Overview
ISO 7760:2001 specifies a spectrophotometric method for the determination of hydroquinone in photographic processing waste. The procedure extracts hydroquinone from aqueous effluents into 1‑pentanol at slightly acidic pH, reacts the extract under alkaline conditions with 1‑ethylquinaldinium iodide, and measures the coloured complex spectrophotometrically (λ = 675 nm). The method applies to hydroquinone concentrations from 200 µg/l to 4 000 µg/l. Aminophenols and phenylenediamines are also measurable by this method; however, sulfonated hydroquinones and further oxidation products of benzoquinone are not determined.
Key topics and technical requirements
- Scope: Measurement of hydroquinone in photographic processing and plant effluents; concentration range 200–4 000 µg/l.
- Principle: Liquid–liquid extraction into 1‑pentanol at pH 4–5, alkaline reaction with 1‑ethylquinaldinium iodide to form a coloured complex, absorbance measurement at 675 nm.
- Sample handling: Minimise air headspace and refrigerate samples to limit aerial oxidation; filtration may be necessary.
- Reagents & apparatus: Uses reagent‑grade chemicals (e.g., sodium hydroxide, citric acid buffer, 1‑pentanol, methanol), matched 1 cm silica cells, separatory funnels, Class A volumetric glassware (ISO 1042, ISO 648).
- Safety: Procedures involve caustic and flammable reagents (e.g., NaOH, methanol, 1‑pentanol) and toxic analyte (hydroquinone); follow lab PPE and hazard codes in the standard.
- Limitations: Does not detect sulfonated hydroquinones or benzoquinone oxidation products; results apply only when sampling and preservation follow guidance.
Applications and users
ISO 7760:2001 is practical for:
- Photographic laboratories and film processing facilities monitoring process waste and complying with effluent regulations.
- Environmental and industrial analytical laboratories performing wastewater and effluent testing.
- Regulatory bodies and consultants assessing photographic chemical discharges and environmental compliance.
- Quality and EHS managers seeking standardized analytical methods for routine monitoring.
This standard supports accurate hydroquinone quantification for environmental monitoring, discharge permitting, pollution prevention, and internal process control.
Related standards
Referenced normative documents include:
- ISO 5667‑1, ‑2, ‑3 (water sampling guidance)
- ISO 648 (one‑mark pipettes), ISO 1042 (volumetric flasks)
- ISO 6353‑1/2/3 (reagents for chemical analysis)
- ISO 10349‑1 (photographic‑grade chemicals - test methods)
Keywords: ISO 7760:2001, hydroquinone determination, photographic processing waste, spectrophotometric method, effluent analysis, 1‑pentanol extraction, 1‑ethylquinaldinium iodide, wastewater monitoring, environmental compliance.
