Buffer Constituents Research Articles

Capillary electrophoresis-mass spectrometry for impurity profiling of basic pharmaceuticals using non-volatile background electrolytes

A generic approach has been developed for coupling capillary electrophoresis (CE) using non-volatile background electrolytes (BGEs) with mass spectrometry (MS) using a sheath liquid interface. CE-MS has been applied for basic and bi-functional compounds using a BGE consisting of 100 mM of TRIS adjusted to pH 2.5 using phosphoric acid. A liquid sheath effect is observed which may influence the CZE separation and hence may complicate the correlation between CE-UV and CE-MS methods. The influence of the liquid sheath effect on the migration behavior of basic pharmaceuticals has been studied by simulation experiments, in which the BGE outlet vial is replaced by sheath liquid in a CE-UV experiment. As a consequence of the liquid sheath effect, phosphate based BGEs can be used without significant loss of MS sensitivity compared to volatile BGEs. The use of buffer constituents such as TRIS can lead to lower detection limits as loss of MS sensitivity can be compensated by better CE performance. TRIS based BGEs permit relatively high injection amounts of about 100 pmol while maintaining high resolution. The ESI-MS parameters were optimized for a generic method with maximum sensitivity and stable operation, in which the composition of the sheath liquid and the position of the capillary were found to be important. Furthermore, the nebulizing pressure strongly influenced the separation efficiency. The system showed stable performance for several days and a reproducibility of about 15% RSD in peak area has been obtained. Nearly all test compounds used in this study could be analyzed with an MS detection limit of 0.05% measured in scan mode using extracted ion chromatograms. As a result, CE-MS was found to be a valuable analytical tool for pharmaceutical impurity profiling.

Nonequivalence of second virial coefficients from sedimentation equilibrium and static light scattering studies of protein solutions

Experimental data for ovalbumin and lysozyme are presented to highlight the nonequivalence of second virial coefficients obtained for proteins by sedimentation equilibrium and light scattering. Theoretical considerations confirm that the quantity deduced from sedimentation equilibrium distributions is B 22, the osmotic second virial coefficient describing thermodynamic nonideality arising solely from protein self-interaction. On the other hand, the virial coefficient determined by light scattering is shown to reflect the combined contributions of protein–protein and protein–buffer interactions to thermodynamic nonideality of the protein solution. Misidentification of the light scattering parameter as B 22 accounts for published reports of negative osmotic second virial coefficients as indicators of conditions conducive to protein crystal growth. Finally, textbook assertions about the equivalence of second virial coefficients obtained by sedimentation equilibrium and light scattering reflect the restriction of consideration to single-solute systems. Although sedimentation equilibrium distributions for buffered protein solutions are, indeed, amenable to interpretation in such terms, the same situation does not apply to light scattering measurements because buffer constituents cannot be regarded as part of the solvent: instead they must be treated as non-scattering cosolutes.

High-performance Liquid Chromatography of Some Alkaloids on n-Octadecylphosphonic Acid-modified Magnesia-Zirconia Stationary Phase

The high-performance liquid chromatographic behavior of some alkaloids was studied on an n-octadecylphosphonic acid-modified magnesia-zirconia (C 18PZM) stationary phase. The effects of the mobile phase variables such as the methanol content, the ionic strength, and the pH on their chromatographic behavior were investigated. The retention mechanism of the alkaloids in the stationary phase was elucidated. The results indicate that both hydrophobic and cation-exchange interactions contribute to the retention of the alkaloids under most chromatographic conditions. The inherent Brönsted-acid sites and the adsorbed Lewis-base anionic buffer constituents on the accessible ZM-surface Lewis-acid sites play a role in the retention of ionized solutes by cation-exchange interaction. However, at high pH, the retention of the alkaloids depends mainly on the hydrophobic interactions between the solutes and the support. A satisfactory separation of the alkaloids was achieved with the mobile phase of pH 10.1. The C 18PZM seems to be an excellent alternative to the silica-based reversed-phase stationary phase for the separation of strongly basic solutes.

Hydrolysis of Maltoheptaose in Flow through Silicon Wafer Microreactors Containing Immobilised α‐Amylase and Glycoamylase

AbstractIn this study a silicon micro immobilised enzyme reactor (μIMER) has been applied for hydrolysis of maltoheptaose as a model maltodextrin and starch using immobilised μ‐amylase (from Aspergillus oryzae) and glycoamylase (from Aspergillus niger). The influence of several parameters was investigated such as immobilisation chemistry, buffer constituents, pH, temperature, flow rate and substrate concentration. The conversion efficiency profile of the substrate was measured and the long‐term stability of the reactor was tested. For separation and detection of the formed hydrolysis products, high‐performance anion‐exchange chromatography with pulsed amperometric detection (HPAEC‐PAD) was used. The results show that the μIMERs can also be used for hydrolysis of starch and also additionally be connected directly on‐line with, e.g., liquid chromatography, making it possible to perform on‐line characterisation and analysis of starch hydrolysis products.

Effect of the aqueous component of the mobile phase on RP-TLC retention and its implication in the determination of lipophilicity for a series of structurally diverse drugs

The reversed-phase TLC retention behavior of a series of structurally diverse drugs, mostly basic compounds, has been investigated with different aqueous mobile-phase components. Phosphate buffer, phosphate-buffered saline, and morpholinepropanesulfonic acid, with or without addition of n -decylamine, at pH 7.4, and phosphate buffer at pH 11.0 were used with different proportions of methanol as the mobile phase. The effect of the buffer constituents on extrapolated R Mw values and the corresponding slopes, S , and their interrelationship, was evaluated. The different sets of R Mw values were correlated with lipophilicity log P and log D 7.4 . MOPS was found to be more suitable than phosphate buffer for assessment of lipophilicity. Use of log D instead of log P , combined with use of the ionization-correction term Q , led to improved correlation and revealed a reduced net effect of ionization on retention.

A new multiphasic buffer system for benzyldimethyl‐n‐hexadecylammonium chloride polyacrylamide gel electrophoresis of proteins providing efficient stacking

Acidic PAGE systems using cationic detergents such as benzyldimethyl-n-hexadecylammonium chloride (16-BAC) or CTAB have proven useful for the detection of methoxy esters sensitive to alkaline pH, resolving basic proteins such as histones and membrane proteins. However, the interesting phosphate-based system suffered from poor stacking, resulting in broadened bands and long running times. Therefore, a new 16-BAC PAGE system based on the theory of moving boundary electrophoresis with properties comparable to the classical SDS-PAGE system was designed. As a result a new multiphasic analytical 16-BAC PAGE system providing efficient stacking and significantly shorter running times is presented here. It is based on acetic acid and methoxyacetic acid as common ion constituents. This PAGE system takes advantage of the additional counter stacking effect due to a cross boundary electrophoresis system resulting from the selected buffer constituents. Furthermore, the concentration of 16-BAC was optimized by determining its previously unknown CMC. Due to efficient focusing of the introduced tracking dye, methyl green, termination of electrophoresis can now be more easily followed as compared to the Schlieren line.

Comparison of capillary zone electrophoresis and isotachophoresis determination of dimethindene enantiomers in pharmaceuticals using charged carboxyethyl-beta-cyclodextrin as a chiral selector

Charged cyclodextrin-mediated capillary electrophoretic methods (capillary zone electrophoresis [CZE] and isotachophoresis [ITP]) in a hydrodynamically closed separation system with suppressed electroosmotic flow and UV absorbance photometric detection (for CZE) or conductivity detection (for ITP) were developed for a highly effective separation and quantitation of dimethindene enantiomers in various pharmaceutical formulations (solution, gel, capsules). Optimized electrolyte systems were based on low-mobility buffer constituents (epsilon-aminocaproic acid, beta-alanine, potassium acetate, acetic acid), negatively charged (at pH > 4.5) carboxyethyl-beta-cyclodextrin (CE-beta-CD), serving as chiral selector, and methylhydroxyethylcellulose, serving as an electroosmotic flow suppressor. Complete enantioseparations of dimethindene in the presence of low concentrations of CE-beta-CD (2.5 mg/ml in CZE, 6.0 mg/ml in ITP) clearly indicated a role of charge of this chiral selector in enantioresolution. It also outlined the potential of charged CD-derivatives as chiral selectors for various CE techniques. The proposed methods were successfully validated, appraising parameters of sensitivity, linearity, precision, accuracy/recovery, and robustness, and then, they were applied to pharmaceutical samples. Consistent results obtained by both CE methods indicate their usefulness for routine use.

Francisella tularensis Proteome: Low Levels of ASB-14 Facilitate the Visualization of Membrane Proteins in Total Protein Extracts

Proteomic analysis of bacterial pathogens isolated from in vivo sources, such as infected tissues, provides many challenges not the least of which is the limited quantity of sample available for analysis. It is, therefore, highly desirable to develop a one-step cellular lysis and protein solubilization method that minimizes protein losses and allows the maximum possible coverage of the proteome. Here, we have used standard sample buffer constituents including urea, thiourea and DTT, but varied the detergent composition of the buffers in order to achieve the best quality of gels and the greatest spot resolution. We found that the most efficient solubilizing solution in this case consisted of 7 M urea, 2 M thiourea, 1% DTT, 0.5% amidosulfobetaine-14 (ASB-14) and 4% 3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Inclusion of low levels of ASB-14 in solutions allowed visualization of a subset of 24 new protein spots in the Live Vaccine Strain (LVS) of Francisella tularensis and 21 spots in a virulent A-strain of the pathogen. Further investigation showed that 15 of the 24 enriched LVS spots were membrane or membrane-associated proteins suggesting that the optimized lysis and solubilization solution aids in the detection of more hydrophobic proteins. This methodology is now being applied to the analysis of Francisella obtained from in vivo sources.

High‐performance liquid chromatography of some basic drugs on a n‐octadecylphosphonic acid modified magnesia‐zirconia stationary phase

The high-performance liquid chromatographic behavior of some basic drugs was studied on a n-octadecylphosphonic acid modified magnesia-zirconia (C18PZM) stationary phase. The effect of mobile phase variables such as methanol content, ionic strength, and pH on their chromatographic behavior was investigated. The retention mechanism of basic drugs on the stationary phase was elucidated. The results indicate that both hydrophobic and cation-exchange interactions contribute to solute retention under most chromatographic conditions. The inherent Brönsted-acid sites and also the adsorbed Lewis base anionic buffer constituents on accessible ZM surface Lewis acid sites play a role in the retention of ionized solutes by cation-exchange interaction. However, especially at high mobile phase pH, the retention of basic drugs depends mainly on hydrophobic interactions between solutes and support. Separations of the basic drugs on the C18PZM phase by a predominantly reversed-phase retention mode were very promising. The mixed-mode retention feature on this phase, as a result of the adsorbed Lewis base anionic buffer constituents acting as sites for cation-exchange, could also be very useful, e.g. for enhancing the chromatographic selectivity of such analytes. The C18PZM seems to be an excellent alternative to silica-based reversed-phase stationary phase for the separation of strongly basic solutes.

Preparation and evaluation of n-octadecylphosphonic acid-modified magnesia–zirconia stationary phases for reversed-phase liquid chromatography

Three n-octadecylphosphonic acid-modified magnesia–zirconia reversed stationary phases (C 18PZM) are prepared via the strong Lewis base interactions between organophosphonate and magnesia–zirconia composite. And two of them are end-capped by using trimethylchlorosilane as end-capping agent in different procedures. Stability studies at extreme high pH conditions (pH 9–12) show that both the non-endcapped and endcapped columns are quite stable at pH 12 mobile phase. The reversed-phase liquid chromatographic behavior of three C 18PZM stationary phases are comparatively investigated in detail using a variety of basic compounds as probes. The retention of basic compounds on the three phases is studied over a wide range of pHs. And the possible retention mechanisms of basic compounds on the three stationary phases are discussed. The results show that the basic solutes retain by a hydrophobic and cation-exchange interaction mixed mechanism on three stationary phases when they are operated in eluents at pH values near to the p K a of the Brönsted conjugate acid form of the analyte, suggesting that inherent zirconol groups on ZM are not expected to interact with bases via cation-exchange interaction at lower pH. Nonetheless, the non-endcapped phase differs markedly from the edncapped ones in retention and selectivity of basic solutes using eluents at pH 4.1, implying a complex retention mechanism at this pH. The cation-exchange sites under such conditions are more likely due to the adsorbed Lewis base anionic buffer constituents (acetate) on accessible ZM surface sites than the chemisorbed phosphonate. Although the three phases exhibit very similar chromatographic behavior with eluents at pH 10.1, and show in general satisfactory separation of basic compounds and alkaloids studied, the performance for a specific analyte, however, differs largely from column to column.

Human Cytomegalovirus UL84 Is a Phosphoprotein That Exhibits UTPase Activity and Is a Putative Member of the DExD/H Box Family of Proteins

Human cytomegalovirus (HCMV) UL84 is required for lytic DNA replication and is proposed to be the key factor in initiation of viral DNA synthesis. We now show that UL84 has a high degree of homology to the DExD/H (where x can be any amino acid) box family of helicases, displays UTPase activity, and is phosphorylated at serine residues. Affinity column-purified UL84-FLAG fusion protein was used in an in vitro nucleoside triphosphatase (NTPase) assay to show that UL84 has NTPase activity, preferring UTP. This UTPase activity was linear with respect to enzyme concentration and slightly enhanced by the addition of nucleic acid substrates. UL84 UTPase was the highest at low salt concentrations, a pH of 7.5, and a temperature of 45 degrees C. The enzyme preferred Mg2+ as the divalent cation but was also able to catalyze the UTPase reaction in the presence of Mn2+, Ca2+, and Zn2+ albeit at lower levels. The evidence presented here suggests that the UL84 UTPase activity may be part of an energy-generating system for helicase activity associated with the initiation of HCMV DNA replication.

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers☆I. Theoretical studies

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers☆I. Theoretical studies

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers☆II. Experimental studies at acidic pH with on-line enrichment

The separation of acidic and basic model proteins was studied in capillary free zone electrophoresis in a polyacrylamide-coated, electroosmosis-free capillary at pH below their isoelectric points (pI) using various buffers at pH 2.7-4.8 with UV detection at 200 nm. The separation performance was significantly dependent on the coating quality, which may even differ within the same batch of capillaries. In addition, a washing step with 2 M HCl and the storage of the capillary in distilled water was essential for the performance. For high efficiency and resolution the choice of buffer constituents was extremely important which is discussed in quantitative terms in Part I. The most promising buffers were ammonium acetate and ammonium hydroxyacetate at pH 4 (ionic strengths: 0.12 and 0.15 M, respectively) with plate numbers up to 1,700,000 plates/m, corresponding to a zone width (2sigma) of only 1 mm in a capillary with 40 cm effective length, when the injected samples were dissolved in a 10-fold diluted background electrolyte (BGE), a zone even narrower than those obtained in polyacrylamide gel electrophoresis, the characteristic feature of which is remarkably thin zones. In the experiment giving this plate number, the calculated variance for longitudinal diffusion was larger than all the other calculated variances (those for the width of the starting zone, Joule heating, sedimentation and the curvature of the capillary). Interestingly, the effect of capillary curvature was significant. In addition, the sum of all other imaginable variances (corresponding to various types of slow on/off kinetics and hyper-sharp peaks) was in the most successful experiments only 28-50% of the variance for longitudinal diffusion. One hundred- to two hundred-fold dilution of the BGE improved the detection limits and provided high precision in both migration times and peak areas with ammonium hydroxyacetate and ammonium acetate as background electrolytes. However, that high dilution increased the variance 140-400% for these buffers, respectively, at least partly due to conductivity or pH differences between the sample and buffer zones (hyper-sharp peaks). Sedimentation of the enriched sample, a factor that has not previously been treated theoretically or experimentally, was probably another reason for our finding that peak heights did not increase when the sample was dissolved in a buffer diluted more than 200-fold, although pH changes and in some cases thermal expansion in the capillary also may contribute. Loss of protein may occur at the ionic strength 0.01 and lower due to precipitation. Limits of detection were in the range 4-17 pmol of proteins with ammonium acetate as BGE. No indication of denaturation of proteins at pH 4 was observed. However, the separation performance at pH 3 was not satisfactory and loss of proteins was observed, possibly indicating such problems. The protein mobilities decreased unexpectedly from pH 4 to 3--a further indication of conformation changes.

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers: I. Theoretical studies

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers: I. Theoretical studies

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers: II. Experimental studies at acidic pH with on-line enrichment

The separation of acidic and basic model proteins was studied in capillary free zone electrophoresis in a polyacrylamide-coated, electroosmosis-free capillary at pH below their isoelectric points (p I) using various buffers at pH 2.7–4.8 with UV detection at 200 nm. The separation performance was significantly dependent on the coating quality, which may even differ within the same batch of capillaries. In addition, a washing step with 2 M HCl and the storage of the capillary in distilled water was essential for the performance. For high efficiency and resolution the choice of buffer constituents was extremely important which is discussed in quantitative terms in Part I. The most promising buffers were ammonium acetate and ammonium hydroxyacetate at pH 4 (ionic strengths: 0.12 and 0.15 M, respectively) with plate numbers up to 1 700 000 plates/m, corresponding to a zone width (2 σ) of only 1 mm in a capillary with 40 cm effective length, when the injected samples were dissolved in a 10-fold diluted background electrolyte (BGE), a zone even narrower than those obtained in polyacrylamide gel electrophoresis, the characteristic feature of which is remarkably thin zones. In the experiment giving this plate number, the calculated variance for longitudinal diffusion was larger than all the other calculated variances (those for the width of the starting zone, Joule heating, sedimentation and the curvature of the capillary). Interestingly, the effect of capillary curvature was significant. In addition, the sum of all other imaginable variances (corresponding to various types of slow on/off kinetics and hyper-sharp peaks) was in the most successful experiments only 28–50% of the variance for longitudinal diffusion. One hundred- to two hundred-fold dilution of the BGE improved the detection limits and provided high precision in both migration times and peak areas with ammonium hydroxyacetate and ammonium acetate as background electrolytes. However, that high dilution increased the variance 140–400% for these buffers, respectively, at least partly due to conductivity or pH differences between the sample and buffer zones (hyper-sharp peaks). Sedimentation of the enriched sample, a factor that has not previously been treated theoretically or experimentally, was probably another reason for our finding that peak heights did not increase when the sample was dissolved in a buffer diluted more than 200-fold, although pH changes and in same cases thermal expansion in the capillary also may contribute. Loss of protein may occur at the ionic strength 0.01 and lower due to precipitation. Limits of detection were in the range 4–17 pmol of proteins with ammonium acetate as BGE. No indication of denaturation of proteins at pH 4 was observed. However, the separation performance at pH 3 was not satisfactory and loss of proteins was observed, possibly indicating such problems. The protein mobilities decreased unexpectedly from pH 4 to 3—a further indication of conformation changes.

X-ray absorption by macromolecular crystals: the effects of wavelength and crystal composition on absorbed dose

Radiation damage restricts the useful lifetime for macromolecular crystals in the X-ray beam, even at cryotemperatures. With the development of structural genomics pipelines, it will be essential to incorporate projected crystal lifetime information into the automated data collection software routines. As a first step towards this goal, a computer program,RADDOSE, is presented which is designed for use by crystallographers in optimizing the amount of data that can be obtained from a particular cryo-cooled crystal at synchrotron beamlines. The program uses the composition of the crystal and buffer constituents, as well as the beam energy, flux and dimensions, to compute the absorption coefficients and hence the theoretical time taken to reach an absorbed dose of 2 × 10^7 Gy, the so-called `Henderson limit'. At this dose, the intensity of the diffraction pattern is predicted to be halved. A `diffraction–dose efficiency' quantity is introduced, for the convenient comparison of absorbed dose per diffracted photon for different crystals. Four example cases are considered, and the implications for anomalous data collection are discussed in the light of the results fromRADDOSE.

Chiral counter-current chromatography of gemifloxacin guided by capillary electrophoresis using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector

(+)-(18-crown-6)-tetracarboxylic acid (18C6H 4) has been known as a highly efficient chiral selector for resolving primary amine enantiomers in capillary electrophoresis (CE). We investigated the chiral separation of gemifloxacin using 18C6H 4 in analytical counter-current chromatography (CCC). The separation conditions for CE, including the binding constant, pH, and run buffer constituents, provided a helpful guideline for chiral CCC. A successful separation of gemifloxacin enantiomers could be achieved using a two-phase solvent system composed of 1-butanol-ethyl-acetate-bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane acetate buffer with a small amount of 18C6H 4. The hydrophobicity of the solvent system and the 18C6H 4 concentration were varied to optimize the chiral separation.

Analysis of clinical isolates of Propionibacterium acnes by optimised RAPD

Random amplification of polymorphic DNA (RAPD) was evaluated as a genotypic method for typing clinical strains of Propionibacterium acnes. RAPD can suffer from problems of reproducibility if parameters are not standardised. In this study the reaction conditions were optimised by adjusting template DNA concentration and buffer constituents. All isolates were typeable using the optimised RAPD protocol which was found to be highly discriminatory (Simpson’s diversity index, 0.98) and reproducible. Typing of P. acnes by optimised RAPD is an invaluable tool for the epidemiological investigation of P. acnes for which no other widely accepted method currently exists.

Sample preparation for two-dimensional gel electrophoresis.

The choice of sample preparation protocol is a critical influential factor for isoelectric focusing which in turn affects the two-dimensional gel result in terms of quality and protein species distribution. The optimal protocol varies depending on the nature of the sample for analysis and the properties of the constituent protein species (hydrophobicity, tendency to form aggregates, copy number) intended for resolution. This review explains the standard sample buffer constituents and illustrates a series of protocols for processing diverse samples for two-dimensional gel electrophoresis, including hydrophobic membrane proteins. Current methods for concentrating lower abundance proteins, by removal of high abundance proteins, are also outlined. Finally, since protein staining is becoming increasingly incorporated into the sample preparation procedure, we describe the principles and applications of current (and future) pre-electrophoretic labelling methods.

Capillary electrochromatography of methylated benzo[ a]pyrene isomers : I. Effect of mobile phase tuning

It is of increasing importance that chromatographic methods be developed for the separation and identification of biological and environmentally harmful compounds such as methylated polycyclic aromatic hydrocarbons (PAH). Capillary electrochromatography (CEC) is fast becoming a useful technique for analysis of PAH, as it offers both high efficiency and superior resolution. The separation of 12 methylated benzo[ a]pyrene (MBAP) isomers is a challenge due to the extreme hydrophobicity and structural similarity of these compounds. In this work, we present Part I of our ongoing study, a method for the systematic mobile phase tuning for CEC separation of the 12 MBAP isomers. The CEC experiments were conducted utilizing a CEC-octadecylsilica (ODS) stationary phase and fused-silica capillary [(75 μm I.D., 363 μm O.D.) 36.5 cm total length, 25.0 cm effective length] which was slurry pressure packed in our laboratory. Several mobile phase parameters were manipulated to provide optimum separation. These included acetonitrile (ACN) concentration, tris(hydroxymethyl) aminomethane (Tris) concentration, pH, and addition of a tertiary buffer constituent such as tetrahydrofuran (THF) and isopropanol (IPA) to ACN–aqueous buffer mixtures. Optimum CEC separation conditions were achieved using 75% (v/v) ACN–25% (v/v) 12.5 m M Tris, pH 8.0, and 30 kV at 25 °C. These mobile phase conditions were then utilized for Part II of our study, the CEC stationary phase optimization for the separation of 12 MBAP isomers.