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International Starch Institute
Science Park Aarhus, Denmark
ISI 03-1e Determination of Sulphated Ash in Starch at 525 oC

1. Scope The method is applicable to native, modified and hydrolysed starch.

 

LT 12. Dec. 1966
Rev. LT 21. Nov. 1997
2. Principle Incineration of starch sample at 525 oC in the presence of sulphuric acid

 

3. Reagents 3.1 Sulphuric acid solution

Add 100 ml of concentrated sulphuric acid to 300 ml of distilled water.

Pour and mix carefully - use eye protection
3.2 Hydrochloric acid solution

Add 100 ml of concentrated hydrochloric acid to 500 ml distilled water

 

Pour and mix carefully - use eye protection
4. Apparatus 4.1 Analytical balance weighing to the nearest 0.1 mg.
4.2 Ashing dish of platinum or quarts
4.3 Electrically heated furnace.
4.4 Desiccator with dry drying agent
4.5 Bunsen burner
4.5 Water bath

 

5. Procedure Careful clean the ashing dish (4.2) and calcinate it 1/2 hour in furnace (4.3) at 525 oC.
Cool dish in desiccator (4.4) to room temperature and weigh on balance (4.1) to nearest 0.1 mg. Weight = w0 Clean always new dish in boiling HCl (3.2) and rinse in water
A sample of starch syrup may conveniently be dissolved in distilled water on a water bath (4.5) by 60 - 70 oC. The solution is allowed to cool to room temperature. An aliquot is used as test portion in stead of the sample itself.
Place 10 g of sample or an aliquot portion of a dissolved sample in ashing dish. Weigh on balance (4.1) to nearest 1 mg. Weight = w1 Take 2 g if ash >10% and 5 g if ash > 5%
Mix sample with 5 ml sulphuric acid solution (3.1). Rinse stirring rod with little water. Collect rinsing in ashing dish.
Incinerate the sample on a Bunsen burner (4.5) or equivalent until completely carbonised. Possibly pre-evaporate on hot plate or equivalent
Finish incineration in the furnace (4.3) at 525 oC until residual carbon has disappeared.

Cool. Moisten ash with several drops of sulphuric acid solution (3.1). Evaporate and incinerate again for 1/2 hour.

Incinerate 2 hours
Cool in desiccator to room temperature. Weigh immediately after removal from desiccator to nearest 0.1 mg. Weight=w2

 

6. Calculation Sulphated ash in percent of sample as is (average two results to the second decimal) =

Ash % = 100 x (w2 - w0) / (w1 - w0)

 

Correct eventually to dry basis
7 Notes Sulphuric acid facilitates ashing (wet combustion) and convert volatile chlorides into non-volatile sulphates.
Consider ash determination in hydrolysates by conductivity; ref: G. Tegge & G. Richter, Starch, 38 (1986) no. 4, 137-142)

 

8. Reference International standard: ISO 5809

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Keywords: laboratory,method,determination,sulphated,ash,starch