Fast determination of strontium radionuclides in milk with the aid of the cryptand 2.2.2

We have previously described a rapid method for determining the pure β-emitters Sr-89 and Sr-90 in liquid milk. This method involves extracting the Sr from the milk with a strontium selective cryptand (cryptand 222) on a strongly acidic cation exchange resin (Marathon C, Na+-form). After washing the resin free of milk residues and removing calcium with aqueous pentasodium tripolyphosphate (0,2 mol/l), Sr is eluted with aqueous sodium chloride (2 mol/l) in dilute hydrochloric acid (1 mol/l). The pH value of the eluate is adjusted to 12 - 12,5 with aqueous sodium hydroxide. The eluate is then passed through a fine sinter filter. Strontium carrier and solid ammonium carbaminate are added to the filtrate to precipitate the Sr-90 (and Sr-89) as strontium carbonate which is collected for counting. Counting is carried out preferably with a low-level liquid scintillation counting technique (LSC) that allows simultaneous counting of Sr-89 and Sr-90 in a single sample irrespective of the Sr-90/Y-90 equilibrium. The applicability of this method to samples contaminated with fresh nuclear fallout has been investigated. In particular, the conditions for efficiently removing interfering Ba-140 with minimal loss of Sr with the aid of a certain form of manganese dioxide powder (precipitated, active from Merck) have been determined. This step is readily included in the radiochemical method as a batch process. The whole method results in a decontamination factor for Ba greater than 800. This value increases at least fivefold when small columns of manganese dioxide are used. Analysis time has been further optimized so that only 4 and 6 hours are required in the absence and presence of Ba, respectively. Sr yields are greater than 80 %. The method minimizes the use of hazardous reagents and creates no toxic waste. Studies have also been carried out on the determination of the Sr yield by LSC measurement to avoid the time consuming g-spectrometric analysis of Sr-85. (orig.)