BINDING OF SR FROM MILK BY SOLID-PHASE EXTRACTION WITH CRYPTAND C222 SORBED ON SILICA-GEL, CATION-EXCHANGE, CHELATING OR ADSORBENT RESINS FOR SIMPLIFIED SR-90 ANALYSIS

Several commercially available resins have been found to bind the bicy clic polyether cryptand C222 from aqueous acetonitrile solutions. The presence of C222 on some of these resins strongly improved their affin ity for Sr, so that relatively small amounts of such resins sorbed Sr from milk. The resins investigated were silica gel, polyacrylic acid c rosslinked with divinylbenzene (DVB), polystyrene crosslinked with div inylbenzene (PS-DVB) and PS-DVB containing sulphonate, aminomethylphos phonate, iminodiacetate and mercapto groups. The resins for which bind ing of C222 resulted in the largest improvement in Sr sorption from mi lk were PS-DVB containing mercapto groups (Chelite S) and silica gel ( Si 60). Thus, 2 mi wet volume of either Chelite S containing 133 mu mo l of C222, or silica gel Si-60 containing 143 mu mol of C222 sorbed 90 and 48%, respectively, of the Sr from 100-ml milk samples. As the sor ption of Sr from milk by these systems is relatively slow, contact tim es of 24-36 h are required to attain these results. The Chelite S-C222 system separates Sr effectively from Cs and Ca. Under the conditions described here some 6% of the natural K-40 in milk sorbs with Sr to th e resin. Ba behaves similarly to Sr. Sr-90/Y-90 sorbed on the silica g el Si-60-C222 system can be measured directly and efficiently by liqui d scintillation counting. If adequate specificity can be attained this system might provide a very simple method of determining Sr-90 in mil k.