Contactless Conductivity Detection Research Articles

Sweat chloride quantification using capillary electrophoresis

BackgroundCystic fibrosis (CF) is the less rare and severe genetic disease among the European population. Biochemical diagnosis of CF is based on the demonstration of increased chloride concentration in sweat samples, obtained during the sweat test (ST). WynSep developed a capillary electrophoresis with contactless conductivity detection (CE-C4D) able to measure sweat chloride with a low sample volume. We evaluated the clinical feasibility of this device in a cohort of patients suspected of CF, in comparison with the common coulometric method (ChloroChek chloridometer). MethodsWe determined sweat chloride concentration of 65 samples from patients referred to our institution to undergo a sweat test. Each sample was submitted to coulometric method first, then WynSep-CE, with or without internal standard (IS) subject to sufficient volume sample. ResultsA total of 53 samples were analysed by both coulometric and WynSep-CE (using IS) methods. The method validation showed comparable analytical performances for both methods; no false positive or false negative was recorded. The two methods showed a high correlation (r = 0.993, p < 0.001) and a close agreement was demonstrated by two different statistical tests (Bland-Altman and Passing-Bablok). ConclusionsWynSep-CE is an accurate, fast, easy-to-use and an appropriate method for CF diagnosis.

A bi-end injection capillary electrophoresis method for simultaneous determination of 37 cations and anions in beers.

Capillary electrophoresis (CE) is excellent at separating all the ions in a sample but is rarely used as a result of its detection issue and easy loss of very fast ions by common one-end injection methods. Herein we propose a newly developed method aimed at simultaneous determination of positive and negative ions with a home-made CE device, featuring bi-end injection and contactless conductivity detection at the middle. By simply using 2.5M acetic acid as a running buffer, the method can separate 37 ions (3 inorganic anions, 8 inorganic cations, 10 biogenic amines, and 16 amino acids) per run, with linearity between 10 and 2000μM (R2 > 0.99), limit of detection of 1.0-16.6μM, and limit of quantification of 2.3-31.7μM. The recovery measured by spiking standards into samples at high, middle, and low levels was between 73% and 110%. The intra- and interday repeatability of the 37 analytes ranged from 0.69% to 8.97% and from 0.68% to 11.04%, respectively. The proposed method was evaluated by analysis of 21 beers and, in addition to acquiring the concentration information, the brands of the tested beers were distinguished. This method is of high throughput, fast, and cost-effective. It could be a promising tool for ionomic analysis. Graphical abstract ᅟ.

Paper-Based Electrophoresis Microchip as a Powerful Tool for Bioanalytical Applications.

This chapter describes the development of paper-based microchip electrophoresis (pME) devices for the separation of clinically relevant compounds. pME were fabricated by laser cut and thermal lamination process using polyester pouches. In addition, hand-drawn pencil electrodes were integrated to the device to perform capacitively coupled contactless conductivity detection (C4D). Finished device costs less than US$ 0.10 and did not require either sophisticated instrumentation or clean room facilities. Furthermore, pME is lightweight, easy to handle, flexible, and robust. pME-C4D device revealed an excellent capacity to separate BSA and creatinine in less than 150s with baseline resolution. The device proposed in this chapter has proven to be a good alternative as a platform for the diagnosis of diseases from renal disorders such as diabetes mellitus and heart disease.

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.

Rapid quantification of quinine by multi-stacking in a portable microchip electrophoresis system.

A new multi-stacking pre-concentration procedure based on field-enhanced sample injection (FESI), field-amplified sample stacking, and transient isotachophoresis was developed and implemented in a compact microchip electrophoresis (MCE) with a double T-junction glass chip, coupled with an on-chip capacitively coupled contactless conductivity detection (C4 D) system. A mixture of the cationic target analyte and the terminating electrolyte (TE) from the two sample reservoirs was injected under FESI conditions within the two sample-loading channels. At the double T-junction, the stacked analyte zones were further concentrated under field-amplified stacking conditions and then subsequently focused by transient-isotachophoresis and separated along the separation channels. The proposed multi-stacking strategy was verified under a Universal Serial Bus (USB) fluorescence microscope employing Rhodamine 6G as the model analyte. This developed approach was subsequently used to monitor the target quinine present in human plasma samples. The total analysis time for quinine was approximately 200s with a sensitivity enhancement factor of approximately 61 when compared to the typical gated injection. The detection and quantification limits of the developed approach for quinine were 3.0μg/mL and 10μg/mL, respectively, with intraday and interday repeatability (%RSDs, n = 5) of 3.6 and 4.4%. Recoveries in spiked human plasma were 98.1-99.8%.

Capillary Scale Admittance and Conductance Detection.

Admittance detection, more commonly called capacitively coupled contactless conductivity detection, is widely used. While the true conductance of a solution is linear with concentration up to ∼1 mequiv/L, the admittance signal is nonlinear. In small-bore capillaries and highly resistive solutions, such as in suppressed open tubular ion chromatography (SOTIC), the admittance signal is exponentially related to concentration. Solution contact conductivity detection is common in microfluidics, but no true conductivity measurement efforts have been made with conventional capillaries in the last two decades. We examine five solution contact cell geometries: (A) wire/disk electrodes perpendicular to the flow direction, (B) annular tubular electrodes facing the flow (that exits through the center tube), (C) ring-disk electrodes facing the flow that exits through the annulus, (D) coplanar parallel wire/disk electrodes facing the flow that exits around the electrodes, and (E) planar electrodes separated by a thin insulating layer with a through-hole in which the liquid flows. Present limitations of the available components as well as the designs themselves do not allow type A and B cells to reach low enough dispersion levels. Types C-E all produce the same efficiency for chloride in a SOTIC setup (12000 ± 200 plates/m), limited by dispersion in the suppressor. Further choice and refinement will be dictated by the availability of a lower dispersion suppressor. All such contact conductance results were linear with concentration, and initial results suggest that attainable LODs will be competitive with those from benchtop ICs.

Rapid separation of post‐blast explosive residues on glass electrophoresis microchips

This study describes the development of an analytical methodology based on the use of microchip electrophoresis (ME) devices integrated with capacitively coupled contactless conductivity detection (C4 D) for the separation and detection of inorganic anions in post-blast explosive residues. The best separation condition was achieved using a running buffer composed of 35mmol/L lactic acid, 10mmol/L histidine and 0.070mmol/L cetyl(trimethyl ammonium) bromide. For C4 D measurements, the highest sensitivity was obtained applying a 700kHz sinusoidal wave with excitation voltage of 20Vpp . The separation of Cl- , NO3 - , NO2 - , SO4 2- , ClO4 - and ClO3 - was performed within ca. 150 s with baseline resolution and efficiencies between 4.4 × 104 and 1.7 × 105 plates/m. The found limits of detection ranged between 2.5 and 9.5μmol/L. Last, real samples of post-blast explosive residues were analyzed on the ME-C4 D devices obtaining successfully the determination of Cl- , NO3 - and SO4 2- . The achieved concentration values varied between 12.8-72.5mg/L for Cl- , 1.7-293.1mg/L for NO3 - and 1.3-201.3 mg/L for SO4 2- . The data obtained using ME-C4 D devices were in good agreement with the concentrations found by ion chromatography. The approach reported herein has provided short analysis time, instrumental simplicity, good analytical performance and low cost. Furthermore, the ME-C4 D devices emerge as a powerful and portable analytical platform for on-site analysis demonstrating to be a promising tool for the crime scene investigation.

Selective capillary electrophoresis separation of mono and divalent cations within a high-surface area-to-volume ratio multi-lumen capillary

In this study, the separation of inorganic mono and divalent cations using multi-lumen silica capillaries (MLCs) of 126 channels, each with either 4 or 8 μm inner diameter, was investigated using capillary electrophoresis and on-capillary capacitively coupled contactless conductivity detection (CE-C4D). MLCs provided sufficiently high surface area-to-volume ratios to generate significant wall ion-exchange interactions for the divalent cations, which significantly affected resultant selectivity, whereas monovalent cations were predominantly separated by simple electrophoresis. The resultant hybrid selectivity was seen for both 4 and 8 μm channel multi-lumen capillaries, without any preconditioning or capillary wall modification. Remarkably, the electrophoretic mobilities for the divalent cations Mg2+ and Ca2+ were reduced 7.5 times compared to those determined using a single channel open tubular capillary of 50 μm i.d., providing much improved selectivity. Apparent electrophoretic mobilities of divalent cations increased as the concentration of BGE increased, while those of monovalent cations decreased parallel to electroosmotic mobility. These results show the electrostatic interaction between the divalent cations and the silica wall. At least, this specific separation of mono- and divalent cations were clearly observed with a mixture standards solution of less than 200 μmol L−1. Using a MLC with 126 × 8 μm i.d. channels and 49.1 cm in length, together with a 20 mmol L−1 MES/His BGE, containing 2 mmol L−1 18-crown-6, monovalent cations (NH4+, K+ Na+ and Li+) and divalent cations (Ca2+ and Mg2+) could be completely separated within 4 min. For monovalent cations, on-capillary detection using C4D provided calibration curve (0–200 μmol L−1) correlation coefficients in the range R2 = 0.995–0.999, and limits of detection of 2.2–6.6 μmol L−1. Relative standard deviations for migration times were less than 0.6%, and recoveries ranged from the 93.8%–105.4%. The new method was applied to the separation and quantitative determination of monovalent and divalent cations in drinking waters and soil extracts.

Capillary electrophoresis for continuous nitrogen quantification in wastewater treatment processes

A water quality analyzer based on the working principle of capillary electrophoresis (CE) was developed to determine ionic inorganic nitrogen compounds contained in wastewater samples. The instrument provides simultaneous quantification of anions and cations by superimposing hydrodynamic pumping with electrokinetic motion. It features a single separation capillary with contactless conductivity detection and a sequential injection manifold for fluid handling. Dynamic adaption of the system calibration was enabled by the use of a high precision pressure regulator to cover a wide measurement range showing low relative standard deviations (< 2 %) and high measurement accuracy comparable to conventional wastewater analyzers. The prototype is transportable, integrated in a 19 in. rack and connected to a membrane filter system developed for direct sample aspiration in the wastewater process. For operation on site, only a power supply and a network connection for remote control is necessary. Continuous operation was demonstrated over 24 h at the aeration tank of a pilot scale wastewater treatment plant at TU Wien and a good correlation with laboratory results was achieved. At this time, there is no device available, on the market, to analyze all nitrogen species in one assembly with limited hardware complexity and chemical demand. This entails a significant step forward towards automated water quality monitoring with respect to the implementation of new advanced wastewater treatment technologies.

A portable eight-channel titrator based on high-throughput capacitively coupled contactless conductivity measurements

Analytical chemists require multichannel and automatic tools for batch measurements. Herein, an eight-channel electronic titrator (8-CET) system was constructed to facilitate high-throughput titrations. In this system, multichannel piston pumps were used for delivery, and an 8-channel capacitively coupled contactless conductivity detector (8-C4D) was used to monitor the conductivity of the titration solutions in arrays of disposable reaction cells. The delivery and the monitoring were both fully software-controlled allowing a simultaneous formation of eight titration curves. Its capacity for classical acid-base and precipitation titration was characterized with satisfactory results. It was also used to measure the content of CH3COOH in batched vinegar samples. The RSD between each reaction cell was 1.9%. There are two outstanding features of this new system: 1) Up to eight samples can be measured simultaneously; and 2) simple operation is realized by avoiding electrode switching and cleaning after each measurement. Therefore, it is reasonable to believe that this 8-CET system is a prospective alternative for developing more automatic and efficient titration platforms.

Simultaneous Determination of Inorganic Anions and Cations in Water and Biological Samples by Capillary Electrophoresis with a Capacitive Coupled Contactless Conductivity Detector Using Capillary Filling Method.

An analytical method for concurrent analysis of inorganic anions and cations has been developed using a capillary electrophoresis (CE)-capacitively coupled contactless conductivity detector (C4D) system. Although hydrodynamic and electrokinetic injection techniques have been widely used in CE, we employed a capillary filling method (CFM) for the analysis of inorganic ions. The procedure is relatively simple and has the advantage that CMF does not require pressure control and vial exchange. Three anions (chloride, sulfate, nitrate) and five cations (ammonium, potassium, sodium, magnesium, calcium) were successfully separated and detected at ppm levels within 80 s using a 9 mM histidine/15 mM malic acid (pH 3.6) containing 50 mM N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate as background electrolyte. Applying this analytical condition, the electroosmotic flow is negligible and anions and cations were migrated concurrently to different polarities according to their electrophoretic mobility. Obtained raw data showed stepwise increases in detected conductivity due to the migration of sample components, which expresses as peak profiles by differentiation of electropherograms. The RSD values of the peak area and migration times for the anions and cations were satisfactory and were less than 5.15 and 2.04%, respectively. The developed method was applied for the analysis of inorganic anions and cations in commercial mineral waters, tap water, urine, and exhaled breath condensate. These results indicate that the CE-C4D system with CFM is suitable for the rapid analysis of inorganic anions and cations in various samples.

On-line electroextraction in capillary electrophoresis: Application on the determination of glutamic acid in soy sauces.

We present an on-line, single step coupling between liquid-liquid extraction and capillary electrophoresis with capacitively coupled contactless conductivity detection, which allows an efficient analysis of complex food matrices with high sodium content. The sodium depletion was demonstrated using an aqueous two-phase system. The aqueous two-phase system enables the electrically driven extraction of the target compounds. The sample was prepared in Dextran-rich phase (8% w/v 500 kDa Dextran, DEX). The background electrolyte (acetic acid 5.0 mol/L) contained 6% w/v of 6 kDa PEG. As proof of applicability, we employed the developed method for glutamic acid quantification on soy sauces. The peak area of glutamic acid presents no significant difference (α=0.05), while the peak area of the sodium presented a reduction of 11.7±0.2 and 19±3% for premium and low-cost soy sauce samples analyzed. The glutamic acid concentration for premium soy sauce sample was 2.7±0.8 and 4.8±0.4 g/L, and for low-cost soy sauce sample, the concentration was 9.9±0.9 g/L, which agreed with those obtained by other analytical techniques.

Dual-channeled capillary electrophoresis coupled with contactless conductivity detection for rapid determination of choline and taurine in energy drinks and dietary supplements

In this study is reported a simple and inexpensive method for concurrent determination of taurine and choline in different supplementary nutrient samples using dual-channeled capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C4D). The objective of the work is to propose a tool for food control activities that allows screening of different target compounds (having different characteristics) in a single run for high throughput and can be realizable even with modest infrastructure. Taurine was analyzed in the first CE channel using the background electrolyte (BGE) composed of 150 mM tris(hydroxymethyl)aminomethane/lactic acid (pH 8.96) whereas choline was simultaneously separated in the second CE channel using a BGE containing 150 mM tris(hydroxymethyl)aminomethane/acetic acid (pH 9.5). The best achieved detection limit was 0.27 mg/L and 0.45 mg/L for taurine and choline, respectively, using the developed CE-C4D method. Good agreement between results obtained from CE-C4D and those with the standard confirmation methods (HPLC-DAD for taurine and LC/MS for choline) was achieved, with the result deviation for the two pairs of data being less than 12%.

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

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

Application of capillary electrophoresis combined with conductometric and UV detection to monitor meteorite simulant bioleaching by Acidithiobacillus ferrooxidans.

The importance of microorganisms and biotechnology in space exploration and future planets colonization has been discussed in the literature. Meteorites are interesting samples to study microbe-mineral interaction focused on space exploration. The chemolithotropic bacterium Acidithiobacillus ferrooxidans has been used as model to understand the iron and sulfur oxidation. In this work, capillary electrophoresis with capacitively coupled contactless conductivity detection and UV detection was used to monitor bacterial growth in a meteorite simulant by measuring the conversion of Fe2+ into Fe+3 . The effect of Co2+ and Ni2+ (metals also found in meteorites) on the bacterial growth was also evaluated. The presented method allowed the analyses of all metals in a single run (less than 8 min). The background electrolyte was composted of 10 mmol/L α-hydroxyisobutyric acid/Histidine. For comparison purpose, the samples were also analyzed by UV-Vis spectrophotometry. The Fe2+ conversion into Fe3+ by A. ferrooxidans was observed up to 36 h with the growth rate constant of 0.19/h and 0.21/h in Tuovinen and Kelly (T&K) and in meteorite simulant media, respectively. The developed method presents favorable prospect to monitor the growth of other chemolithotropic microorganisms for biotechnology applications.

Monitoring of adipose tissue metabolism using microdialysis and capillary electrophoresis with contactless conductivity detection

Metabolism of human adipose tissue during acute exercise is monitored by microdialysis. The metabolites are analysed in the microdialysate using capillary electrophoresis (CE) on a short separation path in combination with a contactless conductivity detector (C4D). Four completely new CE/C4D methods were developed for determination of nutrients and metabolites in 10 µL of microdialysate. All methods are characterised by a short separation time and simple sample preparation based primarily on 4-fold dilution of microdialysate. The intra-day repeatability for the migration time varied in the range 0.4 – 0.9% and that for the peak area equalled 0.7 – 2.4%; the inter-day repeatability of the migration time was in the range 1.2 – 2.3% and the range for the peak area was 2.5 – 5.0%; all the values were measured as RSD. The developed determination was employed for sequenced monitoring of the levels of lactate, glycerol and branched chain amino acids in microdialysates taken from the abdominal adipose tissue during acute physical exercise. The stress test lasted 3 h and the metabolites were monitored at 15 min intervals.

Capillary electrophoresis with capacitively coupled contactless conductivity detection for the determination of propionate and sorbate in bread

We propose a simple and fast method for the determination of the preservatives propionate and sorbate in bread using capillary electrophoresis with capacitively coupled contactless conductivity detection. The preservatives were quickly extracted from bread using ultra-pure water and ultrasonic energy. The separation of the analytes, with good resolution, was achieved in about 7min. The proposed method showed good linearity with coefficients of determination >0.99 for both the preservatives. The limits of quantification of the method were 0.11 and 0.21g/kg for propionate and sorbate, respectively. The accuracy of the method was evaluated by recovery tests, and the obtained recoveries varied from 88 to 94% for sorbate and 86 to 102% for propionate. The proposed method was successfully applied for the determination of propionate and sorbate in commercial samples of sliced white bread.

Injection system for fast capillary electrophoresis based on pressure regulation with flow restrictors.

A fast automated system for rapid electrophoretic separations in short conventional capillaries employing contactless conductivity detection is presented. The instrument is based on pneumatic pressurization and does not require a conventional pump. The required pressures and flow rates for the different steps of the injection and flushing processes are produced with the help of two flow restrictors. The device is implemented on a microfluidic breadboard with dimensions of ca. 13 × 20 cm and employs miniature valves. Nine inorganic cations, namely NH4+, K+ , Na+ , Ca2+ , Mg2+ , Mn2+ , Sr2+ , Li+ , and Ba2+ , could be separated in a capillary of 10 μm inner diameter and 6 cm effective length within 25 s. Following a reduction of the effective length to 4cm, still five inorganic cations could be separated in a time span of 12s. The repeatability of peak areas was better than 3.1% and limits of detection between 3.5 and 5.5 μM were achieved.

Analysis of inorganic cations and amino acids in high salinity samples by capillary electrophoresis and conductivity detection: Implications for in-situ exploration of ocean worlds.

With growing interest in exploring ocean worlds, such as Europa and Enceladus, there is a fundamental need to develop liquid-based analytical techniques capable of handling high salinity samples while performing both bulk and trace species measurements. In this context, CE with capacitively coupled contactless conductivity detection (CE-C4 D) has tremendous potential. One of its advantages is that this combination allows the detection of a wide number of charged species (both organic and inorganic) without the need of derivatization. Amino acids are an example of organic targets that are powerful biosignatures in the search for life beyond Earth. Simultaneous information on the inorganic cations in a sample helps with assessing the habitability of an extraterrestrial environment, as well as providing sample context for any measurements of trace amino acids. In this work, we present a series of flight-compatible methods capable of simultaneously measuring inorganic cations and amino acids in samples of varying salinity by CE-C4 D. Regardless of the sample total salinity, 5.0 M acetic acid was selected as the optimum BGE. The methods were evaluated by analyzing natural samples of low and high salinity from Hot Creek Gorge, Mono Lake, and Santa Monica beach. Prospects for mission implementation are also discussed.

Contactless conductivity detection for analytical techniques: Developments from 2016 to 2018.

The publications concerning capacitively coupled contactless conductivity detection for the 2-year period from mid-2016 to mid-2018 are covered in this update to the earlier reviews of the series. Relatively few reports on fundamental investigations or new designs have appeared in the literature in this time interval, but the development of new applications with the detection method has continued strongly. Most often, contactless conductivity measurements have been employed for the detection of inorganic or small organic ions in conventional capillary electrophoresis, less often in microchip electrophoresis. A number of other uses, such as detection in chromatography or the gauging of bubbles in streams have also been reported.