Search results for "Reversed-phase chromatography"
showing 10 items of 187 documents
Reversed phase liquid chromatography for the enantioseparation of local anaesthetics in polysaccharide-based stationary phases. Application to biodeg…
2020
[EN] A comprehensive study on the chiral separation of bupivacaine, mepivacaine, prilocaine and propanocaine with eight commercial polysaccharide-based chiral stationary phases (CSPs) in reversed phase conditions compatible with MS detection is performed. Methanol and acetonitrile are used as organic modifiers. Retention and resolution values obtained for each compound in the different CSPs and mobile phases are compared. The polysaccharide-based CSPs tested present different enantioselectivity towards the analytes. From the results, the experimental conditions for determining the enantiomers of bupivacaine, mepivacaine, prilocaine and propanocaine in saline aqueous samples using MS detecti…
Performance of amines as silanol suppressors in reversed-phase liquid chromatography
2016
In reversed-phase liquid chromatography, cationic basic compounds yield broad and asymmetrical peaks, as a result of their ionic interaction with the anionic free silanol groups present in the silica-based stationary phases (commonly derivatised with C18 groups). A simple way to improve the peak shape is the addition to the hydro-organic mobile phase of a reagent (usually called additive) with cationic character. This associates with the stationary phase to prevent the access of analytes to the free silanol groups. Cationic additives may interact electrostatically with the anionic silanols. The hydrophobic region of the additive may also associate with the alkyl chains bound to the stationa…
Environmentally friendly LC for the simultaneous determination of ascorbic acid and its derivatives in skin-whitening cosmetics
2008
Ascorbic acid (AA), also known as vitamin C, is a very popular skin-whitening agent used in cosmetics. However, the use of AA (and also its sodium or magnesium salts) in cosmetic products is limited owing to its labile oxidative properties. In order to avoid its early degradation, different derivatives have been designed, such as ascorbyl phosphate (APH; as magnesium or sodium salts) and ascorbyl palmitate (AP), and more recently the ascorbyl glucoside (AG). Bearing in mind that all these chemicals in skin-whitening cosmetic products must be determined in order to control the efficacy of such products, this paper focuses on developing a wide-ranging LC analytical method able to determine th…
Enhancement of retention predictions in reversed-phase liquid chromatography using reference compounds
2004
Abstract The use of reference compounds to correct errors associated with the preparation of mobile phase is studied, in order to enhance modelling of retention for optimisation purposes in reversed-phase liquid chromatography. The method fits individual retention models for a set of reference compounds, which are present in all injections. In second step, mobile-phase composition is corrected for each chromatogram, according to the fitted models of the reference compounds. The enhanced precision provided by the large number of replicates for the reference compounds is partially propagated to the retention models of the analytes. The approach is assayed in the separation of amino acids, aft…
Identification of fish species by reversed-phase high-performance liquid chromatography with photodiode-array detection
1998
A method for the separation of sarcoplasmic fish proteins by RP-HPLC is described. The procedure revealed significant differences useful for reliable identification of fish species. Sixteen of the most common Finnish freshwater fish species were differentiated by species-specific HPLC chromatograms obtained using photodiode-array detection (PAD) at 200-350 nm. The analytical column was a Hi-Pore RP-304 reversed-phase column. The separation was performed by a linear gradient of acetonitrile and water with a small amount of trifluoracetic acid (TFA). Star-symbol plots were constructed from the chromatograms to visualize the data. Clearly different HPLC protein profiles for most fish species w…
Gas-liquid chromatographic analyses
1983
Abstract The gas chromatography of mixtures of n -alkyl acetates (CH 3 COOR, R = C 1 —C 8 ) and methyl esters of aliphatic n -carboxylic acids (R′COOCH 3 , R′ = C 1 —C 8 ) and certain of their monochlorinated derivatives has been studied on Carbowax 20M and SE-30 glass capillary columns under the same operating conditions. The separation of the isomeric monochlorinated esters was complete on Carbowax 20M, whereas on SE-30 the peaks of 6- and 7-chlorooctyl acetates and methyl (ω − 1)- and (ω − 2)-chlorooctanoates and -nonanoates partly overlapped. The complete separation of the mixtures could not be achieved, however, on Carbowax 20M, in spite of the use of various operating conditions. The …
Micellar Liquid Chromatography: Fundamentals
2015
The reversed phase liquid chromatography (RPLC) mode with surfactant above the critical micellar concentration (CMC) has been called micellar liquid chromatography (MLC). In pure micellar systems, the retention behavior is explained by considering three phases or environments: surfactant-modified stationary phase, bulk aqueous solvent, and micellar pseudo-phase. Surfactant adsorption on the porous RPLC packing affects chromatographic retention, owing to the change of diverse surface properties of the stationary phase. In pure micellar systems, the retention behavior is explained by considering three phases or environments: surfactant-modified stationary phase, bulk aqueous solvent, and mice…
Correlation between hydrophobicity and retention data of several antihistamines in reversed-phase liquid chromatography with aqueous-organic and mice…
2000
Abstract The correlation between the retention of 12 antihistamines (carbinoxamine, chlorpheniramine, cyclizine, cyproheptadine, dexbrompheniramine, dexchlorpheniramine, diphenhydramine, doxylamine, pheniramine, phenyltoloxamine, pyrilamine and tripelennamine), in reversed-phase liquid chromatography (RPLC) with aqueous-organic (methanol-water) and micellar-organic (sodium dodecyl sulphate (SDS)-pentanol) mobile phases of varying composition, and their octanol-water partition coefficients expressed as log P o/w (ranging between 2.02 for pheniramine and 4.92 for cyproheptadine), was examined. For this study, the retention of the drugs was measured in six mobile phases of methanol-water, and…
Adsorption of the anionic surfactant sodium dodecyl sulfate on a C18column under micellar and high submicellar conditions in reversed-phase liquid ch…
2015
Micellar liquid chromatography makes use of aqueous solutions or aqueous-organic solutions containing a surfactant, at a concentration above its critical micelle concentration. In the mobile phase, the surfactant monomers aggregate to form micelles, whereas on the surface of the nonpolar alkyl-bonded stationary phases they are significantly adsorbed. If the mobile phase contains a high concentration of organic solvent, micelles break down, and the amount of surfactant adsorbed on the stationary phase is reduced, giving rise to another chromatographic mode named high submicellar liquid chromatography. The presence of a thinner coating of surfactant enhances the selectivity and peak shape, es…
Pressurized flow electrochromatography with reversed phase capillary columns
1995
Pressurized flow electrochromatography (PEC) is a hybrid of capillary LC and capillary electroendosmotic chromatography (CEC). Both a pressure gradient and an electric field are applied across a packed capillary. The feasability of a simple, easy to handle PEC instrumentation is demonstrated. Home made capillary columns with four different silica-based reversed phase packings have been operated under PEC conditions separating non ionic and ionic low molecular weight analytes. The capillary columns have been characterized with respect to their separation efficiency and selectivity and the results have been compared to those obtained with the purely pressure driven system. An electrochromatog…