An investigation of calibration materials for the measurement of metals in ambient particulate matter on filters by LA-ICP-MS

Abstract

Three different types of simple and low-cost calibration material for the measurement of the metals content of ambient particulate matter (PM) on filters using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have been compared: cellulose ester filters spiked with multi-element calibration solutions, pellets of compressed ambient particulate matter certified reference material (CRM), and powdered ambient particulate matter CRM adhered to a surface. Elements determined were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn, each at approximate levels of 1000 ng per filter. Blank filters spiked with multi-elemental standards were found to be significantly more reproducible and repeatable than materials based on powdered reference materials. However, a comparison of these spiked filters with real samples of ambient PM showed that the analytical sensitivities obtained per mass of analyte were significantly different. It is concluded that the spiked filters could act as very effective quality control standards correcting, to within 1%, drifts in LA-ICP-MS measurements of up to 10%, or as indirect calibration materials supported by additional measurements using traditional wet chemical techniques.

Keywords:

• ambient air, particulate matter, metals, calibration, LA-ICP-MS

Acknowledgements

The UK Department for Business, Innovation and Skills’ funding of the National Measurement System Chemical & Biological Metrology Programme, and the UK Department for Environment, Food and Rural Affairs’ funding of NPL's operation and management of the UK Heavy Metals Monitoring Network, are both gratefully acknowledged.