Synergism of capillary isotachophoresis and capillary zone electrophoresis

The combination of capillary isotachophoresis and capillary zone electrophoresis may enhance greatly the performance of analytical capillary electrophoresis with respect to both separation power and the concentration sensitivity. The concentrating effects and the separation power of isotachophoresis allow the analysis of diluted samples and the elimination of interferences due to bulk components. The separation process of zone electrophoresis enables one to resolve the stack of trace analytes and detect the resulting individual zones with high sensitivity. The transition of isotachophoresis into zone electrophoresis plays the key role in the overall performance of this hyphenated technique. This article describes the dynamics of the conversion of isotachophoresis into zone electrophoretic mode and shows that the key role is played by the segments of the leading and terminating zones from the isotachophoretic stage. The magnitude of these segments directly effects the detection time as well as the separation width of the peaks of analytes. It is shown that these effects are also important in the analyses by capillary zone electrophoresis where isotachophoresis is induced by the sample itself. Finally, the paper presents a list of recommended, user-friendly, electrolyte systems which enable one to simply predict the performance of the combination isotachophoresis-zone electrophoresis.     

A modified capillary microrespirometer

Modifications which enable simpler operation of the Cunningham-Barth-Kirk microrespirometer are described and an example of its use is quoted. Added advantages include easy positioning of indicator drop in the capillary and thermal equilibration at atmospheric pressure.     

Chiral ligand-exchange capillary electrophoresis

This review summarizes the application of capillary electrophoresis and capillary electrochromatography for the chiral separation of various substance classes using the principle of ligand exchange. The application of this principle to various substance classes is reported.     

Optimization of capillary coating by hydroxyethyl methacrylate for capillary zone electrophoresis of proteins

This work describes further improvements of coating fused silica capillaries with 2-hydroxyethyl methacrylate (HEMA) by atom transfer radical polymerization (ATRP). First, endcapping with a sterically less bulky silanyl reagent reduces the electrosmotic flow (EOF) by 25% in addition to the 40% EOF reduction caused by HEMA coating compared to a bare fused silica capillary. An additional hydrolysis step was introduced into the preparation of HEMA coated capillaries and leads to better reproducible migration times. The influence of the solvent during ATRP and the resulting polymer coating was investigated by replacement of DMF with water or water-methanol mixtures. The quality of the optimized coating was characterized by protein separations at pH 3. HEMA coated capillaries reveal up to 746000 plates. The polyvinyl alcohol (PVA) coated capillary provides only half of this efficiency. A long-term test at pH 9 shows good stability of the HEMA coated capillaries in basic medium. Also the numbers of plates in this medium was about 30% higher than for separations with the PVA capillary. In addition, the phosphate buffer was replaced by a volatile ammonium acetate buffer for later use with mass spectrometry (MS).     

Characterization of protein behavior in high-performance capillary electrophoresis using a novel capillary system

Original calculations of over a million theoretical plate efficiency for macromolecular solutes in the open tubular high-performance capillary electrophoresis experiment considered axial diffusion to be the efficiency limiting factor. In practice, interactions of biopolymers, such as proteins, with the capillary wall has had a significant impact on readily achieving high efficiencies for a wide variety of proteins. This paper reports a capillary system in which protein-surface interactions have been minimized, resulting in high efficiencies (greater than or equal to 300,000 theoretical plates). This system allows the analysis of a set of protein standards over a wide pI range at neutral pH and moderate ionic strength. The characterization of the behavior of those protein standards in this capillary system is described.     

Integrated capillary fluorescence DNA biosensor

Covalent attachment of dsDNA molecules inside a glass capillary without the need for hybridization is described. It is shown that the glass capillary has a surface density of 2.5 x 10(13) molecules/cm(2) with specific binding capacity of 62.5%. The resulting substrate was used to develop a biosensor for determining fluorescent organic analytes and metal binding with DNA. The biosensor combines highly specific immobilization chemistry with a capillary-geometry flow cell arrangement. The results show that fluorescent dyes are retained in the dsDNA-modified surface and that exposure to concentrations of nickel and lead ions resulted in a recoverable, highly reproducible diminishment of the fluorescence intensity.     

Mathematical modeling of capillary density

Capillary density is important as a determinant for total oxygen transport to tissue. Because both capillary morphology and fiber composition vary considerably from muscle to muscle, measurement of capillary morphology and fiber composition vary considerably from muscle to muscle, measurement of capillary density alone cannot provide the detailed information necessary for analyzing physical phenomena. In this report we consider the capillary:fiber ratio, fiber types, fiber diameters, and fiber composition as components of a unit to express capillary density. We have applied the hexagonal fiber array model to calculate capillary density in cat and dog striated muscle and compared this with experimental data in the literature. The results indicate that this model may be useful for predicting capillary densities from simple biopsy procedures.     

Diagnosing AICA-ribosiduria by capillary electrophoresis

AICA-ribosiduria is a recently discovered inherited metabolic disease caused by a defect in final steps of purine de novo biosynthesis-5-amino-4-imidazolecarboxamide ribotide (AICAR)-transformylase/inosinemonophosphate (IMP)-cyclohydrolase (ATIC). A rapid and selective capillary electrophoretic method for screening of patients with AICA-ribosiduria is described. The method is based on direct ultraviolet detection of 5-amino-4-imidazolecarboxamide (AICA) and 5-amino-4-imidazolecarboxamide riboside (AICAr) in untreated urine. Background electrolyte consists of 100mM malonic acid adjusted with gamma-aminobutyric acid (pH 2.7). Under the given separation conditions both compounds of interest are well separated from other substances with separation efficiency of 1020000 and 130000 theoretical plates/m for AICA and AICAr, respectively. Total analysis time is 3 min with the limits of detection of 3.6 microM and 4.5 microM for AICA and AICAr, respectively. The usefulness of the presented method for screening of patients with ATIC deficiency is demonstrated on samples of Chinese hamster ovary cell line defective in ATIC activity, spiked urine samples and urine samples from patients treated with high-dose MTX which do not excrete increased amounts of AICA and AICAr compared to untreated controls (p<0.05). The described method is fast and effective enough for diagnostic applications.     

Transient phenomena in capillary exchange

The case of a vessel, which supplies a region through which it passes with some substance, is considered for the situation in which the permeability is the limiting factor. Diffusion parallel to the vessel is neglected. The substance may, however, be consumed proportional to its concentration in the inner or outer region. A solution is given for the case in which the input is an arbitrary function of time. It is suggested that the results may be applied in some cases to data on the injection of substances into blood vessels, or they may be applied to the transient effects in the case of vapors or gases passing through the respiratory passages.