Search results for "Liquid Chromatography"
showing 10 items of 942 documents
Off-line dansylation of amines using C18 solid-phase packings: study of the fluorescence and chemiluminescence detection by post-column derivatizatio…
1999
Abstract Dansylation of amines (primaries and secondaries) using C18 solid-phase supports is described. The time of analysis and the handing sample have been markedly improved with respect to those required for solution dansylation. The dansylated amine derivates were injected onto the liquid chromatography system and fluorescence detected. The sensitivity and selectivity is better than the other dansylation procedures described in the literature and also better than other derivatization reagents such 1,2-napthoquinone 4-sulfonate (NQS) or 3,5-dinitrobenzoyl chloride (3,5-DNB). Dansyl compounds can also form chemiluminescent derivatives, therefore a post-column derivatization procedure with…
Method development for the determination of 1,1-dimethylhydrazine by the high-performance liquid chromatography-mass spectrometry technique.
2018
Unsymmetrical dimethyl hydrazine is highly toxic, carcinogenic compound, widely used for organic synthesis and drug development. Therefore, due to its high reactivity, direct analysis is problematic. Current study proposes to use derivatization reaction to increase selectivity and sensitivity of high-performance liquid chromatography–mass spectrometry method. Different derivatization agents were tested and optimal reaction media was found. Derivatization was performed by using small amounts of reagents to lower the cost of analysis. The full validation of the method was performed and it can be used in a routine control in pharmaceutical analysis. Method sensitivity is 0.15 ppm, and lineari…
Improvement of peak shape and separation performance of beta-blockers in conventional reversed-phase columns using solvent modifiers.
2003
A comparative study of peak shape, elution behavior, and resolution of 16 beta-blockers (acebutolol, alprenolol, atenolol, bisoprolol, carteolol, celiprolol, esmolol, labetalol, metoprolol, nadolol, oxprenolol, pindolol, practolol, propranolol, sotalol, and timolol) chromatographed with hybrid mobile phases of triethylamine (TEA)-acetonitrile and sodium dodecyl sulfate (SDS)-propanol is performed using conventional reversed-phase columns and isocratic elution. Both solvent modifiers (TEA and SDS) prevent the interaction of the basic drugs with the alkyl-bonded phase. However, the protection mechanisms of silanols on the packing are different. Whereas TEA associates with the silanol sites (b…
A multinjection strategy for mercury speciation.
2005
Abstract A multiinjection strategy has been developed to increase the sampling throughput of the high-performance liquid chromatography determination of inorganic-mercury, methylmercury, ethylmercury and phenylmercury. The method involves the injection of samples each 3.5 min, in spite of the fact that phenylmercury retention time corresponds to 9.04 min. In the selected conditions, the sampling frequency was 11 h −1 in front of that of 6 h −1 , obtained by conventional injection of each sample after the complete elution of Hg species. Additionally, the analytical reagents consumption was reduced drastically in almost 50%. The main characteristics of the chromatographic separation were main…
Analysis of tricyclic antidepressants in pharmaceuticals by microemulsion liquid chromatography
2021
Abstract Basic compounds yield long retention times and broad and asymmetric peaks in reversed-phase liquid chromatography, due to interaction with residual silanols in the columns. The addition of the surfactant sodium dodecyl sulphate in the so called micellar liquid chromatography enhances the efficiency, but long retention is achieved, due to electrostatic interaction between the cationic species of basic compounds and the anionic sulphate group of the surfactant. This forces the addition of a strong organic solvent to get appropriate times. An alternative is the use of a microemulsion (ME), formed by mixing surfactant, oil and an alcohol as co-surfactant. Association of hydrophobic com…
Comparative study of capillary electroendosmotic chromatography and electrically assisted gradient nano-liquid chromatography for the separation of p…
2000
Capillary electroendoendosmotic chromatography (CEC), being a hybrid of high-performance liquid chromatography (HPLC) and capillary electrophoresis, offers considerable changes to enhance column efficiency, speed of analysis and additional selectivity as compared to the parent methods. The analytes are driven by the electroendosmotic flow (EOF) and separated by surface-solute interactions as well as by differences in electromigration. In this paper on the separation of peptides on C18 reversed-phase and mixed-mode (sulphonic acid-n-alkyl) packings in CEC and electrically assisted reversed-phase gradient nano-LC are investigated. It is shown that mixed mode packings generate a higher EOF tha…
Microporous hypercrosslinked polystyrene Styrosorb as a restricted access packing in sample clean-up for high performance liquid chromatography. Part…
1993
Styrosorb is a beaded microporous polystyrene with particle sizes between 2 and 4 μm. In spite of hypercrosslinkage the material was seen to swell in organic solvents. The native material is functionalized with Tris-groups at the outer surface of the particles. The average pore diameter was determined as 1.45±0.3 nm from size exclusion data using polystyrene and polyethylene standards in THF. The reversed phase behavior of the restricted access phase Styrosorb was investigated by injection of two test mixtures. Mixture I contained five aromatic amines, mixture II consisted of AmperozideR and four related compounds. The optimum range of mobile phase composition was assessed so that analytes …
Prediction of peak shape as a function of retention in reversed-phase liquid chromatography
2004
Optimisation of the resolution of multicomponent samples in HPLC is usually carried out by changing the elution conditions and considering the variation in retention of the analytes, to which a standard peak shape is assigned. However, the change in peak shape with the composition of the mobile phase can ruin the optimisation process, yielding unexpected overlaps in the experimental chromatograms for the predicted optimum, especially for complex mixtures. The possibility of modelling peak shape, in addition to peak position, is therefore attractive. A simple modified-Gaussian model with a parabolic variance, which is a function of conventional experimental parameters: retention time (tR), p…
BEHAVIOUR OF GRAPHITIZED CARBON BLACK IN THE EXTRACTION OF POLAR NON-IONIC NITROGEN-CONTAINING PESTICIDES. A CHECKING OF HYPOTHESES
2000
Graphitized Carbon Black (GCB) extractive cartridges are evaluated for on-line coupling with a C8 analytical column to determine eleven carbamates and one carboximide pesticide from spiked deionized water at the 1.2 μg/L level. Several experiments were carried out to ascertain whether GCB saturation, pesticide degradation on the surface, existence of by-pass channels, mobility among the bulk cartridge, or strong retention on the surface interfere with the determination of pesticides. Problems in on-line CGB elution are partially solved by modifying the acetonitrile/water gradient to contain a front of 100% acetonitrile for a few seconds. Eluting the same GCB cartridges off-line with dichlor…
Rapid method for analysis of nicotine and nicotine-related substances in chewing gum formulations
1998
Abstract Based on environmental requirements and demands for a high throughput a rapid method for the analysis of nicotine and nicotine-related substances in chewing gum formulations was developed. The method is based on sample preparation through liquid–liquid extraction followed by reversed-phase HPLC using gradient elution. It allowed up to nine analytes to be determined within 15 min, including the sample preparation, and was considered as accurate and robust.