Overview
ISO 622:2016 specifies a reduced molybdophosphate photometric method for the determination of total phosphorus content in solid mineral fuels - specifically hard coal, lignites and coke. The standard describes two validated ways to bring phosphorus into solution: (1) extraction from ash after controlled ashing (dry oxidation) using hydrofluoric and sulphuric acids, and (2) repeated acid oxidation of the original coal or coke sample (wet oxidation) to remove carbonaceous matter. The final determination is photometric: formation of the blue reduced molybdophosphate complex and measurement of absorbance with a spectrophotometer.
Key topics and requirements
- Scope and principle: measurement of total phosphorus by converting inorganic phosphate to a molybdophosphate complex, reduced and measured photometrically.
- Two extraction routes:
- Dry oxidation (ashing + acid extraction): ash is treated with hydrofluoric and sulphuric acids and brought into solution.
- Wet oxidation (acid digestion): repeated oxidation with nitric and sulphuric acids in a Kjeldahl-style assembly to destroy organic matter and release phosphorus.
- Reagents: hydrofluoric acid (HF), sulphuric acid (H2SO4), nitric acid (HNO3), ammonium molybdate, ascorbic acid, antimony potassium tartrate and prepared reagent mixture.
- Apparatus: muffle furnace, platinum crucible, Kjeldahl flask and digestion assembly, hot-air bath, spectrophotometer or photoelectric absorptiometer (measurement normally at 710 nm, 40 mm cells).
- Sample preparation: analysis sample ground to pass 212 µm sieve; ash preparation per ISO 1171 where applicable.
- Calibration and linearity: linear response up to specified aliquot phosphorus load (document notes linearity up to about 30 µg P in the aliquot).
- Safety and quality: strict handling precautions for HF (highly corrosive and toxic); use analytical-grade reagents and distilled water. The standard includes instructions for blanks and calculation formulae and addresses method precision (repeatability and reproducibility).
Practical applications and users
- Who uses ISO 622:2016: industrial and commercial analytical laboratories, coal and coke producers, metallurgical coke plants, power stations, environmental monitoring labs, and research institutions performing fuel quality control.
- Why it’s used:
- Quality control of coal and coke for phosphorus content (affects combustion behavior, slagging, downstream metallurgical processes).
- Regulatory and contractual testing where phosphorus limits are specified.
- Research and method development for trace-element analysis in solid mineral fuels.
Related standards
- ISO 1171 - Solid mineral fuels: Determination of ash (used for the dry oxidation route)
- ISO 18283 - Hard coal and coke: Manual sampling
- ISO 383 - Laboratory glassware: Interchangeable conical ground joints
- ISO 565 - Test sieves: Nominal sizes of openings
Keywords: ISO 622:2016, phosphorus determination, solid mineral fuels, reduced molybdophosphate photometric method, coal analysis, coke analysis, ash extraction, wet oxidation, spectrophotometer.
Open preview (PDF)Solid mineral fuels — Determination of phosphorus content — Reduced molybdophosphate photometric method