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

Abstract

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 cross-flow 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 µl of 5 µg 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 µg 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.