2.2. Sample treatment and determination of mineral content
Sample preparation and determination of mineral contents
were according to Jiang, Wu, Feng, Yang, and Shi (2007). Rice powder
(0.5 g) was weighed and placed into a crucible, and then carbonized
at 250 C on an electro thermal plate until the sample
turned into black but not smoking completely. The crucibles with
samples were dry-ashed by heating in a muffle furnace at 550 C
(about 10–12 h). After sample incineration, a white residue was
obtained, which was carefully transferred into a 50 mL volumetric
flask, dissolved with 5 mL of 6 M HCl and then diluted to 50 mL
with water. The diluted solutions were subjected to analysis for
Ca, Mg, Na, K, Fe, Zn, and Cu by inductively coupled plasma mass
spectroscopy (ICP-MS) (Agilent 7500A; Agilent Technologies, Inc.).