4If the sample contains only a sing

4If the sample contains only a single radionuclide, then a time-record of HPLC detector rate-meter output voltage plotted against time on a semi-log scale will yield a straight line whose slope exactly corresponds to the half-life the isotope. However, depending on the purity and degree of enrichment of the original cyclotron target material, a fresh batch of aqueous 18F fluoride (t1/2 = 109.8 minutes) may contain other nuclides, such as 13N (t1/2 = 9.97 minutes) or, conversely, a batch of 13N may contain a small amount of 18F due to the presence of 18O in ‘normal’ 16O target-water used to produce 13N. Moreover, liquid drawn directly from a cyclotron target may contain radionuclides in various chemical forms, including dissolved N2 and oxides of nitrogen in the case of 13N, or volatile or gaseous products in the case of 18F.