This standard specifies the principle, reagents, instruments, samples and determination procedures for the determination of chloride content in fruits, vegetables and their products. This standard is applicable to the determination of chloride content in fruits, vegetables and their products. The determination results are expressed as a percentage of sodium chloride content. GB/T 15667-1995 Determination of chloride content in fruits, vegetables and their products GB/T15667-1995 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Fruits, vegetables and their products---Determination of chloride content
Fruits, vegetables and their products---Determination of chloride contentGB/T 15667--1995
This standard is equivalent to the international standard ISO3634:1979 "Determination of chloride content of vegetable products", and adds the determination of fruits and products.
1 Subject content and scope of application
This standard specifies the principle, reagents, instruments and equipment, samples and determination procedures for the determination of chloride content in fruits, vegetables and products. This standard is applicable to the determination of chloride content in fruits, vegetables and products, and the determination results are expressed as a percentage of sodium chloride content. 2 Determination principle
The chloride in the sample is extracted with boiling water, and an excess of silver nitrate standard solution is added to the extract to precipitate chloride ions. Then, the remaining silver nitrate is titrated with potassium thiocyanate standard catalyst solution to calculate the chloride content in the sample. If the sample contains natural anthocyanin pigment or is oxidized by polyphenol oxidase during sample processing to darken the color, potassium permanganate can be added for oxidation and decolorization. 3 Reagents
Unless otherwise specified, all reagents are analytically pure. The water used for reagent preparation and determination is distilled water or deionized water of equal purity. 3.1 Nitric acid (GB626).
3.2 Nitrobenzene (GB9335).
3.3 Oxalic acid (HG3-—988).
3.4 ​​Saturated potassium permanganate solution: Dissolve potassium permanganate in water and then add excess potassium permanganate to make it saturated. 3.5 Acidify saturated ferric ammonium sulfate solution: Dissolve ferric ammonium sulfate in water and then add excess ferric ammonium sulfate to make it saturated. Add 5 mL of nitric acid for every 100 mL.
3.6 Silver nitrate standard solution (c (AgNO3) = 0.1000mol/LJ: Accurately weigh 16.989:0g of silver nitrate (reference reagent) dried at 150℃ for 2h and cooled in a desiccator, dissolve it in water and make up to 1000mL. 3.7 Silver nitrate standard solution [c (AgNO) = 0.0200mol/LJ: Accurately dilute the silver nitrate standard solution (c (AgNO,) = 0.1000mol/L) with water 5 times. This solution is used for samples with a chloride content of less than 1%. 3.8 Potassium thiocyanate standard solution [c (KSCN) = 0.10mol/LJ: Weigh 9.72g of potassium thiocyanate, dissolve it in water and make up to 1000mL||t t||Accurate concentration is determined as follows: Accurately pipette 20 mL of silver nitrate standard solution [c(AgNO.)=0.1000 mol/L] into a 150 mL conical flask, add 5 mL of nitric acid and 5 mL of acidified saturated ferric ammonium sulfate solution, mix well, and titrate with potassium thiocyanate standard solution [c(KSCN)=0.10 mol/L] until it turns light reddish brown, keep unchanged for 5 min, record the number of milliliters of potassium thiocyanate standard solution consumed, and calculate its accurate concentration according to the following formula:
Approved by the State Administration of Technical Supervision on August 18, 1995 204
Implemented on June 1, 1996
Wherein: c—KSCN concentration, mol/L;
C,--—AgNO Concentration, mol/L;
V——KSCN solution volume, mL;
V.---AgNO, solution volume, mL.
GB/T.15667-1995
3.9 Potassium thiocyanate standard solution (Cc(KSCN)=0.02mol/L): Dilute the potassium thiocyanate standard solution (c(KSCN)=0.10mol/L) accurately by 5 times with water, and calculate the accurate concentration of the diluted solution according to its calibrated accurate concentration. This solution is used for samples with chloride content less than 1%.
4 Instruments and equipment
4.1 Analytical balance: sensitivity 0.00018.
4.2 Pulverizer: volume not less than 500ml. 4.3 Beaker: 250mL.
4.4 Volumetric flask: 250mL.
4.5 Pipette: 5, 10, 20mL.
4.6 Conical flask: 150, 200mL.
4.7 Burette: 10, 25mL.
4.8 Electric furnace: adjustable temperature.
5 Samples
5.1 Solid samples: Take a representative sample after washing, cut it into small pieces, weigh a certain amount and put it in a pounder, add water at a sample-liquid ratio of 1:1, and pound it into a slurry.
5.2 Samples with solid-liquid phases: If the product has clear specifications for solid and liquid phases, a certain amount of sample should be taken according to the specification ratio and pounded into a slurry in a pounder. If there is no specification ratio, all samples should be pounded into a slurry. 5.3 Thick and slurry samples: directly stir evenly. 6 Determination stepsbZxz.net
6.1 Preparation of test solution
Weigh 25.00 g of sample, accurate to 0.01 g, into a 250 ml beaker (4.3), add 100 ml of hot water, mix well, heat to boiling on an electric stove (4.8), keep boiling for 1 min, remove and cool, quantitatively transfer to a 250 ml volumetric flask (4.4) with water, dilute to scale, mix well, let stand for 15 min, filter with rapid qualitative filter paper, and collect the filtrate in a dry container. 6.2 Determination of colorless test solution
Use a pipette (4.5) to draw 20 mL of the filtrate (6.1) into a conical flask (4.6), add 5 mL of nitric acid (3.1) and 5 mL of acidified saturated ferric ammonium sulfate solution (3.5), mix well, and use a burette (4.7) to drop silver nitrate standard bath solution (3.6 or 3.7) so that the amount of silver nitrate solution added is enough to leave 5 to 10 mL of excess silver nitrate solution after the chloride precipitation, then add 3 mL of nitrobenzene (3.2) and shake the contents of the flask vigorously to promote the precipitate to coagulate.
Note: Nitrobenzene is highly toxic, do not adhere to the skin, and operate in a ventilated place. Nitrobenzene may not be added for general determination, but must be added for precise determination such as arbitration.
Back-titrate the excess silver nitrate solution with potassium thiocyanate standard solution (3.8 or 3.9) until a light reddish brown color appears and remains unchanged for 5 minutes. Record the volume of potassium thiocyanate solution used (mL). 6.3 Determination of colored test solution
Use a pipette (4.5) to draw 20 ml of the filtrate (6.1). Add 20 ml of nitric acid (3.1) to a conical flask (4.6). Use a burette (4.7) to drop 20 ml of silver nitrate standard solution (3.6 or 3.7). Heat to boiling at low temperature on an electric furnace (4.8). Keep it at a slight boil for 2 to 3 minutes. Add 0.5 to 1.0 ml of saturated potassium permanganate solution (3.4) at a slight boil each time until the liquid becomes colorless. If manganese dioxide precipitation is produced, add a little oxalic acid (3.3). Continue to boil the colorless solution for 5 minutes, remove and cool, add 5 mL of acidified saturated ammonium ferric sulfate solution (3.5), back-titrate the excess silver nitrate solution with potassium thiocyanate standard solution (3.8 or 3.9) until a light reddish brown color appears and remains unchanged for 5 minutes, and record the volume of potassium thiocyanate solution used (mL).
6.4 Perform at least two parallel determinations for each sample. 7 Expression of determination results
7.1 The percentage of chloride content is given by the following formula: Percentage of sodium chloride content (%) = (Vic1-Vzc2) × 58.45× Wherein: V, — volume of silver nitrate standard solution, mL; Vz- — volume of potassium thiocyanate standard solution, mL; V3 — dilution volume of sample test solution, ml.;
V- — volume of filtrate used for titration, mL;
c concentration of silver nitrate standard solution, mol/L;
concentration of potassium thiocyanate standard solution, mol/L; 58.45 — molar mass of NaCl;
m×1000
100/m×1000——coefficient for converting chloride content into percentage, m is the sample mass, in g. If the sample is diluted with water when crushed, the mass of the diluted water should be deducted.
7.2 Expressed as the arithmetic mean of parallel determinations, retaining two decimal places. 7.3 The allowable difference of parallel determinations is shown in the following table
Nitrogen content, %
Additional remarks:
This standard is proposed by the Ministry of Agriculture of the People's Republic of China. This standard is under the jurisdiction of the National Agricultural Analysis Standardization Committee. This standard is drafted by the Central Laboratory of Sichuan Academy of Agricultural Sciences, and the main drafters of this standard are Li Guo, Fu Shaoqing, Su Fangkang, and Lei Shaorong. 206
Absolute difference, %
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