GB/T 5009.39-2003Method for analysis of hygienic standard of soybean sauce (English PDF)

4.2.1.5 Result calculation

Amino nitrogen content of the sample shall be calculated according to equation (1).

In which:

X – the amino nitrogen content of the sample, in units of grams per hundred milliliters (g/100 mL);

V1 – the volume of consumed sodium hydroxide standard titration solution after formaldehyde is added into the test sample dilution, in units of milliliters (mL);

V2 – the volume of consumed sodium hydroxide standard titration solution after formaldehyde is added into the reagent blank test, in units of milliliters (mL);

V3 - the taken amount of sample dilution, in units of milliliters (ml);

c - the concentration of sodium hydroxide standard titration solution , in units of moles per liter (mol/L);

0.014 – the mass of nitrogen corresponding to 1.00 mL of sodium hydroxide standard titration solution [c(NaOH) = 1.000 mol/L], in units of grams (g).

Calculation result shall retain 2 significant figures.

4.2.1.6 Precision

Under repeatability conditions, the absolute difference obtained from 2 independent test results shall not exceed 10% of the arithmetic mean.

4.2.2 Second method - Colorimetry

4.2.2.1 Principle

In pH 4.8 sodium acetate-acetic acid buffer solution, the amino nitrogen is reacted with acetyl acetone and formaldehyde to form a yellow 3,5-diacetyl-2,6-dimethyl-1,4- dihydropyridine amino acid derivatives. Measure the absorbance at wavelength of 400 nm. Compare quantitatively with the standard series.

4.2.2.2 Reagents

4.2.2.2.1 Acetic acid solution (1 mol/L): Take 5.8 mL of glacial acetic acid. Add water to dilute to 100 mL.

4.2.2.2.2 Sodium acetate solution (1 mol/L): Take 41 g of anhydrous sodium acetate or 68 g of sodium acetate (CH3COONa · 3H2O). Add water to dissolve. And dilute to

500 mL.

GB 17326-1998 standard regression equation. Calculate the sample content.

4.2.2.5 Result calculation

Amino nitrogen content of the sample shall be calculated according to formula (2).

In which:

X – the amino nitrogen content of the sample, in units of grams per hundred milliliters (g/100 mL);

c - the nitrogen mass in test sample solution, in units of micrograms (µg);

V1 - sample volume, in units of milliliters (mL);

V2 - volume of test sample solution, in units of milliliters (mL).

4.2.2.6 Precision

Under repeatability conditions, the absolute difference obtained from 2 independent test results shall not exceed 10% of the arithmetic mean.

4.3 Salt (counted in NaCl)

4.3.1 Principle

Use silver nitrate standard solution to titrate sodium chloride in the sample. Generate silver chloride to precipitate. After all silver chloride is precipitated, the extra titrated silver nitrate and potassium chromate indicator generate silver chromate, until the solution shows orange, that is the end. From the consumption of silver nitrate standard titration solution, calculate the sodium chloride content.

4.3.2 Reagents

4.3.2.1 Silver nitrate standard titration solution [c(AgNO3) = 0.100 mol/L].

4.3.2.2 Potassium chromate solution (50 g/L): Weigh 5 g of potassium chromate. Use

a small amount of water to dissolve. Dilute to 100 mL.

4.3.3 Instruments

10 ml microburette.

4.3.4 Analysis steps

Draw 2.0 mL of sample dilution in a 150 mL-200 mL conical flask. Add 100 mL of water and 1 mL of potassium chromate solution (50 g/L). Mix well. Use silver nitrate standard

GB 17326-1998

4.8 Benzoic acid, sorbic acid

Operate according to GB/T 5009.29.

4.9 Ammonium salt (semi-micro Kjeldahl method)

4.9.1 Principle

Sample is heated in an alkaline solution by distillation. Ammonia is evaporated. It is absorbed by boric acid solution. Then use hydrochloric acid standard solution to titrate and calculate the content.

4.9.2 Reagents

4.9.2.1 Magnesium oxide.

4.9.2.2 Boric acid solution (20 g/L).

4.9.2.3 Hydrochloric acid standard titration solution [c(HCl) = 0.100 mol/L].

4.9.2.4 Mixed indicator solution: 1 portion of methyl red-ethanol solution (2 g/L) and 5 portions of bromocresol green-ethanol solution (2 g/L). Mix well when using.

4.9.3 Analysis steps

Draw 2 mL of sample. Place in a 500 mL distillation flask. Add about 150 mL of water and about 1 g of magnesium oxide. Connect the distillation device. The connection bent tube at lower end of condensation tube is inserted below the liquid surface of receiving bottle. In the receiving bottle, it contains 10 mL of boric acid solution (20 g/L) and 2-3 drops of mixed indicator solution. Heat for distillation. Steam for about 30 min, counted from the boiling. Rinse the bent tube with a little water. Use hydrochloric acid standard solution (0.100 mol/L) to titrate to the end. Take the same amount of water, magnesium oxide, and boric acid solution to conduct reagent blank test according the same method.

4.9.4 Result calculation

Ammonium salt content of the sample (counted in ammonia) shall be calculated according to formula (5).

In which:

X – the ammonium salt content (counted in ammonia), in units of grams per one hundred milliliters (g/100 mL);

V1 - the volume of hydrochloric acid standard titration solution consumed in test

GB 17326-1998 sample dilution, in units of milliliters (mL);

V2 - the volume of hydrochloric acid standard titration solution consumed in reagent blank, in units of milliliters (mL);

c - the actual concentration of hydrochloric acid standard titration solution, in units of moles per liter (mol/L);

0.017 - the ammonium salt (counted in ammonia) mass corresponding to 1.00 ml of hydrochloric acid standard solution [c(HCl)=1.000 mol/L], units in grams (g);

V3 - the sample volume, in units of milliliters (mL).

The result shall retain 2 significant figures.

4.9.5 Precision

Under repeatability conditions, the absolute difference obtained from 2 independent test results shall not exceed 10% of the arithmetic mean.

__________ END __________