(1) 10 g of rice sample was triturated and homogenized. Then a
portion of 3.0 g was dried in an oven at 110 C to constant weight.
The dried sample was placed in a furnace and heated to 450 C, and
concentrated nitric acid was added dropwise until white ashes
appeared. After that, the sample was dissolved in 1 mL 1 mol L1
nitric acid and diluted to 10 mL with deionized water. (2) Pig livers
were heated in an oven at 80 C for 3 h. After drying, 1.0 g sample
was dissolved 5 mL of nitric acid and transferred into a digestion
tube at room temperature overnight. Then the tube was heated
at 160 C until the contents nearly dried. After cooling, 2 mL perchloric
acid was added, and the contents were further heated to
dryness at 210 C. Finally the residue was dissolved with 10 mL
deionized water when the tube was cooled down. (3) Water sample
was filtered using a 0.45 lm filter prior to analysis. (4) 1.0 g of
tea leaves was added in a solution including 5 mL of concentrated
HNO3 and 2 mL of 30% H2O2. Then the mixture was transferred into
a 10 mL flask, and heated 200 C for 20 min. After cooling to the
room temperature, the samples were transferred to a 50 mL
volumetric flask and diluted to the mark. (5) 1.0 g certified reference
material GBW10017 (milk powder) was carbonized in
10 mL concentrated H2SO4 with another 10 min heating. After
cooling, the sample was dissolved in 15 mL 1 mol L1 HNO3 and
diluted to 100 mL with deionized water.
192 Y.