Assay high precision

There is one important simple case in which direct x-ray emission spectrography is useless for the determination of major constituents. Consider the series Fe, FeO, Fe304, Fd203. The assay of these materials for iron by wet methods is, of course, routine and highly precise. In x-ray emission spectrography, the four substances will all give virtually... 

The FDA did not include outlier tests in the USP for chemical assays, but allowed the practice for biological tests. The reason for this could be that because of the high precision, n is usually small in chemical testing with n < 3, outlier tests cannot be conducted. It appears that Judge Wolin followed this recommendation when deliberating his decision. 

Fig. 1. A high-throughput platform of the carbohydrate-based microarrays. A high-precision robot designed to produce cDNA microarrays was utilized to spot carbohydrate antigens onto a chemically modified glass slide. The microspotting capacity of this system is approximately 20,000 spots per chip. The antibody-stained slides were then scanned for fluorescent signals with a Biochip Scanner that was developed for cDNA microarrays. The microarray results were subsequently confirmed by at least one of the conventional alternative assays.

Transil Ready to go plates for 10 compounds per plate for high precision assay, order no. SP200096 (Nimbus Biotechnology Leipzig Germany)... 

A useful enzyme assay must meet four criteria (1) absolute specificity, (2) high sensitivity, (3) high precision, and (4) convenience. Though some compromise of these criteria is usually necessary, it should be emphasized that any substantial compromise may severely limit general applicability of an assay. 

Montoya, J. P., Voss, M., Kaehler, P., and Capone, D. G. (1996). A simple, high precision tracer assay for dinitrogen fixation. Appl. Environ. Microbiol. 62, 986—993. 

It is important to place these recent developments in perspective since the vast majority of laboratories obtain satisfactory data by hand . However, where there is a heavy commitment to routine assay or a special need for high precision, some degree of automation with computer involvement should be considered. 

A charge-transfer spectrophotometric method has been developed for unit-dose assay of the tropane alkaloids and some of their synthetic analogues. The high molar adsorptivities of the charge-transfer bands of the alkaloids with iodine in ethylene chloride give high precision even at low doses, such as in hypodermic and pediatric tablets. 

Precision varies with concentration because of this, precision should be evaluated at the low, middle, and high concentration regions of the standard curve, and should be evaluated in the different matrices that will be encountered in real assays. The precision profile (Section 16.4.3) is used to establish the working range of the assay. 

To minimize complexity and cost, yet retain enough accuracy and precision to meet clinical demands, most commercially available assays for proteins are a compromise In those circumstances in which these are more demanding —for example, for transferring values to a manufacturer s gold standard calibrators and controls—signal level should be maximized and all steps in the assay should be performed with as high precision as possible. The criteria for such an assay have been summarized by Blirup-Jensen. Reference laboratories should also use this or similar protocols to maximize accuracy. 

In this context, there has been a considerable development of enantioselective synthetic methodologies, which have now reached a high degree of diversity and complexity. Simultaneously, this trend has created an intensive demand for stereoselective separation techniques and analytical assays for precise determination of the enantiomeric purity of chiral compounds. The development of chiral stationary phases (CSPs) or chiral selectors for gas chromatography (GC), hquid chromatography (LC) and capillary electrophoresis (CE) rapidly opened a new dimension in the area of separation technologies. 

Recently, ICH guidance Q6A has simplified the development of specifications in several ways, not the least of which is the clarification that impurities if already controlled in the API do not have to be controlled in the dosage form unless they are also degradants. For the release assay, this paves the way for simpler, but no less sophisticated methods that require minimal sample preparation. Thus, the future may bring a return to spectroscopic techniques such as ultraviolet/visible (LJV/vis) spectroscopy. There also may be increased use of other high-speed and high-precision techniques such as flow injection analysis (FIA) and near infrared (NIR) analysis. 

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