Separation of phenolic acids by capillary electrophoresis with indirect contactless conductometric detection

A new method for the electrophoretic separation of nine phenolic acids (derivatives of benzoic and cinnamic acids) with contactless conductometric detection is presented. Based on theoretical calculations, in which the mobility of the electrolyte co- and counterions and mobility of analytes are taken into consideration, the electrolyte composition and detection mode was selected. This approach was found to be especially valuable for optimization of the electrolyte composition for the separation of analytes having medium mobility. Indirect conductometric detection mode was superior to the direct mode as predicted theoretically. The best performance was achieved with 150 mM 2-amino-2-methylpropanol electrolyte at pH 11.6. The separation was carried out in a counter-electroosmotic mode and completed in less than 6 min. The LODs achieved were about 2.3-3.3 microM and could be further improved to 0.12-0.17 microM by using a sample stacking procedure. The method compares well to the UV-Vis detection.     

Separation of perfluorocarboxylic acids using capillary electrophoresis with UV detection

A capillary electrophoretic method with UV detection for separation and quantitation of perfluorocarboxylic acids (PFCAs) from C6-PFCA to C12-PFCA has been developed. The optimization of measurement conditions included the choice of the most appropriate type and concentration of buffer in the background electrolyte (BGE), as well as the type and the content of an organic modifier. The optimal separation of investigated PFCAs was achieved with 50 mM phosphate buffer and 40% isopropanol in the BGE using direct UV detection. The optimum wavelength for direct UV detection was optimized at 190 nm. For indirect detection, several chromophores were studied. Five mM 3,5-Dinitrobenzoic acid (3,5-DNBA) in 20 mM phosphate buffer BGE and indirect UV detection at 280 nm gave the optimal detection and separation performance for the investigated PFCAs. The possibility of on-line preconcentration of solutes by stacking has been examined for indirect detection. The detection limits (LODs) determined for direct UV detection ranged from 2 microg/mL for C6-PFCA to 33 microg/mL for C12-PFCA. The LODs obtained for indirect UV detection were comparable to those obtained for direct UV detection.     

Separation of amino acids in plant tissue extracts by capillary zone electrophoresis with indirect UV detection using aromatic carboxylates as background electrolytes

Summary Amino acids in extracts of plant tissue were separated and detected by capillary zone electrophoresis (CZE) with indirect UV detection. Various aromatic carboxylates such as salicylate, benzoate, phthalate and trimellitate were investigated as background electrolytes (BGEs). A BGE of benzoate gave the best resolution and detector response. Amino acids were separated at a highly alkaline pH to charge amino acids negatively. Separation was achieved by the co-electroosmotic flow (Co-EOF) by the addition of the cationic surfactant myristyltrimethyl-ammonium bromide (MTAB) to the electrolyte. The condtions affecting the separation of amino acids, including electrolyte pH, concentrations of both benzoate and MTAB, were investigated and optimised. Separation of a mixture of 17 amino acids at pH 11.20 with indirect UV detection at 225 nm was achieved with a BGE of 10 mM benzoate containing 1.0 mM MTAB at pH of 11.20. Detection limits ranged between 10 and 50 μM. The proposed method was demonstrated by the determination of amino acids in extracts of Eucalypt leaves with direct injection of samples.     

胶束电动毛细管色谱间接紫外光检测法分离胆汁酸

利用间接紫外光检测法在254 nm进行胆汁酸胶束电动毛细管色谱分离的研究.在对氨基苯磺酸为背景电解质和十二烷基硫酸钠作胶束的体系中,加入高浓度的尿素,有效地改善了两类胆汁酸5组份的分离度,在优化分离缓冲体系10 mmol/L对氨基苯磺酸-5 mmol/L硼砂-30 mmol/LSDS-7 mol/L尿素-10%乙醇(pH 7.5)中,13 min内获得基线分离,分离效率为8.4×104～1.1×105.所建立的方法无需衍生化处理,为胆汁酸的分离提供了新的通用的方法.     

Separation of twenty underivatized essential amino acids by capillary zone electrophoresis with contactless conductivity detection

Twenty underivatized essential amino acids were separated using capillary zone electrophoresis and consequently detected with contactless conductivity detection (CCD). A simple acidic background electrolyte (BGE) containing 2.3 M acetic acid and 0.1% w/w hydroxyethylcellulose (HEC) allowed the electrophoretic separation and sensitive detection of all 20 essential amino acids in their underivatized cationic form. The addition of HEC to the BGE suppressed both, electroosmotic flow and analyte adsorption on the capillary surface resulting in an excellent migration time reproducibility and a very good analyte peak symmetry. Additionally, the HEC addition significantly reduced the noise and long-term fluctuations of the CCD baseline. The optimized electrophoretic separation method together with the CCD was proved to be a powerful technique for determination of amino acid profiles in various natural samples, like beer, yeast, urine, saliva, and herb extracts.     

Determination of rimantadine in pharmaceutical preparations by capillary zone electrophoresis with indirect detection or after derivatization

Summary Rimantadine is synthetic analog of amantadine; both are antiviral agents used for prophylaxis and treatment of influenza A. A capillary zone electrophoretic (CZE) procedure for the determination of rimantadine has been developed. As the direct determination of rimantadine is poorly sensitive because the compound is almost transparent in the UV/Vis range, several indirect methods were studied. Two were found to be the particularly useful: (a) indirect detection using 5 mM 4-methylbenzylamine in 1:4 methanol-water as absorbing background electrolyte, with detection at 210 nm, and (b) derivatization of rimantadine with 1,2-naphthoquinone-4-sulfonic acid in alkaline medium and subsequent determination of the derivative by CZE (40 mM tetraborate, pH 9.2, detection at 280 nm). Uncoated capillary tubing, 44 cm length ×75 μM i.d., was used for both determinations. The detection limits were 0.1 and 2 ppm for methods a and b, respectively. The methods were used to determine rimantadine in pharmaceutical products and for dissolution testing of Flumadin^? tablets.     

Separation of enantiomers in capillary electrophoresis with contactless conductivity detection

Contactless conductivity detection is successfully demonstrated for the enantiomeric separation of basic drugs and amino acids in capillary electrophoresis (CE). Derivatization of the compounds or the addition of a visualization agent as for indirect optical detection schemes were not needed. Non-charged chiral selectors were employed, hydroxypropylated cyclodextrin (CD) for the more lipophilic basic drugs and 18-crown-6-tetracarboxylic acid (18C6H4) for the amino acids. Acidic buffer solutions based on lactic or citric acid were used. The detection limits were determined as 0.3 microM for pseudoephedrine as an example of a basic drug and were in the range from 2.5 to 20 microM for the amino acids.     

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.     

Analysis of carboxylic acid metabolites from the tricarboxylic acid cycle in Bacillus subtilis cell extract by capillary electrophoresis using an indirect photometric detection method

With a growing interest in metabolome analysis, there is a need for developing robust methods for analysis of intracellular metabolites profiles in real samples like e.g., bacteria cell. Due to their weak absorbance properties, tri- and dicarboxylic acids from TCA cycle (citric, isocitric, 2-oxoglutaric, succinic, fumaric, malic) as well as carboxylic acid metabolites from glycolysis pathway, urea cycle and metabolism of amino compounds (formic, pyruvic, lactic, acetic, glutamic) were analyzed by capillary electrophoresis (CE) with indirect UV detection. Using 4 mM 2,6-pyridinedicarboxylic acid as a highly UV absorbing carrier electrolyte, 0.2 mM cetyltrimethylammonium bromide, 10% ethylene glycol and 10% acetonitrile, pH 3.5, carboxylic acids metabolites were analyzed in Bacillus subtilis cell extract from two different cultures: glucose and malate. CE with an electrokinetic injection mode achieved limits of detection in the range of 13-54 ppb (1.12-10(-7) - 5.96-10(-7) M). The reproducibility and linearity of method was investigated with RSD for migration time less than 1.3% and acceptable correlation coefficients. The optimized CE method was used to compare metabolome content of cell extract derived from two different culture media containing either glucose or malate as a carbon source. The changes in carboxylic acid metabolites profile were observed depending from used culture medium. Carboxylic acid concentrations ranged: in cell extract from malate culture from 59 to 0.5 microM for lactate and citrate, respectively, and in cell extract from glucose culture from 133 to 0.5 microM for glutamate and citrate, respectively. Appropriate concentrations of carboxylic acid in the single bacterium cell were estimated at mM and sub-mM levels.     

Optimization of cation detection by capillary zone electrophoresis with indirect UV absorbance

Summary The indirect UV detection of cations by capillary zone electrophoresis gives peaks of very different height or area between cations. We show that the height depends on the electrophoretic mobility of the cation compared with the electrophoretic mobility of the chromophore used. Moreover, the limit of detection can be easily improved by about 4-fold by adjusting the concentration of complexing agent or by using a chromophore with the same velocity as the studied cation. Using a new parameter termedsensitization power we can optimize the limit of detection and have determined the best chromophores for each family of cations.Sensitization power is a maximum for: alkali metals and alkali earths with imidazole and UV Cat 2^?, for transition metal with pyridine, for light rare earth with ephedrine and UV Cat 1^?, for heavy lanthanides with 1-naphthylamine and phenyl-trimethyl-ammonium bromide. Corrected areas of all cations studied have normal distributions directly proportional to their ionic charge. Certain behaviour can be predicted for elements such as actinides. Detection can also be enhanced because the relation of proportionality between ionic charge and corrected area allows comparison of the performance of all chromophores.     

Potential of microcolumn liquid chromatography and capillary electrophoresis with flame photometric detection for determination of polar phosphorus-containing pesticides

Summary The potential of microcolumn liquid chromatography (μlC) and capillary electrophoresis (CE) with on-line, flame photometric detection (FPD) in the P-selective mode has been studied for determination of polar P-containing pesticides, glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), ethephon, fosetyl-aluminium and acephate. Acephate was determined by reversed-phase μLLC-FPD using large-volume injections with peak compression, the other compounds were determined by μLC-FPD and CE-FPD using simple, large-volume injection procedures to obtain limits of detection of 7.5-500 ng·mL⁻¹ and 1.0 μ·mL⁻¹, respectively. The methods showed acceptable repeatability and robustness and were successfully applied for rapid and selective determination of pesticides in fruit, vegetable and water samples.     

Direct UV detection of underivatized amino acids using capillary electrophoresis with online sweeping enrichment

This is an original report proposed a CE method for direct analysis of the underivatized amino acids using UV detection with relatively higher sensitivity, which was based on coordination interactions between amino acids and Cu (II) ions. In addition, an online sweeping preconcentration technique was easily combined to improve the detection sensitivity. Satisfying separations of the amino acids were obtained under optimized conditions: 50 mmol/L CuSO₄–0.05% HAc–H₂O (pH 4.5), and the separation voltage of 15 kV. The LODs for the analytes ranged from 0.1 to 0.5 μmol/L. The linearity of detection for all analytes was two orders of magnitude with the correlation coefficients greater than 0.99. The repeatability was displayed with an RSD less than 3% for migration time and peak height (n = 5). Moreover, some amino acids in real samples of human saliva and green tea were analyzed by this direct UV detection CE method with acceptable sensitivity.     

毛细管电泳-间接紫外检测法测定蜂蜜中的氨基酸

采用毛细管电泳-间接紫外检测法同时分离测定蜂蜜中的赖氨酸、色氨酸、谷氨酸等9种氨基酸。考察了磷酸浓度、进样方式和缓冲液pH对分离效率和重现性的影响。在分离电压为-15 kV、检测波长为220 nm条件下,以含有0.5 mmol/L十六烷基三甲基溴化铵、20 mmol/L烟酸、10%甲醇的10 mmol/L磷酸二氢钠缓冲溶液(pH 10.2)为运行缓冲液,9种组分在11 min内达到基线分离;检出限最低可达到0.3 mg/L;线性范围为1.0~1000 mg/L;日间及日内精密度为0.64%~5.83%。实际样品中除甲硫氨酸外的8种氨基酸的加标回收率为60.00%~118.37%。将该方法应用于不同蜜源植物和产地的蜂蜜样品的测定,在市售的5种蜂蜜中均检测到脯氨酸、丝氨酸和天冬氨酸,而只在荔枝蜜中检测到苏氨酸。该方法可以为蜂蜜的蜜源鉴别及质量评估提供借鉴方法。     

Separation and determination of perfluorinated carboxylic acids using capillary zone electrophoresis with indirect photometric detection

Perfluorinated carboxylic acids (PFCAs) belong to anthropogenic fluoroorganic compounds that have been detected in the natural environment and living organisms including humans. A capillary zone electrophoretic method with indirect UV detection using 2,4-dinitrobenzoic acid (2,4-DNBA) as a chromophore probe has been developed for analysis of PFCAs (C6-C12) in water. Optimal analyte resolution and detection sensitivity was obtained with 50 mM Tris solution of pH 9.0 and 50% methanol as a background electrolyte (BGE). The baseline separation of C6-C12 PFCAs was obtained within 20 min with detection limits in the range from 0.6 to 2.4 ppm.     

高效毛细管电泳-电导检测对四环素衍生物分离测定的研究

运用毛细管电泳-电导检测方法对4种四环素衍生物——土霉素(OTC)、金霉素(CTC)、强力霉素(DOC)和四环素(TC)的分离进行了研究。在3．5mmol/L三羟基氨基甲烷(Tris)-7．5mmol/L柠檬酸(Cit)pH4．0的运行缓冲液中，4种四环素衍生物在15min内获得完全分离。四环素衍生物的线性范围分别为5．0-500μg/mL OTC，3．6-420μg/mL CTC，4.5-470μg/mL DOC和2.5-400μg/mL TC。检测限(S／N＝3)分别为OTC2．0μg/mL，CTC 1．8μg／mL，DOC2．5μg/mL和TC1．0μg/mL。采用本法对实际样品强力霉素片中强力霉素和土霉素片中土霉素进行测定，回收率分别为97．2％和96.4％。     

Indirect photometric detection of anions in nonaqueous capillary electrophoresis employing Orange G as probe and a light-emitting diode-based detector

A method based on indirect photometric detection (IPD) in CE employing a blue LED (473 nm) as a light source and the highly absorbing (478 nm) anionic dye, Orange G, as the probe ion was developed for the sensitive analysis of inorganic and organic anions. The use of nonaqueous solvents was examined as a simple way to reduce the adsorption of the dye onto the capillary wall and to thereby improve the baseline stability. The benefits of this approach were confirmed by experiments using BGEs in methanol (MeOH) and DMSO in which superior baselines were obtained relative to those achieved using aqueous electrolyte systems. A range of commercial LEDs was tested to improve the detection performance, with a difference of 25% in sensitivity being observed between the best and worst performing LED. The final system (4 mM Orange G, 0.05% w/v hydroxypropylcellulose (HPC), 20 mM triethanolamine (TEA) in pure MeOH) exhibited stable baselines and very low LODs (0.10-0.18 microM) for a test mixture comprising nine inorganic and organic anions. These values represent a two- to six-fold improvement over previous studies and the proposed method provides the most sensitive IPD method for the determination of anions using CE published to date. RSDs for ten replicates were in the ranges of 0.42-0.62% for migration time, 1.41-3.46% for peak area and 3.20-5.78% for peak height.     

Direct determination of sialic acids in serum by capillary electrophoresis with UV detection

Summary A novel method for the determination of N-acetylneuraminic acid (NANA) and N-glycolylneuraminic acid (NGNA) has been developed using high-performance capillary electrophoresis with UV detection at 195 nm, without pre or post-column derivatisation. The acids were separated in a 50-cm, fused-silica capillary (50μ i.d, 45.5-cm effective length) with Na₂B₄O₇−Na₂HPO₄ buffer. The detection limit for NANA is a concentration of 9.6×10⁻⁶ M or, in terms of mass:3.879×10⁻¹⁴ mol (39 fmol). This method is applicable to determination of NANA in normal human serum. The results were also compared with those of the colorimetrie method.     

Determination of taurine in human tear fluid by capillary electrophoresis with indirect amperometric detection based on electrogenerated bromine

A new method for the determination of taurine was developed based on indirect amperometric detection after capillary electrophoresis. A serial dual‐electrode detector comprising an on column Pt film electrode (upstream electrode) and an end column Pt microdisk electrode (downstream electrode) was utilized to conduct the indirect amperometric detection. Bromide is oxidized to bromine at upstream electrode and reduced back to bromide at downstream electrode. Since taurine can react with bromine quantitatively and rapidly, its concentration can therefore be determined by the decrease of the current for bromine reduction at the downstream electrode. Principal experimental parameters governing the analytical performance were investigated and optimized. Under the optimal conditions, taurine can be baseline separated from interfering amino acids and the detection limit of 0.18 μM was obtained with a linear correlation coefficient of 0.999 over the concentration range of 0.5–60 μM. The developed method has been successfully applied in the determination of taurine in human tear fluid. The taurine level obtained was in good agreement with previous reports and recoveries for taurine spiked ranged from 92–95% with relative standard deviations within 4.6%, demonstrating the reliability of the developed method in the determination of taurine in human tear fluid.     

Capillary zone electrophoresis with indirect UV detection: Determination of sodium dodecyl sulfate in simulated stream water

SDS (sodium dodecyl sulfate) has been quantitatively determined by capillary zone electrophoresis using a fused silica capillary and a 5 mM dihydroxybenzoic acid / sodium hydroxide buffer in 5% methanol solution at a pH of 8.1. The ion was detected by indirect UV absorption at 250 nm. Detection range was from 0.8 to 50 mg SDS/L. This rapid method requiring only small sample volumes was developed in support of an aquatic toxicology study in a simulated stream water and is applicable to waters containing common inorganic ions.     

Determination of various inorganic anions and organic acids in the atmospheric particulate matter using capillary zone electrophoresis with indirect UV detection

Capillary zone electrophoresis with indirect UV detection was developed for the simultaneous analysis of inorganic anions and organic acids using a mixed solution of 2,6-pyridinedicarboxylic acid and cetyltrimethylammonium hydroxide as the background electrolyte (BGE). The parameters which influence the separation, such as indirect UV detection wavelength, BGE conditions, applied voltage and extraction conditions were investigated. Thirteen inorganic anions and organic acids were detected within 20 min. The calibration curves of each analyte were linear with correlation coefficients greater than 0.991. The relative standard deviations (n = 10) of the peak areas ranged from 0.6% to 3.3%. The detection limits for these species ranged from 0.4 to 1.4 mg/L at a signal-to-noise ratio of 3. The recovery rate of each analyte was more than 80% under optimised extraction conditions, except for nitrite. The proposed method was applied towards the analysis of inorganic anions and organic acids in the atmospheric particulate matter using an Andersen sampler. The particle size of the particulate matter was determined, but not the size of the anions.