Overview - ISO 16264:2002 (Water quality, soluble silicates)
ISO 16264:2002 specifies two automated wet‑chemical methods - flow injection analysis (FIA) and continuous flow analysis (CFA) - for the determination of soluble silicate (expressed as SiO2) in a variety of waters (ground, drinking, surface, leachate and waste water). Results are obtained by forming molybdosilicate and reducing it to molybdenum blue with photometric detection. The standard covers method principle, reagents, apparatus, sampling, calibration, interferences and performance characteristics.
Key topics and technical requirements
- Analytes & ranges: Applicable to silicate mass concentrations from 0.2 mg/L to 20 mg/L SiO2 (two working ranges: 0.2–2.0 mg/L and 2.0–20 mg/L). Other ranges may be used if they cover exactly one decade (e.g., 0.02–0.2 mg/L).
- Methods:
- FIA - sample injected into carrier, molybdate reagent, oxalic acid to remove phosphate interference, reduction with tin(II) chloride, photometric detection (wavelength 720 nm ± 10 nm).
- CFA - continuous segmented flow with molybdate and oxalic acid, reduction with ascorbic acid, photometric detection (wavelength 810 nm ± 10 nm).
- Reagents & calibration: heptamolybdate, oxalic acid, tin(II) chloride or ascorbic acid, surfactants for CFA, silicate stock (50 mg/L SiO2) and multi‑point calibration distributed equidistantly across the working range (per ISO 8466‑1).
- Apparatus: low‑pulse pumps, sample injectors (example volumes 40 µL and 360 µL), inert tubing and flow cells with path length chosen to maintain calibration linearity.
- Interferences & sample treatment: tannins, iron, sulfide, phosphate (oxalic acid treatment), aluminium (may require NaCN), high fluoride (treat with boric acid), oxidizing agents (sodium sulfite), dilution when necessary.
- Quality & performance: guidance on blanks, degassing reagents, precision/reproducibility and test reporting (references ISO 5725‑2).
Practical applications and users
- Environmental and water quality laboratories performing routine silicate monitoring in surface water, drinking water, groundwater, leachate and wastewater.
- Wastewater and process control teams tracking silicate concentrations for treatment optimization.
- Research labs studying silica cycling, eutrophication or industrial discharge.
- Manufacturers and service providers of FIA/CFA analyzers and water‑analysis instrumentation.
- Regulators and consultants needing validated, standardized procedures for reporting SiO2 concentrations.
Notes: Methods can be adapted for seawater by adjusting sensitivity and reagent/calibration solutions to sample salinity.
Related standards
- ISO 3696 - Water for analytical laboratory use
- ISO 5725‑2 - Precision (repeatability and reproducibility)
- ISO 8466‑1 - Calibration and evaluation of analytical methods
Keywords: ISO 16264, water quality, soluble silicates, silicate determination, SiO2, flow injection analysis (FIA), continuous flow analysis (CFA), photometric detection, molybdenum blue, silicate testing.