Spectrochimica Acta Part B 58 (2003) 1553–1565 0584-8547/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0584-8547Ž03.00100-9 Certification of the Cu and Cd amount contents in artificial food digest using isotope dilution inductively coupled plasma mass spectrometry for Pilot Study 13 of the Comite Consultatif pour la ´ Quantite de Matiere  ´ ` E. Vassileva, C.R. Quetel*, I. Petrov ´ European Commission, Joint Research Center, Institute for Reference Materials and Measurements, Isotope Measurements Unit, Retieseweg, Geel B-2440, Belgium Received 15 December 2002; accepted 20 May 2003 Abstract The Comite Consultatif pour la Quantite de Matiere (CCQM) launched the Pilot Study 13, an interlaboratory ´ ´ ` comparison between the metrological organizations worldwide on the determination of Ca, Cu and Cd in artificial food digests. These samples (available in 7% HNO and with a salinity evaluated around 370 mg kg , including y1 3 approx. 30 mg Na kg ) were prepared by gravimetrical mixing, and thus reference values traceable to the Kg for y1 the three elements were available eventually. This paper describes the contribution of IRMM for the certification of the Cu and the Cd amount contents. The analytical protocol developed was based on isotope dilution associated to inductively coupled plasma mass spectrometry (ID-ICP-MS). The Cu measurements required 125-fold dilution of the initial sample solution. An interference of Na Ar on Cu was identified but, since the ratio between both 23 40 q 63 q species was over 1000, it was successfully overcome by the calculation of a correction factor for its effect on the Cu amount content directly. Dilution of the sample was not possible for Cd only present at the low ng g level. Up to y1 1% difference was observed on Cd isotope ratio results between measurements performed directly or after matrix separation. This is rarely shown. As similar results could be obtained either way after the necessary corrections, the direct measurements approach associated to a correction for mass discrimination effects using the CCQM-P13 sample itself (and the IUPAC table values as reference for the natural Cd isotopic composition) was preferred as it was the easiest. SI traceable values were obtained for Cu and Cd with less than 1 and 1.5% combined uncertainty, respectively  This paper was presented at the 5th European Furnace Symposium and 10th International Solid Sampling Colloquium with Atomic Spectroscopy, held in Blagoevgrad, Bulgaria, September 2002 and is published in the Special Section of Spectrochimica Acta Part B, dedicated to that conference. *Corresponding author. Tel.: q32-14571658; fax: q32-14571863. E-mail address: christophe.quetel@cec.eu.int (C.R. Quetel). ´