The Sample Holder

In the case of solutions typically the measurements are performed using plastic, glass or quartz rectangular cells with a square section (see Sect. 3.7.1 and Fig. 3.10), an optical pathway of 1 cm, and they are commonly named cuvettes. There are a great number of commercial cells that differ for shape, material, volume for the diverse applications cylindrical, thermostated, flow, with optical pathways from 1 pm to 10 cm and volumes down to a few microliters, and this allows the study of a wide range of concentrations, of quantities and samples with very low or very high absorbance. 

Whatever cuvette is used, it is always fundamental its location, it has to be fixed in a perfectly reproducible position both in height and orientation. Almost all modern spectrophotometers can be supplied with a series of devices for the control of the sample conditions such as thermostating, stirring, multi-sample holders or auto-samplers. Recently the possibility to study remote samples has been introduced and developed using optical fibers that are able to take the excitation signal from the light source to the remote analyte, but also the transmitted light back to the detector. This allows the measurement of both transmittance and reflectance 

There are also different and efficient solutions to locate solid samples inside the spectrophotometer to study their transmittance or their total reflectance. These housing systems allow to orient the sample at different angles with respect to the incident light to measure both the incident and diffuse reflectance. It is also possible to use the so called integrating spheres that completely surround the sample and are able to collect all the reflected light to measure the value of the total reflectance. 

A deeper discussion on reflectance and solid samples goes beyond the goals of this contribution, and the interested readers can refer to the wide and dedicated literature [7]. 

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A sample holder, including optics for focusing the incident light and collecting the luminescence. Efficient light collection is important, and the sample holder may need to allow for a cryostat, pressure cell, magnet, or electrical contacts. 

The conditioned specimens are cantilevered from the sample holder in the test apparatus, which has been brought to a low temperature (that at which the specimens would be expected to fail). When the... 

Fig. 4-3. Lines from copper, nickel, and iron impurities which appeared in the spectrum of an x-ray tube after the tube had been operated for several hundred hpurs. X-rays from the tube were scattered by filter paper in the sample holder.

Sample loading is done by loosely placing the ground sample into the sample holders of the Norelco Inverted-Sample Three-Position Spectrograph. 

Fig. 8-10. Contour maps showing spectrograph sensitivities for the iron Ka line for various positions of the sample, (a) At surface of sample holder, (b) 0.16 inch below surface of sample holder, (c) 0.32 inch below surface of sample holder. The sensitivity changes with the x-ray optical system, with the goniometer setting, and with the distance of the sample below the surface of the sample holder. The contour interval is 20 counts per second. (Authors unpublished results.)...

As carrier gases dry nitrogen and super-heated steam, both at a pressure of 1 bar, were used. The gas velocity was 4,0 cm. sec for both gases. The samples were flushed from the sample-holder into the pre-heated reactor and reached temperature within a minute. The reactions were stopped by removing the reactor from the oven. 

The first thing to note is that the furnace surrounds the sample-holder containing the differential thermocouples. A separate control thermocouple controls the furnace temperature and should be placed as close as possible to the position of the sample holder. Some commercial manufacturers use the Reference leg of the differential thermocouple to control the temperature. However, if you were to build a DTA using the components as shown in 7.1.14,... 

Figure 3. Exploded view of the sample holder and catalyst disc. (Reproduced with permission from Ref. 7. Copyrifdit 198U, Academic Press.)...

The graduation of material across a wafer was achieved using a wedge shutter controlling the deposition profile of each source independently the principle is discussed in detail elsewhere [Guerin and Hayden, 2006]. For uniform depositions such as carbon and titania support materials, the sample holder was equipped with a motor drive that allowed rotation of the substrate during deposition. 

FIG. 6. Vertical cross section of the reaction chamber. Indicated are (I) the grounded electrode, (2) the RF electrode. (3) the dark space shield, (4) the gas supply. (5) the gas exhaust. (6) the position of the sample holder during deposition. (7) the position of the sample holder when loaded, and (8) the lift mechanism. 

For the DRIFTS study, the Nafion-Ti02 slurries were sonicated for 2 hours, dried at ambient conditions for 5 hr, and ground with a pestle and mortar until a fine powder catalyst was formed. 30 mg of the resulting catalysts were placed on top of 80 mg of inert CaF2 powder (325 mesh, Alfa Aesar) in a DRIFTS cell s sample holder. The sample holder was enclosed by a dome with two IR transparent ZnSe windows and a third CaF2 window for UV illumination. For the ATR study, the Nafion-Ti02 slurries, which were sonicated for two hours, were cast directly on the surface of the ATR ZnSe crystal to form a continuous solid film. The films were enclosed with a stainless steel cover equipped with a CaF2 window for UV illumination. 

Samples may either be those in which the surface of interest has been exposed to the environment before analysis, or the surface to be examined is created in the UHV chamber of the instrument. The latter method is generally preferable, and also argon-ion bombardment is commonly used to clean sample surfaces in situ in the spectrometer. In metallurgical studies, the fracture sample is particularly important the sample is machined to fit the sample holder, and a notch is cut at the desired point for fracture. The fracture stage is isolated from the analytical chamber and is pumped down to UHV. Liquid nitrogen cooling is often provided, as this encourages... 

Both collisional activation (in ion traps) and post source decay (in curved field reflectron TOF analyzers) have been used successfully to obtain sequence ions from peptides prepared in situ on the sample holder. Single Dalton mass windows are advantageous for precursor selection, as are realized in ion-trap and trap-TOF configurations. Publicly available search algorithms can be used... 

Direct insertion probe pyrolysis mass spectrometry (DPMS) utilises a device for introducing a single sample of a solid or liquid, usually contained in a quartz or other non-reactive sample holder, into a mass spectrometer ion source. A direct insertion probe consists of a shaft having a sample holder at one end [70] the probe is inserted through a vacuum lock to place the sample holder near to the ion source of the mass spectrometer. The sample is vaporized by heat from the ion source or by heat from a separate heater that surrounds the sample holder. Sample molecules are evaporated into the ion source where they are then ionized as gas-phase molecules. In a recent study, Uyar et al. [74] used such a device for studying the thermal stability of coalesced polymers of polycarbonate, PMMA and polylvinyl acetate) (PVAc) [75] and their binary and ternary blends [74] obtained from their preparation as inclusion compounds in cyclodextrins. 

Background is measured without the sample - but including the sample holder and all kind of wrapping that does not belong to the material of interest (e.g., aluminum foil, empty cuvette, or cuvette with solvent, respectively). 

The absorption factor of the studied sample is measured by means of the moving slit device, as well. For this purpose the sample is mounted in the sample holder and the moving slit measurement is performed. We measure Ns = 50031 in 16 scans. Because the heights of the moving and the fixed vertical slits are 2 cm, the moving slit registers the SAXS as well - as is required from the definition of absorption. Then... 

Remove the cap from the PreservCyt Sample vial and load it into the sample holder. 

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