M. Lafosse

Porous graphitic carbon: A versatile stationary phase for liquid chromatography

Chromatographic stationary phases based on porous graphitic carbon were invented 30 years ago, while columns have been commercially available for 20 years. This special occasion deserved a complete review on this material. In this paper, we describe current knowledge on graphitic carbon stationary phases, based on over 400 fundamental studies and applications.

Original Synthesis of Linear, Branched and Cyclic Oligoglycerol Standards

A variety of authentic standards of linear, branched and cyclic oligomers of glycerol, with well-defined structures and degrees of polymerisation from 2 to 5, have been efficiently synthesised. Linear oligomers were obtained by means of a convergent approach based on regioselective opening of bis(epoxides) with solketal; branched compounds were synthesised using oxidative cleavage of the corresponding anhydrohexitols as the key step. A 6-exo-trig halocyclisation reaction involving heteroatom-tethered unsaturated alcohols permitted an efficient synthesis of the precursors of selected cyclic dimers; larger cyclic oligomers were prepared by two one-pot Williamson reactions using a ditriflate derived from diglycerol. All these methodologies permitted further scaling up.

Comparison of ethoxylated alcohols and polyethylene glycols by high-performance liquid chromatography and supercritical fluid chromatography using evaporative light-scattering detection☆

Abstract Ethoxylated alcohols are surfactants whose oligomer distributions are conventionally determined by high-performance liquid chromatography. However, this method cannot resolve individual oligomers with a high degree of ethoxylation. Further, normal- and reversed-phase liquid chromatography cannot give the fingerprints for both the ethoxylated alcohols and polyethylene glycols, the synthetic residues without surfactant properties. Supercritical fluid chromatography coupled with evaporative light-scattering detection was developed for the analysis of these mixtures which do not contain chromophores.

Selective solid-phase extraction of a triterpene acid from a plant extract by molecularly imprinted polymer

A molecularly imprinted polymer (MIP) has been prepared by a thermal polymerisation method using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linking agent, chloroform as porogenic solvent and an oleanane triterpene compound (18-beta-glycyrrhetinic acid) as imprinted molecule (template). Equilibrium ligand binding experiments were done to assess the performance of the MIP relative to non-imprinted polymer (NIP). After optimisation of SPE protocol (CHCl3 as washing solvent and MeOH as elution solvent), successful imprinting was confirmed by comparison of the recoveries between NIP (5%) and MIP (97%) cartridges. The binding capacity of the MIP for 18-beta-glycyrrhetinic acid was determined to be 0.94 mg g(-1). Four structurally related oleanane triterpenes (18-alpha-glycyrrhetinic acid, oleanolic acid, echinocystic acid, erythrodiol) were selected to assess the MIP selectivity. Experimental data illustrated the influence of functional groups on the triterpene skeleton. The MIP was applied to the solid-phase extraction of triterpenoids from a plant extract prior HPLC analysis. However, CHCl3 was replaced by ACN during the washing step in order to suppress non-specific interactions due to polar matrix components. A selective extraction of 18-beta-glycyrrhetinic acid from hydrolyzed extract of liquorice roots was achieved with a good extraction yield (98%).

Champs d'application d'un nouveau détecteur évaporatif á diffusion de lumière pour la chromatographie liquide hautes performances et la chromatographie en phase supercritique☆

Abstract Application fields of a new evaporative light scattering detector for high-performance liquid chromatography and supercritical fluid chromatography New application capabilities of detection using the measurement of light scattered by microparticles are shown. They are realized with a new evaporative light scattering detector which is (i) compatible with low volatile eluents; no degradation of thermal sensitive compounds is observed; (ii) compatible with supercritical fluid chromatography. These additonal advantages justify the development of new light scattering detectors that can also be used to the stability control of chromatographic systems.

Analysis of pentacyclic triterpenes by LC–MS. A comparative study between APCI and APPI

The analytical performances of three atmospheric-pressure sources, electrospray (ESI), atmospheric-pressure chemical ionization (APCI), and atmospheric-pressure photoionization (APPI), were evaluated for the analysis of pentacyclic triterpenes in liquid chromatography-mass spectrometry (LC-MS). Among these sources, APPI and APCI are particularly well adapted to sensitive analyses of pentacyclic triterpenes by LC-MS. Detection parameters were optimized for both the sources, and the effects of three dopants (toluene, acetone and anisole) on the detection (sensitivity and ion fingerprints in MS spectra) were studied in detail for APPI-MS.The limits of quantification were measured under selected ion monitoring conditions, in the range of 0.005-0.015 mg l(-1) and 0.002-0.84 mg l(-1) in APPI and APCI, respectively, depending on the studied pentacyclic triterpene. Overall, APPI was found more sensitive than APCI in positive ion mode, whereas APCI shows the greatest sensitivity for acidic triterpenes in negative ion mode.Following this study, the developed LC-MS method was used for the characterization of pentacyclic triterpenes in three plant extracts. High amounts of betulinic acid, betulinic aldehyde and betulinic aldehyde acetate were observed in plane bark. The main component of birch bark is betulin and extracts of okoume resin exhibit high amounts of alpha- and beta-amyrin.

High performance liquid chromatography of raw sugars and polyols using bonded silica gels

SummaryBonded silica columns have been evaluated for their ability to separate carbohydrates and polyols. Mobile phases consisting of dichloromethane/methanol produced the best separations in comparison with the acetonitrile/water mixtures commonly used with amino columns. Of all the bonded phases tested, LiChrospher Diol silica provided the best separations, and selectivities were not very different from those obtained on the most popular system using an amino bonded phase and acetonitrile/water as eluent. In addition, diol columns with a dichloromethane/methanol eluent offer excellent stability with no Schiff’s base formation of reducing sugars. Using an evaporative light scattering detector, low limit detection is obtainable (20 ng of glucose from a column) and gradient elution is quite feasible.

Improved evaporative light-scattering detection for supercritical fluid chromatography with carbon dioxide-methanol mobile phases

Abstract The coupling of evaporative light-scattering detection (LSD) with packed-column supercritical fluid chromatography (SFC) using a carbon dioxide-methanol mixture as the mobile phase was studied. A new column-detector interface is described which allows decompression and nebulization of the mobile phase and efficient evaporation of the methanol. In order to economize on experiments, the main parameters which influence the detector response were studied using factorial designs. Within the investigated range, the best detection conditions were deduced. The detection limit of LSD coupled with SFC was improved, permitting the sensitive analysis of solutes with no chromophoric or fluorophoric groups such as fatty acids and fatty alcohols.

Comparison of the retention behavior of polyethoxylated alcohols on porous graphitic carbon and polar as well as apolar bonded-silica phases

Abstract Porous graphitic carbon (Hypercarb S) is presented as a suitable packing for the analysis of polyethoxylated alcohol surfactants by using organic solvents. The separation mechanism is different from that found in normal-phase liquid chromatography and reversed-phase liquid chromatography. This packing permits to analyse simultaneously polyethylene glycol and polyethoxylated alcohol mixtures under gradient elution using water–acetonitrile then acetonitrile–dichloromethane mixtures as mobile phase with evaporative light scattering detection.

Controle de certains systemes de chromatographie liquide haute performance à láide d'un détecteur évaporatif à diffusion de lumière

Abstract The quasi universal character of the light scattering detection of microparticles permits in the case of sugar analysis to choose the column and to control its evolution as a function of time. A simple test is proposed to induce the beginning of the regeneration of resinous CA2+. LiChrosorb Diol support is preferred to aminopropyl silica to realize at the same time a gradient elution and a good sensitivity (30–50 ng).