Is laser particle size determination possible for carbonate-rich lake sediments?

This paper examines the potential of a relatively new technique – laser diffraction particle size analysis – for use with carbonate-rich lake sediments, material traditionally difficult to analyse. Three experiments are considered. The first two use a carbonate standard to determine optimal instrument conditions – the choice of optical model, and a suitable transport fluid. The third experiment uses sample material from lake cores and compares four different pre-treatment methods: none, removal of carbon by loss on ignition, removal of carbon by digestion with hydrogen peroxide, and finally removal of carbonates with hydrochloric acid and then removal of organic material by digestion with hydrogen peroxide. Only this final method produces repeatable results. As such, whilst the laser diffraction instrument offers improvements in the speed, required sample volume and repeatability of analysis, it does not overcome the problems inherent in the analysis of carbonates. Any catchment disturbance signal preserved in the carbonate fraction will remain undetected.