Search results for "Performance."
showing 10 items of 4178 documents
Micellar versus hydro-organic reversed-phase liquid chromatography: a solvation parameter-based perspective.
2007
The performance of the solvation parameter model is examined for micellar liquid chromatography. The results are compared with those offered with hydro-organic eluents, intending to reveal the properties that influence the retention and distinguish the particular behaviour of micellar systems. The retention data of several series of non-ionisable and ionisable compounds (mainly steroids, polyaromatic hydrocarbons, phenols, sulfonamides, beta-blockers, phenethylamines, antihistamines, and diuretics) were used as probe compounds. The micellar mobile phases contained an anionic (sodium dodecyl sulphate), non-ionic (Brij-35), or cationic (cetyltrimethylamonium bromide) surfactant, with or witho…
Isolation of chlorinated dibenzothiophenes by high-performance thin-layer chromatography
1991
Abstract Chlorinated dibenzothiophenes can cause environmental problems analogous to chlorinated dibenzodioxins and dibenzofurans. In the analysis of chlorinated dibenzodioxins by gas chromatography—mass spectrometry some unknown chlorinated compounds have been found. The chlorinated dibenzothiophenes have the same m/z values as the corresponding dioxins in low-resolution mass spectrometry and they are found in same planar aromatic compound fraction in alumina and carbon column chromatography. Some chlorinated dibenzothiophenes were synthesized to serve as model compounds in analytical work. High-performance thin-layer chromatography (TLC) with different plates and several eluents was tried…
SilicaROD™ — A new challenge in fast high-performance liquid chromatography separations
1998
Abstract High performance liquid chromatography (HPLC) has become one of the most used methods for the analysis of compound mixtures in industry, especially for the quality control of products. Nowadays productivity is the major and dominant upcoming issue, i.e. the goal is to drastically reduce the analysis time and cost per analysis. The solution of the task is higher throughput and faster HPLC methods. Here we describe a new monolithic type of HPLC column, the SilicaROD™ column, which permits the fast HPLC separation of compound mixtures within a few minutes.
Thin-layer chromatography of 2-methyl-4-chlorophenoxyacetic acid and its soil metabolites
1980
Abstract The thin-layer chromatography of 2-methyl-4-chlorophenoxyacetic acid, 4-chloro- o -cresol and 3-methyl-5-chlorocatechol and their pentafluorobenzyl derivatives has been studied on silica gel as adsorbent with 19 solvent systems. The best separation of the individual components occurred with toluene-benzene-acetic acid (2:2:1). Chloroform-diethyl ether-toluene (1:1:1) was suitable for the group separation of the pentafluorobenzyl derivatives.
Development of standard operation procedures for the manufacture of n-octadecyl bonded silicas as packing material in certified reference columns for…
2004
The development of standard operation procedures for the manufacture of a n-octadecyl bonded spherical silica packing from partially condensed tetraethoxysilane as silica source is described. The synthesis comprises five intermediate products and six synthesis steps which were examined according to their reproducibility and robustness. The results led to the optimisation of the manufacturing process for a n-octadecyl bonded silica. Correlations were drawn between the dynamic viscosity of the poly(ethoxy)siloxane (PES), the synthesis parameters, the resulting pore structural properties and particle size distribution of the silicas. Validated procedures were developed to manufacture spherical…
Size Exclusion Chromatography for Semipreparative Scale Separation of Au 38 (SR) 24 and Au 40 (SR) 24 and Larger Clusters
2011
Size exclusion chromatography (SEC) on a semipreparative scale (10 mg and more) was used to size-select ultrasmall gold nanoclusters (2 nm) from polydisperse mixtures. In particular, the ubiquitous byproducts of the etching process toward Au(38)(SR)(24) (SR, thiolate) clusters were separated and gained in high monodispersity (based on mass spectrometry). The isolated fractions were characterized by UV-vis spectroscopy, MALDI mass spectrometry, HPLC, and electron microscopy. Most notably, the separation of Au(38)(SR)(24) and Au(40)(SR)(24) clusters is demonstrated.
Accurate determination of element species by on-line coupling of chromatographic systems with ICP-MS using isotope dilution technique
1998
Abstract The instrumental design for coupling different liquid chromatographic systems such as ion, reversed phase, and size exclusion chromatography as well as capillary gas chromatography, with ICP-MS for the determination of element species is described. For accurate analyses obtaining ‘real time’ concentrations of chromatographic peaks, the isotope dilution mass spectrometric (IDMS) technique is applied. Two different spiking modes are possible, one using species-specific and another one using species-unspecific spike solutions of isotope-enriched labelled compounds. The species-specific mode is only possible for element species well defined in their structure and composition, for examp…
Chromatographic determination of caffeine in pharmaceutical formulations using micellar mobile phases
1996
An HPLC procedure is described for the determination of caffeine in pharmaceutical preparations. A Spherisorb octadecylsilane ODS-2 C18 analytical column and spectrophotometric detection at 273 nm were used. The chromatographic behaviour of caffeine with different micellar eluents containing sodium dodecyl sulphate (SDS) is described. The determination of caffeine in pharmaceutical preparations was performed by use of a mobile phase containing 0.05 M sodium dodecylsulphate (SDS) and 1.5% propanol at pH7. At a 6.0 μg mL−1 concentration level the peak area and peak height repeatability were 2.6 and 2.4%, respectively. The application of the proposed method to the analysis of five pharmaceutic…
Multicommutation-NIR determination of Hexythiazox in pesticide formulations.
2006
A multicommutated flow-system was designed in order to increase analytical throughput and for controlling thermal effects on the NIR spectra for determination of Hexythiazox in pesticide formulations. An on-line standard addition was carried out showing the versatility and repeatability of multicommutation for the on-line mixing and dilution of solutions. Results obtained for commercial samples were statistically comparable with those obtained by an HPLC-reference method. Multicommutation-NIR allows the analysis of 52 samples per hour, in front of the 30 samples per hour analyzed by the NIR-batch procedure and the 7 samples per hour analyzed by HPLC-reference method.
Supercritical fluid extraction of pesticides
1989
The extraction behaviour of 10 μg samples of five pesticides and some related compounds from glass wool with supercritical CO2 has been investigated under several conditions (10 MPa, 20 MPa extraction pressure, 313 K, dry and water saturated CO2). The extraction fluid was decompressed over a line of little columns, filled with 3μ Si60 or RP18, and the amount of deposited material was analyzed by HPLC for each of these columns. Due to the progressive pressure/density reduction along the line, the solubility diminishes and hence the compounds are deposited according to their polarity/vapor pressure earlier or later on the line. Thus extraction and prefractionation of compounds of different po…