General Equation for the Serial Dilution Technique in Microbiological Assays

Abstract

The basis of the serial dilution technique is a comparison of a solution of the sample of material under test with a solution of a standard sample of known strength. In order to make the comparison, serial dilutions of both the standard and test solutions must be made; in cases where the potency (or purity) is roughly known to start with, the number of such dilutions necessary is usually four or five. When, however, there is not even a rough indication of the probable potency of the sample being assayed, a wide range of dilutions is involved, some of which will probably be outside the scope of the tables that may be available for the evaluation of potencies in routine work. It seems desirable, therefore, to have at hand a general expression for evaluating the results of a serial dilution procedure; such an expression, apart from its intrinsic interest, will be useful for application in the cases of certain routine samples as well as of investigational work where unpredictable losses of potency may occur.