Determination of total arsenic in food (1)

There are four national standard methods for the determination of total arsenic in food: hydride atomic fluorescence spectrometry, silver salt colorimetry, arsenic spot colorimetry, and borohydride reduction colorimetry
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Introduce the arsenic spot colorimetry (Ancient Chua's method) (according to the third method of GB/T5009.
11-2003)
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1.
Principle

After the sample is digested, the high-valent arsenic is reduced to trivalent arsenic with potassium iodide and stannous chloride , and then the new ecological hydrogen generated by zinc particles and acid to generate arsine hydrogen, and then with mercury bromide test paper to generate yellow to orange color Spots are quantitative compared with standard arsenic spots .

2.

(1) Nitric acid
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(2) Sulfuric acid
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(3) Hydrochloric acid
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(4) Magnesium oxide
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(5) Arsenic-free zinc particles
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(6) Nitric acid-perchloric acid mixed solution (4+1): Measure 80 mL of nitric acid , add 20 mL of perchloric acid, and mix well
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(7) Magnesium nitrate solution (150g/L): Weigh 15g of magnesium nitrate [Mg(NO ₃ ) ₂ ·6H ₂ O], dissolve in water, and dilute to 100 mL
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(8) Potassium iodide solution (150g/L): stored in a brown bottle
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(9) Acidic stannous chloride solution: Weigh 40g of stannous chloride, add hydrochloric acid to dissolve and dilute to 100mL, and add several metal tin particles
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(10) Hydrochloric acid (1+1): Measure 50ml of hydrochloric acid and dilute to 100ml with water
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(11) Lead acetate solution (100g/L)
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(12) Lead acetate cotton: After soaking the absorbent cotton with a lead acetate solution (100g/L), remove the excess solution and loosen it, dry it below 100°C, and store it in a glass bottle
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(13) Sodium hydroxide solution (200g/L)
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(14) Sulfuric acid (6+94): Measure 6.
0 mL of sulfuric acid and add it to 80 mL of water.
After cooling, add water to dilute to 100 mL
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(15) Arsenic standard stock solution: accurately weigh 0.
1320g of arsenic trioxide dried in a sulfuric acid dryer or dried at 100°C for 2h, add 5mL.
20% sodium hydroxide (200g/L), and add 25mL sulfuric acid ( 6+94), transfer it into a 1000mL volumetric flask, add freshly boiled and cooled water to dilute to the mark, and store in a brown glass bottle
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(16) Arsenic standard solution: draw 1.
0mL arsenic standard stock solution, place it in a 100mL volumetric flask, add 1mL sulfuric acid (6+94), dilute to the mark with water, and store in a brown glass bottle
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(17) Mercury bromide-ethanol solution (50g/L): Weigh 25g of mercury bromide and dissolve it with a small amount of ethanol, and then dilute to 500mlL
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(18) Mercury bromide test paper: Cut into a circular filter paper sheet with a diameter of 2cm, immerse it in a mercury bromide ethanol solution (50g/L) for more than 1 hour, store it in the refrigerator, and take it out before use and place it in a dark place to dry for later use
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3.
Apparatus

The arsenic measurement device is shown in Figure 4-1
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The glass arsenic measuring tube in Figure 4-1 has a total length of 18cm, the upper part is thicker and the lower part is thinner.
The inner diameter of the section from the mouth of the pipe down to 14cm is 6.
5mm, and it has gradually narrowed down from there.
The inner diameter of the end is about 1～3mm, near the end.
There is a hole at 1cm with a diameter of 2mm.
The narrow part is inserted tightly into the rubber stopper, so that the lower part extends until the small hole is just below the rubber stopper
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The bottom of the glass cap in Figure 4-1 is ground flat, with a meniscus groove on the top, a round hole in the center, and a diameter of 6.

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