Overview
ISO 7934:1989 specifies a precise laboratory method for determining the mass concentration of sulfur dioxide (SO₂) emissions from stationary sources such as combustion facilities and industrial processes. This standard outlines the hydrogen peroxide/barium perchlorate/Thorin titration method, which is applicable for sulfur dioxide concentrations starting from 30 mg/m³ under standard conditions of 273.1 K temperature and 101.3 kPa pressure on a dry gas basis.
The method involves absorbing SO₂ from a gas sample into a hydrogen peroxide solution to form sulfuric acid, adjusting the pH, and subsequently titrating the solution with barium perchlorate using Thorin as an indicator to calculate the SO₂ concentration. The standard includes detailed guidance on sampling, reagents, apparatus, interference substances, and analytical procedures for accurate SO₂ quantification.
Key Topics
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Scope and Applicability
- Effective for SO₂ concentrations ≥ 30 mg/m³ with typical 30-minute sampling periods.
- For concentrations above 2,000 mg/m³, the sample gas volume is precisely controlled.
- Concentrations are based on dry gas at standard laboratory conditions (273.1 K, 101.3 kPa).
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Analytical Method Principle
- SO₂ is absorbed by a hydrogen peroxide solution forming sulfuric acid.
- Sample pH is adjusted to 3.5 before titration.
- Mass concentration is determined by titration with barium perchlorate using Thorin indicator.
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Sampling Equipment and Procedures
- Sampling probe with heated jacket to prevent condensation and preserve sample integrity.
- Particle filter to eliminate particulates.
- Absorbers (Drechsel type) to collect the gas sample in the absorption solution.
- Gas meter, thermometer, barometer, and flow regulation to ensure accurate sampling volume and conditions.
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Reagents and Solutions
- Hydrogen peroxide absorption solution prepared fresh on the day of use.
- Standard volumetric barium perchlorate solution titrant.
- Thorin indicator (sodium salt of an azo dye).
- Sodium hydroxide and perchloric acid for pH adjustment.
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Quality Control and Interferences
- Absorption efficiency must be validated regularly (>95%).
- Potential interferences include sulfur trioxide, volatile sulfates, and polyvalent metal salts; the standard provides guidance to mitigate their effect.
- Use of cation exchangers may be necessary to remove interfering metal ions before titration.
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Calculation of Results
- Mass concentration of SO₂ is calculated from the volume of titrant used, normalized to standard pressure and temperature.
- Multiple titrations and blank determinations ensure accuracy and repeatability.
Applications
ISO 7934:1989 serves as a fundamental method for environmental monitoring and regulatory compliance related to air pollution control, specifically for sulfur dioxide emissions from stationary sources. Practical applications include:
- Monitoring emissions from power plants, industrial boilers, and chemical manufacturing processes.
- Assessing the effectiveness of flue gas desulfurization technologies.
- Supporting environmental impact assessments and air quality management programs.
- Facilitating data collection for regulatory reporting under local and international environmental legislation.
- Providing reliable measurement data for industrial hygiene and occupational safety regarding SO₂ exposure.
The method’s sensitivity to a wide concentration range makes it applicable to both low-level monitoring and high-emission scenarios, ensuring accurate SO₂ mass concentration determinations critical for protecting air quality and public health.
Related Standards
- ISO 3696:1987 – Water for analytical laboratory use – Specification and test methods, referenced for reagent water quality.
- ISO 6879:1983 – Air Quality – Concepts related to air quality measuring methods, supporting standard terminology and measurement principles.
- Additional air pollution monitoring standards and methodologies for complementary gases or particulate matter may be used alongside ISO 7934 for comprehensive emission profiling.
Keywords: ISO 7934, sulfur dioxide measurement, stationary source emissions, hydrogen peroxide method, barium perchlorate titration, Thorin indicator, air quality monitoring, SO2 concentration, environmental gas analysis, flue gas sampling
Open preview (PDF)Stationary source emissions — Determination of the mass concentration of sulfur dioxide — Hydrogen peroxide/barium perchlorate/Thorin method