Applications of a portable capillary electrophoresis instrument in environmental science

Abstract

Capillary electrophoresis (CE) is a widely-used separation technique for the analysis of ionic species. It has crucial advantages due to high efficiencies given that small differences in ion mobility are often sufficient for the resolution. The key features of the CE instrument such as portability, rapidity of analysis and the need for only a small sample volume offer the potential to facilitate future work of environmental scientists. This thesis presents new applications of a portable CE instrument in the environment, including the associated sampling techniques and measurement protocols. (i) A new method for the extraction and analysis of lake sediment pore water was developed. The extraction of the pore water from the sediment core was performed with filter tube samplers. Samples were immediately injected and measured by CE. All major cations and anions could be separated at once including the redox sensitive Fe(II) without any sample pretreatment. Along with fast injection, this prevents samples from alterations and contaminations. Sample volumes of only 20 μL allowed a high spatial resolution of the pore water profile, even with low water content. (ii) In a next step, the new method was applied in the field at Lake Baikal. The CE instrument was thus carried by cabin luggage in the plane and assembled in improvised laboratory containers at the shore of the lake. The pore water analysis was performed immediately after coring. High-quality data enabled the explanation of the formation and transformation of very special iron (III) and manganese (IV) oxide layers, which are buried in the reducing part of the sediment. The analysis of Fe (II) and Mn (II) allowed the determination of sharp redox boundaries. Overall, the high-quality data from on-site measurement eliminated doubts concerning artefacts from previous measurements when core squeezing and sample pretreatment had to be practiced. (iii) Besides the analysis of pore water, another challenging field in environmental science involves the surface analysis of rocks and biofilm. Thereby, surface processes are studied in terms of weathering, initial soil formation, as well as growth and vitality of microorganism. We developed a new method for the quantification of mobile ions and adenosine triphosphate (ATP) on surfaces. For the collection of available ions and ATP, a single drop of pure water was spread on the surface of the mineral or lichen and recollected for the analysis by CE and a luminometer, respectively. The heterogeneity of granites and the effect of wetting and freezing and thawing was shown on bare rock surfaces. On lichen, the effect of humidity and age on their vitality was demonstrated.