Hydrogen as carrier gas

In contrast to other organothallium(I) compounds, cyclopentadienyl-thallium(I) is a remarkably stable compound. Samples can be stored in sealed bottles for months without appreciable decomposition occurring it is unaffected by water and dilute alkali and it is only slowly oxidized by air at room temperature. Cyclopentadienyltballium(I) was first prepared by Meister in 1956 by addition of freshly distilled cyclopentadiene to a suspension of thallium(I) sulfate in dilute potassium hydroxide solution 101, 102). A number of variations of this procedure have been described (5, 25, 34, 56), and the compound has been made in other ways 35, 56,110, 164), but Meister s preparation, in which the yield of crude product is greater than 90%, remains the method of choice. Purification of crude cyclopenta-dienylthallium(I) is best accomplished by vacuum sublimation, and purity of samples can readily be assessed by gas-liquid chromatography on silicone oil at 170° C using hydrogen as carrier gas (7). 

Analyses were performed on a Del si DI200 gas chromatograph equipped with a flame ionization detector using hydrogen as carrier gas and adequate capillary columns. Products were identified by comparison with authentic samples and/or by GC-MS analysis. 

Split injection use high carrier gas flow rates to obtain maximum sensitivity low carrier gas flow rates for very high split ratios. High carrier gas flow rates strongly favor use of hydrogen as carrier gas as well as columns... 

The history of thin-layer chromatography has been the subject of a book.158 The first separations on thin layers were performed in 1938. A gas was first used as the mobile phase in adsorption chromatography by Erica Cremer in Innsbruck in 1946. Using hydrogen as carrier gas, she and her student, Fritz Prior, successfully separated air and carbon dioxide using charcoal as the adsorbent. A newly-opened branch of the Deutches Museum in Bonn, devoted to post 1945 developments, has a display featuring the work of Cremer and Prior, with a model of their original apparatus.159... 

As nicely shown by Puddephatt and coworkers, the complexes Ag(hfac)(PR3) and Ag(fod)(PR3) (R = Me, Et) are excellent CVD precursors for deposition of smooth pure silver films (grain size 0.1-0.25 p,m) using moisf hydrogen as carrier gas, as could be... 

In Table I are presented the results for ethyl iodide in hydrogen as carrier-gas. We will discuss— to begin with—only the experiments carried out at 492°-494°. The rates of reaction are expressed in terms of first order constants which must not prejudice the question of the actual... 

The reaction was performed at 703K, using a saturator with cyclohexane at a constant temperature of 284K, and pure hydrogen as carrier gas (20 ml/min). The reaction products were analysed by on-line chromatography (Shimadzu GC-17 ) with a packed Chrompack column (60 m length and 0.32 nm diameter) at 453K. 

Finally, The dehydrogenation of butanediols to y-butyrolactone is an important commercial reaction that was developed by BASF and named the Reppe process. The most probable reaction mechanism via the y-hydroxybutyraldehyde intermediate clearly shows that the reaction proceeds via two separate alcohol dehydrogenation steps with a rearrangement step taking place in-between (Table 1, Scheme 12) [49]. The reaction is usually performed in the gas phase with hydrogen as carrier gas, to reduce catalyst deactivation, which is a characteristic problem. Thus, extensive research is now being conducted in the liquid phase [50,51]. In addition to a lower catalyst deactivation rate, liquid phase reaction also reduces the number of side-products. The drawbacks are, of course, lower activity but also abrasion problems with the catalyst. The catalyst is preferably stabilized as a powder in a silica matrix (Ludox R) [51]. The catalyst most often encountered in the patent literature is a Cu-Cr with a promoter such as Ba or Mn. The catalyst is also preferably doped with Na or K and pretreated very carefully in a reducing atmosphere [52]. 

Dehydrogenation is normally performed at high temperatures and low pressures, preferably with hydrogen as carrier gas. This is acceptable as long as the chemical stability of the molecules tolerates such severe conditions. When this is not so, different alternatives must be considered. Such alternatives are reactions in liquid phase at the appropriate temperature and pressure by use of (i) solvent, (ii) a purging inert gas (iii) hydrogen acceptors or (iv) even low surface-area catalysts. The conditions are a function of the type of reaction and must be adjusted in consequence. 

A mixture of hydrogen and hydrogen chloride may have to be used in depositing Bi to avoid reduction of BiCl3 in the liquid state. Such metal films can also be made by thermal decomposition of the hydrides with hydrogen as carrier gas ... 

Figure 5.9 (g) Analysis of lemon oil using hydrogen as carrier gas and a thin film almost nonpolar column. Rtx-5, 30m, 0.32mm i.d., 75 C, 8min, to 250°C, 4 Cmin H2. 

Figure 5.9 (h) A mushroom aroma using hydrogen as carrier gas and a polar column with split... 

The lifetime behavior of the most promising catalyst D shows a TOS of nearly 100 h at 300 °C and atmospheric pressure with 1.5 Nl/h hydrogen as carrier gas. 

Therefore, a blank run must be checked each working day before processing the samples by running the same GC program temperature as the one used for analysis 45°C hold for 5 min, 10°C/min to 100°C hold for 2 min under hydrogen as carrier gas (flow rate, 1 mL/min) (see Table 29.1). 

The selection of a capillary column depends on the complexity of the sample to be analyzed. The column length, the internal diameter, the stationary phase, and its fdm thickness determine the separation power (resolution), the sample capacity. the speed of analysis, and the detectability or sensitivity. Theoretical considerations [12], [13] indicate that for capillary columns with thin films (< 1 pm), the Wniin value is roughly equal to the column diameter. This is illustrated in Figure 4. which shows experimental H-u curves for columns varying in internal diameter. H was calculated for dodecane at I00°C with hydrogen as carrier gas. measured experimentally is indeed very close to deduced theoretically. By knowing this, the maximum plate number that a capillary column can provide may be calculated without performing any analysis ... 

Amorphous Thin Films Currently, thin amorphous films of silicon nitride for applications as masking layers and as diffusion barriers during semiconductor processing are produced by gas-phase reactions of silicon tetrachloride or silane with ammonia, in the presence of hydrogen as carrier gas. Today, the standard GVD process is augmented by complex molecular excitation methods that include PACVD, laser-excited GVD (LECVD) and photosensitized GVD (PHCVD) enhance-... 

FIGURE 5.2 Golay plots for 10-m-long, thin-film columns of various diameters using hydrogen as carrier gas. A binary diffusion coefficient of 0.4 cm /s and a retention factor of 2.0 are assumed. 

It is frequently observed that shorter columns are more efficient than longer ones at higher flowrates. This is explained entirely by gas compression effects. A decrease in j caused by an increase in inlet pressure associated with longer columns results in a shift in u pt to smaller values. This is seen in Figure 5.3 for various lengths of 0.20-mm-i.d. columns using hydrogen as carrier gas at 50°C with k and Dq values of 2.0 and 0.4 cm /s, respectively. In addition to a shift... 

Figure 3.20 Chromatograms of the separation of calmus oil using (a) hydrogen as carrier gas, 4.2 mL/min at a programming rate of 4.0°C/min and (b) nitrogen as carrier gas, 2.0 mL/min programming rate of 1.6°C/min on a 40 m x 0.3 mm i.d. capillary column (0.12-pm film). (From ref. 64, with permission of Alfred Heuthig Publishers.)...

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