ISO 20729:2017

Overview

ISO 20729:2017 specifies a method for determining the total sulfur content in natural gas using the ultraviolet (UV) fluorescence method. The standard covers sulfur mass concentrations from 1 mg/m3 to 200 mg/m3; higher concentrations can be measured after dilution with a suitable sulfur‑free solvent. The method oxidizes sulfur species to SO2 in a high‑temperature furnace and measures SO2 fluorescence under UV excitation to quantify total sulfur.

Key SEO keywords: ISO 20729:2017, natural gas total sulfur, ultraviolet fluorescence, UV fluorescence method, sulfur compounds, sulfur concentration.

Key topics and requirements

• Scope and range: Measurement range 1–200 mg/m3 (dilute >200 mg/m3).
• Principle: Combustion/oxidation to SO2 → UV excitation → fluorescence detection by photomultiplier.
• Instruments & conditions:
  • High‑temperature furnace at 1000 °C ± 50 °C.
  • Quartz cracking tube, dryer (membrane or osmotic) to remove water vapour.
  • UV fluorescence detector and data recording system.
• Gases & reagents:
  • Carrier gas: argon or helium, purity ≥ 99.99%.
  • Oxygen: purity ≥ 99.99%.
  • Calibration gases: certified working standards (H2S or COS in methane/nitrogen) with certificates per ISO 6141.
• Calibration:
  • At least three concentration points, each injected ≥ three times.
  • Linear regression calibration with correlation coefficient ≥ 0.998.
• Sampling & preparation:
  • Sampling per ISO 10715; materials must be inert to sulfur compounds.
  • Purge lines 30 s to 2 min to avoid sorption effects.
• Precision:
  • Repeatability and reproducibility limits specified by concentration ranges (examples):
    • Repeatability: 1–6 mg/m3 → 0.8 mg/m3; 100–200 mg/m3 → 7.4 mg/m3.
    • Reproducibility: 1–6 mg/m3 → 1.1 mg/m3; 100–200 mg/m3 → 11.6 mg/m3.
• Safety: Warning that many sulfur compounds are extremely toxic - handle with precautions.

Applications and users

Who benefits from ISO 20729:2017:

• Gas laboratories performing routine quality control and compliance testing.
• Pipeline operators and transmission companies monitoring sulfur for corrosion and odorization control.
• Petrochemical and LNG facilities requiring sulfur-speciation or total sulfur monitoring.
• Instrument manufacturers and calibration service providers designing or certifying UV fluorescence analyzers.
• Regulatory bodies and auditors establishing measurement protocols for gas quality and safety.

Practical uses:

• On‑line and off‑line analysis of pipeline and process gas.
• Quality assurance for custody transfer, environmental reporting, and corrosion management.
• Instrument calibration and method validation against certified reference gases.

Related standards

• ISO 6326‑3 (potentiometry for H2S, mercaptans, COS)
• ISO 6326‑5 (Lingener combustion method)
• ISO 19739 (gas chromatography for sulfur compounds)
• ISO 16960 (oxidative microcoulometry for total sulfur)
• ISO 6141, ISO 6142/6144/6145 (reference gas and calibration mixture requirements)
• ISO 10715 (natural gas sampling)

This concise guide helps laboratories and industry professionals understand the scope, technical requirements, and practical value of ISO 20729:2017 for accurate natural gas total sulfur measurement using UV fluorescence.