Apparatus Selection

To ensure electrical apparatus selected for use near combustible liquids and gases is of adequate design and construction to prevent ignitions. 

The USP 27, NF22 (11) now recognizes seven dissolution apparatus specifically, and describes them and, in some cases allowable modifications, in detail. The choice of the dissolution apparatus should be considered during the development of the dissolution methods, since it can affect the results and the duration of the test. The type of dosage form under investigation is the primary consideration in apparatus selection. 

A. When developing a dissolution method, the design qualification is built into the apparatus selection process. The dosage form and delivery system process will dictate at least initially the equipment of choice. For example, the first choice for a beaded product may be United States Pharmacopeia (USP) Apparatus 3, which is designed to confine the beads in a screened-in cylinder. 

This apparatus selects the primary sample, which is then screened repeatedly to produce the final sample. The method is quick and convenient however, variations in materials can cause problems and bias in sampling increases as the plant becomes worn. ... 

During the X-ray apparatus main circuit creation the magnetomotive force for the power winding was selected less than for the high-voltage winding. The yoke cross-section is bigger, than the rod one. 

In essence, a guided-ion beam is a double mass spectrometer. Figure A3.5.9 shows a schematic diagram of a griided-ion beam apparatus [104]. Ions are created and extracted from an ion source. Many types of source have been used and the choice depends upon the application. Combining a flow tube such as that described in this chapter has proven to be versatile and it ensures the ions are thennalized [105]. After extraction, the ions are mass selected. Many types of mass spectrometer can be used a Wien ExB filter is shown. The ions are then injected into an octopole ion trap. The octopole consists of eight parallel rods arranged on a circle. An RF... 

Figure Bl.7.12. A schematic diagram of a typical selected-ion flow (SIFT) apparatus. (Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Advances in Atomic and Molecular Physics vol 24, ed D Bates and B Bederson p 4. Copyright Academic Press, Inc. Reproduced with pennission.)...

It is difficult to observe tliese surface processes directly in CVD and MOCVD apparatus because tliey operate at pressures incompatible witli most teclmiques for surface analysis. Consequently, most fundamental studies have selected one or more of tliese steps for examination by molecular beam scattering, or in simplified model reactors from which samples can be transferred into UHV surface spectrometers witliout air exposure. Reference [4] describes many such studies. Additional tliemes and examples, illustrating botli progress achieved and remaining questions, are presented in section C2.18.4. 

Sensitivity levels more typical of kinetic studies are of the order of lO molecules cm . A schematic diagram of an apparatus for kinetic LIF measurements is shown in figure C3.I.8. A limitation of this approach is that only relative concentrations are easily measured, in contrast to absorjDtion measurements, which yield absolute concentrations. Another important limitation is that not all molecules have measurable fluorescence, as radiationless transitions can be the dominant decay route for electronic excitation in polyatomic molecules. However, the latter situation can also be an advantage in complex molecules, such as proteins, where a lack of background fluorescence allow s the selective introduction of fluorescent chromophores as probes for kinetic studies. (Tryptophan is the only strongly fluorescent amino acid naturally present in proteins, for instance.)... 

First, considerably greater emphasis has been placed on semimicro techniques and their application to preparations, separations, analysis and physical determinations such as those of molecular weight. We have therefore greatly expanded the section on Manipulation on a semi-micro scale which was in the Third Edition, and we have described many more preparations on this scale, some independent and others as alternatives to the larger-scale preparations which immediately precede them. Some 40 separate preparations on the semi-micro scale are described in detail, in addition to specific directions for the preparation of many classes of crystalline derivatives required for identification purposes. The equipment required for these small-scale reactions has been selected on a realistic basis, and care has been taken not to include the very curious pieces of apparatus sometimes suggested as necessary for working on the semi-micro scale. 

The student should read Sections 1,10 to 1,16 carefully before commencing any experimental work. A supply of melting point capillaries is prepared as described in Section 11,10 (compare Fig. 77, R , I). The apparatus illustrated in Fig. 77. 10, 2, a is assembled with concentrated sulphuric acid as the bath liquid the thermometer selected should have a small bulb. The melting points of pure samples of the following compounds are determined in the manner detailed in Section 11,10 —... 

In a word, all these receptors are more or less able to discriminate against cations that are either smaller or larger than thek cavity (44). However, in a strict sense, discrimination of metal-ion spheres does not concern with molecular recognition but selection of the carbon ball C q certainly does. In fact, the fuUerene C q has been included into the cavity of octa-/ f2 butylcalix[8]arene (Fig. 8c) shutting out C q and making a very convenient and efficient C q purification possible without any expensive apparatus (45). 

The selection of a particular deposition process depends on the material to be deposited and its availabiUty rate of deposition limitations imposed by the substrate, eg, maximum deposition temperature adhesion of deposit to substrate throwing power apparatus required cost and ecological considerations. Criteria for CVD, electro deposition, and thermal spraying are given in Table 2 (13). 

Research. A significant impact on research at high pressure has come about with the use of gem quaHty diamonds as Bridgman-type anvils in a smaU compact high pressure device (40—42). With this type of apparatus, pressures greater than those at the center of the earth (360 GPa = 3.6 Mbars) have been reached, and phase transformations of many materials have been studied. Because of the x-ray transparency of diamond, it is possible to determine the stmcture of the phases under pressure. Because of the strenuous environment, crystals selected for this appHcation have to be of very high quaHty. 

Back-diffusion is the transport of co-ions, and an equivalent number of counterions, under the influence of the concentration gradients developed between enriched and depleted compartments during ED. Such back-diffusion counteracts the electrical transport of ions and hence causes a decrease in process efficiency. Back-diffusion depends on the concentration difference across the membrane and the selectivity of the membrane the greater the concentration difference and the lower the selectivity, the greater the back-diffusion. Designers of ED apparatus, therefore, try to minimize concentration differences across membranes and utilize highly selective membranes. Back-diffusion between sodium chloride solutions of zero and one normal is generally [Pg.173]

BS 5345. General Recommendations—Code of Practice for Selection, Installation and Maintenance of Electrical Apparatus for Use in Potentially Explosive Atmospheres. BSI, U.K. 

Specifications for intrinsically safe electrical system i General recommendations on the selection of the appropriate group of electrical apparatus based on safe gaps and minimum igniting currents 3682/1991 BS 5501-7/1977 BS 5501-9/1982 BS 5345-1/1989 ... 

Carbonate ionophore I [ETH 6010] (heptyl 4-trifluoroacetylbenzoate) [129476-47-7] M 316.3, b 170°/0.02 Torr, d 0.909. Purified by flash chromatography (2g of reagent with 30g of Silica Gel 60) and eluted with EtOAc/hexane (1 19). The fractions that absorbed at 260nm were pooled, evapd and dried at room temp (10.3 Torr). The oily residue was distd in a bubbled-tube apparatus (170°/0.02 Torr). Its IR (CHCI3) had peaks at 1720, 1280, 940cm and its sol in tetrahydrofuran is 50mg/0.5mL. It is a lipophilic neutral ionophore selective for carbonate as well as being an optical humidity sensor. [Anal Chim Acta 233 41 1990.]... 

Guidance on the choice of respiratory protection for selected environments is given in Figure 13.6. All persons liable to use such protection should be fully trained this should cover details of hazards, limitations of apparatus, inspection, proper fitting of facepiece, testing, cleaning etc. 

Withdrawn) 1989 AMD 3 Code of practice for selection, installation and maintenance of electncal apparatus for use m potentially explosive atmospheres (other than mining applications or explosives processing and manufacture). Part 1 General recommendations (AMD 7871) dated 15 September 1993. Withdrawn, superseded by BS EN 60079-14 1997 (Withdrawn) 1978 AMD 1 Code of practice for selection, installation and maintenance of electncal apparatus for use m potentially explosive atmospheres (other than mining applications or explosives processing and manufacture). Part 6 Recommendations for type of protection. Increased safety (AMD 5557) dated 30 November 1989. Withdrawn, superseded by BS EN 60079... 

AMD 1 Electrical apparatus for use m the presence of combustible dust. Part 1 Electncal apparatus protected by enclosures - Selection, installation and maintenance (AMD 10763J dated October 1999. Inc.Cor.l(10856jPart.s/s BS 6467-1 1985 and BS 6467-2 1988, remain cuiTcnt... 

The apparatus employed for any given analysis will have operating specifications that are unique to the particular instrument that is selected or that is available. These specifications have been determined by the design and method of manufacture of the instrument and can differ significantly from one chromatograph to another. Some will control and limit the ultimate performance achieved by any column with which the instrument is used. However, it is likely that, as a result of careful design by the manufacturer, the important instrument characteristics affecting column... 

Uniform corrosion is the deterioration of a metal surface that occurs uniformly across the material. It occurs primarily when the surface is in contact with an aqueous environment, which results in a chemical reaction between the metal and the service environment. Since this form of corrosion results in a relatively uniform degradation of apparatus material, it can be accounted for most readily at the time the equipment is designed, either by proper material selection, special coatings or linings, or increased wall thicknesses. 

When designing apparatus with several materials, consider all materials as an integrated entity. More highly resistant materials should be selected for the critical components and for cases in which relatively high fabrication costs are anticipated. Often, a compromise must be made between mechanically advantageous properties and corrosion resistance. 

For service environments in which erosion is anticipated, the wall thickness of the apparatus should be increased. This thickness allowance should secure that various types of corrosion or erosion do not reduce the apparatus wall thickness below that required for mechanical stability of the operation. Where thickness allowance cannot be provided, a proportionally more resistant material should be selected. 

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