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Starch contained in a fabric is hydrolyzed with acid to generate glucose. The reducing power of the glucose is applied to determining starch amount based on Kjeldahl Bertrand method. The reducing power of glucose converts copper present in the Fehling's solution into copper suboxide. This reaction is utilized for the determination.
69.3g of CuSO4,H2O is dissolved into water, and filtered. The filtered solution is placed in a 1L measuring flask and filled up to a marked line.
346g of NaKC4H4O6,6H2O is dissolved into 500cc of water. Aside from this, 103.3g of NaOH is dissolved into 300cc of water. These two solutions are mixed and filtered. The filtered mixed solution is placed in a 1L measuring flask and filled up to a marked line.
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Fe2(SO4)3(NH4)2SO4,24H2O) solution
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100g of Fe2(SO4)3(NH4)2SO4,24H2O) is dissolved into water, and 200g of concentrated sulfuric acid is added thereto. After mixed and cooled down, the solution is filtered with a glass filter. The filtered solution is placed in a 1L measuring flask and filled up to a marked line.
A commercial product is used.
Cu2O+Fe2(SO4)3 +H2SO4 = 2CuSO4+2FeSO4+H2O
10FeSO4+2KMnO4+8H2SO4 = K2SO4+2MnSO4+5Fe2(SO4)3+8H2O
Dry an approximately 10×10cm sample fabric at 100°C for 30min, and then weigh the sample fabric precisely. Next, place the sample fabric in a 100cc test tube, and add 50cc of dilute sulfuric acid (concentrated sulfuric acid 2.5cc/100cc) into the test tube, so that the sample fabric is completely dipped therein. Connect a glass tube having an outer diameter of 6 to 8mm and the length of 1m to the opening of the test tube. Heat the test tube in a boiling bath for 2 hours. After a predetermined time passes, take the test tube out of the bath, and cool it down immediately. Grind the sample fabric uniformly using a glass rod, and then add approximately 18cc of the NaOH solution 100g/L for neutralization. Make the solution quantity precisely 100cc, and filter the solution into a filtering container using a dry filter paper. Next, add 10cc each of the Fehling's reagent A and the Fehling's reagent B into a 100cc test tube, and then add 20cc of the sample solution to the test tube. Heat the test tube precisely for 10 minutes in a boiling water bath. Cool down the test tube immediately, and filter the solution with a glass filter 3G-4. When the copper ion color in the filtered solution disappears, rinse the sample fabric twice with cold water. The filtered solution and the rinsing water are drained. For the red precipitation of copper suboxide, dissolve 20cc of the ferric sulfate ammoniacal solution, and filter the solution. Titrate the filtered solution using a potassium manganate solution. The sulfuric acid degradation leads to hydrolysis of some fibrins. Therefore, a fabric showing no iodine coloration, whose starch has been completely desized using PAS-600, needs to be prepared as a blank fabric, and the same test should be conducted to obtain the amount of glucose contained in the blank fabric. The obtained amount needs to be subtracted. To calculate the desizing ratio, the same test needs to be performed on an original fabric which is not desized. The desizing ratio can be obtained using these three measurement values.
- The consumption amount of potassium permanganate is multiplied by a factor of the N/10 potassium permanganate solution.
- Since 1cc of the N/10 potassium permanganate solution corresponds to 6.35mg of copper, the value resulting from 1) is multiplied by 6.35mg, to obtain the amount (mg) of copper.
- The amount (mg) of glucose is obtained by referring to the table below. The table below always needs to be referred to, since the amount of copper does not have a direct relation to the amount of glucose.
- The obtained amount of glucose is multiplied by 0.9, to convert it into the amount of starch.
- To convert the resulting value into the amount of starch contained in the entire liquid, it is multiplied by 5, and furthermore, divided by the weight of the collected sample fabric, to obtain the amount of starch per 1g sample fabric.
Note:
- Fehling's reagents A and B need to be stored separately, and mixed when used.
- During filtering, the solution should be kept away from air to prevent oxidization of copper suboxide.
- As a value of the blank, not the consumption amount of potassium permanganate or the amount of copper, but the amount of glucose needs to be subtracted.
- When the measured amount of copper is smaller or larger than values given in the table below, the amount of the sample solution should be adjusted and re-analyzed until the amount of copper falls within the table below. The values in the table should not be multiplied or divided in any case.
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