The Kjeldahl method is currently the standard method for measuring crude protein content in food, oil, feed, etc. The amount of nitrogen in the sample is first determined and multiplied by the protein conversion factor. In the determination process, the standard substance with known nitrogen content needs to be used as a control experiment. Frequently, anhydrous sulfuric acid is used. The nitrogen content is 21.19%, but due to the presence of systematic errors, the measured value and the actual nitrogen content are always There must be some error. After years of experimentation and comparison, calculating the nitrogen recovery rate and combining it with protein determination and calculation can effectively solve this problem. The protein analyzer is also the main instrument for the determination of protein content and can be very accurate.
First of all, according to the provisions of national standards, weigh 0.2g of sulfuric acid according to the only true to O.OOOlg) according to the determination of crude protein steps as a control experiment, the following formula to calculate the nitrogen content: N%) = c spine, one:} x14x Total x100................. 1} where: N - measured nitrogen content, %; vi - volume of hydrochloric acid solution when titrating the sample solution, ml;:. ―The blank test consumes the volume of the hydrochloric acid solution, ml; the concentration of the hydrochloric acid solution, mol/1; the volume of the sulfuric acid according to the volume after dissolution, ml:'—the volume of the sulfuric acid that is absorbed by the distillation, the volume of the solution; ml; The mass, mgo, is then calculated according to the following formula: R% = 21.19x100%, and 2) is transformed into: NR% = 21.19. From formula 3, it can be derived: 1 i) The measured value is corrected with the recovery rate. , you can get the actual value. Based on this point of view, dividing both sides by R% simultaneously has: NR% (one, x14xv, xv, half R%=21.19, 4) where:. - The concentration of hydrochloric acid solution to be calibrated; R% - the recovery rate to be measured.
In the entire protein analyzer test process, if the same set of Kjeldahl apparatus is used and the same operating conditions are maintained, and the same batch of hydrochloric acid solution is used, it can be considered that the two “% remain unchanged,†because “匕 can take cR%. As a constant k, in this case, 4) can be expressed as: k(v}-.) x14xv, xv-half = 21.19 Where: v, Iv} IvIv'1, both known or known in the experiment Therefore, you only need to find the value of k. Substituting k into the crude protein formula, the crude protein formula is: crude protein permaphrase, %)=k(v)-vo)x14xPx in x10000, and w(100-M) where the experiment is used. Hydrochloric acid solution volume, ml; volume of hydrochloric acid solution used for blank test, ml;: volume of sample after digestion, ml:'-distilled volume of diluted digestate, mlP-protein conversion factor; ―Sample weight, mg; M―Moisture percentage of sample, %.
According to the results of protein assay, it can be concluded that combining the recovery rate with the determination of protein can minimize the system error, and that the concentration of the hydrochloric acid solution does not need to be calibrated. Therefore, the entire assay process is more simple and convenient. more acurrate.
First of all, according to the provisions of national standards, weigh 0.2g of sulfuric acid according to the only true to O.OOOlg) according to the determination of crude protein steps as a control experiment, the following formula to calculate the nitrogen content: N%) = c spine, one:} x14x Total x100................. 1} where: N - measured nitrogen content, %; vi - volume of hydrochloric acid solution when titrating the sample solution, ml;:. ―The blank test consumes the volume of the hydrochloric acid solution, ml; the concentration of the hydrochloric acid solution, mol/1; the volume of the sulfuric acid according to the volume after dissolution, ml:'—the volume of the sulfuric acid that is absorbed by the distillation, the volume of the solution; ml; The mass, mgo, is then calculated according to the following formula: R% = 21.19x100%, and 2) is transformed into: NR% = 21.19. From formula 3, it can be derived: 1 i) The measured value is corrected with the recovery rate. , you can get the actual value. Based on this point of view, dividing both sides by R% simultaneously has: NR% (one, x14xv, xv, half R%=21.19, 4) where:. - The concentration of hydrochloric acid solution to be calibrated; R% - the recovery rate to be measured.
In the entire protein analyzer test process, if the same set of Kjeldahl apparatus is used and the same operating conditions are maintained, and the same batch of hydrochloric acid solution is used, it can be considered that the two “% remain unchanged,†because “匕 can take cR%. As a constant k, in this case, 4) can be expressed as: k(v}-.) x14xv, xv-half = 21.19 Where: v, Iv} IvIv'1, both known or known in the experiment Therefore, you only need to find the value of k. Substituting k into the crude protein formula, the crude protein formula is: crude protein permaphrase, %)=k(v)-vo)x14xPx in x10000, and w(100-M) where the experiment is used. Hydrochloric acid solution volume, ml; volume of hydrochloric acid solution used for blank test, ml;: volume of sample after digestion, ml:'-distilled volume of diluted digestate, mlP-protein conversion factor; ―Sample weight, mg; M―Moisture percentage of sample, %.
According to the results of protein assay, it can be concluded that combining the recovery rate with the determination of protein can minimize the system error, and that the concentration of the hydrochloric acid solution does not need to be calibrated. Therefore, the entire assay process is more simple and convenient. more acurrate.
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