Preliminary study on aerosol particle addition calibration method for on-line quantitative analysis of airborne radioactive particles with ICP-MS

Abstract

An ambient aerosol concentration enrichment system coupled with ICP-MS for real-time monitoring of airborne radioactive particles is now under development. ICP-MS is very sensitive to sample introduction conditions, so it is necessary to develop an easy-use calibration method for on-line quantitative analysis in field application. In this paper, a calibration method using standard solution instead of monodisperse particles was established and validated preliminarily. First of all, four parameters for the method were determined experimentally, including: uptake flow rate and nebulisation efficiency of the Microconcentric nebuliser, nebulisation/transport efficiency of Aridus Desolvating Sample Introduction System, and Relative Sensitivity Factor between ¹⁵⁹ Tb and ¹⁷⁴ Yb. Then, monodisperse terbium nitrate particles were generated by a commercial Vibrating Orifice Aerosol Generator. Continuous aerosols of ytterbium nitrate droplets were nebulised from standard solution. They were mixed together, desolvated through the membrane dryer and introduced into ICP-MS for on-line analysis of terbium nitrate particles. The air sampled from nuclear environment was also introduced into ICP-MS to investigate the effect of flow rate on instrument responses. Finally, atom numbers of ¹⁵⁹ Tb in discrete terbium nitrate particles were determined using the calibration method and compared to the calculated value. Results show that when air flow rate increase from 10 mL min⁻¹ to 100 mL min⁻¹, the ratio of ¹⁵⁹ Tb ion count to ¹⁷⁴ Yb ion intensity keeps constant although instrument sensitivity decreases by a factor of 25. The relative standard deviation of ¹⁵⁹ Tb atom number measured is better than 18%. The discrepancy with the calculated value could be attributed to the over-estimation of atom number in the particles generated by VOAG because there was some liquid leakage in the VOAG.

Keywords:

• aerosol particle addition calibration method
• on-line quantitative analysis
• airborne radioactive particles
• ICP-MS

Acknowledgement

This work was financially supported by Northwest Institute of Nuclear Technology (NINT) under Contract No. NYS 0506. The authors would like to acknowledge Fred Smith from CETAC for helpful discussion on efficiency of Aridus, and Robert Zhou from TSI Asia Pacific for his advice on maintenance of VOAG.