Determination of Ra-226 in biological samples by adsorption on specific adsorbers

The determination of Ra-226 in biological samples, such as milk and grass, was studied. Ra-226 analysis of cow's milk was studied starting from de-fat ted milk. The proteins were eliminated by coagulation of the colloidal phas e with trichloroacetic acid. Phosphorus was then removed by precipitating i t as molybdophosphate and finally adsorption was carried out by using two d ifferent adsorbers in order to concentrate and purify radium. Lead rhodizon ate (LEHRO) adsorbed on charcoal and partially reduced tin dioxide (PRTD) w ere utilised. A method for the determination of Ra-226 in grass ashes was a lso investigated. The main interference, due to magnesium, hinders the use of LERHO, so the proposed procedure is based on adsorption of radium on PRT D at pH 9.5. The magnesium concentration was depleted by precipitating bari um (carrier) and radium with calcium carbonate at pH 8 before the adsorptio n step. The high phosphorus concentration in grass also interferes in the d etermination of Ra-226; phosphorus was eliminated as above via molybdophosp hate precipitation. The radium was carried by barium and spiked with Ba-133 . The yield of the chemical procedure was evaluated on the basis of Ba-133 activity. Radium samples were alpha -counted and the activity was evaluated with a suitable calibration curve. Both exchangers in the milk analysis an d PRTD in grass analysis were shown to be helpful in order to set up an eas ily performed procedure, which allows many samples to be processed simultan eously. All the methods adopted were shown to be very sensitive. Under the experimental conditions used, with 1 L of milk or 5 g of grass ashes, the l imit was about 3 mBq Ra-226 L-1 milk and < 1 mBq Ra-226 g(-1) grass ashes.