Characterization of fast-decaying PET radiotracers solely through LC-MS/MS of constituent radioactive and carrier isotopologues

EJNMMI Research

Table 1 Calculation of specific radioactivity from the peak areas of [ ¹¹ C] _species and [M + 1] _carrier in radiotracers

Radiotracer	Elution time ^a	Peak areas					SA ^e(GBq/μmol)	SA ^f(GBq/μmol)
	Elution time ^a	¹¹C	¹¹C	M + 1	¹²C	Ratio
	(h:min:s)	×10 ⁻⁴	×10 ^−3b	×10 ⁻⁶	×10 ^−7c	×10 ^4d
[¹¹C]PBR28	10:21:23	2.3920	1.8531	2.6506	2.9849	7.9240	270.4	330.3
[¹¹C]PBR28	10:42:55	1.2103	0.9376	2.7072	3.0486	3.9271	134.0	340.6
[¹¹C](R)-Rolipram	11:15:49	0.5745	0.7009	1.5974	1.1970	4.7490	162.1	463.3
[¹¹C](R)-Rolipram	11:37:19	0.2827	0.3449	1.6280	1.2199	2.2936	78.3	464.9

^aElution time for coeluting LC peaks of [¹¹C]_species and [M + 1]_carrier; ^bcalculated peak area for [¹¹C, M + 1]_species (Equation 1); ^ccalculated peak area from measured M + 1/¹²C ratio in PBR28 and (R)-rolipram; ^dpeak area ratio of [¹¹C]_species to the sum of carrier and [¹¹C]_species; ^especific radioactivity calculated from the peak area ratio; ^fdecay-corrected specific radioactivity.