Overview
ISO 13825:2025 - "Petroleum and related products - Determination of arsenic in crude petroleum using atomic fluorescence spectrometry" - specifies a validated laboratory method for measuring arsenic in crude oil. The method uses a closed microwave digestion pretreatment followed by chemical reduction and hydride generation with detection by atomic fluorescence spectrometry (AFS). Precision was established by an interlaboratory study for arsenic concentrations between 0.35 mg/kg and 3.57 mg/kg; the method can be applied outside this range but without certified precision data.
Key topics and technical requirements
- Sample pretreatment: closed microwave digestion to completely decompose organic/inorganic arsenic compounds and avoid losses.
- Chemical reduction and hydride generation: reduction of As(V) to As(III) (thiourea–ascorbic acid), formation of arsine (AsH3) using sodium tetrahydroborate, and transfer to the atomizer with argon.
- Detection: atomic fluorescence spectrometer with arsenic hollow cathode lamp and a fixed 193.7 nm filter; signals converted to concentration via calibration curve.
- Reagents and materials: high-purity reagents (HNO3, HCl, H2O2, NaBH4, thiourea, ascorbic acid), ISO 3696 grade water, and argon (recommended 99.9% purity).
- Apparatus: microwave digestion system with temperature feedback (final reaction ~240 °C), hydride generation manifold, gas–liquid separator, moisture removal, and an AFS detector.
- Quality and performance: method includes calibration, reagent blanks, limits on validated precision (repeatability r and reproducibility R sections), and requirements for clean glassware and procedural controls.
- Safety: tests must be carried out by trained personnel and appropriate safety measures followed.
Applications and who uses it
- Refinery QC laboratories monitoring arsenic to prevent catalyst poisoning (arsenic levels as low as 10 mg/kg can damage platinum reforming catalysts).
- Petroleum testing labs performing compositional analysis and product release testing.
- Catalyst manufacturers and process engineers evaluating feedstock arsenic for catalyst selection and life-cycle planning.
- Environmental and regulatory labs where arsenic quantification in petroleum streams is required for compliance or risk assessment.
- Research institutions studying arsenic speciation and removal technologies in crude oil.
Related standards
- ISO 3696 - Water for analytical laboratory use (reagent water quality).
- ISO 3170 / ISO 3171 - Guidelines for sampling of crude petroleum (referenced for sampling procedures in ISO 13825:2025).
This standard provides a reproducible, AFS-based analytical route for accurate arsenic quantification in crude oil, supporting catalyst protection, process control, and regulatory compliance.
