ISO 7514:1990

Overview

ISO 7514:1990 - Instant tea in solid form - Determination of total ash specifies a laboratory method to determine the total ash content of solid instant tea. The standard describes sample preparation, reagents, apparatus, a stepwise analytical procedure (acid treatment and incineration) and how to express results on a dry-matter basis. It was prepared by ISO/TC 34 (Agricultural food products).

Key topics and technical requirements

• Scope: Method for determination of total ash in instant tea in solid form (no broader scope provided in the document extract).
• Definition: Total ash is the residue obtained after treatment with hydrochloric acid and incineration at 550 °C ± 25 °C under the specified conditions.
• Reagent: Concentrated hydrochloric acid (density about 1.16–1.18 g·ml⁻¹) of recognized analytical grade - handle with caution (corrosive, irritant vapour).
• Apparatus:
  • Dish ~50 ml capacity (platinum, porcelain or inert material).
  • Furnace controllable at 550 °C ± 25 °C.
  • Thermostatically controlled hot-plate.
  • Desiccator with efficient desiccant.
• Sample and test portion:
  • Sampling per ISO 7516.
  • Thoroughly mix bulk sample; weigh about 2 g test portion to 0.001 g.
• Procedure (summary):
  • Preheat and weigh clean dish.
  • Add test portion; wet with drops (~1 ml) of concentrated HCl.
  • Heat on hot-plate in staged steps (30 min at medium, then progressively higher until fuming ceases).
  • Incinerate in furnace at 550 °C ± 25 °C for 16 h, cool, moisten ash, evaporate to dryness on hot-plate and reheat in furnace for 30 min; cool and weigh to 0.001 g.
• Results expression:
  • Total ash expressed as percentage by mass on a dry basis using the dry matter (RS = 100 − moisture content) from ISO 7513.
• Precision:
  • Repeatability: difference between two determinations by same operator ≤ 0.4% (absolute) for ash content 10–22% (m/m).
  • Reproducibility: inter-laboratory difference ≤ 1.2% (absolute) for ash content 10–22% (m/m).
• Number of determinations: Perform two determinations and report the arithmetic mean if repeatability is satisfied.

Applications and users

• Practical for quality control and compositional analysis in:
  • Instant tea manufacturers and product quality labs.
  • Food testing laboratories performing regulatory or specification testing.
  • Research groups studying tea composition, process optimization or ingredient specification.
• Typical uses: verifying raw material or finished product ash limits, formulation control, raw-material comparisons, and regulatory compliance.

Related standards

• ISO 7513:1990 - Instant tea in solid form - Determination of moisture content (loss in mass at 103 °C).
• ISO 7516:1984 - Instant tea in solid form - Sampling.

Keywords: ISO 7514:1990, instant tea, total ash, ash determination, hydrochloric acid, furnace 550 °C, ISO 7513, ISO 7516, repeatability, reproducibility.