Capillary zone electrophoresis of alpha-helical diastereomeric peptide pairs with anionic ion-pairing reagents

The present study uses an unique capillary electrophoresis (CE) approach, that we have termed ion-interaction capillary zone electrophoresis (II-CZE), for the separation of diastereomeric peptide pairs where a single site in the centre of the non-polar face of an 18-residue amphipathic alpha-helical peptide is substituted by the 19 L- or D-amino acids. Through the addition of perfluorinated acids at very high concentrations (up to 400 mM), such concentration levels not having been used previously in chromatography or CE, to the background electrolyte (pH 2.0), we have been able to achieve baseline resolution of all 19 diastereomeric peptide pairs with an uncoated capillary. Since each diastereomeric peptide pair has the same sequence, identical mass-to-charge ratio and identical intrinsic hydrophobicity, such a separation by CZE has previously been considered theoretically impossible. Excellent resolution was achieved due to maximum advantage being taken of even subtle disruption of peptide structure/conformation (due to the presence of D-amino acids) of the non-polar face of the amphipathic alpha-helix and its interaction with the hydrophobic anionic ion-pairing reagents. In addition, due to the excellent resolution of diastereomeric peptide pairs by this novel CZE approach, we have also been able to separate a mixture of these closely-related alpha-helical peptides.     

Physicochemical characterization of phosphinic pseudopeptides by capillary zone electrophoresis in highly acidic background electrolytes

Phosphinic pseudopeptides (i.e., peptide isosteres with one peptide bond replaced by a phosphinic acid moiety) were analyzed and physicochemically characterized by capillary zone electrophoresis in the pH range of 1.1-3.2, employing phosphoric, phosphinic, oxalic and dichloroacetic acids as background electrolyte (BGE) constituents. The acid dissociation constant (pK(a)) of phosphinate group in phosphinic pseudopeptides and ionic mobilities of these analytes were determined from the pH dependence of their effective electrophoretic mobilities corrected to standard temperature and constant ionic strength of the BGEs. It was shown that these corrections are necessary whenever precise mobility data at very low pH are to be determined. Additionally, it was found that the ionic mobilities of the phosphinic pseudopeptides and pK(a) of their phosphinate group are affected by the BGE constituent used. The variability of migration behavior of the pseudopeptides can be attributed to their ion-pairing formation with the BGE components.     

The use of inverse gas chromatography to study surface thermal oxidation of polypropylene

Thermo-oxidative effects on the surface energy of polypropylene were measured by inverse gas chromatography as a function of exposure time and temperature. Unaltered polypropylene had a surface energy of 33 mJ/m². Oxidized polypropylene, after exposure to air at temperatures of 100 °C and 110 °C, had a range of maximum surface energies from 38 to 41 mJ/m². Comparisons between FTIR carbonyl peak growth and the surface energy showed that both methods detect oxidation, though the increase in surface energy is detected before the carbonyl peak growth is noticeable. The work of adhesion predicted by the surface free energies obtained in this work between a coated calcium carbonate and polypropylene changes by 10% due to the oxidation of the polymer at 110 °C.     

Identification and determination of effective components in Euphrasia regelii by capillary zone electrophoresis

A capillary zone electrophoresis (CZE) method has been developed for simultaneous determination of eukovoside, cinnamic acid and ferulic acid in Euphrasia regelii for the first time. The electrophoresis buffer was 20 mmol/L sodium borate containing 10% (v/v) methanol (pH 8.50). The effects of concentration of borate and electrolyte pH on electrophoretic behavior and separation were studied. Regression equations revealed linear relationships (correlation coefficients 0.9995-0.9998) between the peak area of each analyte and the concentration. The levels of analytes in the different parts of Euphrasia regelii were easily determined with recoveries ranging from 95.5 to 104.2%.     

Capillary Zone Electrophoresis of some organic acids in milk whey

This paper describes a method for analysing some acids of milk whey by Capillary Zone Electrophoresis. After eliminating the whey proteins by ultrafiltration, the whey underwent electrophoretic separation in the presence of anodic electroosmotic flow. The following analytes were detected: citric, orotic, uric, and hippuric acids. A procedure is described for sample preparation and the operating conditions for electrophoretic capillary separation established. Finally, orotic acid is quantitatively determined.     

Precision improvement for the analysis of flavonoids in selected Thai plants by capillary zone electrophoresis

A capillary zone electrophoresis (CZE) method for the analyses of kaempferol in Centella asiatica and Rosa hybrids and rutin in Chromolaena odorata was developed. The optimization was performed on analyses of flavonoids (e.g., rutin, kaempferol, quercetin, myricetin, and apigenin) and organic carboxylic acids (e.g., ethacrynic acid and xanthene-9-carboxylic acid) by investigation of the effects of types and amounts of organic modifiers, background electrolyte concentrations, temperature, and voltage. Baseline separation (R(s) = 2.83) of the compounds was achieved within 10 min in 20 mM NaH2PO4 - Na2HPO4 (pH 8.0) containing 10% v/v ACN and 6% v/v MeOH using a voltage of 25 kV, a temperature of 30 degrees C, and a detection wavelength set at 220 nm. The application of the corrected migration time (t(c)), using ethacrynic acid as the single marker, was efficient to improve the precision of flavonoid identification (% relative standard deviation (RSD) = 0.65%). The method linearity was excellent (r2 > 0.999) over 50-150 microg/mL. Precision (%RSD < 1.66%) and recoveries were good (> 96% and %RSDs < 1.70%) with detection and quantitation limits of 2.23 and 7.14 microg/mL, respectively. Kaempferol in C. asiatica and R. hybrids was 0.014 g/100 g (%RSD = 0.59%) and 0.044 g/100 g (%RSD = 1.04%), respectively, and rutin in C. odorata was 0.088 g/100 g (%RSD = 0.06%).     

A generic approach to the impurity profiling of drugs using standardised and independent capillary zone electrophoresis methods coupled to electrospray ionisation mass spectrometry

Three standardised, capillary zone electrophoresis-electrospray ionisation mass spectrometry (CZE-ESI-MS) methods were developed for the analysis of six drug candidates and their respective process-related impurities comprising a total of 22 analytes with a range of functional groups and lipophilicities. The selected background electrolyte conditions were found to be: 60/40 v/v 10 mM ammonium formate pH 3.5/organic, 60/40 v/v 10 mM ammonium acetate pH 7.0/organic and 10 mM piperidine, pH 10.5, where the organic solvent is 50/50 v/v methanol/acetonitrile. The coaxial sheath flow consisted of either 0.1% v/v formic acid in 50/50 v/v methanol/water, or 10 mM ammonium acetate in 50/50 v/v methanol/water, depending on the mixture being analysed. Factor analysis and informational theory were used to quantify the orthogonality of the methods and predict their complementarities. The three selected CZE-ESI-MS methods allowed the identification of 21 out of 22 of all the drug candidates and their process-related impurities and provided orthogonality with four established high-performance liquid chromatography-mass spectrometry (HPLC-MS) methods. These methodologies therefore form the basis of a generic approach to impurity profiling of pharmaceutical drug candidates and can be applied with little or no analytical method development, thereby offering significant resource and time savings.     

The influence of pH on phosphatidylcholine monolayer at the air/aqueous solution interface

The measurements of the interfacial tension at the air/aqueous subphase interface as the function of pH were performed. The interfacial tension of the air–aqueous subphase interface was divided into contributions of individuals. A simple model of the influence of pH on the phosphatidylcholine monolayer at the air/hydrophobic chains of phosphatidylcholine is presented. The contributions of additive phosphatidylcholine forms (both interfacial tension values and molecular area values) depend on pH. The interfacial tension values and the molecular areas values for LH⁺, LOH⁻ forms of phosphatidylcholine were calculated. The assumed model was verified experimentally.     

pH对毛细管电泳分离多肽的影响

设计了一个针对高年级本科生的毛细管电泳分离实验，用以研究pH对生物小分子多肽分离的影响。5种多肽包括Bradykinin、[Hyp3]-bradykinin、Angiotensin I、Leucine Enkephalin和[Met5]-Enkaphalin，被用于毛细管电泳的分离实验。研究了毛细管电泳生物分析实验中最重要的2个因素即电渗流和样品吸附随pH的变化以及对于分离的影响。在pH=10的条件下，酸性多肽几乎没有吸附，少量的碱性多肽有吸附。在pH=6的条件下，碱性多肽具有非常强的吸附从而导致非常差的分离效果，在pH=2.3的条件下，5种多肽都能被很好地分离，由于多肽此时都带有正电荷因此几乎没有吸附。而在此pH，电渗流消失。对具有一定分析化学基础理论知识的学生而言，这是一个非常好的生物分析实验，有助于学生充分理解相关环境因素对仪器分析的重要影响。     

Recognition of polymer-particle interfacial morphology in mixed matrix membranes through ideal permeation predictive models

Interfacial properties play an important role in determining characteristics and performance of composite materials, especially in membrane gas separation applications. Formation of any undesirable defect at polymer-particle interface can directly influence on membrane permeability and selectivity in addition to unwanted effects on the other mechanical/physical properties. For achieving a quick insight about the role and nature of interfacial morphologies in mixed matrix membranes (MMMs) and their effects on gas transport properties, a new technique mainly in terms of mathematical modeling was developed. Based on the proposed approach, although ideal models often failed in predicting MMMs performance, these models can provide guidelines for discernment of the types of formed interfacial morphology, like current methods in characterization.