1,720,956 research outputs found
Headspace solid-phase microextraction for the determination of benzene, toluene, ethylbenzene and xylenes in urine
No full textA method for the determination of benzene, toluene, ethylbenzene and xylenes (BTEX) in urine of people exposed to these airborne pollutants present in the living environment, has been described. Solid-phase microextraction has been used for sampling BTEX from the headspace of urine and gas chromatography-mass spectrometry has been applied for the selective analysis of chemicals. The method has the following features: small volume of urine (2 ml) needed, linearity in the range of interest (from the limit of detection up to 5000 ng/l) with coefficient of correlation > or =0.998, limit of detection in the range 12-34 ng/l, good repeatability (coefficient of variation 2-7%), high specificity. The stability of the urine sample during storage (-20 degrees C) was evaluated: BTEX remained stable for up to 2 months. The assay has been successfully applied to the biological monitoring of two subjects environmentally exposed to airborne BTEX in an urban area
Biological monitoring of exposure to solven : a method for the gas-chromatographic determination of aromatic hydrocarbons in the blood and urine
No full textA gas chromatographic procedure with dynamic head-space purge and trap preconcentration (HSGC) and FID detection for blood and urinary benzene, toluene, ethylbenzene and xylenes (BTEX) determination at low level exposure is described. Critical steps (sample collection, calibration, HSGC conditions, contamination control) are discussed. The calibration curve is linear in the range 50 ng/l-500 micrograms/l; the calculated detection limit is 50 ng/l for all the considered aromatic hydrocarbons (AH) both in blood and urine; the within-day precision, calculated as variation coefficient (CV) at 400 ng/l and 40 micrograms/l (n = 6) was respectively CV = 13% and CV = 6% for all the studied analytes. The recovery rate was in the range 29-70%, depending on the hydrocarbon and matrix (blood or urine) considered. The procedure was applied to the biological monitoring of 151 workers occupationally or environmentally exposed to BTEX. Occupationally exposed subjects showed blood AH levels of 2-4 order of magnitude higher than environmentally exposed subjects. In white-collar workers exposed to BTEX urban pollution a significant difference in blood and urine levels of AH was observed between nonsmokers and smokers. Nonsmokers showed blood AH median values of respectively benzene = 241 ng/l, toluene = 759 ng/l, ethylbenzene = 140 ng/l, xylenes = 604 ng/l. Significatively higher BTEX blood values were observed in smokers after a median consumption of 5 cigarettes in 5 hours; observed median values were respectively: benzene = 365 ng/l toluene = 1327 ng/l, ethylbenzene = 233 ng/l, xylenes = 794 ng/l.A gas chromatographic procedure with dynamic head-space purge and trap preconcentration (HSGC) and FID detection for blood and urinary benzene, toluene, ethylbenzene and xylenes (BTEX) determination at low level exposure is described. Critical steps (sample collection, calibration, HSGC conditions, contamination control) are discussed. The calibration curve is linear in the range 50 ng/l - 500 μg/l; the calculated detection limit is 50 ng/l for all the considered aromatic hydrocarbons (AH) both in blood and urine; the within-day precision, calculated as variation coefficient (CV) at 400 ng/l and 40 μg/l (n = 6) was respectively CV = 13% and CV = 6% for all the studied analytes. The recovery rate was in the range 29-70%, depending on the hydrocarbon and the matrix (blood or urine) considered. The procedure was applied to the biological monitoring of 151 workers occupationally or environmentally exposed to BTEX. Occupationally exposed subjects showed blood AH levels of 2-4 orders of magnitude higher than environmentally exposed subjects. In white-collar workers exposed to BTEX urban pollution a significant difference in blood and urine levels of AH was observed between nonsmokers and smokers. Nonsmokers showed blood AH median values of respectively benzene = 241 ng/l, toluene = 759 ng/l, ethylbenzene = 140 ng/l, xylenes = 604 ng/l. Significatively higher BTEX blood values were observed in smokers after a median consumption of 5 cigarettes in 5 hours; observed median values were respectively: benzene = 365 ng/l, toluene = 1327 ng/l, ethylbenzene = 233 ng/l, xylenes = 794 ng/l
Comparison between blood and urinary toluene as biomarkers of exposure to toluene
No full textObjectives: To compare blood toluene (TOL-B) and urinary toluene (TOL-U) as biomarkers of occupational exposure to toluene, and to set a suitable procedure for collection and handling of specimens. Method: An assay based on headspace solid-phase microextraction (SPME) was used both for the determination of toluene urine/air partition coefficient (lambda(urine/air)) and for the biological monitoring of exposure to toluene in 31 workers (group A) and in 116 non-occupationally exposed subjects (group B). Environmental toluene (TOL-A) was sampled during the work shift (group A) or during the 24 h before specimen collection (group B. Blood and urine specimens were collected at the end of the shift (group A) or in the morning (group B) and toluene was measured. Results: Toluene lambda(urine/air) was 3.3 +/- 0.9. Based on the specimen/air partition coefficient, it was calculated that the vial in which the sample is collected had to be filled up to 85% of its volume with urine and 50% with blood in order to limit the loss of toluene in the air above the specimen to less than 5%. Environmental and biological monitoring of workers showed that the median personal exposure to toluene (TOL-A) during the work-shift was 80 mg/m(3), the corresponding TOL-B was 82 mu g/l and TOL-U was 13 mu g/l Personal exposure to toluene in environmentally exposed subjects was 0.05 mg/m(3), TOL-B was 0.36 mu g/l and TOL-U was 0.20 mu g/l. A significant correlation (P < 0.05) was observed between TOL-B or TOL-U and TOL-A (Pearson's r = 0.782 and 0.754) in workers, but not in controls. A significant correlation was found between TOL-U and TOL-B both in workers and in controls (r = 0.845 and 0.681). Conclusion: The comparative evaluation of TOL-B and TOL-U showed that they can be considered to be equivalent biomarkers as regards their capacity to distinguish workers and controls and to correlate with exposure. However, considering that TOL-U does not require an invasive specimen collection, it appears to be a more convenient tool for the biological monitoring of exposure to toluene
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The application of olfactometric techniques to limit the olfactive nuisance caused by industrial plants with a high environmental impact
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