Single particle ICP-TOFMS on previously characterised EGRIP ice core samples: new approaches, limitations, and challenges

Abstract. Polar ice contains chemical impurities, which can be used as a proxy for the past climate, using state-of-the-art chemical methods. Despite its capability to access critical physicochemical parameters of insoluble particles, such as number concentration, mass and size distribution, and elemental composition, single particle inductively coupled plasma-time of flight mass spectrometry (SP ICP-TOFMS) has yet to be fully utilised to study polar ice. We demonstrate the largely qualitative SP ICP-TOFMS analysis of eight EGRIP ice core samples, which were previously characterised with Raman spectroscopy and laser ablation inductively coupled plasma-mass spectrometry. This resulted in three major developments. First, by analysing samples from different climate periods over the last 50 ka, we extend available ice core SP data to the Younger Dryas and the Last Glacial, and provide an overview of largely unexplored particulate elements in deep polar ice. Second, we develop an approach for handling discrete samples with highly variable particle concentrations, complementing time-intensive continuous analyses despite certain limitations. Third, we suggest adapting an approach for estimating particle sizes based on mineralogical data from previously conducted Raman spectroscopy analyses. This particle size analysis complements established particle sizing and counting techniques by covering the mostly unexplored nanometre range while providing additional chemical information. Overall, we outline the advantages and disadvantages of conducting SP ICP-TOFMS as the final step in a cascade of complementary techniques applied to the same samples. Given the ongoing endeavour to retrieve and analyse precious “Oldest Ice”, utilising SP ICP-TOFMS, even in a more qualitative way, may become critical for accessing vital information and new depths of insight.