Determination of low-molecular-mass organic acids in any type of beer samples by coelectroosmotic capillary electrophoresis

A separation and determination of a mixture of 19 low-molecular-mass organic acids usually present in beer samples was developed using coelectroosmotic capillary zone electrophoresis. A polycation (hexadimetrine bromide, HDB) has been added to the electrolyte, which dynamically coats the inner surface of the capillary and causes a fast anodic electroosmotic flow. The main factors affecting reversal of the EOF such as type of modifier and concentration and influence of organic solvents were studied. Three types of modifiers, two alkylammonium salts (cethyltrimethylammonium bromide and tetradecyltrimethylammonium bromide) and a polycation (HDB) were investigated. The composition of the running buffer results on a 25% 2-propanol, 0.001% HDB and 50 mM sodium phosphate. The different instrumental parameters affecting the capillary electrophoretic separation were also optimized resulting on a -15 kV voltage with a hydrodynamic injection for 7 s with a UV detection at 210 nm. The applicability of the present method has been demonstrated for the determination of organic acids in different beer samples.     

胶束电动毛细管色谱法检测红曲米中的莫纳可林K

建立了测定红曲米中莫纳可林K含量的胶束电动毛细管色谱(MEKC)方法。考察了运行缓冲液的种类、pH及其浓度、有机添加剂、十二烷基硫酸钠(SDS)的浓度和分离电压等实验条件对电泳分离效果及检测灵敏度的影响。在优化的实验条件下,以20 mmol/L硼砂(pH 10.6,含10%(体积分数)乙醇和40 mmol/L SDS)作为缓冲溶液,莫纳可林K能在23 min内实现很好的基线分离,线性范围为5.00～100.00 mg/L,线性相关系数为0.9976,检出限(以信噪比(S/N)为3计)为0.13 mg/L,加标回收率为98.5%～99.5%。精密度和稳定性试验中,峰面积和迁移时间的相对标准偏差均小于3%,表明重复性良好。该方法简便、快速、灵敏,可用于红曲米中莫纳可林K含量的测定。     

Comparison of enantioseparation of amino acid derivatives in aqueous and mixed aqueous-organic media by capillary zone electrophoresis

The chiral separation of dansyl-amino acids has been performed by capillary zone electrophoresis using ¶β-cyclodextrin as a chiral selector, urea as an additive and 2-propanol and methanol as organic modifiers. The enantiomeric separations of dansyl-amino acids were investigated in aqueous medium and compared with the separation in mixed aqueous-organic medium as background electrolytes. The separation conditions, (concentration of buffer, β-cyclodextrin, methanol, urea and the pH value of buffer) were optimized. In the absence of organic modifier, only five pairs of 8 separated dansyl-amino acids were resolved when run separately. A mixture of up to eight chiral amino acids can be baseline resolved in less than 19 min by β-cyclodextrin-modified capillary zone electrophoresis with a buffer of 60 mmol L^–1 H₃BO₃-KCl/40 mmol L^–1 NaOH (pH 9.0), 4 mol L^–1 urea, 100 mmol L^–1β-cyclodextrin and 10% (v/v) methanol.     

Determination of capsaicin and dihydrocapsaicin by micellar electrokinetic capillary chromatography and its application to various species of Capsicum, Solanaceae.

An easy, rapid and sensitive method of analysis for capsaicin and dihydrocapsaicin and its application for determination of these two amides in fruit extracts of different varieties of Capsicum frutescens by micellar electrokinetic capillary chromatography has been developed. Optimum separation was achieved with a fused-silica capillary column (600 mm x 0.075 mm I.D) and a running buffer at pH 9.0 prepared from 15 mM sodium tetraborate and 15 mM sodium dihydrogenphosphate, and 67.5 mM sodium dodecyl sulphate. Addition of 15% (v/v) methanol in the running buffer was found to be essential for the separation. The applied voltage was +22.5 kV. The compounds were detected by UV at 214 nm. Both capsaicin and dihydrocapsaicin were detected within 11 min, with an excellent resolution.     

Using capillary electrophoresis for the determination of organic acids in Port wine

The simultaneous separation and determination of organic acids in several samples of white and red Port wines was performed by capillary zone electrophoresis using indirect UV detection with 2,6-pyridinedicarboxylic acid as a background electrolyte buffer. Operational parameters like migration time, temperature, voltage and capillary length were optimized. Sixteen samples of red wine and four samples of white wine were used to analyze for tartaric, malic, lactic, succinic and acetic acids using glyoxylic acid as the internal standard. The method is rapid, sensitive and quantitative, and time-consuming sample preparation, such as solid-phase extraction or liquid-liquid extraction procedure, is not required.     

Enantioseparation by CE with vancomycin as chiral selector: Improving the separation performance by dynamic coating of the capillary with poly(dimethylacrylamide)

An approach for improving the separation performance of the enantioseparation by CE with vancomycin as chiral selector is described. In the present method, a solution of poly(dimethylacrylamide) (PDMA) was used for dynamic coating of the capillary wall to minimize the adsorption of vancomycin onto the capillary wall, and to depress the EOF. Compared with the bare fused-silica capillaries and the capillaries coated with the polycationic polymer hexadimethrine bromide (HDB), the PDMA-coated capillary displayed the best separation performance. The resulting coating could withstand hundreds of runs without losing its function. Moreover, a partial filling technique was applied to avoid interference in detection caused by the presence of vancomycin in the buffer. The separation time was shortened when a short-end-injection technique was applied. Several parameters such as buffer pH, vancomycin concentration and plug length of the vancomycin solution for the separation were optimized. Under the optimal conditions, all tested enantiomers, including FMOC amino acids derivatives, ketoprofen and fenoprofen, were baseline-separated in less than 4.2 min.     

Comparison of enantioseparation of amino acid derivatives in aqueous and mixed aqueous-organic media by capillary zone electrophoresis

The chiral separation of dansyl-amino acids has been performed by capillary zone electrophoresis using ?β-cyclodextrin as a chiral selector, urea as an additive and 2-propanol and methanol as organic modifiers. The enantiomeric separations of dansyl-amino acids were investigated in aqueous medium and compared with the separation in mixed aqueous-organic medium as background electrolytes. The separation conditions, (concentration of buffer, β-cyclodextrin, methanol, urea and the pH value of buffer) were optimized. In the absence of organic modifier, only five pairs of 8 separated dansyl-amino acids were resolved when run separately. A mixture of up to eight chiral amino acids can be baseline resolved in less than 19 min by β-cyclodextrin-modified capillary zone electrophoresis with a buffer of 60 mmol L^–1 H₃BO₃-KCl/40 mmol L^–1 NaOH (pH 9.0), 4 mol L^–1 urea, 100 mmol L^–1β-cyclodextrin and 10% (v/v) methanol. Received: 15 March 1999 / Revised: 10 May 1999 / Accepted: 12 May 1999     

Enhanced detection of seven glucoconjugated and hydroxylated porphyrins and chlorins by nonaqueous capillary electrophoresis combined with stacking

The nonaqueous capillary electrophoresis mode which includes a preconcentration step based on a transient pseudo-isotachophoresis to the simultaneous separation of seven glucoconjugated and hydroxylated porphyrins and chlorins, exhibiting very close structures, is reported. A high methanol content, of the buffer solution, was necessary in order to prevent self-assembly of the compounds and to enhance their solubility during separation. With the addition of 66% (v/v) methanol and 1% (w/v) NaCl in the aqueous sample solution, large volumes could be injected (44% capillary volume) without a loss in resolution. Sensitivity of detection was therefore improved by a 100-fold factor with regard to the method employing normal injection (2% capillary volume). Optimum electrophoretic conditions, in terms of sensitivity and performance, were obtained by using 20 mM phosphoric acid buffer, pH 2.2 and 50% methanol. The method was validated and applied to qualitative analysis of glucoconjugates in serum samples.     

Co-electroosmotic capillary electrophoresis determination of phenolic acids in commercial olive oil

Fourteen phenolic acids have been selectively determined in olive-oil samples using the co-electrosmotic capillary electrophoresis mode with UV detection after the LLE extraction system. A polycationic surfactant (hexadimetrine bromide, HDB), which dynamically coats the inner surface of the capillary and causes a fast anodic electroosmotic flow, was added to the electrolyte. The main factors affecting co-electroosmotic flow (EOF) such as type of modifier, concentration, and influence of organic solvents have been studied. Other parameters such as pH, type, and concentration of buffer, applied voltage, and injection time were also optimised using hydrodynamic injection for 8 s and UV detection at 210 nm. The composition optimum of the running buffer used was a 20% 2-propanol, 0.001% HDB, and 50 mM sodium borate at a pH value of 9.6. The method has been applied to determination and quantification of fourteen phenolic acids at ppb levels in olive oil samples after a liquid-liquid extraction.     

Determination of polyphenol components in herbal medicines by micellar electrokinetic capillary chromatography with Tween 20

A simple and convenient method of micellar electrokinetic capillary chromatography (MEKC) using polyoxyethylene sorbitan monolaurate (Tween 20) to form single micelle and methanol as a buffer additive was introduced for the simultaneous determination of five polyphenols, including scopoletin, rutin, esculetin, chlorogenic acid and caffeic acid. A running buffer solution of pH 9.3, 20 mmol/L sodium tetraborate containing 64 mmol/L Tween 20 and 9% (v/v) methanol was adopted in the separation. Because rutin and esculetin were difficult to be separated by capillary zone electrophoresis (CZE) and SDS-based MEKC, Tween 20-based MEKC was adopted and the polyphenols were separated satisfactorily. The proposed method was used to determine the polyphenol components in the herbal medicine of Cortex fraxini. The separation mechanism of Tween 20-based MEKC for the polyphenols was discussed preliminarily.     

Fast enantiomeric separation with vancomycin as chiral additive by co-electroosmotic flow capillary electrophoresis: increase of the detection sensitivity by the partial filling technique

A fast and sensitive method is described by using vancomycin as a chiral additive for enantiomeric separation by capillary electrophoresis (CE). In order to overcome disadvantages associated with use of vancomycin as chiral additive in CE, several strategies including the dynamic coating technique, the co-electroosmotic flow technique, and the partial filling technique were employed sequentially in this method. Using the polycationic polymer hexadimethrine bromide (HDB) as a buffer additive, the capillary wall was dynamically coated with a thin film formed by the adsorbed HDB. Consequently, the adsorption of vancomycin onto the capillary wall was minimized via electrostatic repulsion between the coating of the capillary wall and the vancomycin molecule. In addition, the reversed electroosmotic flow (from cathode to anode) produced by the positively charged capillary wall migrates in the same direction of negatively charged analytes (co-electroosmotic flow electrophoresis). Thereby the electrophoretic mobility of negatively charged analytes were drastically accelerated leading to a short separation time of less than 3.4 min. The separation time was further reduced by the use of a short-end-injection technique. For example, the analysis time was achieved by as short as 55 s for a baseline separation of dansyl-alpha-amino-n-butyric acid. Concurrently, the partial filling technique was used to avoid the loss of detection sensitivity caused by the presence of vancomycin in the running buffer. The effect of several parameters, such as HDB concentration, buffer pH, plug length of the chiral selector, concentration of the chiral selector and applied voltage, on enantioselectivity were investigated toward optimization. Besides the advantage of a very short separation time, the method is characterized by high detection sensitivity, high selectivity, and high efficiency.     

Optimization of the separation of phenolic compounds by micellar electrokinetic capillary chromatography

A group of phenolic compounds including phenolic aldehydes, acids and flavonoids are separated by micellar electrokinetic chromatography (MECC). The influence of buffer (concentration and pH), concentration of sodium dodecylsulphate (SDS) and applied voltage were studied. To increase the selectivity of the separation and the resolution of the solutes organic solvents are added to the separation buffer, the best results were obtained when methanol was used at lower percentages. An optimized buffer (150 mM boric acid (pH 8.5)-50 mM SDS-5% methanol) provides the optimum separation with regard to resolution and migration time. This method was applied to the determination of these compounds in wine samples with good results.     

Simultaneous Capillary Electrophoretic Analysis of Flavonoids and Phenolic Acids in Plants

An efficient capillary electrophoretic method is described for the simultaneous determination of hydroxylated and methoxylated flavonoids and phenolic acids present in plant extracts. The separation of samples injected in pressure injection mode was carried out using fused silica capillary in boric acid buffer (alkaline pH) containing SDS as pseudostationary phase and methanol as organic modifier with direct UV detection at 220nm.     

Analysis of Bioactive Triterpenes from Rubus chingii by Cyclodextrin-Modified Capillary Electrophoresis

A capillary electrophoretic (CE) method with β-cyclodextrin (CD) as modifier has been developed to enable separation, for the first time, of bioactive pentacyclic triterpene acids from the fruits of Rubus chingii. The effects of conditions such as the concentration of the running buffer, amounts of added β-cyclodextrin and organic modifier, applied voltage, and column temperature were systematically investigated to optimize the separation conditions. Baseline separation was achieved for the seven triterpenes by use of background electrolyte consisting of 200 mmol L⁻¹ disodium tetraborate, 15 mmol L⁻¹ β-cyclodextrin, and 12.5% (v/v) methanol. Binding constants between β-cyclodextrin and the triterpenes in the capillary electrophoresis buffer were calculated from the order of migration to elucidate the separation mechanism. The amounts of the triterpenes in the fruits of R. chingii were also determined by use of the method after a relatively simple extraction procedure.Revised: 5 January and 22 April 2005     

Capillary electrochromatographic separation of non-steroidal anti-inflammatory drugs with a histidine bonded phase

An open tubular wall-coated capillary column containing histidine functional groups was prepared and employed for the capillary electrochromatographic separation of non-steroidal anti-inflammatory drugs. The anion exchange along with the hydrogen bonding and hydrophobic properties of the surface coating allowed the separation of analytes with very similar ionic mobility. Selectivity and resolution were studied by changing the pH over the range from 3.5 to 5.0 and the concentration of the buffer from 10 to 25 mM, as well as variation of the organic modifier, such as methanol, ethanol and 1-propanol over the range 7.5 to 20%. The optimum experimental conditions for the separation of a drug mixture, which consisted of indoprofen, ketoprofen, suprofen, naproxen, flurbiprofen, fenoprofen and ibuprofen were using a mixture of acetate buffer (20 mM, pH 5.0)-ethanol (1:5, v/v) as background electrolyte and an applied voltage of -20 kV with UV detection at 220 nm. The separation of these drugs could be achieved with an average plate number of 1.0 x 10(5) m(-1).     

Analysis of metacycline by capillary electrophoresis

The development and validation of an optimized capillary electrophoresis method for the determination of metacycline in the presence of its related substances by capillary electrophoresis is shown. The influence of methanol as organic modifier, buffer pH, buffer concentration, capillary length, column temperature, Triton X-100 and methyl-beta-cyclodextrin was investigated. A central composite design was performed in order to optimize the method. The optimal separation conditions were: uncoated fused-silica capillary (39 cm total length, 31 cm effective length, 50 microm ID); as background electrolyte a solution of 160 mM sodium carbonate and 1 mM EDTA (pH 10.35)/methanol (89:13 v/v); temperature, 15 degrees C; voltage, 12 kV. The method showed good selectivity, repeatability, linearity, and sensitivity. The limits of detection and quantitation are 0.024% and 0.06%, respectively, relative to a 2.5 mg/mL solution. Six commercial samples were analyzed quantitatively.     

Determination of low molecular weight organic acids in soil,plants, and water by capillary zone electrophoresis

Determination of low molecular weight organic acids in soils and plants by capillary zone electrophoresis was accomplished using a phthalate buffer and indirect UV detection mode. The influence of some crucial parameters, such as pH, buffer concentration and surfactant were investigated. A good separation of seven organic acids was achieved within 5 min using an electrolyte containing 15 mmol L(-1) potassium hydrogen phthalate, 0.5 mmol L(-1) myristyltrimethylammonium bromide (MTAB), and 5% methanol (MeOH) (v/v) at pH 5.60, separation voltage -20 kV, and temperature 25 degrees C. The relative standard deviation (n=5) of the method was found to be in range 0.18-0.56% for migration time and 3.2-4.8% for peak area. The limit of detection ranged between 0.5 micro mol L(-1) to 6 micro mol L(-1) at a signal-to-noise ratio of 3. The recovery of standard organic acids added to real samples ranged from 87 to 119%. This method was simple, rapid and reproducible, and could be applied to the simultaneous determination of organic acids in environmental samples.     

Determination of preservatives by integrative coupling method of headspace liquid-phase microextraction and capillary zone electrophoresis

An integrative coupling method of headspace liquid-phase microextraction (HS-LPME) and capillary zone electrophoresis (CZE) was proposed in this paper. In the method, a separation capillary was used to create a microextraction droplet of the running buffer solution of CZE, hold the droplet at the capillary inlet, extract analytes of sample solutions in the headspace of a sample vial, inject concentrated analytes into the capillary and separate the analytes by CZE. The proposed method was applied to determine the preservatives of benzoic acid and sorbic acid in soy sauce and soft drink samples, in which the running buffer solution of 50 mmol/L tetraborate (pH 9.2) was directly used to form the acceptor droplet at the capillary inlet by pressure, and the preservatives in a 6-mL sample solution containing 0.25 g/mL NaCl were extracted at 90°C for 30 min in the headspace of a 14-mL sample vial. Then the concentrated preservatives were injected into the capillary at 10 cm height difference for 20 s and separated by CZE. The enrichment factors of benzoic acid and sorbic acid achieved 266 and 404, and the limits of detection (LODs) were 0.03 and 0.01 μg/mL (S/N=3), respectively. The recoveries were in the range of 88.7-105%. The integrative coupling method of HS-LPME and CZE was simple, convenient, reliable and suitable for concentrating volatile and semi-volatile organic acids and eliminating matrix interferences of real samples.     

Calculation of the electrophoretic mobility of amines in methanol-aqueous electrolyte systems.

An equation for calculating the electrophoretic mobility of an analyte with respect to the concentration of organic modifier in mixed aqueous-organic modifier running buffer was derived from mixture response surface methodology. In order to assess the accuracy and predictability of the proposed model, the electrophoretic mobilities of four aliphatic amines and imidazole (background absorber) were measured in mixed water-methanol running buffer containing 0-100% v/v methanol by capillary zone electrophoresis with indirect UV detection. The accuracy of the proposed model was examined by fitting all the experimental data points. The predictability of the model was then evaluated by employing six training data points to compute the model constants, and the mobility at the other data points was predicted by the trained model. The proposed model gave accurate results for the correlation and prediction, with mean percentage errors for the amines studied of 0.6% to 0.5% and 1.5% to 1.1%, respectively.     

Optimization of the separation of flavonoids by micellar electrokinetic capillary chromatography: Effect of organic solvents

Summary A group of flavonoids of special interest to wine quality were separated by micellar electrokinetic chromatography (MEKC) with diode array detection. Their separation was optimized as a function of the buffer concentration and pH, the concentration of sodium dodecyl sulfate (SDS) and the applied voltage. Selectivity and resolution of the solutes were increased by adding organic solvents to the separation buffer, the best results being obtained at lower concentrations. An optimized buffer with 5% methanol provided optimum separation with regard to efficiency, resolution and migration time. The optimized method was applied to the determination of these compounds in wine samples.