Analysis of Ir in Kofelsit rocks by inductively coupled plasma-sector-field mass spectrometry (ICP-SFMS)

Three different analytical strategies have been evaluated for the quantific ation of Ir in geological samples. Glassy rock samples from Kofels and refe rence material WGB-1 were analyzed directly by inductively coupled plasma s ector field mass spectrometry (ICP-SFMS) at mass resolution 400 using membr ane desolvation and at mass resolution 9500 without membrane desolvation. M atrix separation by anion-exchange pre-concentration was also investigated. The ultrasonic nebulizer USN6000AT(+) (Cetac Technologies, Omaha, NE, USA) incorporating a membrane desolvation unit was used as the sample-introduct ion system. Sample preparation involved complete microwave-assisted acid di gestion of the silicate matrix with HNO3-HCl-HF. The results obtained by th e three methods of quantification were in good agreement, showing that oxid e-type interferences were effectively eliminated solely by membrane desolva tion. The limits of detection were 6 pg g(-1) for low resolution measuremen t with use of the membrane, 15 pg g(-1) at a mass resolution of 9500, and 5 9 pg g(-1) for the ion-exchange procedure. The ultimate precision obtained for the Kofelsit Ir data was, however, compromised by the small sample inta ke (0.3 g), because of the inhomogeneous distribution of Ir in geological s amples.