Determination of strontium-90 in milk samples using a controlled precipitation clean-up step prior to ion-chromatography.
Strontium-90 may be determined by beta-counting its yttrium-90 daughter following separation by ion-chromatography, using a three column system comprising a chelating concentrator column, a cation-exchange column and an anion-exchange separator column. The column system has previously been applied to the determination of strontium-90 in water and urine samples. The applicability of the system to the analysis of milk is hampered by the large concentrations of calcium present, which significantly reduces the extraction of yttrium-90 by the concentrator column. A maximum of approximately 200 mg of calcium can be present for the successful extraction of yttrium-90, which greatly limits the quantity of milk that can be analysed. The quantity of milk analysed can be increased by the inclusion of a controlled precipitation step prior to the ion-chromatographic separation. The precipitation is carried out on acid digested milk samples by the addition of ammonia solution until the addition of one drop causes a reduction in pH resulting in the precipitation of calcium hydrogenphosphate. Under these conditions, approximately 20% of the calcium present in the original milk sample is precipitated, yttrium-90 is precipitated whereas strontium-90 is not precipitated. Dissolution of the precipitate, followed by separation of yttrium-90 using the ion-chromatography system facilitates the analysis of a litre of milk with recoveries of greater than 80%.
Cobb
J
J
Department of Chemistry, Loughborough University of Technology, Leicestershire, UK.
Warwick
P
P
Carpenter
R C
RC
Morrison
R T
RT
D000818:Animals; D002130:Calcium Phosphates; D011232:Chemical Precipitation; D002852:Chromatography, Ion Exchange / Q000379:methods*; D008892:Milk / Q000737:chemistry*; D015203:Reproducibility of Results; D013326:Strontium Radioisotopes / Q000032:analysis*
D002130:Calcium Phosphates; D013326:Strontium Radioisotopes; C485828:alpha-tricalcium phosphate; C485830:tetracalcium phosphate; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous