A mass fragmentographic method of high accuracy for determination of serum urea is
described. A fixed amount of [15N 2] urea is added to a fixed amount of serum, then the urea
is converted into 5, 5-diallyl barbituric acid by coupling with diallyl malonic acid diethyl ester.
The barbiturate is then transferred from an alkaline water phase into an organic phase
containing methyl iodine by ion-pair extraction using tetrabutyl ammonium as the positive
counterion. The amount of urea is determined from the ratio between the recordings at m/e …