ISO 18412:2005

Overview

ISO 18412:2005 specifies a photometric method for the determination of chromium(VI) in weakly contaminated waters, principally drinking water, within a working range of 2 µg/L to 50 µg/L. The method uses 1,5‑diphenylcarbazide (DPC) to form a red‑violet complex with chromium(VI) and measures the absorbance at 540 nm. Samples with higher chromium(VI) concentrations are diluted prior to analysis. The procedure is applicable to weakly polluted ground and surface waters provided no interfering reducing agents are present; it has not been validated for estuarine water or seawater.

Key topics and technical requirements

• Analytical principle: Chromium(VI) oxidizes DPC to diphenylcarbazone, producing a coloured complex measured photometrically (max absorbance at 540 nm).
• Measurement details:
  • Typical sample preparation: 40 mL sample + 4 mL acid mixture (H2SO4/H3PO4) + 500 µL 1% DPC in acetone, dilute to volume, stand 5–20 minutes, measure at 540 nm.
  • Photometer/cuvette path length: 50 mm recommended.
• Calibration: Linear calibration evaluated per ISO 8466-1 (slope = sensitivity). Prepare matrix-matched standards (potassium chromate) and check calibration frequently (new reagent batches).
• Interferences:
  • Reducing agents can cause negative bias-method not suitable where reducing agents are present.
  • Sulfide up to 0.2 mg/L does not interfere.
  • Common disinfectants tolerated up to specified limits: chlorine 0.6 mg/L, chlorine dioxide 0.4 mg/L, hydrogen peroxide 0.2 mg/L, ozone 0.1 mg/L.
• Quality and sampling: Use water of analytical grade (ISO 3696) and sampling guidance from ISO 5667 series. Store samples refrigerated and analyse within 4 days.
• Safety: Handle carcinogenic reagents (e.g., potassium dichromate) with appropriate laboratory safety.

Practical applications and users

• Routine monitoring of drinking water for regulatory compliance and distribution system surveillance.
• Environmental monitoring of weakly contaminated ground and surface waters where matrix validation confirms absence of interfering reducing agents.
• Water quality laboratories, public health agencies, utilities, environmental consultancies and accreditation bodies implementing standardized chromium(VI) analysis.
• Use cases include source-water screening, treatment verification, and spot checks after disinfection or industrial incidents.

Related standards

• ISO 11083 - chromium(VI) determination in wastewater (spectrometric DPC method)
• ISO 3696 - laboratory water quality
• ISO 5667 series - sampling guidance
• ISO 8466 series - calibration and evaluation of analytical methods

Keywords: ISO 18412:2005, chromium(VI), photometric method, water quality, drinking water, 1,5-diphenylcarbazide, spectrophotometry, chromium(VI) determination, calibration, sample preparation.