Search results for " SEP"
showing 10 items of 1106 documents
Chromatographic Efficiency in Micellar Liquid Chromatography: Should it Be Still a Topic of Concern?
2013
Micellar liquid chromatography (MLC) was first proposed as an attractive alternative to avoid the use of organic solvents. It was soon apparent that pure micellar solutions yield poor efficiencies. This problem was remediated by the addition of a small amount of an organic solvent. However, the general opinion of the poor peak shape has prevailed as a handicap for MLC, in spite of the fact that the hybrid mode often offers similar or even improved efficiencies (for basic compounds) relative to that attained in the hydro-organic mode. Only the efficiencies for apolar non-ionizable compounds are still clearly inferior. This work describes the type of interactions and polarity changes with org…
Profiling of endogenous peptides by multidimensional liquid chromatography: On-line automated sample cleanup for biomarker discovery in human urine.
2009
A simple and flexible system, employing a column switching technique, has been designed to allow the analysis of peptides and proteins smaller than 15 kDa by molecular weight in filtered urine samples by performing a direct on-column injection utilising simultaneous sample clean-up and trace enrichment. The positively charged peptides and small proteins in the sample are attracted to the inner, negatively charged pore structure of the RAM-SCX column while the larger proteins and uncharged or negatively charged compounds are excluded. After preconditioning with the biological sample, large amounts of sample can be injected. Several important and adjustable parameters for the proper use of a …
Comparison of the performance of non-ionic and anionic surfactants as mobile phase additives in the RPLC analysis of basic drugs
2011
Surfactants added to the mobile phases in reversed-phase liquid chromatography (RPLC) give rise to a modified stationary phase, due to the adsorption of surfactant monomers. Depending on the surfactant nature (ionic or non-ionic), the coated stationary phase can exhibit a positive net charge, or just change its polarity remaining neutral. Also, micelles in the mobile phase introduce new sites for solute interaction. This affects the chromatographic behavior, especially in the case of basic compounds. Two surfactants of different nature, the non-ionic Brij-35 and the anionic sodium dodecyl sulfate (SDS) added to water or aqueous-organic mixtures, are here compared in the separation of basic …
Determination of organic contaminants in food by capillary electrophoresis
2005
This review addresses recent advances in the analysis of organic contaminants, such as antibiotics, pesticides, biological toxins, and food-borne pathogens, in foods by capillary electrophoresis (CE). Special attention is paid to those aspects that increase sensitivity and/or selectivity, such as sample extraction and concentration, on-line preconcentration techniques (stacking), affinity capillaries or/and specific detectors (laser induced fluorescence (LIF), mass spectrometry (MS)). The various CE modes used to separate the compounds and the quantification strategies are also examined. As a result, this work presents an updated overview on the principal applications of CE, together with a…
A study on the essential oil of Ferulago campestris : How much does extraction method influence the oil composition?
2011
The essential oil of different parts of Ferulago campestris (Bess.) collected in Sicily has been extracted by microwave-assisted hydrodistillation (MAHD) and by classic hydrodistillation (HD). A comparative qualitative-quantitative study on the composition of the oils was carried out. A total of 100 compounds were identified in the oils obtained by MAHD, whereas 88 compounds characterized the HD oils. The most prominent components were, in all different parts of F. campestris and in both extraction methods, 2,4,5-trimethylbenzaldehyde and 2,4,6-trimethylbenzaldehyde isomers; the latter was not previously found. The attempt to evaluate where the oil components are located in all parts of the…
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…
Comparative study of degassing membrane modules for the removal of methane from Expanded Granular Sludge Bed anaerobic reactor effluent
2016
Abstract The feasibility of an emergent technology for in situ removal/recovery of methane from the effluent of an Expanded Granular Sludge Bed (EGSB) anaerobic reactor has been studied. For this purpose, the performances of two commercial hollow fibre degassing contactors with different membrane materials – microporous (polypropylene, PP) and non-porous (polydimethylsiloxane, PDMS) – were compared. The influence of water fluxes (Q L /A membrane ranging from 22.6 to 377.4 L h −1 m −2 ), vacuum pressure (140–800 mbar), sweep gas fluxes (Q N2 /A membrane ranging from 0.14 × 10 3 to 4.44 × 10 3 L h −1 m −2 ), and mode of operation (liquid flowing in the lumen side or the shell side) was stu…
Evaluation of selected buffers for simultaneous determination of ionic and acidic pesticides including glyphosate using anion exchange chromatography…
2019
Ion chromatography coupled with mass spectrometry is an established technique for determination of ionic analytes, however, sophisticated buffer removal equipment is required to eliminate inorganic compounds from the eluate before introduction into the ion source of mass spectrometer. A standard high-performance liquid chromatography coupled with tandem mass spectrometry setup using an ion exchange column (Metrosep® A Supp 5) is proposed as an alternative approach. For that reason, some buffers including non-volatile carboxylic acid based solutions have been evaluated for simultaneous trace determination of ionic and acidic pesticides including glyphosate in the same extract without a need …
Interpretive optimisation of organic solvent content and flow-rate in the separation of β-blockers with a Chromolith RP-18e column
2009
The chromatographic performance of a Chromolith RP-18e column was comprehensively examined for a group of basic drugs (beta-blockers), eluted with isocratic ACN-water mixtures at increasing flow-rate up to 6 mL/min. As the flow-rate increases at fixed mobile phase composition, peak distribution (selectivity) is maintained, but the relative peak widths increase. This reduces the resolution below satisfactory values for closely eluting compounds. With the monolithic column, flow-rate becomes thus an important factor to be optimised, in addition to the mobile phase composition. Since, theoretically, retention factors (k) are independent of the flow-rate, the classical quadratic model relating …
Complete decontamination and regeneration of DNA purification silica colum
2008
Silica columns are among the most used DNA purification systems, allowing a good yield of high-quality nucleic acids without organic extractions. Silica column regeneration protocols reported up to now to remove DNA traces are time-consuming, and their effectiveness on genomic DNA has not been demonstrated. Here we report a very rapid regeneration procedure that ensures no DNA carryover, independent of its size, without impairing column efficiency. The method takes advantage of the improved DNA removal by low concentrations of Triton X-100.