Sample preparation
Certified reference tea sample(GBW07605): 0.2000 g
of certified reference tea sample was weighed into a
100 mL porcelain crucible, and then the powder was
incinerated by a electric furnace. When there is no white
smoking emission from the incinerated powder,
the porcelain crucible with the powder was heated in a
muffle furnace with temperature of 500±25°C for 5 h.
After cooling, the residue was dissolved in 100 mL
1%(v/v) HNO3.
Milk Powder: Milk powder was purchased in the
supermarket, produced by Dumex China). The sample
preparation procedure for milk powder was similar with
that for certified reference tea sample.
Mineral water: The purified water was purchased
in the supermarket, and no special sample pretreatment
was required for this clean water samples.