Analytica Chimica Acta 701 (2011) 37–44 Contents lists available at ScienceDirect Analytica Chimica Acta j ourna l ho me page: www.elsevier.com/locate/aca Determination of the total and extractable mass fractions of cadmium and lead in mineral feed by using isotope dilution inductively coupled plasma mass spectrometry Emilia Vassileva a,∗ , Michel Hoenig b a IAEA-Marine Environment Laboratories, Department of Nuclear Sciences Applications, 4 Quai Antoine 1er MC 98000, Monaco b VAR Research Centre, Leuvensesteenweg 17, B3080 Tervuren, Belgium a r t i c l e i n f o Article history: Received 13 December 2010 Received in revised form 18 May 2011 Accepted 26 May 2011 Available online 2 June 2011 Keywords: Isotope dilution inductively coupled plasma mass spectrometry External calibration Cadmium Lead Mineral feed Total mass fractions Extractable fractions Method validation a b s t r a c t This paper describes the determination of the total and extractable mass fractions of Cd and Pb in mineral feed test sample distributed by the Community Reference Laboratory for Heavy Metals in Feed and Food (CRL-HM), in the frame of the fifth interlaboratory comparison for the European Union National Reference Laboratories (NRL). The developed in this study protocol for the total and extractable mass fractions of Pb and Cd in mineral feed sample is based on isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The applied dual spiking approach reduced by 50% the number of analytical steps. The addition of hydrofluoric acid in the digestion step was found necessary to ensure a full decomposition and complete isotope equi- libration. Quadrupole inductively coupled plasma mass spectrometer equipped with collision reaction interface (CRI) was employed for the measurements of Cd and Pb. Two methods for the determina- tion of Cd were applied and compared. In the first one the high molybdenum content was reduced by introduction of matrix separation step followed by standard ICP-MS mode measurement, whereas in the second one CRI mode was used for the determination of Cd without preliminary matrix separation. The estimation of the combined uncertainty was performed according to the ISO guidelines. Uncertainty propagation was used as a tool for validation of proposed analytical procedure. Contributions from the correction for moisture content, sample homogeneity, procedural blank, instrumental background and dead time effects were evaluated in both cases. The largest uncertainty contributors for Cd and Pb is due to the within bottle homogeneity of the mineral feed sample – 50.3% and 90% respectively. The IUPAC data for isotope composition are the second major contributor to the combined uncertainty of the result for the total mass fraction of Cd in mineral feed – 43.3%. However, the ID ICP-MS results achieved from the two series of samples (partial and total extraction) were in excellent agreement within uncertainty, irrespective of the method used for extraction. The ID ICP-MS results for the total and extractable mass fractions of Cd and Pb in feed sample were compared with the results obtained with external calibration approach and routinely applied in the daily analytical practice of the Belgium National Reference Laboratory for trace elements in food and feed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In many cases the implementation of international and national legislation is based on high quality of measurement results. Therefore laboratories need to be able to demonstrate that their measurement results are reliable, comparable and in compliance with the legislation, international standards, and international recognition arrangements that support the free goal “measured once, accepted everywhere”. Decreasing limits and thresholds as ∗ Corresponding author. Tel.: +377 97 97 72 37; fax: +377 97 97 72 76. E-mail address: e.vasileva-veleva@iaea.org (E. Vassileva). set by some governmental or transnational legislation require accuracy and comparability of measurement results. Important conclusions and decisions linked to the customer protection sphere derive from measurement results that have to be based on reliable data of good quality (e.g. sufficiently small uncertainty). Com- parability can be achieved by making measurements traceable to a common system [1] with a combined uncertainty state- ment to demonstrate the result’s reliability. Accurate measurement of trace elements is of crucial importance to estimate dietary uptake rates, because many of them are toxic and may have adverse effects on animals and eventually can enter into the human food chain. Therefore, development of analytical proce- dures, which lead to reliable and accurate results and which can 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.05.045