Micellar liquid chromatography was used to analyse some drugs illegally used in sport. The spectr... more Micellar liquid chromatography was used to analyse some drugs illegally used in sport. The spectroscopic characteristics, UV absorption and fluorescence, of oxandrolone, methyl testosterone, testosterone enanthate, caffeine, ephedrine, bumetamide, chlortalidone, dihydrochlorothiazide, furosemide, spironolactone and propranolol were established in water and sodium dodecyl sulfate micellar solution. The chromatographic retention parameters were determined
This paper describes intermittent counter-current extraction, a novel method of using a conventio... more This paper describes intermittent counter-current extraction, a novel method of using a conventional twin column counter-current chromatograph to either split a sample into two groups of compounds or extract and enrich a target compound from a crude extract. The first method is demonstrated by splitting a model mixture of four compounds into two groups. The second method is demonstrated by the extraction and enrichment of a high value target compound, triptolide, from a Chinese herbal medicine crude extract of Tripterygium wilfordii Hook. f., where it is found at low concentration (2%). This was achieved by retaining and enriching the target compound within the column while washing away all other components of the crude material. The success of the first method allowed the second method to be carried out without the need for costly preliminary experiments with the high value sample. 188 mg of triptolide at greater than 98% purity was separated from 9.2 g of crude extract, using 10 l of solvent in a 3-h separation.
(3R)-(−)-7,2-Dihydroxy-3 ,4-dimethyl isoflavan-7-O--d-glucopyranoside and (6aR, 11aR) 9,10-di-me... more (3R)-(−)-7,2-Dihydroxy-3 ,4-dimethyl isoflavan-7-O--d-glucopyranoside and (6aR, 11aR) 9,10-di-methoxypterocarpan-3-O--dglucopyranoside were separated from the ethyl acetate extract of the root of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao by high-speed counter-current chromatography (HSCCC). A two-phase system composed of ethyl acetate-ethanol-acetic acid-water (4:1:0.25:5, v/v) was selected by analytical HSCCC. Preparative HSCCC yielded, from 100 mg of the partially purified extract, 50 mg of isoflavan glycoside and 10 mg of pterocarpan glycoside each at over 95% purity by high-performance liquid chromatography (HPLC) analysis. Their structures were identified by MS, 1 H NMR and 13 C NMR.
Heptans-sodlum dodecyl sulfate (SDS)-pentanol-water oll-In-water mkroemuldons were Investigated a... more Heptans-sodlum dodecyl sulfate (SDS)-pentanol-water oll-In-water mkroemuldons were Investigated as a moblle phase In r e v-HquM chromatography. The mass ratb SDS/ pentanol was kept constant, 112, for all compodlons. The retention and peak efflclency of alkylbenzenes, toluene, bu-tyEenzene, heptylbenzene, and decylbenzene, were measured on an octadecyl bonded 15-m column. Water-rlch mkro-emulslo~ (>87% w/w water) of the L1 oll-ln-water structure were able to separate the alkylbenzene homologues with a linear k'vs nc relatlonshlp, nc k the atom carbon number of the alkyl chaln. The dopes and Intercepts of the k'vs nc llnes depend on the relative vdume of organic phase. Heptane and the active blend SDS + pentanol play a similar rob on selectlvlty. They have an oppodte effect on efflclency. A higher content of the active blend SDS + pentanol produced a higher dfklency for the alkylbenzene peaks. Addition of heptane to any SDS-pentanol-water phases produced a dramatic decrease In etllclency, specialty for the long-chain homokgueci. TheoolutemasrtranderdecreasesexpamntWy with the alkyl chaln length. Efficiency studles can be related to physlcochemlcal changes of the mlcroemuldon structure.
1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF 6) was synthesized and purified to be us... more 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF 6) was synthesized and purified to be used as a ionic liquid solvent. Its physicochemical properties were studied. The ionic liquid/water (P il/water) and ionic liquid/heptane (P il/heptane) distribution coefficients of a set of 40 compounds with various functionalities, including organic acids, organic bases, amino acids, antioxidants, and neutral compounds, were measured using liquid chromatography. For ionizable compounds, the P il/water values measured at pH 2, 5.1, and 10 were very different. These allowed the determination of both the molecularP o il /water values and the ionPil /water value for each compound. These coefficients were compared to the corresponding P oct/water coefficients. Marked differences in the partitioning behavior of basic, acidic, and neutral compounds were observed. The relationship between P il/water and P oct/water is different from that reported previously. By using the linear free energy solvation approach and the descriptors found for 12 solutes, the BMIM-PF 6 solvent parameters were calculated for the ionic liquid/water and ionic liquid/heptane biphasic systems. The regression parameters show a low basicity of the BMIM-PF 6 solvent compared to octanol. The high cohesion of the ions in the ionic liquid phase is also indicated by the regression equations obtained. Ionized phenols (phenoxide ions) associate more strongly with BMIM-PF 6 than most other ionized molecules. Amino acids were not soluble in ionic liquid; however, it is possible to extract them partially by adding a crown ether to the ionic liquid phase and working at pH 1. The positive form of amino acids is complexed by the crown ether and the complex is extracted in the ionic liquid phase.
This paper describes a new method of purification of the Lolitrem B, a tremorgenic mycotoxin prod... more This paper describes a new method of purification of the Lolitrem B, a tremorgenic mycotoxin produced in planta by the endophytic fungus Neotyphodium lolii. The method is based on the large-scale isolation of the toxin by countercurrent chromatography (CCC). The lolitrem B content in endophyted ryegrass seed, 11 microg/g or 11 ppm, is extracted by stirring finely ground seeds with ethanol for 3 h at room temperature. The concentrated crude extract contains about 0.6 mg/g or 600 ppm of lolitrem B. It is then submitted to CCC purification with a biphasic four-solvent liquid system. A 160-fold enrichment was obtained in one step producing a raffinate containing 10% or 100 mg/g of the toxin. Further purifications were then performed by thin layer and low pressure liquid chromatography. Twenty-eight micrograms of lolitrem B with a 96% purity grade were obtained from 8 kg of seeds (yield 32%).
The present work deals with the study of water-methylene chloride microemulsions stabilized with ... more The present work deals with the study of water-methylene chloride microemulsions stabilized with an active blend composed of sodium p-octylbenzenesulphonate as surfactant and a series of linear alcohols from propanol to heptanol as cosurfactant. The oil was chosen because of its ability to solubilise water-insoluble compounds which offers potential use in organic electrochemistry. The pseudoternary mass phase diagrams were determined at room temperature for a cosurfactant to surfactant mass ratio equal to 2. They display an isotropic phase area whose shape and size depend greatly on the alcohol and seem to be related, to a great extent, to the capacity of the microemulsions for solubilizing water. Viscosity and conductivity measurements show that the fluidity of the microstructures decreases when the alcohol chain length increases with an abrupt change from pentanol to hexanol. An attempt to better understand the structure and dynamics of the microemulsions has been made by electrochemical measurement of the diffusion coefficients of two electroactive probes: an oil-soluble one (N-methyl phenothiazine) and a water-soluble one (hydroquinone). The measured diffusion coefficients are comparable in their values and their variations to the expected self-diffusion coefficients of methylene chloride and water respectively, and thus provide valuable information about the composition of the continuous and disperse phases. Our results demonstrate once again the relation between the structure of the microemulsions and the nature of the alcohol cosurfactant. The comparison between the behavior of our water-CH2Cl2 system and the well-known waterdodecane system seems to confirm that the influence of the alcohol chain length is invariant with respect to the oil type. More significant features relating the microemulsion structure to the nature of the cosurfactant would be based on the role of the cosurfactant on the fluidity of the structure; it would depend on the mutual solubility of the compounds, the alcohol/surfactant molecular ratio which decreases from propanol to heptanol and a steric and concentration effect of the alcohol on the interphase curvature and flexibility.
Micelle-mimetic ionene-based stationary phases for high-performance liquid chromatography (HPLC) ... more Micelle-mimetic ionene-based stationary phases for high-performance liquid chromatography (HPLC) are prepared by attaching [3,16]- and [3,22]-ionenes to aminopropyl silica through a carbon-nitrogen bond. These [x,y]-ionenes are polyelectrolytic molecules consisting of dimethylammonium charge centers interconnected by alternating alkyl chain segments containing x and y methylene groups, some of which can form aggregate species whose properties mimic those of conventional surfactant micelles. These ionene-bonded stationary phases were characterized using different recommended HPLC test mixtures. Test solute chromatographic behavior on the ionene phases was found to be similar to that of intermediate oligomeric or polymeric C-18 and/or phenyl phases, depending upon the specific test mixture employed. In addition, the phases exhibit significant solute shape recognition ability. The ionene stationary phases were successfully employed for the separation of the components of the recommended ASTM reversed-phase test mixture, as well as for ortho-, meta- and para-disubstituted benzenes and other positional or geometric isomeric compounds. The ionene materials allow for chromatographic separations under either reversed-phase or ion-exchange conditions. The retention mechanism on these multimodal phases can occur by hydrophobic partitioning or electrostatic interactions, depending upon the characteristics of the components of the analyte mixture (neutral or anionic). The effects of alteration of the percent organic modifier, flow rate and temperature of the mobile phase on chromatographic retention and efficiency on these phases were briefly examined.
The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chr... more The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants. Most of the columns (Le., 18) were wall-coated, and four were of the wall-immobilized or of the so-called "bonded" type. A wall-coated capillary squalane column was specially prepared as a polarity reference column. All but two of the CSPs were based on derivatized cyclodextrins (CDs) of different sizes. The overall properties of the CSPs are discussed in terms of the five Rohrschneider-McReynolds constants and their average values. It was found that the derivatized cyclodextrin CSP polarity increased with the CD ring size. The bonded CSPs were significantly less polar than their coated homologues due to the apolar polymer used to immobilize the CD rings. The retention behavior of 14 compounds was studied at 100 "C on the capillary columns. Retention parameters are clearly related to the McReynolds constants. Conversely, the enantiomeric resolution capability of a given stationary phase is not related to the constants. The enantioselective resolution mechanism critically depends on the solute structure and on the nature of the CSP. The efficient separation of racemic mixtures has been one of the most important challenges for analytical chemistry at the end of this century. Tremendous advances have been made in this area in the last 10 years. Chromatographic techniques seem to be the most promising for accurate determination of enantiomer impurities of low levels.' All chromatographic techniques, HPLC? TLC,3-5 SFC,6-* and GC,9-19 can be used for the separation of (1) Ziet M.; Crane, L.
Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cros... more Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cross section of organic molecules (five to six orders of magnitude) when molecules are adsorbed onto metal surfaces. The use of silver hydrosols, obtained by chemical reduction of silver nitrate solutions, is convenient. An important drawback is irreproducibility of hydrosol preparation procedures and the nonlinearity between the SERS response and the analyte concentration. In order that these problems could be overcome, flow injection analysis (FIA) has been used. With FIA, constant, reproducible silver hydrosol formation results. SERS signals of para-aminobenzoic acid (PABA) were measured over four orders of magnitude of concentration range and over three pH units. The precision of FIA-SERS signals for PABA was 5%, and the limit of detection of PABA was in the ppb range with the use of the Raman band at 1605 cm-' with an Ar ÷ laser at 514.5 nm. Index Headings: Surface enhanced Raman scattering; Flow injection analysis; pH Effect; Para-aminobenzoic acid.
Room temperature ionic liquids (RTIL) are molten salts starting to be used as nonmolecular solven... more Room temperature ionic liquids (RTIL) are molten salts starting to be used as nonmolecular solvents in separation methods mainly for their extremely low vapor pressure and thermal stability. RTILs are formed by an anion associated to a cation. This intrinsic structure gives them a dual nature. When used as additives in RPLC mobile phases to enhance basic compound separation, RTILs lose their particular physicochemical properties to become just salts. However, a given RTIL is not equivalent to another one made with the same cation. It is shown that both the anion and the cation contribute to solute retention and peak efficiency extending beyond simple "salting-out" or ion-pairing effects. Nine different alkylmethyl-imidazolium ionic liquids with different alkyl chain length and chloride or BF 4or PF 6anions were used as additives (50 mM max. conc.) in the liquid chromatography separation of some cationic basic solutes on a Kromasil C 18 column. It is shown with sodium salts and an acetonitrile-water 30/70 v/v mobile phase that anions can adsorb on the stationary phase surface according to their lyotropic character. They can also form ion pairs with the cationic basic solutes. Alkyl-imidazolium cations also adsorb on the C 18 bonded stationary phase due to hydrophobic character depending on their alkyl chain length. Anion adsorption dramatically increases the cationic solute retention factors when cation adsorption decreases them. The cation adsorption is mainly responsible for peak shape and efficiency enhancements. RTILs are additives that enhance the basic cationic solute peak shape changing peak position. A wise choice of the appropriate combination of anion lyotropy with imidazolium cation hydrophobicity allows playing with solute selectivity and analysis duration.
Micellar liquid chromatography was used to analyse some drugs illegally used in sport. The spectr... more Micellar liquid chromatography was used to analyse some drugs illegally used in sport. The spectroscopic characteristics, UV absorption and fluorescence, of oxandrolone, methyl testosterone, testosterone enanthate, caffeine, ephedrine, bumetamide, chlortalidone, dihydrochlorothiazide, furosemide, spironolactone and propranolol were established in water and sodium dodecyl sulfate micellar solution. The chromatographic retention parameters were determined
This paper describes intermittent counter-current extraction, a novel method of using a conventio... more This paper describes intermittent counter-current extraction, a novel method of using a conventional twin column counter-current chromatograph to either split a sample into two groups of compounds or extract and enrich a target compound from a crude extract. The first method is demonstrated by splitting a model mixture of four compounds into two groups. The second method is demonstrated by the extraction and enrichment of a high value target compound, triptolide, from a Chinese herbal medicine crude extract of Tripterygium wilfordii Hook. f., where it is found at low concentration (2%). This was achieved by retaining and enriching the target compound within the column while washing away all other components of the crude material. The success of the first method allowed the second method to be carried out without the need for costly preliminary experiments with the high value sample. 188 mg of triptolide at greater than 98% purity was separated from 9.2 g of crude extract, using 10 l of solvent in a 3-h separation.
(3R)-(−)-7,2-Dihydroxy-3 ,4-dimethyl isoflavan-7-O--d-glucopyranoside and (6aR, 11aR) 9,10-di-me... more (3R)-(−)-7,2-Dihydroxy-3 ,4-dimethyl isoflavan-7-O--d-glucopyranoside and (6aR, 11aR) 9,10-di-methoxypterocarpan-3-O--dglucopyranoside were separated from the ethyl acetate extract of the root of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao by high-speed counter-current chromatography (HSCCC). A two-phase system composed of ethyl acetate-ethanol-acetic acid-water (4:1:0.25:5, v/v) was selected by analytical HSCCC. Preparative HSCCC yielded, from 100 mg of the partially purified extract, 50 mg of isoflavan glycoside and 10 mg of pterocarpan glycoside each at over 95% purity by high-performance liquid chromatography (HPLC) analysis. Their structures were identified by MS, 1 H NMR and 13 C NMR.
Heptans-sodlum dodecyl sulfate (SDS)-pentanol-water oll-In-water mkroemuldons were Investigated a... more Heptans-sodlum dodecyl sulfate (SDS)-pentanol-water oll-In-water mkroemuldons were Investigated as a moblle phase In r e v-HquM chromatography. The mass ratb SDS/ pentanol was kept constant, 112, for all compodlons. The retention and peak efflclency of alkylbenzenes, toluene, bu-tyEenzene, heptylbenzene, and decylbenzene, were measured on an octadecyl bonded 15-m column. Water-rlch mkro-emulslo~ (>87% w/w water) of the L1 oll-ln-water structure were able to separate the alkylbenzene homologues with a linear k'vs nc relatlonshlp, nc k the atom carbon number of the alkyl chaln. The dopes and Intercepts of the k'vs nc llnes depend on the relative vdume of organic phase. Heptane and the active blend SDS + pentanol play a similar rob on selectlvlty. They have an oppodte effect on efflclency. A higher content of the active blend SDS + pentanol produced a higher dfklency for the alkylbenzene peaks. Addition of heptane to any SDS-pentanol-water phases produced a dramatic decrease In etllclency, specialty for the long-chain homokgueci. TheoolutemasrtranderdecreasesexpamntWy with the alkyl chaln length. Efficiency studles can be related to physlcochemlcal changes of the mlcroemuldon structure.
1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF 6) was synthesized and purified to be us... more 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF 6) was synthesized and purified to be used as a ionic liquid solvent. Its physicochemical properties were studied. The ionic liquid/water (P il/water) and ionic liquid/heptane (P il/heptane) distribution coefficients of a set of 40 compounds with various functionalities, including organic acids, organic bases, amino acids, antioxidants, and neutral compounds, were measured using liquid chromatography. For ionizable compounds, the P il/water values measured at pH 2, 5.1, and 10 were very different. These allowed the determination of both the molecularP o il /water values and the ionPil /water value for each compound. These coefficients were compared to the corresponding P oct/water coefficients. Marked differences in the partitioning behavior of basic, acidic, and neutral compounds were observed. The relationship between P il/water and P oct/water is different from that reported previously. By using the linear free energy solvation approach and the descriptors found for 12 solutes, the BMIM-PF 6 solvent parameters were calculated for the ionic liquid/water and ionic liquid/heptane biphasic systems. The regression parameters show a low basicity of the BMIM-PF 6 solvent compared to octanol. The high cohesion of the ions in the ionic liquid phase is also indicated by the regression equations obtained. Ionized phenols (phenoxide ions) associate more strongly with BMIM-PF 6 than most other ionized molecules. Amino acids were not soluble in ionic liquid; however, it is possible to extract them partially by adding a crown ether to the ionic liquid phase and working at pH 1. The positive form of amino acids is complexed by the crown ether and the complex is extracted in the ionic liquid phase.
This paper describes a new method of purification of the Lolitrem B, a tremorgenic mycotoxin prod... more This paper describes a new method of purification of the Lolitrem B, a tremorgenic mycotoxin produced in planta by the endophytic fungus Neotyphodium lolii. The method is based on the large-scale isolation of the toxin by countercurrent chromatography (CCC). The lolitrem B content in endophyted ryegrass seed, 11 microg/g or 11 ppm, is extracted by stirring finely ground seeds with ethanol for 3 h at room temperature. The concentrated crude extract contains about 0.6 mg/g or 600 ppm of lolitrem B. It is then submitted to CCC purification with a biphasic four-solvent liquid system. A 160-fold enrichment was obtained in one step producing a raffinate containing 10% or 100 mg/g of the toxin. Further purifications were then performed by thin layer and low pressure liquid chromatography. Twenty-eight micrograms of lolitrem B with a 96% purity grade were obtained from 8 kg of seeds (yield 32%).
The present work deals with the study of water-methylene chloride microemulsions stabilized with ... more The present work deals with the study of water-methylene chloride microemulsions stabilized with an active blend composed of sodium p-octylbenzenesulphonate as surfactant and a series of linear alcohols from propanol to heptanol as cosurfactant. The oil was chosen because of its ability to solubilise water-insoluble compounds which offers potential use in organic electrochemistry. The pseudoternary mass phase diagrams were determined at room temperature for a cosurfactant to surfactant mass ratio equal to 2. They display an isotropic phase area whose shape and size depend greatly on the alcohol and seem to be related, to a great extent, to the capacity of the microemulsions for solubilizing water. Viscosity and conductivity measurements show that the fluidity of the microstructures decreases when the alcohol chain length increases with an abrupt change from pentanol to hexanol. An attempt to better understand the structure and dynamics of the microemulsions has been made by electrochemical measurement of the diffusion coefficients of two electroactive probes: an oil-soluble one (N-methyl phenothiazine) and a water-soluble one (hydroquinone). The measured diffusion coefficients are comparable in their values and their variations to the expected self-diffusion coefficients of methylene chloride and water respectively, and thus provide valuable information about the composition of the continuous and disperse phases. Our results demonstrate once again the relation between the structure of the microemulsions and the nature of the alcohol cosurfactant. The comparison between the behavior of our water-CH2Cl2 system and the well-known waterdodecane system seems to confirm that the influence of the alcohol chain length is invariant with respect to the oil type. More significant features relating the microemulsion structure to the nature of the cosurfactant would be based on the role of the cosurfactant on the fluidity of the structure; it would depend on the mutual solubility of the compounds, the alcohol/surfactant molecular ratio which decreases from propanol to heptanol and a steric and concentration effect of the alcohol on the interphase curvature and flexibility.
Micelle-mimetic ionene-based stationary phases for high-performance liquid chromatography (HPLC) ... more Micelle-mimetic ionene-based stationary phases for high-performance liquid chromatography (HPLC) are prepared by attaching [3,16]- and [3,22]-ionenes to aminopropyl silica through a carbon-nitrogen bond. These [x,y]-ionenes are polyelectrolytic molecules consisting of dimethylammonium charge centers interconnected by alternating alkyl chain segments containing x and y methylene groups, some of which can form aggregate species whose properties mimic those of conventional surfactant micelles. These ionene-bonded stationary phases were characterized using different recommended HPLC test mixtures. Test solute chromatographic behavior on the ionene phases was found to be similar to that of intermediate oligomeric or polymeric C-18 and/or phenyl phases, depending upon the specific test mixture employed. In addition, the phases exhibit significant solute shape recognition ability. The ionene stationary phases were successfully employed for the separation of the components of the recommended ASTM reversed-phase test mixture, as well as for ortho-, meta- and para-disubstituted benzenes and other positional or geometric isomeric compounds. The ionene materials allow for chromatographic separations under either reversed-phase or ion-exchange conditions. The retention mechanism on these multimodal phases can occur by hydrophobic partitioning or electrostatic interactions, depending upon the characteristics of the components of the analyte mixture (neutral or anionic). The effects of alteration of the percent organic modifier, flow rate and temperature of the mobile phase on chromatographic retention and efficiency on these phases were briefly examined.
The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chr... more The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants. Most of the columns (Le., 18) were wall-coated, and four were of the wall-immobilized or of the so-called "bonded" type. A wall-coated capillary squalane column was specially prepared as a polarity reference column. All but two of the CSPs were based on derivatized cyclodextrins (CDs) of different sizes. The overall properties of the CSPs are discussed in terms of the five Rohrschneider-McReynolds constants and their average values. It was found that the derivatized cyclodextrin CSP polarity increased with the CD ring size. The bonded CSPs were significantly less polar than their coated homologues due to the apolar polymer used to immobilize the CD rings. The retention behavior of 14 compounds was studied at 100 "C on the capillary columns. Retention parameters are clearly related to the McReynolds constants. Conversely, the enantiomeric resolution capability of a given stationary phase is not related to the constants. The enantioselective resolution mechanism critically depends on the solute structure and on the nature of the CSP. The efficient separation of racemic mixtures has been one of the most important challenges for analytical chemistry at the end of this century. Tremendous advances have been made in this area in the last 10 years. Chromatographic techniques seem to be the most promising for accurate determination of enantiomer impurities of low levels.' All chromatographic techniques, HPLC? TLC,3-5 SFC,6-* and GC,9-19 can be used for the separation of (1) Ziet M.; Crane, L.
Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cros... more Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cross section of organic molecules (five to six orders of magnitude) when molecules are adsorbed onto metal surfaces. The use of silver hydrosols, obtained by chemical reduction of silver nitrate solutions, is convenient. An important drawback is irreproducibility of hydrosol preparation procedures and the nonlinearity between the SERS response and the analyte concentration. In order that these problems could be overcome, flow injection analysis (FIA) has been used. With FIA, constant, reproducible silver hydrosol formation results. SERS signals of para-aminobenzoic acid (PABA) were measured over four orders of magnitude of concentration range and over three pH units. The precision of FIA-SERS signals for PABA was 5%, and the limit of detection of PABA was in the ppb range with the use of the Raman band at 1605 cm-' with an Ar ÷ laser at 514.5 nm. Index Headings: Surface enhanced Raman scattering; Flow injection analysis; pH Effect; Para-aminobenzoic acid.
Room temperature ionic liquids (RTIL) are molten salts starting to be used as nonmolecular solven... more Room temperature ionic liquids (RTIL) are molten salts starting to be used as nonmolecular solvents in separation methods mainly for their extremely low vapor pressure and thermal stability. RTILs are formed by an anion associated to a cation. This intrinsic structure gives them a dual nature. When used as additives in RPLC mobile phases to enhance basic compound separation, RTILs lose their particular physicochemical properties to become just salts. However, a given RTIL is not equivalent to another one made with the same cation. It is shown that both the anion and the cation contribute to solute retention and peak efficiency extending beyond simple "salting-out" or ion-pairing effects. Nine different alkylmethyl-imidazolium ionic liquids with different alkyl chain length and chloride or BF 4or PF 6anions were used as additives (50 mM max. conc.) in the liquid chromatography separation of some cationic basic solutes on a Kromasil C 18 column. It is shown with sodium salts and an acetonitrile-water 30/70 v/v mobile phase that anions can adsorb on the stationary phase surface according to their lyotropic character. They can also form ion pairs with the cationic basic solutes. Alkyl-imidazolium cations also adsorb on the C 18 bonded stationary phase due to hydrophobic character depending on their alkyl chain length. Anion adsorption dramatically increases the cationic solute retention factors when cation adsorption decreases them. The cation adsorption is mainly responsible for peak shape and efficiency enhancements. RTILs are additives that enhance the basic cationic solute peak shape changing peak position. A wise choice of the appropriate combination of anion lyotropy with imidazolium cation hydrophobicity allows playing with solute selectivity and analysis duration.
As the editor of a journal publishing only review articles in the field of separation methods, a ... more As the editor of a journal publishing only review articles in the field of separation methods, a division of analytical chemistry, the need to delineate what a review article is arose in light of the increasing number of inadequate submissions received.
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Papers by Alain Berthod