boiled back down to 240 ml a portion of the solution obtained above 200 ml was then treated as follows to oxidise trivalent iridium to tetravalent iridium hydrogen peroxide 22 ml 100 vols was added over a period of 24 hours whilst maintaining a gentle reflux after cooling the solution was adjusted to give the final feed solution with a hydrochloric acid concentration of 5 14m a column of length 250 mm and diameter 5 mm was packed with medium rg028 to a bed depth of 202 mm the bottom of the column was then connected to the nebuliser of an icp oes spectrophotometer 1m hcl was pumped through the column and the flow rate adjusted to 0 375 ml min a sample of the feed solution as prepared in example 7 was injected and elution with 1m hcl continued results are shown in fig6 after about 10 minutes the base metals cu and ni were eluted off the column the eluent was then changed to 6m hcl and elution continued for a further 77 minutes rh was eluted off the column first followed by ru the two peaks for ru correspond to the two ruthenium nitrosyl complexes tetravalent iridium was then reduced to trivalent iridium on the column by introducing 1 w v ascorbic acid in 1m hcl for 5 minutes trivalent iridium was then eluted off.