Petr Kuban

New interface for coupling flow-injection and capillary electrophoresis

Abstract A new interface for coupling flow injection analysis (FIA) and capillary electrophoresis (CE) has been developed. An FIA system is connected to a flow-through channel of the interface. One end of a capillary is positioned in a flow-through channel inside the interface together with a platinum electrode. The other end and a second platinum electrode are immersed in a liquid reservoir situated outside the interface. A constant high voltage is applied across the capillary. A sample plug injected in the FIA part of the system is carried by an electrolyte stream towards the interface and when it passes by the first capillary end, a minor fraction of the sample is introduced into the capillary and gets separated. A UV spectrophotometric detector is placed close to the second capillary end. The FIA-CE interface enables multiple injections so that a high sampling throughput can be achieved (up to 150 samples per hour). The interface was tested by running a standard mixture of nine common anions. The repeatability was approximately 2% (r.s.d.). Rapid, qualitative screening of samples can be performed. Real samples such as tap and rain water were also analyzed. The new interface allows mechanized sample handling prior to the CE separation step.

On-line coupling of gas diffusion to capillary electrophoresis

On-line gas diffusion has been coupled to a capillary electrophoresis system (CE) via a specially designed interface. The sample is merged with a modifying solution, e.g., a strong acid, in a flow system to transform the analytes of interest into their respective gaseous forms. These transformed, gaseous analytes permeate through a PTFE membrane into an acceptor stream comprising of a tris-buffer. The continuously flowing acceptor stream is led into an injector forming an integrated part of a flow injection analysis (FIA) system. The sample receiving carrier stream in the FIA system, a chromate buffer, brings the sample, 50 mul, to the FIA-CE interface into which one end of a separation capillary has been inserted. A small portion of the injected sample enters the capillary (electrokinetic injection) and separation takes place. A UV detector is placed at the other capillary end and a run potential of 25 kV is applied to two platinum electrodes positioned in the flow system. Multiple sample injections can be performed in one uninterrupted electrophoretic run. A typical sampling frequency is 15 h(-1); each run may result in quantitation of at least five anions. The overall repeatability is in the range 1.8-3.6% (RSD). The technique has been applied to the analysis of real samples such as soft drinks, vinegar and wine. Selective discrimination of anions which are unable to form volatile species is accomplished. No off-line sample pre-treatment is needed.

INTERFACING OF FLOW INJECTION PRE-TREATMENT SYSTEMS WITH CAPILLARY ELECTROPHORESIS

Abstract This article reviews the interfacing of flow injection analysis (FIA) with capillary electrophoresis (CE). Various sample pre-treatment procedures such as dialysis and gas diffusion can be fully automated as can the application of the electrokinetic injection principle for introduction of the treated sample into the CE system using a specially designed interface. The practical applicability of the FIA–CE technique has been demonstrated by the determination of small anions in, for instance, water, juice and milk samples. Sample throughput rates can reach 170/h and the repeatability is typically 2% (R.S.D.).

On-line flow sample stacking in a flow injection analysis–capillary electrophoresis system: 2000-fold enhancement of detection sensitivity for priority phenol pollutants

A flow injection analysis-capillary electrophoresis system has been used for on-line flow stacking of 11 US Environmental Protection Agency priority phenol pollutants. Samples containing low concentrations of phenols dissolved in deionised water are continuously delivered to the capillary opening by means of a peristaltic pump. The sample components stack at the boundary between the highly conductive separation electrolyte and the introduced sample. By selecting an appropriate electrolyte and stacking conditions the movement of the electrolyte solution inside the capillary can be reduced, thereby improving the stacking efficiency. The electrolyte used here contained 20 mM phosphate, 8% 2-butanol, and 0.001% hexamethonium bromide at pH 11.95, and the stacking was carried out at 2 kV for 240 s. These conditions allowed up to 2000-fold preconcentration of the selected phenols. No matrix removal was necessary.

Calibration principles for flow injection analysis–capillary electrophoresis systems with electrokinetic injection

Abstract The utility of different calibration techniques in flow injection analysis–capillary electrophoresis systems based on electrokinetic injection has been studied in detail and compared. Best results were obtained with the internal standard method or by applying the conductivity corrected peak area method. These methods yielded a relative error of prediction of less than 6% and can be recommended for quantitative analysis.

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 mM 4-aminopyridine and 7 microM 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.

Head column field‐amplified stacking from the flow: Stabilization of the sample plug position by using backpressure

Head column‐field amplified sample stacking (HC‐FASS) is one of the most powerful concentration techniques in capillary electrophoresis. In the present work we demonstrate that a laboratory‐designed pneumatic sampler not only enables us to easily perform HC‐FASS from stagnant sample solutions but also permits us to carry out HC‐FASS from sample stream, which creates an opportunity to lower the detection limit of analytes further. The influence of stacking time in case of the flowing sample on peak efficiencies and resolution is discussed. It is demonstrated that the sample plug length can be kept constant by monitoring the current in the capillary, which controls a feedback system based on backpressure at the capillary outlet.