Analysis of metal ions by inductively coupled plasma mass spectrometry (ICP‐MS)

Iron, copper, and zinc concentrations in the brain homogenates from microdissected organs were evaluated after digestion (1 h at 70°C) in a mixture of 65% nitric acid and 30% hydrogen peroxide. The metal content in the samples was determined by ICP‐MS using an ELAN DRC II instrument (Perkin Elmer Sciex). The total quant technique analytical method, with external calibration using a dynamic reaction cell, was adopted. The coefficients of variation ranged from 4.5 to 7.6% among analytical series and from 5 to 10.5% between the series. The instrument was calibrated using standard solution at a concentration of 10 μg/l (Multielement ICP‐MS Calibration Standard 3, Perkin Elmer Plus). Each sample underwent twofold determination. The accuracy of the method was calculated in ultrapure water. Bovine liver standard reference materials (NIST 1640 and MS1577b, National Institute of Standard and Technology, Gaithersburg, MD, USA) were used to better approximate the results from biological matrices. The detection limit, determined on the basis of three standard deviations of the background signal, was determined at 0.005 μg.