The hair samples were digested using
concentrated nitric acid. The digestion vessels
were placed in a ventilated oven at 110°C for
18 hr and then diluted to 10 mL with deionized
water. The digested samples were analyzed
by inductively coupled plasma-mass spectrometry
(Elan 6000; PerkinElmer, Norwalk, CT,
USA). Mn analyses were performed using an
external calibration method and yttrium as the
internal standard. The CTQ-INSPQ provides
a normal reference range of 0–3 μg/g based on
samples analyzed in Québec and a review article
on hair reference intervals for trace elements
(Miekeley et al. 1998). Here we used the upper
level of this reference (3 μg/g) as a cut-off for
elevated MnH.