Overview
ISO 11215:1998 specifies a validated gas chromatographic (GC) method for measuring adipic acid in modified starch products - specifically acetylated di‑starch adipates. The standard covers determination of total adipic content and free adipic acid using extraction, silylation and capillary‑column GC with an internal standard. Annexes provide typical chromatographic conditions, a sample chromatogram and interlaboratory precision data.
Key topics and technical requirements
- Scope: Quantitative determination of total and free adipic acid in acetylated di‑starch adipates.
- Analytical principle: Hydrolysis (for bound adipate), acidification, extraction with ethyl acetate, evaporation, derivatization by silylation (BSTFA + 1 % TMCS), and GC analysis using a capillary column and flame ionization detector.
- Internal standard: Pimelic acid is used to correct for extraction and injection variability.
- Reagents & gases: Specifies analytical‑grade reagents (NaOH 4 mol/L, conc. HCl, ethyl acetate, acetonitrile) and carrier/detector gases (He, H2, air, N2).
- Sample prep: Sieving (800 μm), grinding if required, dispersion, controlled hydrolysis or washing for free acid, centrifugation, and concentration of extracts.
- Calibration & quantification: Matrix‑matched calibration using waxy maize starch spiked with known adipic acid masses; construct adipic/pimelic peak‑area ratio calibration curve and derive μg adipic acid per test portion.
- Results calculation: Express results as mg/kg dry weight with moisture correction (moisture per ISO 1666). Bound adipic = total − free.
- Precision: Annex C reports repeatability (r) and reproducibility (R) values from an interlaboratory study (example mean total adipic results: 90–659 mg/kg; reported r and R ranges provided).
Applications and users
This standard is intended for:
- Quality control laboratories in the starch and food ingredient industries.
- R&D teams assessing cross‑linking/adipate content in modified starch formulations.
- Contract testing and regulatory labs performing compositional verification or safety assessments.
Practical uses include ensuring product specification compliance, monitoring manufacturing processes (degree of cross‑linking), and providing traceable analytical data for suppliers and customers.
Related standards
- ISO 1666:1996 - moisture determination (oven‑drying) - used for dry‑weight correction.
- ISO 3696:1987 - water for analytical laboratory use.
- ISO 5725 (referenced) - precision of measurement methods (interlaboratory statistics).
Keywords: ISO 11215:1998, modified starch, acetylated di‑starch adipates, adipic acid determination, gas chromatographic method, GC, silylation, BSTFA, pimelic acid, quality control.