Methods for determining stability

From the range of methods for determining stability of a given algorithm such as EX, CN, B1 or BDF, etc., this chapter restricts itself to the heuristic, the Neumann and the matrix methods, as well as a fourth that makes use of the stability function. 

There are many methods for determining stability constants but measurements of electrode potentials, pH titrations or the use of spectroscopic methods for determining the concentrations of species in solution are of particular importance. In the simplest... 

From the above it is easily concluded that a working knowledge of sample/ solvent interaction (above and beyond chemical reactions) is important. One practical method for determining stability is to prepare a standard solution at the beginning of the method validation process. Use this sample as a check standard throughout the validation process. Plotting the recovery versus time will give an accurate estimate of the acceptable shelf-life of the analyte in the preparation solvent. 

Step, these errors are not amplified without bound in subsequent steps. There are various categories of stability, to be seen in the relevant texts [1,16,17] (to cite only three of a multitude of such texts). Below, a rather brief and less technical treatment will be given than is provided in these texts. Several methods for determining stability are described, and some special conditions that can affect stability. 

H. Heloma and E. Kovene, "A Modem Method for Determining the Stabihty and Stabilizers in Sohd Gun PropeUants," in Proceedings of the 6th... 

A common method for determining the stability of pastry, potato chips, and the like is to place a number of broken pieces of the product in 4-ounce mayonnaise jars with screw tops and store them at room temperature or in the Schaal oven in the absence of light. At regular intervals samples are removed and tested for peroxide content and organoleptic rancidity. 

In contrast to the acid, sodium nitrite should not in general be added in excess. Firstly, as far as the ratio of amine to nitrite is concerned, diazotization is practically a quantitative reaction. In consequence, it provides the most important method for determining aromatic amines by titration. Secondly, an excess of nitrous acid exerts a very unfavorable influence on the stability of diazo solutions, as was shown by Gies and Pfeil (1952). Mechanistically the reactions between aromatic diazonium and nitrite ions were investigated more recently by Opgenorth and Rtichardt (1974). They showed that the primary and major reaction is the formation of aryl radicals from the intermediate arenediazonitrite (Ar —N2 —NO2). Details will be discussed in the context of homolytic dediazoniations (Secs. 8.6 and 10.6). 

The Nyquist stability ciiterion is a method for determining the stability of systenas in the frequency domain. It is almost always applied to closedloop systems. A working, but not completely general, statement of the Nyquist stabiU ity criterion is ... 

Current data indicate that the analysis of cellulase enzyme activities may be the best method for determining the projected cellulose conversion of the overall system, and therefore the hydrolytic power of the system under evaluation. With development, the analysis of enzyme activities may also serve as a "real time" method of monitoring the stability of the system, with radical changes in enzyme activities indicative of potential process upset. 

New H n.m.r. methods for determining the relative stability constants have been developed and used to study the 1 1 adducts of NbClj and TaClj with a series of ethers, sulphides, and nitriles. 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

CDj) T. Urbanski, Vol 2(1965), pp 22-31 gives methods for determining the Stability of Nitric Esters, which include Abel Heat Test, Litmus Test (Vieille Test), Heat Test at 134.5°C, Silvered Vessel Test, Loss of Weight Test, Will Test, Bergmann Junk Test and Manometric Test... 

The precise determination of the cluster structure is indispensable in the understanding of the chemical and physical properties of these substances. The development of calculation methods for the stability of defect complexes is expected in the near future. 

The extent of oxidative deterioration will determine the acceptability of a food product. Because of this, methods for determining the degree of oxidation are very useful to the food industry. There are many possible methods that can be utilized (see Commentary) however, due to the stability of some of the end products, and their direct relationship with rancidity, headspace GC provides a fast and reliable method for oxidation measurement. Headspace techniques include static, dynamic, and solid-phase microextraction (SPME) methods. 

S.S. Abbas, Y.M. Fayez, L.-S. Abdel Fattah, Stability indicating methods for determination of donepezil hydrochloride according to ICH guidelines, Chem. Pharm. Bull. 54 (2006) 1447-1450. 

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