Quantitation validation procedure

In conclusion, the advent of combinatorial and HTS approaches to lead discovery has resulted in substantial interest in the development of novel techniques for computer-based compound-selection. This interest is being reflected not only in the application of novel algorithmic approaches to compound selection, e.g., the use of k-D trees [13] and clique detection [55], but also in the increasing emphasis that is being placed on quantitative validation procedures, such as those discussed in the previous section such developments can only further increase the importance of the methods discussed in this chapter. 

In summary, the CSL guidelines can be simply applied in each laboratory and contain very clear instructions. The validated procedures do not focus on the central analytical part only. Important secondary aspects of the whole procedure (sample processing, analyte stability, extraction efficiency) are also considered. For each parameter which is determined, different criteria for the evaluation of quantitative, semi-quantitative and screening methods are given. Here, it should be noted that compared with other guidelines the requirement for the precision of quantitative methods is very stringent (RSD < 10%). 

Kraker, J. J., Hawkins, D. M., Basak, S. C., Natarajan, R., Mills, D. Quantitative structure-activity relationship (QSAR) modebng of juvenile hormone activity Comparison of validation procedures. Chemometr. Intell. Lab. Syst. 2007, 87, 33M2. 

A stability-indicating method is a validated quantitative analytical procedure that can detect the changes with time in the pertinent properties of the drug substance and drug product under defined storage condition. A stability-indicating assay method accurately measures the active ingredient(s) without interference from other peaks and is sensitive... 

Quantitative CE—MS studies were scarcely reported. " This subject is however of prime importance, particularly for the pharmaceutical industry where the reliability of analytical data is essential. For this reason, method development is generally followed by an evaluation of quantitative performance using an appropriate validation procedure performed in agreement with criteria established by the International Conference on Harmonisation of technical requirements for registration of pharmaceuticals for human use (ICH) and the Food and Drug Administraction (FDA) guidelines, or Societe Franqaise des Sciences et Techniques Pharmaceutiques (SFSTP) commissions. ... 

In another work, Parra and coworkers proposed a method based on chemically modified voltammetric electrodes for the identification of adulterations made in wine samples, by addition of a number of forbidden adulterants frequently used in the wine industry to improve the organoleptic characteristics of wines, like, for example, tartaric acid, tannic acid, sucrose, and acetaldehyde (Parra et ah, 2006b). The patterns identified via PCA allowed an efficient detection of the wine samples that had been artificially modified. In the same study, PLS regression was applied for a quantitative prediction of the substances added. Model performances were evaluated by means of a cross-validation procedure. 

Validation of the Mechanism. The process of matching the predictions of the mechanism to experimental smog chamber data is termed validation of the mechanism. The first step in a validation procedure is to establish values for the two major classes of parameters that appear in the mechanism—the reaction rate constants and the stoichiometric coeflBcients. Base values of the rate constants can be estimated from the chemical literature. However, with the sacrifice of chemical detail present in the new, simplified mechanism is a loss in the ability to associate the rate constant values with particular reactions. Therefore, the rate constants in the simplified mechanism are more a quantitative assessment of the relative rates of competing reactions than a reflection of the exact values for particular reactions. Base values for the parameters that appear in the kinetic mechanism are thus established on the basis of published rate constants. However, we must expect that final validation values will consist of those values which produce the best fit of the mechanism to actual smog chamber data. A recent summary of rate constants for specific hydrocarbon systems was made by Johnston et al. 40) from which rate constants for the Reactions in Table I can be estimated for a number of hydrocarbons. 

To understand why HPLC is frequently used in quantitative analytical methods, it is useful to assess whether or not an analytical method is suitable for its intended purpose and, in doing so, consider the deficiencies in methods employing classical measurement steps. Analytical method validation is the process of assessing the fitness for purpose of an analytical method in choosing an analytical method issues such as cost, simphcity, operator experience, availability etc. are of secondary importance to the actual validity of the method under consideration. In the validation procedure, tests are typically carried out for the following properties ... 

This kind of interference is called cross-reactivity, or specific interference, and is usually quantitated by assaying for the interferent in the absence of analyte. Validation procedures involve screening of a large number of potential interferents at concentrations higher than their expected levels in real samples. Cross-reactivity methods for immunoassays have been described in Chapter 6. 

Despite the widespread use of CE-MS for qualitative analysis, few quantitative applications have been pubhshed for routine analysis, and the vahdation of CE-MS methods according to generally accepted criteria is very uncommon. To our knowledge, only a few validation procedures are reported in the hterature. Although CE methods can be validated like chromatographic techniques, there are some specific characteristics to be discussed when quantitative determinations are expected. 

The search for a linear correlation between log k and solute descriptors (Eq. 15.3) allows one to establish in a qualitative and quantitative manner which intermolecular forces govern the phenomenon under investigation. Building QSRR thus demands the use of refined chemometric tools for variable selection, criteria to detect and eliminate outliers, and, ultimately, data validation procedures. 

HPLC is a method for the analysis and characterization of steroid receptors based on characteristics such as molecular weight. Qualitative relationships and multiple forms of the receptor can be maintained by the rapid gel-exclusion system, and contaminants can be readily identified (P2). Advantages of using HPLC include rapid analysis time, minimal receptor modification, improved resolution, and high reproducibility. Unfortunately the HPLC assay is tedious, requiring saturation analysis for each sample and quantitative validity has not been established for this procedure. Other disadvantages associated with HPLC methods include the requirement for expensive equipment and sophisticated technical skills. Therefore, HPLC analysis of receptor proteins is currently used only in research studies. 

Individual procyanidin standards are not used very often, considering the number of quantitative chromatographic procedures described in the literature. This is mainly due to the fact that procyanidins are not commercially available. On the other hand, isolation or synthesis require laborious procedures. Table (9) summerizes the studies which use individual procyanidin standards for quantitation. This approach still remains the only way to quantify procyanidins correctly. In view of the demand for validated protocols on one hand and the countless quantifiable procyanidins in the chromatograms on the other hand, it is more than tempting (and surely reasonable, too) to develop standardized methods using merely one commerically available monomeric reference standard. 

The stages of validation of biomarker assays include establishment of the biomarker (development), so-called prevalidation, prestudy validation, and in-study validation [13-15]. The following short discussion will focus on the GLP-like definitive and relative quantitative assays. As the development and validation of an assay for novel biomarkers is quite diverse, the application of strict validation procedures appears problematic. Therefore, upon establishment of the prototype assay in the development phase, a formalized validation plan should be developed that... 

Stability-indicating assays are validated quantitative analytical procedures that can detect drug alterations over time. They should include tests for integrity of the drug, potency, sterility, and, if applicable, moisture, pH, and preservative stability measured at regular intervals throughout the dating period [16-19]. 

Like all classical quantitative analysis methods, NMR spectroscopy needs calibration, calibration standards and a validation procedure. The standard techniques are used for calibration external calibration, the standard addition method and the internal standard method. A fourth is a special NMR calibration method, the tube-in-tube technique. A small glass tube (capillary) containing a defined amount of standard is put into the normal, larger NMR tube filled with the sample for analysis. In most cases, there are slight differences in the chemical shift of corresponding signals of the same molecule in the inner... 

TABLE 41.1 Summary of Validation Procedures and Performance Goals for Quantitative Assays... 

The disadvantages of CE compared to IC include lower sensitivity, higher concentration detection limits, and somewhat poorer reproducibility of qualitative and quantitative data owing to instability of the electroosmotic flow (EOF). IC has so far been developed more extensively. Validated procedures and computer optimization approaches are available... 

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