Verification of the long term stability of uranium reference solutions of low concentration

The evolution of trace concentrations (sub ng . g(-1)) of uranium in aqueous reference solutions was followed over time by isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). Blank levels and detection limits needed to be determined prior to the actual investigations. Accuracy and precision of the method were determined on the basis of results obtained for uranium reference materials under similar experimental conditions. Reference solutions, certified for uranium concentration were prepared on gravimetrical basis. Analyses were performed over a period of 2 years, Taking into account the accuracy and the precision achieved, no significant change of the concentration is observed with time. Therefore, the mid and long term stability of the concentration of such reference materials was successfully demonstrated.