Intercomparison and certification of some Chinese and international food and biological matrix CRMs for several uncertified ultratrace elements by NAA

Abstract

Radiochemical neutron activation analysis was used for determinationsof 8 rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in two ChineseCRMs, GBW 08503 (wheat) and GBW 09101 (hair), and Cs, Sr, Th and U in fiveNIST SRMs, 1548 (Total Diet), 1486 (Bone Meal), 8414 (Bovine Muscle), 1566a(Oyster Powder) and 1575 (Pine Needles). These determinations are for eventualcertification of above ultratrace elements so far not certified. The radiochemicalseparation scheme used in RNAA of NIST SRMs is an anion exchange followedby the co-precipitation by (REE)F 3 for U and Th, and a SrSO 4 precipitationfor Sr and Cs. For RNAA of the two Chinese CRMs, a one step (REE)F 3 precipitationwas used. Chemical yields were determined for all relevant elements by tracerexperiments. All these materials were also analyzed by ICPMS, that offeredan opportunity to compare the two major trace analytical techniques on theirmerits and drawbacks for these particular cases. RNAA is proven to be oneof the important techniques in ultratrace analysis, especially in certificationof some ultratrace elements. Determination of elements in sub-ng/g level isstill an area to be further investigated because: (1) some such elements areimportant in food and health related environmental studies, (2) many of theseelements have no (or very few) certified values in existing biological CRMs,(3) reliable techniques qualified for ultratrace analysis are needed to beestablished, and (4) sampling behavior of elements at these levels is stillnot very well known (recommended minimum sample size may not be adequate).