QB/T 2186-1995 Determination of nitrogen content in hydrolyzed protein solution by ammonia sensitive electrode method

This standard specifies the method for determining nitrogen content by ammonia sensitive electrode method. The minimum detection concentration of this method is 0.00001 mol/L. This standard is applicable to the determination of nitrogen content in hydrolyzed protein solution. QB/T 2186-1995 Determination of nitrogen content in hydrolyzed protein solution by ammonia sensitive electrode method QB/T2186-1995 Standard download decompression password: www.bzxz.net

Light Industry Standard of the People's Republic of China
Determination of nitrogen content in hydrolyzed protein solution by ammonia sensitive electrode method Subject content and scope of application
QB/T 2186—1995
This standard specifies the method for determining nitrogen content by ammonia sensitive electrode method. The minimum detection concentration of this method is 0.00001 mol/L. This standard is applicable to the determination of nitrogen content in hydrolyzed protein solution. 2 Method Summary
The hydrolyzed protein solution is decomposed with potassium sulfate and copper sulfate in sulfuric acid solution to convert nitrogen in organic compounds into ammonia. In alkaline solution, the released ammonia is determined by an ammonia sensitive electrode. 3 Reagents
Analytical pure reagents should be used in the analysis, and the test water should be redistilled water or deionized water. 3.1 Sodium hydroxide (GB/T629) 11 mol/L. 3.2 Concentrated sulfuric acid (GB/T 625).
3.3 Copper sulfate (GB/T665).
3.4 ​​Potassium sulfate (HG/T3-920).
3.5 Sodium chloride (GB/T1266).
3.6 Potassium nitrate (GB/T647) 0.1mol/L. 3.7 Ammonium fluoride standard solutionbzxZ.net
Weigh 1.337g of high-grade pure ammonium chloride (GB/T658) and dissolve it in water. Make up to 250mL with water. This solution is 0.1mol/L ammonium chloride solution.
3.7.1 Transfer 25ml of the above ammonium chloride solution (3.7) to a 250mL volumetric flask and dilute to the mark with water. This solution is 0.01mol/L ammonium chloride solution.
3.7.2 Transfer 25mL of the above ammonium chloride solution (3.7.1) to a 250mL volumetric flask and dilute to the mark with water. This solution is 0.001mol/L ammonium chloride solution.
3.7.3 Transfer 25mL of the above ammonium fluoride solution (3.7.2) to a 250mL volumetric flask and dilute to the mark with water. This solution is a 0.0001mol/L ammonium chloride solution.
3.7.4 Transfer 25mL of the above ammonium nitride solution (3.7.3) to a 250mL volumetric flask and dilute to the mark with water. This solution is a 0.00001mol/L ammonium fluoride solution.
3.8 Electrode filling solution
Weigh 0.534g of ammonium chloride and 5.844g of sodium chloride and mix them in water. Make up to 1000mL with water. 4 Instruments
4.1 Ion activity meter, including composite PNH3-1 nitrogen sensitive electrode and saturated calomel electrode. 4.2 Magnetic stirrer.
4.3 Volumetric flask: 100ml..250mL, 1000mL. Approved by China Light Industry General Association on December 5, 1995
Implemented on July 1, 1996
4.4 Beaker: 100mL.
QB/T2186—1995
4.5 Pipette: 25mL, 1.5mL, 1mL, 0.1mL. 4.6 Analytical balance: accuracy ±0.0002g. 5 Analysis steps
5.1 Sample pretreatment
Accurately weigh about 0.1 g of hydrolyzed protein solution or 0.1 mL into a nitrogen determination bottle, add 2 g potassium sulfate, 0.2 g copper sulfate, 20 mL concentrated sulfuric acid, heat from low temperature to high temperature to digest, when the solution gradually turns from black to transparent, continue heating for 5 to 10 minutes, cool, transfer the contents to a 100 mL volumetric flask, dilute to 100 ml with water, shake well, and wait for measurement. 5.2 Determination
5.2.1 Instrument preparation
Connect the ion activity meter to the power supply, preheat for 30 minutes, remove the millivolt key of the selector switch, adjust the zero point (make the digital display stable ± 0.000mV), press the nitrogen sensitive electrode, and wash the electrode with water until the millivolt number is lower than -20mV. 5.2.2 Determination steps
Pipette 1 mL of the digestion solution to be tested into a 100 mL beaker, start the magnetic stirrer to stir, add 50 mL of 0.1 mal/L potassium nitrate and 1.5 mL of 11 mol/L sodium hydroxide solution, immediately insert the ammonia sensitive electrode, remove the measurement key, read the stable potential value E (mV), release the measurement key, wash for several minutes until the millivolt number drops below 20mV, then take out the electrode, use absorbent paper to absorb the moisture on the electrode surface, and then measure another sample.
5.2.3 Drawing of standard curve
Pipette 1mL of standard series concentrations of ammonium chloride 0.00001, 0.0001, 0.001, 0.010.1mol/L, measure from low concentration to high concentration according to the measurement steps, read the stable potential value (mV), and draw a graph on semi-logarithmic paper with the potential value as the ordinate and the concentration of 1gNH+ standard solution c (mol/L) as the abscissa. 5.3 Calculation of analysis results
Where: N—nitrogen content,%,
N=14:×100
~According to the potential value of the sample, the sample concentration is obtained from the standard curve, mol/L; G-sampling amount, g;
14.00—molar mass number of nitrogen, g/mol. 6 Allowable difference
The difference between the results of two parallel measurements should not be greater than 0.35. Additional Notes:
This standard was proposed by the Quality Standards Department of China Light Industry Association. This standard is under the jurisdiction of the National Cosmetics Standardization Center. This standard was drafted by the Shanghai Daily Chemical Industry Research Institute. The main drafters of this standard are Lin Yan, Jiang Huimin and Hu Yin.
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