The acidity of starch and its derivatives can be determined by acid-base titration. Specific steps are as follows:
Take a starch sample of a certain quality and add an appropriate amount of deionized water to make a uniform starch slurry.
Take a certain volume of starch slurry and add phenolphthalein indicator.
Use 0.1 mol/L NaOH standard solution, slowly add it dropwise into the starch slurry, while stirring and mixing until the solution changes from light red to obvious bright red, record the volume V1 of NaOH standard solution used.
Take another group of starch samples, and measure it according to the above method, but add dilute hydrochloric acid or other acids before titration, and adjust the pH value to about 3.5. Titrate to bright red, record the volume V2 of NaOH standard solution used.
Acidity value (mg KOH/g) = (V1 - V2) × N × 56.1 / m
Among them, N is the regular concentration of NaOH standard solution in mol/L; m is the sampling mass in g; 56.1 is the molecular weight of KOH.
NBCHAO reminds you: When measuring the acidity of starch samples, you should ensure that the solubility of the starch samples is sufficient, and at the same time pay attention to removing impurities and particles to avoid errors.
