Overview
ISO 11216:1998 specifies a laboratory method for the determination of the content of carboxymethyl groups in carboxymethyl starch (a type of modified starch). The procedure is suitable for carboxymethyl group contents between 1.6 % (m/m) and 10.0 % (m/m). The standard is intended for use in analytical and quality-control testing of carboxymethyl starch used across food, pharmaceutical, paper and other industries.
Key topics and requirements
- Analytical principle: conversion of carboxymethyl salts to the acid form by acidification, precipitation of starch with methanol, drying and reaction of a weighed dry portion with excess NaOH, then back-titration of unused NaOH with dilute HCl.
- Scope of measurement: reliable for 1.6–10.0 % (m/m) carboxymethyl content.
- Reagents & concentrations:
- Methanol (100 %)
- Hydrochloric acid for conversion, c(HCl) = 4 mol/L
- Sodium hydroxide for titration, c(NaOH) = 0.10 mol/L
- Dilute hydrochloric acid for back-titration, c(HCl) = 0.10 mol/L
- Phenolphthalein indicator; carbon dioxide–free water (ISO 3696 grade)
- Apparatus: pH meter, explosion-proof mechanical stirrer, sintered glass crucible (porosity P40), drying oven (40 °C ± 2 °C), magnetic stirrer, mortar and sieve/mill for sample prep.
- Safety: emphasizes methanol toxicity and flammability-work in explosion‑proof fume cupboards and observe waste disposal rules.
- Calculations: carboxymethyl group content is computed from titration volumes, reagent concentrations and sample mass using the molar mass of the carboxymethyl function (58 g·mol−1). Degree of substitution (moles carboxymethyl per mole anhydroglucose) can be derived using anhydroglucose molar mass (162 g·mol−1).
- Precision: interlaboratory data (14 labs) provided. Repeatability relative SD typically 0.7–2.8 %; reproducibility relative SD typically 4.6–8.4 %. Absolute repeatability and reproducibility limits are reported in Annex A.
Applications and users
Who uses ISO 11216:
- Quality control and analytical laboratories in starch and food ingredient manufacturers
- R&D and product development teams working on modified starches
- Regulatory and conformity testing labs assessing product composition
- Suppliers of starch derivatives for pharmaceuticals, paper, textiles and food where carboxymethyl substitution affects functionality (viscosity, solubility, stability)
Practical benefits:
- Provides a standardized, reproducible titrimetric method for composition control
- Enables comparison across suppliers and batches for product specification and compliance
Related standards
- ISO 1666 - Starch: determination of moisture content (oven-drying)
- ISO 3696 - Water for analytical laboratory use (specification)
- ISO 5725 - Precision of test methods (used for interlaboratory statistics)
Keywords: ISO 11216, carboxymethyl starch, modified starch, carboxymethyl groups, titration method, analytical method, quality control, starch industry.