ISO 11214:1996 - Modified starch: Determination of carboxyl group content of oxidized starch
Overview
ISO 11214:1996 specifies a standardized analytical method to determine the carboxyl group content of oxidized starch (modified starch). The method is a wet-chemical titration procedure that converts carboxylate salts to the acid form, removes interfering ions by washing, gelatinizes the washed starch, and titrates the liberated acid with a standard sodium hydroxide solution. It is suitable for carboxyl contents up to 1% (m/m) and includes a correction for phosphate groups in oxidized potato starch.
Key topics and technical requirements
- Principle: Acidify carboxyl salts (conversion to acid form), wash away cations and excess acid, gelatinize starch, then titrate hot with standardized NaOH using phenolphthalein end point (≈ pH 8.3).
- Reagents and concentrations:
- Hydrochloric acid, 0.1 mol/l
- Sodium hydroxide standard solution, c(NaOH) = 0.1 mol/l (CO2-free)
- Phenolphthalein indicator (1 g/l in ethanol)
- Silver nitrate solution (10 g/l) to test for chloride-free washings
- Sample and preparation:
- Typical test portion: 5 g, ground and homogenized; moisture determined per ISO 1666.
- Convert carboxyl salts with 25 ml 0.1 mol/l HCl (stir 30 min), vacuum filter and wash until no chloride (AgNO3 test), gelatinize in boiling water bath and titrate while hot.
- Calculations and corrections:
- Carboxyl content calculated on a dry matter basis using titrant concentration and volume, test mass and moisture.
- For oxidized potato starch, subtract a phosphate-related correction (3 × phosphorus content, wp) to compensate for phosphate groups.
- The standard cites molecular mass factors used in the correction (carboxyl function MC = 0.045; phosphorus Mp = 0.031).
- Precision:
- Interlaboratory data show repeatability and reproducibility limits (repeatability ≈ 6% of higher result; reproducibility ≈ 16%).
Applications and who uses it
- Routine quality control and specification testing for:
- Food ingredient manufacturers (modified/oxidized starches)
- Starch producers and processors
- Pharmaceutical formulators using starch excipients
- Industrial users (paper, textiles, adhesives) requiring starch modification data
- Useful for product specification, regulatory compliance, and R&D involving oxidized starch properties.
Related standards
- ISO 1666 - Starch: determination of moisture (oven-drying)
- ISO 3696 - Water for laboratory use
- ISO 3946 - Determination of total phosphorus in starches
- ISO 5725-1 / ISO 5725-2 - Precision (trueness, repeatability, reproducibility)
Keywords: ISO 11214, modified starch, oxidized starch, carboxyl group content, titration, starch analysis, analytical method, quality control.