Analysis of neutral and sialylatedN-liked oligosaccharides by micellar electrokinetic capillary chromatography with addition of a divalent cation

Summary Micellar electrokinetic capillary chromatography (MECC) has been investigated as an alternative mode of analyzing oligosaccharides released from glycoproteins. The influence on the separation of experimental parameters such as the concentrations of surfactant and electrolyte and the addition of divalent cations was examined. Solubilization, of neutral oligosaccharides by micelles was demonstrated whereas for the sialylated oligosaccharides the electrophoretic mobility remained the predominant factor. The addition of Mg⁺⁺ to sodium dodecyl sulfate (SDS)solutions provided an effective means of enhancing the selectivioty of the separation through both an increase of the time window and the differential complexation of carbohydrate with this divalent cation.     

Influence of pressure on sorption equilibrium: HPLC column packing-mixed eluent

Summary Pronounced base line perturbations were repeatably observed in LC both in alternating recycling and in backflushing experiments when binary eluents and refractometric detectors were used. The perturbations which we call eigenzones appeared immediately after operating the recycling or the backflushing valve, and their size and shape depended on the nature of both the column filling and the mixed mobile phase as well as on the pressure drop across the column.Experimental results presented confirm that the primary causes of the eigenzones were the pressure changes in the columns which influenced the sorption equilibrium of mixed eluent components within the column packing. Some practical consequences of this effect are briefly discussed.Second part of the series discussing the role of pressure in LC. First part: see ref. [1].     

A new multidimensional chromatographic technique: Liquid chromatography with a multiphase eluent

Summary A novel form of liquid chromatography is described which involves the use of multiphase eluents, such as emulsions, for the separation of biopolymers and certain microorganisms.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Micellar Electrokinetic Chromatography of X-Ray Film Developing Baths

A simple and fast micellar electrokinetic chromatographic (MEKC) method for the determination of five main compounds (hydroquinone, metol, phenidone, 2-hydroxy-5-methylaminobenzenesulphonate and 2,5-dihydroxybenzenesulphonate) in X-ray film developing solutions was developed. The optimal conditions for the separation were established by varying the concentration of sodium dodecyl sulfate (SDS), the electrolyte pH and the temperature. Successful results were obtained with a 25mmolL^–1 Tris-phosphate buffer at pH 9.0 in the presence of 50mmolL^–1 SDS using direct UV detection at 214nm. Under these conditions, baseline separation of the five compounds was achieved in less than 8min. The method was validated in terms of precision, linearity, accuracy, and successfully applied to the analysis of X-ray film developing baths.     

Micellar electrokinetic capillary chromatography determination of zinc bacitracin and nystatin in animal feed

An MEKC procedure was developed for the separation of zinc bacitracin (Zn-BC) and nystatin (NYS) in mixtures and in animal feedstuff. The running buffer was 15 mM borate/19 mM phosphate, pH 8.2, containing 20 mM SDS and 10% v/v methanol. Samples were run at 25 degrees C, the applied voltage was 25 kV, and an additional pressure of 5 mbar was applied. Both analytes were detected by UV simultaneously at 215 nm, Zn-BC alone at 192 and 254 nm, and NYS alone at 305 nm. The method was shown to be specific, accurate (recoveries were 100.0 +/- 0.6% and 100.1 +/- 0.6% for Zn-BC and NYS, respectively), linear over the tested range (correlation coefficients 0.9991 and 0.9994), and precise (RSD below 1.3% for both analytes). The method was applied to determine Zn-BC and NYS as additives in animal feed.     

Analysis of lorazepam and its 30-glucuronide in human urine by capillary electrophoresis: evidence for the formation of two distinct diastereoisomeric glucuronides

Lorazepam (LOR) is a 3-hydroxy-1,4-benzodiazepine that is chiral and undergoes enantiomerization at room temperature. In humans, about 75% of the administered dose of LOR is excreted in the urine as its 30-glucuronide. CE-MS with negative ESI was used to confirm the presence of LOR-30-glucuronide in urines that stemmed from a healthy individual who ingested 1 or 2 mg LOR, whereas free LOR could be detected in extracts prepared from enzymatically hydrolyzed urines. As the 30-glucuronidation reaction occurs at the chiral center of the molecule, two diastereoisomers can theoretically be formed, molecules that can no longer interconvert. The stereoselective formation of LOR glucuronides in humans and in vitro was investigated. MEKC analysis of extracts of the nonhydrolyzed urines suggested the presence of the two different LOR glucuronides in the urine. The formation of the same two diastereoisomers was also observed in vitro employing incubations of LOR with human liver microsomes in the presence of uridine 5'-diphospho-glucuronic acid as coenzyme. The absence of other coenzymes excluded the formation of phase I or other phase II metabolites of LOR. Both results revealed a stereoselectivity, one diastereoisomer being formed in a higher amount than the other. After enzymatic hydrolysis using beta-glucuronidase, these peaks could not be detected any more. Instead, LOR was monitored. Analysis of the extracts prepared from enzymatically hydrolyzed urines by MEKC in the presence of 2-hydroxypropyl-beta-CD revealed the enantiomerization process of LOR (observation of two peaks of equal magnitude connected with a plateau zone). The data presented provide for the first time the evidence of the stereoselectivity of the LOR glucuronidation in humans.     

Influence of surfactants on the fading of malachite green

The kinetics of the reaction between malachite green (MG) and sodium hydroxide (MG fading) was studied using a spectrophotometric method in the presence of two cationic surfactants, cetyl-benzyl-dimethyl-ammonium chloride (CBDAC) and hexadecyl-trimethylammonium bromide (HTAB) and one anionic surfactant, sodium dodecyl sulphate (SDS) at concentrations below and above critical micellar concentrations. The cationic surfactants have a catalytic effect, while the anionic surfactant has an inhibitory effect on the reaction. A kinetic model describing the influence of surfactant on reaction rate was developed. The results are discussed on the basis of electrostatic and hydrophobic interactions between the kinetic micelles and malachite green.      

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.     

Selectivity in micellar catalysed reactions: The role of interfacial dipole,compartmentalisation, and specific interactions with the surfactants

Micellar catalysis is playing a major role in green chemistry with ever increasing applications in the efficient and sustainable preparation of natural compounds, drugs, and more recently organic semiconductors for printed electronics. Most of the contributions in the field focus on the developments of surfactants and suitable formulative conditions capable of reproducing – and often improving – the yield of reactions commonly performed in organic solvents. The real ambition of the micellar catalysis approach goes beyond the improvement in the sustainability of existing methods and aims at mimicking not only the efficiency but also the selectivity of enzymatic catalysis. This review summarizes relevant examples of micellar catalysis enabled, efficient, and selective transformations, and discusses the different kind of processes impacting on the product distribution depending on the details of the formulative state achieved.     

Anion-(π)n-π Catalytic Micelles

Anion-π catalysis operates by stabilizing anionic transition states on π-acidic aromatic surfaces. In anion-(π)_n-π catalysis, π stacks add polarizability to strengthen interactions. In search of synthetic methods to extend π stacks beyond the limits of foldamers, the self-assembly of micelles from amphiphilic naphthalenediimides (NDIs) is introduced. To interface substrates and catalysts, charge-transfer complexes with dialkoxynaphthalenes (DANs), a classic in supramolecular chemistry, are installed. In π-stacked micelles, the rates of bioinspired ether cyclizations exceed rates on monomers in organic solvents by far. This is particularly impressive considering that anion-π catalysis in water has been elusive so far. Increasing rates with increasing π acidity of the micelles evince operational anion-(π)_n-π catalysis. At maximal π acidity, autocatalytic behavior emerges. Dependence on position and order in confined micellar space promises access to emergent properties. Anion-(π)_n-π catalytic micelles in water thus expand supramolecular systems catalysis accessible with anion-π interactions with an inspiring topic of general interest and great perspectives.