The spectrophotometric microdetermination of substances on paper disks

The principles and application of a method for the microdetermination of substances on small paper disks are described. Photometric measurements are made at 2 wavelengths, thus eliminating the errors due to inhomogeneity in the paper. A simple device for serial determinations that can be adapted to a common spectrophotometer is described. Microdetermination of RNA with measurement at 260 and 350 mμ is given as an example of the proposed method, and the best means of correcting the effect of paper inhomogeneity is established. Amounts of RNA in the range 0.8–4 μg can be determined with a mean error of ±0.03μg , using 5 μl of solution.