Ratio primary reference measurement procedure (RPRMP) for the determination of iron in biological materials by RNAA

Abstract

A new ratio primary reference measurement procedure (RPRMP), i.e. a definitive method for the determination of iron in biological materials, was devised. It is based on a combination of neutron activation with selective and quantitative post-irradiation separation of ⁵⁹Fe from all accompanying radionuclides followed by γ-ray spectrometric measurement. The novel separation scheme, involving the use of column chromatography on two (anion and cation) exchange columns, was extensively checked using radioactive tracers and was shown to be very selective and truly quantitative. High selectivity of the separation scheme was achieved by exploiting the “anomalous” sorption of Fe(III) on medium cross-linked sulfonic cation exchanger from concentrated hydrobromic acid solution. The accuracy of the RPRMP was demonstrated by the analysis of several certified reference materials. The method was used for the analysis of the three INCT CRMs based on tobacco leaves in which Fe was originally not certified, because widely discordant results by different analytical techniques were obtained in world-wide intercomparisons. The results by RPRMP in those materials were in a very good agreement with our own results by INAA. Tentative certified values (TCV) for Fe were proposed as a combination of RPRMP and INAA results. Some possible sources of systematic errors in other analytical methods were discussed.