Application of Electroanalytical Detectors in Chromatography

Abstract

Just as the gas chromatographic technique became one of the most frequently used analytical methods in the sixties, the development of high-pressure techniques has made liquid chromatography one of the most dynamically developing methods of today.     

Planar chromatographic method development using the PRISMA optimization system and flow charts

This study presents a modern planar chromatographic method-development procedure, based on the "PRISMA" optimization system, in which the optimum separation is achieved systematically and the structures and properties of the substances to be separated are not known. The procedure consists of three stages. In the first of these the basic conditions the stationary phase, vapor phase, and individual solvents are selected with a TLC procedure (generally in nonsaturated chromatographic chambers). In the second stage, the optimum combination of the selected solvents is determined with the PRISMA model. The third part of the procedure includes the selection of the development mode (circular, linear, or anticircular); the selection of an appropriate forced-flow chromatographic technique (over-pressured layer chromatography or rotation planar chromatography) with high-performance thin-layer chromatographic plates; the transfer of the optimized mobile phase to the various analytical, planar, or column preparative liquid chromatographic techniques; and the selection of the operating conditions. For practical reasons, the optimization process is presented with the help of flow charts.     

Characterization of High‐Pressure Liquid Chromatography Columns using Chromatographic Methods

Abstract

A great variety of columns for liquid chromatography (LC) are available in dimensions ranging from industrial scale to micro‐bore, nano‐bore, and capillary size, and on‐chip columns. The columns may be used in various liquid chromatography modes or in capillary electrochromatography, depending on the support materials and stationary phase chemistry. Every year many new column types are introduced on the market, with improved selectivity and efficiency, long lifetime, and mobile phase compatibility, intended for general use, for liquid chromatography/mass spectrometry (LC/MS) applications, proteomic research, or for the analysis of other specific sample types. Considerable improvement in pH, high‐temperature, and high‐pressure stability of new column types, together with advances in the instrumentation, enabled introduction of capillary, high‐temperature, and ultra‐high‐pressure HPLC into routine practice. Even though reversed‐phase mode is still by the most widely used in contemporary LC, applications of other separation modes (such as ion, normal‐phase, or high‐interaction liquid chromatography (HILC)) have become more frequent recently, because of unique separation selectivity for certain sample types.

Characterization of column quality is not a simple task, because a number of factors should be taken into account, that affect the selectivity, efficiency and resolution of sample separation and the reproducibility of chromatographic data. These include the type of the support, the arrangement and density of the stationary phase on the adsorbent surface, the homogeneity of the chromatographic bed, etc. Various physicochemical techniques are used for characterization of the properties of column packings however, most of them are suitable for bulk materials only and cannot be directly applied for commercial columns without damaging them. Not to destroy the columns, often precious and expensive, practicing chromatographers can apply chromatographic methods to characterize columns and evaluate their analytical suitability under real‐life conditions, where the intermolecular interactions between the analytes, the stationary phase, and the mobile phases affect the retention. The present review reports various chromatographic tests and strategies available for column evaluation.     

Two new compounds from <Emphasis Type="Italic">Phyllanthus niruri</Emphasis>

Three compounds were isolated from Phyllanthus niruri Linn. One effective method, improved dry column liquid chromatography for isolating these compounds, was applied on a silica gel column. It is a combination of conventional dry column chromatographic and flash chromatographic techniques. Structures of those obtained compounds were elucidated by means of spectral techniques including IR, MS, and 1D NMR and 2D NMR. Compound 1 was elucidated as 2,3,5,6-tetrahydroxybenzyl acetate. Compound 2 , 2,4,5-trihydroxy-3-(4,6,7-trihydroxy-3-oxo-1,3-dihydroisobenzofuran-5-yl)-benzoic acid methyl ester, was given the name phyllangin, and compound 3 was named corilagin. Compounds 1 and 2 are new compounds.Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 380–382, September–October, 2004.     

Correlation of TLC,HPTLIC and PMD Results and Their Transfer to HPLC Systems

Abstract

The correlation of the results of five thin-layer chromatographic techniques and their transfer to high performance liquid chromatography are reported. The data obtained indicate that high performance thin-layer chromatographic results are faithfully reproduced by high performance liquid chromatography. Although plates were not activated, and mixed solvents were used, no major differences were observed between thin layer and high performance liquid chromatography.     

High Performance Liquid Chroma Tography of Cytokinins

Abstract

Details are presented of normal- and reversed-phase high performance liquid chromatographic systems suitable for the purification and the separation of a range of cytokinins. In the normal-phase mode an aminopropylsilyl column with volatile organic solvents as mobile phases was used while reversed-phase chromatography was carried out with a base deactivated octadecylsilyl column.     

Planar chromatography at the turn of the century.

An overview of the state-of-the-art of modern thin-layer chromatography (planar chromatography) is presented with emphasis on the complementary features of thin-layer and column liquid chromatographic separations. The reasons for selecting thin-layer chromatography for a particular analysis are identified by its attributes: a disposable stationary phase; simultaneous parallel separations; static detection free of time constraints; storage device for chromatographic information; all sample components are observed in the chromatogram. Future prospects for improved separation performance in TLC using zone refocusing, forced flow and electroosmotic flow methods are discussed as well as increasing zone capacity by using two-dimensional development and coupling to column chromatographic methods. Advances in coupling thin-layer chromatography with spectroscopic methods for structural elucidation are also considered. Finally, some predictions are made for how thin-layer chromatography will be practiced in the future.     

Characterization of in Situ Generated Ionene Micellar Mimetic Stationary Phases for Liquid Chromatography

ABSTRACT

Micellar mimetic ionenes are linear cationic polyelectrolytic molecules having dimethylammonium charge centers interconnected by alternating alkyl chain segments containing x and y number of methylene groups where x is equal to 3 and y is greater than 14. These ionenes form intramolecular aggregates with behavior that mimics traditional surfactant micelle properties. In this paper we report the use of [3, 16]-ionene to prepare an in situ generated stationary phase on aminopropylated silica for liquid chromatography. This phase was found to exhibit chromatographic characteristics different from those of conventional amino, C-18 or phenyl stationary phases. This ionene column has facilitated the separation of some cis-, trans-, and ortho-, meta-, para-isomeric components, planar and non-planar aromatic hydrocarbons as well as alpha - beta ring attachment compounds.     

Application to Gel Termination Chromatography of Micro High Performance Liquid Chromatography

Abstract

The raicroscale liquid chromatographic tecnnique was applied to gel perraination chromatography. As the results, the miniaturized GPC column requires smaller amounts of sample, packing materials and carrier solvent than those required with the ordinary GPC column, and it would be applicable to preparatory experiments to select the operation conditions for fractionation by GPC.     

An overview of techniques and strategies for isolation of flavonoids from the genus Erythrina

Plants in the genus Erythrina is a potential source of chemical constituents, one of which is flavonoids, which have diverse bioactivities. To date, literature on the flavonoids from the genus Erythrina has only highlighted the phytochemical aspects, so this review article will discuss isolation techniques and strategies for the first time. More than 420 flavonoids have been reported in the Erythrina genus, which are grouped into 17 categories. These flavonoid compounds were obtained through isolation techniques and strategies using polar, semi-polar, and non-polar solvents. Various chromatographic techniques have been developed to isolate flavonoids using column flash chromatography, quick column chromatography, centrifugally accelerated thin-layer chromatography, radial chromatography, medium-pressure column chromatography, semi-preparative high-performance liquid chromatography, and preparative high-performance liquid chromatography. Chromatographic processes for isolating flavonoids can be optimized using multivariate statistical applications such as response surface methodology with central composite design, Box–Behnken design, Doehlert design, and mixture design.     

Determination of Propylthiouracil in Human Breast Milk by Direct Injection High Performance Liquid Chromatography

Abstract

A high-performance liquid chromatographic(HPLC) method was developed for the assay of propylthiouracil in human breast milk. After filtration with membran filter(Molcut II), the eluent was injected into a liquid chromatogaph equipped with C₁₈ precolumn and analytical column in series according to column switching techniques. This method is sufficiently sensitive for most pharmacokinetic studies in human breast milk. The concentration of propylthiouracil was linear over the 50 – 5000ng/ml range. The recovery and the coefficient of variation was 92.0 – 100.6% and 1.6 – 2.9%, respectivery. This assay has the advantages of specificity, simplicity and reproducibility for the measurement of propylthiouracil in human breast milk.     

Evaluation of the Plasma Chromatograph as a Qualitative Detector for Liquid Chromatography

Abstract

The applicability of the plasma chromatograph as a sensitive, qualitative detector for liquid chromatography (LC) is demonstrated. Only a fraction of an LC column effluent directly introduced is needed to produce a qualitative mobility spectrum. Most LC carrier fluids either exhibit no response in plasma chromatographic spectra or do not interfere with LC peak components. Using an indirect technique, components separated by TLC can be identified by plasma chromatography.     

Microcolumn Liquid Chromatography Combined with Computer-Assisted Retention Prediction System for Polycyclic Aromatic Hydrocarbons in Extract from Diesel Particulate Matter

Abstract

Recent advances in column and instrument technology have made the development of d new generation of high-resolution microcolumn liquid chromatography possible. In addition to offering reduced solvent consumption, this chromatographic technique also yields higher mass sensitivities than those in conventional systems. In this study, the applicability of this technique to the analysis of polycyclic aromatic hydrocarbons (PAH) is investigated. PAH in the extract from diesel particulate matter were analyzed to demonstrate the utility of this approach combined with the computer-assisted retention prediction. The technique proposed in this study makes very clean and high cost-performance environmental analysis possible.     

Identification of Iridoids,Flavonoids and Triterpenes from the Methanolic Extract of Melampyrum bihariense A. Kern. and the Antioxidant Activity of the Extract

Melampyrum bihariense A. Kern. (Scrophulariaceae), a plant species used in traditional medicine for the treatment of rheumatic disorders and skin infections, was investigated with regard to its antioxidant activity and identification of its bioactive chemical constituents. The crude methanolic extract of the aerial parts of M. bihariense was examined by the spectrophotometric DPPH (1,1-diphenyl-2-picrylhydrazyl) and ferric reducing antioxidant power methods. The free radical scavenging capacity (SC₅₀) of the extract was found by the DPPH method to be 27.10 mg mL⁻¹, and the ferric reducing ability equivalent to ascorbic acid at 50 mg mL⁻¹ was 0.709 μg mL⁻¹. The chemical composition of this highly effective in the methanolic extract was analysed, and the main compounds were isolated through solvent–solvent partition, and multiple chromatographic separations, including column chromatography, vacuum liquid chromatography, centrifugal planar chromatography and preparative thin-layer chromatography. The structures were established by one- and two-dimensional NMR and liquid chromatography-mass spectrometry. The iridoids aucubin (1), 8-epi-loganin (2) and mussaenoside (3), the flavones apigenin and luteolin and the triterpene acids ursolic acid and oleanolic acid were identified; components 2, 3, ursolic acid and oleanolic acid for the first time in this species. The present study reveals that M. bihariense exerts antioxidant activity, and the iridoids, flavonoids and triterpene acids may be the main bioactive constituents of its methanolic extract.

     

Analysis of 2-Acetylaminofluorene in Laboratory Animal Chow by Reverse Phase Liquid Chromatography

Abstract

A high speed liquid chromatographic procedure for analysis of 2-acetylaminofluorene (2-AAF) in laboratory animal chow is presented. The procedure is rapid and uncomplicated and provides accurate and precise analysis. The reverse phase liquid chromatography allows minimal clean-up of extracts with good column stability and high sample thru-put. Linearity and minimum detectable limit are discussed.     

A Rapid Isolation of Human Chorionic Gonadotropin and Its Subunits by Reversed-Phase High Performance Liquid Chromatography

Abstract

A rapid isolation of human chorionic gonadotropin and its subunits from a commercially available concentrate of human urine has been achieved using reversed-phase high performance liquid chromatography. With μBondapak C₁₈ columns and a gradient employing aqueous trifluoroacetic acid as one solvent and dilute trifluoroacetic acid in acetonitrile as the other, complete separation can be accomplished in one day whereas standard column chromatographic procedures take about two weeks. Specific radioimmunoassays, polyacrylamide gel electrophoresis, and amino acid analyses were used to identify and characterize chromatographic peaks.     

Interference of Transformer oil Matrices to the Internal Standards on PCB Quantification

Abstract

Polychlorinated biphenyls (PCBs) are toxic, perssstent, global environmental contaminants which were formulated as complex mixtures of congeners. Many methods have been developed in the past to analyze PCB in transformer oil samples for regulatory purposes. The most important consideration in the cleanup procedure is the ability to remove the oil from the sample matrix, since trace amount of oil will interfere with the subsequent GC-MS analysis. Electron capture detection (ECD) has been the most common method for gas chromatographic analysis of PCBs because of its high sensitivity toward halogenated compounds. ECD can also respond to some non-PCB compound resulting in biased concentrations of PCB. In this work, a two-stage cleanup method, using DMSO liquid/liquid extraction and HPLC column chromatography. has been applied to two types of transformer oil. Five internal standards have been selected to show their performance in the presence of different oil matrices. The comparison of the PCB quantification at different conditions for GC-MS and GC-ECD will be demonstrated.     

Sample preparation and isolation using planar chromatographic methods

The state of art of the various preparative planar liquid chromatographic (PLC) methods is summarized, especially for off-line and on-line sample application. The sample purification possibilities for PLC techniques are discussed. Purification and isolation strategies using forced-flow planar chromatographic techniques, such as overpressured layer chromatography and rotation planar chromatography, are suggested in the form of flow charts.     

Semi-Preparative High-Performance Liquid Chromatographic Separation of Potato Glycoalkaloids

Abstract

A semi-preparative high-performance liquid chromatographic method has been developed to separate crude mixtures of the potato glycoalkaloids α-chaconine, α-solanine, commersonine and demissine. Milligram quantities of each substance can be obtained within an 8 hour period. A Zorbax semi-preparative NH₂ column and a solvent system of tetrahydrofuran-water-acetonitrile (55:20:25) were employed for the separation. The flow rate was 1.0 ml/min. Glycoalkaloid separations were monitored using both refractive index and ultraviolet detection (215 nm). Further analyses of these glycoalkaloids were done using analytical high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) to check compound purity and identity.