Determination of long-lived radioisotopes using electrothermal vaporization–inductively coupled plasma mass spectrometry

Abstract

A general method for the determination of long-lived radioisotopes by integrating electrothermal vaporization and inductively coupled plasma-mass spectrometry (ETV–ICP-MS) to vaporize environmental samples with complex inorganic matrices is described. The method required no sample pre-treatment and minimized sample size. The rationale was to use chemical modifiers such as CHF₃ to form metal fluorides with much lower boiling-points than other metal compounds (such as oxides and carbides). Given sufficiently high temperatures and long reaction times, samples in other chemical forms are converted into elemental halides and vaporized. The characterization and application of ETV–ICP-MS for the determination of radioisotopes is described. The detection limits for ⁹⁹Tc, ²³⁸U, ²³⁶U, ²³²Th, ²³⁰Th and ²²⁶Ra were similar to those obtained with ultrasonic nebulization (USN–ICP-MS). Absolute detection limits ranged from 0.6 fg for ²²⁶Ra to 5 fg for ²³⁸U. Analytical calibration plots were linear over a range of 2–3 orders of magnitude. Matrix effects caused by Group IA and IIA elements were minimized by changing the nature of the sample and by using temporal-thermal programming without affecting analytical performance. Comparison studies between ETV–ICP-MS and classical radiometric techniques were performed for various environmental samples.