GB 14883.5-2016National Food Safety Standard -- Determination of radioactive substance polonium - 210 in foods (English PDF)

3.1 Reagents

3.1.1 hydrochloride Hydrazine (N2H4 · 2HCl).

3.1.2 sodium hydroxide (NaOH).

3.1.3 phenolphthalein (C20H14O4).

3.1.4 Ethanol (C2H6O).

3.1.5 nitric acid (HNO3).

3.1.6 hydrochloric acid (HCl).

3.1.7 perchloric acid (HClO4).

3.1.8 ascorbic acid (C6H8O6).

3.1.9 Hydrogen peroxide (H2O2).

3.2 Reagent preparation

3.2.1 25% hydrochloric acid diamide solution. Weigh 25g diamide hydrochloride, dissolved in water and diluted to 100mL.

3.2.2 30% sodium hydroxide solution. Weigh 30g sodium hydroxide dissolved in water and diluted to 100mL.

3.2.3 phenolphthalein indicator (1%). Weigh 0.5g of phenolphthalein dissolved 50mL95% ethanol.

3.3 Standard

210Pb-210Po balance 210Po standard solution or standard solution. radioactivity concentration of about 1 × 103 decays/(min · mL).

3.4 Material

Silver sheet or nickel sheet. the thickness of about 0.1mm electrolytic silver sheet (having a thickness of 0.2mm or electrolytic nickel sheet) cut size, shape and scale the same shape as the quasi supervision source (4.2), in the detergent solution in boiling 10min ~ 20min, washed clean after immersion in water with a spare.

5.1 Sampling

Sampling conducted by GB 14883.1 requirements.

5.2 Sample preparation

5.2.1 FRESH direct analysis. To prevent corruption in the mining milk, may be added to 5mL of formaldehyde per liter of fresh milk.

5.2.2 Weigh sample 5g ~ 50g (accurate to 0.01g) in 500mL beaker was slowly added 100mL nitric acid, heated on a sand bath. for Prevent spillage of sample, should be started when a large amount of sand removed from the beaker bubble bath and stirring constantly, if necessary, can be immersed in cold water in a beaker to slow down the reaction rate, and then heating was continued under stirring, after the disappearance of the foam to the cover with a watch glass, and evaporation was continued when no hydrogen peroxide was added dropwise. According to sample Product amount and kind of decisions of hydrogen peroxide, generally 10mL ~ 60mL. Prior to cooking sticky and no clear solution, concentrated by evaporation and then continue Reduced to about 5mL.

5.2.3 For samples containing more fat, such as milk, meat, fish and eggs, when added to a solution of nitric acid was heated on a sand bath foam disappears the solution obviously divided when oil and water phases, the hot liquid was rapidly poured into a beaker of 250mL separating funnel, standing layer after layer of acid Into the original beaker, 50mL hot oil phase was washed once with nitric acid, combined acid. Discard the oil phase. Continue in the sand bath of nitric acid and hydrogen peroxide Cooking sticky and no solution to clear, and then concentrated to 5mL.

5.2.4 added 15mL 5mL nitric acid and perchloric acid, and evaporation was continued on a sand bath. When nitric acid solution was evaporated and warmed to do with anti-perchlorate Seasonal, most samples will be violent reactions, sometimes rapidly darkening solution. To remove the beaker then press perchlorate handling precautions as soon as possible operating. Coolish, adding 5mL nitric acid and carefully heated. Samples containing organic matter should be repeated several times more heat treatment in the presence of nitric acid, straight Until the solution becomes clear. Remove traces of nitric acid, perchloric acid until a large number of white smoke, and evaporation was continued to dryness, the residue is white, cool.

5.3 Autodeposition

5.3.1 The residue was dissolved with 30mL water, dropping 3 drops of 1% phenolphthalein indicator, 30% sodium hydroxide solution and the solution becomes reddish immediately available, Join 2.5mL hydrochloric acid and diluted with water to 60mL, making it 0.5mol/L hydrochloric acid system.

5.3.2 Add approximately 200mg of ascorbic acid and 0.5mL25% hydrochloric acid diamide solution containing silver flake has been transferred (or nickel plate) and verified to be watertight Deposit bottle at 96 °C water bath deposition mechanical stirring 2.5h. After removing pieces of silver (or nickel plate), rinse the surface with a fine flow deposition After drying at room temperature.

5.4 210Po preparation and detector efficiency standards to determine the source 5.4.1 equipped with a silver sheet or nickel sheet deposition flask, 57.5mL water, 2.5mL hydrochloric acid, the solution becomes 0.5mol/L hydrochloric acid body system. Imbibe a certain amount of 210Pb-210Po standard solution equilibrium (or 210Po standard solution) is deposited into the bottle, according to the deposition 2h from 5.3 above, it Deposition efficiency can reach 99%, it can be used as a standard source for 210Po detector efficiency measurements of 210Po.

5.4.2 The standard source in the prepared 210Po low background alpha radiation measuring instrument measuring instrument detection efficiency 210Po by the formula (1) Calculated.

epsilon =

Where.

epsilon --- detector efficiency of the 210Po;

Net count rate N0 --- 210Po standard source, in units of counts per minute (cpm);

D0 --- added to a standard source of 210Po radioactivity 210Po, decay units per minute (dpm).

5.5 Determination of the chemical recovery

5.5.1 Analysis of samples with the same amount of sample, a solution containing a known accurate standard solution 210Po activity, according to 5.2.2 - 5.3.2 Step Operates to determine the chemical recovery.

5.5.2 chemical yield according to equation (2).

epsilonD

Where.

R --- chemical recovery;

N '--- known amount 210Po determination of chemical recovery was measured count rate in units of counts per minute (cpm);

N --- sample count rate in units of counts per minute (cpm);

epsilon --- detector efficiency of the 210Po;

When added to the sample D --- radioactivity 210Po determination of the chemical recovery unit of decays per minute (dpm).

5.6 Radiometric

5.6.1 Place the sample source 5h, in low background alpha alpha radiation measuring instrument measuring the radioactivity 210Po.

The active area of the same size as the sample source 239Pu or 241Am source standard 5.6.2 source as supervision before and after each batch of samples for routine analysis Efficiency correction.

5.6.3 Samples should be measured before and after the end of the measurement.