Noble metals in the form of cyano complexes are widely used for metal plating in industry and for ornaments and many methods for their determination have been reported, e.g., spectrophotometry', chromatography2-4, atomic absorption spec-trometry5 and inductively coupled plasma atomic emission spectrometry6.
Recently, we reported an isotachophoretic method for the determination of heavy metal ions as cyano complexes '. In this method, the metal cations injected were converted into cyano complexes by reaction with cyanide in the terminating electrolyte in the migration column and migrated as negatively charged ions. The effective mobility of each cyano complex was controlled by complex-forming equilibria between the metal ions and the cyanide in the terminating electrolyte and by the pH of the leading electrolyte. However, application of this migration system to the separation of noble metal ions was difficult because most noble metal ions form very stable or inert complexes with cyanide, which makes it impossible to control the mobilities of such complexes only by complex-forming equilibria with the terminating ion. It is known to be effective to use the interaction of a counter ion or additive in the leading electrolyte in order to control the mobility','. Therefore, in this work, we attempted to use ion-pairing equilibria to separate the cyano complexes of noble metal ions, such as palladium, platinum, gold, silver and nickel. It was established that using ion-pairing equilibria between these complex plex counter cation in water-acetonitrile is effective in aration.
anions and a bivalent comachieving the required sep-
EXPERIMENTAL
Apparatus
A Model IP-1B capillary tube isotachophoretic analyser (Shimadzu, Kyoto, Japan), equipped with a potential gradient detector and a column system consisting of a PTFE preseparation capillary (50 x 1 .O mm I.D.) and a PTFE analytical capillary column (150 x 0.5 mm I.D.), was used. The current was stabilized at 50 PA after migration at 100 PA for 8-10 min. The capillary tube was filled with the leading and the terminating electrolytes by pressure of nitrogen gas.