GB 7303-2018Feed additive - L-Ascorbic acid (Vitamin C) (English PDF)

4.1 Appearance and properties

The product is a white to slightly yellowish crystal or crystalline powder, odourless, with an acid taste. It is readily soluble in water, slightly soluble in ethanol and insoluble in chloroform or ether.

4.2 Technical indicators

The technical indicators shall comply with Table 1.

Table 1 - Technical indicators: L-ascorbic acid (as C6H8O6), %: 99.0 to 100.5; Melting point, °C: 189 to 192; Specific rotation, (°)·dm2/kg: +20.50 to +21.50; Residue on ignition, % <= 0.1; Heavy metals (as Pb), mg/kg <= 10; Total arsenic (as As), mg/kg <= 2.0.

5.1 Sensory inspection

Place an appropriate amount of the sample in a clean, dry white porcelain dish, observe its colour and form under natural light and smell its odour.

5.2 Identification tests

5.2.1 Reagents or materials

5.2.1.1 Silver nitrate solution

rho = 17.5 g/L.

5.2.1.2 Sodium 2,6-dichloroindophenol solution

rho = 1 g/L.

5.2.2 Identification methods

5.2.2.1

Weigh about 0.2 g of the sample and dissolve in 10 mL of water; take 5 mL of the solution and add 0.5 mL of silver nitrate solution (5.2.1.1): a black precipitate of silver is formed.

5.2.2.2

Weigh about 0.2 g of the sample and dissolve in 10 mL of water; take 5 mL of the solution and add 1 to 3 drops of sodium 2,6-dichloroindophenol solution (5.2.1.2): the colour of the test solution disappears immediately.

5.3 Determination of L-ascorbic acid (vitamin C) content

5.3.1 Principle

In an acidic medium, L-ascorbic acid (vitamin C) undergoes a quantitative redox reaction with iodine solution; the end point of the reaction is indicated by the blue colour that the starch indicator solution develops with iodine.

5.3.2 Reagents or materials

5.3.2.1 Acetic acid solution

psi = 6 % (volume fraction).

5.3.2.2 Starch indicator solution

rho = 5 g/L (prepare when needed).

5.3.2.3 Iodine standard titration solution

c(1/2 I2) = 0.1 mol/L.

5.3.3 Test procedure

Weigh about 0.2 g of the sample (to the nearest 0.000 2 g) into a 250 mL iodine flask, add 100 mL of freshly boiled and cooled water and 10 mL of acetic acid solution (5.3.2.1) to dissolve it, add 1 mL of starch indicator solution (5.3.2.2) and titrate immediately with iodine standard titration solution (5.3.2.3) until the solution shows a blue colour that persists for 30 s.

Carry out a blank test at the same time, following the same procedure as for the sample but without the sample.

5.3.4 Test data processing

The mass fraction w1 of L-ascorbic acid (vitamin C) (as C6H8O6), expressed in %, is calculated according to formula (1):

w1 = ((V - V0) × c × 0.088 06) / m × 100 ... (1)

where:

V - volume of iodine standard titration solution consumed by the sample, in millilitres (mL);

V0 - volume of iodine standard titration solution consumed by the blank test, in millilitres (mL);

c - exact concentration of the iodine standard titration solution, in moles per litre (mol/L);

m - mass of the sample, in grams (g);

0.088 06 - mass of L-ascorbic acid (vitamin C), in grams, equivalent to 1 mL of iodine standard solution of 1 mol/L.

5.3.5 Precision

Under repeatability conditions, the absolute difference between the results of two parallel determinations shall not exceed 0.5 %.

5.4 Determination of melting point

Determine in accordance with GB/T 617.

5.5 Determination of specific rotation

5.5.1 Instruments and equipment

Polarimeter.

5.5.2 Test procedure

Weigh about 5 g of the sample (to the nearest 0.000 2 g) into a 50 mL volumetric flask, dissolve in water, dilute to the mark with water and shake well. Proceed otherwise by the method specified in GB/T 613.

5.5.3 Test data processing

The specific rotation alpham(20 °C, D), expressed in (°)·dm2/kg, is calculated according to formula (2):

alpham(20 °C, D) = alpha / (l × rho) ... (2)

where:

alpha - measured optical rotation, in degrees (°);

l - length of the polarimeter tube, in decimetres (dm);

rho - mass concentration of the active component in the solution, in grams per millilitre (g/mL).

5.5.4 Precision

Under repeatability conditions, the absolute difference between the results of two parallel determinations shall not exceed 0.3.

5.6 Determination of residue on ignition

5.6.1 Reagents

Sulfuric acid.

5.6.2 Test procedure

Weigh 2 g to 5 g of the sample (to the nearest 0.000 2 g) into a porcelain crucible previously ignited to constant mass at 700 °C to 800 °C. Heat slowly over a low flame until completely charred; after cooling, moisten with 0.5 mL to 1 mL of sulfuric acid, heat at low temperature until the sulfuric acid fumes are completely driven off, then transfer to a muffle furnace and ignite at 700 °C to 800 °C to constant mass.

5.6.3 Test data processing

The mass fraction w2 of residue on ignition, expressed in %, is calculated according to formula (3):

w2 = (m1 - m2) / m × 100 ... (3)

where:

m1 - mass of the crucible plus residue, in grams (g);

m2 - mass of the crucible, in grams (g);

m - mass of the sample, in grams (g).

5.6.4 Precision

Under repeatability conditions, the absolute difference between the results of two parallel determinations shall not exceed 0.02.

5.7 Determination of heavy metals

5.7.1 Reagents or materials

5.7.1.1 Sodium sulfide solution

rho = 125 g/L (prepare when needed).

Weigh 12.5 g of sodium sulfide to the nearest 0.1 g into a 100 mL volumetric flask, add 75 mL of glycerol and dilute to the mark with water.

5.7.1.2 Lead standard solution

rho(Pb) = 10 µg/mL.

Weigh 0.160 g of lead nitrate to the nearest 0.000 2 g into a 1 000 mL volumetric flask, dissolve in 5 mL of nitric acid and 50 mL of water, dilute to the mark with water and shake well; this is the stock solution. Immediately before use, transfer 10 mL ± 0.02 mL of the stock solution into a 100 mL volumetric flask, dilute to the mark with water and shake well (1 mL is equivalent to 10 µg of Pb). The glassware used for preparation and storage shall be free from lead.

5.7.2 Test procedure

Accurately weigh 1 g of the sample to the nearest 0.000 1 g into a crucible, char it carefully on an electric hot plate, then place it in a muffle furnace and ignite at 550 °C ± 20 °C for 4 h. Dissolve the residue in water, transfer to a 25 mL Nessler colorimetric tube, add 5 drops of sodium sulfide solution (5.7.1.1), dilute to 25 mL with water, shake well and allow to stand for 2 min. At the same time, transfer 1.0 mL of lead standard solution (5.7.1.2) into a 25 mL Nessler colorimetric tube, add about 15 mL of water and 5 drops of sodium sulfide solution (5.7.1.1), dilute to 25 mL with water, shake well and allow to stand for 2 min. Place the sample tube and the reference tube side by side on white paper and view from above: the colour of the sample tube shall not be deeper than that of the lead standard reference tube.

5.8 Determination of total arsenic

Accurately weigh about 2 g of the sample to the nearest 0.000 1 g into an arsine generator, dissolve in 10 mL of water and determine by the silver salt method specified in 5.4.3 of GB/T 13079-2006.

6.1 Batching

Products made from the same materials by the same production process, produced continuously or in the same shift, constitute one batch.

6.2 Sampling

Sampling shall be carried out by the method specified in GB/T 14699.1.

6.3 Factory inspection

The factory inspection items are all the items required in Clause 4.

6.4 Rules of judgement

6.4.1

A product is judged to be qualified when the results of all the items inspected are in conformity with the indicators specified in this standard.

6.4.2

If any indicator does not meet the requirements of this standard, a re-inspection may be carried out on samples taken from twice the number of packages; if even one indicator in the re-inspection result does not meet the requirements of the standard, the batch of product is judged to be unqualified.

7.1 Labelling

Labelling shall be in accordance with GB 10648.

7.2 Packaging

The product is packed in suitable containers and sealed. The packaging shall meet the requirements of transport and storage, or the product may be packed according to the requirements of the user.

7.3 Transport

During transport the product shall be protected from rain, moisture and sun; mixed loading or mixed transport with toxic or harmful substances or other contaminating goods is strictly prohibited.

7.4 Storage

Store in a dry, ventilated place, protected from direct sunlight.

7.5 Shelf life

The shelf life of the product in its unopened original packaging under the specified conditions of transport and storage is 24 months.