Sr/Ca ratio analysis of seashells using laser-induced breakdown spectroscopy under objective-lens focusing and single-lens focusing

Laser-induced breakdown spectroscopy (LIBS) is a new technique for seashell elemental analysis, and now that application is in rapid development. In this work, LIBS was applied for scallop shell [Chlamys (Azumapecten) farreri] analysis using the element ratio Sr/Ca, and the analytical result was compared under objective lens (OL) focusing and single lens (SL) focusing, respectively. It is interesting to find that, under the two focusing arrangements, the ratio (Sr/Ca) variation on the shell cross section performed completely differently, while in technical aspects, the two focusing arrangements presented almost the same characteristics in a standard sample. Also, the seashell annual growth could be well indicated by high values of Sr/Ca intensity ratio when using OL, but under SL focusing no pattern was found. The difference of shell sampling amount and size might be the reason for inconsistent analysis performance under the two focusing arrangements. The scanning electron microscopy (SEM)-energy dispersive spectrometer (EDS) scanning results of the shell proved that LIBS analysis under OL focusing was closer to the actual Sr/Ca distribution than that under SL focusing. The obtained results might be useful for the methodology of LIBS in seashell applications.