Sample cell ambient temperature

At the time of writing, in all papers published on adsorption studies on oxides surfaces, spectra have been reported of samples held at the ambient temperature of the sample compartment. It is obvious that when dealing with very volatile adsorbates, low temperature sample cells may be required to increase adsorption and also to prevent rapid desorption of the adsorbed species. In some instances, it is also desirable to record the spectra of species held at elevated temperatures for better correlation with industrial catalytic systems. It should be noted that there are only a few infrared spectra reported in the literature for high temperature studies of catalytic reactions. Sample emission at elevated temperature is a significant experimental complication in investigations of this type. 

The collected sample at -196°C was isolated from the flow of the GC s helium gas stream and then the loop was warmed to ambient temperature for GC-mass spectroscopic analyses. The gas cell, which contained the isotopic CO2 and the C2Hg standard in helium at one atmosphere, was placed in the injection helium flow of the GC-mass spectrometer for ten minutes, before the mini-switching valve was turned to inject the vapor contents into the instrument. After three minutes, the CO2 peak eluted. The superimposed peaks were sampled ten times during their elution and the relative isotopic quantities of - C02 C02 and C02 were determined. 

The next question to address is to what extent does the study of a (deeply) frozen biological sample provide information that is relevant for an understanding of its functioning in a living cell at whatever the ambient temperature of this cell happens to be First and foremost, let us state the fact of experience that solutions of biomacromolecules such as metalloproteins can be frozen and thawed many times without any detectable deterioration of their biological activity. Combined with the rather low intensity (<0.2 W) of the microwave source of an EPR spectrometer, this leads to the proposition that EPR spectroscopy is a nondestructive technique. 

Finally, in the context of the overall vapor-phase mutagenicity of ambient air, we note that significant fractions of the two powerful human cell and bacterial mutagens discussed earlier, cyclopen ta[c<7]pyrene (XXVIII) and 2-nitrodibenzopyranone (XI), have been found in the gas phase (i.e., trapped on PUF plugs) in samples collected during hot weather at sites in southern California (Fraser et al., 1998, and Arey et al., 1994, respectively). Flence the contributions of such species, which are normally considered to be primarily in the particle phase, to the gas-phase mutagenicity at high ambient temperatures should also be considered. 

Two methods are commonly used to obtain isothermal data from DSC. The first method involves insertion of the sample into the DSC previously equilibrated at the required temperature. In the second method the sample is placed in the DSC cell at ambient temperature and the temperature is then increased at a controlled rapid rate to the required temperature. Small samples are used to ensure the sample temperature remain close to the required value. In both methods there is an initial off-balance signal and the output finally reaches a value corresponding to completion of the reaction. The baseline is usually taken as this final steady state signal, and horizontal negative extrapolation to intersect with the initial exotherm is taken as zero time for the reaction, as shown in Fig. 4. 

Using this instrument in Figure 6.5, Handa (1986b) measured the heat input to a hydrate sample in the sample container S, relative to helium at ambient temperature and 5 kPa in reference cell R. The hydrate was externally prepared from ice in a rolling-rod mill, before a 4 g sample was loaded into the calorimeter at liquid nitrogen temperatures. For heat capacity measurements, a pressure greater than the hydrate dissociation pressure was maintained in the sample cell. By cycling... 

The volumetric adsorption experiment [6] shown in Figure 6.2 consists of a thermostated sample cell of volume Vg at an experimental temperature, T, a container with a precisely determined volume, named the calibrated volume, Vc, a connection to the gas reservoir, and a transducer for pressure measurement. In addition, the volume at stopcock 3, at ambient temperature, Tv and the thermostat is denoted V2, and the volume between stopcocks 1, 2, and 3, also at ambient temperature, Tr, is denoted Vt. 

Sampling was performed at least every third day, in the morning, 4 h after sunrise, using 15 1 carboys that were filled at the surface of the mesocosms. Samples were taken gently to avoid disruption of the colonies. Carboys were stored in the dark at ambient temperature (ca. 4°C). Cells were collected within 1 h from 250 ml subsamples filtered over GF/F filters (47 mm, Whatman) using gravity only. The GF/F filtrate was collected and stored in the dark at 4°C until analysis on the same day. The filters were transferred into test tubes containing 5 ml artificial seawater at 31.5 PSU (ambient salt concentration) which... 

The protein concentration used in the near-IR measurements was about 7 mM in heme. The protein solution was filtered through either a 0.45 pm or a 0.22 pm membrane filter prior to being anaerobically transferred into a gas-tight 1-mm-path-length sample cell. The sample cell was rotated sufficiently quickly to ensure that each photolysis pulse illuminated a fresh volume within the protein sample. The temperature of the sample was about 28°C, which was elevated somewhat from ambient temperature due to heating by the motorized mount. 

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