1.
Purpose requirements
(1) Know how to preprocess the sample to be tested according to the type of sample, the physical and chemical properties of the tested component and the selected analysis method
.
(2) Proficiency in basic operations such as weighing and filtering
.
2.
Principles of training
Choose an appropriate solvent (such as water) as the extractant, extract the soluble sugars in the milk powder, and add zinc acetate and potassium ferrocyanide solution as a clarifying agent to purify the extract to eliminate interference substances such as proteins
.
Then the insoluble matter is separated by filtration, and the filtrate is the test solution for direct titration determination of sugar content
.
3.
Training supplies
(1) Analyze the balance
.
(2) Volumetric flask (250mL)
.
(3) Glass funnel
.
(4) Zinc acetate solution (219g/L): 21.
9g zinc acetate, add 3mL glacial acetic acid , add water to dissolve and dilute to 100mL
.
(5) Potassium ferrocyanide solution (106g/L): 10.
6g potassium ferrocyanide , dissolved in water and diluted to 100mL
.
4.
Safety reminder
Inhalation of potassium ferrocyanide can cause coughing and wheezing, pay attention to safe use
.
5.
Operation steps
Weigh 2.
5～5g milk powder sample, accurate to 0.
001g, place it in a 250mL volumetric flask, add 50mL water, slowly add 5mL zinc acetate solution and 5mL potassium ferrocyanide solution, add water to the mark and mix well, Leave it for 30 minutes, filter with dry filter paper, discard the initial filtrate, and take the subsequent filtrate for later use
.
6.
Tips
(1) The mixed solution of zinc acetate and potassium ferrocyanide can react to form zinc ferrochloride precipitate, thereby entraining or adsorbing interfering substances
.
Suitable for clarification of sample liquid with high protein content
.
(2) The amount of clarifying agent should be appropriate
.
Too little dosage will not achieve the purpose of clarification; too much dosage will cause errors in analysis results
.
Related links: Cognition of the basic procedures of food physical and chemical testing (4)
