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GB 5009.86-2016 English PDF (GB5009.86-2016)

GB 5009.86-2016 English PDF (GB5009.86-2016)

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GB 5009.86-2016: National Food Safety Standard -- Determination of Ascorbic Acid in Foods

This Standard specifies the high-performance liquid chromatography, fluorescence method, 2,6-dichloro-indophenol titration method for the determination of ascorbic acid in food.
GB 5009.86-2016
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
National Food Safety Standard -
Determination of Ascorbic Acid in Foods
ISSUED ON. AUGUST 31, 2016
IMPLEMENTED ON. MARCH 1, 2017
Issued by. National Health and Family Planning Commission of the
People's Republic of China
3. No action is required - Full-copy of this standard will be automatically & immediately delivered to your EMAIL address in 0~60 minutes.
Table of Contents
Foreword ... 3
1 Scope .. 4
2 Terms and definitions ... 4
3 Principle.. 5
4 Reagents and materials .. 5
5 Instruments and equipment ... 6
6 Analysis steps ... 7
7 Expression of analysis results .. 8
8 Precision... 9
9 Other ... 9
10 Principle... 10
11 Reagents and materials .. 10
12 Instruments and equipment .. 11
13 Analysis steps .. 12
14 Result calculation ... 13
15 Precision .. 14
16 Other .. 14
17 Principle... 14
18 Reagents and materials.. 14
19 Determination ... 16
20 Result calculation ... 16
21 Precision .. 17
Annex A L(+)- ascorbic acid, D(+)- ascorbic acid standard chromatogram ... 18 Foreword
This Standard replaces GB/T 5009.86-2003 Determination of total ascorbic acid in fruits, vegetables and derived products - Fluorometric method, GB/T
5009.159-2003 Determination of reductive-form ascorbic acid in foods and GB 6195-1986 Determination of vitamin C in vegetables and fruits (2,6-dechloro- indophenol titration method).
Compared with GB/T 5009.86-2003, the main changes are as follows.
- modified the standard name to ?€?National Food Safety Standard-
Determination of Ascorbic Acid in Foods?€?;
- expanded the application scope of the method;
- added the high-performance liquid chromatography and related
quantitation limitations;
- deleted 2,4-dinitrophenylhydrazine method;
- added 2,6-dichloro-indophenol titration;
- modified the structure of the previous edition according to GB/T 20001.4- 2015.
National Food Safety Standard -
Determination of Ascorbic Acid in Foods
1 Scope
This Standard specifies the high-performance liquid chromatography,
fluorescence method, 2,6-dichloro-indophenol titration method for the
determination of ascorbic acid in food.
Method One of this Standard applies to the determination of total amount of L(+)- ascorbic acid, D(+)- ascorbic acid and L(+)- ascorbic acid in milk powder, cereals, vegetables, fruits and their products, meat products, vitamin
supplements, jellies, gummies, rice pudding, wine. Method Two is applicable to the determination of L(+)- total amount of ascorbic acid in milk powder, vegetables, fruits and their products. Method Three applies to the determination of L(+)- total amount of ascorbic acid in fruits, vegetables and their products. 2 Terms and definitions
2.1 Ascorbic acid. an organic compound with antioxidant properties. It is also known as "Vitamin C," one of the essential nutrients in human body.
2.2 L(+)- ascorbic acid. left-right rotation ascorbic acid that has a strong reduction. It has biological activity on the human body.
2.3 D(+)- ascorbic acid. also known as isoascorbic acid. It has a strong reduction, but basically, it has no biological activity on the human body. 2.4 L(+)- dehydroascorbic acid. L(+)- ascorbic acid is easily oxidized to L(+)- dehydroascorbic acid; L(+)- dehydroascorbic acid can also be reduced to L(+)- ascorbic acid. It is often called as dehydroascorbic acid.
2.5 L(+)- total amount of ascorbic acid. total amount of ascorbic acid obtained when L(+)- dehydroascorbate in the sample is reduced to L(+)- ascorbic acid OR L(+)- dehydroascorbic acid is oxidized by L(+)- ascorbic acid in the sample. Method One -- High performance liquid
chromatography
3 Principle
After ascorbic acid in the sample is dissolved with metaphosphoric acid and extracted by sonication, use ion-pair reagent as mobile phase. Separate it through reverse phase column. L(+)- ascorbic acid and D(+)- ascorbic acid are measured directly with a liquid chromatograph (wavelength of 245 nm)
equipped with a UV detector. After L(+)- dehydroascorbate in the sample is reduced by L-cysteine solution, the content of L(+)- dehydroascorbic acid is determined by measuring the total amount of L(+)- ascorbic acid with a UV detector (wavelength of 245 nm) or by subtracting the L(+)- ascorbic acid content measured in the original sample. Determine the nature by the retention time of chromatographic peak. Quantify in external standard method.
4 Reagents and materials
Unless otherwise specified, the reagents used in this method are of analytical grade pure, water is of grade one specified in GB/T 6682.
4.1 Reagents
4.1.1 Metaphosphoric acid (HPO3)n. content (calculated as HPO3) ???38%
4.1.2 Trisodium phosphate (Na3PO4?€?12H2O)
4.1.3 Potassium dihydrogen phosphate (KH2PO4)
4.1.4 Phosphoric acid (H3PO4). 85%
4.1.5 L-cysteine (C3H7NO2S). excellent grade pure
4.1.6 Cetyltrimethylammonium bromide (C19H42BrN). chromatographically
pure
4.1.7 Methanol (CH3OH). chromatographically pure
4.2 Reagent preparation
4.2.1 Methanophosphoric acid solution (200 g/L). weigh 200 g (to the nearest of 0.1 g) of metaphosphoric acid (4.1.1), dissolve in water and dilute to 1 L; this solution can be stored in a 4??C environment for one month.
4.2.2 Methanophosphoric acid solution (20 g/L). weigh 50 mL of 200 g/L
partial phosphoric acid solution; dilute in water to 500 mL.
4.2.3 Trisodium phosphate solution (100 g/L). weigh 100 g (to the nearest of 0.1g) of trisodium phosphate; dissolve in water and dilute to 1 L.
6.4.1 Chromatographic column. C18 column, column length of 250 mm, inner diameter of 4.6 mm, particle size of 5 ??m, or chromatographic column of same performance.
6.4.2 Detector. diode array detector or UV detector
6.4.3 Mobile phase. A. 6.8 g of potassium dihydrogen phosphate and 0.91 g of cetyltrimethylammonium bromide; use water to dissolve and set volume to 1 L (adjust pH to 2.5 ~ 2.8 with phosphoric acid); B. 100% methanol. Mix
according to A.B=98.2; make it through 0.45 ??m filter membrane; perform ultrasonic degassing.
6.4.4 Flow rate. 0.7 mL/min
6.4.5 Detection wavelength. 245 nm
6.4.6 Column temperature. 25??C
6.4.7 Injection volume. 20 ??L
6.5 Making of standard curve
Respectively determine the ascorbic acid mixed standard series of working solutions. Take the mass concentration (??g/mL) of standard solution of L(+)- ascorbic acid [or D(+)- ascorbic acid] as abscissa, L(+)- ascorbate [or D(+)- ascorbate] peak height or peak area as ordinate to draw standard curve or calculate regression equation. See Figure A.1 in Annex A for L(+)- ascorbic acid, D(+)- ascorbic acid standard chromatogram.
6.6 Determination of sample solution
Determine the sample solution. Obtain the concentration (??g/mL) of L(+)- ascorbate [or D(+)- ascorbate] according to the standard curve.
6.7 Blank test
The blank test refers that perform parallel operation by using identical analysis steps, reagents and dosage, except not adding sample.
7 Expression of analysis results
The amount of L(+)- ascorbic acid [or D(+)- ascorbic acid] and the total amount of L(+)- ascorbic acid in the sample are expressed in milligrams per hundred grams, calculated according to equation (1).
11.2.3 Metaphosphoric acid - acetic acid - sulfuric acid solution. weigh 15 g of metaphosphoric acid; add 40 mL of glacial acetic acid; drop 0.15 mol/L sulfuric acid solution till it is dissolved; and dilute to 500 mL.
11.2.4 Sodium acetate solution (500 g/L). weigh 500 g of sodium acetate; add water to 1000 mL.
11.2.5 Boric acid-sodium acetate solution. weigh 3 g of boric acid; use 500 g/L sodium acetate solution to dissolve and dilute to 100 mL. Prepare when using. 11.2.6 Phenylenediamine solution (200 mg/L). weigh 20 mg of O-
phenylenediamine; dissolve with water and dilute to 100 mL; prepare when using.
11.2.7 Activated carbon. weigh about 200 g of activated carbon powder (75??m ~ 177??m); add into 1L of hydrochloric acid (1+9); heat to reflux 1h. Filter. Wash with water until the filtrate is free of iron ions. Place in a 110??C ~ 120??C oven for 10h, spare for use.
Test method for iron ion. using Prussian blue reaction. Mix 20 g/L potassium ferrocyanide and 1% hydrochloric acid in equal amounts. Drop the above eluted filtrate. If there are iron ions, a blue precipitate shall be generated. 11.2.8 Thymol blue indicator solution (0.4 mg/mL). weigh 0.1g of thymol blue; add about 10.75 mL of 0.02 mol/L sodium hydroxide solution; grind to dissolve in a glass mortar; dilute to 250 mL with water. (discoloration range. red at pH equal to 1.2; yellow at pH equal to 2.8; blue at pH >4).
11.3 Standard product
L(+)- ascorbic acid standard product (C6H8O6). purity ???99%
11.4 Preparation of standard product
11.4.1 L(+)- ascorbate standard solution (1.000 mg/mL). weigh 0.05 g of L(+)- ascorbic acid (to the nearest of 0.01 mg); dissolve with metaphosphoric acid - acetic acid solution and dilute to 50 mL. This stock solution can be stored at 2??C ~ 8??C from light for one week.
11.4.2 L(+)- ascorbic acid standard working solution (100.0 ??g/mL).
accurately pipette 10 mL of L(+)- ascorbate standard solution; dilute to 100 mL with metaphosphoric acid-acetic acid solution; prepare when using.
12 Instruments and equipment
Fluorescence spectrophotometer. with an excitation wavelength of 338nm and 100 - conversion factor;
1000 - conversion factor.
The calculation results are expressed as the arithmetic mean of two
independent determinations obtained under repeatability conditions, resulting in the retention of three significant figures.
15 Precision
The absolute difference between two independent determination results
obtained under repeatability conditions shall not exceed 10% of the arithmetic mean.
16 Other
When the sampling amount is 10 g, the detection limit of total L(+)- ascorbic acid is 0.044 mg/100g, the limit of quantification is 0.7 mg/100g.
Method Three -- 2,6-dichloro-indophenol titration
17 Principle
Use blue basic dye 2,6-dichloro-indophenol standard solution to perform redox titration on acid leachate sample containing L(+)- ascorbic acid. 2,6-dichloro- indophenol is reduced to colorless. At the end of the titration, excess 2,6- dichloro-indophenol is colored as light red in an acidic medium. The content of L(+)- ascorbic acid in the sample is calculated from the consumption of 2,6- dichloro-indophenol.
18 Reagents and materials
Unless otherwise specified, the reagents used in this method are of analytical grade pure, water is of grade three specified in GB/T 6682.
18.1 Reagents
18.1.1 Metaphosphoric acid (HPO3)n. content (calculated as HPO3) ???38%
18.1.2 Oxalic acid (C2H2O4)
18.1.3 Sodium bicarbonate (NaHCO3)
in milliliters (mL).
18.3 Standard product
L(+)- ascorbic acid standard (C6H8O6). purity ???99%
18.4 Preparation of standard solution
L(+)- ascorbate standard solution (1.000 mg/mL). weigh 100 mg (to the nearest of 0.1 mg) of L(+)- ascorbate standard product, dissolve in methanoic acid solution or oxalic acid solution and set volume to 100 mL. This stock solution can be stored at 2??C ~ 8??C from light for one week.
19 Determination
The entire testing process shall be carried out under dark conditions.
19.1 Preparation of test solution. weigh 100 g of edible part of representative sample; put into grinder; add 100 g of methanoic acid solution or oxalic acid solution; quickly pound into homogenate. Accurately weigh 10g ~ 40g of
homogenate sample (to the nearest of 0.01 g) into a beaker. Transfer the sample to a 100-mL volumetric flask with metaphosphoric a...

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