Fluoride Analysis of Ice Cores Using Fast Ion Chromatography

Scientists from the University of Florence in Italy have developed a novel fast ion chromatographic (FIC) method for the analysis of fluoride in Antarctic snow and ice. Data from fluoride analysis has the potential to assist scientists to build up a picture of past volcanic activity.

Polar ice sheets are one of the “cleanest” sampling locations on Earth and are relatively unaffected by human activity. As ice layers form, minerals from the atmosphere and environment are trapped and preserved. Each layer is associated with a specific time frame, rather like counting tree rings. Environmental scientists can take advantage of this by drilling into the ice, and extracting ice cores for analysis.

Various analytical techniques are available to prepare ice core samples for analysis. Typically, a system is setup whereby the ice core sample is slowly and continuously melted releasing each layer to be analyzed by continuous flow analysis (CFA), inductively coupled plasma–mass spectrometry (ICP–MS), and FIC.

Analysis of ice cores can allow reconstruction of past changes in climate systems, including a record of volcanic activity over thousands of years. Dust, ash, and sulphur deposited in the atmosphere can be trapped ready for identification. However, there are issues with sulphur analysis of ice cores because there are a number of different sources (sea salt, continental dust), and it requires decontamination before analysis.

Hydrofluoric acid (HF) is a potential marker that can be used instead. According to the paper, published in Environmental Science and Technology, at around the time of the eruption and degassing of Mount Erebus on the Ross Ice Shelf-McMurdo Sound there are records of relatively high concentrations of HF. Furthermore, ice cores from 17,500 ± 500 years old show a “main event” when a layer of fluoride was deposited around 170 years ago. This is thought to be attributable to a series of eruption from a subglacial volcano in West Antarctica.

Mirko Severi, lead author of the paper, told The Column: “Following the idea of the FIC method setup for the analysis of chloride, nitrate, and sulphate in the two EPICA [European Project for Ice Coring in Antarctica] ice cores, we decided to set up a similar method for the determination of fluoride.”

More than 450 samples were analyzed. Heart-cut column switching was utilized to preconcentrate analytes from the continuous melting of ice, separating analytes from highly retained compounds, before passing onto an analytical column for identification purposes. Severi said: “This novel method could be added to the several chemical flow analysis and FIC methods that are already run in the field of ice-core analysis. The challenge was to find a chromatographic method able to be ‘fast’ in eluting the fluoride peak (the total analysis time is less than 3 min) when analyzing samples containing anions with higher retention times such as sulphate.” — B.D.

Reference
Mirko Severi et al., Environmental Science and Technology 48, 1795–1802 (2014).

This story originally appeared in The Column. Click here to view that issue.