The Liquid Nitrogen Trap

For the analysis of 5 N, all the COj must be removed quantitatively to avoid an interference of CO generated from CO2 in the ion source with the N2 analyte. This is achieved by immersing the deactivated fused silica capillary between the water removal and the open split into a liquid nitrogen cryo trap. The trapped CO2 is easily released after the measurement series with no risk of CO2 contamination of the ion source by using the movable open split. 

A quantitative pyrolysis by high temperature conversion of organic matter is applied for the conversion of organic oxygen and hydrogen to form the 

For the determination of 5 0, the analyte must not contact the ceramic tube that is used to protect against air. For the conversion to CO, the pyrolysis takes place in an inert platinum inlay of the reactor. Due to the catalytic properties of the platinum, the reaction can be performed at 1280°C. For the determination of 5D from organic compounds, the reaction is performed in an empty ceramic tube at 1450°C. Such high temperatures are required to ensure a quantitative conversion. 

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For purification of the product, tubes A and B are cleaned, dried, and reassembled with a dry glass-wool insert in B. Tube C, containing the initially formed product, is attached to tube B as shown in Fig. 2. The system is evacuated and this time left open to the vacuum. The two furnaces are separated by ca. 1.5 cm. Furnace I is heated to 80° and furnace II to 130 to 140°. Sublimation is allowed to continue until all the titanium(IV) iodide has left tube C (12 to 16 hours). The purified product crystallizes in tube B at the separation of the two furnaces. The major impurity, iodine, crystallizes in tube A and in the liquid-nitrogen trap. A fluffy tan residue of negligible weight (0.04 to 0.06 g.) remains in tube C. If desired, further purification can be accomplished by moving tube B farther into furnace II, which results in a second sublimation of the product. 

Caution. Relatively large amounts of hydrogen are produced from the reaction. The size of the liquid nitrogen traps should be adequate to retain the borazine without clogging. 

Following the reaction, the borazine collected in the liquid-nitrogen traps (I) is further purified by a single vacuum fractionation,9 as shown in Figure 2, through a U-trap series cooled at — 45°C (A), — 78°C (B), and — 196°C (C). In the — 78°C trap (B), 13.1 g (0.16 mol, 60% yield based on starting BH4) of borazine is condensed. No other products are detected in the IR, nB NMR, H NMR (see below), or GC/MS spectra of the product, and its vapor pressure (85 Torr at 0°C) matches the literature value,10 indicating that the borazine is obtained in excellent purity. 

After combustion of the sample and carriers in an oxygen stream, reducing conditions are achieved by a flow of carbon monoxide over the sample ash. Arsenic, zinc, cadmium, and any remaining selenium and mercury are reduced to elemental form. When the sample is heated to 1150°C in a slow carbon monoxide stream in a quartz tube in a furnace, recovery of all five elements in the liquid nitrogen trap is complete in 30 min. The recovery trap is washed with nitric acid to dissolve all the metals, and the radioactivity of a nitric acid solution of the products is counted with a Ge(Li) detector. 

The remaining traces of acetone and other volatile products are removed by vacuum distillation into the liquid-nitrogen trap by... 

A slow stream of helium is maintained during the reaction to prevent access of moisture and the condensation of liquid oxygen in the liquid nitrogen traps. Carbon monoxide is admitted at a rate of about 10 l./hr., although this rate is not critical. An exothermic reaction takes place, as evidenced by a hot zone on the copper reactor. The progress of the reaction is readily determined by following the passage of the hot zone the reaction is complete when the far end of the tube returns to room temperature. The... 

DP systems can be shut down when not in use to conserve energy. If a liquid-nitrogen trap is incorporated, the manner in which this trap is warmed up and the DP is cooled down should be determined by the presence or absence of a valve between the chamber and the liquid-nitrogen trap. In critical systems, this head valve can be included in order to permit rapid shutdown and rapid return to operation. The assertion that dry nitrogen gas can be used to sweep contamination from traps and pumps in such manner that oil contamination is prevented from running counter to the nitrogen-sweeping flow direction is questionable. Proper placement of valves can eliminate the need of a sweep gas. 

It is important to note that although water vapor is undoubtedly given off during the prolonged heating of the furnace tube, this effect will not influence these measurements since the water vapor is removed by the liquid nitrogen traps and also is not measured by the McLeod gage. 

The product gases from the cracker R-7 were cooled and all condensed phases (H2O, I2 and unreacted HI) recycled to the main loop. The cooled gas was purified in the liquid nitrogen traps TR-5 and TR-6 and the product H2 collected in a graduated cylinder. 

This oily liquid is distilled under reduced pressure and a nitrogen leak. Because of occasional blockages in the liquid-nitrogen traps it is advisable to use two traps in parallel followed by a third in series, permitting one trap to be emptied without losing continuity in the distillation. The fraction boiling 128-136° at 2.5 torr is collected. This is a yellow liquid when hot but on cooling is a red viscous substance. Yield 114 g (65%). 

The contents of the liquid-nitrogen traps (silane and traces of ether) are combined in one trap, and the material in the —95° trap (mainly diethyl ether) is discarded. The silane is freed of last traces of ether by passing it five times through a —130° trap (r -pentane slush) into a —196° trap. Typically, this procedure gives 0.016 mole of pure silane (80% based on SiCU). 

C, respectively). These arsines, when formed in a reaction vessel, were trapped in a U-shaped tube immersed in liquid nitrogen. The liquid nitrogen was then removed and the tube warmed up for sequential evaporation, separation and detection of the arsines. At pH > 6, only the more toxic trivalent As species could be transformed into their arsines without interference from the pentavalent species (Andreae 1977, Norin and Vahter 1981). Avoiding the liquid nitrogen trap, the separation was also performed by ion-exchange chromatography (Tam et al. 1978). Since arsenobetaine is not transformed into a volatile hydride, these procedures allowed easy differentiation between toxic and practically... 

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