Simultaneous multi-element and isotope ratio imaging of fish otoliths by laser ablation split stream ICP-MS/MC ICP-MS

Abstract

The simultaneous retrieval of spatially resolved information on the elemental content and isotope ratios from the same sampling spot (e.g. in incrementally grown biological material) still represents an analytical challenge. In order to assess multi-elemental (Sr/Ca; Mg/Ca; Ba/Ca; Na/Ca) and isotopic (87Sr/86Sr) data simultaneously on a fish otolith surface, a laser ablation (LA) system was coupled simultaneously to a multicollector inductively coupled plasma mass spectrometer (MC ICP-MS) and a quadrupole (single collector) ICP-MS via an aerosol split. In addition, a membrane desolvation nebulizer was used for introducing liquid standards in-line to the MC ICP-MS system. The recorded time resolved data of different data density (number of data points/time unit were by a factor of 4 higher using MC ICP-MS) were spatially referenced to the picture using ArcGIS® software. This allowed for the creation of elemental and isotopic images and the combination of data of different spatial resolution. Finally, regions of similar chemical composition were retrieved by cluster analysis. The method was applied to analyze an otolith of a lenok (Brachymystax lenok) caught in the river Eg (northern Mongolia) to assess habitat use and migration in a river system, where only little is known about the migrations of native fish. The combined statistical evaluations of the data showed that the Sr/Ca elemental and 87Sr/86Sr isotope ratios assessed in the otolith were the main discriminators of three clearly different zones on the otolith, indicating habitat shifts. Split-stream LA-ICP-MS/MC ICP-MS proved to be a compelling approach to gain elemental and isotopic data simultaneously from the same sampling spots on solid samples with a minimum loss of information.