Overview
EN ISO 6878:2004 - Water quality: Determination of phosphorus - Ammonium molybdate spectrometric method specifies validated procedures for measuring different forms of phosphorus in waters using the ammonium molybdate / molybdenum blue spectrometric reaction. The standard covers determination of orthophosphate, orthophosphate after solvent extraction, hydrolysable phosphate plus orthophosphate, and total phosphorus after decomposition. It is applicable to all types of water including seawater and effluents, with a routine measurement range of 0.005 mg/L to 0.8 mg/L and a solvent-extraction detection limit of about 0.0005 mg/L.
Key topics and technical requirements
- Analytical principle: formation of an antimony–phosphomolybdate complex followed by reduction with ascorbic acid to form a blue molybdenum complex; absorbance is measured spectrophotometrically.
- Measurement: recommended wavelengths include 880 nm (most sensitive) or 700 nm; optical cell path lengths typically 10–50 mm (higher sensitivity with up to 100 mm).
- Forms covered:
- Orthophosphate (dissolved reactive phosphate)
- Orthophosphate after solvent extraction (for ultra-trace levels)
- Hydrolysable phosphate (after sulfuric acid hydrolysis) plus orthophosphate
- Total phosphorus (after peroxodisulfate oxidation or nitric/sulfuric acid digestion)
- Reagents and apparatus: use analytical-grade reagents (e.g., ammonium heptamolybdate, antimony potassium tartrate, ascorbic acid, acids for digestion) and spectrometers suitable for visible/near-IR absorbance.
- Sampling and sample prep: filtration (nominal 0.45 µm), pH adjustment if required (pH 3–10), careful control of contamination (use phosphate-free detergents and clean glassware).
- Interferences and quality control: Annex A lists known interferences; users should verify and mitigate matrix effects. Precision data are provided (Annex B).
Applications
- Routine monitoring of surface water, groundwater, industrial effluents and seawater for compliance and environmental assessment.
- Research and process control in wastewater treatment plants (WWTPs) where phosphorus removal is critical.
- Baseline surveys, nutrient loading studies, eutrophication risk assessment, and laboratory accreditation.
Who should use this standard
- Environmental and water quality laboratories
- Municipal and industrial wastewater monitoring teams
- Regulatory bodies and compliance officers
- Consultants and researchers working on nutrient cycling and eutrophication
Related standards
- EN 1189:1996 (superseded by EN ISO 6878:2004)
- Prepared by ISO/TC 147 (Water quality) and CEN/TC 230 (Water analysis)
EN ISO 6878:2004 provides a widely accepted, reproducible spectrometric method for phosphorus analysis - essential for compliance monitoring, environmental protection, and process control where accurate phosphorus determination is required.
