GB 5009.256-2025National food safety standard - Determination of phosphates in foods (English PDF)

3.1 Reagents

3.1.1 Sodium hydroxide (NaOH).

3.1.2 Potassium hydroxide (KOH).

3.1.3 Methanol (CH3OH). chromatographically pure.

3.2.1 Sodium hydroxide solution (10 mmol/L). weigh-take

0.4 g of sodium hydroxide, add water to dissolve it and reach a constant volume of 1,000 mL.

3.2.2 Sodium hydroxide solution (50 mmol/L). weigh-take

2.0 g of sodium hydroxide, add water to dissolve it and reach a constant volume of 1,000 mL.

3.2.3 Potassium hydroxide solution (2 mol/L). weigh-take 112.0 g of potassium hydroxide, add water to dissolve it and reach a constant volume of 1,000 mL.

3.3 Standard Substances

3.3.1 Sodium phosphate (Na3PO4, CAS No.. 7601-54-9), purity 98%, or standard substance certified by the state and awarded with the standard substance certificate.

3.3.2 Sodium pyrophosphate (Na4P2O7, CAS No.. 7722-88-5), purity 98%, or standard substance certified by the state and awarded with the standard substance certificate.

3.3.3 Sodium trimetaphosphate [(NaPO3)3, CAS No.. 7785-84-4], purity 98%, or standard substance certified by the state and awarded with the standard substance certificate.

3.3.4 Sodium tripolyphosphate (Na5P3O10, CAS No.. 7758-29-4), purity 98%, or standard substance certified by the state and awarded with the standard substance certificate.

3.4.1 Phosphate radical standard stock solution (1,000 mg/L). accurately weigh-take

0.173 g (accurate to 0.0001

g) of sodium phosphate standard substance, use 10 mmol/L sodium hydroxide solution to dissolve it and reach a constant volume of 100 mL. Per 1 L of this solution contains

1.0 g of phosphate radical. Store in a sealed container at room temperature, and it shall remain valid for 6 months.

3.4.2 Pyrophosphate standard stock solution (1,000 mg/L). accurately weigh-take

0.153 g (accurate to 0.0001

g) of sodium pyrophosphate, use 10 mmol/L sodium hydroxide solution to dissolve it and reach a constant volume of 100 mL. Per 1 L of this solution contains

1.0 g of pyrophosphate. Store in a sealed container at room temperature, and it shall remain valid for 6 months.

3.4.3 Trimetaphosphate standard stock solution (1,000 mg/L). dry the sodium trimetaphosphate in an oven at 103 C 2 C for 3 h. After cooling to room temperature in a desiccator, accurately weigh-take

0.132 g (accurate to 0.0001

g) of sodium trimetaphosphate standard substance, use 10 mmol/L sodium hydroxide solution to dissolve it and reach a constant volume of 100 mL. Per 1 L of this solution contains

1.0 g of trimetaphosphate. Store in a sealed container at room temperature, and it shall remain valid for 6 months.

3.4.4 Tripolyphosphate standard stock solution (1,000 mg/L). dry the sodium tripolyphosphate in an oven at 103 C 2 C for 3 h. After cooling to room temperature in a desiccator, accurately weigh-take

0.148 g (accurate to 0.0001

g) of sodium tripolyphosphate standard substance, use 10 mmol/L sodium hydroxide solution to dissolve it and reach a constant volume of 100 mL. Per 1 L of this solution contains

1.0 g of tripolyphosphate. Store in a sealed container at room temperature, and it shall remain valid for 6 months.

5.1.3 Milk powder, milk and dairy products, beverages, etc.. by repeatedly shaking and inverting the container, thoroughly mix the sample, until the sample is homogenized.

5.1.4 Solid grease, fats, cocoa products, chocolate and chocolate products, frozen drinks, etc.. take 500 g of sample, freeze it at -18 C, use a food pulverizer to pulverize it and evenly mix it for later use.

5.1.5 Cereals, wheat flour and its products, jelly, candy, syrup, canned vegetables, baked food, puffed food, cooked nuts and seeds, etc.. take 500 g of the edible part and use a food pulverizer to pulverize it for later use.

5.2.1 Sample extraction

5.2.1.1 Vegetables, fruits, jelly, chocolate and candy, coarse cereals, wheat flour and its products, milk powder, milk and dairy products, beverages, etc.. weigh-take

2.5 g (accurate to

0.001 g, the sampling amount of the specimen can be appropriately adjusted) of the specimen, use 50 mmol/L sodium hydroxide solution to wash it into a 50 mL colorimetric tube, evenly mix it and reach a constant volume to the scale; extract it at 80 C for 30 min with ultrasound, and every 5 min, shake it once to make the sample completely dispersed. After cooling to room temperature, use filter paper to filter the solution; take the filtrate, and at 4 C, centrifuge it at 8,000 r/min for 10 min, and take the supernatant for later use.

5.2.1.2 Puffed food, cooked nuts and seeds, cereals and starch desserts, rice flour, infant formula and complementary food, etc.. weigh-take

2.5 g (accurate to

0.001 g, the sampling amount of the specimen can be appropriately adjusted) of the specimen, and use 50 mmol/L sodium hydroxide solution to wash it into a 25 mL colorimetric tube, evenly mix it and reach a constant volume to the scale; extract it at 80 C for 30 min with ultrasound, and every 5 min, shake it once to make the sample completely dispersed. After cooling to room temperature, use filter paper to filter the solution; take the filtrate, and at 4 C, centrifuge it at 8,000 r/min for 10 min, and take the supernatant for later use.

5.2.1.3 Grease, fats, seasonings, etc.. weigh-take 1 g (accurate to 0.001g, the sampling amount of the specimen can be appropriately adjusted) of the specimen, use 50 mmol/L sodium hydroxide solution to wash it into a 50 mL colorimetric tube, evenly mix it and reach a constant volume to the scale; extract it at 80 C for 30 min with ultrasound, and every 5 min, shake it once to make the sample completely dispersed. After cooling to room temperature, use filter paper to filter the solution; take the filtrate, and at 4 C, centrifuge it at 8,000 r/min for 10 min, and take the supernatant for later use.

5.2.1.4 Aquatic products, eggs, meat and their products. weigh-take

2.5 g (accurate to

0.001 g, the sampling amount of the specimen can be appropriately adjusted) of the specimen, use 50 mmol/L sodium hydroxide solution to wash it into a 100 mL colorimetric tube, evenly mix it and reach a constant volume to the scale; extract it at 80 C for 30 min with ultrasound, and every 5 min, shake it once to make the sample completely dispersed. After cooling to room temperature, use filter paper to filter the solution; take the filtrate, and at 4 C, centrifuge it at 8,000 r/min for 10 min, and take the supernatant for later use.

5.2.2 Sample purification Take 15 mL of the supernatant after the treatment in 5.2.1, pass it through a 0.45 m water- soluble membrane syringe filter and a polydivinylbenzene polymer reverse phase packed column, discard the first 3 mL (if the chloride ion is greater than 100 mg/L, then, it needs to successively pass through a syringe filter, a polydivinylbenzene polymer reverse phase packed column, an Ag column and a Na column, and discard the first 7 mL), and collect the remaining eluate for testing. Before determination, the solution to be tested shall be appropriately diluted in accordance with the sample content. Before use, the solid phase extraction column needs to be activated. For example, when using a polydivinylbenzene polymer reverse phase packed column (

1.0 mL), an Ag column (

1.0 mL), or a Na column (

1.0 mL), the activation process is as follows: before use, the polydivinylbenzene polymer reverse phase packed column (

1.0 mL) is successively passed with 10 mL of methanol and 15 mL of water and left to stand for activation for 30 min. The Ag column (

1.0 mL) and the Na column (

1.0 mL) are passed with 10 mL of water and left to stand for activation for 30 min.

5.3 Reference Chromatographic Conditions

5.3.1 Chromatographic columns. anion exchange column (4 mm 250 mm); guard column. anion exchange column (4 mm 50 mm) with the same filler, or an ion chromatography column with equivalent performance.

5.3.2 Eluent. potassium hydroxide solution. The gradient elution time and potassium hydroxide concentration are shown in Table

1.The flow rate is

5.3.3 Suppressor. anion suppressor or equivalent suppression device.

5.3.4 Detector. conductivity detector, detection cell temperature is 35 C.

5.3.5 Column oven. the temperature of the column oven is 30 C.

5.3.6 Injection volume. 100 L. rhoi

---the determined value of the ith phosphate radical in the sample solution, expressed in (mg/L); rho0i

---the determined value of the ith phosphate radical in the sample blank solution, expressed in (mg/L); V

---the constant volume of the sample extracting solution, expressed in (mL); m

---the weighed mass of the sample, expressed in (g); 1,000

---the conversion factor. The calculation result is expressed as the arithmetic mean of two independent determination results obtained under repeatability conditions, and the result shall retain three significant figures. If the analytical result needs to be expressed in terms of phosphate radical content, see Appendix B, and multiply the polyphosphate content by the conversion factor F. The total phosphate radical in the sample is the sum of phosphate radicals converted from polyphosphates (except hexametaphosphate).

10.1 Reagents

10.1.1 Nitric acid (HNO3). mass concentration is 65%.

10.1.2 Sodium carbonate (Na2CO3).

10.1.3 Sodium hydroxide (NaOH).

10.1.4 Potassium hydroxide (KOH).

10.2 Preparation of Reagents

10.2.1 Nitric acid solution (volume fraction 30%). measure-take 30 mL of nitric acid and slowly add it into 50 mL of water. After cooling to room temperature, dilute it to 100 mL.

10.2.2 Sodium hydroxide solution (50 mmol/L). same as 3.2.2.

10.2.3 Potassium hydroxide solution (2 mol/L). same as 3.2.3.

10.2.4 Sodium carbonate (15 mmol/L)-sodium hydroxide (2 mmol/L) mixed solution. respectively weigh-take

1.590 g of sodium carbonate and

0.080 g of sodium hydroxide, dissolve them in a beaker, cool to room temperature, then, transfer to a volumetric flask, and reach a constant volume of 1,000 mL.

10.3 Standard Substance Sodium phosphate (Na3PO4, CAS No.. 7601-54-9), purity 98%, or standard substance certified by the state and awarded with the standard substance certificate.

12.3.1 Potassium hydroxide eluent system

12.3.1.1 Chromatographic columns. hydroxide selective, anion exchange column (250 mm 4 mm), guard column. anion exchange column (50 mm 4 mm) with the same filler, or an ion chromatography column with equivalent performance.

12.3.1.2 Eluent. potassium hydroxide eluent, concentration is 20 mmol/L, flow rate is

12.3.1.3 Suppressor. anion suppressor.

12.3.2 Carbonate eluent system

12.3.2.1 Chromatographic column. carbonate selective, anion exchange column (4 mm 150 mm), guard column. anion exchange column (1 mm

3.5 mm) with the same filler, or an ion chromatography column with equivalent performance.

12.3.2.2 Eluent. sodium carbonate (15 mmol/L) + sodium hydroxide (2 mmol/L) mixed eluent, flow rate is

0.6 mL/min.