the tea samples were ground into powder. Approximately 0.25 g of dried tea powder was weighed and added into the polytetrafluoroethylene digestion vessel with 7 mL of concentrated HNO3 and 1 mL of hydrogen peroxide (H2O2). Subsequently, the samples were digested using a two-step temperature program. During the first step, the temperature was linearly increased to 190°C over 10 minutes; the maximum power of the rotating magnetron was 1000 W. During the second step, the temperature was maintained at 190°C for 30 minutes. After digestion and cooling, each solution was evaporated to ∼2 mL and diluted with deionized water in a 50 mL volumetric flask for the GFAAS analysis. The results were reported as the average of three repeated measurements, and all digestions were conducted in triplicate.
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