Endpoint methods

The endpoint methods discussed here continue to be very useful for estimation of binding affinity and exploring interactions that contribute to drug binding in the system studied. These methods... 

Protection Agency/European Union properties, environmental fate parameters, ecotoxicological and human health endpoints. methods Protection Agency (1994)... 

Srisawasdi P, Chaichanajarernkul U, Teerakranjana N, Kroll MH. Implementation of cellulomonas cholesterol oxidase for total serum cholesterol determination by the endpoint method. J Clin Lab Anal. 2008 22 50-58. 

The approved variations [14] in the Karl Fischer method include volumetric titration methods to either a visual (excess iodine or addition of an indicator) or volta-metric endpoint detection method. The visual or voltametric endpoint methods usually require 30-40 mg of sample for analysis for freeze-dried biological products containing from 1.0% to 3.0% residual moisture. Coulometric Karl Fischer instruments generate the iodine from potassium iodide for water titration at the electrodes. Only 10-20 mg of freeze-dried sample is required for accurate analysis. 

Dulbecco, R. (1994) Endpoint method—measurement of the infectious titer of a viral sample, in Virology, 2nd ed., Lippincott, Philadelphia, pp. 22-25. 

Both open and closed continuous flow systems rely on the fixed time, or endpoint method for the determination of substrate concentrations. At a fixed and constant flow rate, the injected volume of substrate will spend a fixed time on the column, and this time is related to the volume of the column (that volume not occupied by stationary phase) and the mobile-phase flow rate. 

Determination of ozone in aqueous solution is perhaps the most problematic for a variety of reasons (1) ozone is unstable (2) ozone is volatile and easily lost from solution and (3) ozone reacts with many organic compounds to form products such as ozonides and hydrogen peroxide that are also good oxidants. Careful study of the use of iodometric methods for the determination of ozone in aqueous solution has revealed that the stoichiometric ratio of ozone reacted with iodine produced in the reaction varies from 0.65 to 1.5, depending on pFI, buffer composition and concentration, iodide ion concentration, and other reaction conditions. As a result, iodometric methods are not recommended. Ozone can be determined iodimetrically by addition of an excess of a standard solution of As(III), followed by titration of the excess As(III) with a standard solution of iodine to a starch endpoint. Methods using DPD, syringaldazine, and amperometric titrations have also been developed. 

In a clinical lab, creatinine is normally determined using a commercial analyzer utilizing an absorption method based on the Jaffe reaction. In the Jaffe reaction, creatinine is reacted with alkaline sodium picrate solution to form an orange creatinine-picrate complex. The absorbance at 510 nm can then be measured after a specified reaction time (endpoint method). There are, however, a variety of modifications to the basic method because of the positive... 

The kinetic method employed for substrate determination is the measurement of the rate of an enzymatically catalyzed reaction, as is used to determine enzyme activity. Rate methods are generally more rapid than the endpoint method. Complete conversion reactions, on the other hand, are less subject to interference from enzyme inhibitors or activators as long as sufficient time is allowed for completion conversion. 

Digestibility assays Serial dilution assays Radioimmunoassay Endpoint methods... 

Turbidimetric and nephelometric assay Nephelo-metry and turbidimetry, because of their speed and ease of use, are most widely used. These techniques can be used either by measuring the amount of Ag-Ab complex formation (endpoint methods) or by measuring the rate of complex formation (kinetic methods). The kinetic methods are more rapid because measurements are accomplished within 20 s, and are more precise because sample blanks are not necessary. Kinetic assays are, however, somewhat less sensitive because low-affinity antibodies do not have time to react. The occurrence of Ag-Ab formation is related to the amount of light scattering and is used as the basis for antigen quantification. This approach has been accompanied by the development of... 

After collecting spectral data at different locations in the blender and at various hme points, Sanchez et al. [7] evaluated several qualita-hve blend endpoint methods. A mean standard deviation for the spectra collected at each hme point was compared over time to determine homogeneity. This method allowed authors to determine the character-ishcs of the mixture spectrum, corresponding to the desired blend state. Using that mixture spectrum, they defined a dissimilarity index based on the orthogonal projection of spectra collected at various hmes points onto the mixture spectrum. The norm of the resulting vector was then employed to evaluate the blend state. 

Table 2.17. Enzyme concentrations used in the endpoint method of enzymatic food analysis...

Substrate concentration is obtained using a method based on kinetics by measuring the reaction rate. To reduce the time required per assay, the requirement for the quantitative conversion of substrate is abandoned. Since kinetic methods are less susceptible to interference than the endpoint method, they are advantageous for automated methods of enzymatic analysis. 

Lolekha, P.H., Srisawasdi, P., Jearanaikoon, P., Wetprasit, N., Sriwanthana, B., KroU, M.H., 2004. Performance of four sources of cholesterol oxidase for serum cholesterol determination by the enzymatic endpoint method. Clin. Chim. Acta 339, 135—145. 

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