Steroid profiles determined by capillary electrochromatography, laser-induced fluorescence detection and electrospray-mass spectrometry

High Performance Liquid Chromatography (HPLC) with Fluorescence Detection for Quantification of Steroids in Clinical, Pharmaceutical, and Environmental Samples: A Review

Steroids are compounds widely available in nature and synthesized for therapeutic and medical purposes. Although several analytical techniques are available for the quantification of steroids, their analysis is challenging due to their low levels and complex matrices of the samples. The efficiency and quick separation of the HPLC combined with the sensitivity, selectivity, simplicity, and cost-efficiency of fluorescence, make HPLC coupled to fluorescence detection (HPLC-FLD) an ideal tool for routine measurement and detection of steroids. In this review, we covered HPLC-FLD methods reported in the literature for the steroids quantification in clinical, pharmaceutical, and environmental applications, focusing on the various approaches of fluorescent derivatization. The aspects related to analytical methodology including sample preparation, derivatization reagents, and chromatographic conditions will be discussed.

The evolution of methods for urinary steroid metabolomics in clinical investigations particularly in childhood

The metabolites of cortisol, and the intermediates in the pathways from cholesterol to cortisol and the adrenal sex steroids can be analysed in a single separation of steroids by gas chromatography (GC) coupled to MS to give a urinary steroid profile (USP). Steroids individually and in profile are now commonly measured in plasma by liquid chromatography (LC) coupled with MS/MS. The steroid conjugates in urine can be determined after hydrolysis and derivative formation and for the first time without hydrolysis using GC-MS, GC-MS/MS and liquid chromatography with mass spectrometry (LC-MS/MS). The evolution of the technology, practicalities and clinical applications are examined in this review. The patterns and quantities of steroids changes through childhood. Information can be obtained on production rates, from which children with steroid excess and deficiency states can be recognised when presenting with obesity, adrenarche, adrenal suppression, hypertension, adrenal tumours, intersex condition and early puberty, as examples. Genetic defects in steroid production and action can be detected by abnormalities from the GC-MS of steroids in urine. New mechanisms of steroid synthesis and metabolism have been recognised through steroid profiling. GC with tandem mass spectrometry (GC-MS/MS) has been used for the tentative identification of unknown steroids in urine from newborn infants with congenital adrenal hyperplasia. Suggestions are made as to areas for future research and for future applications of steroid profiling. As routine hospital laboratories become more familiar with the problems of chromatographic and MS analysis they can consider steroid profiling in their test repertoire although with LC-MS/MS of urinary steroids this is unlikely to become a routine test because of the availability, cost and purity of the internal standards and the complexity of data interpretation. Steroid profiling with quantitative analysis by mass spectrometry (MS) after chromatography now provides the most versatile of tests of adrenal function in childhood.

Simultaneous extraction and determination of free and conjugated phytosterols in tobacco

Acid hydrolysis and alkaline saponification were incorporated into a microwave-assisted extraction process for the simultaneous extraction of free and conjugated phytosterols from tobacco. The crude extract of the microwave-assisted extraction was purified by C18 solid-phase extraction and then determined by high-performance liquid chromatography. Phytosterols of cholesterol, ergosterol, stigmasterol, campesterol, and β-sitosterol were determined by chromatographic quantification. The multiple parameters of microwave-assisted extraction were optimized by a uniform design method. The optimal ratio of extraction ethanol solvent to tobacco mass was 30 mL/g. The microwave-assisted extraction acid hydrolysis was carried out in sulfuric acid medium by heating for 10 min at 55°C. The microwave-assisted extraction alkaline saponification was performed after adding excessive sodium hydroxide by heating another 10 min. The repeatability of the proposed method was acceptable with recoveries from 69.68 to 88.17% for the phytosterols. Five target phytosterols were all found in the tobacco samples, and the contents were significantly different in samples from different producing areas.

Monoliths in capillary electrochromatography and capillary liquid chromatography in conjunction with mass spectrometry

Here, we have reviewed separation studies utilizing monolithic capillary columns for separation of compounds preceding MS analysis. The review is divided in two parts according to the used separation method, namely CEC and capillary LC (cLC). Based on our overview, monolithic CEC-MS technique have been more focused on the syntheses of highly specialized and selective separation phase materials for fast and efficient separation of specific types of analytes. In contrast, monolithic cLC-MS is more widely used and is often employed, for instance, in the analysis of oligonucleotides, metabolites, and peptides and proteins in proteomic studies. While poly(styrene-divinylbenzene)-based and silica-based monolithic capillaries found their place in proteomic analyses, the other laboratory-synthesized monoliths still wait for their wider utilization in routine analyses. The development of new monolithic materials will most likely continue due to the demand of more efficient and rapid separation of increasingly complex samples.

Tuning preparation conditions towards optimized separation performance of thermally polymerized organo-silica monolithic columns in capillary liquid chromatography

Tuning of preparation conditions, such as variations in the amount of a porogen, concentration of an aqueous acid catalyst, and adjustment in polymerization temperature and time, towards optimized chromatographic performance of thermally polymerized monolithic capillaries prepared from 3-(methacryloyloxy)propyltrimethoxysilane has been carried out. Performance of capillary columns in reversed-phase liquid chromatography was assessed utilizing various sets of solutes. Results describing hydrophobicity, steric selectivity, and extent of hydrogen bonding enabled comparison of performance of hybrid monolithic columns prepared under thermal (TSG) and photopolymerized (PSG) conditions. Reduced amounts of porogen in the polymerization mixture, and prolonged reaction times were necessary for the preparation of monolithic columns with enhanced retention and column efficiency that reached to 111,000 plates/m for alkylbenzenes with shorter alkyl chains. Both increased concentration of catalyst and higher temperature resulted in faster polymerization but inevitably in insufficient time for pore formation. Thermally polymerized monoliths produced surfaces, which were slightly more hydrophobic (a methylene selectivity of 1.28±0.002 TSG vs 1.20±0.002 PSG), with reduced number of residual silanols (a caffeine/phenol selectivity of 0.13±0.001 TSG vs 0.17±0.003 PSG). However, steric selectivity of 1.70±0.01 was the same for both types of columns. The batch-to-batch repeatability was better using thermal initiation compared to monolithic columns prepared under photopolymerized conditions. RSD for retention factor of benzene was 3.7% for TSG capillaries (n=42) vs. 6.6% for PSG capillaries (n=18). A similar trend was observed for columns prepared within the same batch.

A combination of single-drop microextraction and open tubular capillary electrochromatography with carbon nanotubes as stationary phase for the determination of low concentration of illicit drugs in horse urine

In this study we developed an interesting alternative to HPLC-mass spectrometry for the quantification of seven important drugs of abuse in racehorses. The procedure proposed in this work is a combination of single-drop microextraction (SDME) and an open tubular capillary electrochromatography (OT-CEC) using multi-wall carbon nanotubes (MWCTs) immobilized into a fused-silica capillary as a stationary phase. The SDME showed to be a powerful tool for extraction/preconcentration of the seven drugs analyzed in the study, showing an enrichment factor between 38- and 102-fold depending on the drug. We have investigated the electrophoretic features of MWCTs immobilized fused-silica capillary by covalent modification of the inner surface of the capillary. The results show a good run-to-run, day-to-day and capillary-to-capillary reproducibility of the method. Compared with the capillary zone electrophoresis (CZE), the coating of the capillary allowed the separation of the analytes with high resolution, with less band-broadening and without distortion of the baseline. The interactions between the analytes and the MWCTs resulted in an increased migration time and probably this was the reason of the front tailing effect. The results showed a good capillary efficiencies and an improved of the electrophoretic separation.

[Recent advances in capillary electrochromatography and its coupling techniques]

As a novel micro-separation technique, capillary electrochromatography (CEC) has the merits of high efficiency, high selectivity, high resolution and rapid analysis. However, the small-volume injection manipulated in capillary dimensions poses a great challenge for detectors in achieving high sensitivity. Currently, one of the major researches into CEC involves the development of some sensitive detection modes. The general introduction, which includes the historical perspectives and the principles of CEC, is briefly described. The recent advances about CEC coupled with various detectors and its applications in the separation of complex samples are summarized. A total of 141 references are reviewed.

CEC of phytochemical bioactive compounds

Although there are many publications related to technological or methodological developments of CEC, few focus on the analysis of natural products, especially phytochemical bioactive compounds. This review summarized the application of CEC in the analysis of phytochemical bioactive components, including flavonoids, nucleosides, steroids, lignans, quinones and coumarins, as well as fingerprint analysis of herbs. The strategies for optimization of CEC conditions and detection were also discussed.

CEC: selected developments that caught my eye since the year 2000

During the last decade, a number of new developments have emerged in the field of CEC. This paper focuses only on monolithic columns prepared from synthetic polymers. Monolithic columns have become a well-established format of stationary phases for CEC immediately after their inception in the mid-1990s. They are readily prepared in situ from liquid precursors. Also, the control over both porous properties and surface chemistries is easy to achieve. These advantages make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. Since the number of papers concerned with just this single topic of polymer-based monolithic CEC columns is large, this overview describes only those approaches this author found interesting.

Capillary electrochromatography and on-line concentration

Capillary electrochromatography (CEC) is a micro-separation technique that combines the advantages of capillary zone electrophoresis with those of high-performance liquid chromatography. Accordingly, it has attracted extensive attention over the last decade. Among the stationary phases for CEC, monolithic stationary phase has been regarded as the most suitable stationary phase for CEC because of its simple preparation, the elimination of frits, and its excellent performance. In this chapter, procedures for preparing CEC monolithic columns with an improved configuration, in which there are stationary phases at both sides of detection window and no stationary phase at detection window, are presented. The separation of acidic and basic compounds on such monolithic columns is used as an example to demonstrate CEC separation protocol. Additionally, an on-line concentration technique in CEC is presented. As a result of the coexistence of stationary phase and electric field in a CEC column, it is possible to employ chromatographic zone sharpening and field-amplified sample stacking effects simultaneously to improve CEC detection sensitivity.

Mixture-designed electrolytes for the MEKC separation of natural and synthetic steroids

In this work, the separation of 11 natural and synthetic steroids was studied using MEKC electrolytes modified by property-selected organic solvents: ethanol, ACN, and THF. The interplay between electrophoretic behavior and structural features was disclosed and the effects of organic modifiers to modulate retention and to alter selectivity were discussed in terms of system linear solvation energy relationships (LSER). The LSER indicated the total organic solvent percentage in the electrolyte as a major parameter to control retention and as a minor contribution, the hydrogen bond acidity. By evaluating the electropherograms obtained from mixture-designed electrolytes, a favorable separation condition for all solutes was achieved in ca. 25 min with an electrolyte composed of 20 mmol/L sodium tetraborate at pH 9.4, 20 mmol/L SDS and 20% EtOH (0.80% CV for migration time and 2.5% CV for peak area, n = five consecutive injections). The applicability of the proposed separation condition was demonstrated by the inspection of estrogens in urine sample (puberty stage).

Analysis of free and conjugated phytosterols in tobacco by an improved method using gas chromatography-flame ionization detection

An improved and simple method using capillary gas chromatography coupled with a flame ionization detection system (GC-FID) has been developed for quantitative analysis of free and conjugated phytosterols in tobacco. Direct acid and alkaline hydrolysis were first introduced into tobacco analysis to liberate free phytosterols from conjugates, followed by extraction with hexane, derivatization to trimethylsilyl ether derivatives and finally GC quantitative determination. The generality and applicability of this improved method for analyzing free and conjugated phytosterols in tobacco were validated after a series of optimization and comparison were done. Compared with traditional methods, this improved method not only simplified procedures, but also saved time and solvent. The limits of detection (LODs) of phytosterols varied from 0.35 to 0.10 microg mL(-1), the relative standard deviations (RSD) were from 2.3% to 3.3% and recovery ranged from 87% to 99%. The analysis results showed that total phytosterols' content in tobacco ranged from 1.0 to 2.5 mg g(-1), and most phytosterols existed as conjugates, only approximately 15-25% phytosterols existed in free-form. Ergosterol was only found in mildewy flued-cured tobacco and the level was approximately 0.2-0.25 mg g(-1).

Wide-bore monolithic column for electrochromatography

A new wide-bore electrophoresis (WE) system adopting an inner cooling device was set up to perform electrochromatography. In this system, a quartz tube of 1.2 mm inner diameter was used as the separation channel. The Joule heat generated during electrophoresis was removed timely through the outer surface of the quartz tube and a cooling capillary inserted into the quartz tube. A proper coolant passed through the cooling capillary to further improve the cooling efficiency. In the primary research, a polyacrylamide monolithic column was successfully prepared in this quartz tube. Then it was evaluated in the electrochromatographic mode. An electric field strength as high as 625 V/cm can be applied to this system without obvious deviation of the current from the linear curve of the Ohm plot. Sample volume as high as 1 microL was injected into the WE system and reasonable efficiency was obtained for separation of the test compounds.

Development of a quality evaluation method forFructus schisandraeby pressurized capillary electrochromatography

A pressurized CEC (pCEC) method with postcolumn detection cell had been developed for quantifying the lignans from Fructus schisandrae extracts. The effects of different experimental conditions, such as the ACN content of the mobile phase, the concentration and pH of the buffer, the applied voltage, and the supplementary pressure were studied. Five lignans (schisandrin, gomisin A, schisantherin C, deoxyschizandrin, schisandrin B) were baseline separated using a mobile phase of ACN-phosphate buffer (pH 5.4; 5 mM) (40:60 v/v) under -4 kV applied voltage. The method showed the satisfactory retention time and peak area repeatability. The calibration curves were linear in the range 50.0-1000.0 microg/mL for schisandrin, 20.0-500.0 microg/mL for gomisin A, 10.0-200.0 microg/mL for schisantherin C, 20.0-500.0 microg/mL for deoxyschizandrin, and 20.0-500.0 microg/mL for schisandrin B. The correlation coefficients were between 0.9978 and 0.9989. With this pCEC system, fingerprints of F. schisandrae were preliminarily established to distinguish two members S. chinensis (Turcz.) Baill. and S. sphenanthera Rehd. Et Wils. of F. schisandrae by characteristic peaks, and evaluate the quality of various sources of raw materials by determining the contents of the five lignans.

Porous polyacrylamide monoliths in hydrophilic interaction capillary electrochromatography of oligosaccharides

Capillary electrochromatography (CEC) of oligosaccharides in porous polyacrylamide monoliths has been explored. While it is possible to alter separation capacity for various compounds by copolymerization of suitable separation ligands in the polymerization backbone, "blank" acrylamide matrix is also capable of sufficient resolution of oligosaccharides in the hydrophilic interaction mode. The "blank" acrylamide network, formed with a more rigid crosslinker, provides maximum efficiency for separations (routinely up to 350,000 theoretical plates/m for fluorescently-labeled oligosaccharides). These columns yield a high spatial resolution of the branched glycan isomers and large column permeabilities. From the structural point of view, some voids are observable in the monoliths at the mesoporous range (mean pore radius ca. 35 nm, surface area of 74 m2/g), as measured by intrusion porosimetry in the dry state.

Preparation of particle-fixed silica monoliths used in capillary electrochromatography

Fused-silica capillarieswere packed with porous 1 microm bare silica microspheres and immobilized by potassium silicate-formamide in order to obtain columns with silica-based monolithic packing. After curing, the particle-fixed monolithic columns were octadecylated insitu with dimethyloctadecylchlorosilane. The columns were mechanically strong and permeable. No noticeable loss in efficiency was found after using a column continuously for 1 month. The performances of the particle-fixed silica monolithic columns were evaluated for CEC under RP conditions. High separation efficiency (about125 200 plates/m) was obtained by using these new types of columns.

Application of monolithic (continuous bed) chromatographic columns in phytochemical analysis

One and a half decade passed since the pioneering work on synthesis and application of non-particulate monolithic stationary phases for liquid chromatography was published by S. Hjertén et al. [S. Hjertén, J.L. Liao, R. Zhang, J. Chromatogr. 473 (1989) 273]. This technique attracted much interest and effort of the researchers developing chromatographic methods and designing chromatographic stationary phases due to several generic qualities of the monolithic (continuous bed) technique. Advantages include: flexibility of the technique in sense of chemistries and functional compositions of the resultant stationary phases; low separation impedance (ratio of pressure drop and efficiency) of monolithic columns; compatibility with micro and nanoformat separations; low time and labour consumption and cost-efficiency. Not surprisingly, these materials attracted interest from phytochemists as plants constitute a complex matrix. However to date, not many successful studies were published in the area of monolithic materials for solving plant metabolomics problems or substituting common particulate materials with monolithic stationary phases in phytochemical analysis. This paper provides an overview.

A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries

Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent.

Recent applications of capillary electrophoresis-electrospray ionisation-mass spectrometry in drug analysis

A critical review of applications for the period 2000-2004, taken from the Web of Knowledge database, of the technique capillary electrophoresis-electrospray ionisation-mass spectrometry (CE-ESI-MS) in drug analysis is presented. The review is concerned with molecules of mass less than 500 Da, chosen according to selected structural classes in which they give ESI signals primarily as [M+H](+) ions although other ions, such as [M-H](-), [M+Na](+), and [M+NH(4)](+), are also reported. These structural classes are drugs with amine-containing side chains, drugs with N-containing saturated ring structures, 1,4-benzodiazepines, other heterocyclic hypnotics, carbohydrates, sulphonylureas, anthracyclines, sulphonamides, penicillins, cephalosporins, tetracyclines, nitrocatechols, steroids, flavonoids/polyphenols, cannabinols, and miscellaneous molecules. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion-trap, triple quadrupole, and time of flight-mass spectrometers. The review gives a critical evaluation of these recent CE-ESI-MS analytical methods in drug analysis. Analytical information on, for example, sample concentration techniques, CE separation conditions, recoveries from biological media and limits of detection (LODs) are provided. Potential applications of CE-MS to particular drugs or drug classes are also briefly discussed in the text.

Phosphorescence of 8-azasteroids and related compounds

We have investigated the electron absorption, fluorescence and phosphorescence spectra of 8-azasteroids and model compounds containing enaminodicarbonyl fragment. It has been shown that the investigated compounds have absorption and phosphorescence spectra similar in form and position. The results obtained permit the conclusion that the main deactivation channel of the excited singlet state is the intersystem crossing. It is suggested that the investigated 8-azasteroids of enaminodicarbonyl series under light irradiation undergo phototransformations presumably into derivatives with a gamma-pyridone fragment.

Recent developments in the field of monolithic stationary phases for capillary electrochromatography

This review summarizes the contributions to the rapidly growing area of monolithic columns based on both silica and synthetic polymers for capillary electrochromatography and chip electrochromatography, with a focus on those published during the year 2004. A wide variety of both modified approaches to the "old" monoliths and new monoliths have been reported despite the very short period of time covered. This demonstrates that monolithic stationary phases have become a well-established format in the field of electrochromatography. The simplicity of their preparation as well as the good control over their porous properties and surface chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials.

Review coupling of capillary electrochromatography to mass spectrometry

This review discusses the development of capillary electrochromatography (CEC) coupled to mass spectrometric (MS) detection over the last few years. Major topics addressed are instrumental setups employed and applications of this technology published in the recent literature. The instrumental section includes a discussion of the most commonly used interfaces for the hyphenation of CEC and MS as well as ionization techniques. Applications reviewed in this paper come from a variety of different fields such as the analysis of biomolecules like proteins, peptides, amino acids or carbohydrates, chiral separations or the analysis of pharmaceutical an their metabolites in a series of matrices.

Capillary electrochromatography of sterols and related steryl esters derived from vegetable oils

Capillary electrochromatographic (CEC) separations of plant sterols and related esters were evaluated under various conditions. Stationary phases included octadecylsilica (C18) and triacontylsilica (C30). Mobile phases comprised acetonitrile, tetrahydrofuran, and tris(hydroxymethyl) aminomethane buffers in aqueous or non-aqueous systems. Apart from notable differences in component resolution, both C18 and C30 phases had dramatic influence on the elution behavior of the title compounds. Generally, C18 had greater selectivity for most components with elution patterns in consistence with the hydrophobicity of side chain structures, while no predictable trend of analyte elution was observed in CEC with C30. In the latter column systems, analyte separations appeared to be improved by conversion to benzoates or ferulates. Twenty-four-epimers of campesterol acetate and 7-campestenol acetate as well as the campesterol-stigmasterol pair were readily resolved by CEC with either phase. However, the cholesterol-stigmasterol pair was barely resolved and had an elution order opposite to that of their acetates or benzoates. Potential applicability of the CEC technique in the analysis of sterols and sterol ferulates in vegetable oil is demonstrated.

Preparation and characterization of alkylated polymethacrylate monolithic columns for micro-HPLC of proteins

Protein separations were carried out by micro-high performance liquid chromatography (micro-HPLC) with surface alkylated monolithic columns, which were prepared by in situ copolymerization of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) in the presence of dodecanol and toluene as porogens. First, glycidyl groups at the surface of the porous monolith were hydrolyzed with sulfuric acid. The hydroxyl groups thus formed were then reacted with n-alkyl chloride to form alkylated stationary phase. Separation performance for proteins on columns with C18 and C8 stationary phases was compared. The results showed that a poly(GMA-EGDMA) support derivatized with octadecyl moieties could achieve much better resolution than one with octyl groups. A protein mixture was separated with the octadecylated poly-(GMA-EGDMA) monolithic column, and the effluent peaks were collected and analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The physical properties of the monolithic columns such as column morphology, surface area, mesopore size distribution, and column permeability were further characterized by scanning electron microscopy (SEM), multipoint BET nitrogen adsorption/desorption, and Darcy's law, respectively.

State-of-the-art of the hyphenation of capillary electrochromatography with mass spectrometry

The high separation efficiency and loading capacity of capillary electrochromatography (CEC) make it an attractive separation mode for coupling with mass spectrometry (MS), which has the ability to unambiguously identify analytes with high selectivity and sensitivity. We present an overview of recent advances on both instrumentation and separation columns employed in CEC-MS systems. In particular, the main characteristics of the stationary phases, as well as the configurations of the column outlet that are related with the coupling arrangements of the MS ionization sources, are reported. At present, packed columns and conventional electrospray ionization (ESI) sources are mainly employed in CEC-MS. Nevertheless, the use of monolithic capillary columns and nanoelectrospray sources has the potential for wide acceptance in the next future. Moreover, the main features of several mass analyzers including ion trap, quadrupole, time-of-flight, magnetic sector, and Fourier transform-ion cyclotron resonance are examined. Finally, current applications of this technology, mainly in the pharmaceutical field and proteomics, are reviewed.

Development and application of polymeric monolithic stationary phases for capillary electrochromatography

Monolithic columns for capillary electrochromatography are receiving quite remarkable attention. This review summarizes results excerpted from numerous papers concerning this rapidly growing area with a focus on monoliths prepared from synthetic polymers. Both the simplicity of the in situ preparation and the large number of readily available chemistries make the monolithic separation media a vital alternative to capillary columns packed with particulate materials. Therefore, they are now a well-established stationary phase format in the field of capillary electrochromatography. A wide variety of synthetic approaches as well as materials used for the preparation of the monolithic stationary phases are presented in detail. The analytical potential of these columns is demonstrated with separations involving various families of compounds and different chromatographic modes.

Structural characterization of neutral oligosaccharide mixtures through a combination of capillary electrochromatography and ion trap tandem mass spectrometry

A CEC/ESI-MS/MS combined system has been developed for the separation and on-line structural analysis of neutral oligosaccharides. Various types of isomeric oligosaccharides were first successfully separated by CEC using polar monolithic columns, while the on-line tandem mass spectrometry has been explored to differentiate and elucidate the structures of isomeric oligosaccharides. The experimentally obtained tandem spectra usually provide sequence, branching, and linkage information. Oligosaccharide isomers with a different monomeric composition and branching showed different patterns of glycosidic linkage cleavage (B- and Y-ion series), allowing us to deduce their sequence and branching points. Isomers with different linkages were distinguished by identifying cross-ring fragment ions (A-ion series). While (1-->4) linkages yielded dominant (0,2)A ions, (1-->6) linkages showed an extensive and complete cross-ring cleavage series: (0,2)A, (0,3)A, and (0,4)A ions. Although the anomeric configurations and monosaccharide identification are rarely obtained from tandem MS, the relevant mixture components can be completely resolved with high-efficiency CEC columns featuring a polar functionality.

Capillary electrochromatography: a rapidly emerging separation method

This overview concerns the new chromatographic method--capillary electrochromatography (CEC)--that is recently receiving remarkable attention. The principles of this method based on a combination of electroosmotic flow and analyte-stationary phase interactions, CEC instrumentation, capillary column technology, separation conditions, and examples of a variety of applications are discussed in detail.

Adsorption equilibria of butyl- and amylbenzene on monolithic silica-based columns

The adsorption isotherms of butyl- and amylbenzene on silica monolithic columns were measured by frontal analysis. The external, internal and total porosities of these columns were determined by inverse size-exclusion chromatography. The adsorption isotherms are concave upward in the entire concentration range investigated. They were fitted to the anti-Langmuir model, an unusual model in liquid-solid and liquid-liquid phase equilibria. Band profiles under overloaded conditions were recorded. They were in good agreement with the profiles calculated using th,e lumped pore diffusion model of chromatography and these adsorption isotherms.

Separation and detection of neuroactive steroids from biological matrices

This review is based on a selection of research papers published mainly in the last decade and it describes various analytical aspects of separation and detection of neuroactive steroids in biological matrices.

Separation of peptides on mixed mode of reversed-phase and ion-exchange capillary electrochromatography with a monolithic column

The mixed mode of reversed phase (RP) and strong cation-exchange (SCX) capillary electrochromatography (CEC) based on a monolithic capillary column has been developed. The capillary monolithic column was prepared by in situ copolymerization of 2-(sulfooxy)ethyl methacrylate (SEMA) and ethylene dimethacrylate (EDMA) in the presence of porogens. The sulfate group provided by the monomer SEMA on the monolithic bed is used for the generation of the electroosmotic flow (EOF) from the anode to the cathode, but at the same time serves as a SCX stationary phase. A mixed-mode (RP/SCX) mechanism for separation of peptides was observed in the monolithic column, comprising hydrophobic and electrostatic interaction as well as electrophoretic migration at a low pH value of mobile phase. A column efficiency of more than 280,000 plates/m for the unretained compound has been obtained on the prepared monoliths. The relative standard deviations observed for t(0) and retention factors of peptides were about 0.32% and less than 0.71% for ten consecutive runs, respectively. Effects of mobile phase compositions on the EOF of the monolithic column and on the separation of peptides were investigated. The selectivity on separation of peptides in the monolithic capillary column could be easily manipulated by varying the mobile phase composition.

Monolithic stationary phases for liquid chromatography and capillary electrochromatography

A monolithic stationary phase is the continuous unitary porous structure prepared by in situ polymerization or consolidation inside the column tubing and, if necessary, the surface is functionalized to convert it into a sorbent with the desired chromatographic binding properties [J. Chromatogr. A 855 (1999) 273]. Monolithic stationary phases have attracted considerable attention in liquid chromatography and capillary electrochromatography in recent years due to their simple preparation procedure, unique properties and excellent performance, especially for separation of biopolymers. This review summarizes the preparation, characterization and applications of the monolithic stationary phases. In addition, the disadvantages and limitations of the monolithic stationary phases are also briefly discussed.

Metabolomics--the link between genotypes and phenotypes

Metabolites are the end products of cellular regulatory processes, and their levels can be regarded as the ultimate response of biological systems to genetic or environmental changes. In parallel to the terms 'transcriptome' and proteome', the set of metabolites synthesized by a biological system constitute its 'metabolome'. Yet, unlike other functional genomics approaches, the unbiased simultaneous identification and quantification of plant metabolomes has been largely neglected. Until recently, most analyses were restricted to profiling selected classes of compounds, or to fingerprinting metabolic changes without sufficient analytical resolution to determine metabolite levels and identities individually. As a prerequisite for metabolomic analysis, careful consideration of the methods employed for tissue extraction, sample preparation, data acquisition, and data mining must be taken. In this review, the differences among metabolite target analysis, metabolite profiling, and metabolic fingerprinting are clarified, and terms are defined. Current approaches are examined, and potential applications are summarized with a special emphasis on data mining and mathematical modelling of metabolism.

Chromatographic analysis of plant sterols in foods and vegetable oils

This paper reviews recently published chromatographic methods for the analysis of plant sterols in various sample matrices with emphasis on vegetable oils. An overview of structural complexities and biological/nutritional aspects including hypocholesterolemic activities of phytosterols is provided in the Section 1. The principal themes of the review highlight the development and application of chromatographic techniques for the isolation, purification, separation and detection of the title compounds. Pertinent gas chromatographic and high-performance liquid chromatographic methods from the literature are tabulated to illustrate common trends and methodological variability. The review also covers specific analyses of natural/synthetic standard mixtures to shed light on potential applicability in plant sample assays. Examples of combined chromatographic techniques linked in tandem for the analysis of complex samples are included. Elution characteristics of sterol components are discussed in the context of analyte substituent effects, structural factors and stationary/mobile phase considerations.

Gas chromatography and high-performance liquid chromatography of natural steroids

This review article underlines the importance of gas chromatography (GC), high-performance liquid chromatography (HPLC) and their hyphenated techniques using mass spectrometry (MS) for the determination of natural steroids, especially in human biological fluids. Steroids are divided into eight categories based on their structures and functions, and recent references using the above methodologies for the analysis of these steroids are cited. GC and GC-MS are commonly used for the determination of volatile steroids. Although HPLC is a widely used analytical method for the determination of steroids including the conjugated type in biological fluids, LC-MS is considered to be the most promising one for this purpose because of its sensitivity, specificity and versatility.

Recent applications of capillary electrochromatography

A review is presented of the most important recent applications of capillary electrochromatography (CEC) for the analysis of acidic, basic, and neutral compounds, of biomolecules, environmental substances, natural products, pharmaceuticals, and chiral compounds. Packed-column CEC (packed-CEC), open-tubular (OT-CEC), as well as pressure-assisted CEC (pseudo-CEC) are hereby considered. Papers published between July 1999 and April 2001 were taken into account. Applications before July 1999 have been reviewed in Electrophoresis 1999, 20, 3027-3065.

Capillary electrochromatography for separation of peptides driven with electrophoretic mobility on monolithic column

A mode of capillary electrochromatography for separation of ionic compounds driven by electrophoretic mobility on a neutrally hydrophobic monolithic column was developed. The monolithic column was prepared from the in situ copolymerization of lauryl methacrylate and ethylene dimethacrylate to form a C12 hydrophobic stationary phase. It was found that EOF in this hydrophobic monolithic column was very poor, even the pH value of mobile phase at 8.0. The peptides at acidic buffer were separated on the basis of their differences in electrophoretic mobility and hydrophobic interaction with the stationary phase; therefore, different separation selectivity can be obtained in CEC from that in capillary zone electrophoresis (CZE). Separation of peptides has been realized with high column efficiency (up to 150,000 plates/meter) and good reproducibility (migration time with RSD <0.5%), and all of the peptides, including some basic peptides, showed good peak symmetry. Effects of the mobile phase compositions on the retention of peptides at low pH have been investigated in a hydrophobic capillary monolithic column. The significant difference in selectivity of peptides in CZE and CEC has been observed. Some peptide isomers that cannot be separated by CZE have been successfully separated on the capillary monolithic column in this mode with the same buffer used.

Application of capillary electrochromatography using macroporous polyacrylamide columns for the analysis of lignans from seeds of Schisandra chinensis

Capillary electrochromatography (CEC) using polymer-based monolithic stationary phase has been developed as a promising method for the determination of lignans of Schisandra chinensis. The columns were prepared by in situ copolymerisation of acrylamide, N,N'-methylenebisacrylamide, vinylsulfonic acid and lauryl acrylate in presence of poly(ethylene glycol) as a porogenic agent. The columns [33 cm (24.5 cm effective length) x 75 microm I.D.] were successfully used to analyse and quantify the major lignans in extract of the seeds of Schisandra chinensis. Good separations were achieved in less than 35 min. The calibration graphs were linear in the range 0.025-1.0 mg/ml of given lignan with correlation coefficients between 0.9951 and 0.9996. The inter-day reproducibility of the peak area were below 3.9% and the inter-day reproducibility of the migration time were below 4.2%. The results of quantitative CEC analyses were compared with those obtained by reversed-phase HPLC, the levels of schizandrin, gomisin A, gomisin N and wuweizisu C determined by CEC were in a good agreement with those determined by HPLC.