Determination of six components in Rhubarb by cyclodextrin-modified micellar electrokinetic chromatography using a mixed micellar system of sodium cholate and sodium taurocholate

A cyclodextrin-modified micellar electrokinetic chromatographic method was established to determine five anthraquinone derivatives and a distyrene derivative in Rhubarb. The six components were successfully separated by using the mixed micellar system consisting of 20 mmol/l SC and 20 mmol/l STC with 15 mmol/l β-CD in the BGE of 20 mmol/l borax buffer (pH 11) in less than 20 min. Effect of SC and STC concentrations, pH of BGE and concentration of β-CD on the separation was studied. The analytical performance of the method was discussed in terms of linearity response, precision, detection limits, quantitation limits and recoveries. The method developed was applied to the determination of three commercial Rhubarb samples. The results obtained agreed with those of the reported documents.     

Sol-gel monolithic anion-exchange column for capillary electrochromatography

A single-step approach has been used to prepare a monolithic electrochromatographic column by sol-gel processing of an organofunctional silicon alkoxide precursor that contains a propyl-N,N,N-trimethylammonium group. We have found that the time of adding the porogen, poly(ethylene glycol), during the sol-gel reaction affected the separation performance. Since the surface charge of this material is switchable in sign upon manipulation of solution pH, the direction and magnitude of the electroosmotic flow (EOF) can be controlled by adjusting the pH of the running electrolyte. By controlling the direction of the EOF from cathode to anode, inorganic anions can be separated in a short time. Because of the quaternary ammonium functional group, the resulting material is anion exchangeable. Interestingly, the anion-exchange selectivity of inorganic anions on this column changes with solution pH or applied voltage. The column shows excellent run to run reproducibility (R.S.D. < 0.4%), good day to day reproducibility (R.S.D. < 4%), and reasonable column to column reproducibility (R.S.D. < 9%).     

Polymeric ionic liquid as additive for the high speed and efficient separation of aromatic acids by co-electroosmotic capillary electrophoresis

A simple and reliable co-electroosmotic capillary electrophoresis system for the fast determination of aromatic acids has been developed by employing poly (1-vinyl-3-butylimidazolium bromide) as the background electrolyte modifier. The polymeric ionic liquid was synthesized by the conventional radical polymerization. The reversed electroosmotic flow was obtained by adding a small amount of the polymeric ionic liquid (0.0006%, w/v) to the electrolyte. To further improve the resolution of aromatic acids, conditions including the concentration of polymeric ionic liquid and pH of background electrolytes were optimized. All eight aromatic acids were baseline resolved in one measurement in a short time (less than 3.5 min) under optimized conditions, 100 mM NaH₂PO₄ buffer containing 0.006% (w/v) polymeric ionic liquid, pH 6.0. Separation efficiencies were in the range from 355,000 to 943,000 (plates/m). Satisfactory reproducibility on the basis of the migration time of analytes was achieved. RSDs (n = 3) were less than 0.33% except the p-aminobenzoic acid (0.9%). The applicability of the present method has been demonstrated for the determination of water-soluble aromatic acids in a common drug for external use.     

Determination of amino acids in Sargassum fusiforme by high performance capillary electrophoresis

High performance capillary electrophoresis (HPCE) was developed for quantitative determination of 18 phenylthiohydantoin (PTH)-amino acids. The influence of electrolyte concentration, pH, organic modifier and applied voltage on HPCE performance was investigated. The HPCE separation of a PTH-amino acids mixture was much improved by adding organic modifier and Tris-boric acid buffer to the run buffer. After optimization of the method, 17 PTH-amino acids in a solution containing 18 PTH-amino acids could be separated using 400 mmol l⁻¹ Tris-boric acid, 1.0 mmol l⁻¹ diethylamine at pH 9.5 adjusted with 0.1 mol l⁻¹ NaOH as a run buffer, voltage of 25 kV was applied, temperature was maintained at 25 °C, detection wavelength was 254 nm. The precision (n = 7) of this method is less than 3.2% (peak area) and 1.1% (migration time) of relative standard deviation (R.S.D.). Linearity was established over the concentration range 50-1000 μM of each derivative, with correlation coefficients (r) ranging between 0.9904 and 0.9993. The detection limits (S/N = 3) range from 2 to 48 μmol l⁻¹. The method was applied to determine amino acids in Sargassum fusiforme, a marine algae collected from Tongtou County of Zhejiang Province in China with satisfactory results.     

Rapid capillary electrophoretic determination of glutaraldehyde in photographic developers using a cationic polymer coating

A new capillary electrophoretic (CE) method was developed for the rapid and simple determination of glutaraldehyde in photographic developing solutions. The proposed system is based on the selective pre-capillary derivatization of glutaraldehyde with sulfite and CE determination of anionic glutaraldehyde-bisulfite adduct formed. Since the developing solutions contain large amounts of sulfite ions, the only procedure required for derivatization is a dilution of the sample with carrier electrolyte. For separations of sulfite, acetate, glutaraldehyde-bisulfite and hydroquinone sulfonate anions, capillaries coated with poly(diallyldimethylammonium chloride) prior to analysis were used. Separation of four anions was accomplished in less than 3 min in 5 mmol l⁻¹p-hydroxybenzoate-imidazole (p-HB) electrolyte at pH 6.0 using indirect UV detection at 254 nm. The optimal conditions for the derivatization reaction were established by varying concentration of sulfite, pH and reaction time. The recovery tests established for photographic developer samples were within the range 94.0-98.4%.     

Speciation of mercury by ionic liquid-based single-drop microextraction combined with high-performance liquid chromatography-photodiode array detection

Room temperature ionic liquids can be considered as environmentally benign solvents with unique physicochemical properties. Ionic liquids can be used as extractant phases in SDME, being compatible with chromatographic systems. A single-drop microextraction method was developed for separation and preconcentration of mercury species (MeHg⁺, EtHg⁺, PhHg⁺ and Hg²⁺), which relies on the formation of the corresponding dithizonates and microextraction of these neutral chelates onto a microdrop of an ionic liquid. Afterwards, the separation and determination were carried out by high-performance liquid chromatography with a photodiode array detector. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were: microextraction time, 20 min; stirring rate, 900 rpm; pH, 11; ionic liquid type, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]); drop volume, 4 μL; and no sodium chloride addition. Limits of detection were between 1.0 and 22.8 μg L⁻¹ for the four species of mercury, while the repeatability of the method, expressed as relative standard deviation, was between 3.7 and 11.6% (n = 8). The method was finally applied to the determination of mercury species in different water samples.     

Dynamically coating the capillary with 1-alkyl-3-methylimidazolium-based ionic liquids for separation of basic proteins by capillary electrophoresis

Ionic substances with melting points close to room temperature are referred to as ionic liquids. Because ionic liquids are environmentally benign and are good solvents for a wide range of both organic and inorganic materials, interest for their potential uses in different chemical processes is increasing. In this paper, a capillary electrophoretic method for the analysis of basic proteins including lysozyme, cytochrome c, trypsinoge, and α-chymotyypsinogen A is reported. The method, in which 1-alkyl-3-methylimidazolium-based ionic liquids are used as the running electrolytes, leads to a surface charge reversal on the capillary wall. The effects of the alkyl group, imidazolium counterion, and the concentration of the ionic liquids were discussed. The optimum buffer system was a 90 mM 1-ethyl-3-methylimidazolium tetrafluoroborate (1E-3MI-TFB) solution. The applied voltage was −15 kV and detection was performed by monitoring absorbance at 240 nm. Baseline separation, high efficiencies, and symmetrical peaks of four proteins were obtained. The R.S.D. values of migration times and peak areas were <0.68 and <3.0%, respectively. The separation mechanism seems to involve association between the imidazolium cations and the proteins.     

Cyclodextrin-MEEKC for the analysis of oxybutynin and its impurities

The development of a cyclodextrin-MEEKC method for the analysis of oxybutynin and five related impurities is described. Experimental design strategies were applied in order to reach baseline separation of the compounds in a short analysis time. Mixture design made it possible to find the best composition for the microemulsion acting as pseudostationary phase, which was constituted by 89.1% 10 mM borate buffer pH 9.2, 1.7% n-heptane, 9.2% SDS/n-butanol in 1:2 ratio. The addition of (2-hydroxypropyl)-β-cyclodextrin to the background electrolyte was found to improve analysis performance. A Doehlert design, for the factors cyclodextrin concentration and voltage, was carried out and Derringer desirability function led to the identification of 18 mM and 29 kV as the optimal values. Applying the optimum conditions, separation of all the compounds, including the enantiomers of impurity 1, was obtained in less than 12 min. The method was validated according to ICH guidelines for drug assay and determination of impurities and was applied to oxybutynin tablet analysis.     

Measurement and modeling of osmotic coefficients of aqueous solution of ionic liquids using vapor pressure osmometry method

Osmotic coefficients of binary mixtures containing an ionic liquid, (1-butyl-3-methylimidazolium tetrafluoroborate, [BMIm]BF₄, 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIm]ES, and 1-butyl-3-methylimidazolium methyl sulfate, [BMIm]MS) with water were measured until about 3 molal concentrations using vapor pressure osmometry method (VPO) at temperature ranges 298.15–328.15 K and modeled using different electrolyte excess Gibbs free energy models including electrolyte non-random two liquids (NRTL), modified NRTL (MNRTL), mean spherical approximation NRTL (MSA-NRTL), non random factor (NRF), and extended Wilson models. The results show that osmotic coefficient data increase with increasing temperature. The calculated standard deviations of the studied systems show that the applicability of these models for the correlation of VLE properties of ionic liquid solutions. The average standard deviations for the models have the order σ(?) MNRTL < σ(?) Wilson < σ(?) NRTL < σ(?) MSA-NRTL < σ(?)NRF. The results show MNRTL model is able to reproduce experimental osmotic coefficients of aqueous solution of studied ionic liquids with good precision.     

Electro membrane extraction of biological anions with ion chromatographic analysis

A simple and sensitive single step electro membrane extraction (EME) procedure was demonstrated for biological organic anions with determination by ion chromatography (IC). Nitrite, adipate, oxalate, iodide, fumarate, thiocyanate and perchlorate were extracted from aqueous donor solutions, across a supported liquid membrane (SLM) consisting of methanol impregnated in the walls of a porous polypropylene membrane bag and into an alkaline aqueous acceptor solution in the lumen of the propylene envelope by the application of potential of 12 V applied across the SLM. The acceptor solution was analyzed by IC. Parameters affecting the extraction performance such as type of SLM, extraction time, pH of the donor and acceptor solution, and extraction voltage were studied. The most favorable EME conditions were methanol as the SLM, extraction time of 5 min, pH of acceptor and sample solutions of 12 and 4, respectively, and a voltage of 12 V. Portable 12 V batteries were used in the study. Under these optimized conditions, all anions had enrichment factors ranging from 3.6 to 36.2 with relative standard deviations (n = 3) of between 6.6 and 17.5%. Good linearity ranging from 0.1 to 10 μg mL⁻¹ with coefficients of correlation (r) of between 0.9981 and 0.9996 were obtained. The limits of detection of the EME-IC method were from 0.01 to 0.14 μg mL⁻¹. The developed methodology was applied to amniotic fluid samples to evaluate the feasibility of the method for real applications.     

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) (∼1 × 10⁻⁵ to 1 × 10⁻³), mellitate and trimellitate (∼5 × 10⁻⁶ to 5 × 10⁻⁴), and about one range (∼1 × 10⁻⁴ to 5 × 10⁻³) for oxalate and benzoate. Accuracy of the procedure is checked by the “added-found” method in standard mixture solutions. Relative standard deviation is within the range of 2–10% and the recovery is in the range of 90–110%. This method is applied for the analysis of real UC dissolution samples.     

Polymeric ionic liquid as a dynamic coating additive for separation of basic proteins by capillary electrophoresis

A simple and economical capillary electrophoresis method has been developed for the analysis of four model basic proteins by employing a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium) bromide, as the dynamic coating additive. When a small amount of PIL was present in the background electrolyte, a cationic coating on the inner surface of fused-silica capillary was established. These PIL modified capillaries not only generated a stable reversed electroosmotic flow, but also effectively eliminated the wall adsorption of proteins. Several important parameters such as the PIL concentration in the background electrolyte, pH values and concentrations of the background electrolyte were optimized to improve the separation of basic proteins. Consequently, under the optimum conditions, a satisfied separation of basic proteins with peak efficiencies ranging from 247,000 to 540,000 (plates m⁻¹) had been accomplished within 11 min. The run-to-run RSDs (n = 3) of the migration times for the four basic proteins were all less than 0.37%.     

Direct analysis of formate in human plasma,serum and whole blood by in-line coupling of microdialysis to capillary electrophoresis for rapid diagnosis of methanol poisoning

A simple method using direct injection of human blood samples and quantitative analysis of formate was developed for rapid diagnosis of methanol poisoning. A sample pretreatment device including a 500 Da molecular weight cut-off dialysis membrane was in-line coupled to capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D). 50 μL of 1:9 diluted blood samples and 50 μL of DI water were filled into the donor and the acceptor chamber, respectively, and small ionic species in blood samples were electrokinetically injected across the dialysis membrane directly into the separation capillary. Matrix components, such as red blood cells, proteins, lipids and other high molecular weight compounds, were retained by the dialysis membrane and did not interfere with subsequent CE separation. Formate was separated from other small anions in an optimized background electrolyte solution consisting of 20 mM l-histidine and 25 mM l-glutamic acid at pH 4.8. The method showed excellent analytical parameters in terms of repeatability and linearity; RSD values for migration times and peak areas at a formate concentration typical for methanol poisoning were below 0.3% and 7.4%, respectively, and linear calibration curves with correlation coefficients better than 0.999 were obtained. Limit of detection and limit of quantification were 15 and 50 μM formate in original (undiluted) blood samples, respectively. The method was applied to determination of formate in serum samples of a patient diagnosed with acute methanol poisoning.     

Determination of total phosphorus in soya food samples by capillary isotachophoresis (cITP)

Capillary isotachophoresis (cITP) was applied for the determination of total phosphorus in soya food. The leading electrolyte was 8 mM HCl adjusted with β-alanine to pH=3.55 plus 3 mM bis-tris-propane and 0.2% hydroxyethylcellulose, whereas the terminating electrolyte 5 mM citric acid. Obtained results were compared with the spectrophotometric method. The correlation coefficients were 0.9996 for cITP and 0.9986 for standard method indicating the satisfactory precision of the calibration curves. The separation of anions was achieved within 25 min. Accuracy was determined using standard reference material (non-fat milk powder) and recovery assay based on standard additions method. Obtained results were discussed in respect to the accuracy and statistical parameters. Satisfactory values of recovery ranged between 99.22 and 99.85%, whereas R.S.D.<1% what demonstrate the advantage of cITP method in the routine analyses of phosphorus content in food samples.     

Simultaneous determination of tetracyclines in pharmaceuticals by CZE using experimental design

An optimized capillary zone electrophoresis (CZE) method for the analysis of tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DXC) is described. Using fused-silica capillaries, the influence of the electrolyte composition, pH and concentration, as well as temperature and applied voltage were investigated. A factorial and central composite design was performed to optimize the method in a simple way. The optimal separation conditions were 50 mmol L⁻¹ sodium carbonate + 1 mmol L⁻¹ EDTA, pH 10; voltage 13 kV and temperature 23 °C. The method was validated for TC determination in pharmaceuticals through the following performance criteria: linearity and linear range, sensitivity, selectivity, intra-assay and inter-assay precision, detectability, accuracy and ruggedness. In comparison with the recommended HPLC method in the United States Pharmacopeia, this CZE-method exhibited the same performance as the official method, with the advantage that the same method could be used for the simultaneous determination of the different tetracyclines in pharmaceutical formulations.     

Determination of preservatives in soft drinks by capillary electrophoresis with ionic liquids as the electrolyte additives

A capillary electrophoresis method for separating preservatives with various ionic liquids as the electrolyte additives has been developed. The performances for separation of the preservatives using five ionic liquids with different anions and different substituted group numbers on imidazole ring were studied. After investigating the influence of the key parameters on the separation (the concentration of ionic liquids, pH, and the concentration of borax), it has been found that the separation efficiency could be improved obviously using the ionic liquids as the electrolyte additives and tested preservatives were baseline separated. The proposed capillary electrophoresis method exhibited favorable quantitative analysis property of the preservatives with good linearity (r² = 0.998), repeatability (relative standard deviations ≤ 3.3%) and high recovery (79.4–117.5%). Furthermore, this feasible and efficient capillary electrophoresis method was applied in detecting the preservatives in soft drinks, introducing a new way for assaying the preservatives in food products.     

Preconcentration/preelution ion chromatography for the determination of perchlorate in complex samples

The determination of perchlorate in complex matrices by ion chromatography (IC) with an online preconcentration and preelution technique is discussed. The method was applied to different sample types containing large concentrations of matrix anions that would otherwise interfere with analysis via conventional IC. The present approach was highly effective in removing most of the matrix anions and was thus resistant to the interferences commonly encountered in a high ionic strength background. Method performance was evaluated by analyzing for low-level perchlorate in synthetic high ionic strength solutions, tissue extracts, and hydroponic nitrate fertilizer samples. Not only is it easier to practice the present method compared to USEPA Method 314.0, but for most of these samples the present approach provided equal to or better recovery of perchlorate than Method 314.0. With a sample of specific conductance 12,650 μS cm⁻¹, for example, the present method provided a perchlorate recovery of 101% at the 25 μg L⁻¹ level versus 89% by EPA Method 314.0. Method detection limits of perchlorate in hydroponic fertilizer samples with this method (130-190 μg kg⁻¹) are the lowest thus far reported.     

In-vial liquid–liquid microextraction-capillary electrophoresis method for the determination of phenolic acids in vegetable oils

An in-vial liquid–liquid microextraction method was developed for the selective extraction of the phenolic acids (caffeic, gallic, cinnamic, ferulic, chlorogenic, syringic, vanillic, benzoic, p-hydroxybenzoic, 2,4-dihydroxybenzoic, o-coumaric, m-coumaric and p-coumaric) in vegetable oil samples. The optimised extraction conditions for 20 g sample were: volume of diluent (n-hexane), 2 mL; extractant, methanol: 5 mM sodium hydroxide (60:40; v/v); volume of extractant, 300 μL (twice); vortex, 1 min; centrifugation, 5 min. Recoveries for the studied phenolic acids were 80.1–119.5%. The simultaneous determination of the phenolic acid extracts was investigated by capillary electrophoresis (CE). Separations were carried out on a bare fused-silica capillary (50 μm i.d. × 40 cm length) involving 25 mM sodium tetraborate (pH 9.15) and 5% methanol as CE background electrolyte in the normal polarity mode, voltage of 30 kV, temperature of 25 °C, injection time of 4 s (50 mbar) and electropherograms were recorded at 200 nm. The phenolic acids were successfully separated in less than 10 min. The validated in-vial LLME-CE method was applied to the determination of phenolic acids in vegetable oil samples (extra virgin olive oil, virgin olive oil, pure olive oil, walnut oil and grapeseed oil). The developed method shows significant advantages over the current methods as lengthy evaporation step is not required.     

Development of a fast capillary electrophoresis method for the determination of propranolol—Total analysis time reduction strategies

The aim of this study was to develop a fast capillary electrophoresis method for the determination of propranolol in pharmaceutical preparations. In the method development the pH and constituents of the background electrolyte were selected using the effective mobility versus pH curves. Benzylamine was used as the internal standard. The background electrolyte was composed of 60 mmol L⁻¹ tris(hydroxymethyl)aminomethane and 30 mmol L⁻¹ 2-hydroxyisobutyric acid, at pH 8.1. Separation was conducted in a fused-silica capillary (32 cm total length and 8.5 cm effective length, 50 μm I.D.) with a short-end injection configuration and direct UV detection at 214 nm. The run time was only 14 s. Three different strategies were studied in order to develop a fast CE method with low total analysis time for propranolol analysis: low flush time (Lflush) 35 runs/h, without flush (Wflush) 52 runs/h, and Invert (switched polarity) 45 runs/h. Since the three strategies developed are statistically equivalent, Wflush was selected due to the higher analytical frequency in comparison with the other methods. A few figures of merit of the proposed method include: good linearity (R² > 0.9999); limit of detection of 0.5 mg L⁻¹; inter-day precision better than 1.03% (n = 9) and recovery in the range of 95.1–104.5%.     

A novel polymeric membrane electrode for the potentiometric analysis of Cu in drinking water

Based on a novel ionophore, an ion-selective electrode has been developed for the determination of Cu²⁺ in drinking water. Its selectivity behavior is characterized and its lower detection limit optimized for measurements with different electrolyte backgrounds. The lower detection limit was 2 × 10⁻⁹ M Cu²⁺ for samples with low ionic background and 1 × 10⁻⁷ M Cu²⁺ with ionic background typically found in drinking water.