Capillary zone electrophoresis for polymide composition analysis

Capillary zone electrophoresis (CZE) was employed in polyimide composition analysis. Polymide was decomposed to its corresponding aromatic diamine and aromatic acid monomers by an alkali fusion reaction. Sample treatment is much simpler than published methods, and electropherograms show a good separation of decomposed products under the proper conditions.     

Validation of a capillary zone electrophoresis method for the comparative determination of etoricoxib in pharmaceutical formulations

A CZE method was developed and validated for the analysis of etoricoxib in pharmaceutical dosage forms, using prilocaine as an internal standard. The CZE method was carried out on a fused-silica capillary (50 microm id, effective length 40 cm). The BGE consisted of 25 mM tris-phosphate solution at pH 2.5. The capillary temperature was maintained at 35 degrees C, the applied voltage was 25 kV, the injection was performed using the pressure mode at 50 mbar for 5 s, with detection at 234 nm using a photodiode array detector. The method was linear in the range of 2-150 microg/mL (r(2) = 0.9999). The specificity and stability-indicating capability were proven through the degradation studies and showing also that there was no interference of the excipients of the formulation. The accuracy was 99.49% with RSD of 0.66%. The limits of quantitation and detection were 2 and 0.58 microg/mL, respectively. Moreover, method validation demonstrated acceptable results for the precision, sensitivity, and robustness. The proposed method was successfully applied for the quantitative analysis of etoricoxib pharmaceutical formulations, and the results compared to the HPLC and LC-MS/MS methods, showing nonsignificant difference (p >0.05).     

毛细管区带电泳法测定粉针剂中头孢拉定的含量

用毛细管区带电泳法测定头孢拉定的含量 ,未涂层毛细管柱 (75 μm×48.5cm ,有效长度 40cm) ,电压 2 8kV ,检测波长 2 3 0nm ,温度 2 0℃ ,进样 5×1 0 3Pa× 3s。运行缓冲液为 2 5mmol/L硼砂缓冲液。方法的线性范围 3 1 .2 2μg/mL～ 749.2 8μg/mL ,检测限为 1 .1 7μg/mL。     

An automatic sampling device for capillary zone electrophoresis

An automatic sampling device has been developed for capillary zone electrophoresis. The sample is introduced to the column electrokinetically by rapidly exchanging buffer for sample in a narrow channel drilled in a plexiglass block. The autosampler is capable, under computer control, of performing multiple sample injections from a large volume sample source (such as a reaction vessel) as the sample concentration changes, and thus presents the possibility of analyzing time-varying processes by CZE. Peak area reproducibility in electropherograms obtained after use of the sampler is less than 1% and efficiency is more than 2.2 × 10⁵ theoretical plates.     

毛细管区带电泳用于酶微反应器酶解条件的研究

将氨基酰化酶通过戊二醛固定在毛细管内壁,制备毛细管酶微反应器,用毛细管区带电泳对毛细管酶微反应器的酶解产物进行分离,以生成物的峰面积优化底物N-乙酰-DL-蛋氨酸的酶解条件。实验结果表明,在温度37℃的条件下,10μg/mL N-乙酰-DL-蛋氨酸磷酸盐缓冲溶液(pH7.5)以4μL/min的速度通过15 cm长的毛细管酶微反应器,具有良好的酶解效果。利用毛细管酶微反应器对底物N-乙酰-DL-蛋氨酸进行酶解,每天酶解5次,10天后酶活仅下降了8.66%,说明制备的毛细管酶微反应器具有良好的稳定性。     

Pesticides analysis by liquid chromatography and capillary electrophoresis

Nowadays, a wide range of pesticides are used in agricultural production, and their monitoring in samples of environmental and alimentary interest is of extreme importance to ensure, among others, the safety of consumption of foods. The aim of this work is to provide updated information about the major developments in CE and HPLC in pesticide analysis, covering relevant publications between 2004 and early 2006. The use of different sample pretreatment steps to provide a suitable extraction of these compounds from the different matrices as well as to increase the sensitivity of the determination is also discussed.     

Separation of organic and inorganic arsenic species by capillary zone electrophoresis

Summary Capillary zone electrophoresis has been used to separate arsenite, arsenate, dimethylarsinic acid, and phenyl-,p-aminophenyl-, ando-aminophenylarsinic acids. Identification and quantification of the arsenic species at mg L⁻¹ levels was possible by use of direct UV detection at 200 nm. The relative standard deviation (n=7) ranged from 0.97 to 1.52% for migration times and from 2.08 to 4.31% for peak areas. A method for rapid separation of inorganic arsenic species was also developed; by use of this method arsenite and arsenate could be separated within 2 min. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Comparative study of capillary zone electrophoresis and micellar electrokinetic chromatography for the separation of twelve aromatic sulphonate compounds

Summary Two modes of capillary electrophoresis (CE), capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC), were investigated for the separation of 12 aromatic sulphonate compounds. In CZE, although the voltage applied, the buffer concentration and the pH were optimized for effective separation of the compounds studied, under the best conditions four of the five amino compounds coeluted, as did naphthalene-1-sulphonic acid and naphthalene-2-sulphonic acid. In MEKC, sodium dodecyl sulphate (SDS) and Brij 35 were chosen as the anionic and nonionic surfactants and the effect of the concentration of micelles was examined. The effect of adding methanol as the organic modifier was also investigated with each of these micellar systems. All the analytes, including the isomers, were completely separated by use of MEKC with Brij 35 but when SDS was used only 11 compounds were separated because two amino compounds coeluted.     

Formamide as solvent for capillary zone electrophoresis

A comprehensive investigation of a number of aspects when using formamide as background electrolyte solvent in capillary zone electrophoresis was presented. It included (i) the change of the ion mobility with ionic strength, (ii) the influence of the ionic strength on diffusion coefficients, and (iii) on the separation efficiency expressed by the maximum reachable plate numbers (when only longitudinal diffusion contributed to zone broadening), (iv) the effect of the solvent on pKa values (taken from the literature) of neutral and cation acids, (v) the establishment of the a pH scale in formamide by dissolving acids with known pKa values and their salts at defined proportion (thus circumventing the problem of calibrating the pH meter), (vi) the agreement between the experimentally derived and the theoretical dependence of the effective mobility on pH, (vii) the uptake of water of this hygroscopic solvent from the humidity of the environment and its consequence to the ion mobilities, pKa values, and the chemical stability of the solvent (e.g., hydrolysis), and finally (viii) the use of conductivity and indirect UV absorption to enable detection of analytes below the optical cutoff of formamide.     

Analytical potential of enzyme-coated capillary reactors in capillary zone electrophoresis

Enzymes immobilized on the inner surface of an electrophoretic capillary were used to increase sensitivity and resolution in capillary zone electrophoresis (CZE). Sensitivity is enhanced by inserting a piece of capillary containing the immobilized enzyme into the main capillary, located before the detector, in order to transform the analyte into a product with a higher absorptivity. This approach was used to determine ethanol. In order to improve resolution, capillary pieces containing immobilized enzymes were inserted at various strategic positions along the electrophoretic capillary. On reaching the enzyme, the analyte was converted into a product with a high electrophoretic mobility, the migration time for which was a function of the position of the enzyme reactor. This approach was applied to the separation and determination of acetaldehyde and pyruvate. Finally, the proposed method was validated with the determination of ethanol, acetaldehyde, and pyruvate in beer and wine samples.     

A sulfonated capillary that gives reproducible migration times for capillary zone electrophoresis and micellar electrokinetic chromatography

To obtain reproducible migration times and rapid analyses of analytes, sulfonate groups were chemically introduced to the inner wall of untreated fused-silica capillary with 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane. The sulfonated capillary showed relatively constant electroosmotic mobility which was greater than that obtained by an untreated fused-silica capillary over the pH range studied (pH 2-9). In both CZE and MEKC, the RSDs of the migration times of analytes with the sulfonated capillary were less than 0.2% which were significantly lower than those obtained with an untreated fused-silica capillary (0.5-3.5%). When BGE were set at pH 7.0 for CZE and MEKC, the analysis times with the sulfonated capillary were about half those obtained with an untreated fused-silica capillary. These results indicate that the sulfonated capillary can provide highly reproducible and rapid analyses in CE.     

Two-dimensional separation system of coupling capillary liquid chromatography to capillary electrophoresis for analysis of Escherichia coli metabolites

A two-dimensional (2-D) separation system of coupling chromatography to electrophoresis was developed for profiling Escherichia coli metabolites. Capillary liquid chromatography (LC) with a monolithic silica-octadecyl silica column (500 x 0.2 mm ID) was used as the first dimension, from which the effluent fractions were further analyzed by capillary electrophoresis (CE) acting as the second dimension. Field-enhanced stacking was selectively employed as a concentration strategy to interface the two dimensions, which proved to be beneficial for the detection of metabolites. An artificial sample containing 118 standards, some of which lack chromophores or have weak UV absorbance, was used to optimize the 2-D separation system. Under the optimum conditions, 63 components in the artificial sample having absorbance at 254 nm could be well resolved and detected. The utility of the system was demonstrated by comprehensive analysis of E. coli metabolites. Comparing with the previous 2-D separation system we published in Anal. Chem. 2004, 76, 1419-1428, using a longer monolithic column in the first dimension improved the separation efficiency and offered the possibility of increasing the injection volume without compromising the separation efficiency. In the second dimension, field-enhanced stacking was used to improve the concentration sensitivity of the metabolites, and more metabolites in E. coli cell extract were detected and identified using the developed 2-D separation system. In addition, preliminary investigation for future CE-mass spectrometry coupling was also made in the study by using volatile buffers in the capillary LC and CE techniques.     

Rapid capillary zone electrophoresis method for the determination of metal cations in beverages

A rapid and reliable capillary zone electrophoresis method for the determination of inorganic cations was developed. The complete separation of K⁺, Ba²⁺, Ca²⁺, Na⁺, Mg²⁺, Mn²⁺, Ni²⁺, Cd²⁺, Li⁺ and Cu²⁺ can be achieved in 4 min with a simple electrolyte composed by 10 mM imidazole as the carrier buffer and background absorbance provider and acetic acid as the complexing agent (pH 3.60). Injection was performed hydrostatically by elevating the sample at 10 cm for 30 s. The running voltage was +25 kV at room temperature. Indirect UV-absorption detection was achieved at 185 nm. The detection limit was in the range between 0.06 mg/l (Mg²⁺) and 0.57 mg/l (K⁺) and the quantification limits ranged from 0.10 mg/l (Ni²⁺) to 0.80 mg/l (Cu²⁺). The calibration graphs were linear in the concentration range from the quantification limit till at least 1 g/l in K⁺, 10 mg/l in Ba²⁺, Ca²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Cd²⁺, 40 mg/l in Na⁺ and 12 mg/l in Li⁺ and Cu²⁺. The repeatability, intraday and interday analysis were ≤1.55% and ≤3.64% for migration time and ≤3.38% and ≤3.63% for peak area. The method developed has been applied to several beverage samples with only a simple dilution and filtration treatment of the sample. The proposed method is simple, fast, cheap and it is achieved with common products in either laboratory. For these reasons, it is a very useful method for routine analysis.     

Peptide nucleic acid and amino acid modified peptide nucleic acid analysis by capillary zone electrophoresis

A rapid, high resolution, and low sample consumption CZE method is developed for peptide nucleic acid (PNA) analysis for the first time. 30% v/v acetonitrile in PNA sample and 20% v/v acetonitrile in 50 mM borax‐boric acid (pH 8.7) as BGE were employed after optimization. The calibration curves were linear for PNA concentration ranging from 1 to 50 μmol/L. LOD and LOQ of PNA were 0.2 and 1.0 μmol/L, respectively. Since the commercially available reagent gives rise to huge PNA peak and an apparent impurity peak, the purity of PNA was evaluated to be about 81.4% by CZE method, obviously lower than the supplier's purity value of 99.9% evaluated by RP–HPLC, and also lower than 94.8% determined with RP–HPLC by our research group. The CZE method takes only 5 min, needs only 90 nL PNA, much less than 20 min and 20 μL PNA in RP–HPLC method. Moreover, the CZE method is applicable for the analysis of glutamic acid modified and lysine modified PNAs, they show different migration time with their corresponding complementary PNAs. Our results show CZE provides a new choice for PNA and modified PNA analysis, also their purity or quality evaluation.     

Metal ion capillary zone electrophoresis with direct UV detection: Comparison of different migration modes for negatively charged chelates

Summary Several migration modes suitable for capillary zone electrophoretic (CZE) separation of metal ions in the form of 8-hydroxyquinoline-5-sulphonic acid complexes are described and compared. Superior analysis time, resolution, efficiency and detectability were achieved using reversed movement of anionic metal complexes (in the anode-to-cathode direction) under the action of the electroosmotic flow. This method allows the CZE analysis of multicomponent mixtures of transition metal ions as well as aluminium within about six minutes.     

Determination of egg white lysozyme by on-line coupled capillary isotachophoresis with capillary zone electrophoresis

An on-line coupled capillary isotachophoresis - capillary zone electrophoresis method for the determination of lysozyme in selected food products is described. The optimized electrolyte system consisted of 10 mM NH(4)OH + 20 mM acetic acid (leading electrolyte), 5 mM epsilon -aminocaproic acid +5 mM acetic acid (terminating electrolyte), and 20 mM epsilon -aminocaproic acid +5 mM acetic acid +0.1% m/v hydroxypropylmethylcellulose (background electrolyte). A clear separation of lysozyme from other components of acidic sample extract was achieved within 15 min. Method characteristics, i.e., linearity (0-50 micrograms/mL), accuracy (recovery 96+/-5%), intra-assay (3.8%), quantification limit (1 microgram/ml), and detection limit (0.25 microgram/mL) were determined. Low laboriousness, sufficient sensitivity and low running costs are important attributes of this method. The developed method is suitable for the quantification of the egg content in egg pasta.     

Enantiomeric analysis of rivastigmine in pharmaceuticals by cyclodextrin-modified capillary zone electrophoresis

Chiral separation method development is usually very time-consuming due to the diversity in chemical structures of pharmaceutical drug substances as well as the suitable separation conditions and the problem to choose the appropriate chiral selector. This paper shows capillary zone electrophoresis (CZE) which was developed for chiral separation of a basic compound - rivastigmine (RIV) using 30 cm × 50 μm i.d. polyacrylamide (PAA)-coated fused-silica capillary (effective length 20 cm), amine-modified phosphate buffer of pH 2.5 and sulfated-β-CD (S-β-CD) as chiral selector. Other selected native or derivatized cyclodextrins (CDs) were also tested: β-CD (5, 30 mM), carboxymethyl-β-CD (5, 30 mM), dimethyl-β-CD (15 mM), hydroxypropyl-β-CD (5, 30 mM), hydroxypropyl-α-CD (5, 30 mM) and hydroxypropyl-γ-CD (5, 30 mM). Complete enantiomeric separation of RIV was achieved at 20 kV, 18 °C and detection at 200 nm within 8 min with R.S.D. for the absolute migration time reproducibility of less than 2.1%. Rectilinear calibration range was 5.0-500.0 μM of each enantiomer (r = 0.9994-0.9995). The CZE method proposed was used for the control of chiral purity of pharmaceutically active S-RIV and for the analysis of Exelon caps preparation.     

Mechanism of sequence-based separation of single-stranded DNA in capillary zone electrophoresis

Separation of DNA by length using CGE is a mature field. Separation of DNA by sequence, in contrast, is a more difficult problem. Existing techniques generally rely upon changes in intrinsic or induced differences in conformation. Previous work in our group showed that sets of ssDNA of the same length differing in sequence by as little as a single base could be separated by CZE using simple buffers at high ionic strength. Here, we explore the basis of the separation using circular dichroism spectroscopy, fluorescence anisotropy, and small angle X-ray scattering. The results reveal sequence-dependent differences among the same length strands, but the trends in the differences are not correlated to the migration order of the strands in the CZE separation. They also indicate that the separation is based on intrinsic differences among the strands that do not change with increasing ionic strength; rather, increasing ionic strength has a greater effect on electroosmotic mobility in the normal direction than on electrophoretic mobility of the strands in the reverse direction. This increases the migration time of the strands in the normal direction, allowing more time for the same-length strands to be teased apart based on very small differences in the intrinsic properties of the strands of different sequence. Regression analysis was used to model the intrinsic differences among DNA strands in order to gain insight into the relationship between mobility and sequence that underlies the separation.