Showing papers in "Analytical Chemistry in 1981"

Chemical class separation and characterization of organic compounds in synthetic fuels

Abstract: A separation method is described for the identification of organic compounds in synthetic fuel products. Prefractionation of crude synfuel materials into discrete chemical classes was prformed by adsorption column chromatography using small quantities of neutral aluminum oxide and silicic acid. Subsequent high-resolution separation of individual components was achieved by using capillary column gas chromatography, and specific compound types were determined by gas chromatographic retention data and combined gas chromatography-mass spectrometry. The principal chemical classes investigated in a solvent-refined coal liquid were aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, polycyclic aromatic sulfur heterocycles nitrogen polycyclic aromatic compounds, and hydroxyl polycyclic aromatic hydrocarbons. The nitrogen-containing aromatic compounds were further separated into secondary nitrogen polycyclic aromatic heterocycles, amino polycyclic aromatic hydrocarbons, and tertiary nitrogen polycyclic aromatic heterocycles to facilitate their identification.

Quality Assurance of Chemical Measurements

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Microwave-excited atmospheric pressure helium plasma emission detection characteristics in fused silica capillary gas chromatography

Abstract: Interfacing of fused silica gas chromatographic capillary columns to a microwave-excited atmospheric pressure helium plasma (MED) is investigated. The system for glass and fused silica capillary operation incorporates an interface where excess solvent can be vented by a chemically deactivated fluidic-logic gas switching system. A TM/sub 010/ resonant cavity allows axial viewing of plasma emission. A quartz refractor plate background corrector improves selectivity ratios for elements whose emission occurs in the high-carbon (cyanogen) background region. Background emission characteristics of the helium plasma under various conditions are established from 200 to 500 nm. Calibration curves, selectivity ratios, and detection limits are established for the elements vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, nickel, mercury, boron, aluminum, carbon, silicon, germanium, tin, lead, phosphorus, arsenic, sulfur, selenium, fluorine, chlorine, bromine, iodine, hydrogen, and deuterium.

Isotopic Determination of Uranium in Picomole andSubpicomole Quantities

Abstract: A procedure for the separation of U and measurement of U Isotopes in meteoritic, lunar, and terrestrial samples Is described. Accurate ^(238)U/^(235)U ratios and U concentration measurements can be done on a routine basis at the level of ~ 10^(-13) mol of U by Isotope dilution using a double tracer composed of ^(233)U and ^(238)U. Precise determination of the number of U atoms In a sample can be done at the level of 10^8-10^9 atoms. The technique Involves careful control of the chemical procedures to eliminate laboratory contamination and precise calibration of the mass spectrometer In order to obtain high reproducibility. The ^(238)U/^(235)U ratios were measured on a wide variety of samples which Include bulk meterorltes, lunar samples, coarse-grained Ca-AITI- rlch Inclusions and fine-grained AI-Mg-Na-rich Inclusions from the Allende meteorite, and phosphates from three meteorites. The results show the same Isotopic values within limits of errors as that measured on normal terrestrial U to within 4‰. All of the analyzed meteorite samples are very ancient and several of them show large fractionations of U relative to Th and Nd. These data Imply that ^(247)Cm was not abundant In the early solar system (^(247)Cm/^(235)U « 4 X 10^(-3)) and that the last major "r" process terminated at ~ 10^8 years prior to the formation of the solar system.

Identification of organic compounds on diesel engine soot

Abstract: Several studies have shown that extracts of soot collected from light-duty diesel engines cause mutations in bacteria and mammalian cells both with and without metabolic activation. To help identify the specific compounds responsible for these biological effects, the detailed chemical composition of one such extract by gas chromatographic mass spectrometry was investigated. The two most mutagenic fractions contain alkylated phenanthrenes, fluorenes, fluorenones, and other polycyclic aromatic hydrocarbons, aldehydes, and quinones. One nitro polycyclic aromatic compound was also identified. The biological implications of these findings are discussed.