This paper describes the determination of Co in two samples of high purity Ni by means of ion-exchange in combination with Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and by means of Graphite Furnace - Atomic Absorption Spectrometry (GF-AAS). These samples were both Nickel metal of 99.75%. nominal purity of which one was in the form of a 0.1 mm thick foil and the other a 0.5 mm diameter wire. The Co content in these; samples was determined in the process of a certification campaign and these samples are intended to serve as reference material for Reactor Neutron Dosimetry. The sample treatment and the detection of Co both via ICP-AES and GF-AAS are discussed. The values obtained for both Nickel samples are in accordance with the later certified value.