Cooling the Samples

As an example, PL can be used to precisely measure the alloy composition xof a number of direct-gap III-V semiconductor compounds such as Alj Gai j, Inj Gai jfAs, and GaAsjfPj j(, since the band gap is directly related to x. This is possible in extremely thin layers that would be difficult to measure by other techniques. A calibration curve of composition versus band gap is used for quantification. Cooling the sample to cryogenic temperatures can narrow the peaks and enhance the precision. A precision of 1 meV in bandgap peak position corresponds to a value of 0.001 for xin AljfGai j, which may be usefiil for comparative purposes even if it exceeds the accuracy of the x-versus-bandgap calibration. 

SIMS, and SNMS in rare cases, such as for HgCdJTei samples or some polymers, the sample structure can be modified by the incident ion beam. These effects can often be eliminated or minimized by limitii the total number of particles incident on the sample, increasing the analytical area, or by cooling the sample. Also, if channeling of the ion beam occurs in a crystal sample, this must be included in the data analysis or serious inaccuracies can result. To avoid unwanted channelii, samples are often manipulated during the analysis to present an average or random crystal orientation. 

The Conradson test (ASTM D-189) measures carbon residue by evaporative and destructive distillation. The sample is placed in a preweighed sample dish. The sample is heated, using a gas burner, until vapor ceases to burn and no blue smoke is observed. After cooling, the sample dish is reweighed to calculate the percent carbon residue. The test, though popular, is not a good measure of the cokeforming tendency of FCC feed because it indicates thermal, rather than catalytic, coke. In addition, the test is labor intensive and is usually not reproducible, and the procedure tends to be subjective. 

CO2 gas. The use of dry ice (i.e. adding small pieces of dry ice during extraction) has the merit of cooling the sample in addition to displacing oxygen with CO2 gas. The method cannot be used if the... 

The catalytic activity of the pure /3-palladium hydride has been studied under the appropriate temperature and pressure conditions. The palladium sample was converted into the hydride in a manner which bypassed the area of coexistence of the phases. This was achieved by suitably saturating the metal with hydrogen at 35 atm above the critical temperature and then subsequently cooling the sample to the required temperature and reducing the hydrogen pressure. This method of sample prepare tion allowed one to avoid cracking the palladium crystallites, which would... 

When sampling condensate, ensure that the line is thoroughly flushed and use a container that can be quickly capped. Where a sample cooler is not available, fill the container to the top, apply the cap loosely, and keep it closed while cooling the sample. This minimizes the absorption or evolution of carbon dioxide, which can cause distortions of the true pH level. The collection of condensate (as for BW) should be done prior to BD or the addition of treatment, if this is added on a periodic shot basis. 

Restricted rotation has been observed in tris-o-tolylphosphine sulphide and selenide (39). The spectrum of the selenide shows two methyl environments in the ratio 2 1 at 30 °C but the methyl signals of the sulphide resolved to this pattern only upon cooling the sample. The corresponding oxide and the parent phosphine showed only one methyl environment down to — 60 °C. Y-Ray diffraction of the selenide showed that the methyl group on one aryl group is directly behind the phosphorus atom in the crystal, as shown in (39). 

Cool the sample extract to room temperature and filter the extract through a Whatman No. 1 (11-cm) filter paper (pre-rinsed with 5mL of acetone) into a filter flask using a Buchner funnel and vacuum (15 inHg). Rinse the boiling flask with 2 x 25 mL of acetone and pass the rinsate through the post-reflux solid and filter paper. Transfer the filtrate into a 200-mL TurboVap vessel. Rinse the filter flask with 5 mL of acetone and add the rinsate to the TurboVap vessel. Concentrate the filtrate to <25 mL (not to dryness) using a TurboVap Evaporator (water-bath at 50 °C increase the pressure up to 30 psi as the volume decreases). All traces of acetone must be removed. 

Absorption of carbon monoxide was used to probe the acidity of the various OH groups to understand their role in catalysis. The study is therefore focussed on OH groups in the supercage of the zeolite, hence the bands between 3600 and 3700 cm"1. Better-resolved spectra were obtained by cooling the samples down to 100 K, the temperature at which the experiment is done. Five different v(OH) bands, shifted from 5 cm"1 to higher frequency at low temperature, were detected in the OHHf band group, at 3645 3635, 3625, 3608 and 3600 cm 1 (for HF0, HFi, HF2, HF3, HF4, respectively) with various intensities. 

Measurements were performed by cooling the sample down to 4.2 K and then recording the interference signal versus temperature during the sample warm up. 

Although there are other ways, one of the most convenient and rapid ways to measure AH is by differential scanning calorimetry. When the temperature is reached at which a phase transition occurs, heat is absorbed, so more heat must flow to the sample in order to keep the temperature equal to that of the reference. This produces a peak in the endothermic direction. If the transition is readily reversible, cooling the sample will result in heat being liberated as the sample is transformed into the original phase, and a peak in the exothermic direction will be observed. The area of the peak is proportional to the enthalpy change for transformation of the sample into the new phase. Before the sample is completely transformed into the new phase, the fraction transformed at a specific temperature can be determined by comparing the partial peak area up to that temperature to the total area. That fraction, a, determined as a function of temperature can be used as the variable for kinetic analysis of the transformation. 

Heat capacities at high temperatures, T > 1000 K, are most accurately determined by drop calorimetry [23, 24], Here a sample is heated to a known temperature and is then dropped into a receiving calorimeter, which is usually operated around room temperature. The calorimeter measures the heat evolved in cooling the sample to the calorimeter temperature. The main sources of error relate to temperature measurement and the attainment of equilibrium in the furnace, to evaluation of heat losses during drop, to the measurements of the heat release in the calorimeter, and to the reproducibility of the initial and final states of the sample. This type of calorimeter is in principle unsurpassed for enthalpy increment determinations of substances with negligible intrinsic or extrinsic defect concentrations... 

The experimental approach discussed in this article is, in contrast, particularly amenable to investigating solvent contributions to the interfacial properties 131. Species, which electrolyte solutions are composed of, are dosed in controlled amounts from the gas phase, in ultrahigh vacuum, onto clean metal substrates. Sticking is ensured, where necessary, by cooling the sample to sufficiently low temperature. Again surface-sensitive techniques can be used, to characterize microscopically the interaction of solvent molecules and ionic species with the solid surface. Even without further consideration such information is certainly most valuable. The ultimate goal in these studies, however, is to actually mimic structural elements of the interfacial region and to be able to assess the extent to which this may be achieved. 

Cool the sample and add 2 mL of water and 3 mL of 30% hydrogen peroxide (H202). Warm the sample with the ribbed watch glass in place until effervescence slows. Allow the sample to cool and add 1 mL of water and again warm. Repeat this step until the sample does not change in appearance. Note do not add more than 10 mL H202. Add to the ribbed watch glass and warm until the volume is 5 mL. 

In the Murphy and Riley [85] method 10ml of demineralized water and 2ml of concentrated nitric acid were added to 0.15-0.2g of dry sediment (predried at 103°C) or plant material in a 100ml Erlenmeyer Flask. After a preliminary oxidation by evaporation of water and nitric acid on a hot plate, 2ml of concentrated perchloric acid were added, and the sample was boiled until clear. After cooling, the sample was diluted to 100 ml and an aliquot was withdrawn for orthophosphate determination by the ascorbic acid reduction method of Murphy and Riley [85]. Blanks and standards were treated as samples. 

The content of quercetin in human plasma after consuming canned green tea has been determined by RP-HPLC and electrochemical detection. Hydrolysis of quercetin in green tea samples was carried out by mixing 1 ml of tea with 1.5 ml of mobile phase, ultrasoni-cated for 3 min, mixed again with 0.5 ml of 6 M HC1 and heated at 90°C for 2 h. After cooling the sample was filtered, diluted 100 times and injected into the column. 

Ideally, one would like to study one single adsorbed molecule at 0 K but for practical reasons one has to study an ensemble of molecules at Anite temperatures. Even if it is feasible to cool the sample to very low temperatures. 

Cool the samples to RT and transfer the content to 15 ml falcon tubes. 

---