Some general comments on, and practical aspects of, assay design

2 Some general comments on, and practical aspects of, assay design 

It is important that assasts are specific, sensitive, accurate and precise. It should go without saying that it is also important that they should also be as rapid and as inexpensive as possible. There is no point in having a simple assay which gives imprecise results however, it is equally true that very sensitive assays are commonly less robust and more expensive and should be avoided unless required. 

The specificity of biochemical assays often depends not on the chromophores measured (these are fairly restricted e.g. p-nitrophenol, NADH, phospho-molybdate, chloronaphthol etc.) but on the specificity of the enzyme or antibody employed. For example, the use of LDH to measure lactate will also give an increase at 340 nm with a small number of related compounds. However, this is not usually a problem as, of these structures, only lactate is usually encountered in most biological systems. 

As described above, it is often the case that an enzyme reaction is used to monitor an anal5h e and the reaction will be allowed go to completion. If the signal is not amplified in some way (see Section 3.3), then the sensitivity is limited by the magnitude of the extinction coefficient. For example, the extinction 

---