This standard specifies the method for the determination of vitamin C by fluorescence method. This standard is applicable to the determination of vitamin C in various infant formula foods and milk powder. GB/T 5413.18-1997 Determination of vitamin C in infant formula foods and milk powder GB/T5413.18-1997 Standard download decompression password: www.bzxz.net

GB/T5413.18—1997
Vitamin C in infant formula and milk powder exists in two forms: reduced and oxidized, and both have biological efficacy. The commonly used titration method and high pressure liquid chromatography can only determine the reduced vitamin C. The fluorescence spectrophotometry method given in this standard determines the total content of vitamin C.
This series of standards will replace GB5413—85 from the date of implementation. This standard is proposed by the China Light Industry Federation.
This standard is under the jurisdiction of the National Dairy Standardization Center. The responsible drafting unit of this standard: National Dairy Quality Supervision and Inspection Center. Participating drafting units of this standard: Food Hygiene Supervision and Inspection Institute of the Ministry of Health, Zhejiang Light Industry Research Institute, Harbin Morinaga Dairy Co., Ltd., Nestlé (China) Investment Services Co., Ltd. The main drafters of this standard: Yang Jinbao, Wang Yun, Lang Zhaobin. 297
National Standard of the People's Republic of China
Infant formula foods and milk powder
Determination of vitamin C
Milk powder and formula foods for infant and young children--Determination of vitamin C content1 Scope
This standard specifies the method for the determination of vitamin C by fluorescence. This standard is applicable to the determination of vitamin C in various infant formula foods and milk powder. 2 Summary of the method
GB/T 5413.18-1997
Replaces GB5413-85bzxZ.net
Ascorbic acid (vitamin C) can be oxidized to dehydroascorbic acid in the presence of activated carbon, which reacts with o-phenylenediamine to form a fluorophore, which has a maximum excitation wavelength at about 350nm and a maximum fluorescence at about 430nm. The fluorescence intensity is proportional to the concentration. Before adding o-phenylenediamine, ascorbic acid is allowed to form HBO:-dehydroascorbic acid complex to prevent it from forming fluorescent products. Any residual fluorescence is caused by foreign matter and can be used as a "blank". The content of ascorbic acid can be calculated by comparing the fluorescence intensity of the sample and the standard sample that have undergone the same oxidation treatment. 3 Reagents
All reagents, if the specifications are not specified, are analytically pure; all experimental water, if no other requirements are specified, refers to grade tertiary water. 3.1 Taka-Disatase. 3.2 Metaphosphoric acid-acetic acid solution: Weigh 15g of metaphosphoric acid and 40mL of acetic acid in 200mL of water, dissolve and dilute to 500mL for use. 3.3 Acidic activated carbon: weigh 200g activated carbon (chemically pure), add 1L hydrochloric acid with a volume ratio of 19, heat to boiling, vacuum filter, remove the agglomerate in a large beaker, add 1L water, stir and filter, then wash with water once, dry in an oven at 110-120℃ overnight before use.
3.4 ​​Sodium acetate solution: dissolve 500g sodium acetate trihydrate in water and dilute to 1L. 3.5 Boric acid-sodium acetate: weigh 3g boric acid, dissolve and dilute to 100mL with sodium acetate solution (3.4), prepare before use. 3.6 o-phenylenediamine solution: mass concentration 200mg/L. Weigh 20mg o-phenylenediamine, dilute to 100mL with water, prepare before use. 3.7 Vitamin C standard solution: concentration 100pg/mL. Weigh 0.0500g of ascorbic acid, dissolve it in metaphosphoric acid-acetic acid solution (3.2) and dilute it to 50mL. Take 10mL of this solution and dilute it to 100mL with metaphosphoric acid-acetic acid solution (3.2) to make a standard solution. Prepare it before use. 4 Instruments
Common laboratory instruments and fluorescence spectrophotometer. 5 Operation steps
5.1 Sample treatment
5.1.1 Samples containing starch
Approved by the State Administration of Technical Supervision on May 28, 1997 298
Implemented on September 1, 1998
GB/T 5413. 18--1997
Accurately weigh 5 g of sample into a 150 mL conical flask, add 0.5 g of Gaofeng's amylase (3.1), then add 15 mL of 45-50 ° C distilled water, mix well, remove the air in the flask with nitrogen, cover the bottle stopper, put it in a 45 ° C oven for 30 minutes, take it out and cool it to room temperature, transfer it to a 100 mL volumetric flask with metaphosphoric acid-acetic acid solution (3.2), and make up to volume. 5.1.2 Samples without starch
Accurately weigh 5 g of sample, dissolve it with metaphosphoric acid-acetic acid solution (3.2), and make up to volume to 100 mL. 5.2 Determination
5.2.1 Transfer the above sample solution to a 250mL Erlenmeyer flask containing about 2g of acidic activated carbon (3.3), shake vigorously, filter, discard the first few milliliters of filtrate, then take 5mL of the sample and standard solution filtrate and place them in 25mL and 100mL volumetric flasks containing 5mL of boric acid-sodium acetate solution (3.5), let it stand for 15 minutes, and then dilute to volume with distilled water. This is used as the blank solution for the standard solution and sample. 5.2.2 Within this 15 minutes, take another 5mL of sample and standard into two other 25mL and 100mL volumetric flasks containing 5mL of sodium acetate solution (3.4) and about 15mL of water, and dilute to the mark with water. 5.2.3 Take 2mL of sample, standard, and blank solution of sample and standard into 4 test tubes respectively. 5.2.4 Add 5mL o-phenylenediamine (3.6) to each test tube, shake well, place in dark conditions for 35 minutes, and immediately measure its fluorescence value under the conditions of excitation wavelength 350nm and emission wavelength 430nm. 6 Expression of analysis results
Vitamin C content in sample (mg/100g): Where: 1—-sample fluorescence value;
I.-—sample blank solution fluorescence value;
1.--standard sample fluorescence value;
I—standard sample blank solution fluorescence value;
C standard sample mass concentration, mg/mL;
D sample dilution multiple;
m——sample mass, g.
7 Allowable difference
(I l)×c × 5× D
(1. Tb) × m × 100
The difference between two measured values ​​of the same sample shall not exceed 10% of the average value of the two measurements. X 100
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