Sorption traps

Table IV shows X-ray data (55) on the homogeneity of Pd-Ag films prepared by simultaneous evaporation from separate sources, either in conventional vacuum or in UHV, with the substrate maintained at 0°C. The second group of films was prepared using a stainless steel system incorporating a large (100 1/sec) getter-ion pump, sorption trap, etc., but deposited inside a glass vessel. By the tests of homogeneity adopted, alloy films evaporated in conventional vacuum were not satisfactory, i.e., the lattice constants were generally outside the limits of the experimental error, 0.004 A, and the X-ray line profiles were not always symmetrical. In contrast, alloy films evaporated in UHV were satisfactorily homogeneous. Further, electron micrographs showed that these latter films were reasonably unsintered and thus, this method provides clean Pd-Ag alloy films with the required characteristics for surface studies.

Instead of rotary pumps, large water jet, steam ejector, or water ring pumps can be used. For batch evacuation, and the production of hydrocarbon-free fore vacuum for sputter-ion pumps, adsorption pumps (see Section 2.1.8.1) are suitable. If the use of oil-sealed rotary vane pumps cannot be avoided, basically two-stage rotary vane pumps should be used. The small amount of oil vapor that backstreams out of the Inlet ports of these pumps can be almost completely removed by a sorption trap (see Section 2.1.4) Inserted In the pumping line. 

For the pumping of large quantities of gas in this pressure region, vapor ejector pumps are by far the most suitable. With mercury vapor ejector pumps, completely oil-free vacua can be produced. As a precaution, the insertion of a cold trap chilled with liquid nitrogen is recommended so that the harmful mercury vapor does not enter the vessel. With the medium vacuum sorption traps described under a), it is possible with two-stage rotary vane pumps to produce almost oil-free vacua down to below 10" mbar. 

Sanchez, J.M., Sacks, R.D. (2006) Development of a multibed sorption trap, comprehensive two-dimensional gas chromatography, and time-of-flight mass spectrometry system for the analysis of volatile organic compounds in human breath. Anal. Chem. 78 3046-3054. 

Needle Trap Device Particularly interesting is development of the needle trap device (NTD) in an attempt at miniaturization of the sorption traps used in the analysis of gas samples. A sorbent bed positioned inside a needle (mounted in a gas-tight syringe) acts as a sorption trap. Different materials such as polydimethyl-siloxane (PDMS), carboxenes, carbopacks, Tenax, divinylbenzene (DVB), and other polymers have been employed as sorbents. 

This paper summarizes the types of compounds found by our technique while biomonitoring for a variety of volatile and semi-volatile organic contaminant residues. Briefly, hive atmospheres were drawn through multibed sorption traps and subsequently analyzed by thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS). 

FIGURE 5.10 Reverse-flow sorption trap (a) and the chromatogram of a 42-component mixture in an air sample collected with the device (b). The three adsorption beds are graded bed A is the weakest absorber and C is the strongest (largest surface area) adsorber. The flow direction is reversed between sample collection and injection. Compounds are 1, acetaldehyde 2, methyl alcohol 3, n-pentane 4, isoprene 5, acetone 6, ethyl alcohol 7, 2-propyl alcohol 8, n-hexane 9, butanone 10, ethylacetate 11, 1-propyl alcohol 12, 2-butyl alcohol 13, trichloromethane 14, benzene 15, isooctane 16, n-heptane 17, 2-pentanone 18, 2,5-drmethylfuran 19, 1-butylalcohol 20, tolnene 21, n-octane 22, hexanal 23, butylacetate 24, ethylbenzene 25, m-xylene 26, n-nonane 27, o-xylene 28, cumene 29, a-pinene 30, -pinene 31, n-decane 32, 1,2,4-trimethylbenzene 33, benzaldehyde 34, d-limonene 35, 1,2,3-trimethylbenzene 36, 1,2-dichlorobenzene 38, n-dodecane 39, 3-pentanone 40, 1-pentyl alcohol 41, 2-heptanone 42, n-undecane. 

A wide variety of guest molecules may be trapped by the Wemer-type crystalline host lattice, ranging, eg, from noble gases to condensed aromatic hydrocarbons. These clathrates may be formed from solution or by sorption. Kinetics of sorption—desorption have been studied (83). 

Gc/ftir has both industrial and environmental appHcations. The flavor and aroma components in fragrances, flavorings, and foodstuffs can be identified and quantified via gc/ftir (see Food additives). Volatile contaminants in air, water, and soil can be analy2ed. Those in air are usually trapped in a sorption tube then injected into the chromatograph. Those in water or soil are sparged, extracted, or thermally desorbed, then trapped and injected (63,64). 

A represents mechanical pump or steam ejector B, booster pump D, cryo, turbomolecular, sorption, ion, or trapped diffusion pumps. 

Such vessels can also be baked at a temperature of several hundred degrees, to drive off any gas adsorbed on metal surfaces. The pumping function of an ion gauge was developed into efficient ionic pumps and turbomolecular pumps , supplemented by low-temperature traps and cryopumps. Finally, sputter-ion pumps, which rely on sorption processes initiated by ionised gas, were introduced. A vacuum of 10 "-10 Torr, true UHV, became routinely accessible in the late 1950s, and surface science could be launched. 

Analysis of environmental samples is similar to that of biological samples. The most common methods of analyses are GC coupled to MS, ECD, a Hall s electrolytic conductivity detector (HECD), or a flame-ionization detector (FID). Preconcentration of samples is usually done by sorption on a solid sorbent for air and by the purge-and-trap method for liquid and solid matrices. Alternatively, headspace above liquid and... 

The mere exposure of diphenyl-polyenes (DPP) to medium pore acidic ZSM-5 was found to induce spontaneous ionization with radical cation formation and subsequent charge transfer to stabilize electron-hole pair. Diffuse reflectance UV-visible absorption and EPR spectroscopies provide evidence of the sorption process and point out charge separation with ultra stable electron hole pair formation. The tight fit between DPP and zeolite pore size combined with efficient polarizing effect of proton and aluminium electron trapping sites appear to be the most important factors responsible for the stabilization of charge separated state that hinder efficiently the charge recombination. 

In a sorption pump, the gas is trapped within the adsorbing material (zeolites or active charcoal) called molecular sieve. Zeolites are porous aluminium silicates which adsorb large amount of gas when cooled to low temperature (usually 77K). The pump is filled with zeolite and put in a bucket containing liquid nitrogen (see Fig. 1.11). 

The sorption pumps are clean but are one shot , that is, two pumps in parallel and connected by valves alternatively are needed for a continuous pumping. When the first pump is saturated, the second pump is started, while the first is regenerated removing the liquid nitrogen, the trapped gas is expelled through the blow-off valve. The pump (with zeolite) is heated to 200-300°C to remove water vapour. Charcoal pumps are heated to about 100°C. 

Sorption — Attached to soil particles and trapped within soil pores (can be above or below the water table) ... 

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