Nomogram for calculation of concentration for colorimetric systems in which absorbance decreases linearly as concentration increases.

NOMOGRAMS ARE used regularly in our laboratory for various routine calculations (1). A frequent calculation, which may be performed rapidly with the nomogram presented here, is typified by the colorimetric determination of glucose concentration with a reaction in which absorbance decreases as glucose concentration increases (Figure 1). The system uses an AutoAnalyzer and depends upon the reduction of yellow ferricyanide to colorless ferrocyanide (2). The linear relationship between glucose concentration (x) and absorbance (y) may be expressed by the equation