Extraction and characterisation of trace element species from porcine liver samples using online HPLC-ICP-MS and offline HPLC-ESI-MS

The characterisation of trace element species in solid biomatrices like liver is necessary to obtain a more detailed knowledge of the complex functions and interactions of these compounds in organisms. Gentle i.e. species-preserving extraction techniques and chromatographic separation with multielement detection are useful methods for this purpose. In the present study extracts from porcine liver were investigated. Especially, Fe-, Cu-, Zn- and Mn-species were considered. Size exclusion chromatography and reversed phase chromatography were applied coupled either online to ICP-MS for species quantification via their trace element content or offline to ESI-MS for species identification via their molecular weight. Transferrin, metallothionein and superoxide dismutase were characterized. Additionally, total element contents in extracts and residues were determined with ICP-AES. Different sample pretreatment procedures were evaluated and the results from three previously optimised extraction procedures were compared in respect of extraction efficiency and species stability. Moreover, a cell fractionation of a liver homogenate was performed to investigate the subcellular location of selected trace element species. The results showed that freezing for several weeks does not significantly affect the stability of the quantified species. The Tris buffer provided the best extraction results. Cu- and Zn- species were detected mainly in the cytosolic fraction, Fe predominantly in the microsomal fraction. Mn is present in the cytosolic fraction as well as the mitochondrial/lysosomal fraction.