The Sample Tubes

The quality of the tube (e.g., concentricity, wall thickness) is very important when very good resolution is required. Also, each type of probe has a lowest recommended quality sample tube and the use of lower quality tubes can lead to the damage of the probe. Each manufacturer specifies the quality parameters in terms of inner and outer diameters, waU thickness and concentricity. Each product has a specified tolerance for these parameters. Apart form the catalogue quality, the history of the tube is also very important (e.g., how it was cleaned, dried, stored, even what samples have been previously analyzed in it, as these operations might lower its quahty). 

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The molar diamagnetic susceptibility of thiazole and some derivatives was initially determined by the classical Curie-Cheneveau method (5,315,316) and later confirmed by a method (317) based on the difference of NMR proton chemical shift of a sample of tetramethylsilane immersed in the liquid to be investigated, according to the shape (cylindrical or spherical) of the sample tube (Table 1-47) (318),... 

S ample Analysis. The fohowing procedure is used for sample analysis (/) after sample connections are made and the sample tubing purged for 30 minutes, the tubing is connected to the sampling manifold which serves to distribute sample gas to each of the analy2ers, and should analy2ers have specific pressure... 

When the burner went out, the solenoid valve took a few see-onds to elose, and during this time some oil entered the furnaee. In addition, the line between the last valve and the furnaee may have drained into the furnaee. The flash point of the fuel oil was 65°C, too high for the oil to be deteeted by the eombustible gas deteetor. Even though the oil was vaporized by the hot furnaee, it would have eondensed in the sample tube of the gas deteetor or on the sintered metal that surrounds the deteetor head. 

The amount of rotation observed in a polarimetry experiment depends on the number of optically active molecules encountered by the light beam. This number, in turn, depends on sample concentration and sample pathlength. If the concentration of sample is doubled, the observed rotation doubles. If the concentration is kept constant but the length of the sample tube is doubled, the observed rotation is doubled. It also happens that the amount of rotation depends on the wavelength of the light used. 

In the 1H NMR spectrum, the acidic -C02H proton normally absorbs as a singlet near 12 5. As with alcohols (Section 17.11), the -C02H proton can be replaced by deuterium when D20 is added to the sample tube, causing the absorption to disappear horn the NMR spectrum. Figure 20.6 shows the H NMR spectrum of phenylacetic acid. Note that the carboxyl proton absorption occurs at 12.0 8. 

AOS surfactant concentration was 0.50% wt in deionized water. Aqueous phase pH was 8.5. The headspace was flushed with nitrogen. All samples were equilibrated at test temperature for 24 h prior to shaking the sample tubes for 1.0 min to generate the foam. Times given are elapsed time from the termination of foam generation. 

The analytical method must have been run using a variety of compounds that might turn up as impurities (synthesis byproducts, degradation products) to prove that there is sufficient selectivity. Materials in contact with the sample (tubing, filters, etc.) that might interfere with the analytes of interest must be proven to be innocuous. 

The procedure we have adopted for introducing samples into the MS-9 is shown in Figure 6. It provides reproducible analyses at a high level of sensitivity. The sample tubes are made from 1 mm id melting point capillaries. A Hamilton 10-pl syringe is used to introduce a 3-4 pi portion of the residue into the sample tube. With a small flame the sample tube is drawn out just above the level of the liquid to produce a capillary constriction about 20 mm long. The solvent is then... 

Inside the probe is a wire coil that surrounds the sample tube. This wire transmits the radiofrequency pulses to the sample and then receives... 

ESR characterization was performed in situ in order to avoid any contact of the pretreated solids with air. Spectra, recorded as the first derivative of the absorption, were obtained at room temperature or 77K using a Varian E9 spectrometer working in the X band. The g values were measured relative to a DPPH reference (g = 2.0036). The sample tubes were filled with the solid to a height greater than the depth of the resonant cavity and the number of paramagnetic species was calculated by double integration of the recorded spectra normalized to that of Varian Strong Pitch sample (g = 2.0028, 3. lO spins, cm" ). 

For routine studies with the ESR spectrometer, it is most convenient to work at X-band frequencies ( 9.5 MHz or 3 cm). The sample is usually contained in a 4 or 5 mm diameter quartz tube having a sensitive region about 2 cm in length. An alternative frequency is at Q-band ( 35,000 MHz or 1 cm). Here, the cavity dimensions are much smaller and the diameter of the sample tube is less than 2 mm. This creates some problems in handling and degassing powder samples. By varying the frequency it is possible to determine which features in a spectrum are due to Zeeman interactions... 

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