GB/T 27741-2018Paper and board—Determination of migratable fluorescent whitening agents (English PDF)

4.1 Sampling

The sample is taken according to the provisions of GB/T 450.

4.2 Preparation of specimen

Cut the specimen into small pieces of about 5 mm x 5 mm. Mix them uniformly.

5.1 Principles

After using an extract having a pH of 7.5 ~ 9.0 to extract the fluorescent whitening agent in paper and board, adjust the pH of the filtrate to 3.0 ~ 5.0.

5.2 Reagents and materials

Unless otherwise stated, the reagents used are of analytical pure and the test water shall meet the grade-3 water as specified in GB/T 6682. The reagents and materials used shall be free of fluorescence under UV light.

5.2.1 Gauze. The size is about 5 cm x 5 cm.

5.3 Instruments

5.3.1 Conical flask. 250 mL.

5.3.2 Glass funnel. Glass core funnel with specification G1.

5.3.3 Glass watch glass.

5.4 Test procedure

5.4.1 Extraction of specimen

Accurately weigh 2.0 g of the specimen and place it in a conical flask (5.3.1).

Add 100 mL of the extract (5.2.4) to the flask. Whilst slowing shaking the flask, extract it at room temperature for 10 min.

5.4.2 Blank test

Except for not adding specimen, follow the procedures of 5.4.1 to perform the blank test.

5.4.3 Testing

Place the watch glass on which the specimen gauze (5.4.1) and the blank test gauze (5.4.2) are placed at about 20 cm under the UV lamp (5.3.6) in the dark room or dark box, to observe the gauze's fluorescence phenomenon. Each specimen is subjected two parallel determinations.

6.1 UV-visible spectrophotometry

6.1.1 Principle

The specimen is extracted by a water bath at 80 °C. After the extraction solution is filtered, use an ultraviolet-visible spectrophotometer to determine the absorbance of the fluorescent whitening agent in the specimen filtrate. With reference to the working curve of VBL standard solution of the fluorescent whitening agent, determine contents of the fluorescent whitening agent in the sample.

6.1.2 Reagents and materials

Unless otherwise stated, the reagents used are of analytical pure and the test water shall meet the grade-2 water as specified in GB/T 6682.

6.1.2.5 Fluorescent whitening agent VBL standard working solution. Accurately transfer a certain volume of fluorescent whitening agent VBL standard stock solution (6.1.2.4) as needed. Use the extract (6.1.2.2) to dilute it to the appropriate concentration of standard working solution. The standard working solution is prepared before use. The linear range of the measurement under different working conditions of different instruments is different. The linearity of the standard solution concentration range from 1 mg/L to 20 mg/L has been proved to be satisfactory.

6.1.2.6 Microporous membrane. 0.45 µm.

6.1.3 Instruments

6.1.4 Test procedure

6.1.5 Calculation and representation of results

Calculate the content of the migratable fluorescent whitening agent w (in VBL) in the specimen according to formula (1).

6.2 High performance liquid chromatography

6.2.1 Principle

The specimen is extracted by a water bath at 80 °C. After the extracted solution is filtered, use the high performance liquid chromatography to analyze it. Use the retention time for qualitative and the external standard method for quantitative.

6.2.2 Reagents and materials

Unless otherwise stated, the reagents used are of analytical pure and the test water shall meet the grade-1 water as specified in GB/T 6682.

6.2.2.4 Ammonia. 0.1%.

6.2.2.5 Extract. The aqueous solution the pH of which is adjusted by 0.1% ammonia (6.2.2.4). The pH of the solution is 7.5 ~ 9.0.

6.2.2.6 Fluorescent whitening agent standard stock solution (1000 mg/L). Accurately weigh 0.1000 g of the fluorescent whitening agent standard substance as listed in Appendix A. Respectively, use extract (6.2.2.5) to dissolve it. Make its volume reach to 100 mL.

6.2.3 Instruments

6.2.3.1 High performance liquid chromatograph, equipped with a fluorescence detector (FLD).

6.2.3.2 Balance. The sensitivities are 0.1 g and 0.1 mg.

6.2.4 Test procedure

6.2.4.1 Extraction of specimen

It is performed according to 6.1.4.1.

6.2.4.2 Blank test

Except for not adding specimen, follow the procedures of 6.1.4.1 to carry out the blank test.

6.2.4.3 Determination