Overview
ISO 7579:2009 - Dyestuffs: Determination of solubility in organic solvents (gravimetric and photometric methods) specifies two standardized laboratory procedures for measuring how much dyestuff will dissolve in an organic solvent. The methods apply when the dyestuff does not react chemically with the solvent and remains stable and non‑volatile under the drying conditions used. The standard covers sample preparation, mixing (typically at 23 °C for 3 h), centrifugation, and quantitative measurement of dissolved dyestuff by either gravimetric residue or photometric absorbance.
Key topics and technical requirements
- Two validated procedures
- Gravimetric method: determine non‑volatile residue of the supernatant after solvent evaporation and drying to constant mass.
- Photometric method: measure absorbance of the clarified supernatant against a calibration solution (Beer–Lambert law compliance required).
- Method selection
- Gravimetric is recommended for more volatile solvents (boiling point < 120 °C).
- Photometric is recommended for less volatile solvents (boiling point > 120 °C).
- Choice should be made case‑by‑case considering solvent volatility, dyestuff stability and solution viscosity.
- Typical test conditions
- Mixing at (23 ± 2) °C for 3 hours, centrifugation (e.g., 2 000–3 000 min‑1) and careful decanting of supernatant.
- Concentration range normally 1 g/L to 1 000 g/L; higher concentrations allowed if viscosity permits.
- Drying procedures must be validated to constant mass; some dyestuffs (e.g., metal complexes) can tolerate up to ~150 °C.
- Measurement and reporting
- Gravimetric weighings to high precision; photometric results require validated calibration and stable spectral peak selection.
- Results reported in g/L with specified rounding rules; methods are not intended to quantify insoluble impurities.
- Limitations
- Not suitable when dyestuff chemically alters in solvent or when volatile under drying conditions.
- Viscosity or non‑compliance with Beer–Lambert behavior can limit applicability.
Applications
- Routine solubility testing during dyestuff development, quality control, raw material qualification, solvent selection and formulation work for inks, paints, coatings and colorants.
- Supporting regulatory dossiers or supplier specifications where standardized solubility data are required.
- Selecting appropriate solvent systems and concentrations for manufacturing, dyeing, or colorant dispersion processes.
Who should use it
- Analytical chemists, quality control laboratories, R&D teams in pigments/dyes, paint and coatings manufacturers, colorant suppliers and standards laboratories.
Related standards
- ISO 787‑2 - Determination of matter volatile at 105 °C (non‑volatile‑matter procedures referenced).
- ISO 2811‑1 - Density measurement (pyknometer method) for solvent density at 23 °C.
- ISO 15528 - Sampling procedures for paints, varnishes and raw materials.
Keywords: ISO 7579:2009, dyestuffs solubility, organic solvents, gravimetric method, photometric method, solubility determination, saturation concentration, spectrophotometer, centrifugation, dye quality control.
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