Conductivity Detection Method Research Articles

PCB-C4D coupled with paper-based microfluidic sampling for the rapid detection of liquid conductivity.

The detection of liquid electrical conductivity has board applications in food safety testing, water quality monitoring, and agricultural soil analysis. Electrodes used in traditional liquid electrical conductivity detection come into direct contact with liquid, leading to electrode contamination and affecting the accuracy of the detection results. The capacitively coupled contactless conductivity detection (C4D) method effectively addresses this issue. However, impurity particles present in the solution can compromise the consistency and repeatability of detection results. This study combines paper-based microfluidic technology with printed circuit board-capacitively coupled contactless conductivity detection (PCB-C4D) to address this issue. Prior to sample detection, in situ rapid filtration is employed to remove impurity particles from the raw solution sample, significantly enhancing detection consistency and reliability. Simultaneously, Optimization of PCB-C4D parameters, channel size, filtration time, and solution drop rate ensures optimal detection conditions. A compact kit design facilitates reliable assembly of the PCB-C4D electrodes and paper-based channel, enhancing practicality. Practical measurements on the conductivity of orange juice, cucumber, and soil solution further validate the method's accuracy, rapidity, and effectiveness in in situ conductivity detection. This work advances the practical application of PCB-C4D technology.

Separation and quantification of the urinary enantiomers of 2-hydroxyglutaric acid by capillary electrophoresis with capacitively coupled contactless conductivity detection: Application to the diagnosis of D- and L-2-hydroxyglutaric aciduria.

2-hydroxyglutaric aciduria is an inherited neurometabolic disorder with two major types: D-2-hydroxyglutaric aciduria and L-2-hydroxyglutaric aciduria. An easy and fast capillary electrophoresis system combined with a capacitively coupled contactless conductivity detection method was developed for the enantioseparation and determination of D- and L-2-hydroxyglutaric acid in urine. D- and L-2-hydroxyglutaric acids were separated using vancomycin as the chiral selector. The optimal separation conditions for enantiomers were achieved by the use of a buffer containing 50mM 4-(N-morpholino) butane sulfonic acid solution (pH 6.5), an electroosmotic flow modifier (0.001% [w/v] polybrene), and 30mM vancomycin as chiral selector. The analysis time was 6min under optimal conditions. The optimized and validated method was successfully implemented for quantifying D- and L-2-hydroxyglutaric aciduria in patients' urine, without any pretreatment step. The linearity of the method was determined to be in the range of 2-100mg/L for D- and L-2-hydroxyglutaric acid in urine. The precision (relative standard deviation%) was obtained at about 7%. For D- and L-2-hydroxyglutaric acids, the limits of detection were 0.567 and 0.497mg/L, respectively.

Design of nitrogen‐containing organic thermal stabilizer with resistance to “zinc burning” and its application

AbstractUsing maleic anhydride and 6‐amino‐1,3‐dimethyluracil as raw materials, by adding zinc oxide and introducing metal ions, the aminouracil zinc maleate (AM‐Zn) was synthesized. The structure of the product was analyzed by Fourier transform infrared spectroscopy and 1H NMR spectroscopy. The molecule contains ester group, carbon–carbon double bond, carboxylate and diazo group, which can be used as the main thermal stabilizer for poly(vinyl chloride) (PVC). The thermal stability and excellent resistance to zinc burning of AM‐Zn were characterized by Congo red method, thermal aging method, thermal weight loss method, electrical conductivity, and other detection methods. In addition, the compound use of AM‐Zn and CaSt2 could further improve the thermal stability performance, which was excellent compared with the commercially available CaSt2/ZnSt2. The thermal stabilization effect was the best when CaSt2/AM‐Zn = 2:1, the initial whiteness could reach 50 min, and it was not completely blackened and aged within 80 min. The static stabilization time was 65 min, and the thermal stabilization time is increased by 40 min compared with CaSt2/ZnSt2. The thermal stabilization mechanism was analyzed, and the designed and synthesized AM‐Zn, a multifunctional molecular structure, had a strong potential as a thermal stabilizer for PVC.

High-Performance Anion-Exchange chromatography with conductivity detection method for simultaneous determination of nitrogen and phosphorus in polysaccharides

Capsular polysaccharides of Streptococcus pneumoniae contain a characteristic mix of monosaccharides in their structure resulting in immunologically distinct serotypes. Pneumococcal capsular polysaccharides include sugars such as hexoses, uronic acids, hexosamines, methyl pentoses, other functional groups are attached to the sugars are N and O-acetyl groups, nitrogen and phosphorus. Most of these components can be quantified using different colorimetric methods. However, available methods for quantifying nitrogen and phosphorus are not sensitive enough and laborious. We report a highly sensitive high-performance anion-exchange chromatography-conductivity detector (HPAEC-CD) method for quantifying nitrogen and phosphorus present in pneumococcal capsular polysaccharides. The method is reliable, robust and reproducible with no interference. The LOQ for nitrogen and phosphorus of 3.125 and 62.5 ng/mL, respectively, is highly critical for estimating low levels of total nitrogen and total phosphorus. We have implemented this method to quantify total nitrogen in Typhoid Vi polysaccharide and phosphorus in Haemophilus influenzae type-b polysaccharide. This method has greater application for quantification of nitrogen and phosphorus present in low concentrations in polysaccharide vaccines/biologicals.

A voltage trade study for the design of capillary electrophoresis instruments for spaceflight.

Capillary electrophoresis (CE) systems have undergone extensive development for spaceflight applications. A flight-compatible high voltage power supply and the necessary voltage isolation for other energized components can be large contributors to both the volume and mass of a CE system, especially if typical high voltage levels of 25-30kV are used. Here, we took advantage of our custom CE hardware to perform a trade study for simultaneous optimization of capillary length, high voltage level, and separation time, without sacrificing method performance. A capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4 D) method recently developed by our group to target inorganic cations and amino acids relevant to astrobiology was used as a test case. The results indicate that a 50cm long capillary with 15kV applied voltage (half of that used in the original method) can be used to achieve measurement goals while minimizing instrument size.

Development of On-Site Rapid Detection Device for Soil Macronutrients Based on Capillary Electrophoresis and Capacitively Coupled Contactless Conductivity Detection (C4D) Method

The acquisition of nutrient data on a precise scale has played a vital role in nutrient management processes for soils. However, the lack of rapid precise and multi-index detection techniques for soil macronutrient contents hinders both rational fertilization and cost reduction. In this paper, a rapid detection method and device were devised, combining capillary electrophoresis (CE) and capacitively coupled contactless conductivity detection (C4D), and presented to detect macronutrient contents of soil. The device consisted of a capillary channel, C4D detector, high-voltage system, etc. It separated macronutrient ions using capillary electrophoresis and then measured the ion concentration based on the C4D principle. Lime concretion black soil samples from a complete field were collected and detected. NO3−, NH4+, H2PO4− and K+ in sample solutions could be detected in 5 min with relative standard deviations (RSDs) from 1.0 to 7.51%. The injection voltage was set to 10 kV for 5 s, and the separation voltage was set to 14 kV. This demonstrated the excellent performance of the C4D device on the detection of soil macronutrients, which could help to guide fertilization operations more effectively.

Simultaneous separation of 12 different classes of antibiotics under the condition of complete protonation by capillary electrophoresis-coupled contactless conductivity detection.

A novel capillary electrophoresis - capacitively coupled contactless conductivity detection (CE-C4D) method for the separation of 12 antibiotics, including four types of aminoglycosides, three types of fluoroquinolones, two types of tetracyclines, and three types of macrolides, was developed. Half of these antibiotics were not determined by ultraviolet (UV) because of their lack of UV-absorbing groups. Formic acid (FA) (pH 2.50) with low conductivity was employed as the background electrolyte (BGE) in comparison with three BGE systems (i.e., HAc, HCl and H3PO4), which not only allowed complete protonation and electrophoresis separation but provided more cost-effectiveness and shorter analysis time. Under these conditions, a UV detector was employed as an additional detection mode to evaluate the qualitative analysis of 6 antibiotics possessing UV absorbing groups. Moreover, it was found that the sensitivities of the C4D and UV detectors were similar. Albeit a slightly reduced sensitivity of C4D in the analysis of norfloxacin, enrofloxacin and tylosin compared to UV, enough points were achieved to detect all analytes by C4D. The repeatability with respect to peak areas and migration times was better than 4.69% and 2.48% (n = 5), respectively. Mixed liquid pharmaceutical formulations of tobramycin eye drops having non-UV absorbing groups and ofloxacin eye drops possessing UV absorbing groups have been separated and detected in a single run by this technique. The studied recoveries of the two were 100% and 103%, respectively.

A Rapid and Simple Dual-Channeled Capillary Electrophoresis with Contactless Conductivity Detection Method for the Determination of Adenosine, Cordycepin, and Inosine in Ophiocordyceps sinensis-Based Products

This study aims to propose a tool for food control activities that can be realizable even with a modest infrastructure, using purpose-made capillary electrophoresis (CE) instrumentation with capacitively coupled contactless conductivity detection (C4D). For demonstration of a featured application, we reported herein a simple and inexpensive method for authentication and quality control of Ophiocordyceps sinensis-based products (literally known as “summer grass, winter worm”). This species, originally found on the Tibetan plateau and in the Himalayas, between elevations of 3000–5000 m, is classified as a medicinal mushroom and has been used as a precious component in traditional Chinese and Vietnamese medicine. Due to its high value and rareness, counterfeit products have emerged, leading to the need for quality control activities. For this purpose, a CE-C4D methodology was developed to determine their adenosine, cordycepin, and inosine contents. These compounds were analyzed on two channels of the purpose-made instrument, with the best-achieved detection limits of 11.2–22.0 μg/g using the developed CE-C4D methods. Cross-checking data using the reference method (HPLC-DAD) was provided to prove the reliability of the analytical results obtained with CE-C4D. Good agreement for the two pairs of data was achieved, with the result deviation being less than 12%.

SIMULTANEOUS DETERMINATION OF FLUORIDE, ACETATE, FORMATE, CHLORIDE, NITRATE, AND SULFATE IN DISTILLED ALCOHOLIC BEVERAGES WITH ION CHROMATOGRAPHY/CONDUCTIVITY DETECTOR

A novel ion chromatography with suppressed conductivity detection method was developed for simultaneous determination of fluoride, acetate, formate, chloride, nitrate, and sulphate in distilled alcoholic beverages. In this study, bromide was used as an internal standard. The separation of the anions was accomplished by utilising an anion exchange column with gradient eluent program. The chromatographic conditions were as follows: the suppressor current was 31 mA; the flow rate of the mobile phase was 0.25 mL min-1; the column and detector compartment temperature were 35 °C and 40 °C, respectively; sample loop volume was 10 μL. All the calibration curves showed good linearity (r2 ≥ 0.999). The limits of detection (LOD) values were between 0.56 and 13.2 μg L-1 while the limits of quantification (LOQ) values were between 1.80 and 43.9 μg L-1. To evaluate the accuracy, a raki sample was spiked with standard solutions at three different concentration levels and the average recoveries were found in the range of 94.90% - 101.71%. Intra-day and inter-day precision studies were also investigated and the relative standard deviations (RSDs %) were less than 5.99%. The validated method was applied to the three kinds of commercial samples: Turkish raki, vodka, and gin.

Salinity Independent Flow Measurement of Vertical Upward Gas-Liquid Flows in a Small Pipe Using Conductance Method.

Flow measurement in gas-liquid two-phase flow is always a challenging work, because of the non-uniform phase distribution, severe slippage effect between phases, and different flow structures. Furthermore, the variation of salinity changes the water conductivity, which brings more difficulties to multiphase flow measurement. In this study, a methodology for flow measurement using the conductance method in gas-liquid two-phase flow with salinity change is proposed. The methodology includes the suitable conductivity detection method, the strategy of using combined sensors, and the measurement models of flow parameters. A suitable conductivity detection method that can guarantee that the sensor output is linearly proportional to the conductivity is proposed. This conductivity detection method can ensure that the sensors have a high and constant resolution in the conductivity variation caused by water holdup under the conditions of water conductivity change. Afterward, a combined sensor system consisting of a water holdup sensor, velocity sensor, and water conductivity sensor is designed and experimentally evaluated in gas-water two-phase flow in a 20 mm inner diameter pipe. Considering the non-uniform phase distribution, severe slippage effect between phases, different flow structures, and the variation of salinity, a new water holdup measurement model and flow velocity measurement models are established to achieve salinity independent water holdup measurement and flow velocity measurement for the first time.

Determination of trace bromate in various water samples by direct-injection ion chromatography and UV/Visible detection using post-column reaction with triiodide

Bromate is a disinfection by-product generated mainly from the oxidation of bromide during the ozonation and disinfection process in order to remove pathogenic microorganism of drinking water, and classified as a possible human carcinogen by International Agency for Research of Cancer (IARC) and World Health Organization (WHO). For the purpose of determining the trace level concentration of bromate, several sensitive techniques are applied mostly based on suppressed conductivity detection and UV/Visible detection after postcolumn reaction (PCR). In this study, the suppressed conductivity detection method and the PCR-UV/Visible detection method through the triiodide reaction were compared to analyze the trace bromate in water samples and estimated for the availability of these analytical methods. In addtion, the state-of-the-art techniques was applied for the determination of trace level bromate in various water matrices, i.e., soft drinking water, hard drinking water, mineral water, swimming pool water, and raw water. In comparison of two analytical methods, it was found that the conductivity detection had the suitable advantage to simultaneously analyze bromate and inorganic anions, however, the bromate might not be precisely quantified due to the matrix effect especially by chloride ion. On the other hand, the trace bromate was analyzed effectively by the method of PCR-UV/ Visible detection through triiodide reaction to satisfactorily minimize the matrix interference of chloride ion in various water samples, showing the good linearity and reproducibility. Furthermore, the method detection limit (MDL) and recovery were 0.161 μg/L and 101.0–108.1 %, respectively, with a better availability compared to conductivity detection.

Salt‐spray corrosion behavior of a Cu–Al composite plate under AC current

AbstractCu–Al composite plate corrosion tests, under a 0–100 A AC current, were conducted for 48 hr in a neutral salt spray. The morphology and corrosion products were studied by scanning electron microscope and X‐ray powder diffraction, through which the effect of the current was analyzed. Meanwhile, the rate and degree of corrosion were evaluated by weight loss, electrochemical and electrolytic conductivity detection methods. The results showed that when the current increased, the corrosion rate initially increased and then decreased. When the current value was 50 A, the corrosion rate was the highest. The corrosion of the Cu–Al composite plate mainly included galvanic corrosion at the interface and pitting on the aluminum matrix, with no corrosion on the copper matrix. The state of the passivation film changed to loose, peeling, rupture, accumulation, compact, and so on when the current value increased. The type of corrosion product was not affected by the current value. The current affects the electromobility of the chloride ions by influencing the conductivity of the corrosion medium. The higher the electromobility of the chloride ions, the less the destruction of the passivation film and as a result, there is a decreased rate and degree of corrosion.

Generic Ion Chromatography–Conductivity Detection Method for Analysis of Palladium Scavengers in New Drug Substances

The revolution of palladium-catalyzed reactions in the synthesis of new molecules has created an unprecedented need for highly efficient palladium (Pd) removal processes. Metal scavengers with very selective and efficient removal properties are being extensively applied across process research and development (PRD however, developing methodologies to detect a variety of Pd scavengers in multicomponent reaction mixtures is currently considered an emerging challenge in pharmaceutical analysis. Herein a simple and efficient generic ion chromatography–conductivity detection (IC–CD) method on a Dionex IonPac AS19 column in conjunction with a fully aqueous eluent profile (potassium-hydroxide-based) capable of chromatographically resolving over 10 Pd scavenger species commonly used in PR&D workflows is described. Computer-assisted separation modeling using an ACD Labs/LC si...

Optimization of a capillary zone electrophoresis-contactless conductivity detection method for the determination of nisin.

Determination of natural preservatives using electrophoretic or chromatographic techniques in fermented milk products is a complex task due to the following reasons: (i) the concentrations of the analytes can be below the detection limits, (ii) complex matrix and comigrating/coeluting compounds in the sample can interfere with the analytes of the interest, (iii) low recovery of the analytes, and (iv) the necessity of complex sample preparation. The aim of this study was to apply capillary zone electrophoresis coupled with contactless conductivity detection for the separation and determination of nisin in fermented milk products. In this work, separation and determination of natural preservative-nisin in fermented milk products is described. Optimized conditions using capillary zone electrophoresis coupled with capacitance-to-digital technology based contactless conductivity detector and data conditioning, which filter the noise of the electropherogram adaptively to the peak migration time, allowed precise, accurate, sensitive (limit of quantification: 0.02μg/mL), and most importantly requiring very minute sample preparation, determination of nisin. Sample preparation includes following steps: (i) extraction/dilution and (ii) centrifugation. This method was applied for the determination of nisin in real samples, i.e. fermented milk products. The values of different nisin forms were ranging from 0.056±0.003μg/mL to 9.307±0.437μg/g.

Ion Chromatography with Post-column Reaction and Serial Conductivity and Spectrophotometric Detection Method Development for Quantification of Transition Metal Dissolution in Lithium Ion Battery Electrolytes

We present a method for the separation and determination of transition metals in electrolytes based on ion chromatography (IC) with post-column reaction (PCR) and serial conductivity and spectrophotometric detection. Three IC columns [Metrosep C4—250/4.0 (column A), Metrosep C6—250/4.0 (column B), and Nucleosil 100-5SA—250/4.6 (column C)] with different capacities, and stationary phases were used and compared with each other for method development. All spectrophotometric measurements were carried out with 4-(2-pyridylazo)resorcinol (PAR) as PCR reagent at a wavelength of 500 nm. To characterize the precision of the separation, the selectivity for the analysis of transition metals (nickel, cobalt, copper, and manganese) in the presence of large amounts of lithium and the resolution of the peaks were determined and compared with one another. Furthermore, the limits of detection (LOD) and quantification (LOQ) were determined for the transition metals. The LODs and LOQs determined by column C were as follows: cobalt (LOD/LOQ): 9.4 µg L−1/31.3 µg L−1, manganese (LOD/LOQ): 7.0 µg L−1/23.5 µg L−1, and nickel (LOD/LOQ): 6.3 µg L−1/21.1 µg L−1. Finally, the concentration of transition metal dissolution of the cathode material Li1Ni1/3Co1/3Mn1/3O2 (NCM) was investigated for different charge cut-off voltages by the developed IC method.

Tributyl phosphate assisted hollow-fiber liquid-phase microextraction of short-chain fatty acids in microbial degradation fluid using capillary electrophoresis-contactless coupled conductivity detection

A tributyl phosphate assisted hollow-fiber liquid-phase microextraction coupled with capillary electrophoresis-contactless coupled conductivity detection (HF-LPME/CE-C4D) method has been developed for trace analysis of common short-chain fatty acids (SCFAs) without derivatization. Under the optimum conditions, ten SCFAs including a pair of isomers were well separated from their homologous FAs and the main coexisting inorganic anions within 40 min. Tributyl phosphate assisted HF-LPME produced excellent purification and enrichment for the model sample with high-salt matrix, microbial degradation fluid, and the limits of detection could reach 0.072–0.67 ng/mL (S/N = 3). Owing to its high sensitivity, good linearity, and acceptable recovery, this proposed method provided a sensitive and environment-friendly alternative for trace analysis of SCFAs in complicated samples.

Determination of phospholipid and fatty glyceride in liposome by RP-HPLC with capacitively coupled contactless conductivity detector

In this study, a gradient RP-HPLC with capacitively coupled contactless conductivity detection (RP-HPLC-C4D) method for simultaneous determination of phospholipid and fatty glyceride in liposome was developed.

Capillary electrophoresis with capacitively coupled contactless conductivity detection method development and validation for the determination of azithromycin, clarithromycin, and clindamycin.

A capillary electrophoresis with capacitively coupled contactless conductivity detection based method for the assay of azithromycin, clarithromycin and clindamycin was optimized and validated in this study. A buffer solution of 20mM 2-(N-morpholino) ethane sulfonic acid, 40mM l-histidine and 0.6mM cetyltrimethylammonium bromide (pH 6.39) was used for the electrophoresis. An uncoated, bare-fused silica capillary (total length 60cm, effective length 32cm, 75μm id) was used at 25°C. The sample was injected hydrodynamically at 0.5psi for 5s. The electrophoresis was conducted at 30kV in reverse polarity for 6min with 3 and 2min of in-between sodium hydroxide (0.1M) and background electrolyte rinsing, respectively. Ammonium acetate was used as internal standard. This simple and robust method showed reasonable limit of detection and limit of quantitation for azithromycin (0.0125/0.03mg/mL), clarithromycin (0.017/0.03mg/mL), and clindamycin (0.038/0.06mg/mL), with good selectivity, precision both intraday (relative standard deviation≤1.0%) and interday (relative standard deviation<3.7%), linearity (R2 >0.999) and recovery (99-101.7%). The method was successfully applied for the determination of azithromycin, clarithromycin and clindamycin in formulations.

A rapid ion chromatography column-switching method for online sample pretreatment and determination ofl-carnitine, choline and mineral ions in milk and powdered infant formula

A simple and rapid column-switching ion chromatography with non-suppressed conductivity detection method was developed for simultaneous determination ofl-carnitine, choline and mineral ions in milk and powdered infant formula samples.

Electromembrane extraction of diamine plastic restricted substances in soft drinks followed by capillary electrophoresis with contactless conductivity detection.

Ethane-1,2-diamine (EA) and hexane-1,6-diamine (HA) are two important plastic restricted substances commonly existing in food contact materials. A capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) method has been developed for direct determination of above analytes, and the detection sensitivity has been significantly improved based on electromembrane extraction (EME). Under the optimum conditions, EA and HA could be well separated from their aliphatic diamine homologs as well as the common inorganic cations within 25min. The limits of detection could reach sub-ng/mL level, and good linearity (r>0.998) between peak area and analyte concentration could be obtained at three orders of magnitude. This EME/CE-C4D method provided a novel application for determining these plastic restricted substances in different bottled soft drinks, providing an alternative for the sensitive analyses of diamine substances.