Quantification general considerations

Danzer K (2001) Selectivity and specificity in analytical chemistry. General considerations and attempt of a definition and quantification. Fresenius J Anal Chem 369 397... 

Quantitative TLC is the subject of Chapter 10 of Ref. I. The theory and techniques of densitometric TLC are elaborated in Chapter 10 of this Handbook, and general considerations and instrumental aspects of densitometric chromatogram evaluation are presented in Chapter 5. Quantification of 1 ipids and other types of compounds on quartz rods coated with an immobilized layer of silica gel or other sorbent with direct interfacing to a flame ionization detector (the Chromarod system) was reviewed by Shantha (188) and Ackman et al. (189) and is described in Chapter 13. 

CE has been included as a distinct analytical technique in a general monograph in the Ph.Eur., JP, and USP. These monographs have been harmonized and at present only some minor differences exist between the different pharmacopoeias. They give an overview of the general principles, instrumental considerations, and the different separation modes. Also, attention is paid to quantification and system suitability aspects. 

Generally, enzymatic hydrolysis of nitriles to the corresponding acids can either proceed stepwise, which is the case for catalysis by the nitrile hydratase/amidase enzyme system, or in one step in the case of nitrilases. Both systems have been investigated for surface hydrolysis of PAN [10], Complete hydrolysis with either system was monitored by quantification of ammonia and/or polyacrylic acid formed as a consequence of hydrolysis of nitrile groups [70-72], As a result, considerable increases in colour levels (e.g. 156% for commercial nitrilase) were found upon dyeing [72],... 

Kinetic Considerations. The reaction kinetics are masked by a desorption process as shown below and are further complicated by rate deactivation. The independence of the 400-sec rate on reactant mole ratio is not indicative of zero-order kinetics but results because of the nature of the particular kinetic, desorption, and rate decay relationships under these conditions. It would not be expected to be more generally observed under widely varying conditions. The initial rate behavior is considered more indicative of the intrinsic kinetics of the system and is consistent with a model involving competitive adsorption between the two reactants with the olefin being more strongly adsorbed. Such kinetic behavior is consistent with that reported by Venuto (16). Kinetic analysis depends on the assumption that quasi-steady state behavior holds for the rate during rate decay and that the exponential decay extrapolation is valid as time approaches zero. Detailed quantification of the intrinsic kinetics was not attempted in this work. 

The basic framework for the waste classification system developed in this Report is depicted in Figure 6.1. Starting with the objectives that the classification system should apply to any waste that contains radionuclides or hazardous chemicals and that all such waste should be classified based on risks to the public posed by its hazardous constituents, the fundamental principle of the proposed system is that hazardous waste should be classified in relation to disposal systems (technologies) that are expected to be generally acceptable in protecting public health. This principle leads to the definitions of three classes of waste, and to quantification of the boundaries of the different waste classes based on considerations of risks that arise from different methods of disposal. The boundaries normally would be specified in terms of limits on concentrations of hazardous substances. At the present time, nearly all hazardous and nonhazardous wastes are intended for disposal in a near-surface facility or a geologic repository, and these are the two types of disposal systems assumed in classifying waste. The three waste classes and their relationship to acceptable disposal systems are described in more detail in Section 6.2. 

Currently, there are inconsistencies in the application and methodology for uncertainty analysis in exposure assessment. While several sophisticated quantitative techniques exist, their general application is hampered not only by their complexity (and resulting need for considerable supporting information) but also by the lack of methodology to facilitate the specification of uncertainty sources prior to the quantification of their specific weight. 

A rationale for the inclusion or exclusion of impurities in a specification should be presented. The rationale should include a discussion of the impurity profiles observed in the safety and clinical development batches, together with a consideration of the impurity profile of batches manufactured by the proposed commercial process. Specified, identified impurities should be included along with specified, unidentified impurities estimated to be present at a level greater than the identification threshold given. For impurities known to be tmu-sually potent or that produce toxic or unexpected pharmacological effects, the quantification/detection limit of the analytical procedures should be commensurate with the level at which the impurities should be controlled. For unidentified impurities, the procedure used and assumptions made in establishing the level of the impurity should be clearly stated. Specified, unidentified impurities should be referred to by an appropriate qualitative analytical descriptive label (e.g., "unidentified A," "unidentified with relative retention of 0.9"). A general acceptance criterion of not more than the identification threshold for any unspecified impurity and an acceptance criterion for total impurities should be included. 

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