Flow Injection Capillary Electrophoresis Research Articles

Application of Experimental Design in Optimization of the Separation Condition for Determination of Four Active Components in Cold Medicines by Flow Injection-Capillary Electrophoresis

Orthogonal design (OD) was employed to optimize the separation condition of flow injection-capillary electrophoresis (FI-CE). In order to compare the optimum condition, uniform design and univariate approach were also adopted. The influences of variables such as buffer pH, buffer concentration, acetonitrile (ACN) percentage, and separation voltage were discussed. The optimum separation condition was established. The limits of detection were 1.94 × 10(-2), 6.40 × 10(-3), 1.16 × 10(-2) and 1.94 × 10(-2) μg/mL for dextromethorphan hydrobromide (Dex), chlorphenamine hydrogen maleate (Chl), pseudoephedrine hydrochloride (Pse), and paracetamol (Par), respectively. The RSDs of peaks areas were less than 2.0%. The results showed the OD was an effective method among experimental designs for optimizing the separation conditions of CE. The optimum condition was used for separation and determination of Dex, Chl, Pse, and Par in cold medicines. The average recovery was between 96.68-101.25%.

A novel cross-H-channel interface for flow injection-capillary electrophoresis to reduce sample requirement and improve sensitivity

In this study, a cross-H-channel interface was constructed for coupling flow injection with capillary electrophoresis (FI-CE) to reduce sample requirement and sensitivity loss in the typical FI-CE. Based on this cross-H-channel interface, a new FI-CE system was established, in which sample introduction was performed by directly injecting sample solution along a thin capillary (50 μm, i.d.) to the interface from an injection syringe. The sample requirement was reduced distinctly and usual sample dilution in the sample transport process was obviously decreased, thereby spontaneously enhancing the sensitivity. Moreover, because of the unique construction of the cross-H-channel interface, field amplified sample stacking (FASS) and high-speed CE were skillfully combined to further improve the sensitivity and to shorten separation time. The versatility of this new FI-CE was demonstrated by determination of ephedrine (E) and pseudoephedrine (PE) in human urine. Up to 45 repeated injections per hour and clearly baseline separation of E and PE in less than 1 min were achieved, giving limits of detection (LODs) of 0.23 and 0.21 μg mL(-1) for E and PE, respectively, and yielding relative standard deviation (RSD) values of the migration time and the peak height (n=5) of 2.6% and 3.1% for E, 2.3% and 3.3% for PE, respectively. In contrast to typical FI-CE, approximately 8-250-fold decreases in sample volume requirement, 7-fold shortening in separation time and 50-fold improvements in sensitivity were obtained.

Flow injection-capillary electrophoresis frontal analysis method for the study of the interactions of a series of drugs with human serum albumin

In this paper, a fast method for the study on the interactions of a series of drugs used in the treatment of hypertension with human serum albumin (HSA) by flow injection-capillary electrophoresis (FI-CE) was developed based on the principle of frontal analysis (FA). The binding parameters were determined by FI-CE-FA from Scatchard equation and compared with results obtained by non-CE methods and literature values. A multiple linear regression (MLR) model between the drug–protein binding constants ( K) and structural descriptors of drugs was constructed. L-tryptophan ( L-try) and phenylbutazone (PB) were used as displacement reagents to investigate the binding sites of a series of drugs on HSA. The binding synergism effect between drugs and the effects of many metal ions existing in human plasma on protein binding were also investigated systematically.

On-Line Flow Injection—Capillary Electrophoresis Instrument with Contactless Conductivity Detection for Sensitive Cation Analyses

A new system for on-line analyses of metal cations has been developed by combining flow injection sample introduction with on-line capillary electrophoresis. The on-line analysis instrument has a simple construction and it allows fast sample introduction from a flowing solution. The ends of the separation capillary and the electrodes were placed opposite to each other into tubings that were installed over them behaving as flow-through channels. The capillary temperature during the analyses was controlled by water cooling and the analyte monitoring was conducted with a contactless conductivity detector. The construction allowed compound detection of very low concentrations. The instrument was used for simultaneous determination of ammonium, potassium, calcium, magnesium, and sodium as complexes in aqueous 18-crown-6 ether – acetate electrolyte solution. Flow injection analysis of sample introduction was kept apart from the ligand modified electrolyte solution. Calibration with standard mixtures of alkali metals, alkaline earth metals, and ammonium was linear in the range from 10 ng/mL to 1 µg/mL for each analyte. The intraday reproducibility for the separations was 2% (RSD). The detection limit for the cations was 10 ng/mL. The studies showed the performance of the method to be sensitive for the monitoring of inorganic ions in water treatment.

Chemometrical examination of active parameters and interactions in flow injection‐capillary electrophoresis

The first detailed examination of flow injection-capillary electrophoresis (FI-CE) active parameters and their interactions via response surface methodology (RSM) is presented. Specifically, RSM in the form of a Box-Behnken design was implemented to effectively predict the significance of capillary length, voltage and injection volume on the optimization of an in-house built FI-CE analyzer. Initial studies were performed assessing peak height and peak shape of the model compound N,N-dimethylformamide. Optimum model conditions were then derived and used in the model separation of two small molecules, nicotinamide adenine dinucleotide, reduced form (NADH) and benzenesulfonamide. By implementing the RSM approach, detailed examination of active FI-CE parameters was possible, including the ability to reveal a significant interactive effect. This work is not only highly significant for advancing FI-CE developments, but instructive for investigators actively exploring other coupled analytical techniques and associated experimental parameters.

Online Concentration by Head-column Field-amplified with Large-volume Sample Stacking Using Flow Injection-Capillary Electrophoresis for the Analysis of Four Active Components in Cold Medicines

A simple, effective, and sensitive online concentration method for the detection of dextromethorphan hydrobromide (Dex), chlorphenamine hydrogen maleate (Chl), pseudoephedrine hydrochloride (Pse) and paracetamol (Par) based on flow injection-capillary electrophoresis (FI-CE) analysis with head-column field-amplified sample stacking and large-volume sample stacking was developed. The background electrolyte (BGE) was a solution composed of 55 mM borate-15% (v/v) acetonitrile (ACN) (pH 9.3). The sample was injected electrokinetically between plugs of water. Under the optimum conditions, about a 30-fold improvement in the concentration sensitivity relative to normal CE methods was achieved, giving low limits of detection (LOD) of 1.94 x 10(-5), 0.64 x 10(-5), 1.16 x 10(-5) and 2.84 x 10(-5) mg/mL for Dex, Chl, Pse and Par, respectively. The repeatability (defined as RSD) was 1.01, 1.91, 0.89 and 0.92% with the peak-area evaluation and 1.94, 3.98, 2.66 and 3.27% with the peak-height evaluation for Dex, Chl, Pse and Par, respectively. This method has been successfully applied to the analysis of commercial pharmaceutical preparations containing Dex, Chl, Pse and Par.

Evaluation of a simple hyphenated system for flow injection solid-phase pre-concentration and capillary electrophoresis

In this work, the development and evaluation of a hyphenated flow injection-capillary electrophoresis system with on-line pre-concentration is described. Preliminary tests were performed to investigate the influence of flow rates over the analytical signals. Results revealed losses in terms of sensitivity of the FIA-CE system when compared to the conventional CE system. To overcome signal decrease and to make the system more efficient, a lower flow rate was set and an anionic resin column was added to the flow manifold in order to pre-concentrate the analyte. The pre-concentration FIA-CE system presented a sensitivity improvement of about 660% and there was only a small increase of 8% in total peak dispersion. These results have confirmed the great potential of the proposed system for many analytical tasks especially for low concentration samples.

An Alternative Interface for a Flow Injection-Capillary Electrophoresis System with Electrokinetic Injection

An alternative interface for flow injection-capillary electrophoresis based on electrokinetic injection is described. The interface basically consists of tubular platinum and a commercially available standard tee connector. The tubular platinum works as not only an electrode, but also a waste outlet of a split sample solution. The availability of the proposed interface is evaluated by the separation of several transition metals, such as vanadium, iron, and cobalt with 1,10-phenanthroline, and by the determination of iron in steel.

Separation and determination of three water-soluble compounds in Salvia miltiorrhiza Bunge and two related traditional medicinal preparations by flow injection-capillary electrophoresis

A sensitive and reproducible method was developed for the separation and determination of three water-soluble components—protocatechuic aldehyde (PAH), β-(3,4-dihydroxyphenyl) lactic acid (DSS) and protocatechuic acid (PA) in medicine plant Salvia miltiorrhiza Bunge and two related traditional medicinal preparations using flow injection-capillary electrophoresis system. This analysis was carried out by using an unmodified fused-silica capillary (28.4 cm × 75 μm i.d. × 375 μm o.d., 25 cm effective separation length) and direct ultraviolet detection at 214 nm, 7.0 kV applied voltage. With boric acid (200 mM) adjusted to pH 7.8 as a background electrolyte. The separation was achieved in 9 min. The sample throughput rate could reach up to 15 h −1. Calibration curves showed good linearity with correlation coefficients ( r) more than 0.9986. The repeatability (defined as R.S.D.) were 0.20%, 0.46%, 0.47% with migration time evaluation and 0.62%, 3.66%, 1.50% with peak area evaluation for PAH, DSS and PA, respectively. The limits of detection (S/N = 3) were 0.36 μg/mL, 0.84 μg/mL, and 0.73 μg/mL for PAH, DSS, and PA, respectively. The mean recoveries of PAH, DSS and PA were 103.2%, 98.1% and 100.5%, respectively. This method has been applied successfully to monitor these three components in Salvia miltiorrhiza Bunge and its two traditional medicinal preparations.

Separation and determination of four active components in medicinal preparations by flow injection-capillary electrophoresis

A simple, rapid and accurate method for the separation and determination of paracetamol (Par), pseudoephedrine hydrochloride (Pse), dextromethorphan hydrobromide (Dex) and chlorphenamine hydrogen maleate (Chl) was developed by combination of flow injection and capillary zone electrophoresis for the first time. The analysis was carried out using an unmodified fused-silica capillary (75 mm × 75 μm i.d. × 375 μm o.d., effective separation length of 45 mm) and direct ultraviolet detection at 214 nm, 1.0 kV applied voltage. The optimized running buffer composed of 75 mM sodium borate–15% (v/v) acetonitrile (ACN) (pH * 9.30) was applied for the separation of the four analytes. The separation was achieved in 4.5 min. The sample throughput rate could reach up to 19 h −1. The repeatability (defined as relative standard deviation) was 0.6%, 1.0%, 2.1%, 1.9% with peak height evaluation and 0.7%, 1.8%, 0.7%, 1.1% with peak area evaluation for Par, Pse, Dex and Chl, respectively. The limits of detection (S/N = 3) were 0.22 μg/ml, 0.29 μg/ml, 0.42 μg/ml and 0.70 μg/ml for Par, Pse, Dex and Chl, respectively. The method was successfully applied to determine the four compounds in three cold medicines with recoveries in the range of 97.18–105.15%.

Study on characteristics of bias caused by FI-CE split flow electrokinetic injection

The characteristics of bias caused by split-flow electrokinetic injection (SEKI), a new type of sample injection method used in coupled flow injection-capillary electrophoresis system (FI-CE), was investigated using pseudoephedrine hydrochloride, a basic drug, and ibuprofen, an acidic drug, as model analytes. It was found that bias imposed by SEKI under the condition of continuous sample matrix/running buffer was similar to that done by electrokinetic injection (EKI). The linearity of calibration curve provided by SEKI was similar to that offered by non-bias hydrodynamic injection (HDI) but significantly better than that obtained by EKI. These features were exploited to improve analytical performances in simultaneous determination of the minor ingredient of pseudoephedrine hydrochloride and the major ingredient of ibuprofen in a pharmaceutical preparation. Detectability of 0.7 mg/l for pseudoephedrine hydrochloride was achieved at a sample throughput rate of 24 times per hour, which is 30% lower than that obtained by HDI-based conventional CE. Relative standard deviations (RSDs) of 2.8% for the minor ingredient and 1.2% for the major ingredient were produced in 11 runs of a test solution containing 13.1 mg/l pseudoephedrine hydrochloride and 81.4 mg/l ibuprofen. This is an improvement compared to that obtained by HDI-based conventional CE. Analytical results for two batches of compound ibuprofen tablets by the SEKI-based FI-CE approach were in good agreement with that obtained by a conventional high performance liquid chromatographic method.

Separation and determination of honokiol and magnolol in herbal medicines by flow injection-capillary electrophoresis

A simple, rapid, and accurate method for the separation and determination of honokiol and magnolol in Magnolia officinalis and related herbal medicines was developed by combination of flow injection (FI) and capillary zone electrophoresis (CZE). The analysis was carried out using an unmodified fused-silica capillary (50-microm I.D.; total length 7.5 cm; effective length 4.5 cm). A series of optimization steps afforded the following conditions: the sample solvent consisted of 150 mM NaOH and a running buffer composed of 10 mM sodium tetraborate/10 mM sodium dihydrogenphosphate (NaH2PO4) at pH 12 was applied for the separation of the analytes. The separation could be achieved within 5 min with a sample throughput rate of up to 28 h(-1). The repeatability (defined as the relative standard deviation, RSD) for honokiol and magnolol was 2.0% and 1.6% with peak area evaluation, 3.6% and 2.0% with peak height evaluation, and 2.0% and 1.4% with migration time evaluation, respectively. Regression equations revealed linear relationships (r = 0.9991-0.9998) between the peak area of each analyte and the concentration.

Flow Injection-Capillary Electrophoresis (FI-CE): Recent Advances and Applications

This paper presents a comprehensive review of how recent advances in flow injection-capillary electrophoresis (FI-CE) technology have led to enhanced separation capabilities of a wide range of analytes in such areas as biological, environmental, food, medical and pharmaceutical analysis. Significant developments in design, detection methodology and applications made in the last five years are reported. In addition, future perspectives in FI-CE are considered.

Separation and determination of four active anthraquinones in Chinese herbal preparations by flow injection-capillary electrophoresis

A simple, rapid, and accurate method for the separation and determination of physcion, chrysophanol, aloe-emodin, and emodin in Rhubarb, Juemingzi, and Chinese herbal preparations was developed by combination of flow injection-capillary zone electrophoresis for the first time. The analysis was carried out using an unmodified fused-silica capillary (75 mm x 50 microm ID x 375 microm OD, effective separation length of 48 mm) and direct ultraviolet detection at 254 nm. By a series of optimization, the sample solvent consisted of NaOH (100 mmol/L) and ACN (1:1 v/v), and a running buffer composed of 15 mmol/L sodium borate - 12.5 mmol/L sodium dihydrogen phosphate - 42% v/v ACN (pH 10.1) was applied for the separation of the four anthraquinones. The separation was rapid and highly reproducible, with complete resolution of all four compounds within 6 min. The sample throughput rate could reach up to 12 per h. The repeatability (defined as relative standard deviation) was 4.45, 4.44, 4.34, 0.61% with peak height evaluation and 1.62, 0.89, 2.49, 2.19% with peak area evaluation for physcion, chrysophanol, aloe-emodin, and emodin, respectively.

The combination of flow injection with electrophoresis using capillaries and chips

The combined flow injection capillary electrophoresis (FI-CE) system that integrates the essential favorable merits of FI and CE, can significantly expand the application scope of CE by exploring the various on-line sample pretreatments and preconcentration of FI. The principle behind this technique, some innovative designs of the split-flow interface, as well as novel applications to a variety of analytical problems, are reviewed and discussed. Some salient features and unique advantages of this technique are outlined.

On-site simultaneous determination of anions and cations in drainage water using a flow injection-capillary electrophoresis system with contactless conductivity detection.

Drainage water diverted from a farm pasture, which was heavily loaded with manure, was monitored during a rain event. Concurrent anion and cation determinations at intervals of 10 min could be achieved with a new capillary electrophoresis system employing dual injection at opposite ends of the separation capillary. The flow injection approach enabled automation of the sampling process. Interruption of the separation voltage was not necessary. Contactless conductivity detection with an electrolyte solution optimized for the purpose allowed the facile simultaneous detection of the inorganic ions Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), NO(2)(-), NH(4)(+), K(+), Ca(2+), Na(+) and Mg(2+) and the acquisition of temporal concentration profiles of these species. The detection limits achieved were between 20 and 200 [micro sign]g l(-1) for all ions and the repeatability of peak areas and peak heights was better than 1%. The quantitative results were verified by analysing individual samples later in the laboratory with photometry and ion chromatography and the average deviations were found to be between 4 and 12%. This contribution presents a further step in the development of capillary electrophoresis towards a fully automated, low maintenance field method.

Rapid speciation of Se(IV) and Se(VI) by flow injection-capillary electrophoresis system with contactless conductivity detection.

A flow injection-capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM L-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 microg L(-1) and 7.5 microg L(-1) for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.

A Coupled Flow Injection‐Capillary Electrophoresis System for Kinetic Study of Aspirin Hydrolysis in Aqueous Solution

A coupled flow injection‐capillary electrophoresis (FI‐CE) system was developed for automated determination of rate constants of chemical reactions. The system consists of a probe for sampling, a knotted reactor for on‐line quenching reaction, an injection valve in combination with a split‐flow interface for on‐line electrokinetic injection, and a CE unit for separation and detection. Aspirin was used as a model compound to validate the performance of the coupled system. Under the optimized conditions, the coupled system achieved a sampling rate of 20 per hour, and a RSD of 1.1% for 25 consecutive determinations in 75 min. These features of the coupled FI‐CE system allowed it to monitor reactions with half‐reaction time being no less than 15 min. Several rate constants of aspirin hydrolysis in slightly alkaline media were determined with the developed system.

Flow injection-capillary electrophoresis system with contactless conductivity detection and hydrostatic pressure generated flow. Application to the quantitative analysis of inorganic anions in water samples.

A simple and inexpensive flow injection-capillary electrophoresis (FI-CE) system with contactless conductivity detection (CCD) for automated quantitative analysis of chloride, nitrate, and sulfate in various water samples is demonstrated. A glass bottle containing the background electrolyte that is raised above the FI-CE interface generates a pulse-free, highly reproducible flow of the electrolyte through the FI-CE interface. The system operates at a flow rate of 300 microLmin(-1) with an injection volume of only 4 microL. The repeatability of peak areas (n = 18) was better than 0.81% RSD and the sample throughput was 90 samples per hour using the background electrolyte containing 12 mM L-histidine adjusted to pH 4.00 with acetic acid. The limits of detection were better than 125 microgL(-1) and were comparable to those obtained by conventional CE systems with CCD. Various calibration methods for FI-CE system with electrokinetic injection were tested and their suitability for the analysis of anions in real samples was evaluated.

On‐line conversion and determination of aspirin using a flow injection–capillary electrophoresis system

AbstractA novel, rapid, and simple capillary electrophoresis (CE) method has been developed for the determination of aspirin by on‐line treatment with alkali. Such on‐line reaction with 0.20 mol/L NaOH solution for 2.5 min at 45°C automatically and reproducibly converts aspirin into its hydrolysis product salicylic acid. Analysis is carried out in less than 12 min after conversion of aspirin in a flow injection (FI) system coupled to a CE instrument via a split‐flow interface cell, and a sampling frequency of 9 h–1 is achievable. The on‐line conversion method has been used to determine aspirin in four commercial pharmaceutical preparations, and the results are satisfactory.