ISO 928:1997

Overview

ISO 928:1997 specifies an analytical method for the determination of total ash in spices and condiments. The method measures inorganic residue remaining after incineration of a prepared laboratory sample under controlled conditions. It is intended for routine quality control, specification testing and comparative laboratory work on the majority of spices, with the caveat that some spice matrices may require method adjustments or alternate procedures noted in their individual standards.

Key topics and technical requirements

• Scope: Procedure for total ash expressed as percentage by mass of sample.
• Principle: Destruction of organic matter by heating to a stable residue at (550 – 25) °C (as specified in the standard).
• Sample preparation: Follow ISO 948 (sampling) and ISO 2825 (preparation of a ground test portion).
• Reagents and water: Use laboratory water meeting ISO 3696 (grade 3).
• Apparatus: Inert capsules (platinum, quartz, porcelain or equivalent), electric hotplate, muffle furnace, desiccator, analytical balance (0.0001 g), water bath.
• Procedure (summary):
  • Heat and tare capsules, weigh ~2 g prepared sample into capsule.
  • Carbonize sample on hotplate, then incinerate in muffle furnace at the specified temperature until constant mass.
  • Moisten ashes, dry (water bath and hotplate), reheat in furnace and repeat until successive weighings differ by ≤ 0.0005 g.
  • Perform two determinations and report the mean to one decimal place.
• Calculation: Total ash percentage wTA = (m3 − m1) / (m2 − m1) × 100%, where
  • m1 = mass of empty capsule,
  • m2 = capsule + sample,
  • m3 = capsule + residue after incineration.
• Moisture correction: Option to express ash on dry basis using the sample humidity value.
• Precision: Annex A summarizes an interlaboratory study (15 labs, Germany, 1994) with repeatability and reproducibility statistics for example spices (black pepper, oregano, clove).

Applications and who uses it

• Food testing laboratories performing compositional and quality analyses of spices and seasonings.
• Spice manufacturers and processors for incoming material QC, process monitoring and product specifications.
• Regulatory agencies and certification bodies for compliance, labeling verification and trade disputes.
• Research & development groups investigating mineral content, adulteration, or processing effects on spices.

Related standards

• ISO 948:1980 - Sampling of spices
• ISO 2825:1981 - Preparation of a ground sample for analysis
• ISO 3696:1987 - Water for laboratory use (specification and test methods)

Keywords: ISO 928:1997, total ash in spices, ash determination, spice testing, muffle furnace, analytical method, food quality control.