Physical and chemical parameter testing of agricultural products

1 Scope: Part - of this standard specifies the method for determining total mercury in food. The first part of this standard is applicable to the determination of total mercury in food. The second part of this standard specifies the liquid chromatography-atomic fluorescence spectrometry (LC-AFS) method for the determination of methylmercury content in food. The second part of this standard is applicable to the determination of methylmercury content in food. After the sample is digested by acid heating, in an acidic medium, the mercury in the sample is reduced to atomic mercury by potassium borohydride or sodium borohydride. The carrier gas (argon gas) is brought into the atomizer, and under the irradiation of a mercury hollow cathode lamp, the ground state mercury atom is excited to a high-energy state. When the high-energy state returns to the ground state, it emits fluorescence at a characteristic wavelength, and its fluorescence intensity is proportional to the mercury content, which is quantitatively compared to the standard series solution. 3 Reagents and Material Notes: Unless otherwise specified, the reagents used in this method are all high-grade pure, and the water is the first grade water specified in GB/T 6682. 3.1 Reagent 3.1.1 Nitric acid (HNOs). 3.1.2 Hydrogen peroxide (H, O). 3.1.3 Sulfuric acid (HgSO). 3.1.4 Potassium hydroxide (KOH). 3.1.5 Potassium borohydride (KBH): analytically pure. 3.2 Reagent preparation 3.2.1 Nitric acid solution (1+9); Measure 50 mL of nitric acid and slowly add it to 450 mL of water. 3.2.2 Nitric acid solution (5+95): Measure 5 mL of nitric acid and slowly add it to 95 mL of water. 3.2.3 Potassium hydroxide solution (5 g/L); Weigh 5.0 g of potassium hydroxide, dissolve in pure water and bring to a constant volume of 1000 mL, and mix well. 3.2.4: Potassium borohydride solution (5 g/L); Weigh 5.0 g of potassium borohydride, dissolve in 5 g/L of potassium hydroxide solution and bring to a constant volume of 1000 mL, and mix well. Ready to use and ready to use. 3.2.5 Potassium dichromate nitric acid solution (0.5 g/L): Weigh 0.05 g of potassium dichromate and dissolve it in 100 mL of nitric acid solution (5+95). 3.2.6 Nitric acid perchloric acid mixed solution (5:1): Measure 500 mL of nitric acid and 100 mL of perchloric acid, and mix well

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