Overview
EN ISO 11216:1998 (ISO 11216:1998) specifies a standardized analytical method for determining the content of carboxymethyl groups in carboxymethyl starch (CMS). The method is suitable for CMS contents between 1.6 % and 10.0 % (m/m). It establishes a wet-chemistry titrimetric procedure that converts carboxymethyl salts to the acid form, isolates the starch, and quantifies the carboxymethyl groups by base consumption and back-titration.
Key topics and technical requirements
- Scope and definition: Defines carboxymethyl group content as the mass of carboxymethyl groups (acid form) per mass of test portion (expressed % m/m).
- Analytical principle: Acidify a starch suspension to convert salts to the acid form, precipitate the starch with methanol, wash and dry, then react a weighed dry portion with excess NaOH and back-titrate the unused NaOH with HCl.
- Reagents & concentrations: Examples in the standard include HCl c = 4 mol·L−1 for conversion and dilute HCl c = 0.1 mol·L−1 for titration; NaOH c = 0.10 mol·L−1 for neutralization; methanol (100 %) for precipitation.
- Critical apparatus & conditions: pH meter, explosion-proof stirrers and ovens, sintered-glass crucibles (porosity P40), drying at 40 °C ± 2 °C; carry out work in an explosion-proof fume cupboard due to methanol use.
- Endpoints & alternatives: Phenolphthalein indicator titration to colourless or potentiometric titration with pH 9.0 endpoint.
- Calculation: Formulae are provided to compute carboxymethyl group content and to convert content to degree of carboxymethyl substitution (DS) (moles per anhydroglucose unit).
- Precision: Interlaboratory data are given. Repeatability relative standard deviations range roughly from ~0.7 % to ~2.8 %; reproducibility relative SDs are approximately 4.6 % to 8.4 % depending on CMS level (see annex A for details).
Applications and users
- Who uses it: QC laboratories, starch and modified-starch manufacturers, food ingredient suppliers, paper and textile formulators, and pharmaceutical excipient producers.
- Practical uses:
- Product specification and batch release testing for carboxymethyl starch.
- Quality control during synthesis and modification of starch (monitoring degree of substitution).
- Regulatory compliance and supplier verification for functional additives (thickeners, binders, stabilizers).
- R&D for formulation development where CMS functionality depends on substitution level.
Related standards
- ISO 1666:1996 - Starch - Determination of moisture content (used for moisture correction in results).
- ISO 3696:1987 - Water for analytical laboratory use (water quality requirements).
- ISO 5725 (referenced) - Precision of measurement methods (basis for interlaboratory precision analysis).
Keywords: EN ISO 11216:1998, ISO 11216:1998, carboxymethyl starch, modified starch testing, determination of carboxymethyl groups, titration method, degree of substitution, starch quality control.