Short Capillary Electrophoresis Research Articles

Enhancing separation in short-capillary electrophoresis via pressure-driven backflow.

We present a novel easy-to-operate and efficient method to improve the separation efficiency in short-capillary electrophoresis by introducing steady backflow to counterbalance electro-osmotic flow without the use of any external pressure. The backflow was easily generated by tapering the capillary end, which was achieved by heating a straight capillary and stretching it with a constant force. We investigated the net fluidic transport rate under different tip lengths and separation voltages. Good run-to-run repeatability and capillary-to-capillary reproducibility of the present method were obtained with RSD less than 1.5%, indicating the stability of the fluid transport rate in the tapered capillary, which ensures the quantification and repeatability of capillary zone electrophoresis (CZE) analysis. Enhanced separation of the tapered short capillary electrophoresis was demonstrated by CZE analyzing amino acids and positional isomers. Baseline separations were achieved in less than 60 s using a tapered capillary with the effective length of 5 cm, while no separation was achieved using a normal capillary without a tapered tip. The present study provides a promising method to use pressure-driven backflow to enhance separation efficiency in short-capillary electrophoresis, which would be of potential value in a wide application for fast analysis of complex samples.

Pressure-assisted introduction of urine samples into a short capillary for electrophoretic separation with contactless conductivity and UV spectrometry detection.

A computer-controlled hydrodynamic sample introduction method has been proposed for short-capillary electrophoresis. In the method, the BGE flushes sample from the loop of a six-way sampling valve and is carried to the injection end of the capillary. A short pressure impulse is generated in the electrolyte stream at the time when the sample zone is at the capillary, leading to injection of the sample into the capillary. Then the electrolyte flow is stopped and the separation voltage is turned on. This way of sample introduction does not involve movement of the capillary and both of its ends remain constantly in the solution during both sample injection and separation. The amount of sample introduced to the capillary is controlled by the duration of the pressure pulse. The new sample introduction method was tested in the determination of ammonia, creatinine, uric acid, and hippuric acid in human urine. The determination was performed in a capillary with an overall length of 10.5 cm, in two BGEs with compositions 50 mM MES + 5 mM NaOH (pH 5.1) and 1 M acetic acid + 1.5 mM crown ether 18-crown-6 (pH 2.4). A dual contactless conductivity/UV spectrometric detector was used for the detection.

High-speed separation and detection of amino acids in laver using a short capillary electrophoresis system.

A high-speed separation method of capillary MEKC with LIF detection had been developed for separation and determination of amino acids in laver. The CE system comprised a manual slotted-vial array (SVA) for sample introduction that could improve the separation efficiency by reducing injection volume. Using a capillary with 80 mm effective separation length, the separation conditions for amino acids were optimized. Applied with the separation electric field strength of 300 V/cm, the ten amino acids could be completely separated within 2.5 min with 10 mol/L Na2HPO4-NaOH buffer (pH = 11.5) including 30 mmol/L SDS. Theoretical plates for amino acids ranged from 72,000 to 40,000 (corresponding to 1.1-2.0 μm plate heights) and the detection limits were between 25 and 80 nmol/L. Finally, this method was applied to analyze the composition of amino acids in laver and eight known amino acids could be found in the sample. The contents of five amino acids, tyrosine, glutamic acid, glycine, lysine, and aspartic acid that could be completely separated in real sample were determined. The recoveries ranged from 82.3% to 123% that indicated the good reliability for this method in laver sample analysis.

Rapid determinations of saccharides in high-energy drinks by short-capillary electrophoresis with contactless conductivity detection

The methodology for separations of saccharides in standard electrophoretic systems has been transferred to the short-capillary electrophoresis format. The laboratory-designed apparatus used employs a quartz capillary with an internal diameter of 10 μm, a total length of 10 cm, and an effective length of 4 cm, in combination with contactless conductivity detection. It has been applied to separations of neutral mono- and disaccharides. The saccharides are separated in the anionic form, in solutions of alkali hydroxides, namely, KOH, NaOH, and LiOH. The separation of a model mixture of five saccharides (sucrose, lactose, glucose, fructose, and ribose) takes less than 1 min, the LOD equaling 15, 35, 19, 17, and 24 mg L(-1) and the LOQ equaling 52, 117, 63, 53, and 79 mg L(-1) for sucrose, lactose, glucose, fructose, and ribose, respectively. The technique developed has been used to determine sucrose, glucose and fructose in high-energy drinks. The separation is finished within less than 50 s; the saccharide contents determined are identical with the declared values within the reliability interval in most cases, the RSD value being mostly less than 2%. In general, the separation system developed is very convenient for rapid analyses of large sets of similar samples, e.g., in product quality control or environmental monitoring.

Short-capillary electrophoresis with electrochemiluminescence detection using porous etched joint for fast analysis of lidocaine and ofloxacin

Fast analysis of ofloxacin and lidocaine, as bactericide and analgesic or anesthetics, is of clinic importance for understanding the patient's medical process. This paper presented a high throughput, simple analysis method of lidocaine and ofloxacin by capillary electrophoresis coupled with electrochemiluminescence (ECL) using porous etched joint. To shorten the analysis time and to improve the analytical performance, a capillary with 10 cm in length was used as the separation channel. The cyclic voltammograms of Ru(bpy) 3 2+ with different capillary length at same field strength showed that the porous etched joint eliminated the effect of electrophoretic current on the ECL detection. Following micro total analysis systems (μTAS), some advantages of which this approach has, the fabrication of channel in chip was not needed. Compared with capillary electrophoresis with 40-cm-long capillary, the high sample throughput and low zone broadening may be the main advantage of the present system. Under optimal condition, the detection limits of lidocaine and ofloxacin based on peak height were 3.0 × 10 −8 and 5.0 × 10 −7 mol L −1 and a 60 h −1 of sampling frequency was obtained. The precision (R.S.D.) of the migration time and the peak height for five replicate injections of a mixture of lidocaine (1.0 × 10 −6 mol L −1) and ofloxacin (4.0 × 10 −6 mol L −1) were 3.2–3.9% and 4.7–5.3%, respectively.