ISI 18-1e Determination of Hydroxyethyl Content in Starch



1. Scope The method is applicable to hydroxyethylated starch LT 20.06.1966
Rev. 17.03.1998
2. Principle The hydroxyethyl ether is cleaved in boiling HJ-solution. The ethylene is distilled and titrated.

 
3. Apparatus 3.1 Analytical balance weighing to the nearest 0.1 mg.

3.2 Oil bath, thermostatic

3.3 Distilling apparatus with five collection flasks

 
4. Reagents 4.1 Iodine hydrogen solution (HJ) for alkoxide determination; density 1.70; boiling point 126 -127 oC

4.2 Alcoholic silver nitrate solution: 15.0 g AgNO3 is dissolved in 28 ml distilled water. The solution is poured into 422 ml 95% ethanol. A few drops of concentrated nitric acid are added. 10.00 ml of the solution is titrated with (4.3) and with (4.4) as indicator (according to Vogel). Titre = A. Store solution in brown flask.

4.3 Ammonium thiocyanide 0.05N NH4SCN. Normality = N2

4.4 Ferric sulphate indicator: Nitric acid is added to a saturated solution until the brownish colour disappears.

4.5 Bromine-acetic acid solution: 600 ml conc. acetic acid is saturated with dry KBr (approx. 10 g). 2 ml bromine is added. 15.00 ml is titrated with (4.6). Titre = B. Keep dark and cool in brown tight flask. The solution is stable a couple of days after preparation.

4.6 Na-thiosulphate solution 0.05N Na2S2O3. Normality = N1

4.7 Potassium iodine solution, 10%: 10 g KJ ad 100 ml with distilled water.

4.8 Starch indicator, 1%: 1 g ad 100 ml with distilled water.

4.9 Cadmium sulphate, 5%: 5 g ad 100 ml with distilled water.

4.10 Red phosphorous, amorphous powder.

4.11 Carbon dioxide, dried gas

 
5. Procedure Weigh approximate 1 g (g) water free sample to the nearest mg into the distillation flask and add 40 ml (4.1).
Prepare distillation apparatus (3.3) and fill the flasks:

Washing flask no.1: 0.5 g (4.10) and add (4.9) to 3 cm above inlet tube.

Collection flask no. 2: 10.00 ml (4.2)

Collection flask no. 3. 15.00 ml (4.5)

Collection flask no. 4: 15.00 ml (4.7)

Flask no. 5: 10 ml (4.7) and 150 ml distilled water
Flask and cooler is assembled immediately. Carbon dioxide (4.11) is added one bobble/s

Cleavage

 The distillation flask is heated on oil bath kept at 140 - 145 oC for one hour and heating is stopped.
1. Heat collector no 2 to 40 - 50 oC
2. Open valve no 5 slowly and close CO2 supply
3. Empty collector no 3 and 4 into a 500 ml flask.

Titrate C2H4

 4. Flush with distilled water and titrate immediately with (4.6) and 2 ml (4.8) as indicator. Titre = a.
5. Empty collector 2 into a 500 ml flask with 150 ml distilled water and flush. Heat to boiling and cool.

Titrate C2H5J

 6. Titrate with (4.3) and 3-5 ml (4.4) as indicator. Titre = b.
7. Run a blank with 1 g native starch. Blank on potato starch is approx. 0.2% C2H4O
6. Calculation Calculate ethylene-oxide content of sample dry matter by averaging results of two samples with two decimals.

C2H4O % = x + y - blank, where

x = 2.203 (A-a) N1 / g = C2H4O % distilled as C2H4

y = 4.405 (B-b) N2 / g = C2H4O % distilled as C2H5J

 

 Molecular weight of C2H4O = M = 44.05
7. Reference H. J. Lortz; Anal. Chem. 28, 892 (1956)

 
8. Diagram

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