Overview
ISO 11653:1997 specifies a laboratory potentiometric titration method for the determination of high cobalt content in steel after separation by anion-exchange chromatography. The standard describes sample dissolution, separation of cobalt from interfering elements on an ion-exchange column, oxidation and cleanup, reaction with potassium hexacyanoferrate(III), and potentiometric titration of the remaining reagent with a cobalt standard solution. It includes procedural details, reagent and apparatus specifications, and interlaboratory precision data.
Key topics and technical requirements
- Scope and applicability
- The published scope text indicates applicability to specific high cobalt contents (see standard text); precision trials cover a range of cobalt levels (examples in the standard include 0.202 %, 10.0 %, 15.0 %, 17.0 % and 50.0 % (m/m)).
- Principle
- Dissolve steel sample in hydrochloric/nitric acid, separate cobalt from Cr/Mn/Ni on an anion-exchange column, oxidize with perchloric acid, remove dissolved chlorine/oxygen with nitrogen, add ammonium citrate/ammonium hydroxide and excess K3[Fe(CN)6], then titrate excess reagent potentiometrically with standard Co solution.
- Reagents
- Specified reagent grades and water (ISO 3696). Key reagents: HCl, HNO3, HClO4 (perchloric acid), ammonium citrate, ammonium hydroxide, potassium hexacyanoferrate(III) standard solution and a 2.00 g Co·L−1 cobalt standard.
- Ion-exchange separation
- Uses an anion exchange resin (alkyl quaternary ammonium, chloride form; nominal 8 % crosslinkage, 200–400 mesh) and a column ~25 mm × 300 mm. Flow control and bed-height limits are specified; typical flow ≤ 3.0 mL·min−1.
- Potentiometric titration apparatus
- Bright platinum indicator electrode, Ag/AgCl or calomel reference, high-impedance voltmeter or pH-meter; automatic titrators/potentiographs recommended for reproducible end‑point detection.
- Safety
- Strong warning on use of fuming perchloric acid and requirement for suitable fume cupboards.
Applications and who uses it
- Metallurgical and quality-control laboratories testing cobalt-rich steels and alloys.
- Alloy manufacturers, certification bodies, and materials research labs needing quantitative cobalt analysis for specification compliance, process control, and R&D.
- Useful for traceability and interlaboratory comparisons given the included precision and reproducibility data.
Related standards
Normative references include ISO 385-1 (burettes), ISO 648 (pipettes), ISO 1042 (volumetric flasks), ISO 3696 (water for lab use), ISO 5725 series (accuracy/precision) and ISO 14284 (sampling and preparation for chemical analysis of steel).
Keywords: ISO 11653, cobalt determination, steel analysis, potentiometric titration, ion exchange, potassium hexacyanoferrate, analytical method, laboratory procedure, cobalt in steel.