ISI 15-1e Determination of Aldehyde Groups in Starch

ISI 15-1e Determination of Aldehyde Groups in Starch

1. ScopeThe method is applicable to oxidised starch

 

2. PrincipleFree sulphur dioxide is determined in a mixture of starch and sodiumbisulphite with and without an alkaline treatment. The difference is the aldehyde bound sulphur dioxide.

 

LT 30 Nov 1964
Rev. LT 03 Sep 1999
3. Apparatus3.1 Analytical balance weighing to the nearest 0.1 mg.
3.2 Conical flask 1000 ml
3.3 Burette 25 ml

 

4. Reagents4.1 Sodium bisulphite: 4 g NaHSO3 is dissolved in water. Make up to 1000 ml with water.
4.2 Sodium thiosulphate 0.1N
4.3 Iodine 0.1N
4.4 Hydrochloric acid 1 N
4.5 Sodium hydroxide 0.1 N
4.6 Sodium thiosulphate 0.02N: 20.0 ml (4.2) Sodium thiosulphate 0.1N diluted to 100 ml with distilled water. Keep one day only.
4.7 Iodine 0.02N: 20.0 ml (4.3) Iodine 0.1N diluted to 100 ml with distilled water. Keep one day only.

 

5. ProcedureWeigh 15 g (w) sample to the nearest 0.1 mg in a 1000 ml conical flask

 Gelatinising

Add 550 ml distilled water and gelatinise by heating

 Solution A

Cool to room temperature. Add 25 ml (4.1) Sodium bisulphite and make up with distilled water to 600 g. Mix well and let rest for 30 minutes. Label as "Solution A".

Determination of free SO2

Add to a 1000 ml conical flask 20.0 ml (4.7) Iodine 0.02N and 15 ml (4.4) Hydrochloric acid 1 N and 100 g "Solution A" and 300 ml distilled water. Titrate excess iodine with (4.6) Sodium thiosulphate 0.02N. Titer = (b) ml

Determination of free and aldehyde bound SO2

Add to a 1000 ml conical flask 100 g "Solution A" and 25 ml (4.5) Sodium hydroxide. Mix and let rest for 15 minutes. Add 20.0 ml (4.7) Iodine 0.02N and 40 ml (4.4) Hydrochloric acid 1 N and  and 300 ml distilled water. Titrate excess iodine with (4.6) Sodium thiosulphate 0.02N. Titer = (c) ml

 

6. CalculationCalculate aldehyd groups of sample by averaging results of two samples with two significant digits.

meqv (milli-equivalent) Aldehyde groups per 100 g starch dry matter = (b-c )*Nthio*100 / F; where

w = sample weight, g
a = starch dry matter g/100 g
F = Dry matter of "Solution A" = w*a/600
b =  ml thiosulphate used to titrate free SO2
c =  ml thiosulphate used to titrate free and Aldehyde bound SO2
Nthio =  Normality of (4.6) Sodium thiosulphate 0.02N

 

7. ReferenceDie Stärke 15, 217 (1963)

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