Additional pressure and flow regulation was achieved by using dummy columns. The pressure of the gas is controlled with four ultraclean stainless-steel diaphragm pressure regulators. The carrier gas is purified with a charcoal and a hydrocarbon-O2 trap. UPC grade N2 is used throughout the system. The design of the gas distribution system is critical for obtaining good chromatograms from very small signals that are obtained from natural levels of SF 6. Figure B shows the system that is currently used. The system was modified in 2009 when the HNU GC was replaced with a Shimadzu GC model GC-8A. The analytical system for SF6 is described by Law and others, 1994 Busenberg and Plummer, 2000. The stripper is re-evacuated and prepared to receive the next sample. After all the water is expelled, the valves V-A and V-B are closed. After the stripping is completed (5 minutes) the stripper is isolated and pressurized with N2 which expels the water to waste after the water-to-waste valve is opened. The stripped gases are dried and then collected on to the large trap of the Analytical System. After the cell is filled to the 950 mL mark, the water inlet valve is closed, and ultra-pure N2 that was further purified by an activated charcoal trap is bubbled through the water, degassing the water. The water is sprayed through four small nozzles partially degassing the water. A valve is opened and the vacuum pulls the water sample into the stripping cell. The water sampling tube, a 3.2-mm outer diameter ss tube, is placed in the bottom of the bottle containing the water sample. The stripper is isolated from the vacuum. First, a vacuum is pulled into the 950 mL gas stripper cylinder. The apparatus consists of a 950 mL glass stripping vessel and various valves that control the flow of gases, water, and the vacuum. The apparatus used for vacuum extraction of SF6 from groundwater (Figure A) is similar to the system described by Law and others (1994) and Busenberg and Plummer (2000). Photo of SF 6 Instrument Extraction and Measurement of SF 6 This section provides an over view of the analysis procedure including extraction and measurement, calibration standards, accuracy and precision, and quality control. Struct.SF 6 is determined in the laboratory using a purge and trap gas chromatography procedure with an electron capture detector. Miller, Basic Gas Chromatography (Wiley, Hoboken, 2011), pp. Urbański, Chemistry and Technology of Explosives (Pergamon Press, Oxford, 1984), pp. Kaye, Encyclopaedia of Explosives and Related Items (Dover, NJ, 1980) Here, some conventional compounds such as 2,6-DNT, 2,4-DNT, 3,4-DNT, 2,4,5-TNT (γ-TNT), 2,3,4-TNT (β-TNT) and aniline derivatives were identified by standard solutions then their concentrations were quantitatively determined by internal standard calibration method. Also, the qualification of final product was characterized by gas chromatography–electron capture detector method. In this paper, TNT was purified by sodium sulfite solution with putting flaked TNT in digestion condition to remove existing impurities, and the effect of four main factors, digestion temperature, digestion time, concentration of sulfite solution and reaction time of sulfite with impurities on this purification process, was statistically investigated and optimized using central composite design of experiment (CCD) by Minitab software.
Chemical treatment with sulfite solution is an important method for the purification of TNT. For this reason, separation and analysis of impurities are valuable. Unwanted compounds in 2,4,6-trinitrotoluene (TNT) explosive, such as dinitrotoluene (DNT) and TNT isomers, can lead to exudation defects in the ammunition.
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