AOAC Official Method 974.37 Strontium-89 and Strontium-90 in Milk Ion Exchange Method
First Action 1974
Final Action 1976
A. Principle
Fresh milk samples are preserved withHCHOand stored to obtain 90Y ingrowth. After storage, Y, Sr, and Ba carriers and citrate solution are added. Citrate forms Y complex which is adsorbed on anion exchange resin. Y is desorbed and separated from radionuclides by tributyl phosphate extraction.Yis re-extracted into diluteHNO3 and precipitated as oxalate, which is weighed and counted for 90Y activity to calculate 90Sr.
Radio-Sr is desorbed along with Ca and radio-Ba; Ca, radio-Ba,and rare earth radionuclides are separated by repetitive precipitations; Sr is precipitated as SrCO3 and counted. Total radio-Sr minus 90Sr by 90Y measurement yields value for 89Sr. Milk containing known increments of 89Sr and 90Sr determined in triplicate by 11 laboratories showed following results (average of triplicates; see Table 974.37A):
B. Operating Notes
Radio-Ba and La radionuclides will interfere without purification.Purification from Ca is important for recovery tests but need not be as thorough if Sr recovery is determined by 85Sr tracer or flame photometry. Thoroughly desorb columns before re-use and test periodically to assure complete desorption.
