Flow Injection-capillary Electrophoresis System Research Articles

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.

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.

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.

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.

On-line conversion and determination of artemisinin using a flow-injection capillary electrophoresis system.

A novel, rapid, and simple capillary electrophoresis (CE) method has been developed for the determination of antimalarial artemisinin by on-line treatment with alkaline. By on-line reaction, artemisinin was automatically and reproducibly converted to the strongly UV-absorbing compound, Q292, by treating it with 0.20 mol/L NaOH solution for 3 min at 40 degrees C. Analysis was carried out in less than 12 min after conversion of artemisinin in a flow injection (FI) system that was coupled to CE equipment via a split-flow interface cell, and a sampling frequency of 8 h(-1) is achievable. The on-line conversion method has been applied to the determination of artemisinin in the traditional Chinese herbal drug Artemisia annua L., and the results are satisfactory.

Combination of flow injection with capillary electrophoresis. Part 6.: A bias-free sample introduction system based on electroosmotic-flow traction

A bias-free sample injection method based on electroosmotic-flow (EOF) traction was developed for the combined flow injection-capillary electrophoresis system. A Nafion joint implemented at a capillary fracture close to the capillary inlet was used for isolating the electric field during the split-flow sample injection, the sample solution being drawn into the capillary by EOF without bias effects. An electronic time relay system was adopted to control the switching of high voltage between the capillary inlet end and the joint. The peak area ratios of two model compounds, dimethyl sulfoxide and benzoic acid obtained using the proposed system were identical to those with gravity injection. Relative standard deviations of 0.5–2.5% ( n = 32) were achieved for peak height and peak area evaluation in the consecutive injections of a series of replicate sample solutions at a sampling frequency of 15 h −1 . Similar performance of the system was obtained with a reversed EOF background electrolyte after reversing the electrode polarity for a mixture of the anions, Cl −, SO 4 2−, NO 3 − and F − using indirect UV detection. The performance of the system for the analysis of real samples was demonstrated by bias-free sample injection in the separation of caffeine, theobromine and theophylline in beverage samples with satisfactory recoveries in the 92–107% range.

Direct determination of small cations in proteinaceous samples using a flow injection–capillary electrophoresis system

A method is described for the direct determination of small inorganic cations in samples containing large amounts of proteins, such as milk or blood plasma. The method is based on electrokinetic injection in a flow injection analysis–capillary electrophoresis (CE) system. The selected CE-electrolyte, containing 5 m M 4-aminopyridine and 7 μ M cetyltrimethylammonium bromide at pH 4.5, prevents detrimental protein adsorption on the capillary walls. Therefore, no sample pretreatment, except for dilution, is required. Up to 30 repeated injections in one electrophoretic run can be performed, yielding RSD values of the migration time of less than 1 and 2.5% ( n=30) for milk and blood plasma samples, respectively.