Contactless Conductometric Detection Research Articles

3D printed two-in-one on-capillary detector: Combining contactless conductometric and photometric detection for capillary electrophoresis

In this work, for the first time, a 3D printed two-in-one on-capillary detector, combining contactless conductometric detection (C4D) and photometric detection (PD), is fabricated for capillary electrophoresis (CE). The C4D Faraday shield (FS) is printed using electrically conductive composite polylactic acid (PLA) to minimize the stray capacitance. Non-conductive PLA is also used to print the insulator of FS to prevent the electrical conduction with two stainless steel electrodes. A novel collimator, consisting of two partially aligned pinholes, is printed by conductive material to collimate the light-emitting diode beam. The C4D detection has a signal-to-noise ratio of 1092 ± 2 for 200 μM potassium on a 25 μm id capillary. The PD detection shows excellent linearity with stray light down to 8% and an effective path length at 73% of a 75 μm id capillary. The analytical performance is demonstrated by CE separation and detection of cations. PD shows limits of detection (LODs) of 1.3, 0.9, and 1.7 μM for cobalt, copper and zinc, which are complexed with 4-(2-Pyridylazo) resorcinol, while C4D shows LODs of 1.2, 1.4, 21 and 2.6 μM for potassium, sodium, cobalt and zinc, respectively.

P037 Skin-wipe sweat samples: sensitivity and specificity of (Cl−+ Na+)/K+ ratio

Ion ratio in sweat sample obtained by skin-wipe test andanalysed by capillary electrophoresis with contactless conductometricdetection appears to be a promising alternative to the usual sweat test. Theobjective of the study was to determine the cut-off value of ion ratio thatcan reliably differentiate between CF patients and healthy individuals.

Study of Various Parameters that Influence the Content of Exhaled Breath Condensate Used in the Diagnosis of Gastroesophageal Reflux Disease

Abstract In this work, various parameters that influence the ionic content and pH of exhaled breath condensate in of the noninvasive diagnosis of gastroesophageal reflux disease were studied. Exhaled breath condensate samples were collected using a miniature and inexpensive sampling device. Capillary electrophoresis with contactless conductometric detection was used to monitor the ionic content of exhaled breath condensate. Background electrolyte composed of 20 mM of 2-(N-Morpholino)ethanesulfonic acid, 20 mM of L-Histidine, 2 mM of 18-Crown-6 and 30 M of cetyltrimethylammonium bromide facilitated the rapid separation of anions and cations, both in less than 2 minutes. The possibility of contamination of the exhaled breath condensate by saliva is discussed in detail. The day-to-day repeatability (n=5) of the ionic content and pH of the exhaled breath condensate was studied and was satisfactory, reflecting mainly the physiological variability

Capillary Electrophoretic Analysis of Exhaled Breath Condensate in the Diagnosis of Gastroesophageal Reflux Disease

Abstract In this work, capillary electrophoresis with contactless conductometric detection (CCD) was used for the analysis of the ionic content of exhaled breath condensate (EBC) to differentiate between healthy individuals and patients with gastroesophageal reflux disease (GERD). The exhaled breath condensate was collected using a miniature sample collection device and the content analyzed using a separation electrolyte composed of 20 mM 2-(N-morpholino)ethanesulfonic acid, 20 mM L-histidine, 2 mM 18-Crown-6 and 30 M cetyltrimethylammonium bromide. The separation of anions took less than 2.5 minutes, while the cations were separated in less than 1.5 minutes. The most significantly elevated ions in the group of patients suffering from gastroesophageal reflux disease were chloride, nitrate, propionate and butyrate. Although the number of subjects was too small to draw definite conclusions with regard to the discriminatory power of these ions, the pilot data are promising for EBC as a useful non-invasive alternative for other methods used in the diagnosis of gastroesophageal reflux disease

Fast blood plasma separation device for point-of-care applications

In this work, a simple device for extremely fast separation of blood plasma from diluted whole blood was developed. The device accommodates an asymmetric polysulfone membrane/supporting membrane sandwich that allows collection of 10 µL blood plasma into a narrow glass capillary in less than 10 s. The composition of diluent solution was optimized in order to achieve maximum recoveries for selected metabolites of alcohol intoxication. 5% solution of [tris(hydroxymethyl)methylamino] propanesulfonic acid provided recoveries of formate, oxalate and glycolate close to 100% and only moderate erythrocyte lysis. Both charged and uncharged compounds from the whole blood samples can be analyzed in the separated blood plasma by capillary electrophoresis with contactless conductometric detection and spectrophotometry, respectively. The developed device might find wide application in on-site testing and point-of-care analysis, when only microliter volumes of whole blood are available.

New approach for cystic fibrosis diagnosis based on chloride/potassium ratio analyzed in non-invasively obtained skin-wipe sweat samples by capillary electrophoresis with contactless conductometric detection

A new approach for sweat analysis used in cystic fibrosis (CF) diagnosis is proposed. It consists of a noninvasive skin-wipe sampling followed by analysis of target ions using capillary electrophoresis with contactless conductometric detection (C4D). The skin-wipe sampling consists of wiping a defined skin area with precleaned cotton swab moistened with 100μL deionized water. The skin-wipe sample is then extracted for 3min into 400μL deionized water, and the extract is analyzed directly. The developed sampling method is cheap, simple, fast, and painless, and can replace the conventional pilocarpine-induced sweat chloride test commonly applied in CF diagnosis. The aqueous extract of the skin-wipe sample content is analyzed simultaneously by capillary electrophoresis with contactless conductometric detection using a double opposite end injection. A 20mmol/L L-histidine/2-(N-morpholino)ethanesulfonic acid and 2mmol/L 18-crown-6 at pH6 electrolyte can separate all the major ions in less than 7min. Skin-wipe sample extracts from 30 study participants-ten adult patients with CF (25-50 years old), ten pediatric patients with CF (1-15 years old), and ten healthy control individuals (1-18 years old)-were obtained and analyzed. From the analyzed ions in all samples, a significant difference between chloride and potassium concentrations was found in the CF patients and healthy controls. We propose the use of the Cl-/K+ ratio rather than the absolute Cl- concentration and a cutoff value of 4 in skin-wipe sample extracts as an alternative to the conventional sweat chloride analysis. The proposed Cl-/K+ ion ratio proved to be a more reliable indicator, is independent of the patient's age, and allows better differentiation between non-CF individuals and CF patients having intermediate values on the Cl- sweat test. Figure New approach for cystic fibrosis diagnosis based on skin-wipe sampling of forearm and analysis of ionic content (Cl-/K+ ratio) in skin-wipe extracts by capillary electrophoresis with contactless conductometric detection.

Single-breath analysis using a novel simple sampler and capillary electrophoresis with contactless conductometric detection.

The analysis of ionic content of exhaled breath condensate (EBC) from one single breath by CE with C(4) D is demonstrated for the first time. A miniature sampler made from a 2-mL syringe and an aluminum cooling cylinder for collection of EBC was developed. Various parameters of the sampler that influence its collection efficiency, repeatability, and effect of respiratory patterns were studied in detail. Efficient procedures for the cleanup of the miniature sampler were also developed and resulted in significant improvement of sampling repeatability. Analysis of EBC was performed by CE-C(4) D in a 60 mM MES/l-histidine BGE with 30 μM CTAB and 2 mM 18-crown-6 at pH 6 and excellent repeatability of migration times (RSD < 1.3% (n = 7)) and peak areas (RSD < 7% (n = 7)) of 12 inorganic anions, cations, and organic acids was obtained. It has been shown that the breathing pattern has a significant impact on the concentration of the analytes in the collected EBC. As the ventilatory pattern can be easily controlled during single exhalation, the developed collection system and method provides a highly reproducible and fast way of collecting EBC with applicability in point-of-care diagnostics.

Double opposite end injection capillary electrophoresis with contactless conductometric detection for simultaneous determination of chloride, sodium and potassium in cystic fibrosis diagnosis

A novel approach for diagnosis of cystic fibrosis is presented. A simple and fast procedure to obtain sweat sample was developed. It consists of repeatedly wiping the skin of the forearm with deionized water moisturized cotton swab and extraction in 1mL of deionized water. Double opposite end injection capillary electrophoresis with contactless conductometric detection is used for the analysis of the extract. Chloride, sodium and potassium as the three target ions that participate in the ion transfer across the cellular membranes, and are affected by CF, are simultaneously determined in approximately 3min in a background electrolyte containing 20mM 2-(N-morpholino)ethanesulfonic acid, 20mM l-histidine and 2mM 18-crown-6. By using the target ion ratios rather than the concentrations of each individual ion combined with principal component analysis, the diagnosis of CF can be made more accurately and greatly reduce the number of false positive or negative results as is often the case when single ion (chloride) is analyzed.

THE ANALYSIS OF SMALL IONS WITH PHYSIOLOGICAL IMPLICATIONS USING CAPILLARY ELECTROPHORESIS WITH CONTACTLESS CONDUCTIVITY DETECTION

Simultaneous electrophoretic separation of inorganic anions and cations from ground waters by dual opposite end injection and their capacitively coupled contactless conductometric detection is described. The chemometry assisted method development revealed that using this type of detection, apart from many advantages, implies a careful fine tuning of experimental variables. Proper choice of buffer components is the most critical aspect of the recorded signal's quality and the obtained resolution, where minor changes could lead to major changes in the recorded electropherograms. From a big variety of acidic and basic electrolytes, a pyromellitic acid/citric acid based buffer (pH = 3.70) was chosen for the baseline separation of 11 cations and anions in a single, less than 3 min run, using a PVA coated fused silica capillary. The estimated limits of detection (0.07–2 ppm) and defined limits of quantification (0.3–7 ppm) were comparable or better than those described for indirect UV detection, allowing much broader linear ranges (up to 120 ppm) for most of the studied ions. Following method validation the method was successfully applied for the assessment of inorganic ion content of 51 geotagged drinking water (domestic well) samples collected from the rural area of Cluj County, Romania, and correlations between sample composition and their geographical origin were identified by multivariate data analysis.

Simultaneous and rapid determination of caffeine and taurine in energy drinks by MEKC in a short capillary with dual contactless conductivity/photometry detection

A method has been developed for the simultaneous determination of taurine and caffeine using a laboratory-made instrument enabling separation analysis in a short 10.5 cm capillary. The substances are detected using a contactless conductometry/ultraviolet (UV) photometry detector that enables recording both signals at one place in the capillary. The separation of caffeine and taurine was performed using the MEKC technique in a BGE with the composition 40 mM CHES, 15 mM NaOH, and 50 mM SDS, pH 9.36. Under these conditions, the migration time of caffeine is 43 s and of taurine 60 s; LOD for caffeine is 4 mg/L using photometric detection and LOD for taurine is 24 mg/L using contactless conductometric detection. The standard addition method was used for determination in Red Bull energy drink of caffeine 317 mg/L and taurine 3860 mg/L; the contents in Kamikaze drink were 468 mg/L caffeine and 4110 mg/L taurine. The determined values are in good agreement with the declared contents of these substances. RSD does not exceed 3%.

Separation of oxalate, formate and glycolate in human body fluid samples by capillary electrophoresis with contactless conductometric detection

A new method for rapid determination of toxic metabolites after methanol and ethylene glycol intoxication – oxalate, formate and glycolate in various body fluid samples (blood serum, saliva, urine, exhaled breath condensate) by capillary electrophoresis with contactless conductometric detection was developed. A selective separation of the three target analytes from other constituents present in the analyzed biological matrices was achieved in less than 6min in a fused silica capillary of 25μm I.D. using an electrolyte comprising 50mM l-histidine and 50mM 2-(N-morpholino)ethanesulfonic acid at pH 6.1. The only sample preparation was dilution with deionized water. The limits of detection were 0.4, 0.6 and 1.3μM and limits of quantitation 1.3, 1.9 and 4.2μM for oxalate, formate and glycolate, respectively. The method provides a simple and rapid diagnostic test in suspected intoxication and is able to distinguish the ingested liquid, based on its metabolite trace. The method presents a fast screening tool that can be applicable in clinical practice.

Capillary electrophoresis with contactless conductometric detection for rapid screening of formate in blood serum after methanol intoxication

A new method for rapid, direct determination of formate in blood serum samples by capillary electrophoresis with contactless conductometric detection is presented. A selective separation of formate was achieved in approximately 1min using an electrolyte system comprising 10mM l-histidine, 15mM glutamic acid and 30μM cetyltrimethylammonium bromide at pH 4.56. The only sample preparation was dilution (1:100) with deionized water. The limit of detection and limit of quantitation was 2.2μM and 7.3μM, respectively, which corresponds to 0.22mM and 0.73mM in undiluted blood serum. The method provides a simple and rapid diagnostic test in suspected methanol intoxication cases. The method has been successfully tested on determination of formate in blood of a patient admitted to the hospital under acute methanol intoxication. The peak concentration of formate detected in the patient blood serum was 12.4mM, which is 10- to 100-fold higher than the normal values in healthy population. The developed method presents the fastest test currently available to detect formate in blood samples.

Capillary electrophoresis – A new tool for ionic analysis of exhaled breath condensate

Exhaled breath condensate has been analyzed for its ionic content by capillary electrophoresis with capacitively coupled contactless conductometric detection. A simple device for collection of small volumes (100–200μL) of exhaled breath condensate in less than 2min was developed. A method for simultaneous determination of inorganic cations, inorganic anions and organic anions from the samples using dual-opposite end injection principle with a short fused silica capillary (35cm, 50μm I.D.) was developed. A background electrolyte composed of 20mM 2-(N-morpholino)ethanesulfonic acid, 20mM l-histidine, 30μM cetyltrimethylammonium bromide and 2mM 18-crown-6 was used. The analysis time was less than 3min with limits of detection reaching low μM levels for most of the anions and cations. It has been shown that changes of nitrite could be observed in acute inflammation of upper airways and in a person with diagnosed mild chronic obstructive pulmonary disease, while changes of other ions could also be observed. Lactate concentrations could also be monitored and about 4-fold increase of lactate concentration in exhaled breath condensate was determined following an exhaustive cycling exercise. The developed non-invasive sampling of exhaled breath condensate, followed by rapid capillary electrophoretic analysis, could be very useful in lung inflammatory disease screening as well as in monitoring fast metabolic processes such as lactate build-up and removal.

Application of Contactless Impedance Detection to Determination of Substances in Gaseous Phase

AbstractA simple cell, consisting of two insulated wire electrodes placed in a PTFE tube through which the test gaseous phase flows, has been applied to capacitively coupled contactless conductometric detection (C4D) and determination of water vapour in the air, to examine the possibilities of the use of C4D for analyses of gaseous samples. It has been found that the measurement is sufficiently sensitive and reliable for determinations of common concentrations of water in the air. The dynamic characteristics and the signal stability demonstrate that the cell will be suitable for long‐term continuous monitoring of the air humidity. Qualitative tests indicate that vapours of organic solvents can also be monitored. To the authors knowledge, this is the first attempt to use C4D in gas analyses.

In situ determination of nerve agents in various matrices by portable capillary electropherograph with contactless conductivity detection

Rapid, efficient and robust methods for sampling and extracting genuine nerve agents sarin, soman and VX were developed for analyzing these compounds on various solid matrices, such as concrete, tile, soil and vegetation. A portable capillary electrophoretic (CE) system with contactless conductometric detection was used for the in situ analysis of the extracted samples. A 7.5 mM MES/HIS-based separation electrolyte accomplished the analysis of target analytes in less than 5 min. The overall duration of the process including instrument start-up, sample extraction and analysis was less than 10 min, which is the fastest screening of nerve agents achieved with liquid phase separation methods to date. The procedure can easily be performed by a person in a protective suit and is therefore suitable for real-life applications. The CE results were validated by an independent GC–MS method and a satisfactory correlation was obtained. The use of a proper sampling strategy with two internal standards and “smart” data-processing software can overcome the low reproducibility of CE. This has a significant impact on the potential acceptance of portable CE instrumentation for the detection and analysis of genuine chemical warfare agents (CWA).

Versatile microanalytical system with porous polypropylene capillary membrane for calibration gas generation and trace gaseous pollutants sampling applied to the analysis of formaldehyde, formic acid, acetic acid and ammonia in outdoor air

The analytical determination of atmospheric pollutants still presents challenges due to the low-level concentrations (frequently in the μg m −3 range) and their variations with sampling site and time. In this work, a capillary membrane diffusion scrubber (CMDS) was scaled down to match with capillary electrophoresis (CE), a quick separation technique that requires nothing more than some nanoliters of sample and, when combined with capacitively coupled contactless conductometric detection (C 4D), is particularly favorable for ionic species that do not absorb in the UV–vis region, like the target analytes formaldehyde, formic acid, acetic acid and ammonium. The CMDS was coaxially assembled inside a PTFE tube and fed with acceptor phase (deionized water for species with a high Henry's constant such as formaldehyde and carboxylic acids, or acidic solution for ammonia sampling with equilibrium displacement to the non-volatile ammonium ion) at a low flow rate (8.3 nL s −1), while the sample was aspirated through the annular gap of the concentric tubes at 2.5 mL s −1. A second unit, in all similar to the CMDS, was operated as a capillary membrane diffusion emitter (CMDE), generating a gas flow with know concentrations of ammonia for the evaluation of the CMDS. The fluids of the system were driven with inexpensive aquarium air pumps, and the collected samples were stored in vials cooled by a Peltier element. Complete protocols were developed for the analysis, in air, of NH 3, CH 3COOH, HCOOH and, with a derivatization setup, CH 2O, by associating the CMDS collection with the determination by CE-C 4D. The ammonia concentrations obtained by electrophoresis were checked against the reference spectrophotometric method based on Berthelot's reaction. Sensitivity enhancements of this reference method were achieved by using a modified Berthelot reaction, solenoid micro-pumps for liquid propulsion and a long optical path cell based on a liquid core waveguide (LCW). All techniques and methods of this work are in line with the green analytical chemistry trends.

Polyelectrolyte multilayers as stationary phases for open tubular ion chromatography

Polyelectrolyte multilayers deposited on the wall of fused silica capillaries were used as stationary phases in open tubular ion chromatography. The multilayers were formed by flushing the capillaries with solutions of polyanions and polycations such as polydiallyldimethylammonium chloride and dextran sulphate. Columns with several bi-layers were constructed and used in low pressure non-suppressed open tubular ion chromatography of common inorganic anions (F −, Cl −, NO 3 −) and cations (Li +, Na +, NH 4 +, K +, Cs +) with contactless conductometric detection. Using sodium benzoate and tartaric acid eluents the separations were typically achieved in less than 35 min with separation efficiencies between 2000 and 9000 theoretical plates. A bi-functional column was prepared that contains both anionic and cationic functional groups and was used for simultaneous separation of anions and cations.

Gravity‐flow open tubular cation chromatography

We describe ion chromatography (IC) on open tubular cation exchange columns with a controllable capacity multilayered stationary phase architecture. The columns of relatively large bore (75 microm id) are fabricated by coating fused-silica capillaries with multiple layers of poly(butadiene-maleic acid) (PBMA) copolymer and crosslinking the deposited layers by thermally initiated radical polymerisation. Column capacity increases in a predictable manner with increase in the number of successively coated layers. Gravity flow with a modest head (< 2 m) can provide the desired separations within a reasonable period. We provide a minimalist configuration where no suppression is used, the sample is injected hydrodynamically as in CE, and detection is accomplished by an inexpensive homebuilt contactless conductivity detector or a capacitance to voltage digital converter. A 1 m long 75 microm bore column coated with two layers of PBMA allows gravity-flow open tubular IC to separate four alkali cations in < 10 min with a 1 mM tartaric acid (TA) eluent. Simultaneous separation of alkali and alkaline earth metal cations can be accomplished in less than 25 min using 1.75 mM pyridinedicarboxylic acid as an eluent. Contactless conductometric detection (C(4)D) allows LODs down to 150 nmol/L, corresponding to 30 fmol injections. Analysis of real water samples is demonstrated.

Open Tubular Anion Exchange Chromatography. Controlled Layered Architecture of Stationary Phase by Successive Condensation Polymerization

The preparation and performance of a multilayered stationary phase for open tubular anion exchange chromatography in relatively large bore (75 microm diameter) columns are described. The inner surface of a fused-silica capillary tube is coated with up to 25 successive porous polymeric layers formed by condensation polymerization of a primary amine with a diepoxide. Each layer of the anion exchange stationary phase consists of copolymer of methylamine (MA) and 1,4-butanedioldiglycidyl ether (BDDE). The polymer layers are sufficiently porous or permeable; each successive layer of the stationary phase incrementally increases the observed column capacity and chromatographic performance in the open tubular mode. Even though the column inner diameter is far from optimum for open tubular liquid chromatography, we demonstrate the baseline separation of a suite of inorganic anions (F-, Cl-, NO2-, Br-, NO3-) in a 5 m x 75 microm column coated with 25 layers of the anion exchange polymer using 1 mM KOH eluent and suppressed contactless conductometric detection at a flow rate of 1 microL/min (operating pressure of approximately 1 bar) with a plate count of >30,000. Strategies for construction of microsuppressor devices used in open tubular ion chromatography are discussed.

Ion exchange preconcentration and separation of mercury species by CE with indirect contactless conductometric detection

Capillary electrophoretic separation of four mercury species (inorganic Hg(2+), methyl-, ethyl-, and phenylmercury) was achieved in less than 8 min with an electrolyte consisting of 150 mM 2-amino-2-methyl-propanol (AMP) at pH 11.6. The analytes were complexed with 0.1% mercaptopropionic acid (MPA), separated in counter-EOF as anionic complexes, and detected by a contactless conductometric detector. Ion exchange preconcentration with on-column formation of MPA-mercury complexes was developed. Preconcentration factors of 25-150 were achieved and LODs in the range of 2.9-6.9 ng/mL were feasible. This method may prove to be applicable as a rapid screening method for mercury speciation in environmental samples.