| Home | Profile | Market Place | Sweeteners | Lab Methods | Glossary | Search |
| Master Index | Environment | Application | Starch | Statistics | Tables | Write us |
International Starch Institute
Science Park Aarhus, Denmark
ISI 10-2e Determination of Carboxyl Groups in Starch
| 1. Scope | The method is applicable to oxidised starch | LT 18. Dec. 1964 Rev. LT 15. marts 1998 |
| 2. Principle | Carboxyl groups are titrated by the Paste Titration Method
|
|
| 3. Apparatus | 3.1 Analytical balance weighing to the nearest 0.1 mg. 3.2 Shaking boiling water bath. 3.3 Büchner funnel 55 mm |
|
| 4. Reagents | 4.1 Hydrochloric acid 0.1 N 4.2 Sodium hydroxide 0.1 N 4.3 Phenolphthalein: 1 g in 1 litre ethanol 90% 4.4 Silver nitrate, 0.1%
|
|
| 5. Procedure | Weigh 5 g (w) sample to the nearest 0.1 mg in a 100 ml beaker | |
Conversion |
Add 25 ml hydrochloric acid (4.1) and stir for 1/2 hour. | Use magnetic stirrer |
Washing |
Filter on filter (3.3) or glass crucible. Flush beaker and filter with water until filtrate is free of chloride - test with silver nitrate (4.4) | Increase hydrolysis parameters if flux too low |
Gelatinising |
Slurry filter cake with 300 ml distilled water in beaker. Place beaker in boiling water bath (3.2) for 15 min. | Stir |
Titration |
Titrate with (4.2) and (4.3) while still hot. V = ml (4.2). N = normality of (4.2)
|
To pH 8.3 |
| 6. Calculation | Calculate carboxyl content of sample by averaging results of two samples
with two decimals. COOH % = (100 N V M ) / (1000 w) - c Degree of Substitution (DS) = 0.036 x COOH% |
Molecular weight of COOH = M = 45 c corrects for lipids and P - see notes |
| Eventually correct to value on sample dry matter.
|
||
| 7. Notes | c = approx. 0.1% on dry basis for maize and wheat starch. c = 0 for wheat and maize starch defatted by Soxhlet extraction |
Correction for lipids |
| c = 3p for potato starch, where p = phosphorous as P %
|
p ~ 0.03 - 0.09% | |
| 8. Reference | ISO 11214 |
| Top of Page | LabIndex |
Copyright© 1999. Read Disclaimer notice.
All rights reserved. International Starch Institute, Science Park Aarhus, Denmark.
Keywords: laboratory,method,determination,carboxyl,COOH group,oxidised,starch