Overview
EN ISO 11215:1998 specifies a validated gas‑chromatographic method to determine the total and free adipic acid content of acetylated di‑starch adipates (modified starch). The method is intended for laboratories performing quality control and regulatory testing of starch derivatives used in food and industrial applications. The procedure uses silylation and capillary GC with an internal standard (pimelic acid) to achieve reliable quantification.
Key Topics
- Scope and principle: Hydrolysis of adipyl linkages with NaOH releases adipic acid from the starch matrix. After acidification, adipic acid is extracted into ethyl acetate, concentrated, silylated (BSTFA + 1% TMCS) and analysed by GC with flame ionization detection.
- Reagents and reference materials: water (ISO 3696 grade), waxy maize starch as base material, adipic acid and pimelic acid standard solutions (50 mg/l), NaOH (4 mol/l), concentrated HCl, ethyl acetate, acetonitrile, BSTFA/TMCS, and carrier gases (He, H2, N2, air).
- Apparatus: capillary GC with FID and on‑column injection, ultrasonic bath, centrifuge, rotary shaker, nitrogen evaporation device and standard lab glassware.
- Calibration and quantification: Use calibration tubes containing known adipic acid masses added to waxy maize starch and pimelic acid as the internal standard. Plot adipic/pimelic peak area ratios vs. mass to derive the calibration curve and determine sample adipic content.
- Precision: The standard includes interlaboratory precision data. Example values from the collaborative trial: for a mean total adipic acid content of about 430 mg/kg, repeatability standard deviation s(r) = 22 mg/kg and reproducibility limit R = 142 mg/kg.
Applications
- Routine quality control of modified starch (acetylated di‑starch adipates) in food ingredient manufacturing and ingredient supply chains.
- Verification of free vs. bound adipic acid to assess hydrolysis, storage stability, or processing effects.
- Regulatory compliance testing where quantification of residual adipic acid is required for safety and labelling.
Practical value: The method provides a clear analytical workflow - extraction, concentration, silylation and GC - using commonly available reagents and instrumentation. The internal standard approach (pimelic acid) improves accuracy and compensates for extraction/derivatisation variability.
Related Standards
- ISO 1666:1996 - Starch - Determination of moisture content (oven‑drying method).
- ISO 3696:1987 - Water for analytical laboratory use - Specification and test methods.
- ISO 5725 - Precision of measurement methods (referenced for interlaboratory statistics).
For laboratories implementing EN ISO 11215:1998, following the described sample preparation, calibration and reporting requirements ensures reproducible, traceable results for adipic acid analysis in modified starch products.