Analytical method transfer assay

Methods have successfully been transferred to various laboratories in inter-company cross-validation exercises for a chiral separation, for an assay of the main component in a formulation and for drug stoichiometry. Revalidation is an alternative to method transfer in case of changes in product composition or analytical procedure (cf. Section I.L). Although a method transfer in CE is not a major difficulty, some aspects have to be considered, especially if a method is transferred to an instrument of another manufacturer. 

A significant amount of work on microdevices has recently focused on proteins and peptides. Some of this was initiated as part of the larger proteomics effort, but currently the work is centered largely on the transfer of current analytical methods to microchips. This includes enzymatic assays and immunoassays, both of which are routinely utilized in clinical laboratories. We have included these... 

Table 7.1 (p. 150-151) lists analytical methods used for in-process control. Some of these applications may be adapted for in-process controls other than those listed. In considering transferring methods to other sites, the ability to perform some assays may be limited by the relative cost of the instruments, as indicated in the last column. Some of the less-often used IPCs can be useful and are mentioned in the following pages. 

McGonigle, E. Assay validation and inter-laboratory transfer. In Development ami Validation of Analytical Methods (C. M. Riley andT. W. Rosanske, Eds.), pp. 3-13. Elsevier, New York, 1996. 

Eurachem guide [285], which discusses when, why, and how methods should be validated. However, for the pharmaceutical industry, the main reference source is the ICH Guidelines [286], which provides recommendations on the various characteristics to be tested for the most common types of analytical procedures developed in a pharmaceutical laboratory. The main characteristics of any analytical method to be tested are specificity, linearity, accuracy, precision, solution stability, limits of detection and quantification, and robustness. Specific aspects should be considered for a CE method including method transfer between instrument manufacturers, reagent purity and source, electrolyte stability, capillary treatment and variations in new capillaries, and buffer depletion. Fabre and Altria [284] discuss CE method validation in more detail and include a number of examples of validated CE methods for pharmaceutical analysis. Included in Table 4.3 are a number of validated pharmaceutical assay methods. 

The short life of NO and its low concentration in biological systems make the measurement of this molecule a challenging analytical problem. Among several methods (biochemical assays, UV-Visible spectroscopy, chemiluminescence, EPR) electrochemical methods are considered to be the most suitable for in situ detection of NO in biological milieu. " Generally, the electrochemical oxidation of nitric oxide on solid electrodes proceeds via a two-step (EC mechanism) with an electrochemical reaction as the initial step (heterogenous electron transfer) followed by a chemical reaction. The first electrochemical step is a one-electron transfer from a NO molecule to the electrode residting in the formation of a nitrosonium ion ... 

Reproducible assays are the second key in developing reliable IPCs. Consistent sample preparation and rugged assay methods are crucial. Samples should be promptly prepared after aliquots are withdrawn from the reactor, as any extended processing can change the temperature of a sample and affect the product distribution and impurity profile. (This may be more important than is at first obvious, because it may take time to transfer the sample from the scale-up floor to the analytical lab ) Diluting a sample into solvent or mobile phase also ensures a rapid quench and a more accurate analysis of the current reaction state. Guidelines are summarized in Table 7.2 [9]. 

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