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 quantification of Ir in geological samples. Glassy rock samples from Kofels and reference material WGB-1 were analyzed directly by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) at mass resolution 400 using membrane desolvation and at mass resolution 9500 without membrane desolvation. Matrix 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-introduction system. Sample preparation involved complete microwave-assisted acid digestion of the silicate matrix with HNO3-HCl-HF. The results obtained by the three methods of quantification were in good agreement, showing that oxide-type interferences were effectively eliminated solely by membrane desolvation. The limits of detection were 6 pg g(-1) for low resolution measurement with use of the membrane, 15 pg g(-1) at a mass resolution of 9500, and 59 pg g(-1) for the ion-exchange procedure. The ultimate precision obtained for the Kofelsit Ir data was, however, compromised by the small sample intake (0.3 g), because of the inhomogeneous distribution of Ir in geological samples.