The separation and determination of nitrophenol isomers by high-performance capillary zone electrophoresis

o-Nitrophenol, m-nitrophenol, and p-nitrophenol could well be separated by capillary zone electrophoresis (CZE) by only adjusting the run buffer with methanol. Efficiency up to 10⁵ theoretical plates per meter was achieved. The effects of several important factors were investigated to find optimum conditions. The linear range, regression equation, and the recovery were given. This method possessed the advantages of simplicity, rapidity, and good reproducibility; it can be developed for the separation of practical samples in environment analysis.     

Separation of various electrolyte mixtures by unilateral capillary isotachophoresis

A new electrophysical method is proposed for a rapid diagnosis of liquid products relating quality and identification. The method is widely prospective for practical application.     

Host-guest complexation in capillary isotachophoresis. II. Determination of aminophenol and diaminobenzene isomers in permanent hair colorants by using capillary isotachophoresis

The separation of 2-, 3- and 4-aminophenol and 1,2-, 1,3- and 1,4-diaminobenzene is studied by using capillary isotachophoresis. In order to obtain complete resolution of the six cations beta-cyclodextrin was used. The analytical method was used for the determination of aminophenol and diaminobenzene isomers in permanent hair colorant creams.     

Separation of porphyrin-based photosensitizer isomers by laser-induced fluorescence capillary electrophoresis

Methods for the separation of photosensitizer isomers, such as benzoporphyrin derivative monoacid, benzoporphyrin ethyl monoacid, 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a, diethyleneglycol diester benzoporphyrin derivative, tin ethyl etiopurpurin, and phthalocyanine tetrasulfonate, have been systematically developed by CE. Detection was accomplished by UV absorption at 214 nm or by LIF with excitation at 442/488 nm and emission at 690 nm. The effects of three major experimental parameters of buffer types, organic solvents, and surfactant additives are described. The optimized separation conditions were determined so as to provide satisfactory separation efficiency and analysis time. The methods are shown to be suitable for the separation and determination of porphyrin and phthalocyanines regioisomers, diastereoisomers, and enantiomers.     

Separation of conjugated trienoic fatty acid isomers by capillary electrophoresis

A method for direct resolution of conjugated trienoic fatty acid isomers by capillary electrophoresis has been developed. To obtain complete separation a dual cyclodextrin system was used. This contained heptakis-(6-sulfo)-beta-cyclodextrin (charged). Beta-cyclodextrin (uncharged) and sodium dodecylsulfate. Under optimized conditions, all seven isomers were well separated. On average, separation efficiency was 2.9 x 10(5) plates/m.     

Application of capillary isotachophoresis in peptide analysis

This paper gives a broad and detailed review of the applications of one of the modern high-performance electromigration separation techniques--capillary isotachophoresis (ITP)--in peptide analysis. Examples are presented of the utilization of capillary ITP for peptide analysis in the fields of chemistry, general and clinical biochemistry, biology, biotechnology, pharmacy and the food industry. The complete composition of all the electrolyte systems used for peptide ITP analyses in both cationic and anionic techniques is given in tabular form. According to the purpose of analysis the applications are divided into several sections: model studies, determination of physico-chemical characteristics, purity control of both intermediate and final peptide preparations, including the determination of low-molecular-mass ionogenic admixtures, and the analysis of peptides in biological fluids and tissue extracts. In addition to the main applications the theoretical and methodological aspects of peptide ITP analysis are discussed. The basic electromigration properties of peptides (their polyampholyte character, effective and absolute mobilities, acid-base equilibria) are explained and the selection of parameters for peptide ITP analysis is described in detail. The advantages and disadvantages of ITP compared with other electrophoretic and chromatographic methods used for peptide analysis are discussed.     

Determination of metoprolol tartrate by capillary isotachophoresis

This paper describes two isotachophoretic methods of metoprolol tartrate (MT) determination in pure and dosage forms. The first method was used for direct analysis where the following electrolyte system was applied: 10 mmol dm⁻³ 3-morpholino-2-hydroxypropanesulfonic acid, 10 mmol dm⁻³ NaCl, 2 % hydroxyethylocelulose as leading (LE) and 10 mmol dm⁻³ glycyl-glycine as terminating (TE) electrolytes. The second method was used for indirect analysis of MT as tartrate ions. In this case, the leading electrolyte consisted of 10 mmol dm⁻³ HCl, β-alanine (BALA), pH 4-5, and the terminating one of 5 mmol dm⁻³ glutamic acid, 10 mmol dm⁻³ β-alanine. Calibration curves were calculated as follows: for system A: y = (0.52 ± 0.05)x − (0.9 ± 0.2) (LOD = 13.0 mg dm⁻³, LOQ = 31.7 mg dm⁻³); and for system B: y = (0.240 +- 0.001)x + (0.18 ± 0.06) (LOD = 1.8 mg dm⁻³, LOQ = 4.4 mg dm⁻³). The isotachophoretic method was compared with the pharmacopoeial one by statistical tests.     

Separation and determination of nitroaniline isomers by capillary zone electrophoresis with amperometric detection

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous separation and determination of nitroaniline positional isomers. The three analytes could be perfectly analyzed by using the buffer of extreme pH. The effects of several important factors were investigated to find optimum conditions. A carbon-disk electrode was used as working electrode. The optimal conditions were 40 mmol/L tartaric acid-sodium tartrate (pH 1.2) as running buffer, 17 kV as separation voltage and 1.10 V (versus saturated calomel reference electrode, SCE) as detection potential. Under the optimum conditions, o-, m- and p-nitroaniline were separated successfully and good linearity, reproducibility and recovery results were obtained. The detection limit for m-nitroaniline was as low as at 9.06 × 10⁻⁹ mol/L. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 1.8% for migration time and 1.1% for peak areas. The utility of this method was demonstrated by monitoring dyestuff wastewater and the assay results were satisfactory.     

Separation of positional isomers by cucurbit[7]uril-mediated capillary electrophoresis

A novel macrocyclic molecule, cucurbit[7]uril (CB[7]) was for the first time employed as an additive in capillary electrophoresis (CE). In similarity to other macrocyclic molecules, such as crown ethers, cyclodextrins (CDs) and calixarenes, CB[7] can form inclusion complexes with a variety of guest molecules due to its inner cavity. Thus, it can be used like other macrocyclic molecules to manipulate selectivities in CE. During the running process, CB[7] bears a positive charge under the studied pH range (pH 2.5-7) and can be adsorbed onto the inner wall of a fused-silica capillary, leading to a reversal of the electroosmotic flow (EOF). Electrophoretic behaviors of nitrotoluene, nitrophenol, nitroaniline, and methylaniline isomers were studied under various conditions. The electrophoretic separations of the isomers can be accomplished with a buffer containing CB[7]. Furthermore, a probable separation mechanism in the presence of CB[7] was also proposed.     

Separation of alkadien-1-ol acetate geometric isomers by capillary gas-liquid chromatography

Summary Gas-liquid chromatographic data have been presented for the analyses of alkadien-1-ol acetates; these compounds have importance in the field of insect sex attractants. The use of a support-coated open tubular column prepared with diethylene glycol succinate liquid phase for these analyses has been of great utility in monitoring geometric purity. The geometric purity of such compounds must be determined to assure accurate evaluation as insect sex attractants since contamination with small amounts of another isomer may result in complete inactivation.     

Determination of some antirheumatics by capillary isotachophoresis

Isotachophoresis (ITP) was applied for the determination of some antirheumatic drugs (fenoprofen, naproxen, ibuprofen, and ketoprofen) in human serum. The leading electrolyte contained hydrochloric acid (10 mmol x L(-1)), creatinine (pH 4.5) and methylhydroxyethyl cellulose (0.1%). The terminating electrolyte was 2-(N-morpholino)ethanesulfonic acid (10 mmol x L(-1)) adjusted with tris(hydroxymethyl)aminomethane to pH 6.9. The ITP separations were carried out in column-coupling configuration of the separation unit provided with a preseparation column of 160 x 0.8 mm inner diameter (ID) and analytical column of 160 x 0.3 mm ID. The limit of detection for ibuprofen, fenoprofen, and naproxen in serum by direct sampling was 0.008, 0.005 and 0.004 mmol x L(-1). The limit of detection for ketoprofen in serum after ethanol precipitation was 0.001 mmol x L(-1).     

Separation and migration behavior of positional and structural naphthalenesulfonate isomers by cyclodextrin-mediated capillary electrophoresis

The effects of the type of buffer system, buffer pH, the polarity of electrode, and both the type and the concentration of cyclodextrins (CDs) on the separation and migration behavior of seven positional and structural naphthalenesulfonate isomers in CD-mediated capillary electrophoresis were systematically investigated. The most effective separation conditions were to use 20 mM phosphate buffer with beta-CD at pH 3.0, while the polarity of the electrodes were reversed across the capillary. Under such conditions, these isomers can be separated in 10 min. The results also indicate that the interactions of naphthalenesulfonate derivatives with CDs are strongly affected by the position of the substituent(s) on the aromatic ring. The inclusion complex formation constants of these compounds were evaluated to improve our understanding of the interaction between the naphthalenesulfonate derivatives and CDs. Moreover, the formation constants of naphthalene-2-sulfonate to beta-CD agreed closely with the data in the literature obtained by a spectrophotometric method and by CE methods in various pH buffers.     

Electroosmotic pump‐supported molecularly imprinted monolithic column for capillary chromatographic separation of nitrophenol isomers

In this work, a novel molecularly imprinted polymer (MIP) monolithic column with integrated in‐column electroosmotic pump (EOP) was designed and successfully prepared to facilitate the capillary chromatography with MIP column. A silica‐based EOP was synthesized at the detection end of the MIP monolithic capillary column by so‐gel to provide the hydrodynamic driven force for the capillary chromatography. Because of large surface area and low fluidic resistance of the silica monolith,a strong and steady EOF was generated by silica‐based EOP, indicating that the EOP was quite compatible with MIP capillary column. With the sufficient EOF provided by EOP, the electro‐driven based capillary chromatographic separation of nitrophenol isomers was achieved in 4‐vinylpyridine‐based MIP monolithic capillary, which was originally proved infeasible because of the EOF shortage. No significant influence upon the specific recognition of the MIP was found due to the setting of EOP after the detection window of the column. The influence of experimental parameters on the EOF such as voltage and pH value of running buffer was investigated. The column was also evaluated by capillary liquid chromatographic mode to compare with EOP‐driven capillary chromatography. Higher column efficiency was obtained by EOP‐driven separation with improved peak shape. The results suggested that EOP‐supported technique would be a good way to solve the problem of weak EOF generation in electro‐driven capillary chromatography.     

Instrumentation for capillary isotachophoresis

Modular instrumentation for capillary isotachophoresis provides an easy way to assemble a desirable configuration of the separation unit with respect to detection limits, load capacity, time and economy of analysis. New developments in the field may thus be quickly accepted.     

Separations of enantiomers by preparative capillary isotachophoresis.

The use of capillary isotachophoresis (ITP), operating in a discontinuous fractionation mode, for preparative separations of enantiomers of chiral compounds was studied. The ITP separations were carried out in the column-coupling configuration of the separation unit provided with the preseparation column of a 1.0 mm ID and the trapping column of a 0.8 mm ID. Such a configuration of the CE separation unit offers several working regimes suitable to preparative separations of enantiomers. 2,4-Dinitrophenyl-DL-norleucine (DNP-Norleu) was employed as a model analyte in our experiments with beta-cyclodextrin serving in the electrolyte solutions as a chiral selector. The preparative separations lasting about 20 min were evaluated by ITP and (more often) by capillary zone electrophoresis (CZE). It was found that one preparative run provided up to 14 microg of pure DNP-Norleu enantiomers. This corresponded to a 75 times higher production rate of ITP relative to a maximum value of this parameter as estimated for preparative CZE runs in cylindrical capillaries (0.5 pmol/s). About 75% of the DNP-Norleu enantiomers loaded into the preparative equipment could be recovered in pure enantiomer fractions. Contiguous natures of the zones in the ITP stack and adsorption losses of the enantiomers in the isolation step were found to set practical limits for a further enhancement of the recovery rates in the isolation of pure enantiomers.     

Determination of potassium in sea-water by capillary isotachophoresis

Summary A new analytical procedure for the determination of potassium in sea-water was developed using capillary isotachophoresis and ion-exchange. After the sea-water sample was passed through the column packed with an ammonium form cation-exchange resin, sodium ion was removed with 2×10^–2 mol/l ammonium chloride solution and then potassium ion was eluted with 3×10^–1 mol/l ammonium chloride solution. Simultaneous determination of potassium and sodium ions was performed with a newly developed electrolyte system; the leading electrolyte was 5 mmol/l cesium hydroxide containing 2 mmol/l 18-crown-6, 0.01% hydroxypropyl methylcellulose (HPMC) and 70% methanol; the terminating electrolyte was 5 mmol/l tetrabutylammonium bromide containing 0.01% HPMC and 70% methanol. A large amount of ammonium in the eluate did not interfere with the isotachophoretic measurement of potassium and sodium ions. A linear working curve was obtained for artificial sea-water samples containing up to 700 mg/l potassium ion. The proposed method was applied to the determination of potassium in surface and bottom sea-water samples.

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Kaliumbestimmung in Meereswasser durch Capillar-Isotachophorese