The most important rmpurrtres in refined rhodium are Ir, Pd, Fe, Nr and Si, and Pt, Ru, Au, Ag, Cu, Sn, Pb, Zn and Co1 Since the complete separation of rhodrum from iridium 1s very difficult, the iridium content of rhodium is a good measure of rts purrfication. Small amounts of iridium (a few per cent) c'annot be determmed accurately in rhodium by wet chemical analysrs: 2 independent analyses often drffcr by a factor of 5. Spcctrographrc techniques have been described by GERLACH ct ~2.2-3, BABAEVA AND LAPIR~ and LEWIS et al.', but the sensitivity is insufficient in many cases, cu. 0.25% Ir only for 25 mg rhodrum sponge or black KURAPI;OV et al 6 developed a specral spectrographic techmque and attained a sensitivity of o I%, but matrix and third-element effects limit the accuracy of the analysis Several authors have applied neutron activation to this problema-MORRIS et al 11 used an addition method to avoid neutron-shreldmg differences between samples and standards. No other analytical methods, such as colorrmetry, polarography or X-ray fluorescence, are described in the literaturer2~13
Neutron activation 1s very favourable in this case, because no chemical separation is necessary, the periods of the produced rhodium isotopes being 4 4-min