Detection limit of measurement of pharmaceuticals labeled with short-lived isotopes in HPLC with flow-through γ-counter

This paper proposes a method for estimating the detection limit, which is defined as 3.3 times the standard deviation (S.D.) of blank measurements under the situations where the repetition of measurement is difficult or impossible because of a short half-life of radioactivity. The FUMI theory, which can estimate an S.D. value without repetition in various instrumental analyses, is adopted and proved here to be available in a radio-HPLC system as well. 99mTc-ECD (T1/2 = 360.6 min) that is a lipophilic compound for the diagnosis of regional brain perfusion is taken as an example.