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection for simultaneous quantification of potassium, losartan and hydrochlorothiazide. Cation (potassium) and anions (losartan and hydrochlorothiazide) were analyzed in a single run using a background electrolyte composed by 10.0 mmol L-1 boric acid (pH = 9.0, adjusted with sodium hydroxide). The limits of detection were 4.0, 3.0 and 10.0 μmol L-1 for potassium, losartan and hydrochlorothiazide, respectively. The proposed method is simple, fast, with minimal waste generation, and accurate (recovery values between 98 and 102%). The results obtained with the CE method were statistically similar (95% confidence level) to those obtained by high-performance liquid chromatography (losartan and hydrochlorothiazide) and flame photometry (potassium).

Using Multi-Material Fused Deposition Modeling (Fdm) for One-Step 3d Printing of a Microfluidic Capillary Electrophoresis Device with Integrated Electrodes for Capacitively Coupled Contactless Conductivity Detection

Using Multi-Material Fused Deposition Modeling (Fdm) for One-Step 3d Printing of a Microfluidic Capillary Electrophoresis Device with Integrated Electrodes for Capacitively Coupled Contactless Conductivity Detection

Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection for Quantitative Analysis of Dried Blood Spots with Unknown Blood Volume.

Blood volume in dried blood spot (DBS) analysis is assumed to be constant for DBS punches with a fixed area. However, blood volume in the punch is dependent on several factors associated with the blood composition and is preferentially normalized by off-line analysis for quantitative purposes. Instead of using external instrumentation, we present an all-in-one approach for the simultaneous determination of exact blood volume in the DBS punch and the quantitation of target analytes. A DBS is eluted with 500 μL of elution solvent in a sample vial, and the eluate is directly subjected to an automated analysis by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D). The capillary blood volume in the eluate is calculated from the concentrations of the inorganic blood constituents (K+, Na+, or Cl-) determined by CE-C4D, which are linearly proportional to the blood volume originally sampled onto the DBS card. Alternatively, conductivity of the DBS eluate can be used for the blood volume determination by using C4D in a nonseparation flow-through mode. The methods are suitable for the determination of blood volume in unknown DBS samples by punching out the entire DBS or by subpunching a small section of a large DBS with variations of the true vs the determined volume ≤5.5%. Practical suitability was demonstrated by the simultaneous CE-C4D determination of K+ and Na+ (for DBS volume calculation) and amino acids (target analytes) in unknown DBS samples. Quantitative analysis of selected amino acids (related to inborn metabolic disorders) in the unknown DBS was compared with a standard analytical procedure using wet-blood chemistry, and an excellent fit was obtained. The use of CE-C4D represents an important milestone in quantitative DBS analysis since the detection technique is universal, and the separation technique enables the determination of cations and/or anions and the use of multiple detectors, which further enhance selectivity/sensitivity of the analysis and the range of detectable analytes.

Development of a Passive Capacitively Coupled Contactless Conductivity Detection (PC4D) Sensor System for Fluidic Channel Analysis Toward Point-of-Care Applications

A sensor system based on a modified capacitively coupled contactless conductivity detection sensor is proposed and developed. The proposed system provides a passive and wireless readout technique, through which the conductivity of fluidic flow can be analyzed and foreign objects occurring in the fluidic flow can be detected. The proposed sensor system takes advantage of the series resonance principle and detects shifts in the resonance frequency and reflection coefficient to estimate the conductivity of the fluidic flow. In this paper, the working principle of the device is proposed and analyzed using a multiphysics simulation, and its performance is validated experimentally. The sensing performance is confirmed by measuring the conductivity of the fluidic media and the detection of foreign objects, such as air bubbles or water droplets, occurring in the flow. The influence of the distance between the inductors on the resonance frequency for different solution conductivities is also investigated and reported. The proposed sensor system shows its potential for use in various applications in biomedicine and chemistry, particularly in point-of-care applications, where the sensing chip can be easily set up for measurement and disposed of after use.

Development and Validation of a CE Method for the Determination of Tetracyclines with Capacitively Coupled Contactless Conductivity Detection

In this study, a simple and robust capillary electrophoresis method with capacitively coupled contactless conductivity detection (C4D) is developed for the determination of the tetracycline antibiotics (1) tetracycline, (2) chlortetracycline and (3) oxytetracycline. An uncoated, fused silica capillary (60.2 cm long, 75 µm i.d.) and a solution of 50 mM tris(hydroxymethyl) aminomethane, 50 mM l-histidine and 5 mM methyl-β-cyclodextrin, without pH adjustment (pH 8.76), was used as background electrolyte. Electrophoresis at + 25 kV showed a rapid analysis with sufficient resolution among the three antibiotics in the order of tetracycline, chlortetracycline and oxytetracycline. Successive inter-injection rinsing (20 psi) of the capillary ensured intra- and inter-day repeatability (0.9–2.2% RSD and 2.0–4.5% RSD, respectively, for relative peak areas). The method showed satisfactory performance in terms of selectivity, accuracy (99.3–101.4%) and linearity (R2 = 0.999). Finally, the method was applied to commercial samples of tetracycline, oxytetracycline and chlortetracycline. This method can be applied for rapid quality control in developing countries in particular, and across the globe in general.

Method Validation for Determination of Metformin Hydrochloride in Pharmaceutical Formulations by Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

A method for the determination of metformin hydrochloride (MH) in pharmaceutical formulations by capillary electrophoresis with capacitively coupled contactless conductivity (C4D) detection was investigated. The separation was achieved under normal polarity mode at 17.5°C, 30 kV, hydrodynamic injection (50 mbar for 8 s) and using a bare fused silica capillary 72 cm × 75 µm i.d. (detection length, 10.5 cm from the outlet end of the capillary). The optimized background electrolyte consisted of 10 mM 2-morpholinoethanesulfonic acid and 10 mM histidine, pH 6.8. C4D parameters were set at fixed amplitude of 100 V and frequency of 650 kHz. Under the optimum conditions, the method shows good linearity over the range of 10-30 µg mL-1 MH (r2=0.9971). Limits of detection and quantitation based on S/N ratio of 3 and 10 were 0.049 and 0.15 µg mL-1, respectively. The proposed method was successfully applied to the assay of MH in pharmaceutical formulations and establishing the dissolution profiles for both immediate and extended release formulations of MH.

Determination of Biogenic Amines in Seawater Using Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection.

A rapid and green analytical method based on capillary electrophoresis with capacitively coupled contactless conductivity detection (C4D) for the determination of eight environmental pollutants, the biogenic amines (putrescine, cadaverine, spermidine, spermine, tyramine, 2-phenylamine, histamine and tryptamine), is described. The separation was achieved under normal polarity mode at 24 °C and 25 kV with a hydrodynamic injection (50 mbar for 5 s) and using a bare fused-silica capillary (95 cm length × 50 µm i.d.) (detection length of 10.5 cm from the outlet end of the capillary). The optimized background electrolyte consisted of 400 mM malic acid. C4D parameters were set at a fixed amplitude (50 V) and frequency (600 kHz). Under the optimum conditions, the method exhibited good linearity over the range of 1.0–100 µg mL−1 (R2 ≥ 0.981). The limits of detection based on signal to noise (S/N) ratios of 3 and 10 were ≤0.029 µg mL−1. The method was used for the determination of seawater samples that were spiked with biogenic amines. Good recoveries (77–93%) were found.

Determination of topiramate by capillary electrophoresis with capacitively-coupled contactless conductivity detection: A powerful tool for therapeutic monitoring in epileptic patients.

Topiramate (TPM) is the main antiepileptic drug used for the control of partial and generalized seizures in both adults and children. In association with clinical observations, the analysis of plasmatic concentration of TPM is of utmost importance for the individual adjustment of the administered dose to the patient. In the present work, a bioanalytical method was developed and validated for TPM analysis in plasma samples by capillary electrophoresis with capacitively-coupled contactless conductivity detection (CE-C4 D). A simple background electrolyte composed of 15 mmol/L triethylamine, hydrodynamic injections (0.8 psi for 5 s) and a moderate separation voltage (20 kV) were used, rendering relatively short analysis times (<3 min). The sample pre-treatment was carried out by liquid-liquid extraction using methyl terc-butyl ether as solvent and 200 μL of plasma. The method was validated according to the official guidelines from the European Medicine Agency and showed linearity in plasmatic concentration range from 1 to 30μg/mL, which covers the clinically-relevant interval. The lower limit of quantification of 1 μg/mL obtained also allows following patients with low dosage of the drug. The method was successfully applied to analysis of plasma samples and allowed the identification of 80% under-medicated patients in the analyzed patient pool.

Improved C5D Electronic Realization of Conductivity Detector for Capillary Electrophoresis

The axial C4D (Capacitively Coupled Contactless Conductivity Detection) measurement electronics for capillary electrophoresis is considered and a new improved C5D compensated detection concept is proposed and tested. Using the idle compensation channel with inversed signal and immediate analogue summation of the active and idle channel currents yields effective suppression of the influence of the parasitic stray capacitance. Preliminary experiments have confirmed at least three-fold improvements of measurement resolution. Realisation of electronics allows flexible tuning of frequency from 0.2 MHz to 2 MHz. The relatively high voltage supply of 15 V for the AC measurement units together with 24-bit accurate analogue-to-digital converter yields additional improvement for the sensitivity.DOI: http://dx.doi.org/10.5755/j01.eie.22.3.15311

非接触型電気伝導度検出CEを用いる薄膜水耕における循環水耕液中の主要無機イオンの定量

非接触型電気伝導度検出CEを用いる薄膜水耕における循環水耕液中の主要無機イオンの定量

Sensitive Determination of Metal Ions in Drinking Water by Capillary Electrophoresis Coupled with Contactless Conductivity Detection Using 18-Crown-6 Ether and Hexadecyltrimethylammonium Bromide as Complexing Reagents

A simple, economical, and sensitive capillary electrophoresis (CE) method integrated with capacitively coupled contactless conductivity detection was developed for the determination of metal ions such as K+, Na+, Mg2+, Sr2+, Ca2+ in drinking water. 18-Crown-6 ether and Hexadecyltrimethylammonium Bromide (CTAB) were employed as complexing reagents. The effects of electrolyte additives, citric acid buffer solution, and other separation conditions of CE were comprehensively investigated and carefully optimized. The best results were obtained in a running buffer solution composed of citric acid (12 mM), 18-crown-6 ether (0.2 mM), and CTAB (0.015 mM) at pH 3.5. Under these conditions, a complete separation of five metal ions was successfully achieved in less than 12 min. The limits of detection for the optimal procedure were determined to be in the range of 0.02 - 0.2 mg·L-1. The repeatability with respect to migration times and peak areas, expressed as relative standard deviations, was better than 2.3% and 5.1%, respectively. Evaluation of the efficiency of the methodology indicated that it was reliable for the determination of metal ions in six different brands of drinking water samples.

Voidage measurement of gas–liquid two-phase flow based on Capacitively Coupled Contactless Conductivity Detection

Based on Capacitively Coupled Contactless Conductivity Detection (C4D) technique, a new method for the voidage measurement of conductive gas–liquid two-phase flow is proposed. 15 Conductance signals, which reflect voidage distribution of gas–liquid two-phase flow, are obtained by a six-electrode C4D sensor. With the conductance signals, the flow pattern of gas–liquid two-phase flow is identified by flow pattern classifiers and then the voidage measurement is implemented by a corresponding voidage measurement model (for each typical flow pattern, a corresponding voidage measurement model is developed). The conductance measurement of the six-electrode C4D sensor is implemented by phase sensitivity demodulation (PSD) method. The flow pattern classifiers and the voidage measurement models are developed by partial least squares (PLS) technique and least squares support vector machine (LS-SVM) technique. Static voidage measurement experiments and dynamic voidage measurement experiments show that the proposed voidage measurement method is effective, the developed six-electrode C4D sensor is successful and the measurement accuracy is satisfactory.

A new method for void fraction measurement of gas–liquid two-phase flow in millimeter-scale pipe

This work attempts to investigate the feasibility and potential of Capacitively Coupled Contactless Conductivity Detection (C4D) technique in the void fraction measurement of gas–liquid two-phase flow in millimeter-scale pipe and hence to propose a new void fraction measurement method based on C4D technique. A new C4D sensor is developed and a void fraction measurement system is constructed. As a preliminary study, the research work is focused on the void fraction measurement of two typical flow patterns (bubble flow and slug flow) in millimeter-scale horizontal pipe. The relationship between the conductance value and the void fraction is investigated. It is found that there is obvious linear relationship between the conductance value and the void fraction and flow pattern has significant influence on void fraction measurement. To overcome the influence of flow pattern, different void fraction measurement models are developed for different flow patterns. In the practical void fraction measurement process, flow pattern is firstly identified, then a corresponding void fraction measurement model is selected, and finally the void fraction measurement is implemented with the selected model and the conductance measurement obtained by the new C4D sensor. Void fraction measurement experiments are carried out (the inner diameters of the pipes are 2.8mm, 3.9mm, 5.3mm and 7.0mm, respectively). The experiment results show that the application of C4D technique to the void fraction measurement of gas–liquid two-phase flow in millimeter-scale pipe is feasible. The proposed void fraction measurement method is effective and the measurement performance is satisfactory (the maximum absolute error of void fraction measurement is less than 7%). The research results also indicate that C4D technique may have a broad application prospective and potential in the research field of two-phase flow.

Image reconstruction algorithm for capacitively coupled electrical resistance tomography

Capacitively Coupled Electrical Resistance Tomography (CCERT), which is on the basis of Capacitively Coupled Contactless Conductivity Detection (C4D), is a novel electrical tomography technique. As a developing technique, more research work should be undertaken. This work focuses on the study of image reconstruction algorithm of CCERT. Combining Tikhonov regularization principle and Simultaneous Iterative Reconstruction Technique (SIRT), a new hybrid image reconstruction algorithm is proposed. Tikhonov regularization is introduced to obtain the initial reconstructed image. SIRT is used to obtain the final reconstructed image. With a 12-electrode CCERT prototype, image reconstruction experiments are carried out. Experimental results show that the images reconstructed by the proposed image reconstruction algorithm are satisfactory and are in accord with the actual distributions of two-phase flows. The research work also indicates that the proposed image reconstruction algorithm is more suitable for image reconstruction of CCERT, comparing with the conventional image reconstruction algorithms of Electrical Capacitance Tomography (ECT) and Electrical Resistance Tomography (ERT).