Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GAS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1977

The analysis of organic water pollutants by gas chromatography and gas chromatography-mass spectrometry.

Four methods for the analysis of trace levels or organic compounds in water have been discussed: direct aqueous injection, vapor stripping, solvent extraction, and lipophilic adsorption. Table 6 presents a comparison of these techniques. Direct injection is applicable to compounds having a wide range of polarities and volatilities, but it is not a very sensitive technique. For applications in which low sensitivity is acceptable, direct injection offers a very rapid and potentially accurate means of measuring organics in water. Vapor stripping is a factor of 10(6) more sensitive than direct injection, but this is achieved at the expense of simplicity. This method is applicable to compounds of volatilities less than that of eicosane. A subtle operational problem with most vapor stripping techniques is that the contents of the trap are consumed with one analysis; if anything goes awry, the analysis of that trapped sample cannot be repeated. Solvent extraction has a respectable sensitivity (about 0.5 ppb) and operationally it is very simple. Furthermore, aliquots of the resulting extract can be analyzed many times with different techniques if necessary. Because of the evaporation step, very volatile compounds (greater than that of decane) cannot be measured effectively with solvent extraction. The introduction of a solvent into the water carries with it the potential for contamination. Thus, ultrapure solvents must be used and all glassware should be carefully cleaned [96]. Lipophilic adsorption has the unique property of sampling many hundreds of liters of water. Thus, the method is quite sensitive (potentially in the ppt range) and, in addition, it can provide several milligrams of an isolated component. This latter feature is of considerable advantage if one wants to complement GC-MS analyses with infrared or NMR for difficult structural identifications. As a solvent extraction, the evaporation of the final solvent limits the applicability of adsorption methods to compounds with volatilities greater than that of decane. Finally, the importance of avoiding contamination should be emphasized. Many of the compounds encountered in environmental samples are also common laboratory artifacts, for example plasticizers and antioxidants. When one finds such compounds in a water sample, it is absolutely essential to demonstrate that they are indeed present in the water and are not the result of laboratory contamination. The best such demonstration is procedural blank analyses that are indeed blank.

Chromatography, Gas↗
PubMed1979

[Treatment of psoriasis vulgaris with external sulfur mustard gas with particular reference to its potential carcinogenic risk. III. Clinical and experimental studies on the extent of percutaneous and inhalational uptake of sulfur mustard gas].

Concerning the often discussed carcinogenic risk of psoriasis treatment with 0.005% S-mustard-vaseline (so-called Russian Ointment) -- especially by inhalation -- 19 patients were treated with a radioactive labeled S-mustard-ointment and examined. The patients' whole bodies were inuncted for 1--2 days with about 50 g of radioactive S-mustard vaseline (U14C, 3 muCi/g). Afterwards the radioactivity was determined in the patients' expired air, blood, urine, and in their surrounding air. In three patients punch biopsy material from normal and psoriatic skin was assayed for radioactivity after combustion. In the skin, radioactivity distinctly decreased from the epidermis (13.1 pCi/mg) to the subcutis (0.77 pCi/mg) without significant differences between normal skin and psoriatic lesions as confirmed by autoradiography. In all samples of air, body fluids and tissue, definitive amounts of radioactivity were found, which, however, were far below the US-American MAK-values. Between skin surface and shirt, the values varied from 1.5 to 13.7 nCi/20 l air, at a distance of 2 meters by 0.3 nCi/100 l air, in the breath by 0.5 nCi/20 l. The radioactivity decreased to 1/10 of the maximum values after 1--2 hours. In blood the activity was at the limit of detection and was parallelled by the activity of the urine. Generally, 1--7% of the radioactivity applied to the skin was eliminated with the urine within one week. Thus, the carcinogenic risk may be very low in the external S-mustard therapy of psoriasis and other skin diseases.

Air↗