Ultra-pure water with a resistivity of 18.2 MV cm Milli Q from
Millipore (Bedford-USA) was employed. The following chemicals
were used for mineralization: 69% (w/w) HNO3, 35% (w/w) H2O2,
and 30% (w/w) HCl, all of them from Scharlau (Barcelona, Spain).
The reduction solution was prepared with stannous chloride at 2%
(w/v), dissolving SnCl22H2O from Scharlau in 10% (v/v) HCl which
remained for 30 min in a stream of nitrogen with constant stirring
to eliminate any mercury traces. A stock solution of KBr and KBrO3,
both from Scharlau was prepared daily containing 0.1 mol L1 KBr
and 0.017 mol L1 KBrO3. The use of this solution is important
because it allows a complete conversion of bromate to Br2. A stock
solution of 12% (w/v) hydroxylamine hydrochloride from Scharlau
was used in order to complete the digestion and to remove the
excess of oxidant and the nitrous oxides generated during the
digestion, which have an unfavourable impact on the reduction of
mercury with stannous chloride.