Plate tests principle

The guarded hot-plate test is based on the principle of heat flow across a large flat sample at steady state, in which the heat flow is unidirectional through the thickness. A temperature diflerential across the sample provides the driving force for heat transfer, following the Fourier equation ... 

Most test designs are based on classical microbiological techniques and use colony enumeration on agar plates. The principle is to spike the product to be tested with selected organisms and to follow the disappearance of these organisms over a certain time. 

The underlying problem in testing the validity of the additivity principle in corrosion, mineral extraction, and electroless plating is that the electrode metal itself forms part of one of the half-reactions involved, e.g., zinc in equation (5) and copper in equations (8) and (12). A much better test system is provided by the interaction of two couples at an inert metal electrode that does not form a chemical part of either couple. A good example is the heterogeneous catalysis by platinum or a similar inert metal of the reaction... 

According to the practical equipment there are useful tools, so-called test kits, which are units that contain all the reagents and a simple instrumentation in form of plates, tubes and wells. The test kits work rapidly, are easily to handle and field-portable. Frequently, biochemical principles are applied, especially immunoassay techniques which use body-antibody reactions. 

These principles lead to the conclusion that each test substance requires an individual formulation. Sometimes different ingredients will be required for different concentrations to obtain the maximum rate of release. No universal vehicle is available for any route, but a number of approaches are. Any dosage preparation lab should be equipped with glassware, a stirring hot plate, a sonicator, a good homogenizer, and a stock of the basic formulating material, as detailed at the end of this chapter. 

Thus, because the test can be carried out on 96-well microtiter plates, high throughput is possible. Of course, the inherent disadvantage noted above for some of the colorimetric tests also applies here, namely, the fact that the optimization of a potential catalyst is focused on a specific substrate 11 modified by incorporation of a probe, in this case the fluorogenic moiety 14. However, one can expect the test to be useful in directed evolution projects in which proof of principle is the goal. Moreover, this kind of approach can be used in very practical applications, namely as a pre-test for the activity of enzymes. 

The Delvotest-P-Multitest is a modification of the original Delvotest-P test (50). This is not an ampoule test but a polystyrene plate-based test with cups similar in principle to the original version. Its main advantage is that it permits up to 96 test cups to be used at one time. Following a collaborative study (51), both tests have been adopted by the Association of Official Analytical Chemists (AOAC) as official tests for the detection of -lactams in milk and milk products. 

The principle of the compression plastimeter is very simple - the test piece is compressed between parallel plates under a constant force and the compressed thickness measured. This simplicity accounts for the early adoption of this type of instrument and its subsequent continued popularity. The work of Williams16 led to the first widely used parallel plate instrument and eventually to various modified forms all working on the same principle. Apart from simplicity, the compression principle has no real inherent advantages but a number of disadvantages ... 

This unit will introduce two fundamental protocols—the Wilhelmy plate method (see Basic Protocol 1 and Alternate Protocol 1) and the du Noiiy ring method (see Alternate Protocol 2)—that can be used to determine static interfacial tension (Dukhin et al., 1995). Since the two methods use the same experimental setup, they will be discussed together. Two advanced protocols that have the capability to determine dynamic interfacial tension—the drop volume technique (see Basic Protocol 2) and the drop shape method (see Alternate Protocol 3)—will also be presented. The basic principles of each of these techniques will be briefly outlined in the Background Information. Critical Parameters as well as Time Considerations for the different tests will be discussed. References and Internet Resources are listed to provide a more in-depth understanding of each of these techniques and allow the reader to contact commercial vendors to obtain information about costs and availability of surface science instrumentation. 

The principle approach to immunoassay is illustrated in Figure 1, which shows a basic sandwich immunoassay. In this type of assay, an antibody to the analyte to be measured is immobilized onto a solid surface, such as a bead or a plastic (microtiter) plate. The test sample suspected of containing the analyte is mixed with the antibody beads or placed in the plastic plate, resulting in the formation of the antibody—analyte complex. A second antibody which carries an indicator reagent is then added to the mixture. This indicator may be a radioisotope, for RIA an enzyme, for EIA or a fluorophore, for fluorescence immunoassay (FIA). The antibody-indicator binds to the first antibody—analyte complex, free second antibody-indicator is washed away, and the two-antibody—analyte complex is quantified using a method compatible with the indicator reagent, such as quantifying radioactivity or enzyme-mediated color formation (see Automated instrumentation, clinical chemistry). 

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