ISO 11543:2000

Overview

ISO 11543:2000 specifies a proton NMR (1H NMR) spectrometric method to determine the hydroxypropyl content of granular modified starch. The method quantifies the hydroxypropyl substitution by measuring the methyl proton signal of the hydroxypropyl group relative to an internal standard (TSPSA) after partial hydrolysis and dissolution in deuterated solvent. Results are reported on a dry-mass basis to the nearest 0.1% (by mass).

Keywords: ISO 11543:2000, modified starch, hydroxypropyl content, proton NMR, NMR spectrometry, analytical method.

Key topics and technical requirements

• Principle: Partial hydrolysis in deuterium chloride (DCl) in deuterium oxide (D2O) followed by quantitative 1H NMR integration of the hydroxypropyl methyl doublet (~1.2 ppm) against the internal standard peak (TSPSA at 0 ppm).
• Reagents: High-purity D2O (≥99.8–99.95%), DCl solution (≈2 mol/L), and 3‑trimethylsilyl‑1‑propane sulfonic acid (TSPSA) sodium salt as internal standard.
• Sample preparation: Sieve to 800 µm (grind if necessary), wash starch with water, vacuum-dry (≈30 ±5 °C), determine moisture (ISO 1666) and weigh an accurately measured dry test portion (~12 mg).
• Instrument requirements: Proton NMR spectrometer (minimum 60 MHz) capable of quantitative analysis; use spinning 5 mm NMR tubes; recommended FT-NMR relaxation delay ≥15 s; spectral window –0.5 to 6 ppm.
• Calculation: Formula provided using integrated areas, masses, and molar masses (TSPSA M = 218 g·mol⁻¹; hydroxypropyl M = 59 g·mol⁻¹). Report as % (mass) on dry basis.
• Precision: Precision data from an interlaboratory study are given. Example repeatability (r) and reproducibility (R) limits for various mean hydroxypropyl contents include:
  • Mean 0.82%: r = 0.31%, R = 0.48%
  • Mean 3.35%: r = 0.98%, R = 0.98%
  • Mean 5.80%: r = 0.70%, R = 1.72%
  • Mean 6.40%: r = 2.33%, R = 2.59%

Applications

• Quality control and specification testing for food starch ethers, pharmaceutical excipients, and industrial starch derivatives where hydroxypropyl substitution affects functionality (e.g., viscosity, stability, film-forming).
• Regulatory compliance testing when composition or labelling requires quantification of chemical modification.
• Research and development to monitor reaction degree during starch modification or cross-linking processes.

Who would use this standard

• Analytical chemists and laboratories performing starch characterization by NMR.
• Quality assurance teams in food, pharmaceutical, and starch-processing industries.
• R&D scientists developing modified starches and polymer chemists assessing substitution degrees.

Related standards

• ISO 1666:1996 - Starch - Determination of moisture content - Oven-drying method (referenced for moisture correction).
• ISO 3696:1987 - Water for analytical laboratory use - Specifications (reagent-grade water).
• ISO guidance on precision and accuracy (ISO 5725 series) is cited for interlaboratory precision assessment.

This standard is essential for accurate, reproducible quantification of hydroxypropyl content using proton NMR, providing clear procedures for sample prep, instrumentation settings, calculation, and reporting.