Vergleich der Meßgenauigkeit der Szintillations-Zählung 3H- und/oder 14C-markierter Proben durch externe bzw. interne Standardisierung und Anwendung auf die Sauerstoff-Kolben-Verbrennung

After oxygen flask combustion scintillation samples often show an increase in counting rates for several hours. Even after such a time identically prepared samples are statistically significantly more different as one should expect by weighing and pipetting errors. The inconstant cpm values during the first hours and the differences between the samples can mostly be eliminated by quench correction curves (dependence of counting efficiency and external channel ratio upon oxygen concentration). The dpm values achieved according to this method show smaller standard deviations than by internal standardisation. The procedure of the external standardisation was examined for error propagation. A system of toluene/methanol/phenethylamine absorbs carbon dioxide and water quantitatively. With this mixture the following counting efficiencies are achieved: 25% for ³H, 85% for ¹⁴C and for samples containing ³H and ¹⁴C 15% for ³H and 10% for ¹⁴C if the ³H channel is adjusted according to Klein and Eisler.