Selectivity of an assay

First of all, the allelopathic activity of a compound (or of a mixture of compounds) isolated as per the above methods should be tested in agar diffusion assays using different algal strains The selection of an assay alga depends primarily on its ability to grow satisfactory under the chosen... 

The spectra of some drugs change with pH and the sensitivity and selectivity of an assay can sometimes be controlled by changing the eluent pH. The influence of such changes on the chromatography must also be considered. 

In the selection of an appropriate cell culture system, a number of criteria must be considered (Table 3). These include not only the characteristics of the cell type but also the controllable parameters of the complete transport system such as the permeants, the filter properties, and the assay conditions. In general, most transport experiments employ the experimental design shown schematically in Figure 4 with modifications as discussed below. Typically, the desired cell is seeded onto some sort of semipermeable filter support and allowed to reach confluence. The filter containing the cell monolayer separates the donor and receiver... 

PAbs against 2,4,5-TCP have been prepared after theoretical and molecular modeling chemical studies [226]. Competitive direct and indirect ELIS As have been developed, but as before the latter format was shown to be more robust. The indirect immunoassay has an excellent LOD near 0.05 pg L . The selectivity of the assay is high in relation to other chlorophenols frequently present in real samples, but as with the 2,4,6-TCP assay the brominated analogs may also be recognized. The 2,4,5-TCP immunoassay is stable in media with pH... 

Because of the complex and polymorphic nature of the Lp(a) lipoprotein, together with the homology of the apo(a) moiety with plasminogen, a number of specific problems arise concerning the immunochemical quantification of Lp(a). These include the selection of a suitable type of immunoassay, its specificity and sensitivity, and the type of antisera used in the assay (L2). Moreover, the selection of an appropriate standard and of the units of mass to express the amount of Lp(a) require careful consideration (L4). 

The ultimate goal of an assay method is the separation and visualization of all components in a single chromatogram. Proper selection of detection wavelength is a critical part of method development. When choosing a detection wavelength, the following factors need to be taken into consideration ... 

The issue of which antibody to select for an assay is not a new problem. Certainly anyone involved in the development of an immunoassay has been faced with this choice. Consider attempting to create a multianalyte, microarray-based micro-ELISA of modest density (10 to 100 analytes) and determining which capture antibodies to use based upon their affinities, stabilities, and cross-reactivities. For a sandwich assay, add in the 10 to 100 analyte-specific secondary (reporter) antibodies and determine their levels of cross-reactivity with each other and with the specified antigens and capture antibodies. In other words, achieving high performance for all analytes with a microarray immunoassay is indeed a formidable challenge. 

Low permeability can itself be the cause of apparent discrepancies between biochemical and cell-based assays and may or may not have physiological relevance. Independent of the solubility limitation mentioned above, the selection of an appropriate loading concentration in cell-based permeability assays impacts on the assay outcome and depends on what information one wants to extract from the measurement loading at high concentration (i.e., 100 pM) will essentially cancel the effect of active transports unless passive diffusion is low. When high loading concentrations are used, poor recovery and bioanalytics are usually not an issue. 

In addition, protein kinase phosphorylation-based tissue microarray potentially provides clues at the molecular level for the selection of an optimal therapy for breast cancers. It should be noted that one of the major challenges for this technique is the specificity and availability for the antibodies. Each antibody should be evaluated for specificity with Western blot analysis prior to being applied to tissue microarray assays. 

When attempting to convert a manual method into an automated method, there are certain elements, such as tablet size and solvent selection, which will have an impact on the ease of the conversion from manual to automated. For instance, some of the elements of an assay method that would make it easier to automate would be that the dosage form fits into a test tube the extraction uses neutral media or acid not more concentrated than 0.1 M makes use of nonvolatile, low-toxicity solvents does not use surfactants and uses premixed, room-temperature solvents. Some of the elements of a dissolution method that would make it easier to automate would be that the dosage form fits in the sample carousel, does not use media more concentrated than 0.1 M acid, does not use isopropanol or surfactant in large quantities, uses magnetic sinkers or no sinkers at all, and uses no or minimal reagent addition volumes for pH control. 

Rojickova-Padrtova, R., Marsalek, B. and Holoubek, I. (1998) Evaluation of alternative and standard toxicity assays for screening of environmental samples selection of an optimal test battery, Chemosphere 37, 495-507. 

Selectivity is the ability of an assay to measure the analyte of interest in the presence of other constituents in the sample. Because IAs are often performed without sample extraction, they are more prone to matrix interference than are chromatographic methods with extraction. Matrix interference could come from crossreactivity with structurally similar components in the sample, or from nonspecific binding to structurally dissimilar components in the matrix. The results are high background noise, loss of sensitivity, and inaccurate and nonreproducible data. Sometimes, the problem may only occur in a few exceptional patient samples that have structurally similar components such as unknown metabolites, or dissimilar components from samples with hyperlipidemia, hemolysis, complement components, rheumatoid factors, binding proteins, autoantibodies, and heterophilic anti-immunoglobulin Ab. 

Although well designed LC-MS/MS assays generally outperform immunoassays due to their accuracy, sensitivity, precision, and inherent multiplexing capability, they are not free from analytical problems. Besides limitations in selectivity— isobaric analytes cannot be distinguished—sudden and unpredictable ion yield attenuations, often known as ion suppression effect, have to be considered the Achilles heel of quantitative bio-analytical mass spectrometry. Ion yield attenuation is compromising both the accuracy of an assay and its precision. It can easily lead to gross errors in analyte quantification. 

After the selection of the specific techniques to be employed, one must determine how to quantify the genes associated with the phenotype of interest. The design of an assay that acts as a reporter or a molecular sensor can prove to be the most challenging step in designing a successful RNAi screen. The assay must be both highly reproducible and sensitive, without noise, and exhibiting minimal standard error. Traditional assay development techniques must be taken into account for all RNAi screens as they are for conventional compound-based screens. 

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