A rapid method for analysis of non-equilibrated ⁹⁰Sr/⁹⁰Y in infant formula

A rapid analytical method for quantifying ⁹⁰Sr in infant formula prior to secular equilibrium is presented. The approach is dependent on the use of two separations of ⁹⁰Sr from ⁹⁰Y, with the first providing an ⁹⁰Y ingrowth start point and the second providing an ⁹⁰Y ingrowth end point. Data were obtained at activity concentrations of approximately 6 Bq/kg and 160 Bq/kg, the latter of which is representative of the US Food and Drug Administration (FDA) Derived Intervention Levels (DIL). Experiments were designed to collect data from ingrowth periods ranging from 16 h to 2 weeks. Activities obtained with a separation interval as low as 16 h ranged from 92.7 to 109.4% of the known value. When ⁹⁰Y ingrowth was allowed to occur for 24 h or longer, the activities ranged from 93.2 to 106.2% of the known value and the precision of this group improved from 5.2 to 3.1%. The limit of quantification (LOQ) was 0.5 Bq/kg using 250 g sample portions.