Purge samples

The same authors (92) also report a substantial loss of sulfur in an H2 posttreatment of the sulfided catalyst. This is probably due to the purging action of H2 removing adsorbed H2S rather than a true loss of sulfide sulfur as they assumed. Owens and Amberg (93) mention an appreciable loss of adsorbed H2S but very little sulfide sulfur loss in a similar treatment. Massoth and Kibby (94) showed this treatment did not result in loss of any appreciable sulfur on well-purged samples. 

De Beer et al. (7) also mention that disulfide species found on exposure of sulfided catalysts to air (46) can cause incorrect assessment of sulfur stoichiometry. Again, however, this can be attributed to adsorbed H2S on their catalyst and its overall contribution to the sulfur content of well-purged samples was found to be small (33). 

C Cgxfract X Vextract - sample — w, Csample is compound concentration in the sample (/ig/kg or p/T) Cextract is compound concentration in the final extract (/ig/ml) Vextract is total volume of extract (ml) Wsample is the weight (kg) or volume (liter) of the extracted or purged sample... 

Sample Characterization. Infrared spectra of the adsorbed films were obtained with a Perkin-Elmer 1710 FTIR Spectrometer, equipped with a DTGS detector and a nitrogen-purged sample chamber. The transmission IR spectra (high frequency range >2000 cm 1) of the adsorbed species were directly measured on the glass slides. The... 

Landfill leachate Purge sample and trap on Tenax-silica gel thermally desorb GC/FID/FID 1 pg/L NR Stuart et al. 1984... 

For single point measurements, individual cells were selected from the visually acquired sample image, as seen on the screen. For each cell position on the sample substrate, the aperture was selected to straddle the cell, and typically was 30 gm x 30 gm. The cell position and apertures were stored for each cell, and the data acquisition of aU stored positions proceeded automatically. The microscope and optical bench were continuously purged with purified, dry air. In addihon, the sample area in the focal plane of the microscope was enclosed in a purged sample chamber. 

Purge sample with inert GC/PID gas adsorb vapor in trap heat trap backflush to GC... 

This phosphorescence emission was obtained at room temperature and with air equilibrated samples. Oxygen diffusion inside the silicalite channels is reduced into the channels which already have -phenylpropiophenone molecules and many triplet excited molecules are not quenched and are therefore emitting. In argon purged samples the triplet lifetime increases about ten times [83c]. jfl-Phenylpropiophenone included within microcrystalline cellulose chains enabled us to detect the ketyl radical of this species and therefore contrast with its solution photochemical inertia [83a]. 

Another very important conclusion that emerged from these studies (where microcrystalline cellulose was used as powdered substrate) was that molecular oxygen did not quench the triplet state of molecules entrapped within the polymer chains of this natural polymer. All these studies could be done with air equilibrated samples, and nitrogen or argon purged samples provide similar results for the efficiencies of the quenching process, within experimental error. This property of cellulose makes it a very special substrate to be used for room temperature fluorescence and phosphorescence studies. 

Figure 2 Schematic diagram of purge and trap (A) purge nxxle -valve positioned to purge sample onto trap (B) desorb mode -valve position rotated to desorb sample from trap and onto the GC column. (Courtesy of Restek Corp., used by permission.)...

Sample preparation was greatly simplified in the late 1990s by the introduction of commercial diamond attenuated total internal reflection (ATR) systems. These use a small diamond as a single-pass ATR element held in a metal plate. The sample is placed on the diamond, a plate is then brought down onto it and clamped in position. This ensures excellent contact between the ATR element and the sample, so immediately eliminates the problem of poor contact that made ATR so problematical for use with solids, particularly powders. The accessory can be permanently installed in the purged sample compartment of the spectrometer, so there is only a very short pathlength that is in the open air. This means that there is no need to wait for the sample compartment to purge to reduce the atmospheric water and carbon dioxide absorption. The result is that the sample can be placed in the accessory and scanned immediately. 

GC plays a key role in the analysis of VOCs and SVOCs in industrial effluents. VOCs that have boiling points below 200°C can be extracted from water sample matrices using a P T system. Purged sample components are trapped in a tube containing suitable sorbent materials. When purging is complete, the sorbent tube is heated and backflushed with helium to desorb trapped sample components onto a GC... 

As all spectroscopists know and have observed, spectrometers do not always collect data with an ideal baseline. Due to a variety of problems (detector drift, changing environmental conditions such as temperature, spectrometer purge, sampling accessories, etc.), the baseline of a given spec-... 

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