Analyzing Antarctic Ice Cores Using Capillary IC

Ice cores contain an abundance of information about climate and the changes it is undergoing. Brett Paull and Estrella Sanz Rodriguez from the Australian Centre for Research on Separation Science (ACROSS) at the University of Tasmania, Hobart, Australia, spoke to LCGC about their work on the analysis of Antarctic ice cores and the important role of capillary ion chromatography (cap-IC) in this area of research.  

Q. In 2015, your group published a study on the analysis of Antarctic ice cores using capillary ion chromatography (IC) (1). What led your group to begin this study?

A:

Within our Centre, the Australian Centre for Research on Separation Science (ACROSS), we have a long history of collaboration with national and international groups on fundamental and applied projects. As we are based within Hobart, Tasmania, which is now Australia’s hub location for Antarctic research, we have a history of collaborative projects with both the University’s Institute for Marine and Antarctic Studies (IMAS) and the Australian Antarctic Division (AAD), specifically on the application of ion chromatography (IC) to Antarctic seawater and freshwater samples. In this current study, the problem of analysis of low volume, high value ice-core samples was put to us, and our immediate solution was to move down to capillary format ion chromatography (cap-IC). Standard IC provides the selectivity required for the ions of interest within these samples, and our collaborators have long been using the technique as the “gold standard” method for trace anions in such samples (2). However, we were aware from former research projects within ACROSS that the selectivity of standard IC columns is very well matched with that available using capillary formats (3), and so were confident we could reproduce the desired chromatograms using the smaller column format, and achieve this whilst requiring much smaller sample volumes.  

Q. What is the importance of your research?

A:

The wider significance of this whole area is of course related to environmental and climatic change and the ability to develop accurate longer-term historical data sets (based upon the measurement of established climate change proxies) from sources such as ice cores. Currently, there is a clear demand for ever-greater temporal resolution from the scientists modelling ice core data. However, the nature of the sample itself is such that greater temporal resolution can only be achieved through increased sample analysis per ice core unit volume. In this study our main objective was to develop the analytical capability to move our temporal resolution from yearly cycles, down to seasonal and potentially monthly data.   

Q. What were your key findings?

A:

Using cap-IC to replace former standard format IC methods enabled us to not only reduce the sample volumes required per analysis, without compromising on detection limits for target ions, but also allowed sample analysis to be performed in triplicate, providing greater analytical confidence in our data. Given the rarity and costs of these samples, even duplicate analysis has historically been an often‑ignored luxury. However, the move to capillary format has enabled routine triplicate analysis of each sample to be performed, whilst still requiring smaller sample volumes (< 1 mL) than previous methods.   

Q. What can capillary IC offer that other analytical techniques cannot? 

A:

In this particular application, the enormous costs associated with collection of ice cores (particularly from Antarctica), together with the high demand from partner laboratories for such samples, essentially meant that more samples were needed from smaller core volumes. In addition, their subsequent analysis had to be performed without compromising analytical performance, and specifically target ion limits of detection (LODs). The only solution to this problem was a move to capillary format. Cap-IC can match standard format IC in each of the important chromatographic parameters of selectivity, resolution, and efficiency, whilst also matching concentration sensitivity, albeit based upon approximately one tenth of the required sample volume. Other more general advantages of the capillary format include low eluent requirements, which could see the system left running continuously for days, or even weeks, whilst requiring less than a single litre of deionized water (electrolytic eluent generation).   

Q. What challenges were associated with this application of IC?

A:

Reaching the target ion LODs was a challenge because we were specifically interested in methane sulphonate concentrations. Former methods had applied off-column preconcentration techniques. This approach obviously increases sample volume requirements and method complexity, both of which we sought to avoid in this current study. We therefore investigated on-capillary focusing and large volume injection. This sounds like a contradiction given the above comments, but here we are talking in relative terms, and our “large volume” injection onto the start of our capillary column was just 40 μL. With the application of a shallow elution gradient, our target ions were focused on the start of the capillary column prior to their separation, meaning that we could readily achieve our low μg/L target LODs without resorting to off-column preconcentration. Of course, the nature of the sample helps us in this regard because we are essentially dealing with very pure water samples, with a very simple sample matrix, which enabled us to achieve a very focused band of ions within a small volume of stationary phase at the start of our capillary column.  

Q. Why have you chosen to study this location?

A:

In this current study the location was one that had already been well-studied using former IC methods. This enabled us to have direct historical data to compare with when developing our new methods. Currently, we are working on a larger sample set from alternative sites within Antarctica (in a collaborative project with Dr. Mark Curran of the Australian Antarctic Division). Sites are obviously chosen based upon specific investigations, which are often part of much larger multifaceted programmes. In the case of methane sulphonate, proximity to the coast and the regions of cycling sea ice are important because this ion is an established proxy for the annual growth and contraction of the sea ice, although as mentioned, within each core there may be multiple targets and related processes under investigation. A better record (by which we mean more temporal resolution and improved accuracy) of methane sulphonate concentrations within these samples can lead to a more reliable and detailed reconstruction of seasonal variations in the Antarctic sea ice, which is of course just one more piece of the puzzle in the great climate change debate. This work represents a very 
tiny link in one of the world’s most pressing scientific questions, and its 
long-term implications or significance are yet to be seen.  

Q. What challenges do you face in your field of research regarding analytical methodology?

A:

In our field of research, as in most, our challenges are numerous. We are often looking at ultra-trace concentrations of a target species, in an often complex and potentially interfering sample matrix. At least with ice-core samples the latter is relatively simple. However, as with all analytical science problems, challenges can originate at the source, namely sample collection, handling, and storage. As analytical chemists we are very good at improving precision, accuracy, sensitivity, and selectivity; however, we often neglect the most important factors, namely the integrity of the sample.

In-situ

analysis can provide some cover in this regard, but when the sample is taken from a remote frozen region of Antarctica, a whole new set of limitations and complications exist. An example of one such “complication” relates to national quarantine regulations. Australia has very tough quarantine rules, and even samples of what essentially amounts to very pure water are subject to such rules. Therefore, analysis has to be undertaken within laboratories with quarantine clearance for handling these samples, which in our case means relocation of the instrumentation itself. This means samples are not moved from the laboratory in which they were first prepared and stored, as anytime they are in transport could see important changes in sample integrity. Essentially, collaboration between groups is the key for studies such as these because it’s simply not possible to take on this type of investigation alone.  

Q. What is your group working on next?

A:

We have recently been successful in attracting funding from the Ian Potter Foundation to expand this work further and develop IC coupled with mass spectrometry (IC–MS) for investigation of ice core samples, and the identification and quantification of a number of organic ions thought to be present. The exciting element of this work is the thought that unknown yet potentially important proxies may exist within these cores (which are essentially time capsules), which could lead to greater understanding, or more accurate models of how our environment has been changing over past millennia.  

References

  1. Brett Paull

et al.

,

Journal of Chromatography A

1409

, 182–188 (2015). 2. M.A. Curran and A.S. Palmer,

J. Chromatogr. A

919

(1), 107–113 (2001).   3. B.K. Ng, R.A. Shellie, G.W. Dicinoski, C. Bloomfield, Y. Liu, C.A. Pohl, and P.R. Haddad,

Journal of Chromatography A

1218

(32), 
5512–5519 (2011).  

Prof Brett Paull

is the Director of the Australian Centre for Research on Separation Science (ACROSS), at the University of Tasmania, Hobart, Australia. Brett has been involved in analytical chemistry research for over 20 years, and was awarded his B.Sc, Ph.D., and D.Sc from the University of Plymouth in the UK. Brett’s broader research interests are based within the field of analytical and materials science, with specific interests in the development and application of ion chromatography and related techniques for pharmaceutical, biomedical, and environmental analysis.               

Dr. Estrella Sanz Rodriguez

obtained the degrees of B.Sc and Ph.D in analytical chemistry from the University Complutense of Madrid (Spain). She is currently a University Associate at the University of Tasmania and Post-doctoral fellow within ACROSS. She has over 18 years’ experience as an analytical chemist, with her research interests focused on the development of new analytical methods based on chromatographic techniques coupled to mass spectrometry.