ISO 735:1977

Overview

ISO 735:1977 specifies a laboratory method for the determination of ash insoluble in hydrochloric acid in oilseed residues. The procedure applies to residues produced by extraction of oil from oilseeds (pressure or solvent extraction), excluding compounded products. The method treats the total ash (see ISO 749) with hydrochloric acid to dissolve acid‑soluble material, then incinerates and weighs the remaining insoluble residue.

Keywords: ISO 735, oilseed residues, ash insoluble in hydrochloric acid, determination, total ash, incineration, HCl.

Key topics and technical requirements

• Scope and definition

  • Targets the fraction of total ash that remains undissolved after HCl treatment.
  • Applies to oilseed cake and meal residues from oil extraction.

• Principle

  • Treat total ash with hydrochloric acid, remove soluble fraction, incinerate and weigh the insoluble residue.

• Reagents and materials

  • Hydrochloric acid: 3 N solution.
  • Silver nitrate solution for chloride testing.
  • Hardened, ash‑free filter paper.

• Apparatus

  • Analytical balance (readability 0.001 g), muffle furnace (550 ± 15 °C), flat-bottomed incineration dish, desiccator.

• Procedure highlights

  • Prepare total ash as per ISO 749.
  • Moisten ash with HCl, wash and boil; filter and wash until chloride-free (silver nitrate test).
  • Carbonize filter + residue, incinerate at 550 ± 15 °C until free of carbon, cool in desiccator and weigh.
  • Repeat heating and weighing until successive weighings differ ≤ 0.001 g.

• Calculation and reporting

  • Result reported as percentage by mass of sample as received; optional conversion to dry‑matter basis using moisture per ISO 771.
  • Carry out two simultaneous determinations and report the arithmetic mean if repeatability criteria met.
  • Repeatability: difference between two results by same analyst should not exceed 0.2 g ash insoluble in HCl per 100 g sample.
  • Report results to one decimal place.

Applications and users

• Quality control in oilseed processing (meal and cake quality).
• Chemical analysis laboratories in food/feed testing.
• Research laboratories studying mineral or silica content of residues.
• Commodity inspection and regulatory testing where ash composition affects grading or utilization (e.g., feed formulation, fertilizer use).

Related standards

• ISO 749 - Oilseed residues - Determination of total ash (method to obtain the total ash input to this procedure).
• ISO 771 - Oilseed residues - Determination of moisture and volatile matter (used for dry‑matter calculations).

This standard is practical for laboratories performing routine compositional analysis of oilseed residues and provides a reproducible, internationally recognized procedure for assessing the acid‑insoluble ash fraction.