Direct Conductivity Detection Research Articles

A Study on Double Inputs Direct Contact and Single Output Capacitively Coupled Conductivity Detector.

In this paper, an improved double inputs direct contact and single output capacitively coupled conductivity detector (DISODCD) based on traditional contactless capacitively coupled conductivity detector (C4D) is developed. The sensor uses double inputs of the contact electrode and capacitively coupled output of the contactless electrode and a lock-in amplifier to reduce interfering noise signals and amplify gain. Parallel circuit counteracts the part of the adverse capacitance reactance introduced by electrode polarization and reduces the effect of the impedance caused by the coupled wall capacitance to measure the resistance of solution. The sensor reduces limit of detection (LOD) of analyte and improves the sensitivity of the device. The LOD of the potassium chloride solution is 1 nM, and the detection range is 0.01 μM to 10 mM in actual testing for a single sample. The ratio of the response of potassium chloride solution to background ultrapure water at low concentrations is better than that of double input capacitively coupled contactless conductivity detector (DIC4D) and direct contact conductivity detection (DCD) under the same condition. In the case that the test cell is contaminated with impurities, pollution of impurities has little effect on the response of DISODCD. In practical application, it has a good service life.

Reversed-phase ion-pair solid-phase extraction and ion chromatography analysis of pyrrolidinium ionic liquid cations in environmental water samples.

A method of reversed-phase ion-pair solid-phase extraction combined with ion chromatography for determination of pyrrolidinium ionic liquid cations (N-methyl-N-ethyl pyrrolidinium, N-methyl-N-propyl pyrrolidinium, and N-methyl-N-butyl pyrrolidinium) in water samples was developed in this study. First, ion-pair reagent sodium heptanesulfonate was added to the water samples after static, centrifugation and filteration. Then, pyrrolidinium cations in the samples were enriched and purified by a reversed-phase solid-phase extraction column, and eluted from the column with methanol aqueous solution as eluent. Finally, the eluate collected was analyzed by ion chromatography. The separation and direct conductivity detection of these pyrrolidinium cations by ion-exchange column using 1.0mM methanesulfonic acid (in water)/acetonitrile (97:3, v:v) as mobile phase was achieved within 10min. By using this method, pyrrolidinium cations in Songhua River and Hulan River were successfully extracted with the recoveries ranging from 74.2 to 97.1% and the enrichment factor assessed as 60. Pyrrolidinium cations with the concentration of 0.001-0.03mg/L can be enriched and detected in the water samples. The developed method for the determination of pyrrolidinium ionic liquid cations in water samples is simple and reliable, which provides a reference for the study of the potential impact of ionic liquids on the environment.

Analytical Methods for Ionic Profile of Dialysate Iron Therapy Drug Ferric Pyrophosphate Citrate By Ion Chromatography using Suppressed and Non-Suppressed Conductivity Detection

In present study, ionic profile of pharmaceutical drug molecule ferric pyrophosphate citrate by ion exchange chromatography using conductivity detection was carried out. Ferric pyrophosphate citrate is an iron organic complex used for hemodialysis for the chronic kidney disease patients. The drug is used as iron supplementation to balance the iron loss during the dialysis for the kidney affected patients. Anions, cation and metal ion were analyzed by ion chromatographic method. Relevant anions sulphate, phosphate, citrate and pyrophosphate were analyzed by suppressed conductivity detection. Both isocratic and gradient separation methods were developed for the anions analysis. Cation sodium was analyzed by non-suppressed conductivity detection. Metal iron was determined by direct conductivity detection. All the analyses were done covering selectivity, precision, linearity and accuracy aspects of analysis. Calibration outcome of RSD 0.4 to 3.0% and correlation coefficient values greater than 0.999 were observed during the studies. Spiking studies were done to check the accuracy of the analysis and the recovery values ranging from 93 to 110% were observed. Around 90% ionic content of the drug molecule can be characterized using the developed ion chromatographic methods. These methods can be directly applied for the routine analysis of drug in the pharmaceutical industries.

Extraction and determination of pyridinium ionic liquid cations in environmental water samples by using strong cation exchange solid phase extraction and ion chromatography

ABSTRACTThis paper presents a novel analytical method for the determination of pyridinium ionic liquid cations in environmental water samples by ion chromatography coupled with solid phase extraction. The water samples were purified and enriched by a sulphonic acid extraction column, and then the impurities were washed with 10 mL water – 20% (v/v) acetonitrile solution and the analytes eluted with 0.5 mol L−1 phosphoric acid – sodium dihydrogen phosphate buffer solution – 55% methanol. The eluted analytes were determined by ion chromatography with 3.0 mmol L−1 methane sulphonic acid – 8% acetonitrile as the mobile phase and direct conductivity detection. Three pyridinium cations were completely separated in 20 min and the retention mechanism basically conforms to the ion exchange mode. The newly developed method has been successfully applied to the analysis of pyridinium cations in spiked environmental water samples, which provided satisfactory recoveries in the range of 98.8% to 100.0% with the relative standard deviations less than 2.8%. The concentration of 0.004 to 0.01 mg L−1 in water samples can be preconcentrated by this method. The method is accurate, reliable, simple and practical. This research provides a new reference for detecting ionic liquid cations in environmental water samples and studying the environmental risk assessment of ionic liquids.

Determination of morpholinium ionic liquid cations in environmental water samples: development of solid-phase extraction method and ion chromatography.

An ion chromatography and solid-phase extraction method has been applied for the separation and detection of morpholinium cations in environmental water samples. The water samples were purified and enriched by a UF-SCX sulfonic acid extraction column and eluted with 0.5molL-1 phosphoric acid/sodium dihydrogen phosphate buffer solution/55% methanol. The target compounds were separated on a carboxylic acid cation exchange column with 5.0mmolL-1 methane sulfonic acid/2% acetonitrile as the mobile phase and direct conductivity detection. The method has been successfully applied to extract morpholinium cations from spiked water samples of Songhua River, Hulan River, East Lake, and Mopanshan Reservoir in China with the recoveries ranging from 75.0% to 98.3%. The relative standard deviations of intraday precision and interday precision are 2.1% and 5.9% or less, respectively. Using this method it is possible to preconcentrate water samples to 0.01-0.04mgL-1. The results show that the method is applicable to detection of morpholinium ionic liquid cations in environmental water samples and provides a new approach for monitoring ionic liquids in environmental water. Graphical abstract The analysis procedure of morpholinium ionic liquids in environmental water samples.

Rapid and simultaneous determination of piperidinium and pyrrolidinium ionic liquid cations by ion pair chromatography coupled with direct conductivity detection

A method of ion-pair chromatography with direct conductivity detection was developed on a silica-based monolithic column for the fast and simultaneous determination of piperidinium and pyrrolidinium ionic liquid cations. The effects of the mobile phase, column temperature and flow rate on the retention of the cations were investigated. The retention rules were discussed. As an ion-pair reagent, sodium heptanesulfonate is more suitable than sodium pentanesulfonate for the separation and determination of piperidinium and pyrrolidinium cations. The increase of ion-pair reagent concentration led to the increased retention time of the cations. When acetonitrile content and mobile phase flow were increased, the retention time of the cations became shorter. The retention of piperidinium and pyrrolidinium cations is an exothermic process, and the retention of the cations conforms to the carbon number rule. The chromatographic analysis was performed using the Chromolith Speed ROD RP-18e column, 0.5mmol/L sodium heptanesulfonate-5% acetonitrile as the mobile phase at a flow rate of 3.0mL/min and column temperature of 30°C. Separation of N-methyl-N-ethyl piperidinium, N-methyl-N-propyl piperidinium, N-methyl-N-butyl piperidinium and N-methyl-N-ethyl pyrrolidinium, N-methyl-N-propyl pyrrolidinium, N-methyl-N-butyl pyrrolidinium cations were achieved within 10min. The detection limits (S/N=3) were between 0.19 and 3.08mg/L. Relative standard deviations (n=5) for peak areas were less than 1.2%. The method has been applied to the determination of piperidinium and pyrrolidinium cations in ionic liquid samples. The spiked recoveries of ionic liquid cations were between 96% and 111%. The method is accurate, reliable, rapid, and has a better practicability.

Ion Chromatography of Tri-Substituted Imidazolium Ionic Liquid Cations: Method and Application for Octanol–Water Partition Coefficient (KOW) Determination

A method was developed for simultaneous determination of four trisubstituted imidazolium ionic liquid cations (1-ethyl-2,3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-pentyl-2,3-dimethylimidazolium) by ion chromatography using a carboxylic acid cation exchanger bonded to a silica-based column and direct (nonsuppressed) conductivity detection. The effects of the type of eluents, organic acid concentration, acetonitrile volume fraction, and column temperature on the cations retention were investigated. The optimal conditions for the method were 5 mmol L−1 methanesulfonic acid +10% acetonitrile as an eluent, 1.0 mL min−1 flow rate, and a column temperature of 30°C. The detection limit (S/N = 3) were 0.82–2.39 mg L−1 for the cations. The method was validated, accurate, and reproducible. This method was successfully applied to determine trisubstituted imidazolium ionic liquid cations in spiked tap water. The octanol–water partition coefficients (Kow) of these four trisubstituted imidazole substances were also reported in this study.

Analysis of piperidinium ionic liquid cations by ion chromatography with direct conductivity detection

A method of ion chromatography with direct conductivity detection was established to determine three piperidinium ionic liquid cations, i. e. N-methyl, ethyl piperidinium cation ([MEPi]+), N-methyl, propyl piperidinium cation ([MPPi]+) and N-methyl, butyl piperidinium cation ([MBPi]+). The effects of eluent types, eluent concentration and column temperature on the retention of the cations were investigated with sulfonic acid base cation exchange column using ethylenediamine-citric acid-acetonitrile as eluent. The results indicated that, with the increase of column temperature, the retention times of piperidinium cations were reduced, so the retention process of piperidinium cations was exothermic. The retentions of piperidinium cation homologue accorded with carbon number rule. The successful separation of the three piperidinium cations within 7 min was achieved using the optimized eluent of 0.2 mmol/L ethylenediamine-0.3 mmol/L citric acid-3% acetonitrile (pH 4.4) at a flow rate of 1.0 mL/min and the column temperature of 30 degrees C. Under these conditions, the detection limits at a signal-to-noise ratio of 3 for [MEPi]+, [MPPi] and [MBPi]+ were 0.14, 0.20 and 0.56 mg/L, respec-tively. The relative standard deviations (n = 5) for peak areas were less than 1.2%. The method has been applied to the determination of piperidinium ionic liquids synthesized in chemical laboratory with the spiked recoveries of 97.6% to 105.1%. The method is accurate, reliable, rapid, and has better practicability.

Analysis of piperidinium ionic liquid cations by ion chromatography with direct conductivity detection

Analysis of piperidinium ionic liquid cations by ion chromatography with direct conductivity detection

Determination of ionic liquid anions of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate by ion-pair chromatography with direct conductivity detection

An ion-pair chromatographic method with direct conductivity detection was established on a reversed-phase silica-based column for the simultaneous determination of ionic liquid anions of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate. The analytes were separated using a mobile phase of ion pair reagent-malic acid-acetonitrile on the Diamonsil C18 column. The effects of mobile phase composition and column temperature on the retention of the anions were investigated. The optimized chromatographic conditions were as follows: 0.15 mmol/L tetrabutylammonium hydroxide-0.099 mmol/L malic acid-20% (v/v) acetonitrile aqueous solution (pH 6.5) as mobile phase, a column temperature of 25 degrees C. Under the optimal conditions, the baseline separation of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate was achieved without any interference by other ordinary anions (fluoride, chloride, bromide, nitrate, sulfate). The detection limits (S/N = 3) were 0.21, 0.07, 0.36 and 0.12 mg/L for trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate, respectively. The method has been applied to the determination of the four anions in ionic liquids. The spiked recoveries of the anions were from 95.0% to 104.6%. The results demonstrate that the convenience, rapidity, sensitivity and accuracy are fit for the requirements of quantitative analysis of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate in ionic liquids.

Fast analysis of thiocyanate by ion-pair chromatography with direct conductivity detection on a monolithic column

Abstract Fast analysis of thiocyanate by ion-pair chromatography using a silica-based monolithic column and direct conductivity detection was carried out. Chromatographic separation was performed on a Chromolith Speed ROD RP-18e using tetrabutylammonium hydroxide (TBA)–phthalic acid–acetonitrile as eluent. The effects of eluent concentration, eluent pH value, column temperature and flow rate on retention time of thiocyanate were investigated. The optimized chromatographic conditions for the determination of thiocyanate were as follows: 0.25 mmol/L TBA–0.18 mmol/L phthalate–7% acetonitrile (pH 5.5) as eluent, column temperature of 30 °C, and flow rate of 6.0 mL/min. Retention time of thiocyanate was less than 1 min under the conditions. Common anions (Cl−, NO3−, SO42− and I−) did not interfere with the determination of thiocyanate. Detection limit (S/N = 3) of thiocyanate was 0.96 mg/L. Calibration graph between peak area and the concentration of thiocyanate was linear in the range of 2.0–100.0 mg/L. Relative standard deviation (RSD) of chromatographic peak area was 1.4% (n = 5). This method has been applied to the determination of thiocyanate in ionic liquids. Recoveries of thiocyanate after spiking were 100.5%.

Separation and determination of pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection

Abstract A method for rapid and simultaneous determination of multiple pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection was developed. Chromatographic separations were performed on a cation exchange column using ethylenediamine-acetonitrile as the mobile phase. The effects of chromatographic column and the mobile phase, as well as the column temperature on the retention of the cations were investigated. The retention rules of the cations under different chromatographic conditions were formulated. The retention of the cations followed the carbon number rule. The method has been successfully applied to the determination of three ionic liquids synthesized by a chemical laboratory.

RAPID AND SIMULTANEOUS DETERMINATION OF TRIFLUOROACETATE, TRIFLUOROMETHANESULFONATE, TETRAFLUOROBORATE, AND HEXAFLUOROPHOSPHATE ORGANIC AND INORGANIC ANIONS OF IONIC LIQUIDS BY ION-PAIR CHROMATOGRAPHY USING A REVERSED-PHASE SILICA-BASED MONOLITHIC COLUMN AND CONDUCTIVITY DETECTION

An ion-pair chromatographic method was developed on a reversed-phase silica-based monolithic column for the fast and simultaneous determination of trifluoroacetate (CF3COO−), trifluoromethanesulfonate (), tetrafluoroborate (), and hexafluorophosphate () organic and inorganic anions of ionic liquids. The analytes were separated using a mobile phase of tetrabutylammonium hydroxide–citric acid–acetonitrile on the Chromolith Speed ROD RP-18e column with direct conductivity detection. The effects of eluent, column temperature, and flow rate on the retention of anions were investigated. The experimental phenomenon was discussed according to ion-exchange and hydrophobic interaction mechanism in the separation. The optimized chromatographic conditions were selected. Under the optimal conditions, the baseline separation of CF3COO−, , , and was achieved without any interference by other anions (Cl−, Br−, I−, , , and ). The detection limit (S/N = 3) was 3.33, 0.58, 0.27, and 1.42 mg/L for CF3COO−, , , and , respectively. The method has been successfully applied to the determination of , CF3COO−, , and in ionic liquids. The spiked recoveries of the anions were from 100.1–104.4%.

DETERMINATION OF PYRIDINIUM IONIC LIQUID CATIONS BY ION CHROMATOGRAPHY WITH DIRECT CONDUCTIVITY DETECTION

Determination of two pyridinium ionic liquid cations (1-ethyl pyridinium cation and 1-butyl pyridinium cation) by ion chromatography using a carboxylic acid based cation-exchange column and direct conductivity detection was carried out. The optimized chromatographic conditions were 8.0 m mol L−1 methanesulfonic acid +5% acetonitrile (v/v) as eluent, flow rate of 1.0 mL min−1, and column temperature of 45°C. Detection limits (S/N = 3) for the two cations were 1.93 and 4.68 mg L−1, respectively. Relative standard deviations (n = 5) for peak areas were less than 0.8%. This simple method was successfully applied to determine pyridinium ionic liquids in spiked surface water.

Analytical Methods for the Determination of Traces of Cr(VI) in Water Samples with Suppressed Ion Chromatography

A rapid and sensitive method for the direct determination of hexavalent chromium in natural waters has been developed. Anion exchange chromatography was used for the fast separation of chromates from matrix anions, within 15 minutes, using a 35 mM KOH eluant. Mobile phase suppression was employed prior to direct conductivity (CD) detection, comparing two different electrolytic suppressor models and achieving a 10 times lower detection limit. Post column derivatization of Cr(VI) with diphenylcarbazide was used for further selective diode array (PDA) detection. Possible Cr(III) interference was evaluated with the addition of concentrations up to 10 mg/L of Cr(III) in a Cr(VI) positive natural water sample resulting in negligible interference. Both detection techniques gave instrumental LOD of 0.05 µg/L and method LOD of 0.08 µg/L for CD and 0.05 µg/L for PDA detection in underground water. Average repeatability and reproducibility (%RSD) was 1.3% and 5.4% for CD and 1.3% and 6.1% for PDA detection for two concentration levels. Recovery ranged from 70% to 103% for CD and from 90% to 100% for PDA. Method accuracy was additionally confirmed by analyzing positive samples with LC-ICP-MS. The method was successfully applied to the determination of Cr(VI) in several tap, spring and groundwater samples from the wider area of Asopos River, Greece. High concentrations where confirmed to the majority of the analyzed samples, revealing the serious and expanded problem of industrial pollution.

Rapid Determination of Trifluoromethanesulfonate and p-Toluenesulfonate by Ion-Pair Chromatography Using a Reversed-Phase Silica-Based Monolithic Column: Application to the Analysis of Ionic Liquids

A method of ion-pair chromatography was developed on a reversed-phase silica-based monolithic column for the fast and simultaneous determination of trifluoromethanesulfonate (CF3SO3−) and p-toluenesulfonate (C7H7SO3−). The analysis was performed using a mobile phase of tetrabutylammonium hydroxide + citric acid + acetonitrile on the Chromolith Speed ROD RP-18e column with direct conductivity detection. The effects of the eluent, column temperature and flow rate on the retention of the anions were investigated. The experimental phenomenon was discussed according to hydrophobic interaction and ion-exchange mechanism in the separation. The optimized chromatographic conditions were selected. The optimized eluent for the separation consisted of 0.2 mmol L−1 tetrabutylammonium hydroxide + 0.10 mmol L−1 citric acid + 9% acetonitrile (pH 5.5). The flow rate was set at 6.0 mL min−1. The column temperature was 25 °C. Under the optimal conditions, the better separation of CF3SO3− and C7H7SO3− was achieved without any interference by other anions (Cl−, Br−, I−, NO3−, SO42−, ClO3−, BF4− and PF6−). The detection limit (S/N = 3) was 0.28 and 0.71 mg L−1 for CF3SO3− and C7H7SO3−, respectively. The method has been applied to the determination of CF3SO3− and C7H7SO3− in ionic liquids. The spiked recoveries of CF3SO3− and C7H7SO3− were 101.1 and 100.2%, respectively.

Determination of Homologue Imidazolium Ionic Liquid Cations by Ion Chromatography Using a Carboxyl Acid Cation-Exchange Column with Direct Conductivity Detection

An investigation into the determination of four imidazolium ionic liquid cations by ion chromatography using a carboxyl acid cation exchange column and direct conductivity detection was carried out. This research has developed a simple, selective, and accurate ion chromatographic method for separation of imidazolium ionic liquid cations. Detection limits (S/N = 3) for the cations were 3.2–24.3 mg/L. Relative standard deviations (RSD, n = 5) for peak areas were less than 1.6%. The method has been successfully applied to the determination of two ionic liquids synthesized by organic chemistry lab.

Simultaneous determination of trifluoroacetate, tetrafluoroborate and halide ions in ionic liquid by ion chromatography

A method was developed for the simultaneous determination of trifluoroacetate, tetrafluoroborate and halide ions (FF-, Cl-, Br-) by ion chromatography with direct conductivity detection. The chromatographic separation was performed on a Shim-pack IC-A3 anion-exchange column with potassium biphthalate, phthalic acid + tris (hydroxymethyl) -aminomethane, and p-hydroxybenzoic acid + tris (hydroxymethyl) -aminomethane + boric acid as eluent, separately. The effects of the nature of eluent, eluent concentration, acetonitrile concentration and column temperature on the separation and the retention factors of the anions were investigated. The optimized chromatographic conditions for the determination of the anions were as follows: 1.2 mmol/L potassium biphthalate as eluent, a column temperature of 45 degrees C and a flow rate of 1.0 mL/min. Under the optimal conditions, the anions were baseline separated. Moreover, the symmetries of peaks were better. The limits of detection (S/N = 3) for the anions were in the range of 0.01 - 0.50 mg/L. The relative standard deviations (RSDs) of the chromatographic retention time and peak area for the anions were not more than 0.2% and 1.2% (n = 5), respectively. The method has been applied to the determination of trifluoroacetate, tetrafluoroborate and halide ions in ionic liquids. The spiked recoveries of the anions were from 98.0% to 103.2%. The method is simple, accurate and reliable, and has better practicability.

Rapid and Simultaneous Determination of Tetrafluoroborate, Thiocyanate and Hexafluorophosphate by High-Performance Liquid Chromatography Using a Monolithic Column and Direct Conductivity Detection

A method was developed for fast and simultaneous determination of tetrafluoroborate (BF(4)(-)), thiocyanate (SCN(-)) and hexafluorophosphate (PF(6)(-)) by high-performance liquid chromatography using a silica-based monolithic column and direct (non-suppressed) conductivity detection. Chromatographic separation was performed on a Chromolith Speed ROD RP-18e column with tetrabutylammonium hydroxide (TBA) + citric acid + acetonitrile as eluent. The effects of the types of eluent, TBA concentration, acetonitrile volume fraction, eluent pH, column temperature and flow rate on the retention of anions were investigated. The optimized chromatographic conditions were selected. Under the optimal conditions, the baseline separation of BF(4)(-), SCN(-) and PF(6)(-) was achieved without any interference by other anions (F(-), Cl(-), Br(-), I(-), NO(3)(-), ClO(3)(-) and SO(4)(2-)). The detection limit (S/N = 3) was 0.42, 0.46 and 1.42 mg L(-1) for BF(4)(-), SCN(-) and PF(6)(-), respectively. The present method was successfully applied to the determination of BF(4)(-), SCN(-) and PF(6)(-) in ionic liquids.

LC Analysis of Hexafluorophosphate on a Monolithic Column: Application to the Analysis of Ionic Liquids

A silica-based monolithic column with tetrabutylammonium hydroxide–phthalic acid–acetonitrile as mobile phase has been used for LC analysis of hexafluorophosphate with direct conductivity detection. The effects of mobile phase composition, column temperature, and flow rate on retention of hexafluorophosphate were investigated and the optimum chromatographic conditions were selected. Common anions and tetrafluoroborate did not interfere with analysis of hexafluorophosphate. The detection limit (S/N = 3) for hexafluorophosphate was 6.2 mg L−1. Relative standard deviation (n = 5) for peak area was 0.1%. The method was successfully used for analysis of hexafluorophosphate in ionic liquids.