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61.
Three different types of SCD combustion source have been evaluated for use in the chromatographic analysis of atmospheric sulfur compounds. The conventional FID source and the newer inverted burner source were found to be less sensitive and less stable than the flameless design. Overall, the flameless source was superior for use with HRGC-SCD. 相似文献
62.
Thermal lens detection with a 325.0 nm He-Cd excitation laser is used for thermooptical indirect detection in combination with the capillary electrophoretic separation of organic anions. The optimization of indirect thermooptical detection is discussed. With Mordant Yellow 7 (an azo dye) chosen as a probe ion limits of detection for 1-heptane-, 1-pentane-, 1-butane-, 1-propanesulfonic, and acetic acid at a level of n × 10−7 M were achieved with a separation electrolyte containing 50 μM of the probe ion and 5 mM Tris pH 9.90. A further increase in the detection sensitivity (twofold decrease in the limit of detection ) was obtained with a separation electrolyte containing a volume fraction of 20% acetonitrile. 相似文献
63.
Norbert V. Fehringer Dalia M. Gilvydis Stephen M. Walters Colin F. Poole 《Journal of separation science》1992,15(2):124-127
The combination of open tubular column gas chromatography with electrolytic conductivity detection has been evaluated for the determination of nitrogen-containing pesticide residues in food extracts. Optimization of the column position at the column-detector interface was crucial to the successful operation of the detector. The signal-to-noise ratio and response stability of the detector are greatly influenced by the composition of the electrolyte solvent. Large volume splitless injections using retention gaps and optimized detector operating conditions enabled pesticide residues in food extracts to be determined at sub parts-per-million levels. Although the electrolytic conductivity detector is less sensitive than the thermionic ionization detector, its greater nitrogen selectivity can he crucial to the determination of nitrogen-containing contaminants in food extracts, particularly in complex mixtures where phosphorus-containing contaminants or matrix compounds are also present. 相似文献
64.
A multidimensional GC-system containing two capillary columns of different polarities, operated within a double oven instrument, was used for the optimized separation of complex isomeric mixtures of various types of chlorinated aromatic compounds such as PCB, PCDD, or PCDF. Electron capture was applied parallel to flame ionization detection to obtain sensitive signals of the PCB or PCDD and the n-alkane standards required for identification by Kovats indices, respectively. Electron capture detection within a valvelessly operated MDGC system forced changes in the usual instrumental set-up, the live-switching coupling piece being located within the second oven of the double oven instrument. This oven is operated isothermally to ensure optimal and interference-free detection, for stable flow conditions within the coupling piece and for the determination of the isothermal retention indices (Kovats), which are much more suitable for identification by retention than the so-called “linear” indices. 相似文献
65.
Matthew R OatesWilliam Clarke Alden Zimlich IIDavid S Hage 《Analytica chimica acta》2002,470(1):37-50
Various practical and theoretical considerations were examined in the creation and optimization of a high-performance liquid chromatography (HPLC)-based one-site immunometric assay. This method used an HPLC analyte analog column and post-column chemiluminescence detection. The specific analyte chosen as the model for this study was l-thyroxine (also known as T4). In this technique, a sample containing thyroxine was first combined with an excess of anti-T4 antibody Fab fragments that had earlier been conjugated with chemiluminescent acridinium ester labels. After incubation, the mixture was injected onto a column that contained immobilized T4. The amount of thyroxine in the original sample was then determined by measuring the labeled Fab fragments that appeared in the non-retained fraction, or the decrease in excess Fab fragments that were bound to and later eluted from the column. Items considered in creating this assay included the preparation of acridinium ester-labeled Fab fragments, the detection of these fragments with a post-column reactor, and the creation of a suitable immobilized analog column for capturing excess labeled Fab fragments. The final method could measure T4 in standards at clinically-relevant concentrations and provided a response within 1.5 min of sample injection, following a 20-45 min incubation with the labeled Fab fragments. Possible applications of this method include its use in clinical chemistry and the screening of proteomic or combinatorial libraries. 相似文献
66.
Capillary GC coupled to an atomic emission detector (AED) provides a powerful new hyphenated technique for the separation and characterization of complex mixtures and compounds. The AED provides simultaneous and truly specific multi-element detection. The specificity of detection reduces the need for the complex sample pretreatment procedures which are necessary to reduce the interference from co-eluted substances which is experienced with detectors such as the FID and the ECD. A range of environmentally significant problems has been studied, including PCB analysis, the characterization of the reaction products of a novel waste treatment process, and the profiling of sulfur-containing species formed by the pyrolysis of various types of coal. 相似文献
67.
Summary Retention models for ionic compounds in reversed-phase ion-pair chromatographic systems have been developed on the basis of
the capacity ratios of solutes and ionic mobile phase components using indirect detection. The binding to the adsorbent, μBondapak
Phenyl, has been expressed by ion-pair distribution constants and tested in the retention models by non-linear regression.
All the ionic compounds followed adsorption models of the Langmuir type comprising two kinds of binding sites with widely
different adsorption capacities and binding constants. The results indicate certain differences between the two sites regarding
the binding of cationic and anionic components, respectively. 相似文献
68.
Solid solutions NaCl—CdCl2 were studied in an interval of CdCl2 concentrations of 0.05—3 mol.% by Raman spectroscopy. The molecular form Na2CdCl4 decomposes: Na2CdCl4 2Na+ + Cd2+ + 2Cl2
– + 2e–; 2Na + 2e– 2Na0. Free sodium atoms form color centers of crystal (F centers) in the region of jumpwise changing the partition coefficient of CdCl2 in NaCl (K jump). 相似文献
69.
Summary Conditions have been established for identification and quantification of cefuroxime axetil and cefuroxime by thin-layer chromatography and densitometry. Good separation of these compounds was achieved on silica gel by use of chloroform–ethyl acetate–glacial acetic acid–water, 4:4:4:1 (v/v), as mobile phase. UV densitometry was used to detect spots on chromatograms. Under these conditions the limits of detection for cefuroxime axetil and cefuroxime were 40 ng and 30 ng, respectively. Recoveries of cefuroxime axetil and cefuroxime were 99.93% and 97.94%, respectively. 相似文献
70.
郝高麟 《光纤与电缆及其应用技术》2006,(3):38-43
介绍了电缆充气的必要性,电缆充气设备的选型,电缆施工和维护的具体要求和标准,这将有助于提高电缆电气特性和传输质量,延长电缆使用寿命,及时发现与减少电缆故障,确保通信质量. 相似文献