GB 14883.2-2016National Food Safety Standard -- Determination of radioactive material -- Hydrogen (English PDF)

3.1 Reagents

3.1.1 Potassium persulfate (K2S2O8).

3.1.2 Sodium peroxide (Na2O2).

3.1.3 phosphoric acid solution. concentration of 85%, commercially available.

3.1.4 2,5-diphenyl oxazole [OC (C6H5) = NCH = CC6H5]. abbreviation PPO, pure flashes.

3.1.5 1,4-bis-2- (5-phenyl-yl) - benzene ([OC (C6H5) = CHN = C] 2C6H4). short POPOP, flashing pure.

3.1.6 naphthalene (C10H8).

3.1.7 1,4-dioxane (C4H8O2).

3.1.8 The bottom water. conductivity less than 2 × 10-6ohm · cm-1. The water should be taken from the bottom level as low as possible 3H activity concentration of water, such as (deep) groundwater. Distillation to obtain water samples Determination of 3H activity concentration (Bq/m3), and record the measurement date (t = 0). Packed in borosilicate glass bottles Constant temperature kept in the dark.

3.2 Reagent preparation

Scintillation fluid. Take 6gPPO, 0.3gPOPOP naphthalene and 100g, was dissolved in purified distilled 1,4-dioxane (dioxane Ring) and diluted to 1L. Save wrapped in black good brown bottle, dark standby. PPO and POPOP flashes are pure. You can also use Have a good product with a commercial scintillation fluid, but should try to use low toxicity, high flash point solubility good safe and efficient products. Users should test alternative Goods scintillation fluid performance and optimal conditions to ensure acceptability.

3.3 Standard

Standard 3H Water. known accurately 3H activity, was diluted with water background backup.

5.1 Sampling and pretreatment

Sampling and pretreatment according to the provisions of GB 14883.1.

Combustion and oxidation of the sample 5.2 5.2.1 weighed 1.00kg washed, dried food fresh sample was charged in the combustion chamber 3H oxidation combustion device.

5.2.2 First pass oxygen flow rate control in 0.5L/min ~ 0.7L/min, catch air device inside the net.

5.2.3 the power is turned on high-temperature furnace. The temperature of the oxidation chamber is raised to 700 deg.] C, and then heating the combustion chamber, when the temperature was raised to 100 deg.] C, water alone it flows into the receiving flask. Maintain this temperature until the water flows out slow and then slowly warmed.

5.2.4 When the temperature rose to 200 °C ~ 300 °C, warming slowly as possible, and carefully observe the situation through oxygen. General combustion chamber temperature was raised to on no more than 500 °C fraction outflow.

5.2.5 controlling the temperature at 600 °C, continue to burn for some time, so that complete oxidation of food samples, then cuts off the heating and ventilation.

Combustion chamber gas generated by the oxidation is oxidized by water vapor condenser collected in the receiving flask.

5.3 Purified water samples

By measuring the total volume of water collected later transferred to 500mL distillation flask was added 20g ~ 30g potassium persulfate, peroxide reflux for approximately 2h, if dissolved Still colored liquid can be added after about 10g of potassium persulfate reflux for 2h. Repeat the operation until complete oxidation reflux fade. The retort access Distillation apparatus was distilled, the resulting water-necked flask sealed in the mill.

5.4 Electrolytic concentration

5.4.1 electrolysis process is carried out in FIG. 2 device. Before recording the electrolysis of purified water sample volume and a 1% sodium peroxide solution dubbed as electricity Hydrolyzate.

5.4.2 Electrolytic nickel electrode before (see Figure 3) in advance immersed in hot dilute phosphoric acid solution for a few minutes, rinse with water after drying out, and then into electricity Solution pool (see Figure 2).

5.4.3 electrolysis current density of 65mA/cm2, with water cooling, each sample electrolysis of water at the same time, the symmetrical position in the electrolysis cell Electrolysis of water samples added two other standard 3H sample volume of water to determine the electrolytic process 3H recovery.

5.4.4 electrolysis electrolyte until the volume is reduced by about 10 times over, electrolytic recording volume.

5.4.5 After the completion of electrolysis, direct distillation sample three times the concentration of 3H the water is separated from the electrolyte.

Concentration coefficient 5.4.6 electrolyzed water sample according to equation (1).

Where.

P --- concentration coefficient;

Volume Vi --- sample before electrolysis of water in milliliters (mL);

Volume of the sample water after Ve --- electrolysis, in milliliters (mL).

5.4.7 standard 3H water according to step 5.4.1 ~ 5.4.5 process according to the formula (2) calculate 3H recovery electrolysis process.

IeVe

IiVi

Where.

Y --- electrolysis process 3H recovery;

Ie --- standard 3H radioactivity after electrolysis units of becquerels (Bq);

Volume Ve --- standard 3H water electrolysis after milliliters (mL);

Ii --- standard 3H radioactivity before the water electrolysis unit is becquerel (Bq);

Volume Vi --- standard 3H water electrolysis before milliliters (mL).

5.5 Sample Preparation

5.5.1 Preparation of test samples

Imbibe after concentrated water samples 2.00mL and 8.00mL scintillation fluid mixing, add 10mL sample counting vials, screw caps and shaken Mixed for use.

The bottom sample preparation 5.5.2 After this bottom water by electrolysis 5.4 after distillation, imbibe distilled water samples 2.00mL and 8.00mL scintillation fluid mixing, add 10mL sample Product count bottle, screw cap, shaking after mixing for use.

5.5.3 Preparation of standard samples

Imbibe 3H standard solution 2.00mL and 8.00mL water samples scintillation fluid, add 10mL sample counting vials, screw caps, vibration Swing after mixing for use.

5.5.4 from light

After the prepared sample (including the bottom of the sample, the sample and standard samples), wet cotton ball with alcohol wipe clean the bottle, at the same time put Liquid scintillation counter sample chamber, protected from light more than 12h (typically made of the same day sample into the sample chamber to the next measurement).

5.5.5 Prevent cross-contamination

In the operation of each step could cause cross-contamination between samples, to avoid cross-contamination. Operating according to a low level, after high Level order.

5.6 Measuring

5.6.1 Instrument Preparation

Debugging instrument to normal working condition. Select and determine the energy channel width 3H measurement, the instrument measuring channel the spirit of the sample being measured Sensitivity is maximized.

Determined length measurement 5.6.2 Low sample requires a long measurement time, and measurement accuracy required, generally less than 1000min. Counting time should be able to protect Statistical fluctuation syndrome samples to meet the measurement requirements.

5.6.3 Determination of the background count rate

Background counting time of preparation of the sample is measured to determine. For the measurement of low levels of sample counting time background samples shall Less than 1000min.

Measuring instruments 5.6.4 Efficiency Preparation of standard samples were measured according to equation (3) calculate the counting efficiency of the instrument.

epsilon =

Ns-Nb

60As

Where.

Counting efficiency epsilon --- instrument;

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

Nb --- samples background count rate in units of counts per minute (cpm);

As --- added to the standard sample 3H activity, units of becquerels (Bq), should be corrected to the activity detection, scintillation fluid sample mixed the quenched material may result in counting efficiency. It can be used inside or outside the standard method standard channels ratio method quenching correction.

5.6.5 Sample Measurement

Samples should be measured in the following order. the bottom of the sample - the sample - the standard sample, measured length should be the same for each sample.

5.7 Blank test

A blank test reagent should be replaced or detection of different batches of samples.