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