The identification of a suitable stationary phase in supercritical fluid chromatography (SFC) is ... more The identification of a suitable stationary phase in supercritical fluid chromatography (SFC) is a major source of difficulty for those with little experience in this technique. Several protocols have been suggested for column classification in high-performance liquid chromatography (HPLC), gas chromatography (GC), and SFC. However, none of the proposed classification schemes received general acceptance. A fair way to compare columns was proposed with the sum of ranking differences (SRD). In this project, we used the retention data obtained for 86 test compounds with varied polarity and structure, analyzed on 71 different stationary phases encompassing the full range in polarity of commercial packed columns currently available to the SFC chromatographer, with a single set of mobile phase and operating conditions (carbon dioxide-methanol mobile phase, 25°C, 150bar outlet pressure, 3ml/min). First, a reference column was selected and the 70 remaining columns were ranked based on this ...
The low viscosity of supercritical fluids enables the coupling of columns, which favours both the... more The low viscosity of supercritical fluids enables the coupling of columns, which favours both the high efficiency of separation and the ability of tuning the selectivity. However, it increases the inlet pressure then modifies the fluid density, i.e. the eluotropic strength of the mobile phase. In this case, the latter is rather different depending on the number of coupled columns. This fact prevents the calculation of the chromatographic parameters for coupled columns from the results obtained from one. In subcritical conditions, by using silica rod columns, which have bimodal porous structure, the flow resistance parameter is dramatically reduced. Consequently, the addition of monolithic columns induces only slight internal pressure changes and the fluid density does not vary with the column length. In this case, the calculation of retention factor and selectivity based on retention values obtained on each separate column provides accurate results allowing to determine the optimum column length in regard to the studied separation. After a better characterisation of the stationary phase included in the Chromolith column, this paper describes the -carotene isomers separation obtained by coupling up to six Chromolith columns to an octadecyl bonded particulate one. These compounds were studied because of the difficulty to separate these cis/trans isomers. No abnormal apparent dead volume change due to fluid density variation was reported, and good correlations between experimental and calculated retention factors and selectivities were observed. The optimum separation requires five highly porous columns coupled to a YMC Pack Pro. Moreover, the use of monolith packing allows to decrease both the retention factor and the analytical time by comparison to previous studies.
This paper investigates classification models for packed columns used in supercritical fluid chro... more This paper investigates classification models for packed columns used in supercritical fluid chromatography (SFC). Forty-eight columns of varied stationary phase chemistries available on the market are evaluated. The retention factors of 134 selected test compounds are used to compute hierarchical cluster analysis (HCA), principal component analysis (PCA), and quantitative structure-retention relationships (QSRRs). The use of HCA in conjunction with either PCA of QSRRs provides a classification of columns that is consistent with the experience of the SFC chromatographer. Besides, different coefficients, namely, Pearson correlation coefficient (r), selectivity difference (s 2 ), distance (L), and angle (θ), were calculated between all couples of columns to identify a ranking index, which would provide meaningful information whenever two columns need to be compared on an objective basis. This can be the case either when an equivalent is sought for replacement of a reference column or when an orthogonal column is desired to achieve complementary selectivity. It is concluded that the θ angle and the normalized distance L /u are the best coefficients, allowing for a meaningful comparison between two columns.
The use of an evaporative light scattering detector (ELSD) with high performance liquid chromatog... more The use of an evaporative light scattering detector (ELSD) with high performance liquid chromatography (HPLC) has been well documented. However, because the mobile phase is nebulized to produce droplets the use of supercritical fluids as the mobile phase with an ELSD is also favourable because the fluid depressurizes before the detector entrance, which allows the formation of aerosol. This article investigates the ELSD response variation with supercritical carbon dioxide-based mobile phases and compares the response (peak area) with HPLC.
Chiral chromatographic techniques in the liquid, gas or supercritical fluid state (HPLC, GC and S... more Chiral chromatographic techniques in the liquid, gas or supercritical fluid state (HPLC, GC and SFC) using chiral stationary phases (CSPs) are widely used for analytical and preparative separations of enantiomers. Since a versatile CSP capable to achieve any enantioseparation does not exist yet, huge efforts have been done to build predictive models. A chemoinformatics approach is currently applied to correlate chromatographic data (separation factor α and retention factors kE1, kE2) with molecular descriptors reflecting the properties of the chromatographic system. However, among the large number of descriptors, the choice of suitable ones is a delicate step to finally answer the question: how does chiral chromatography work? The molecular structure of the solute, the configuration of the stationary phase, the nature and the composition of the mobile phase and the thermodynamic parameters (pressure and temperature), all impact discrimination between two enantiomers. We report the u...
Impurity profiling of organic products that are synthesized as possible drug candidates requires ... more Impurity profiling of organic products that are synthesized as possible drug candidates requires complementary analytical methods to ensure that all impurities are identified. Supercritical fluid chromatography (SFC) is a very useful tool to achieve this objective, as an adequate selection of stationary phases can provide orthogonal separations so as to maximize the chances to see all impurities. In this series of papers, we have developed a method for achiral SFC-MS profiling of drug candidates, based on a selection of 160 analytes issued from Servier Research Laboratories. In the first part of this study, focusing on mobile phase selection, a gradient elution with carbon dioxide and methanol comprising 2% water and 20mM ammonium acetate proved to be the best in terms of chromatographic performance, while also providing good MS response [1]. The objective of this second part was the selection of an orthogonal set of ultra-high performance stationary phases, that was carried out in ...
The use of anabolic agents in food producing animals is prohibited within the EU since 1988 (96/2... more The use of anabolic agents in food producing animals is prohibited within the EU since 1988 (96/22/EC directive). However, steroid hormones may be still fraudulently employed for anabolic purpose. Nowadays, efficient method based on isotopic deviation measurement (δ13C) to confirm the illegal use of natural steroids is applied in laboratories in charge of the control. Nevertheless, in order to guarantee a precise isotopic deviation value, purification of the targeted analytes from urine samples has to be maximized. This constraint implies a huge sample preparation including at least three consecutive SPE, LLE and HPLC steps before injection in GC-C-IRMS. In order to reduce this latter, the use of supercritical fluids as chromatographic mobile phases was considered. Indeed, the lower eluent viscosities and higher solute diffusivities in SFC often translate into increased efficiency and reduced separation times when compared with HPLC. The aim of this study was to assess different sta...
We report herein the Pd-catalyzed P-C cross-coupling reaction between enol phosphates and seconda... more We report herein the Pd-catalyzed P-C cross-coupling reaction between enol phosphates and secondary phosphane-borane complexes or phosphane oxides. The reaction was performed under mild conditions, owing to Pd activation of the P-H bonds of the phosphane-boranes (or phosphane oxides)
Packed column sub- and supercritical fluid chromatography (SFC) is a versatile separation method:... more Packed column sub- and supercritical fluid chromatography (SFC) is a versatile separation method: on the one hand the number of parameters acting on the quality of a separation is very large, and the effects of these parameters can be complex (and not always fully understood). But on another hand, due to numerous advantageous properties of CO2-based mobile phases, method development is a fast task. This paper is a review of the main features of SFC, focusing essentially on achiral separations. However, several fundamental aspects discussed here are also relevant to chiral SFC separations. This is not intended to be an extensive review, as the way to practice SFC has somewhat evolved with time. We rather wished to provide an expert opinion on the characteristics of the method, pointing at the sources of difficulty and displaying the wide possibilities that it offers. A large number of selected applications concerning several different areas are also presented.
The direct separation of the enantiomers of 1-(␣-aminoarylmethyl)-2-naphthol, 1-(␣-aminoalkyl)-2n... more The direct separation of the enantiomers of 1-(␣-aminoarylmethyl)-2-naphthol, 1-(␣-aminoalkyl)-2naphthol, 2-(␣-aminoarylmethyl)-1-naphthol analogues and 2-(1-amino-2-methylpropyl)-1-naphthol) was investigated in supercritical fluid chromatography. Five commercially available chiral stationary phases based on immobilized polysaccharide chiral selectors (Chiralpak IA, IB, IC, ID and IE) were evaluated. Chiralpak IB was by far the most efficient to achieve the separation of these racemates and was further selected for optimization of elution conditions. The effects of column temperature (varying between 5 and 45 • C) and co-solvent added to carbon dioxide (methanol, ethanol, isopropanol and dichloromethane) were investigated. A particular attention was paid to mobile-phase additives. Several of them, acids, bases or salts (namely water, formic acid, acetic acid, trifluoroacetic acid, diethylamine, diethanolamine, triethylamine, triethanolamine, dimethylethanolamine, ammonia and ammonium acetate), were tested in order to improve peak shapes while maintaining selectivity. With the help of other achiral naphthol derivatives, the additive effects were examined.
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h r o m a Insig... more j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h r o m a Insights into chiral recognition mechanisms in supercritical fluid chromatography V. Effect of the nature and proportion of alcohol mobile phase modifier with amylose and cellulose tris-(3,5-dimethylphenylcarbamate) stationary phases a b s t r a c t
Journal of Pharmaceutical and Biomedical Analysis, 2015
A rapid and efficient chiral supercritical fluid chromatography (SFC) method has been developed f... more A rapid and efficient chiral supercritical fluid chromatography (SFC) method has been developed for the quantitative determination of panthenol enantiomers in cosmetic formulations (cream, lotion, wipe, and exfoliant). Indeed, the pharmacological effect only depends on the D form (Dexpanthenol) thus accurate measurement of its enantiomeric purity in formulated cosmetic products is of interest. The samples were prepared with liquid-liquid extraction followed by solid-phase extraction on Adsorbex amino cartridges. After testing several enantioselective columns in an attempt at reversing the elution order to have the minor enantiomer eluted first, the best separation of enantiomers and internal standard (N-acetyl-l-alanine) was achieved on a 3 m-amylose-type immobilized polysaccharide chiral stationary phase (Chiralpak IA) in less than 6 min with a simple mobile phase comprising carbon dioxide and 11% methanol pumped at 2.3 mL/min, 25 • C and 150 bar backpressure. Supercritical fluid chromatography coupled to both an optical diode-array detector and a user-friendly single-quadrupole mass spectrometer (Waters QDa) equipped with electrospray ionization source has been used. The on-line coupling ensures the technique to be more informative and improves detection sensitivity, as underivatized panthenol has a poor UV absorption. The limit of quantification (LOQ) achieved with single-ion recording was 0.5 g/mL. The method was validated in terms of linearity, precision and accuracy and satisfactory results were obtained.
The chiral recognition mechanism for a successful enantioseparation on polysaccharide stationary ... more The chiral recognition mechanism for a successful enantioseparation on polysaccharide stationary phases are still poorly understood. In this series of papers, we aim to provide some insight into the retention and separation mechanisms occurring in enantioselective supercritical fluid chromatography (SFC). This paper presents a thorough investigation on chlorinated polysaccharide chiral stationary phases (CSP) comprising five coated and three immobilized phases from different manufacturers. The columns are also compared to four non-chlorinated phases to unravel the most significant differences brought about by the introduction of electron-withdrawing atoms on the aromatic ligands. Chemometrics are used to (i) get an overview of all columns (cluster analysis), (ii) describe retention (modified solvation parameter model) and (iii) describe enantioseparation (discriminant analysis). Sample applications are provided to support the discussion.
Stationary phases containing pyridine, phenol, aniline and morpholine groups were synthesized usi... more Stationary phases containing pyridine, phenol, aniline and morpholine groups were synthesized using copper (I)-catalyzed azide-alkyne cycloaddition click reactions. The backbone of the stationary phases was aminopropyl silica. The stationary phases were evaluated in packed-column supercritical fluid chromatography (pSFC) with acidic and basic solutes without addition of additives. The analysis of metoclopromide and its impurities by SFC-time-of-flight mass spectrometry (SFC-TOFMS) on the phenol phase is presented. In the click reaction, the 1,2,3-triazole ring is formed and to assess its influence on the polarity/selectivity, the click phases were compared to a commercial available 1,2,4-triazole hydrophilic interaction liquid chromatography (HILIC) phase. The phases were also compared to two extensively used stationary phases in SFC namely 2-ethyl pyridine and bare silica. To allow comparison with other phases used in SFC, linear solvation energy relationships (LSER) of the click phases were determined. Synthesis of stationary phases containing pyridine, phenol, aniline and morpholine via click chemistry and their characterization and evaluation in supercritical fluid chromatography Dunkle M et al. Synthesis of stationary phases containing pyridine, phenol, aniline and morpholine 86 Scientia Chromatographica 2014; 6(2):85-103 Synthesis of stationary phases containing pyridine, phenol, aniline and morpholine Dunkle M et al. Scientia Chromatographica 2014; 6(2):85-103
Comments on the paper ''Characterization of stationary phases by a linear solvation energy relati... more Comments on the paper ''Characterization of stationary phases by a linear solvation energy relationship utilizing supercritical fluid chromatography'' by C. R. Mitchell, N. J. Benz, S. Zhang
In supercritical fluid chromatography (SFC), the effects of adding a co-solvent to carbon dioxide... more In supercritical fluid chromatography (SFC), the effects of adding a co-solvent to carbon dioxide are numerous. In this work, the changes in retention and selectivity occurring when the nature of the cosolvent (methanol, ethanol, isopropanol, acetonitrile) in the SFC mobile phase is varied, are studied on seven columns with different stationary phase chemistry (cyanopropyl-, pyridine-ethyl-, phenyloxypropyl-, phenyl-propyl-, phenyl-hexyl-, pentafluorophenyl-propyl-and octadecyl-bonded silica). Hierarchical cluster analysis and quantitative structure-retention relationships with the solvation parameter model are employed to evaluate these effects, based on the observed retention for over a hundred probe compounds. It appears that some columns are somewhat more affected than others by the change of solvent nature. Acetonitrile induces the strongest differences, essentially due to its poor capabilities as an eluent for bases and possibly because it does not adequately cover residual silanol groups. Ethanol appears to be a possible green alternative to the most-used methanol. Some hints on a possible partition-adsorption mixed mechanism are offered. Finally, sample applications with three different test mixtures relevant to cosmetic and pharmaceutical applications (flavanones, non-steroidal anti-inflammatory drugs and barbiturates) are presented.
Stationary phases (SP) prepared by immobilization of polymers on silica or metalized silica are i... more Stationary phases (SP) prepared by immobilization of polymers on silica or metalized silica are interesting for use in reversed-phase high-performance liquid chromatography (RP-HPLC) due to better protection of residual silanols or Lewis acid sites, as well as ease of preparation. On the other hand, there are no previous reports of the use of such phases in packed column supercritical fluid chromatography (SFC). Fourteen different SPs based on polysiloxanes (phenyl, C1, C8, C14, C18) thermally immobilized onto different supports (silica, titanized silica, zirconized silica) and one chemically bonded and end-capped C18 stationary phase having a doubly zirconized silica support, were characterized with identical SFC conditions (CO 2 with 10% of methanol, 25 • C, 15.0 MPa backpressure). Characterization was achieved based on retention factors measured for 85 test compounds and linear solvation energy relationships (LSER), namely the solvation parameter model based on Abraham descriptors. The polysiloxane SP were compared to a commercial C18-bonded silica (Kromasil C18), and to the native silica and metalized silica supports to better unravel the effects of stationary phase chemistry on chromatographic behavior. Together, 19 stationary phases were compared. The results highlight the variety of polarities provided by the column set. The polysiloxane backbone contributes significantly to the SP polarity as evidenced by the comparison to a classical alkylsiloxane-bonded SP. Metalization also appears to modify the polar characteristics of the SP, particularly toward basic compounds. Sample applications illustrate the applicability of these SP in SFC to the analysis of compounds of interest to the pharmaceutical and cosmetic industries.
All stationary phase chemistries are useful to achiral packed-column supercritical fluid chromato... more All stationary phase chemistries are useful to achiral packed-column supercritical fluid chromatography (pSFC), but the majority of recent applications are based on polar stationary phases of the type used in normal-phase HPLC. Some manufacturers have recently introduced pSFC-tailored stationary phases, while others simply advocate the use of selected HPLC columns among their brands for SFC use. Indeed, any column developed for HPLC use can be used with supercritical fluids. Besides, hydrophilic interaction liquid chromatography (HILIC) is facing an increasing interest. Consequently, a number of HILIC-devoted stationary phases are now commercialized by most column manufacturers. As HILIC stationary phases are polar, their possible use in pSFC seems obvious, although literature examples are not numerous. However, whether they provide acceptable peak shapes in SFC conditions is a serious concern for them to find applicability. Indeed, columns optimized for HILIC mobile phases may not be optimum for SFC mobile phases. We present the characterization of eleven HILIC-type stationary phases used with carbon dioxide-methanol mobile phases in the isocratic mode. The columns are compared in terms of their retention and separation characteristics assessed by the solvation parameter model, and based on peak shapes. For this purpose, hundred and forty-six low molecular weight molecules, comprising neutral, basic and acidic compounds, were eluted on each column. Data analysis is carried out with hierarchical cluster analysis and principal component analysis in order to define three clusters of columns with similar selectivity: the first cluster comprises neutral stationary phases like amide and diol phases; the second one comprises basic stationary phases like aminopropyl-bonded silica; the last cluster comprises bare silica stationary phases. Sample applications with three different test mixtures relevant to pharmaceutical applications (barbiturates, benzodiazepines and propionic acids) are presented to assess the complementarity of some selected columns.
Due to the renewal of the use of supercritical fluid chromatography (SFC), the coupling of SFC wi... more Due to the renewal of the use of supercritical fluid chromatography (SFC), the coupling of SFC with evaporative light scattering detection (ELSD) needs to be revisited. Indeed, SFC and ELSD apparatus have evolved, while understanding of the nebulisation process has improved. This detector, first developed for polymer analyses can be used for a lot of compounds that do not display sufficient UV absorption. Because the response of ELSD is related to numerous parameters, such as mobile phase composition, the velocity difference between the mobile phase and the nebulisation gas, or the nebulisation temperature, many additional studies are necessary to understand its behaviour in SFC as compared to HPLC. The effects of the nature of co-solvent added to carbon dioxide (methanol, ethanol and acetonitrile), the injected volume and the flow rate on the ELSD response were studied. Certain parameters induce great changes on the nebulisation recovery (the proportion of mobile phase entering the drift tube), allowing for a dramatic improvement in peak area. Moreover, effects of the particle size in the aerosol were also observed, related, as expected, to the modifier nature, but strangely also to the injected volume. Specific and positive behaviour of the ELSD detection on the apparent peak efficiency was confirmed in SFC, for large injected volumes. Finally, a flow rate increase reduces peak area, showing that the use of high flow rates, although attractive to shorten analysis duration, is not favourable to ELSD response. Numerous parameters acting on detector response are modified by the flow rate change, such as the mobile phase velocity. Moreover, measurement of the nebulisation chamber temperature shows the strong decrease of temperature for high flow rates, due to the supercritical fluid depressurisation.
The identification of a suitable stationary phase in supercritical fluid chromatography (SFC) is ... more The identification of a suitable stationary phase in supercritical fluid chromatography (SFC) is a major source of difficulty for those with little experience in this technique. Several protocols have been suggested for column classification in high-performance liquid chromatography (HPLC), gas chromatography (GC), and SFC. However, none of the proposed classification schemes received general acceptance. A fair way to compare columns was proposed with the sum of ranking differences (SRD). In this project, we used the retention data obtained for 86 test compounds with varied polarity and structure, analyzed on 71 different stationary phases encompassing the full range in polarity of commercial packed columns currently available to the SFC chromatographer, with a single set of mobile phase and operating conditions (carbon dioxide-methanol mobile phase, 25°C, 150bar outlet pressure, 3ml/min). First, a reference column was selected and the 70 remaining columns were ranked based on this ...
The low viscosity of supercritical fluids enables the coupling of columns, which favours both the... more The low viscosity of supercritical fluids enables the coupling of columns, which favours both the high efficiency of separation and the ability of tuning the selectivity. However, it increases the inlet pressure then modifies the fluid density, i.e. the eluotropic strength of the mobile phase. In this case, the latter is rather different depending on the number of coupled columns. This fact prevents the calculation of the chromatographic parameters for coupled columns from the results obtained from one. In subcritical conditions, by using silica rod columns, which have bimodal porous structure, the flow resistance parameter is dramatically reduced. Consequently, the addition of monolithic columns induces only slight internal pressure changes and the fluid density does not vary with the column length. In this case, the calculation of retention factor and selectivity based on retention values obtained on each separate column provides accurate results allowing to determine the optimum column length in regard to the studied separation. After a better characterisation of the stationary phase included in the Chromolith column, this paper describes the -carotene isomers separation obtained by coupling up to six Chromolith columns to an octadecyl bonded particulate one. These compounds were studied because of the difficulty to separate these cis/trans isomers. No abnormal apparent dead volume change due to fluid density variation was reported, and good correlations between experimental and calculated retention factors and selectivities were observed. The optimum separation requires five highly porous columns coupled to a YMC Pack Pro. Moreover, the use of monolith packing allows to decrease both the retention factor and the analytical time by comparison to previous studies.
This paper investigates classification models for packed columns used in supercritical fluid chro... more This paper investigates classification models for packed columns used in supercritical fluid chromatography (SFC). Forty-eight columns of varied stationary phase chemistries available on the market are evaluated. The retention factors of 134 selected test compounds are used to compute hierarchical cluster analysis (HCA), principal component analysis (PCA), and quantitative structure-retention relationships (QSRRs). The use of HCA in conjunction with either PCA of QSRRs provides a classification of columns that is consistent with the experience of the SFC chromatographer. Besides, different coefficients, namely, Pearson correlation coefficient (r), selectivity difference (s 2 ), distance (L), and angle (θ), were calculated between all couples of columns to identify a ranking index, which would provide meaningful information whenever two columns need to be compared on an objective basis. This can be the case either when an equivalent is sought for replacement of a reference column or when an orthogonal column is desired to achieve complementary selectivity. It is concluded that the θ angle and the normalized distance L /u are the best coefficients, allowing for a meaningful comparison between two columns.
The use of an evaporative light scattering detector (ELSD) with high performance liquid chromatog... more The use of an evaporative light scattering detector (ELSD) with high performance liquid chromatography (HPLC) has been well documented. However, because the mobile phase is nebulized to produce droplets the use of supercritical fluids as the mobile phase with an ELSD is also favourable because the fluid depressurizes before the detector entrance, which allows the formation of aerosol. This article investigates the ELSD response variation with supercritical carbon dioxide-based mobile phases and compares the response (peak area) with HPLC.
Chiral chromatographic techniques in the liquid, gas or supercritical fluid state (HPLC, GC and S... more Chiral chromatographic techniques in the liquid, gas or supercritical fluid state (HPLC, GC and SFC) using chiral stationary phases (CSPs) are widely used for analytical and preparative separations of enantiomers. Since a versatile CSP capable to achieve any enantioseparation does not exist yet, huge efforts have been done to build predictive models. A chemoinformatics approach is currently applied to correlate chromatographic data (separation factor α and retention factors kE1, kE2) with molecular descriptors reflecting the properties of the chromatographic system. However, among the large number of descriptors, the choice of suitable ones is a delicate step to finally answer the question: how does chiral chromatography work? The molecular structure of the solute, the configuration of the stationary phase, the nature and the composition of the mobile phase and the thermodynamic parameters (pressure and temperature), all impact discrimination between two enantiomers. We report the u...
Impurity profiling of organic products that are synthesized as possible drug candidates requires ... more Impurity profiling of organic products that are synthesized as possible drug candidates requires complementary analytical methods to ensure that all impurities are identified. Supercritical fluid chromatography (SFC) is a very useful tool to achieve this objective, as an adequate selection of stationary phases can provide orthogonal separations so as to maximize the chances to see all impurities. In this series of papers, we have developed a method for achiral SFC-MS profiling of drug candidates, based on a selection of 160 analytes issued from Servier Research Laboratories. In the first part of this study, focusing on mobile phase selection, a gradient elution with carbon dioxide and methanol comprising 2% water and 20mM ammonium acetate proved to be the best in terms of chromatographic performance, while also providing good MS response [1]. The objective of this second part was the selection of an orthogonal set of ultra-high performance stationary phases, that was carried out in ...
The use of anabolic agents in food producing animals is prohibited within the EU since 1988 (96/2... more The use of anabolic agents in food producing animals is prohibited within the EU since 1988 (96/22/EC directive). However, steroid hormones may be still fraudulently employed for anabolic purpose. Nowadays, efficient method based on isotopic deviation measurement (δ13C) to confirm the illegal use of natural steroids is applied in laboratories in charge of the control. Nevertheless, in order to guarantee a precise isotopic deviation value, purification of the targeted analytes from urine samples has to be maximized. This constraint implies a huge sample preparation including at least three consecutive SPE, LLE and HPLC steps before injection in GC-C-IRMS. In order to reduce this latter, the use of supercritical fluids as chromatographic mobile phases was considered. Indeed, the lower eluent viscosities and higher solute diffusivities in SFC often translate into increased efficiency and reduced separation times when compared with HPLC. The aim of this study was to assess different sta...
We report herein the Pd-catalyzed P-C cross-coupling reaction between enol phosphates and seconda... more We report herein the Pd-catalyzed P-C cross-coupling reaction between enol phosphates and secondary phosphane-borane complexes or phosphane oxides. The reaction was performed under mild conditions, owing to Pd activation of the P-H bonds of the phosphane-boranes (or phosphane oxides)
Packed column sub- and supercritical fluid chromatography (SFC) is a versatile separation method:... more Packed column sub- and supercritical fluid chromatography (SFC) is a versatile separation method: on the one hand the number of parameters acting on the quality of a separation is very large, and the effects of these parameters can be complex (and not always fully understood). But on another hand, due to numerous advantageous properties of CO2-based mobile phases, method development is a fast task. This paper is a review of the main features of SFC, focusing essentially on achiral separations. However, several fundamental aspects discussed here are also relevant to chiral SFC separations. This is not intended to be an extensive review, as the way to practice SFC has somewhat evolved with time. We rather wished to provide an expert opinion on the characteristics of the method, pointing at the sources of difficulty and displaying the wide possibilities that it offers. A large number of selected applications concerning several different areas are also presented.
The direct separation of the enantiomers of 1-(␣-aminoarylmethyl)-2-naphthol, 1-(␣-aminoalkyl)-2n... more The direct separation of the enantiomers of 1-(␣-aminoarylmethyl)-2-naphthol, 1-(␣-aminoalkyl)-2naphthol, 2-(␣-aminoarylmethyl)-1-naphthol analogues and 2-(1-amino-2-methylpropyl)-1-naphthol) was investigated in supercritical fluid chromatography. Five commercially available chiral stationary phases based on immobilized polysaccharide chiral selectors (Chiralpak IA, IB, IC, ID and IE) were evaluated. Chiralpak IB was by far the most efficient to achieve the separation of these racemates and was further selected for optimization of elution conditions. The effects of column temperature (varying between 5 and 45 • C) and co-solvent added to carbon dioxide (methanol, ethanol, isopropanol and dichloromethane) were investigated. A particular attention was paid to mobile-phase additives. Several of them, acids, bases or salts (namely water, formic acid, acetic acid, trifluoroacetic acid, diethylamine, diethanolamine, triethylamine, triethanolamine, dimethylethanolamine, ammonia and ammonium acetate), were tested in order to improve peak shapes while maintaining selectivity. With the help of other achiral naphthol derivatives, the additive effects were examined.
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h r o m a Insig... more j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h r o m a Insights into chiral recognition mechanisms in supercritical fluid chromatography V. Effect of the nature and proportion of alcohol mobile phase modifier with amylose and cellulose tris-(3,5-dimethylphenylcarbamate) stationary phases a b s t r a c t
Journal of Pharmaceutical and Biomedical Analysis, 2015
A rapid and efficient chiral supercritical fluid chromatography (SFC) method has been developed f... more A rapid and efficient chiral supercritical fluid chromatography (SFC) method has been developed for the quantitative determination of panthenol enantiomers in cosmetic formulations (cream, lotion, wipe, and exfoliant). Indeed, the pharmacological effect only depends on the D form (Dexpanthenol) thus accurate measurement of its enantiomeric purity in formulated cosmetic products is of interest. The samples were prepared with liquid-liquid extraction followed by solid-phase extraction on Adsorbex amino cartridges. After testing several enantioselective columns in an attempt at reversing the elution order to have the minor enantiomer eluted first, the best separation of enantiomers and internal standard (N-acetyl-l-alanine) was achieved on a 3 m-amylose-type immobilized polysaccharide chiral stationary phase (Chiralpak IA) in less than 6 min with a simple mobile phase comprising carbon dioxide and 11% methanol pumped at 2.3 mL/min, 25 • C and 150 bar backpressure. Supercritical fluid chromatography coupled to both an optical diode-array detector and a user-friendly single-quadrupole mass spectrometer (Waters QDa) equipped with electrospray ionization source has been used. The on-line coupling ensures the technique to be more informative and improves detection sensitivity, as underivatized panthenol has a poor UV absorption. The limit of quantification (LOQ) achieved with single-ion recording was 0.5 g/mL. The method was validated in terms of linearity, precision and accuracy and satisfactory results were obtained.
The chiral recognition mechanism for a successful enantioseparation on polysaccharide stationary ... more The chiral recognition mechanism for a successful enantioseparation on polysaccharide stationary phases are still poorly understood. In this series of papers, we aim to provide some insight into the retention and separation mechanisms occurring in enantioselective supercritical fluid chromatography (SFC). This paper presents a thorough investigation on chlorinated polysaccharide chiral stationary phases (CSP) comprising five coated and three immobilized phases from different manufacturers. The columns are also compared to four non-chlorinated phases to unravel the most significant differences brought about by the introduction of electron-withdrawing atoms on the aromatic ligands. Chemometrics are used to (i) get an overview of all columns (cluster analysis), (ii) describe retention (modified solvation parameter model) and (iii) describe enantioseparation (discriminant analysis). Sample applications are provided to support the discussion.
Stationary phases containing pyridine, phenol, aniline and morpholine groups were synthesized usi... more Stationary phases containing pyridine, phenol, aniline and morpholine groups were synthesized using copper (I)-catalyzed azide-alkyne cycloaddition click reactions. The backbone of the stationary phases was aminopropyl silica. The stationary phases were evaluated in packed-column supercritical fluid chromatography (pSFC) with acidic and basic solutes without addition of additives. The analysis of metoclopromide and its impurities by SFC-time-of-flight mass spectrometry (SFC-TOFMS) on the phenol phase is presented. In the click reaction, the 1,2,3-triazole ring is formed and to assess its influence on the polarity/selectivity, the click phases were compared to a commercial available 1,2,4-triazole hydrophilic interaction liquid chromatography (HILIC) phase. The phases were also compared to two extensively used stationary phases in SFC namely 2-ethyl pyridine and bare silica. To allow comparison with other phases used in SFC, linear solvation energy relationships (LSER) of the click phases were determined. Synthesis of stationary phases containing pyridine, phenol, aniline and morpholine via click chemistry and their characterization and evaluation in supercritical fluid chromatography Dunkle M et al. Synthesis of stationary phases containing pyridine, phenol, aniline and morpholine 86 Scientia Chromatographica 2014; 6(2):85-103 Synthesis of stationary phases containing pyridine, phenol, aniline and morpholine Dunkle M et al. Scientia Chromatographica 2014; 6(2):85-103
Comments on the paper ''Characterization of stationary phases by a linear solvation energy relati... more Comments on the paper ''Characterization of stationary phases by a linear solvation energy relationship utilizing supercritical fluid chromatography'' by C. R. Mitchell, N. J. Benz, S. Zhang
In supercritical fluid chromatography (SFC), the effects of adding a co-solvent to carbon dioxide... more In supercritical fluid chromatography (SFC), the effects of adding a co-solvent to carbon dioxide are numerous. In this work, the changes in retention and selectivity occurring when the nature of the cosolvent (methanol, ethanol, isopropanol, acetonitrile) in the SFC mobile phase is varied, are studied on seven columns with different stationary phase chemistry (cyanopropyl-, pyridine-ethyl-, phenyloxypropyl-, phenyl-propyl-, phenyl-hexyl-, pentafluorophenyl-propyl-and octadecyl-bonded silica). Hierarchical cluster analysis and quantitative structure-retention relationships with the solvation parameter model are employed to evaluate these effects, based on the observed retention for over a hundred probe compounds. It appears that some columns are somewhat more affected than others by the change of solvent nature. Acetonitrile induces the strongest differences, essentially due to its poor capabilities as an eluent for bases and possibly because it does not adequately cover residual silanol groups. Ethanol appears to be a possible green alternative to the most-used methanol. Some hints on a possible partition-adsorption mixed mechanism are offered. Finally, sample applications with three different test mixtures relevant to cosmetic and pharmaceutical applications (flavanones, non-steroidal anti-inflammatory drugs and barbiturates) are presented.
Stationary phases (SP) prepared by immobilization of polymers on silica or metalized silica are i... more Stationary phases (SP) prepared by immobilization of polymers on silica or metalized silica are interesting for use in reversed-phase high-performance liquid chromatography (RP-HPLC) due to better protection of residual silanols or Lewis acid sites, as well as ease of preparation. On the other hand, there are no previous reports of the use of such phases in packed column supercritical fluid chromatography (SFC). Fourteen different SPs based on polysiloxanes (phenyl, C1, C8, C14, C18) thermally immobilized onto different supports (silica, titanized silica, zirconized silica) and one chemically bonded and end-capped C18 stationary phase having a doubly zirconized silica support, were characterized with identical SFC conditions (CO 2 with 10% of methanol, 25 • C, 15.0 MPa backpressure). Characterization was achieved based on retention factors measured for 85 test compounds and linear solvation energy relationships (LSER), namely the solvation parameter model based on Abraham descriptors. The polysiloxane SP were compared to a commercial C18-bonded silica (Kromasil C18), and to the native silica and metalized silica supports to better unravel the effects of stationary phase chemistry on chromatographic behavior. Together, 19 stationary phases were compared. The results highlight the variety of polarities provided by the column set. The polysiloxane backbone contributes significantly to the SP polarity as evidenced by the comparison to a classical alkylsiloxane-bonded SP. Metalization also appears to modify the polar characteristics of the SP, particularly toward basic compounds. Sample applications illustrate the applicability of these SP in SFC to the analysis of compounds of interest to the pharmaceutical and cosmetic industries.
All stationary phase chemistries are useful to achiral packed-column supercritical fluid chromato... more All stationary phase chemistries are useful to achiral packed-column supercritical fluid chromatography (pSFC), but the majority of recent applications are based on polar stationary phases of the type used in normal-phase HPLC. Some manufacturers have recently introduced pSFC-tailored stationary phases, while others simply advocate the use of selected HPLC columns among their brands for SFC use. Indeed, any column developed for HPLC use can be used with supercritical fluids. Besides, hydrophilic interaction liquid chromatography (HILIC) is facing an increasing interest. Consequently, a number of HILIC-devoted stationary phases are now commercialized by most column manufacturers. As HILIC stationary phases are polar, their possible use in pSFC seems obvious, although literature examples are not numerous. However, whether they provide acceptable peak shapes in SFC conditions is a serious concern for them to find applicability. Indeed, columns optimized for HILIC mobile phases may not be optimum for SFC mobile phases. We present the characterization of eleven HILIC-type stationary phases used with carbon dioxide-methanol mobile phases in the isocratic mode. The columns are compared in terms of their retention and separation characteristics assessed by the solvation parameter model, and based on peak shapes. For this purpose, hundred and forty-six low molecular weight molecules, comprising neutral, basic and acidic compounds, were eluted on each column. Data analysis is carried out with hierarchical cluster analysis and principal component analysis in order to define three clusters of columns with similar selectivity: the first cluster comprises neutral stationary phases like amide and diol phases; the second one comprises basic stationary phases like aminopropyl-bonded silica; the last cluster comprises bare silica stationary phases. Sample applications with three different test mixtures relevant to pharmaceutical applications (barbiturates, benzodiazepines and propionic acids) are presented to assess the complementarity of some selected columns.
Due to the renewal of the use of supercritical fluid chromatography (SFC), the coupling of SFC wi... more Due to the renewal of the use of supercritical fluid chromatography (SFC), the coupling of SFC with evaporative light scattering detection (ELSD) needs to be revisited. Indeed, SFC and ELSD apparatus have evolved, while understanding of the nebulisation process has improved. This detector, first developed for polymer analyses can be used for a lot of compounds that do not display sufficient UV absorption. Because the response of ELSD is related to numerous parameters, such as mobile phase composition, the velocity difference between the mobile phase and the nebulisation gas, or the nebulisation temperature, many additional studies are necessary to understand its behaviour in SFC as compared to HPLC. The effects of the nature of co-solvent added to carbon dioxide (methanol, ethanol and acetonitrile), the injected volume and the flow rate on the ELSD response were studied. Certain parameters induce great changes on the nebulisation recovery (the proportion of mobile phase entering the drift tube), allowing for a dramatic improvement in peak area. Moreover, effects of the particle size in the aerosol were also observed, related, as expected, to the modifier nature, but strangely also to the injected volume. Specific and positive behaviour of the ELSD detection on the apparent peak efficiency was confirmed in SFC, for large injected volumes. Finally, a flow rate increase reduces peak area, showing that the use of high flow rates, although attractive to shorten analysis duration, is not favourable to ELSD response. Numerous parameters acting on detector response are modified by the flow rate change, such as the mobile phase velocity. Moreover, measurement of the nebulisation chamber temperature shows the strong decrease of temperature for high flow rates, due to the supercritical fluid depressurisation.
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Papers by Caroline West