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。     

On-line pretreatment and determination of parabens in cosmetic products by combination of flow injection analysis, solid-phase extraction and micellar electrokinetic chromatography

A convenient and automated method for on-line pretreatment and determination of three parabens (i.e. methyl, ethyl and propyl p-hydroxybenzoate) in cosmetic products is proposed by using flow injection analysis (FIA), solid-phase extraction (SPE) and micellar electrokinetic chromatography (MEKC). An improved split–flow interface is used to couple SPE on C₈-bonded silica with MEKC separation, which can avoid running buffer contamination and reduce buffer consumption, especially, containing expensive reagents. The analytes are loaded onto a C₈ column at 0.6 mL/min for 60 s and eluted with a mixed eluent of 40% (v/v) 10 mmol/L sodium tetraborate buffer (pH 9.3) and 60% (v/v) ethanol at 0.75 mL/min. The MEKC separation is accomplished with a running buffer of 20 mmol/L sodium tetraborate (pH 9.3) containing 100 mmol/L sodium dodecyl sulfate (SDS) at 15 kV. For butyl p-hydroxybenzoate did not be detected in the cosmetic products, it was used as an internal standard (IS) added into the real samples. This FIA–SPE–MEKC method using IS allows the sample separation within 12 min and the sample throughput of five samples per hour with the relative standard deviation (R.S.D.) less than 2.3% (n = 5). The limits of detection (LOD) are in the range from 0.07 to 0.1 μg/mL (S/N = 3 and n = 11). The proposed method has been used to determine three parabens in real cosmetic products satisfactorily.     

Chiral separation of phenylalanine and tryptophan by capillary electrophoresis using a mixture of β‐CD and chiral ionic liquid ([TBA] [l‐ASP]) as selectors

In this paper, a simple, effective and green capillary electrophoresis separation and detection method was developed for the quantification of underivatized amino acids (dl ‐phenylalanine; dl ‐tryptophan) using β‐Cyclodextrin and chiral ionic liquid ([TBA] [l ‐ASP]) as selectors. Separation parameters such as buffer concentrations, pH, β‐CD and chiral ionic liquid concentrations and separation voltage were investigated for the enantioseparation in order to achieve the maximum possible resolution. A good separation was achieved in a background electrolyte composed of 15 mm sodium tetraborate, 5 mm β‐CD and 4 mm chiral ionic liquid at pH 9.5, and an applied voltage of 10 kV. Under optimum conditions, linearity was achieved within concentration ranges from 0.08 to 10 µg/mL for the analytes with correlation coefficients from 0.9956 to 0.9998, and the analytes were separated in less than 6 min with efficiencies up to 970,000 plates/m. The proposed method was successfully applied to the determination of amino acid enantiomers in compound amino acids injections, such as 18AA‐I, 18AA‐II and 3AA. Copyright © 2013 John Wiley & Sons, Ltd.     

Nonaqueous capillary electrophoresis with laser-induced fluorescence detection: a case study of comparison with aqueous media

A novel method based on separation by nonaqueous capillary electrophoresis (NACE) combined with laser-induced fluorescence (LIF) detection was developed and compared with classic aqueous modes of electrophoresis in terms of resolution of solutes of interest and sensitivity of the fluorescence detection. Catecholamines derivatized with 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) were chosen as test analytes for their subtle fluorescence properties. In aqueous systems, capillary zone electrophoresis (CZE) was not suitable for the analysis of test analytes due to complete fluorescence quenching of NBD-labeled catecholamines in neat aqueous buffer. The addition of micelles or microemulsion droplets into aqueous running buffer can dramatically improve the fluorescence response, and the enhancement seems to be comparable for micellar electrokinetic chromatography (MEKC) and microemulsion electrokinetic chromatography (MEEKC). As another alternative, NACE separation was advantageous when performing the analysis under the optimum separation condition of 20 mM sodium tetraborate, 20 mM sodium dodecyl sulfate (SDS), 0.1% (v/v) glacial acetic acid, 20% (v/v) acetonitrile (ACN) in methanol medium after derivatization in ACN/dimethyl sulfoxide (DMSO) (3:2, v/v) mixed aprotic solvents containing 20 mM ammonium acetate. Compared with derivatization and separation in aqueous media, NACE-LIF procedure was proved to be superior, providing high sensitivity and short migration time. Under respective optimum conditions, the NACE procedure offered the best fluorescence response with 5-24 folds enhancement for catecholamines compared to aqueous procedures. In addition, the mechanisms of derivatization and separation in nonaqueous media were elucidated in detail.     

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.     

Analytical potential of 6-oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl) fluorescein for the determination of amino compounds by capillary electrophoresis with laser-induced fluorescence detection

The analytical potential of a fluorescein analogue, 6-oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl) fluorescein (SAMF), for the first time synthesized in our laboratory, as a labeling reagent for the labeling and determination of amino compounds by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection was investigated. Biogenic monoamines and amino acids were chosen as model analytes to evaluate the analytical possibilities of this approach. The derivatization conditions and separation parameters for the biogenic amines were optimized in detail. The derivatization was performed at 30 degrees C for 6 min in boric acid buffer (pH 8.0). The derivatives were baseline-separated in 15 min with 25 mM boric acid running buffer (pH 9.0), containing 24 mM SDS and 12.5% v/v acetonitrile. The concentration detection limit for biogenic amines reaches 8 x 10(-11) mol.L(-1) (signal-to-noise ratio = 3). The application of CE in the analysis of the SAMF-derivatized amino acids was also exploited. The optimal running buffer for amino acids suggested that weak acidic background electrolyte offered better separation than the basic one. The proposed method was applied to the determination of biogenic amines in three different beer samples with satisfying recoveries varying from 92.8% to 104.8%. Finally, comparison of several fluorescein-based probes for amino compounds was discussed. With good labeling reaction, excellent photostability, pH-independent fluorescence (pH 4-9), and the resultant widely suited running buffer pH, SAMF has a great prospect in the determination of amino compounds in CE.     

Migration behavior and separation of benzenediamines, aminophenols and benzenediols by capillary zone electrophoresis

The migration behavior and separation of five benzendiamines, five aminophenols and three benzenediols were investigated in capillary zone electrophoresis. The results indicate that benzendiamines and aminophenols are optimally separated with a phosphate buffer at pH 5, whereas benzenediol isomers are best separated at pH about 12. The addition of surfactant monomers of tetradecyltrimethylammonium bromide to a phosphate buffer at pH 5 under the conditions of reversed electroosmotic flow is effective for separating these dye intermediates, except for the separation of 1,2-benzenediol from 1,3-benzenediol. The addition of sodium tetraborate as an electrolyte modifier is effective in the separation of 1,2-benzenediol from 1,3-benzenediol, but the latter comigrates with the 1,4-benzenediol isomer at pH 5.0. The electrophoretic mobility of ionized analytes can be described with Offord's equation, and the migration order depends on their ratios of charge to mass. In addition, the pKa values of these analytes in 50 mM phosphate buffer are reported.     

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.     

Synthesis and application of dehydroabietylisothiocyante as a new chiral derivatizing agent for the enantiomeric separation of chiral compounds by capillary electrophoretic

A new chiral derivatizing reagent, dehydroabietylisothiocyante (DHAIC), was synthesized and used for the enantiomeric separation of chiral compounds in capillary electrophoresis (CE). The synthetic route to obtain DHAIC is described. The separation conditions for the chiral separation of several chiral compounds, such as protein amino acids and chiral drug DOPA were optimized. Best results for the chiral separation of DHAIC derivatized amino acids and DOPA were obtained in a running buffer consisted of 50 mM borate (pH 9.5), 5 mM sodium dodecyl sulphate (SDS) and 20% acetonitrile for amino acids and 60 mM Na₂HPO₄ (pH 8.0), 17 mM SDS and 25% acetonitrile for DOPA. Under the conditions studied, chiral separation of five amino acids including Ser, Val, Ala, Thr, Cys and a chiral drug DOPA as their diastereomeric DHAIC derivatives has been achieved by micellar electrokinetic chromatography (MEKC).     

Analysis of ecdysteroids by micellar electrokinetic chromatography with on-line preconcentration

In order to enhance the UV detection sensitivity, an application study of an on-line preconcentration technique for micellar electrokinetic chromatographic (MEKC) was carried out. The simultaneous determination of four test ecdysteroids, 20-hydroxyecdysone, ajugasterone C, polypodine B and ponasterone A has been investigated by using the normal stacking mode in MEKC with UV detection. The effects of anionic surfactant composition and concentration, the applied voltage, the pH buffer, the kind and the amount of organic solvent and the injection time on the analyte resolution were evaluated. The optimised conditions for the separation involved the use of a 50 mM borate as the running buffer containing 50 mM of a mixture of sodium dodecyl sulphate (SDS) and sodium cholate (SC) in the ratio of 1:1 together with a concentration of 10% (v/v) of 2-PrOH at pH 9.0. Hydrodynamic injection of 12 s at 50 mbar and separation voltage of 20 kV at temperature of 20 degrees C were employed. These conditions allowed a repeatability separation within 21 min. Concentration detection limit for the neutral analytes studied improve about an order of magnitude. The method was also applied to the determination of ecdysteroids in a real sample.     

Simultaneous determination of seven phenolic acids in three Salvia species by capillary zone electrophoresis with β‐cyclodextrin as modifier

A capillary zone electrophoresis method was developed for the simultaneous determination of seven phenolic acids, including protocatechuic aldehyde ( 1 ), salvianolic acid C ( 2 ), rosmarinic acid ( 3 ), salvianolic acid A ( 4 ), danshensu ( 5 ), salvianolic acid B ( 6 ), and protocatechuic acid ( 7 ), in Danshen and related medicinal plants. A running buffer composed of 20 mM sodium tetraborate adjusted to pH 9.0, and containing 12 mM β‐cyclodextrin as modifier. Baseline separation was achieved within 17 min running at the voltage of 20 kV, temperature of 25°C and detection wavelength of 280 nm. The relative standard deviations of migration time ranged from 0.2 to 0.7% and the peak area ranged from 1.5 to 3.7% for the seven analytes, indicating the good repeatability of the proposed method. The method was extensively validated by evaluating the linearity (R² ≥ 0.9992), limits of detection (0.14–0.36 μg/mL), limits of quantification (0.47–1.19 μg/mL), and recovery (96.0–102.6%). Under the optimum conditions, samples of Danshen and related medicinal plants were analyzed using the developed method with high separation efficiency.     

Separation of N2-ethyl-2'-deoxyguanosine-5'-monophosphate and four native deoxyribonucleoside monophosphates using capillary zone electrophoresis with polyethylene glycol as buffer additive

We investigated the separation of five deoxyribonucleoside monophosphates: 2'-deoxyguanosine-5'-monophosphate (dGMP), 2'-deoxyadenosine-5'-monophosphate (dAMP), 2'-deoxycytosine-5'-monophosphate (dCMP), 2'-deoxythymidine-5'-monophosphate (dTMP) and a dGMP adduct possessing N2-ethyl-guanine, which has been noted in relation to mutagenesis of alcohol, using capillary zone electrophoresis (CZE). The concentration of polyethylene glycol (PEG) as a modifier and the pH of the running solutions can efficiently control the observed separation. Interaction of PEG with analytes was quantitatively evaluated. PEG worked effectively as a hydrophobic selector in these separations. The values of pKa of the acidic-NH-groups in the base moieties of dGMP, dTMP, and the dGMP adduct are close to that of boric acid used as buffer of the running solutions. The control of their charge was facilitated, enabling improved separations. A more sufficient and fast separation was achieved by both optimization of pH of the running solutions and PEG concentration compared with that obtained by pH control alone. On-line concentration using a stacking method followed by the PEG-assisted CZE was briefly studied.     

Separation and determination of isoflavones in red clover by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatography (MECC) method has been developed for the determination of the four isoflavones, i.e. biochanin A, formononetin, genstein and daidzein in red clover (Trifolium Pratense L.). The effect of running buffer pH and concentration were investigated. An electrolyte composed of 30 mm borate, 20 mm sodium dodecyl sulfate (SDS) and 4 mg/mL HP-beta-CD containing 5% (v/v) ethanol at pH 10.1 provides a satisfactory separation for all the analytes. The applied voltage was 25 kV, and the capillary temperature was kept constant at 25 degrees C with a UV detection at 254 nm. The relative standard deviations (RSD) of the migration time and peak area were less than 1.73 and 3.94% (intra-day), and 2.29 and 4.38% (inter-day), respectively, under the optimized separation conditions. Regression equations revealed a good linear relationship between the peak area of each compound and its concentration. The contents of the four compounds in red clover were successfully determined with satisfactory repeatability and recovery.     

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。     

Capillary electrochromatography with zwitterionic stationary phase on the lysine-bonded poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic capillary column

A polymer-based neutral monolithic capillary column was prepared by radical polymerization of glycidyl methacrylate and ethylene dimethacrylate in a 100 mum id fused-silica capillary, and the prepared monolithic column was subsequently modified based on a ring opening reaction of epoxide groups with 1 M lysine in solution (pH 8.0) at 75 degrees C for 10 h to produce a lysine chemically bonded stationary phases in capillary column. The ring opening reaction conditions were optimized so that the column could generate substantial EOF. Due to the zwitterionic functional groups of the lysine covalently bonded on the polymer monolithic rod, the prepared column can generate cathodic and anodic EOF by varying the pH values of running buffer during CEC separation. EOF reached the maximum of -2.0 x 10(-8) m2v(-1)s(-1) and 2.6 x 10(-8) m2v(-1)s(-1) with pH of the running buffer of 2.25 and 10, respectively. As a consequence, neutral compounds, ionic solutes such as phenols, aromatic acids, anilines, and basic pharmaceuticals were all successfully separated on the column by CEC. Hydrophobic interaction is responsible for separation of neutral analytes. In addition, the electrostatic and hydrophobic interaction and the electrophoretic migration play a significant role in separation of the ionic or ionizable analytes.     

Rapid analysis of amino acids in Japanese green tea by microchip electrophoresis using plastic microchip and fluorescence detection

Microchip electrophoresis for the short-time analysis of amino acids in Japanese green tea was developed. The amino acids in Japanese green tea were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). The derivatives were filtered and directly analyzed by electrophoresis on a plastic microchip with a 31-mm long separation channel with fluorescence detection. Amino acid analysis of Japanese green tea was improved by removing polyphenols using a polyvinylpolypyrrolidone pretreatment. Elution profiles of NBD-amino acids were examined under different running buffer conditions, and the sodium dodecyl sulphate in the running buffer exhibited a dramatically high-separation efficiency of amino acids by inhibiting their adsorption on the channel walls. Under the optimized conditions (5 mM phosphate buffer (pH 5.5) containing 0.05 mM sodium dodecylsulfate as running buffer), the main amino acids contained in Japanese green tea were well separated within 2 min, and theanine (1475 mg/100 g tea leaf), Arg (408 mg/100 g tea leaf) and Gln (217 mg/100 g tea leaf) were detected in Japanese green tea.     

Separation and selectivity in micellar electrokinetic chromatography using sodium dodecyl sulfate micelles or Tween 20-modified mixed micelles

The separation and selectivity of eight aromatic compounds ranging from hydrophilic to hydrophobic properties in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) micelles or Tween 20-modified mixed micelles were investigated. The effect of different operation conditions such as SDS and Tween 20 modifier surfactant concentration, buffer pH, and applied voltage was studied. The resolution and selectivity of analytes could be markedly affected by changing the SDS micelle concentration or Tween 20 content in the mixed micelles. Applied voltage and pH of running buffers were used mainly to shorten the separation time. Complete separation of eight analytes could be achieved with an appropriate choice of the concentration of SDS micelles or Tween 20-modified mixed micelles. Quicker elution and better precision could be obtained with SDS-Tween 20 mixed micelles than with SDS micelles. The mechanisms that migration order of those analytes was mainly based on their structures and solute-micelle interactions, including hydrophobic, electrostatic, and hydrogen bonding interactions, were discussed.     

毛细管胶束电动色谱法分析PTH氨基酸

建立了用毛细管胶束电动色谱法（MEKC）分离19种PTH氨基酸的方法,并探讨了电压、pH值、温度、胶束浓度对氨基酸迁移时间的影响。方法具有速度快、灵敏度高、样品用量少的优点。     

Capillary electrophoresis direct enantioseparation of aromatic amino acids based on mixed chelate-inclusion complexation of aminoethylamino-beta-cyclodextrin

6(A)-(2-Aminoethylamino)-6(A)-deoxy-beta-cyclodextrin (CDen) was synthesized and formed a binary complex with Cu(II) which was shown to be an effective chiral selector for separation of underivatized amino acid enantiomers in capillary electrophoresis (CE). Moreover, the chiral resolution was greatly enhanced by the presence of polyethyl glycol (PEG) and tert-butyl alcohol in the running buffer. The optimum experimental conditions were 20 mmol/L CDen, 20 mmol/L CuSO(4).5H(2)O, 5.0 mg/mL PEG20000 and 1.0% v/v tert-butyl alcohol, pH 5.80. With the proposed method, the four selected aromatic chiral amino acid pairs were separated in less than 15 min.     

Heptakis(6-amino-6-deoxy)-beta-cyclodextrin as a chiral selector for the separation of anionic analyte enantiomers by capillary electrophoresis

A hepta-substituted beta-cyclodextrin bearing seven amino groups, heptakis(6-amino-6-deoxy)-beta-cyclodextrin (per-6-NH2-beta-CD) was successfully used as a chiral selector for the enantioseparation of different anionic analytes. The running buffer pH and chiral selector concentration were the studied parameters crucial in achieving the maximum possible enantioresolution. Enantiomeric separation of a mixture of seven carboxybenzyl-amino acids was achieved in 24 min. Excellent resolution was obtained for carboxybenzyl-tryptophan (Rs = 11.2).