Search results for "performance"
showing 10 items of 4457 documents
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…
Stability of tocopherols in adapted milk-based infant formulas during storage
2004
Abstract An evaluation is made of the effects of added α -tocopherol ( α -T) or α -tocopherol acetate ( α -TAc) combined with iron lactate or sulfate, storage time (up to 17 months) and storage temperature (22°C and 37°C) on the α -TAc, α -T, γ -tocopherol ( γ -T) and δ -tocopherol ( δ -T) content of infant formulas. Tocopherols were measured by normal phase HPLC and fluorescence detection after direct extraction, which allows the determination of both α -TAc and α -T. The α -TAc content was not affected by temperature or storage time, although the α -, γ - and δ -T contents, which were lower at 37°C than at 22°C, were significantly affected. The type of iron salt added (lactate or sulfate)…
Determination of α-Tocopherol in Plasma by High Performance Liquid Chromatography with Fluorescence Detection and Stability of α-Tocopherol under Dif…
2011
In order to study the clinical effects of the antioxidant alpha-tocopherol (tocofersolan, CAS 30999-06-5) a simple, robust, sensitive and reliable high performance liquid chromatography (HPLC) method using fluorescence detection for the daily measurement of alpha-tocopherol concentration in plasma is described. Several methods of HPLC analysis using fluorescence techniques are published, however, investigations of the stability of alpha-tocopherol during sample preparation under different conditions are relevant in the routine measurements and have to date not been reported. Therefore a modified method, both sensitive and robust, qualified for the day-by-day measurement of alpha-tocopherol …
Towards the optimization of complementary systems in reversed-phase liquid chromatography
2002
Previously reported optimization methodology, which seeks complementary mobile phases (CMP) in isocratic chromatography, has been extended to include more than one system simultaneously (i.e. more than one organic solvent and/or column). In the literature the benefits of complementarity are not usually fully exploited—few working conditions giving rise to interactions as different as possible are examined, without developing a fully linked optimization. The proposed approach is compared critically with use of a single mobile phase or CMP which consider one system only. The strategy greatly expands the capability of isocratic chromatography in the analysis of complex samples that cannot be r…
Possible interferences of mercury sulfur compounds with ethylated and methylated mercury species using HPLC-ICP-MS
2002
The HPLC-ICP-MS coupling technique is able to separate and detect methyl, ethyl and inorganic mercury isotopes specifically. An identification of ethyl mercury(+) is not possible when the widely used sodium tetraethylborate derivatisation method in combination with GC-AFS/AAS or ICP-MS techniques is performed because it contains ethyl groups.An unidentified compound with the same retention time as ethyl mercury was found in the HPLC chromatograms of industrial sewage samples and humic-rich soils of microcosm experiments after applying water vapour distillation. We also observed such unidentified peaks in samples of heavily contaminated sites in Eastern Germany, separated by HPLC fractionati…