Determination of endogenous concentrations of the lanthanides in body fluids and tissues using electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract

A method was developed for the determination of endogenous concentrations of the lanthanides in body fluids and tissues with electrothermal vaporization inductively coupled plasma mass spectrometry. The method was applied to the analysis of rat liver and human blood plasma as well as to some reference materials,viz., Oyster Tissue, Bovine Liver, Seronorm Trace Element Serum and Human Hair. Microwave digestion in high-pressure containers was used to digest the various biological materials. Analyses of undigested biological tissues by slurry sampling and body fluids by direct injection were also performed. For undigested samples, hydrogen peroxide injected directly onto the sample inside the graphite furnace was found to be effective in preventing the build-up of ash in the furnace. Trifluoromethane (Freon-23) was used as an effective chemical modifier that lowered the vaporization temperature and the memory effect significantly for most of the lanthanides. The absolute detection limits were, with few exceptions, in the range 1–20 fg for all the lanthanides in the various biological materials. The relative detection limits varied with the level of dilution and the method used. For Seronorm Trace Element Serum, the relative detection limits were in the range 0.05–1.2 ng l^–1. The analytical results for slurry and digested samples of the same material were similar with respect to accuracy and precision. The intermediate precision, i.e., the overall relative standard deviation obtained for the CRMs analysed on three different (not consecutive) days, was less than 25% for the lanthanides with concentrations higher than 1 ng g^–1 dry material. In the few cases where a certified or indicative value existed for the concentrations of the lanthanides in the reference materials, good agreement between these concentrations and the concentrations obtained in the present work was found. Blood plasma samples from 30 healthy volunteers and liver samples from ten unexposed rats were analysed. All the lanthanides were above the detection limit in the various samples analysed.