Carrier gas impurities

Even ultrapure gases for GC applications sometimes contain oxygen in the ppm concentration range. This leads to slow but certain deterioration of capillary columns at higher temperatures causing shifts in retention times, reduced column efficiency and baseline drift. This is a particular hazard for columns with thin layers of stationary phase (0.15-0.2S pm), as are used for CB determinations. 

Polyethylene and Teflon are not allowed as gas supply tubing materials, because oxygen may enter the gas by diffusion or through small leaks. It is essential to insert a combination 

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It does not respond to common carrier gas impurities such as water or... 

Older columns may have to be subjected to higher temperatures periodically to remove carrier gas impurities that have accumulated. The ECD may remain connected to the column provided that it is kept at an elevated temperature (300-320 °C). 

The number and type of point defects in the growing crystal depend on microscopic processes of incorporation of basic growth units and impurities on the particular crystal faces. For HVPE, these growth mechanisms can be influenced by changing temperature, flows of reacting gases, and chemical environment in the system (carrier gas, impurities). 

The checkers found that gas chromatographic analysis of one sample using a 305 cm. by 0.3 cm. column packed with 10% SF-96 on Chromosorb P operated at 70° with a 60 ml./minute helium carrier gas flow rate gave five minor impurity peaks, two at shorter retention times, and three at longer retention times. None of these impurities was present in greater than 1.1% total impurities wrere 3%. 

Similar to the analytical procedure for trace analysis in high purity GaAs wafers after matrix separation, discussed previously,52 the volatilization of Ga and As has been performed via their chlorides in a stream of aqua regia vapours (at 210 °C) using nitrogen as the carrier gas for trace/matrix separation.58 The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Ag, Cd, Ba and Pb determined after a nearly quantitative volatilization of matrix elements (99.8 %) were found to be between 94 and 101 % (except for Ag and Cr with 80 %). The concentrations of impurities measured by ICP-DRC-MS (Elan 6100 DRC, PerkinElmer Sciex) after matrix separation were compared with ICP-SFMS (Element 2, Thermo Fisher Scientific) and total reflection X-ray fluorescence analysis (TXRF Phillips). The limits of detection obtained for trace elements in GaAs were in the low ngg-1 range and below.58... 

Mobile phases are generally inert gases such as helium, argon, or nitrogen. The choice of carrier gas is often dependent upon the type of detector used. Gas is obtained from a tank, or sometimes from an electrolysis cell, and is passed through a series of reductors, equalizing valves, and traps to ensure constancy of pressure or flow and elimination of impurities as well. 

Materials. Cyclohexene, obtained by dehydration of reagent grade cyclohexanol (3), was heated at reflux over sodium metal, fractionated on a 60-cm. Helix packed column, stored over sodium, and filtered just before use. No impurity was found by gas chromatography (column, TCP and Si-550 carrier gas, helium). Propylene (Neriki Research Grade) used showed no impurity by gas chromatography (column, active carbon and acetonylacetone). 

An exhausted chemical trap is a source of temperature-induced drift. When the trap is in equilibrium with the carrier gas, if the ambient temperature drops, then the trap is no longer saturated, and it begins to absorb impurities again. This causes the baseline to drift downwards. If the temperature is raised, then the trap adds impurities to the carrier gas. If chemical traps are not going to be maintained, they should be removed from the flow system. 

There is one such pair of charged species formed for approximately every 100,000 carbon atoms introduced. This proportion holds true from the impurities in the purest tank of carrier gas, all the way up to a candle flame, where there is no hydrogen sup-... 

Conventional high pressure NICI spectra were obtained using a Hewlett-Packard 5985B quadrupole GC/MS, as described previously (1). Methane was used as the Cl reagent gas and was maintained in the source at 0.2-0.4 torr as measured through the direct inlet with a thermocouple gauge. A 200 eV electron beam was used to ionize the Cl gas, and the entire source was maintained at a temperature of 200° C. Samples were introduced into the spectrometer via the gas chromatograph which was equipped with a 25 meter fused silica capillary column directly interfaced with the ion source. For all experiments, a column coated with bonded 5% methyl phenyl silicon stationary phase, (Quadrex, Inc.) was used and helium was employed as the carrier gas at a head pressure of 20 lbs. Molecular sieve/silica gel traps were used to remove water and impurities from the carrier gas. 

Assay (See Chromatography, Appendix IIA.) Determine the content of propan-2-ol and volatile impurities using a suitable gas chromatograph equipped with flame-ionization detector and a 1.8-m x 6-mm (id) steel column, or equivalent, packed with 10% P.E.G. 400 on 60- to 80-mesh Chromosorb W (or equivalent). Maintain the column at 90°, and set both the injection port temperature and the detector temperature to 150°. Use helium as the carrier gas, with a flow rate of 45 mL/min. Inject between l-p,L and 5-p,L samples, and from the chromatograms so obtained, determine the content of each constituent by the method of area normalization. 

Some preliminary runs were made on the Al O support in the absence of Pt. Heating this alumina without CO pulsing showed a small peak appearing near 100°C. This was identified as N adsorbed as an impurity from the carrier gas. CO completely displaces the on pulsing at room temperature and, as previously reported, probably results from the presence of Lewis acid-base sites gn the alumina (8). The amount of this peak was approximately 10 moles per g of Al O which represents less than 5% of the CO desorbing from a well dispersed Pt catalyst of 0.4 wt% loading. Runs without the in-situ H O and 0 trap had shown that C0 desorbed with the CO. However, with the In-situ trap minimal CO was observed. This was confirmed by a pair of runs shown in Figure 1 with and without Al O (CO2 trap) placed at the exit of the desorption tube. 

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