All chemicals in the digestion
procedure were of the analytical-reagent grade obtained from J&K
Scientific Ltd. (Beijing, China). Concentrated nitric acid was used
for sample digestion. High purity water (resistivity 18.2 MΩ/cm)
obtained using a Milli-Q purification system (Millipore Corp.) was
used in solution preparation. Analytical grade methanol, sodium azide,
disodium hydrogen phosphate dodecahydrates (Na2HPO4·12H2O), and sodium dihydrogen phosphate dihydrate
(NaH2PO4·2H2O) were purchased
from Nanjing Chemical Reagent Co., Ltd (Nanjing, China). Stock solutions
(1 mg/mL in 1% nitric acid) of elements Ca, Mg, K, Na, P, Co, Cr,
Cu, Fe, Ni, Mn, and Zn were used to prepare working standard solutions,
which were obtained from the National nonferrous metal and electronic
materials analysis and testing center (Beijing, China). Deuterium
oxide (D2O, 99.9% D), 1,1-diphenyl-2-picrylhydrazyl (DPPH),
and sodium 3-trimethylsilyl [2,2,3,3-2D4] propionate (TSP)
were purchased from J&K Scientific Ltd. (Beijing, China).
procedure were of the analytical-reagent grade obtained from J&K
Scientific Ltd. (Beijing, China). Concentrated nitric acid was used
for sample digestion. High purity water (resistivity 18.2 MΩ/cm)
obtained using a Milli-Q purification system (Millipore Corp.) was
used in solution preparation. Analytical grade methanol, sodium azide,
disodium hydrogen phosphate dodecahydrates (Na2HPO4·12H2O), and sodium dihydrogen phosphate dihydrate
(NaH2PO4·2H2O) were purchased
from Nanjing Chemical Reagent Co., Ltd (Nanjing, China). Stock solutions
(1 mg/mL in 1% nitric acid) of elements Ca, Mg, K, Na, P, Co, Cr,
Cu, Fe, Ni, Mn, and Zn were used to prepare working standard solutions,
which were obtained from the National nonferrous metal and electronic
materials analysis and testing center (Beijing, China). Deuterium
oxide (D2O, 99.9% D), 1,1-diphenyl-2-picrylhydrazyl (DPPH),
and sodium 3-trimethylsilyl [2,2,3,3-2D4] propionate (TSP)
were purchased from J&K Scientific Ltd. (Beijing, China).