[4−14C] phenylbutazone (4-butyl-1,2-diphenyl-3,5-[4−14C] pyrazolidinedione) has been synthesised on the 5 mmole scale. [2−14C] Diethyl malonate was reacted with n-butyl bromide and the product condensed with hydrazobenzene in the same reaction vessel.
The radiochemical yield of highly purified product was 48%. It is proposed that care should be taken in analyses for metabolic
products, particularly by TLC, since 4-hydroxyphenylbutazone was shown to be an oxidation product of phenylbutazone in solution
and on TLC plates under quite mild conditions. A pure sample of 4-hydroxy [4−14C] phenylbutazone was isolated.
A method for quench correction of samples with double radioactive labelling is described. Each nuclide makes a contribution
to the counting rate of three channels of a liquid scintillation counter. This channel overlap is an essential requirement
of the calibration procedure rather than a limitation, and allows more freedom in the choice of counting conditions. After
calibration with suitable standards the method will tolerate wide variations in the ratio of one isotope to the other extending
to single label samples of either isotope. This is the outstanding advantage over the channel ratio method which requires
a statistically significant counting rate for the higher energy isotope. The method takes advantage of the facilities offered
by a computer which may be on line or remote.14C and tritium are used to demonstrate the utility of the method.