Packed trap

The cables from a variable transformer are clamped to the ends of the trap to pass a low-voltage, high amperage AC current (=25 A at =3V) through it, which heats the trap to 120 °C and thus desorbs the halocarbons. A thermocouple is attached to the trap, and a temperature controller (Omega CN370) turns the electrical power on and off by way of a solid-state relay. The trap is electrically insulated by deactivated fused silica tubing inserted between the trap and the valve. 

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Newly packed traps should be conditioned overnight at 230°C with an inert gas flow of at least 20 ml/min. The trap is also conditioned prior to daily use by backflush-ing at 180°C for 10 min. 

During the desorption phase, when the GC carrier gas passes through the trap, the optimal flow rate is determined by the GCcolunm used. The P T system described in this chapter was built for a megabore capillary column with an optimal gas flow of=8mL/min. However, as mass spectrometers become increasingly robust and suitable for field work, packed traps have been developed for the lower carrier gas flow rates (l-2mL/min) which these... 

To satisfy the Resource Conservation and Recovery Act (1977) and its amendment for hazardous and solid waste (1984), the 80(K) Series Methods have been designed to analyze solid waste, soUs, and groundwater. In particular, methods 8240/8260 require the use of a purge-and-trap device in conjunction with packed or capillary GC/MS, respectively, for the analysis of purgeable organic compounds. Methods 8250/8270 concern analyses for the less-volatile bases, neutrals, and acids by GC/MS after extraction from the matrix by an organic solvent. 

The proper volume of acetylene is measured with a water gasometer as described in Ovg. Synth., Colleat. Vol. 1 1941, 230, with two modifications (a) Two traps immersed in an acetone-dry ice bath at -65°C are placed between the acetylene tank and the gasometer in order to remove acetone. (b) The washing bottles between the gasometer and the reaction flask are replaced by a drying tube (2 x 30-cm column packed with anhydrous CaCl2). 

Note 1). The mixture is heated with a mantle with stirring for 32 hr under a 50-cm fractionating column packed with 5-nm glass beads and topped by a Dean-Stark trap. The reaction mixture is then distilled through the packed column. The fraction which boils at 120 -126°C is collected. The yield is 86.0-87.3 g (77-78%) of 2,2-dimethyl-4-pentenal (1) as a clear, colorless oil, n 1.4216 (Note 2). 

Calcium oxide. (Preheated to 700-900° before use.) Suitable for alcohols and amines (but does not dry them completely). Need not be removed before distillation, but in that case the head of the distillation column should be packed with glass wool to trap any calcium oxide powder that might be carried over. Unsuitable for acidic compounds and esters. Suitable for drying gaseous amines and ammonia. 

Dicblorodifluoromethane (Freon 12) 175-71-8] M 120.9, m -158", b -29.8"/atm, 42.5"/10atm. Passage through saturated aqueous KOH then cone H2SO4, and a tower packed with activated copper on Kielselguhr at 200° removed CO2 and O2. A trap cooled to -29° removed a trace of high boiling material. It is a non-flammable propellant. 

Ketene [463-51-4] M 42.0, b 127-130 , d 1.093, n 1.441. Prepared by pyrolysis of acetic anhydride. Purified by passage through a trap at -75° and collected in a liquid-nitrogen-cooled trap. Ethylene was removed by evacuating the ethylene in an isopentane-liquid-nitrogen slush pack at -160°. Stored at room temperature in a suitable container in the dark. See diketene on p. 209. 

Trimethylsilyl trifluoromethane (trifluoromethyl trimethylsilane) [81290-20-2] M 142.2, b 54-55°, 55-55.5°, d 0.962, n 1.332. Purified by distilling from trap to trap in a vacuum of 20mm using a bath at 45° and Dry ice-Me2CO bath for the trap. The liquid in the trap is then washed with ice cold H2O (3x), the top layer is collected, dried (Na2S04), the liquid was decanted and fractionated through a helices packed column at atmospheric pressure. H, C, F, and Si NMR can be used for assessing the purity of fractions. [Tetrahedron Lett 25 2195 1984 J Org Chem 56 984 1991.]... 

Gases or vapours that are not water soluble but are slowly reactive, with absorbing agent Condensation Freezing traps or low temperature condensers Glass or metal Dry 1-5 90-100 (depends on vapour pressures at reduced temperature) Can be packed with glass beads or other extended surfaces... 

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