Accurate measurement of boron isotopes in foraminfera
Boron isotope studies in core samples can account for the observed changes in atmospheric carbon dioxide (CO2) in glacial and interglacial periods. This in turn will help to identify natural sources and sinks of carbon dioxide (CO2). In order to measure trace element isotope levels and apply numerical modeling, project partners from Universität Münster in Germany measured boron isotope levels in foraminifer (marine protozoa) shells from a core study. In order to acquire high precision isotope ratio measurements, the team used a resonant laser secondary neutral mass spectrometer (r-laser-SNMS). The laser is a highly focused (50nm in diameter) energetic ionic beam for bombarding the solid sample used in conjunction with a time-of-flight (ToF) mass spectrometer to analyse the sputtered particles. Since energy spectrums of discrete excited states for each element are unique, resonant multiphoton post-ionisation (RMPI) analysis is extremely valuable in high-precision detection of ultra-trace elements in complex samples. As r-laser-SNMS ionises the majority of sputtered neutral boron atoms which are less affected by the surface properties, this leads to greater accuracy of measurement. One of the innovations behind the study was the optimisation of experimental conditions that ensured a steady and high boron neutrals flux from the calcite surface of the shells. To achieve this, the r-laser-SNMS analyses were performed with various boron concentrations under differing analysis conditions. To further increase the accuracy of data, several other modifications could be implemented. These include increasing the analysis time and number of repetition rates of the analysis cycle. The use of a high current ion gun would also increase the primary ion current. The advantages of the r-Laser include those of excellent sensitivity, efficiency and selectivity, together with reduced fractionation and matrix effects. Furthermore, integrating the RMPI with ToF mass spectrometry allows for performing imaging of nanostructures where ultra-trace elements can be detected and quantified by r-laser-SNMS. Looking to other fields, the development can be used in biomedical, geological and chemical fields. Overall, the technology can be applied where analysis and resolution are required at the nanometre level.
