Separation and on-line concentration of bisphenol A and alkylphenols by micellar electrokinetic chromatography with anionic surfactant

Separation and on-line concentration of bisphenol A and three alkylphenols were investigated by micellar electrokinetic chromatography with the anionic surfactant, sodium dodecyl sulfate. The separation conditions were optimized by the simultaneous addition of the organic solvent and cyclodextrin to the running solution. The separation of hydrophobic analytes and 4-nonylphenol isomers was improved by the addition of 10% methanol and 5 mM beta-cyclodextrin to the running solution. When the sweeping with the running solution was used as the on-line concentration procedure, 69-, 48-, 55- and 41-fold increases in detection sensitivity were obtained for bisphenol A, 4-tert.-butylphenol and 4-(1,1,3,3-tetramethylbutyl)phenol, and the second peak of 4-nonylphenol isomers, respectively. The detection limits were 0.0071, 0.0065, 0.021 and 0.055 mg/l, respectively. These results were better than those with the cationic surfactant, tetradecyltrimethylammonium bromide.     

Separation of bisphenol A and three alkylphenols by micellar electrokinetic chromatography

Analytical conditions of pH, surfactants, and additives were investigated for the simultaneous separation of bisphenol A and alkylphenols by micellar electrokinetic chromatography. Reproducibility of migration time was improved at higher pH (pH 8.0). When five surfactants having linear alkyl chains or four bile salts were used, the separation of hydrophobic phenols and 4-nonylphenol isomers was not achieved. In order to improve the separation, the use of additives with sodium dodecyl sulfate solution was investigated. The separation of hydrophobic phenols was improved by the addition of organic solvents, however, isomers were not separated. Their separation was achieved by the addition of beta- or gamma-cyclodextrin.     

样品堆积MEKC富集分离双酚A和三种烷基苯酚

基于当携带有分析物的β -环糊精穿过1-金刚烷酸溶液区带时,分析物被1-金刚烷酸置换下来后经分配进入SDS胶束而使分析物迁移速度降低的机理,建立了一种样品堆积MEKC富集分离方法,使BPA和三种烷基苯酚得到了10倍左右的富集.另外,采用此样品堆积MEKC富集分离测定方法在实际湖水样中检测到了两种未知化合物.     

On-line concentration of s-triazine herbicides in micellar electrokinetic chromatography using a cationic surfactant

A new method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was investigated using high-performance ion-exclusion/cation-exchange chromatography with conductimetric detection on a separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin in the hydrogen-form and an eluent comprising 1.5 mM sulfosalicylic acid–6 mM 18-crown-6 at pH 2.6, operated at 1.5 ml/min. Effective separation and highly sensitive conductimetric detection for the anions and the cations was achieved in about 14 min. Since the ionic balance (equivalents of anions/equivalents of cations) of acid rain waters of different pH (4.40–4.67) ranged from 0.97 to 0.94, evaluation of the water quality of acid rain was possible. This method was successfully applied to the simultaneous determination of the anions and the cations in acid rain transported from mainland China and North Korea to central Japan monitored by a meteorological satellite data analyzer.     

Separation of biogenic amines by micellar electrokinetic chromatography with on-line chemiluminescence detection

A method of on-line chemiluminescence detection with capillary electrophoresis for biogenic amines (diaminopropane, putrescine, cadaverine and diaminohexane) labeled with N-(4-aminobutyl)-N-ethylisoluminol is reported for the first time. Two separation modes, capillary zone electrophoresis and micellar electrokinetic chromatography (MEKC), were studied. The results show that excellent resolution was achieved in MEKC. Parameters affecting separation process and chemiluminescence detection have been examined in detail. Under the optimum conditions, the baseline separation of four amines was obtained within 7.5 min. The detection limits (S/N=3) of diaminopropane, putrescine, cadaverine and diaminohexane are 3.5 x 10(-8), 3.5 x 10(-8), 3.9 x 10(-8) and 1.2 x 10(-7) M, respectively. The method was applied to the analysis of biogenic amines in lake water.     

On-line sample concentration in micellar electrokinetic chromatography using cationic surfactants

Two on-line sample concentration techniques, sample stacking and sweeping, were evaluated using cationic surfactants as pseudostationary phases in micellar electrokinetic chromatography. As cationic surfactant micelles, tetradecyltrimethylammonium bromide and cetyltrimethylammonium chloride were employed. About 10-fold and 1000-fold increases in detection sensitivity in terms of peak heights were observed by sample stacking and sweeping, respectively, without suppression of the electroosmotic flow. In particular, the concentration limits of detection (S/N=3) for test naphthalenesulfonic acids obtained with sweeping were from 0.96 to 0.47 ppb with UV detection without any preconcentration procedure.     

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.     

Determination of antihyperglycemic drugs in nanomolar concentration levels by micellar electrokinetic chromatography with non-ionic surfactant

A method for the separation of six selected antihyperglycemic (antidiabetic) drugs (tolbutamide, gliclazide, glimepiride, glibenclamide, repaglinide, and glipizide) was developed with use of micellar electrokinetic chromatography. Two non-ionic poly(ethylene glycol)-based surfactants Genapol X-080 and Triton X-114 (reduced) were studied as neutral pseudostationary phases. High alkaline pH 10.0 was used to obtain negative charges of separated antidiabetic drugs and non-ionic surfactants were employed for selectivity alteration. Both non-ionic surfactants provided good selectivity at concentration 0.2% (v/v) in sodium borate buffer and the separation of six drugs was obtained within 5 min. An on-line preconcentration method based on reversed electrode polarity switching was employed for the determination of antihyperglycemic drugs in blood serum after acetonitrile protein precipitation. The limits of detection ranged from 20.8 nmol L⁻¹ for tolbutamide to 6.5 nmol L⁻¹ for glibenclamide, respectively.     

Reversed migration micellar electrokinetic chromatography with off-line and on-line concentration analysis of phenylurea herbicides

Three environmentally important phenylurea herbicides (monuron, isoproturon, diuron) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 50 mM sodium dodecyl sulfate, 50 mM phosphoric acid, and 15 mM gamma-cyclodextrin. Three on-line concentration techniques are then evaluated to increase the detection sensitivity of the RM-MEKC system. Stacking with reverse migrating micelles (SRMM, water as the sample solvent) provided the best results among the focusing techniques studied. Using a z-shaped detection cell, more than 500-fold increase in peak height is obtained. As a sample preparation and off-line concentration method, solid-phase extraction (SPE) that further improved detection sensitivity was used in the analysis of spiked tap and pond water. For example, 1 parts per billion of each herbicide spiked in tap or pond water was detected by MEKC after SPE and SRMM.     

Separation of coumarins by micellar electrokinetic capillary chromatography

Nine coumarins were successfully separated simultaneously using micellar electrokinetic capillary chromatography with 4-hydroxybenzoic acid as an internal standard. A carrier composed of buffer solution (20 mM sodium dodecyl sulfate-15 mM sodium borate-15 mM sodium dihydrogenphosphate)-acetonitrile (24:1) was found to be the most suitable electrolyte for this separation. The analysis time (22 min) was shorter than that using high-performance liquid chromatography (47 min). Contents of coumarins in the crude drug of Angelicae Tuhou Radix could be easily determined by the proposed method.     

Separation of beta-lactam antibiotics by micellar electrokinetic chromatography

The retention behaviour of beta-lactam antibiotics in micellar electrokinetic chromatography (EKC) was investigated. Sodium dodecyl sulphate (SDS) and sodium N-lauroyl-N-methyltaurate were used an anionic surfactants at concentrations of 0.05-0.3 M. It was found that the retention of ionic substances in micellar EKC is determined by the following three factors: the electrophoretic migration of the ionic substances, the interaction between the ionic substances and ionic surfactants and solubilization of the solute by the micellar phase. A difference in the retention behaviours of cationic substances was observed between the two anionic surfactants, which have different groups neighbouring the charge-bearing groups. The effect of an ion-pairing reagent was also investigated to make the effect of the micelle clearer. All test solutes were successfully separated by micellar EKC at SDS concentrations above 0.1 M, with theoretical plate numbers ranging from 70,000 to 260,000.     

Separation of xylidine isomers by micellar electrokinetic chromatography

Xylidines are important precursors for the production of dyes, drugs, and various other products. Because of the high carcinogenic nature of some xylidine isomers it becomes very essential and relevant to develop suitable analytical procedures to separate isomers as well as enhance detection at very low concentrations. Micellar electrokinetic chromatography has been standardized at various influencing parameters such as pH, ionic strength, and micelle modifiers, and the optimum conditions have been ascertained for the best separation and sensitivity of standard mixtures. The applicability of the procedure in environmental samples is studied.     

Simultaneous electrokinetic and hydrodynamic injection with on-line sample concentration via micelle to solvent stacking in micellar electrokinetic chromatography

Simultaneous electrokinetic and hydrodynamic injection (SEHI) of organic cations (tricyclic antidepressant and beta blocker drugs) with on-line sample concentration using micelle to solvent stacking (MSS) was studied in micellar electrokinetic chromatography. Compared to conventional injection, >300-fold improvements in signals were obtained by hydrodynamic injection. However, with SEHI the amount of sample ions introduced into the capillary was increased which afforded a higher gain of up to 4000-fold without compromise to separation efficiency. The electrokinetic injection at negative polarity (anode at the detector end) introduced the micelle bound analytes. The hydrodynamic injection also maintained the MSS boundary inside the capillary. The stability of the MSS boundary affected SEHI where mild conditions that were low voltage as well as pressure injection were desired. The limits of detection were in the range from 0.6–4.2 ng mL⁻¹. A strategy for optimization was described and the method was applied to the ng mL⁻¹ analysis of spiked wastewater after simple dilution and centrifugation.     

On-line sample concentration in micellar electrokinetic chromatography with cationic micelles in a coated capillary

The electroosmotic flow was successfully suppressed even in the presence of cationic surfactants, when a polyacrylamide-coated capillary was employed. Two on-line sample concentration techniques of sample stacking and sweeping were evaluated in micellar electrokinetic chromatography (MEKC) using the polyacrylamide-coated capillary. Cationic surfactants were used as pseudostationary phases in MEKC. At least 60-fold and about 600-fold increases in detection sensitivity were obtained in terms of peak heights by sample stacking and sweeping, respectively.     

Separation of some chiral flavanones by micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC) was applied for enantioseparation of selected flavanones, including naringin, hesperidin, neohesperidin, naringenin, hesperetin, pinostrobin, isosakuranetin, eriodictyol, and homoeriodictyol. gamma-Cyclodextrin (gamma-CD) and sodium cholate (SCh) were used as chiral modifiers inducing enantioselectivity to the background electrolyte. From among many investigated selectors only these two appeared to possess the best enantioselective properties in respect to studied flavanones. The mechanisms of their action are a little different; SCh used above critical micelle point concentration forms chiral micelles itself while gamma-CD is deprived of this property and requires addition of surfactants as, e.g., sodium dodecyl sulfate. It was found that SCh enables separation of flavanone glycosides diastereomers while separation of enantiomers of flavanone aglycones may be achieved with gamma-CD. Consideration of structural relation led to the suggestion that interaction of sugar moiety of glycosides with SCh micelles give rise to chiral recognition. MEKC appeared to be a suitable and efficient analytical tool to follow enantiomeric composition of flavanones.     

Separation of antithrombin III variants by micellar electrokinetic chromatography

The characterisation of proteins is still one of the most challenging analytical tasks in modern bioanalysis. Due to the complex structure of proteins, several analytical techniques are often required to get sufficient information. Antithrombin III (AT III), a high-molecular-mass plasma glycoprotein which is an important protease inhibitor and the main modulator of thrombin activity, circulates in plasma in two isoforms, the so-called AT III-alpha (90-95%) and -beta (5-10%). Micellar electrokinetic chromatography was used to analytically separate these AT III variants, which differ in their affinity to the polysaccharide heparin.     

Separation of anabolic steroids by micellar electrokinetic capillary chromatography

Summary The separation of seven analogous anabolic steroids was studied by micellar electrokinetic capillary chromatography (MECC). The retention order was found to be dependent on polarity. All of these steroids were well separated by the addition of organic modifiers to the separation buffer. Of the organic modifiers tested, 1-propanol gave the best separation, better than methanol or acetonitrile.     

Separation of aromatic hydrophobic sulfonates by micellar electrokinetic chromatography

Two different buffer systems for the separation of 12 aromatic hydrophobic sulfonates by micellar electrokinetic chromatography (MEKC) were developed. The following buffer systems were used: aqueous phosphate buffers containing either cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS). Eleven aromatic sulfonates were simultaneously separated in less than 35 min employing 20 mM phosphate buffer, pH 7.0 containing 50 mM SDS and 10% of acetonitrile.