RESUMO
A low-volume, inert sampling and enrichment device for semivolatile organic vapors is described. The device consists of two concentric fused silica capillaries. A small portion of the inter-capillary volume, cooled with a burst of compressed carbon dioxide, serves as a trap for the semivolatile organics. The low mass of the trap permits rapid sampling and desorption cycles suitable for applications requiring fast monitoring of semivolatile chemicals. The device is devoid of switching valves in the sampling train and consequently does not suffer from analyte loss due to irreversible adsorption or interference resulting from cross contamination. The device was successfully used for sampling low concentrations of highly adsorptive nitroaromatic compounds and is applicable for polychlorinated dibenzo-p-dioxins (PCDDs) and polyaromatic hydrocarbons (PAHs).
Assuntos
Monitoramento Ambiental/instrumentação , Compostos Orgânicos/análise , Dióxido de Carbono/química , Monitoramento Ambiental/métodos , Desenho de Equipamento , Dibenzodioxinas Policloradas/análogos & derivados , Dibenzodioxinas Policloradas/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , Dióxido de Silício , Poluentes do Solo/análise , Manejo de Espécimes , VolatilizaçãoRESUMO
The United States Environmental Protection Agency (US EPA) guidelines allow removal of polychlorinated biphenyls (PCBs) from soils via solvent extraction. This option holds promise for removal of other recalcitrant organic contaminants as well. A study was undertaken to evaluate the effectiveness of solvent extraction with two tandem degradation techniques. The degradation techniques were chemical dehalogenation with immobilized reagents and gamma-ray irradiation. The integrated approach was evaluated with contaminated soils from wood treatment and electric power substation sites. Evaluations were carried out on a bench scale in the laboratory and on a semi-pilot scale at a contaminated site. Binary solvent mixture of alkanes and alcohols yielded the highest extraction efficiencies. Extraction efficiencies in excess of 90% were obtained for PCBs, polychlorinated dibenzo-p-dioxins (PCDDs) and polynuclear aromatic hydrocarbons (PAHs). Extracted PCBs were rapidly degraded through chemical dehalogenation or with high doses of the gamma-ray irradiation. The residual organics in the solvent mixture were removed with activated carbon, and the solvent was recycled for subsequent soil extractions. Contaminants adsorbed on the activated carbon were destroyed with a counter flow oxidation process.
Assuntos
Poluentes Ambientais/análise , Bifenilos Policlorados/análise , Dibenzodioxinas Policloradas/análise , Poluentes do Solo/análise , Carbono/análise , Técnicas de Química Analítica/métodos , Compostos Clorados/química , Halogênios/química , Dibenzodioxinas Policloradas/análogos & derivados , Centrais Elétricas , Sensibilidade e Especificidade , SolventesRESUMO
The differences in the extent of electron-attachment reactions between thermal electrons and selected classes of organic molecules with high electron affinities were investigated. The investigations showed that interactions of thermal electrons with nitroaromatic compounds lead to the formation of neutral products with very low electron affinities. By contrast, a number of other analytes with high electron affinities such as polyhalogenated organic compounds, lead to products with high electron affinities. This difference was exploited to differentiate between nitroaromatic and polychlorinated organic compounds with a tandem arrangement consisting of two electron-capture detectors connected in series with an electron-attachment reactor.
Assuntos
Hidrocarbonetos Aromáticos/análise , Compostos de Nitrogênio/análise , Elétrons , ExplosõesRESUMO
Multivariate regression methods were used to create two equations for calculation of the "iron index," a predictor of bone marrow iron scores. With the use of the most efficient cut-off point, approximately 90% of 210 patients could be diagnosed correctly. Selection of a criterion that minimizes false negatives (missed iron deficiency) would increase the number of unnecessary bone marrow aspirations, but, even then, more than a third of such tests could be avoided. Rapid turnaround time would be desirable for all measurements used to calculate the iron index, although it is recognized that for most hospitalized patients the length of hospital stay is determined by severity of an underlying disease, not the presence of anemia.