High-performance capillary electrophoresis of SDS-protein complexes using UV-transparent polymer networks

Use of Taylor-Aris Dispersion for Measurement of a Solute Diffusion Coefficient in Thin Capillaries

A method for the fast measurement of the diffusion coefficients of both small and large molecules in thin capillaries is reported. The method relies on Taylor-Aris dispersion theory and uses standard instrumentation for capillary zone electrophoresis. With this equipment, which consists of thin capillaries (50 to 100 micrometers in inner diameter), an injection system, detector ports, and computer data acquisition, a sample plug is pumped through the capillary at known velocity and the peak dispersion coefficient (D(*)) is measured. With the experimentally measured values of D(*) and flow velocity, and knowledge of the inner diameter of the capillary, the molecular diffusion coefficient (D) can be rapidly derived. For example, for ovalbumin a D value of 0.759 x 10(-6) square centimeter per second is found versus a tabulated value of 0.776 x 10(-6) square centimeter per second (error, 2 percent). For hemoglobin a D value of 0.676 x 10(-6) square centimeter per second is obtained versus a literature value of 0.690 x 10(-6) square centimeter per second (error, 1.5 percent).

Mixed polymer networks in the direct analysis of pharmaceuticals in urine by capillary electrophoresis

Two-component polymer mixtures of polyethylene oxide-polydextran have been investigated as unique separation media for capillary electrophoresis. The effects of concentration of the individual polymers and their mixtures on the electroosmotic velocity and electrophoretic mobility of small pharmaceutical compounds were investigated. The molecular masses of polymers, buffer concentrations and percentages of organic solvents and cyclodextrins were varied to explore their effects on the separation process. The plate height against field strength curves were also generated for a better understanding of the kinetic processes involved. The two-component polymer mixtures were found as stable and selective media for the analysis of an anti-ulcer drug famotidine directly in untreated urine.

Electrophoretic mobilities of the complexes between sodium dodecyl sulfate and various peptides or proteins determined by free solution electrophoresis using coated capillaries

Electrophoretic mobilities of various proteins or peptides complexed with sodium dodecyl sulfate (SDS) were determined by free solution capillary electrophoresis. The complexes formed between SDS and protein polypeptide showed electrophoretic mobilities virtually insensitive to the protein molecular weight. On the other hand, scattered and larger negative electrophoretic mobilities were observed for peptides of molecular weights less than 10000. Mobility differences as small as 0.3-3% among the three differently modified derivatives of bovine serum albumin could also be successfully determined due to the high resolving power of capillary electrophoresis.

High-performance capillary electrophoresis of SDS-proteins using pullulan solution as separation matrix

Sodium dodecyl sulphate (SDS) capillary electrophoresis using pullulan solution as a separation matrix was developed for the separation and molecular mass determination of proteins. The silanol functions on the inner surface of a fused-silica capillary were deactivated by coating with linear polyacrylamide through Si-C linkages, into which the pullulan solution was filled. The stability of the coating was examined by exposure to an alkaline buffer solution (pH 9.2) for up to 30 days. Compared with conventional coatings with linear polyacrylamide through siloxane linkages, the present capillary was more stable even under alkaline conditions and markedly reduced electroosmotic flow. Thus, polymer solutions of low viscosity such as pullulan solution could be stabilized in the capillary, resulting in a prolonged life-span of the capillary and improved reproducibility of separations. An excellent linear relationship was obtained between the mobility and the logarithm of the molecular mass of SDS-proteins. The relative standard deviation of migration times was below 0.5% when the pullulan solution was refilled in each analysis (n = 10). The calibration plots of the integrated peak areas at 214 nm vs. concentration of standard proteins were linear in the range 5 micrograms/ml-0.1 mg/ml.

Enhanced chiral separation of dansylated amino acids with cyclodextrin-dextran polymer network by capillary electrophoresis

A method for the chiral separation of dansyl-DL-amino acid mixtures using a dextran (M(r) 2,000,000) polymer network containing beta-cyclodextrin (beta-CD) in HPCE was developed. Mixtures of up to seven amino acids could be baseline resolved by this method under neutral pH conditions. Resolution was dependent on the dextran concentration in the polymer network. Temperature effects on the chiral separation were studied. Optimal efficiency and resolution of DL-enantiomeric pairs of amino acid samples were obtained at 25 degrees C. The resolution of different amino acids used in this work decreased with an increase in temperature.

A transient entanglement coupling mechanism for DNA separation by capillary electrophoresis in ultradilute polymer solutions

Using capillary electrophoresis, large DNA molecules (2.0-23.1 kbp) may be rapidly separated in ultradilute polymer solutions (< 0.002% w/w) under a high-voltage, steady field (265 V/cm). At this polymer concentration, the separation mechanism appears to be significantly different from that postulated to occur in crosslinked gels. Based on experimental results obtained with DNA restriction fragments and with negatively charged latex microspheres, we conclude that the Ogston and reptation models typically used to describe gel electrophoresis are not appropriate for DNA separations in such dilute polymer solutions. Electrophoresis experiments employing solutions of both small and large hydroxyethyl cellulose polymers highlight the importance of polymer length and concentration for the optimum resolution of DNA fragments varying in size from 72 bp to 23.1 kbp. A transient entanglement coupling mechanism for DNA separation in dilute polymer solutions is developed, which suggests that there is no a priori upper size limit to DNA that can be separated by capillary electrophoresis in a constant field.

UV-transparent, replaceable agarose gels for molecular-sieve (capillary) electrophoresis of proteins and nucleic acids

Gels of methoxylated agarose (gelling point 25.6 degrees C) and other low-melting agarose derivatives compare favorably with cross-linked polyacrylamide gels for capillary and slab molecular-sieve electrophoresis of proteins and DNA. These agarose gels can be pressed out of the capillary following a run and replaced by an agarose solution with a temperature of 35-40 degrees C. Gelation occurs upon lowering temperature and the same capillary can thus be reused for another analysis with a fresh gel. The methoxylated, non UV-absorbing agarose gels are, accordingly, replaceable, which makes them very attractive for series analyses with modern, automated capillary electrophoresis apparatus. The high resolution of these agarose gels is demonstrated with a separation of an albumin sample into monomers, dimers, trimers, tetramers, pentamers, hexamers, heptamers, and of DNA fragments.

Effect of operational variables on the separation of proteins by capillary sodium dodecyl sulfate-gel electrophoresis

Capillary sodium dodecyl sulfate (SDS)-gel electrophoresis, for fast and high-resolution separations of protein molecules based on their molecular masses was investigated, employing a polymeric sieving network of polyethylene oxide (PEO). A standard mixture of five proteins ranging from 14.2-66.0 kDa in molecular mass was used to evaluate the sieving matrix. A general migration velocity equation was derived for capillary SDS-gel electrophoresis of proteins and supported by the experimental data. This equation gives a better understanding of SDS-protein separations via capillary gel electrophoresis. Results are presented regarding the effects of different operational variables such as gel concentration, electric field strength, molecular mass, and temperature on the electrophoretic migration properties of the different size protein molecules.

Rapid capillary gel electrophoresis of proteins

The rapid separation of sodium dodecyl sulphate-protein complexes according to their molecular masses (M(r)) by capillary gel electrophoresis is described. Using commercial equipment, standard proteins with M(r) in the range 29,000-97,400 were resolved to the baseline in less than 2 min by utilizing a separation distance of 7 cm. A linear relationship between migration time and log M(r) was found and rapid determination of the molecular mass of light and heavy chains of human immunoglobulin G is reported. The results are compared with applications using longer separation distances, showing that rapid and efficient analysis and adequate resolution can be obtained by using short separation distances.

Electromigration behavior of polysaccharides in capillary electrophoresis under pulsed-field conditions

Various polysaccharides can successfully migrate through entangled polymer solutions during high-voltage capillary electrophoresis. For neutral polysaccharides, complexation with borate provides the electric charge needed for electromigration, while a fluorescent tag is needed to detect the solute bands with adequate sensitivity. At constant potentials between 50 and 300 V/cm, the charged polysaccharides undergo molecular stretching, resisting the desired separation according to their molecular mass. This problem can be overcome through the use of variable fields, pulsed along the separation capillary at a 180 degree angle. Variables of the pulsing experiment appear to have a profound influence on molecular shape rearrangements of polysaccharides with respect to the separation medium, as demonstrated here with highly efficient separations of polydextrans (8,000-2,000,000 Da).

Evaluation of sodium dodecyl sulfate non-acrylamide, polymer gel-filled capillary electrophoresis for molecular size separation of recombinant bovine somatotropin

Sodium dodecyl sulfate (SDS) non-acrylamide, polymer gel-filled capillary electrophoresis was examined as an alternative to the high-performance size-exclusion chromatographic (HPSEC) method for the analysis of recombinant bovine somatotropin (bovine growth hormone, rbSt). A calibration curve for the molecular mass of protein standards (M(r) 14,000 to 97,000) was linear (r2 = 0.998) when the molecular mass of the proteins and their peak migration time were plotted on a logarithmic (log-log) scale. Relative standard deviation (R.S.D.) of the molecular mass determination was approximately 2-3%. A pre-production as well as a production lot of the SDS gel-filled capillary columns were examined. Performance of both of these columns were equivalent. Peak migration time remained relatively constant beyond 140 sample injections. Gradual loss of theoretical plates was noted over the course of the assay; however, the peak resolution remained adequate for the analysis of rbSt. Peaks corresponding to monomer, dimer, trimer, and tetramer of rbSt were base-line resolved by the SDS gel-filled capillary electrophoresis. Theoretical plate of the monomer peak was approximately 28,000-30,000 per 40 cm column. Both the monomer and the dimer recovery studies indicated that the calibration curves are linear (r2 > 0.993) and the slopes are not different from one. Amounts of the components in rbSt determined by the SDS gel-filled capillary electrophoresis compared well with those of the HPSEC method. The results of this study indicated that the SDS non-acrylamide gel-filled capillary electrophoresis may be a viable alternative to the HPSEC method for the molecular size separation and analysis of recombinant proteins.

Automated Ferguson analysis of glycoproteins by capillary electrophoresis using a replaceable sieving matrix

Obtaining accurate molecular weight estimates for glycoproteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) has been difficult due to the lack of SDS binding by the carbohydrate moieties of the proteins. This leads to lower charge-to-mass ratios for SDS-glycoprotein complexes, resulting in over-estimation of molecular weights by SDS-PAGE. In order to minimize these inaccuracies for proteins with abnormal charge-to-mass ratios, a Ferguson plot may be employed. This application requires the determination of relative mobilities for standard proteins in addition to unknowns at several different gel concentrations. Historically, this technique has not been popular because it requires time-consuming preparation of gels with varying matrix concentrations, electrophoresis, and staining/destaining of gels. In this paper a procedure is demonstrated which automatically generates all of the data required for a Ferguson plot using a replaceable sieving matrix (thereby eliminating gel polymerization) in a capillary format. In addition, this technique possesses the advantages inherent to capillary electrophoresis, namely, very fast separation times, and on-line monitoring which allows quantitation and precludes post-separation staining and destaining of gels.

DNA shape and separation efficiency in polymer media: a computerized method based on electrophoretic mobility data

The computer program ELPHOFIT for evaluation of the nonlinear plots of log-(mobility) vs. polymer concentration (Ferguson plots) in terms of molecular and polymer properties has been extended to yield a measure of the molecular sieving capacity of the polymer medium. The usefulness of the extended program, version 2.2, was exemplified by the evaluation of DNA shape and separation efficiency in solutions and gels of agarose and polyacrylamide, using previous reports in the literature as a data base. That application of the extended program yields the following results:(i) The size of migrating DNA can be compared with an equivalent sphere having the same free mobility for a particular set of experimental conditions. The decrease in size of the equivalent sphere with polymer concentration previously demonstrated for agarose solutions applies to all of these polymer media; it reveals a steep, hyperbolic decline of that radius in uncrosslinked polyacrylamide solutions in contrast to the shallow decline in the other three media. (ii) The separation efficiency of polyacrylamide gels exceeds that of uncrosslinked polyacrylamide solutions; the separation efficiency of agarose solutions for DNA smaller than 1 kb in length is higher than that of polyacrylamide solutions. Program ELPHOFIT 2.2 is available on request from the first author.