xem bóng đá trực tiếp trên youtubeTechnical standards for chemical indicators for metal chopsticks in Vietnam

Hello, Lawnet would like to answer as follows:

1. Overview of finished chopsticks

What are chopsticks?

Chopsticks are utensils consisting of a pair of sticks of the same shape xem bóng đá trực tiếp trên youtube size, made of bamboo, wood, synthetic plastic, xem bóng đá trực tiếp trên youtube metal, in direct contact with food.

Bonded requirements

- Chopsticks must have a clean, smooth surface without cracks or scratches xem bóng đá trực tiếp trên youtube no unpleasant odor.

- Chopsticks must have a balanced structure, except in special cases as agreed by the parties involved;

- The edges must be rounded, without edges or sharp edges;

- Metal chopsticks must be evenly shiny, without pits or discoloration, xem bóng đá trực tiếp trên youtube must not be rusty.

2. Technical standards for chemical indicators for metal chopsticks in Vietnam

xem bóng đá trựcstipulates the testing method for chemical indicators for metal chopsticks as follows:

(1) Prepare test solution

Rinse the sample with distilled water, then soak the sample in a soaking solution. The corresponding soaking conditions are specified in Table 21 at a ratio of 2 ml/cm2 of sample surface area.

(2) Determination of arsenic (As) content

Carry out the determination according to A.4 with soaking solution only, xem bóng đá trực tiếp trên youtube the corresponding soaking conditions are specified in Table 21 inxem bóng đá trực.

(3) Determination of cadmium (Cd) xem bóng đá trực tiếp trên youtube lead (Pb) content

Carry out the determination according to A.5 with soaking solution only, xem bóng đá trực tiếp trên youtube the corresponding soaking conditions are specified in Table 21 inxem bóng đá trực.

(4) Determination of phenol content

- Prepare stock standard phenol solution: accurately weigh 1.0 g of phenol xem bóng đá trực tiếp trên youtube dissolve it in 100 ml of water.

- Prepare intermediate standard phenol solution: Take exactly 1 ml of stock standard solution into a volumetric flask xem bóng đá trực tiếp trên youtube add distilled water to make 100 ml.

- Prepare working standard phenol solution: Take exactly 1 ml of the intermediate standard solution xem bóng đá trực tiếp trên youtube add distilled water to make 20 ml. The working standard phenol solution has a concentration of 5 μg/ml.

- Prepare boric acid buffer solution. Prepare 2 solutions.

Solution No. 1: Dissolve 4.0 g of NaOH in water xem bóng đá trực tiếp trên youtube add water to make 100 ml.

Solution No. 2: Dissolve 6.2 g of boric acid in water xem bóng đá trực tiếp trên youtube add water to make 100 ml. Take an equal amount of each solution xem bóng đá trực tiếp trên youtube shake well.

- How to proceed

Take exactly 20 ml of test solution, add 3 ml of boric acid buffer, xem bóng đá trực tiếp trên youtube mix well. Then add 5 ml of 4-amine antipyrin solution, 2.5 ml of ferricyanide solution, xem bóng đá trực tiếp trên youtube water to make 100 ml. Mix well xem bóng đá trực tiếp trên youtube let stand for 10 minutes at room temperature.

Proceed similarly with 20 ml of working standard solution instead of 20 ml of test solution. Measure the optical absorbance of the two mixtures at wavelength 510 nm; The optical absorption of the test sample must not be greater than the optical absorption of the standard sample.

(5) Formaldehyde

- How to proceed

Put into a 200-ml graduated cylinder an amount of 10 ml of sample solution with 1 ml of 20% phosphoric acid, then add 5 ml to 10 ml of water xem bóng đá trực tiếp trên youtube carry out steam distillation with the condenser submerged in water. When distilling about 190 ml, stop xem bóng đá trực tiếp trên youtube add water to make the volume 200 ml. Take 5 ml of this solution into a 15-mm-diameter test tube xem bóng đá trực tiếp trên youtube add 5 ml of acetyl acetone reagent. Stir well, xem bóng đá trực tiếp trên youtube heat in a boiling water bath for 10 minutes.

Comparison solution: Use a test tube with a diameter of 15 mm, add 5 ml of water, xem bóng đá trực tiếp trên youtube add 5 ml of acetyl acetone reagent. Stir well, xem bóng đá trực tiếp trên youtube heat in a boiling water bath for 10 minutes. Observe the test tubes on a white background; the test solution must not be darker than the comparison solution.

(6) Vinyl chloride

- Prepare standard vinyl chloride solution

Take about 190 ml of ethanol into a 200 ml volumetric flask, cover the flask with a silicone rubber stopper, xem bóng đá trực tiếp trên youtube weigh the mass. Cool the volumetric flask with dry ice methanol xem bóng đá trực tiếp trên youtube inject 200 mg of liquefied vinyl chloride. Inject ethanol cooled with dry ice methanol into the flask xem bóng đá trực tiếp trên youtube make up to 200 ml. Continue cooling the flask with dry ice xem bóng đá trực tiếp trên youtube methanol. Take 1 ml of the above solution xem bóng đá trực tiếp trên youtube add ethanol cooled with dry ice methanol. Make up to 100 ml xem bóng đá trực tiếp trên youtube store in dry ice methanol. The resulting solution has a concentration of 10 μg/ml. Ethanol (99.5%) used in the experiment must not contain impurities that affect the substances used in the test.

- How to proceed

Pour 50 μl of the vinyl chloride standard solution into a stoppered glass flask containing 2.5 ml of N,N dimethyl acetamide, xem bóng đá trực tiếp trên youtube immediately close the lid. Do the same with the test sample. Then, heat the flask containing the sample solution xem bóng đá trực tiếp trên youtube the flask containing the standard solution for 1 h, maintaining the temperature at 90 °C, shaking the flask occasionally. Next, take 0.5 ml of vapor from each flask, run the gas chromatography according to the instructions described below, xem bóng đá trực tiếp trên youtube then compare the retention times of the peaks in the chromatograms of the test solution xem bóng đá trực tiếp trên youtube the vinyl chloride standard solution.

More details can be found inxem bóng đá trực.

Best regards!

Key word: metal chopsticks | chopsticks | in Vietnam | chemical indicators |

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