Determination of long-lived radionuclides by inductively coupled plasma quadrupole mass spectrometry using different nebulizers

Different nebulizers (cross-flow, ultrasonic and two microconcentric nebulizers) were used for sample introduction of radioactive solutions into a quadrupole-based inductively coupled plasma mass spectrometer (ICP-QMS). The best sensitivity (from 420 to 850 MHz, which is about one order of magnitude higher in comparison with the crossflow nebulizer) for long-lived radionuclides ((226)Ra, (230)Th, (237)Np, (238)U and (241)Am) was observed using the ultrasonic nebulizer. However, using the ultrasonic nebulizer, a significantly higher sample size (26-fold) in comparison with the micronebulizers is required. Sample introduction by micronebulization with a small sample size in the low picogram range is the method of choice for the determination of long-lived radionuclides. The precision of determination of a 10 ng l(-1) concentration was in the low-% range (and sub-% range) for all measurements using different nebulizer types. The detection limits for the determination of long-lived radionuclides in aqueous solutions applying the different nebulizers were 0.01-0.6 ng l(-1). The flow injection analysis approach was optimized for isotope dilution analysis of (232)Th (using 20 mu l of 5 mu g l(-1) (230)Th) by ICP-QMS. The isotopic abundance ratios of (230)Th-(232)Th isotope mixtures ((230)Th/(232)Th = 0.01, 0.001 and 0.0001) were determined using a microconcentric nebulizer and 1 mu g l(-1) Th solutions with a relative external standard deviation of long-term stability measurements (over 20 h) of 0.17, 0.62 and 2.66%, respectively.