GB/T 34448-2017Tissue paper and disposable products - Determination of formaldehyde (English PDF)

3.1 Principle

After the specimen is subjected to water extract for a certain time, free formaldehyde and hydrolyzed formaldehyde in the specimen are transferred to the extraction liquid. The extraction liquid reacts with acetylacetone to generate a yellow compound, and then determine the absorbance of the solution at a wavelenght of 412 nm after cooling. Calculate the content of formaldehyde in the specimen according to the standard working curve of formaldehyde.

3.2 Reagents and materials

3.2.1

Water, GB/T 6682, Grade III.

3.2.2

Formaldehyde solution, with a concentration of about 37% (g/g), analytically pure.

3.2.3 Acetylacetone solution

Add 150 g of ammonium acetate into a 1,000 mL volumetric flask, dissolve it with 800 mL of water; then, add 3 mL of glacial acetic acid and 2 mL of acetylacetone, dilute it to the scale with water, and store it in a brown bottle.

Note: Store the reagent for 12 h before use because the solution will become darker in color during the first 12 h of storage. The reagent is valid within 6 weeks, and its sensitivity may change after long-term storage, so the standard working curve shall be made once a week.

3.2.4 Dimedone solution

Dissolve 1 g of dimedone (dimethyl-dihydroxy-resorcinol or 5,5-dimethyl-cyclohexanedione) in ethanol and diluted it to 100 mL. This solution shall be prepared immediately before use.

3.2.5

Normal saline, 0.9% sodium chloride solution.

3.3 Apparatus

3.3.1

250 mL triangular flask with stopper.

Note: An automatic pipetting system as accurate as a manual pipette may be used.

3.3.3

Spectrophotometer, capable of detecting at a wavelength of 412 nm.

3.3.5

Thermostatic oscillating water bath.

3.3.7

Balance, with a sensibility of 0.1 mg.

3.4 Sampling and preparation of test solution

3.4.1

Take out the specimen from the sample, cut the specimen into small test portions of 5 mm×5 mm and mix them. At the same time, take another specimen from the sample and measure the moisture content according to GB/T 462.

3.4.2

For products without super absorbent polymer, weigh 2.5 g of test portion (to the nearest of 0.1 mg) and put it into a 250 mL triangular flask with stopper, add 100 mL of water and then cover the stopper. For products containing super absorbent polymer, weigh 2.0 g of test portion (to the nearest of 0.1 mg) and put it into a 250 mL triangular flask with stopper. Add 100 mL of 0.9% normal saline and then cover the stopper. If there is no free water, the amount of normal saline may be appropriately increased.

3.4.3

Place the triangular flask in a thermostatic water bath at (40±2)°C for oscillating and extraction for (60±5) min. After extraction, filter the extraction solution with 0.45 µm filter membrane (3.3.6), and keep the filtrate for testing.

3.4.4

Prepare two portions of specimen solution in parallel. Prepare two portions of blank solution according to 3.4.2 and 3.4.3 without specimen being put in.

Note: Before testing, put the sample in polyethylene bags or aluminum foil bags for sealed preservation.

3.5 Test procedures

3.5.1 Preparation of standard formaldehyde solution

Take 28 mL of formaldehyde solution (3.2.2), dilute it to 1,000 mL with water, and determine the exact concentration of formaldehyde solution by iodometric method or sodium sulfite method. According to the determined concentration, calculate the volume of formaldehyde solution containing 10 g formaldehyde, pipette this volume of formaldehyde solution into a 1 L volumetric flask, and dilute it to the scale with water to prepare 10 mg/mL standard formaldehyde solution. Standard formaldehyde solution conforming to the requirements may be directly purchased.

3.5.2 Preparation of formaldehyde standard working solution

Pipette 1 mL of standard formaldehyde solution (3.5.1) and put it into a 1 L volumetric flask, then dilute it to the scale with water to prepare 10 µg/mL formaldehyde standard working solution.

3.5.3 Construction of standard working curve

Accurately pipette 0 mL, 5.0 mL, 10.0 mL, 15.0 mL, 20.0 mL, and 25.0 mL of the formaldehyde standard working solution (3.5.2) into 100 mL volumetric flasks respectively and dilute them to the scale with water. Then transfer 5.0 mL of solution from each flasks to a 25 mL test tube with stopper and add 5.0 mL of acetylacetone reagent (3.2.3) respectively; develop color in a thermostatic oscillating water bath at (40±2)°C for (30±5) min, let them stand and cool in the dark for 30 min at normal temperature, and then determine the absorbance at a wavelength of 412 nm on the spectrophotometer with a 10 mm cuvette. Plot the standard working curve by taking the concentration of formaldehyde as the X-coordinate and the absorbance as the Y-coordinate.

3.5.4 Determination of formaldehyde content

Pipette 5.0 mL of the specimen solution (3.4.4) into a 25 mL test tube with stopper, add 5.0 mL of acetylacetone reagent, develop color in a thermostatic oscillating water bath at (40±2)°C for (30±5) min, and let it stand and cool in the dark for 30 min at normal temperature, then determine the absorbance at the wavelength of 412 on the spectrophotometer with a 10 mm cuvette. Carry out the blank test under the same conditions, and the absorbance of blank test shall be less than 0.01, otherwise, re-prepare acetylacetone reagent.

3.5.5 Dimedone confirmation test

3.5.5.1

If the absorbance is suspected to be caused by interference such as the color of the specimen solution, it may be confirmed by the dimedone test according to the 3.5.5.2.

3.5.5.2

Pipette 5.0 mL of specimen solution (3.4.4) into a 25 mL test tube with stopper, add 1.0 mL of dimedone solution (3.2.4), develop color in a thermostatic oscillating water bath at (40±2)°C for (10±1) min, add 5.0 mL of acetylacetone reagent, and then develop color again in a thermostatic oscillating water bath at (40±2)°C for (30±5) min. Let it stand and cool in the dark for 30 min at normal temperature, and determine the absorbance at the wavelength of 412 on the spectrophotometer with a 10 mm cuvette. Carry out the blank test under the same conditions, which shows that the absorbance of formaldehyde will disappear at a wavelength of 412 nm.