Overview
ISO 22743:2006 specifies a laboratory method for the determination of sulfates in water by continuous flow analysis (CFA). The standard covers procedures, reagents, apparatus and quality checks for measuring sulfate (SO4) mass concentrations typically from 30 mg/l to 300 mg/l (other ranges allowed provided they span exactly one decade). It is applicable to groundwater, drinking water and wastewater and is intended for routine, high‑throughput water quality testing.
Key Topics and Requirements
- Principle: Sulfate is precipitated as barium sulfate in acidic solution; excess barium reacts with methylthymol blue and the absorbance of the non‑chelated dye is measured (nominal detection at 460 nm ± 10 nm).
- Range & Calibration: Typical working range 30–300 mg/l SO4. Calibration requires at least five calibration solutions across the range; calibration and linearity evaluation follow ISO 8466‑1 (and ISO 8466‑2 for non‑linear fits).
- Interferences: Calcium, magnesium, iron and aluminium cause negative bias - removed using a cation exchange column (e.g., DOWEX 50W‑X8). Sulfide, sulfite, phosphate and tannic acids can cause positive bias at high concentrations.
- Reagents & Stability: Key reagents include barium chloride, methylthymol blue, buffered Na‑EDTA, NaOH and prepared sulfate standards. Examples of stability: barium chloride solution (stable ~1 month at 2–6 °C), methylthymol blue solution (stable ~1 week at 2–6 °C).
- Apparatus: Typical CFA system components - sampler, reagent containers, low‑pulse pump, inlet connector, photometer with flow cell (e.g., 10 mm path length), data acquisition.
- Performance Checks: System must produce ≥0.260 absorbance/cm for ~100 mg/l standard; 30 mg/l standard must yield signal‑to‑noise ≥3:1. Daily sensitivity and baseline stabilization procedures are specified.
- Sampling & Pretreatment: Follow ISO 5667‑3 for sampling, preservation and handling; filter samples if necessary. Cation exchange pretreatment is required when hardness metals are present.
Applications and Users
- Routine water quality monitoring in drinking water and groundwater surveillance.
- Environmental and industrial laboratories performing high‑throughput sulfate analysis.
- Wastewater treatment facilities for process control and compliance testing.
- Regulatory agencies and accredited testing labs needing an ISO‑aligned CFA sulfate method.
Related Standards
- ISO 3696 – Water for analytical laboratory use (reagent water quality)
- ISO 5667‑3 – Water sampling, preservation and handling
- ISO 8466‑1 / ISO 8466‑2 – Calibration and evaluation of analytical methods
ISO 22743:2006 is a practical, automated CFA method for reliable sulfate determination in various water matrices, offering standardized procedures for reagents, instrument setup, interference control and calibration to support accurate water quality monitoring.