How to use the Kjeldahl tester to test the total nitrogen content in fishmeal - Master's thesis - Dissertation

Kaixin micro test

Test - lowercase jpg

Test probe P100-M3

1 How to use Kjeldahl nitrogen analyzer to test the total nitrogen content in fish meal, using Kjeldahl nitrogen analyzer Shanghai Qihong NKB3100; XTG5200 carbon fiber digestion instrument; one ten thousand electronic balance;

Kjeldahl nitrogen analyzer NKB3100

Concentrated sulfuric acid (98%); catalyst tablets (copper sulfate and potassium sulfate); 40% sodium hydroxide; 2% boric acid; 0.1008 hydrochloric acid standard titration solution; methyl red-bromocresol green mixed indicator;

Kjeldahl NKB is widely used in food, beverage, soil, feed, food and other fields. NKB3100 Nitrogen Analyzer is an intelligent nitrogen and protein content analysis instrument. It adopts built-in computer control to automate the distillation process. The large screen touches the setting parameters. It only needs to be gently pushed to the nitrifying tube handle, and the safety handle nitrification tube. Placed in the working part, close the acrylic safety door, automatically add water, add alkali and distillation, automatically shut down and beep after the work is completed.

The instrument is not only highly intelligent, the design is rigorous, the material selection is strict, the test recovery rate is high, and it conforms to international/national standards. It is widely welcomed by laboratory personnel because of its fast test speed, stable and reliable operation, and suitable for large sample volume continuous work.

1.2 method

1.2.1 Principle: After the sample is digested, it is heated and distilled in an alkaline solution, and the ammonia is freely distilled out, absorbed by the boric acid solution, and then titrated with a hydrochloric acid standard solution and calculated.

1.2.2 Sampling: The balance was weighed into the digestive tract with a tens of thousands of analytical scales, and one catalyst piece and 8 ml of concentrated sulfuric acid were added to each digestive tube. At the same time do blank.

1.2.3 Digestion: The curve heating parameters are as follows:

Numbering

Temperature (°C)

Time (min)

1

200

5

2

350

10

3

420

90

1.2.4 Distillation titration: Select the distillation mode while distilling, add 15ml of dilution water, 30ml of boric acid, 40ml of 40% sodium hydroxide, and distill for 5min.

2 results discussion

The total nitrogen content of the sample is calculated as follows:

Where: X1 - the total nitrogen content of the sample (in terms of nitrogen), g / 100g;

V2-titration sample consumes 0.1mol/L hydrochloric acid standard titration solution volume, mL;

V1-blank test consumes 0.1mol/L hydrochloric acid standard titration solution volume, mL;

C1-hydrochloric acid standard titration solution concentration, mol / L;

The concentration of 0.014-1.00 mL is [c(HCL)=1.00 mol/L]. The standard titration solution of hydrochloric acid can titrate 0.014 g of N.

Numbering

1

2

3

4

5

Fishmeal weight (g)

0.2021

0.2003

0.1995

0.2011

0.1999

Nitrogen content%

68.16

68.16

68.21

68.18

68.19

Remarks: Remarks: The standard requires more than five parallel samples, and the relative standard deviation of five consecutive results is within 0.5%. The test results meet the requirements.