ISO 7890-3:1988

Overview

ISO 7890-3:1988 specifies a standardized spectrometric method using sulfosalicylic acid for the determination of nitrate concentration in raw and potable water. This internationally recognized procedure provides accurate measurement of nitrate nitrogen levels up to 0.2 mg/L with a detection limit ranging from 0.003 to 0.013 mg/L when using a 25 ml test portion and 40 mm path length cells. The standard plays a critical role in monitoring water quality by ensuring safe nitrate levels, essential for public health and environmental protection.

Key Topics

• Scope and Sample Types
  Applicable to raw and potable water samples, ISO 7890-3 enables precise nitrate quantification in a broad range of water qualities, including slightly colored or suspended samples, given proper sample preparation and correction.

• Detection Range and Sensitivity
  The method reliably detects low nitrate concentrations between 0.003 and 0.013 mg/L nitrogen using spectrometric absorbance at 415 nm.

• Principle of the Method
  Nitrate ions react with sulfosalicylic acid in an acidic medium after an alkali treatment, forming a yellow compound measurable via spectrometry. Additives like disodium ethylenediaminetetraacetate (Na2EDTA) prevent precipitation of interfering salts, while sodium azide neutralizes nitrite interference.

• Interference and Corrections
  Potential interferences from substances such as chlorides, orthophosphates, magnesium, and manganese are identified and quantified, with detailed interference effects addressed in Annex A. Absorbance corrections compensate for sample coloration or turbidity to improve accuracy.

• Reagents and Equipment
  The method requires high-purity analytical reagents, including sulfuric acid, acetic acid, sodium hydroxide, sodium azide, and sodium salicylate, plus a spectrometer capable of measurements at 415 nm with 40-50 mm cuvettes.

• Calibration and Quality Control
  Calibration involves preparing a series of nitrate standard solutions to establish a linear absorbance curve versus nitrate mass. The standard outlines procedures for blank tests, sample preparation, and absorbance measurement to ensure repeatability and reproducibility.

Applications

ISO 7890-3:1988 is essential for:

• Water Quality Monitoring
  Ensuring nitrate levels in drinking water and natural water sources meet safety regulations, preventing potential health risks such as methemoglobinemia.

• Environmental Assessment
  Tracking nitrate contamination from agricultural runoff, wastewater discharge, or industrial sources in surface and groundwater.

• Laboratory Standardization
  Harmonizing nitrate testing methods across water quality laboratories internationally, facilitating reliable data comparison and regulatory compliance.

• Research and Development
  Studying nitrate dynamics and water treatment efficiency with a method offering sensitive and reproducible nitrate quantification.

Related Standards

ISO 7890 is a multipart series addressing nitrate determination in water:

• ISO 7890-1: Spectrometric method using dimethyl-2,6-phenol
• ISO 7890-2: Spectrometric method using fluoro-phenol after distillation
• ISO 7890-3: Spectrometric method using sulfosalicylic acid (this part)

Complementary standards and methods for water quality parameters and chemical analysis include:

• ISO/TC 147: Committee on water quality standards development
• Other water quality standards for parameters like nitrite, phosphate, and heavy metals

Keywords: nitrate determination, water quality, ISO 7890-3, spectrometric method, sulfosalicylic acid, nitrate analysis, potable water testing, nitrate nitrogen detection, water contaminants, analytical procedure, water safety standards