Separation of organic cations using novel background electrolytes by capillary electrophoresis

A background electrolyte for capillary electrophoresis containing tris(-hydroxymethyl) aminomethane (THAM) and ethanesulfonic acid (ESA) gives excellent efficiency for separation of drug cations with actual theoretical plate numbers as high as 300,000. However, the analyte cations often elute too quickly and consequently offer only a narrow window for separation. The best way to correct this is to induce a reverse electroosmotic flow (EOF) that will spread out the peaks by slowing their migration rates, but this has always been difficult to accomplish in a controlled manner. A new method for producing a variable EOF is described in which a low variable concentration of tributylammonium- or triethylammonium ESA is added to the BGE. The additive equilibrates with the capillary wall to give it a positive charge and thereby produce a controlled opposing EOF. Excellent separations of complex drug mixtures were obtained by this method.     

Separation and determination of cations in beverage products by capillary zone electrophoresis

Cation determination is important for quality control of beverage products. To determine a large group simultaneously, a capillary electrophoresis procedure is developed with indirect UV at 214 nm in a three-complex buffer system (10 mM N,N-dimethylbenzylamine (DBA), 8 mM lactic acid and 2 mM 18-crown-6) with good mobility matching with desired cations. Under optimized conditions with pH adjusted to 4.65, a baseline separation is achieved for 14 cations (Rb(+), NH(4)(+), K(+), Ca(2+), Na(+), Mg(2+), Mn(2+), Co(2+), Fe(2+), Cd(2+), Cr(3+), Ni(2+), Zn(2+) and Cu(2+)) within 7 min using an uncoated silica column. To cover ng/l to mug/l range, both hydrostatic and electrokinetic sampling are studied, showing working ranges within (0.05-50)/(0.005-2) microg/l and detection limits (13-78)/(1.4-10) ng/l, respectively with satisfactory repeatability (RSD 0.31-0.47% for migration time, and 3.0-4.0% for peak height measurement). Agreeable results with established inductively coupled plasma-atomic emission spectrometry method have been obtained for orange juice and tea samples.     

Separation of bacteria by capillary electrophoresis

Differences in the surface charges of bacteria can be exploited for their separation by capillary electrophoresis. Because of their low electrophoretic mobility, the separation is not always easy to perform, especially in the presence of the electroosmotic flow. Elimination of electroosmotic flow by capillary wall modification with γ‐(trimethoxysilyl)propyl methacrylate followed by acrylamide bonding permits separation over a distance of 8.5 cm.     

Separation of siderophores by capillary electrophoresis

Capillary electrophoresis (CE) was applied as a fast method of siderophore separation. Siderophores are iron binding and regulating cell products, which facilitate iron transport into cells. A fast and efficient method of siderophore analysis is important for better understanding of the iron pathways in a sea environment or marine organisms. The best results of CE analysis were obtained using free zone CE in 25 mM phosphate buffer at basic pH using a constant voltage of 20 kV. Under these conditions it was possible to detect the presence of siderophores in seawater.     

Separation of ionic liquid cations and related imidazole derivatives by alpha-cyclodextrin modified capillary zone electrophoresis

The separation and detection of 1-alkyl-3-methylimidazolium, including isomers, and related imidazole derivatives was performed by alpha-cyclodextrin (alpha-CD) modified capillary zone electrophoresis. The separations were carried out in a running buffer comprising 5.0 mM triethylamine and 2.0 mM alpha-CD adjusted to pH 4.5 by acetic acid. All the analytes were baseline separated within 8 min and the detection limits (signal-to-noise ratio = 3) ranged between 0.42 and 1.36 ppm. The method showed good linearity (within 3-50 times the detection limits, r > 0.99) and reproducibility (relative standard deviation < 0.8% for migration times and < 3% for peak areas), which should make it suitable for routine analysis. It was employed in detecting impurities in commercial chemicals, and 0.27% 1-methylimidazole in 1-ethyl-3-methylimidazolium chloride and 0.55% imidazole in 2-ethylimidazole were found. In addition, it was employed in process analysis during synthesis of ionic liquids and demonstrated a potential to provide information on the reaction mechanism.     

Separation and determination of inorganic cations in beverages by capillary electrophoresis with indirect UV detection

A rapid, simple and reliable capillary electrophoresis method for the separation and quantitation of inorganic cations with indirect UV detection at 214 nm was developed. The electrolyte was: 12 mM imidazole as background absorbance provider; 5 mM malic acid and 1.0 mM 18-crown-6 ether as complexing agents; and 20% D₂O (v/v) to improve ion mobility. The pH was 4.25. The applied voltage was 22 kV at 22°C. Nine ions were completely separated and determined with correlation coefficients of 0.9979-0.9992. The relative standard deviations (RSD) were less than 0.5% for migration time and less than 5.2% for peak area (n=8). The detection limits (S/N=3) were from 0.08 mg L⁻¹ (for Na⁺) to 0.51 mg L⁻¹ (for Cu²⁺). To assess the reliability atomic absorption (AA) was also used to determine the same samples. Satisfactory results were obtained for real samples of jasmine tea drink and coconut milk.      

Separation of diadenosine polyphosphates by capillary electrophoresis

The influence of buffer composition and pH on the electrophoretic behavior of diadenosine polyphosphates with a phosphate chain ranging from two to five phosphate groups has been examined. The electrophoretic mobility in carbonate buffer increases according to the number of phosphates, whereas in borate buffer the mobility changes in an irregular way as a function of pH. This finding can be rationalized by a well-known interaction of borate with ribose rings, which modifies the charge and the hydrodynamic radius of each diadenosine polyphosphate in a different way. Our study shows that the best separation of diadenosine polyphosphates can be achieved at the highest pH values of the range examined both in borate and carbonate buffers.     

Separation of metal ions by capillary electrophoresis

A number of experimental parameters have been optimized for the separation of 26 metal ions, including alkali, alkaline earth, transition and lanthanide metal ions. Experimental parameters that were evaluated included nature of indirect-detection reagent, pH of electrolyte, concentration of complexing agent and nature of the surface of the capillary; unbonded and C₁ and C₁₈ bonded phases were studied. In addition the effect of internal diameter on linearity and signal-to-noise ratio was examined, and separation efficiency was determined for a variety of experimental conditions. Detection limits (signal-to-noise RATIO = 3) were ca. 1 μg/ml for the lanthanides, ca. 0.6 μg/ml for transition and alkaline earth ions and ca. 0.1–0.8 μg/ml for alkali metal ions. The average relative standard deviations of were 3.7, 5.1 and 2.5% on unbonded, C₁ and C₁₈ capillaries, respectively. Whereas conventional regression analysis suggested that the calibration curves were linear over the range of 1·10⁻⁵ to 4·10⁻⁴ mol/l, sensitivity plots showed that the results were actually linear to within 6% only over the range of 2.5·10⁻⁵ to 4·10⁻⁴ mol/l.     

Separation of neutral carbohydrates by capillary electrophoresis

The basic strategies for analysis of neutral carbohydrates by capillary electrophoresis are summarized. Neutral carbohydrates are dissociated in strong alkali to give anions, hence they can be separated directly by zone electrophoresis based on the difference between their dissociation constants. However, neutral carbohydrates are not electrically charged under normal conditions. Therefore, they should be converted to ions prior to or during analysis. Precapillary introduction of a basic or an acidic group to a neutral carbohydrate gives the derivative positive (in acidic media) or negative (in alkaline media) charge, respectively. The derivatives thus obtained can be separated by zone electrophoresis. Analysis of carbohydrates in a carrier containing an oxyacid salt (such as sodium borate) or an alkaline metal salt (such as calcium acetate) causes in situ conversion to anionic or cationic complexes, respectively, which are separated by zone electrophoresis. The effective uses of electrokinetic chromatography in sodium dodecyl sulfate micelles for hydrophobic derivatives (such as 1-phenyl-3-methyl-5-pyrazolone derivatives) and size-exclusion electrophoresis in gel-packed capillaris for size different oligosaccharides are also discussed. Each separation mode has its inherent method(s) for detection, which are also described here.     

Separation of nitrophenols by capillary zone electrophoresis

Separation conditions suitable to a rapid resolution of a group of eight nitrophenols by capillary zone electrophoresis (CZE) were found. Required differences in their effective mobilities were achieved via host-guest complexation of -cyclodextrin combined with intermolecular interactions involved by polyvinylpyrrolidone. When both additives were present in the carrier electrolyte at pH=9.1 nitrophenols could be separated in the column of a, 300 m I.D. and 180 mm in the length within 8–9 minutes. It is shown that the column of such an I.D. providing enhanced sample load capacity, can operate with high separation efficiencies as maintaining zone dispersions due to Joule heating on a tolerable level. CZE on-line coupled with isotachophoretic sample pretreatment is shown to provide the concentration limits of detection at low ppb concentrations by using an on-column photometric detector operating at 254 and 405 nm detection wavelengths.     

Separation of peptides and proteins by capillary electrophoresis using acidic buffers containing tetraalkylammonium cations and cyclodextrins

A method for improving separations of peptides and other positively charged species in capillary zone electrophoresis with untreated capillaries using acidic buffers containing tetraalkylammonium cations is described. Tetramethylammonium and tetrabutylammonium cations dynamically modify the capillary surface, leading to a reversal in the direction of the electroosmotic flow. As a result, the adsorption of positively charged peptides and proteins is minimized, and resolution and peak capacity are improved as the migration of cationic analytes is counterbalanced by the electroosmotic flow. The combining effect of reversing electroosmotic flow and cyclodextrin inclusion complexation on separations of closely related peptides and a protein mixture, as well as tryptic digest of hemoglobin is demonstrated.     

Separation of metal cations in acidic solution by capillary electrophoresis with direct and indirect UV detection

Methods for the detectionn of metal cations under acidic conditions, near PH 2, in capillary electrophoresis (CE) were investigatged. Conditions for direct UV detection of UV absorbing metal cations such as Cr³⁺, Cu²⁺, Fe³⁺, UO₂²⁺, VO²⁺, and VO²⁺ were established With aqueous HCl or HClO₄ as the electroyte carrier. The speciation of vanadium(IV) and vanadium(V) at PH 2.3 by CE was achieved with direct detection at 185 nm. With the strong absorbance at 185 nm, no complexation was needed to detect the metal cations. An indirect UV detrection scheme for acidic conditions was also investigated. Several background carrier electolytes (BCES) were studied including 4-methylbenzylamince, nicontinamide, pyridazine, guanidine, 3-picoline, and chromium (III) to determine their effectivencess under very acidic conditions. The efect of ioni c surfactants and the nonionic surfactant, Trition X-100, on the peak heights and N Values was also studied.     

Separation of negatively charged carbohydrates by capillary electrophoresis

Capillary electrophoresis (CE) has recently emerged as a highly promising technique consuming an extremely small amount of sample and capable of the rapid, high-resolution separation, characterization, and quantitation of analytes. CE has been used for the separation of biopolymers, including acidic carbohydrates. Since CE is basically an analytical method for ions, acidic carbohydrates that give anions in weakly acid, neutral, or alkaline media are often the direct objects of this method. The scope of this review is limited to the use of CE for the analysis of carbohydrates containing carboxylate, sulfate, and phosphate groups as well as neutral carbohydrates that have been derivatized to incorporate strongly acidic functionality, such as sulfonate groups.     

Separation of human fibrinopeptides by capillary zone electrophoresis

We describe a method for the simultaneous determination of the five fibrinopeptide forms derived from the thrombin-promoted activation of human fibrinogen by capillary zone electrophoresis (CZE). The fibrinopeptide mixture was first desalted by a solid-phase extraction (SPE) step. The analysis was performed in reversed polarity in a highly cross-linked polyethylene glycol (PEG)-coated capillary with UV-light absorption detection at 200 nm. Several parameters including buffer concentration and pH, presence of an organic modifier, temperature, and applied voltage, have been tested. The best separations were obtained within 20 min, utilizing a 20 mM sodium phosphate buffer without organic modifier, in the narrow 6.1-6.2 pH range, at 25 degrees C, with an applied voltage of 20 kV. Quantitative analysis is made possible by the use of sheep fibrinopeptide A as an internal standard to correct for both extraction and injection errors.     

Separation and detection of lanthanides by capillary electrophoresis

Due to the importance of application of lanthanides in various industries especially the nuclear ones, and the advantages of capillary electrophoresis method in separation of metal cations, this research was carried out in order to investigate the separation potential of lanthanides using capillary electrophoresis via simulation method at laboratory scale. Since the properties of various types of lanthanides are very similar, the separation of lanthanides using the usual approaches was not possible. Thus, the separation of lanthanides was devised upon partial, competing complexation in order to differentiate their properties. Salicylic acid was firstly used as the primary UV-absorbing ligand, whereas formic, acetic, lactic, tartaric and citric acids, which showed no absorption in UV-spectrum and had weaker complexes in comparison to salicylic acid, were used as auxiliary ligands. Upon the results of spectrometry, the wave length of 210 nm was selected for detecting lanthanides. The properties and stability of lanthanides were examined and furthermore acetic and citric acids were selected as auxiliary ligands. The simulation was carried out with respect to the transport phenomena in the unsteady state. The ion species dissociation was found to be directly dependent upon the concentration, and was also used in complexation. The results of simulation showed that the diffusion control of H⁺ and homogenizing electrical field promoted separation quality. The separation conditions were optimized by using the simulation results as well as the tests obtained. In order to optimize the experimental conditions, variable factors such as voltage, injection time, pH, temperature and ionic strength were examined. Also, methanol was used as dissolving modifier as well as noise reducer on the base line. Sodium nitrate was used as ionic strength controller and sucrose for increasing viscosity which optimized separation quality.     

Separation of cold medicine ingredients by capillary electrophoresis

This study demonstrates the separation of cold medicine ingredients (e.g., phenylpropanolamine, dextromethorphan, chlorpheniramine maleate, and paracetamol) by capillary zone electrophoresis and micellar electrokinetic chromatography. Factors affecting their separations were the buffer pH and the concentrations of buffer, surfactant and organic modifiers. Optimum results were obtained with a 10 mM sodium dihydrogen-phosphate-sodium tetraborate buffer containing 50 mM sodium dodecyl sulfate (SDS) and 5% methanol (MeOH), pH 9.0. The carrier electrolyte gave a baseline separation of phenylpropanolamine, dextromethorphan, chlorpheniramine maleate, and paracetamol with a resolution of 1.2, and the total migration time was 11.38 min.     

Separation of derivatized carbohydrates by co-electroosmotic capillary electrophoresis

Summary The separation of derivatized carbohydrates has been performed by co-electroosmotic capillary electrophoresis. Derivatization was performed by reductive amination of the carbohydrates with ethylp-aminobenzoate or withp-aminobenzonitrile. Separation selectivity is optimized using buffer electrolytes containing high concentrations of borate, organic solvents, and mixtures thereof; this enabled separation of the carbohydrate derivatives then direct UV detection. Co-directional migration of the anionic analytes with the electroosmotic flow was achieved by adding a cationic polyer (hexadimethrine bromide, HDB) to the electrolyte. With this method it is possible to determine specific carbohydrates, such as arabinose, mannose, and glucose, which are difficult to separate by other CE methods. The applicability of the method is demonstrated for the analysis of plant hydrolyzates     

Separation of nicotine metabolites by capillary zone electrophoresis and capillary zone electrophoresis/mass spectrometry

The use of capillary zone electrophoresis (CZE) and capillary zone electrophoresis/mass spectrometry (CZE/MS) has been demonstrated, in principle, for the separation of nicotine and nicotine metabolites. The buffer system developed for separation and detection by CZE/UV was modified for use in CZE/MS analysis. Several of the metabolites are isobaric and tandem mass spectrometric (MS/MS) techniques have been used to differentiate such analytes.     

Separation of sulfonylurea metabolites in water by capillary electrophoresis

The potential of capillary electrophoresis (CE) for the separation and detection of the metabolites of nine sulfonylurea herbicides in aqueous solution was evaluated. A relationship between the structure of the sulfonylureas tested and the metabolites formed was found: the non-o-benzene-substituted sulfonylurea rimsulfuron gave only one metabolite, whereas the other eight, o-benzene-substituted, sulfonylureas gave 4–6 metabolites. CE was confirmed to be a very efficient separation technique, suitable for the determination of sulfonylurea herbicides and their metabolites formed during hydrolysis.     

Separation of quaternary ammonium diastereomeric oligomers by capillary electrophoresis

The separation of novel diastereomeric trimers (3M) and pentamers (5M), derived from quaternary ammonium salts, was studied in conventional, uncoated and coated capillaries using capillary zone electrophoresis (CZE) with a variety of buffers and additives. Resolution of 5M diastereomers was best achieved using gamma-cyclodextrin (gamma-CD) as a chiral selector, while no diastereomeric resolution was realized for the 3M material.