Multiple sample holder

Currently, various models of autosamplers have been designed, including the use of a multiple sample holder-turntable or a 96-well microtiter plate as a sample holder (6,8,45,46). 

Figure 2.13. Effect of crucible and multiplate sample holder on TG curve of CuS04 5H20 (24) ------, crucible, 500 mg --------—. multiplate. 200 mg heating rale of lO C/min----------.

The difference in TG curves for CuS04. 5H20 obtained using a crucible and the multiplate sample holder is illustrated in Figure 2.13 (421. Curve (1) was obtained by use of a crucible, while in obtaining curve (2) the sample was- placed as a thin layer on the surfaces of a multiplate holder. The latter type of holder yielded better separation of overlapping reactions and also resulted in lower procedural decomposition temperatures. A similar effect was reported by Paulik and Paulik (21). 

To increase the number of samples that can be studied at any one given time, experimenters have described various multiple sample holders capable of studying three, four, five, or six samples simultaneously. Several arrangements of these holders are illustrated in Figure 6.4. 

The multiple sample holder, as shown in (b), contains four separate sample reference pairs, as well as a monitor thermocouple. Slits are cut at various radial intervals in the block to prevent thermal gradients from one sample interfering with an adjacent reference well. Four separate dc amplifiers are used in conjunction with a four-channel recorder. 

Mass loss determinations refer to the total change resulting from reactant decomposition and usually include contributions from a mixture of product compounds, some of which would normally be condensed under conditions used for accumulatory pressure measurements. Such information concerned with the overall process is, however, often usefully supplemented by evolved gas analyses (EGA) using appropriate analytical methods. Sestak [130] has made a detailed investigation of the effects of size and shape of reactant container on decomposition kinetics and has recommended that the sample be spread as a thin layer on the surfaces of a multiple plate holder. The catalytic activity of platinum as a reactant support may modify [131] the apparent kinetic behaviour. 

For the spectrophotometric method, there is no sample workup, allowing one to run -4 assays/hr. This can be increased to -16 to 100 or more samples/hr depending on equipment features and automation, such as multiple cuvette holders/changers and 96-well microplate readers. For the colorimetric procedure, sample workup requires -10 min/subsample, but several samples can be batch processed simulta-... 

Another method used for starch is the non-contact mode, where the starch granules are simply spread onto an adhesive tape fixed on the AFM sample holder. Using this technique, both nodules (20-50 nm in diameter) and smooth areas without any visible features were observed at the surface of potato starch granules.114 Multiple freeze-thaw cycles have revealed an internal, lamellar structure of chain clusters bundled into blocklets 50-300 nm in diameter.115... 

Thermometers. The sensor probe should be placed in the bath in a central location removed from the heater and stirrer units. If a single cell or sample holder immersed in the bath is the only object of interest, the probe should be placed near this cell but not touching it. The measuring thermometer should be placed in good thermal contact with the cell or sample holder if there is only one or positioned close to the location of multiple cells. 

A solid compact sample or a tablet produced from powder may be placed directly in the sample holder. The spectrum is often improved by irradiating a fine hole within the sample with the laser beam and by analyzing the Raman radiation emerging from the hole. The multiple reflection of exciting and Raman radiation inside the hole enhances the efficiency of the transformation of laser radiation into Raman scattered radiation. 

The process of scanning a sample is quite simple and very rapid. The sample holder and surface must first be gently cleaned of debris and a reference (usually an internal ceramic Coor s standard) scan taken. The sample may then be placed in the sample holder, which may hold one or more of a specific type of sample. The sample is positioned, the lid closed, and the scan taken. Scan times are usually approximately 40 s. If multiple scans of the same sample are needed, the sample may be removed and rescanned. Instrument software facilitates the process and allows the spectra to be named and stored in data files. 

In these earlier studies, the polysaccharides were In open sample holders within the rf reactor. Thus, samples were exposed to fast moving high temperature electrons, the slower moving positive and negative ions, and free radicals as well as to uv irradiations. In all types of rf plasmas investigated, changes In surface properties of the polysaccharides were analyzed by the techniques of electron spectroscopy for chemical analyses (ESCA), electron spin resonance (ESR), multiple internal reflectance infrared spectroscopy (MIR) and chemiluminescence (CL). 

Fig. 4.5. Schematic side view of the positioning in a spectrometer beam of a sample cut with a 45° geometry allowing for multiple internal reflections, and of the two mirrors of the sample holder (not shown) redirecting the output beam along the optical axis. The beam delimited by dashes is the normal beam (courtesy C. Naud)...

Open the cell compartment door and notice two holders, one for a single reference cell and a multiple sample cell holder. Push the lever on the front of the chamber and watch how the cell holder turns. 

Alternatively, the writer has found fhaf small portions of plastic fluorescent-light diffuser panels, containing multiple square chambers, can also be used for sample holders. The panel can be cut with a hacksaw into "2-hole," "3-hole," or "4-hole" containers, the latter arrangement particularly useful for studying the raw feed—the >125-pm fraction, the >45-pm insoluble residue from acetic acid and that from hydrochloric acid, and the feed as received, all in the same thin section. Small fragments of clinkers may also be encap-... 

Figures 4.179 and 4.180 illustrate two furnaces for TGA for different temperature ranges. The figures are self-explanatory. Several different sample holders are shown in the bottom portions of the figures. The multiple holders can be used for simultaneous thermogravimetry and DTA, the single cmcibles are used for simple thermogravimetry. The major problem for the combined thermogravimetry and DTA technique is to bring the thermocouple wires out of the balance without interference with the weighing process. Even the temperature control of the sample holder may be a major problem in vacuum experiments since the thermocouple does not touch the sample. The cmcibles are made of platinum or sintered aluminum oxide. Typical sample masses may vary from a few to several hundred milUgrams.

Figure 4.6. Schematic arrangement of conventionai diffuse-reflectance accessory for measuring multiple-transmission spectra of microsamples. (1,2) focusing optical system of accessory (3) sample holder (4) plate under study (5) metallic mirrors, (a) Plate with polished surfaces placed between ground metallic surfaces. (6) Plate with ground surfaces placed between polished mirrors. Reprinted, by permission, from V. P. Tolstoy, Methodsof UV-Vis and IR Spectroscopy of Nanolayers, St. Petersburg University Press, 1998, p. 130, Fig. 4.10. Copyright 1998 St. Petersburg University Press.

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