Isotope Abundances for Potassium of Biological Origin

The results of measurements of potassium-39/potassium-41 isotope ratios on biological samples presented in this paper do not support earlier claims (4,7,8) that the isotopes of potassium are fractionated by biological systems. Ratios obtained for potassium nitrate isolated from normal and malignant human tissues, pig and human foetal tissue and plant tissue did not differ significantly from the mean value found for A.R. potassium nitrate 14.09 ± .01 (s.e.). The ratios obtained for impure (ashed) tissue samples similarly were not significantly different from the mean found for the A.R. potassium salt. This differs from the results presented by Reutersward(12) and Kendall(15) who found a higher ratio for samples from which the potassium was not chemically isolated.