Modification of the Basic Dilution Equation for the Programming of Serial Dilutions

Stock solutions made with accurately weighable quantities of biologically active compounds often do not result in physically measurable delivery volumes, delivered to cell cultures, assay buffers etc., consequently requiring delineation of the serial dilution steps of the stock solution in a case by case manner. The basic dilution equation (C1V1 = C2V2) alone is not amenable for the programming and computerization of the serial dilutions. The best solution to this dilemma is to develop an equation with the delivery volume as one of the variables. We present here a modified dilution equation (MDA) that has the delivered volume as one of the variables. We demonstrate with examples how the equation can be used in delineating serial dilution steps either manually or through programming. The equation is D = C1p/C2V2, where D is the fold dilution required of a stock solution of C1 concentration which is diluted and delivered (pipetted) at a volume p to cell culture media, assay mixture etc., of volume (V2 – p), to achieve a final concentration of C2. The equation is useful when the volume of the stock solution made up to the final volume as calculated with basic dilution equation is not measurable physically.