Détermination des volumes morts et des eff ets extra-colonne en chromatographie liquide de partage à polarité de phase inversée

Les notions de volume mort et de temps de rétention nulle sont primordiales en chromatographie. Elles interviennent dans la détermination des principales grandeurs chromatographiques, indispensables pour s’assurer de la validité d’un système chromatographique, décrire des modèles de rétention théoriques, prédire la rétention des analytes etc. En chromatographie liquide haute performance de partage à polarité de phase inversée, le concept de volume mort est l’objet de polémiques à cause de l’ambiguïté de sa défi nition et des diff érentes méthodes expérimentales mises en œuvre pour le déterminer. Nous avons comparé diff érentes méthodes de mesure des volumes morts totaux et extra-colonne. La pertinence de chaque méthode étudiée est discutée en fonction des objectifs de l’analyste.Void volume and void time are of the utmost importance in chromatography. They are essential for an accurate determination of fundamental chromatographic values. These fundamental values are used for system suitability issues, for theoretical retention descriptions, for prediction of retention of both small and large molecules and for many other issues. In reversed phase liquid chromatography, void volume concept has proven to be controversial because of its defi nition ambiguity and the many different methods proposed. The present work deals with the comparison of the principal methods carried out to determine void volume but also band broadening effect. We discuss also about the care to take in method selection depending on the objectives of the chromatographers

Investigation of the chromatographic process via pulsed-gradient spin−echo nuclear magnetic resonance. Role of the solvent composition in partitioning chromatography

The diffusional properties of molecules in solution vary dramatically upon addition of a solid chromatographic phase. This effect can be monitored via pulsed-gradient spin - echo NMR used in conjunction with moderately fast rotation of the sample (high-resolution magic angle spin- ning) to produce exploitable spectra. The molecular diffusion coefficients observed in this condition are aver- ages reflecting the equilibrium population distribution among the different phases. It is thus possible to use this information for investigating a crucial step of reversed- phase chromatography, namely, the partitioning of the analyte between different phases. In this work, we de- scribe the evolution of the apparent diffusion coefficient of typical solutes for water/acetonitrile solvent mixtures of varying proportions

Simplified analysis of mixtures of small molecules by chromatographic NMR spectroscopy

International audienc

Détermination des volumes morts et des eff ets extra-colonne en chromatographie liquide de partage à polarité de phase inversée

National audienceVoid volume and void time are of the utmost importance in chromatography. They are essential for an accurate determination of fundamental chromatographic values. These fundamental values are used for system suitability issues, for theoretical retention descriptions, for prediction of retention of both small and large molecules and for many other issues. In reversed phase liquid chromatography, void volume concept has proven to be controversial because of its defi nition ambiguity and the many different methods proposed. The present work deals with the comparison of the principal methods carried out to determine void volume but also band broadening effect. We discuss also about the care to take in method selection depending on the objectives of the chromatographers.Les notions de volume mort et de temps de rétention nulle sont primordiales en chromatographie. Elles interviennent dans la détermination des principales grandeurs chromatographiques, indispensables pour s’assurer de la validité d’un système chromatographique, décrire des modèles de rétention théoriques, prédire la rétention des analytes etc. En chromatographie liquide haute performance de partage à polarité de phase inversée, le concept de volume mort est l’objet de polémiques à cause de l’ambiguïté de sa défi nition et des diff érentes méthodes expérimentales mises en œuvre pour le déterminer. Nous avons comparé diff érentes méthodes de mesure des volumes morts totaux et extra-colonne. La pertinence de chaque méthode étudiée est discutée en fonction des objectifs de l’analyste

Détermination des volumes morts et des eff ets extra-colonne en chromatographie liquide de partage à polarité de phase inversée

National audienceVoid volume and void time are of the utmost importance in chromatography. They are essential for an accurate determination of fundamental chromatographic values. These fundamental values are used for system suitability issues, for theoretical retention descriptions, for prediction of retention of both small and large molecules and for many other issues. In reversed phase liquid chromatography, void volume concept has proven to be controversial because of its defi nition ambiguity and the many different methods proposed. The present work deals with the comparison of the principal methods carried out to determine void volume but also band broadening effect. We discuss also about the care to take in method selection depending on the objectives of the chromatographers.Les notions de volume mort et de temps de rétention nulle sont primordiales en chromatographie. Elles interviennent dans la détermination des principales grandeurs chromatographiques, indispensables pour s’assurer de la validité d’un système chromatographique, décrire des modèles de rétention théoriques, prédire la rétention des analytes etc. En chromatographie liquide haute performance de partage à polarité de phase inversée, le concept de volume mort est l’objet de polémiques à cause de l’ambiguïté de sa défi nition et des diff érentes méthodes expérimentales mises en œuvre pour le déterminer. Nous avons comparé diff érentes méthodes de mesure des volumes morts totaux et extra-colonne. La pertinence de chaque méthode étudiée est discutée en fonction des objectifs de l’analyste

Cholesteric bonded stationary phases for high performance liquid chromatography II: synthesis, physico-chemical characterization and chromatographic behavior of a phospho-cholesteric bonded support. A new way to mimic drug/membrane interactions?

International audienceAmong the various methods exploitable to deter- mine the bioavailability of drugs, reversed-phase liquid chromatography (RPLC) appears to be suited to creation of patterns of prediction. In this context a new stationary phase was designed in this work to reproduce, in terms of chemical structure, as accurately as possible, the main elements of cellular membranes; which include phospholipids and cho- lesterol molecules. An efficient synthetic pathway was developed to prepare ligands that contain a phosphate head, a long alkyl chain chemically bonded to silica, and a cholesteric moiety, in order to mimic both hydrophilic and hydrophobic interactions, and "membrane-like" organization, respectively. The new stationary phase was characterized by Fourier- transform infra red (FTIR) and 1H-13C, 1H-31P, and 1H-29Si cross-polarization magic-angle-spinning nuclear magnetic resonance (CP MAS NMR) spectroscopy. Its chromato- graphic behavior has been studied by classical classification tests for RPLC columns. Despite its low surface coverage, thematerial produced exhibits high shape selectivity, possibly due to the organization of the grafted moieties

Cholesteric bonded stationary phases for high-performance liquid chromatography: a comparative study of the chromatographic behavior

International audienceThe properties of four cholesteric bonded sta- tionary phases differing in the nature of the spacer and the end-capping were assessed using simple chromatographic tests based on the retention of nonpolar compounds and of planar or nonplanar probe solutes. All cholesteric columns showed a hydrophobicity close to that of conventional octadecyldimethylsilyl (ODS) materials. Non-end-capped cholesteric bonded phases showed greater selectivity than ODS ones and both end-capped cholesteric bonded phases exhibit behavior intermediate between that of the non-end- capped original material and that of the ODS bonded phase

Different chemometric approaches to optimize the assay of St. John's Wort active ingredients

In this paper, we describe the optimization procedure for the quantitative assay of naphthodianthrones in St. John's Wort dry extract by reversed phase liquid chromatography. Lately, a project for European Pharmacopoeia monograph including an HPLC assay for the active moieties in St. John's Wort dry extract was published with a view to provoking reactions from other researchers. We therefore decided to use different chemometric approaches to evaluate the influence of both analytical and preparative factors to demonstrate the robustness of the optimized method. An asymmetric screening design was built in order to evaluate the weight of each level for each factor – the sonication duration, the light exposure duration, the flow rate and the type of column – on the response: the total hypericin content. Considering the results so obtained, we were compelled to modify some parameters. Thus we built a screening design to apprehend the reliability of the new sample pre-treatment process, the interpretation and identification of active factors were performed according to various methods. We used a third chemometric approach: a sequential bifurcation to check out the method's robustness. In a second step, an eluent compatible with Mass Spectrometry detection was determined by a combined design. To cope with both separation and analysis time, desirability functions were used. Optimal conditions are finally given by ternary system at an optimized temperature (40°C) and all the naphthodianthrones are separated in 10min on conventional endcapped octadecyl silica gel column

Mass Transport of Volatile Molecules in Porous Materials: Evaporation-Condensation Phenomena Described by NMR Diffusometry

International audienceThe transport mechanism of benzene in chromatographic-grade porous silica gel (10 nm pore size, 5,mu m sphere diameter) was described by pulsed-field gradient (PFG) high-resolution magic-angle spinning (HRMAS) NMR by measuring the molecular mobility in a series of samples with variable filling levels of the void volume. The relevance of vapor-phase diffusion for benzene, pure or dissolved in chloroform, was established, and it implies migration of benzene between silica particles through an evaporation-condensation mechanism