This standard specifies the instruments, reagents, operating procedures and result calculation methods required for the determination of calcium in cereals and cereal products. This standard is applicable to samples with a calcium content of not less than 1 mg/g. GB/T 14610-1993 Determination of calcium in cereals and cereal products GB/T14610-1993 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Determination of calcium in cereals and cereal products
Method for determination of calcium incereals and cereal products
1 Subject content and scope of application
GB/T 14610--93
This standard specifies the instruments, reagents, operating procedures and result calculation methods required for the determination of calcium in cereals and cereal products. This standard is applicable to samples with a calcium content of not less than 1 mg/g. 2 Reference standards
GB601 Preparation of standard solutions for titration analysis (volume analysis) of chemical reagents GB5009.3 Determination of water content in food 3 Principle
After the sample is ashed, calcium in acidic solution reacts with oxalic acid to form calcium oxalate, which is dissolved in sulfuric acid and titrated with potassium permanganate standard solution to calculate the calcium content.
4 Apparatus
4.1 Quartz or porcelain crucible, diameter about 60mm, volume not less than 35mL. If porcelain crucible is used, it should be free of cracked glaze, smooth surface and completely free of cracks.
4.2 Muffle furnace.
4.3 Porous glass filter G. or equivalent. 4.4 Burette 10 mL.
4.5 2 Filter bottle 2500mL. bZxz.net
4.6 Conical flask 250 mL.
4.7 Beaker 400mL.
4.8 Volumetric flask 1000mL.
5 Reagents
5.1 Nitric acid of high purity.
5.2 Hydrochloric acid 6 mol/L Take 500 mL of concentrated hydrochloric acid (d=1.18; GB 622) and add 500 mL of water and mix well. 5.3 0.5 mol/L hydrochloric acid Take 80 mL of hydrochloric acid (5.2) and dilute it to 1000 mL with water. 5.4 3% oxalic acid solution Weigh 3.9 g of oxalic acid (HzC, 0.·2H, 0) and dissolve it in 1000 mL of water. 5.5 20% sodium acetate solution Weigh 33 g of sodium acetate and dissolve it in 100 mL of water. 5.6 1% bromocresol green indicator Weigh 1.0 g of bromocresol green and dissolve it in 2~3 mL of 10% sodium hydroxide solution, add water to 100 mL. 5.7 0.01 mol/L potassium permanganate standard solution Weigh 1.58 g of potassium permanganate (GB643), dissolve it in 1000 mL of water, and calibrate it according to GB601.
Approved by the State Administration of Technical Supervision on September 5, 1993, and implemented on July 1, 1994
6 Kneading steps
6.1 Sample preparation
GB/T 14610-93
Evenly select the sample to be tested, crush it until it passes through a 40-mesh sieve, and prepare at least 50g of sample according to the analysis requirements. Determine the sample moisture content according to GB5009.3, and the reported test results are calculated on a dry basis. 6.2 Determination
6.2.1 Accurately weigh 310g of sample in a crucible (4.1) (the sample weight depends on the actual calcium content of the sample), place it on a hot plate and carbonize it until there is no smoke, then move it to a preheated muffle furnace and ash it at 550℃ until there is actually no carbon particles (about 5 to 6 hours). 6.2.2 In order to shorten the ashing time or to treat samples that are difficult to burn to be free of carbon particles, high-grade pure nitric acid can be used as an ashing aid. 6.2.3 Take out the ash-treated sample (to prevent the crucible from cracking due to sudden cooling, the muffle furnace can be turned off overnight), add 5 mL of hydrochloric acid (5.2), rinse the walls of the crucible from the top, and then place it on a steam bath or hot plate to evaporate until it is almost dry. 6.2.4 Add 2.0 mL of hydrochloric acid (5.3) to (6.2.3) to dissolve the residue, cover it with blood, and heat it on a steam bath or hot plate for 5 min.
6.2.5 Rinse the surface III with water, then filter the dissolved matter in the glass quantitatively into a 400 mL beaker and dilute to about 150 mL. 6.2.6 Add 8 to 10 drops of bromocresol green indicator (5.6) and sufficient 20% sodium acetate to make the solution blue (the pH value is 4.8 to 5.0 at this time). Cover it with blood and heat it on a steam bath or hot plate until it boils. 6.2.7 Use a dropper to slowly drip in a 3% oxalic acid solution (pH value is 4.4-4.6). If the solution is yellowish green or blue, it will be unfavorable for calcium oxalate precipitation and the result will be low.
6.2.8 Boil the above solution and let it stand for more than 4 hours. Too short a standing time will be unfavorable for the formation of calcium oxalate crystals and may cause the test result to be low.
6.2.9 Filter the upper clear liquid with a porous glass filter (4.3), wash the precipitate and rinse the beaker, repeat 2-3 times, and combine and filter, a total of about 150mL.
6.2.10 Wash the porous glass filter with a sulfuric acid-water mixture (5+125) heated to 80-90℃. 6.3 Titration
6.3.1 Use 0.01mol/L (or other suitable concentration) potassium permanganate standard solution to titrate the filtrate (6.2.10) that has been preheated to 70~90℃ until it turns light pink and maintains for 30s without fading. 6.3.2 Take about 150mL of sulfuric acid-water mixture (5+125) and heat it to 70~90℃, and use potassium permanganate standard solution (same as 6.3.1) to titrate until it turns light pink and maintains for 30s without fading, as the blank value. 7 Calculation
The sample content is expressed in milligrams of calcium per gram of sample. 7.1 Calculation formula
Calcium content in sample (mg/g)-Vo)XM×100W
Where: V-the number of milliliters of potassium permanganate standard solution consumed by the sample, mLV. -————the number of milliliters of potassium permanganate standard solution consumed by the blank, mL. M- molar concentration of potassium permanganate standard solution, mol/L. W- sample weight, g.
100--1 mol/L potassium permanganate solution is equivalent to the number of milligrams of calcium. 7.2 Allowable difference
If the parallel determination results meet the allowable difference requirements, take the average value as the result and keep two decimal places. The allowable difference between two consecutive determination results by the same analyst shall not exceed: 0.15 mg absolute difference when the sample calcium content is greater than 1 mg/g); 432
GB/T14610--93
0.10 mg (absolute difference) when the sample calcium content is less than 1 mg/g. Additional remarks:
This standard was proposed by the Ministry of Commerce of the People's Republic of China. This standard is under the jurisdiction of the Grain Storage and Transportation Bureau of the Ministry of Commerce. This standard was drafted by the Institute of Cereal Oil Chemistry of the Ministry of Commerce. The main drafter of this standard is Lei Ting.
This standard is equivalent to the method AACC40--20 "Determination of Calcium in Bread and Flour" approved by the American Association of Cereal Chemists.
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