Sequential inductively coupled plasma quadrupole mass-spectrometric quantification of radioactive strontium-90 incorporating cascade separation steps for radioactive contamination rapid survey

Abstract

Radioactive strontium-90 scattered by a nuclear power plant accident was specifically quantified by conventional inductively coupled plasma quadrupole mass-spectrometry (ICP-QMS) preceded by on-line chelate column separation (based on lab-on-valve) and oxygen reaction (designated the cascade step). The proposed system overcomes the isobaric interference of ⁹⁰Zr, whose soil concentration exceeds that of ⁹⁰Sr by more than six orders of magnitude. In addition, the system requires no ultimate mass spectrometry or radioactive ⁹⁰Sr standards. The radioactive ⁹⁰Sr standard was replaced with the stable isotope ⁸⁸Sr as a pseudo-standard. The modified ICP-QMS system yielded a precise, reproducible sharp ⁹⁰Sr peak in the ICP-MS profile. The elution time of ⁹⁰Sr was highly reproducible (RSD = 0.5%). After implementing the cascade-step, the detection limit (DL) was 2.3 Bq L⁻¹ (equivalent to 0.46 ppq as ⁹⁰Sr). Analysis of microwave-digested soil yielded a DL of 3.9 Bq kg⁻¹ (equivalent to 0.77 ppq as ⁹⁰Sr). The ⁹⁰Sr from environmental contaminated soil samples collected from areas at a distance of 10 and 20 km from the Fukushima Daiichi nuclear power plant ranged from 52 Bq kg⁻¹ to 73 Bq kg⁻¹, with no statistical difference between the proposed and general methods at 95% confidence level. The proposed method offers an attractive alternative use for ICP-other ionization mass spectrometry as an enrichment or purification step, thereby expanding the scope of ICP-mass-spectrometric analysis.