ISO 3987:2010

ISO 3987:2010 - Petroleum products: Determination of sulfated ash in lubricating oils and additives

Overview

ISO 3987:2010 specifies an analytical procedure for determining sulfated ash (mass percentage) in unused lubricating oils and additive concentrates. The method targets metal-containing additives (barium, calcium, magnesium, zinc, potassium, sodium, tin) and accounts for combined elements such as sulfur, phosphorus and chlorine. The procedure has a lower applicability limit of 0.005 % (m/m) and special considerations for results below 0.02 % (m/m).

Key topics and technical requirements

• Principle: Ignite and carbonize the oil sample, treat the residue with sulfuric acid, then heat at 775 °C ± 25 °C in a muffle furnace until oxidation of carbon is complete; repeat acid treatment and ignition to constant mass.
• Calculation: Sulfated ash (%) = (mass of sulfated ash / mass of test portion) × 100.
• Limits & applicability:
  • Lower limit: 0.005 % (m/m) sulfated ash.
  • Application below 0.02 % (m/m) restricted to oils with ashless additives.
  • Not intended for used engine oils containing lead; non-additive oils are better served by ISO 6245.
• Reagents & solvents: high-purity sulfuric acid (concentrated and 1+1 dilution), isopropanol (propan-2-ol), toluene, and low-ash mineral (white) oil for dilution or blanks.
• Apparatus: porcelain/fused silica/platinum crucibles (special size guidance for low-ash samples), electric muffle furnace, balance with 0.1 mg resolution, ashless filter paper.
• Quality control: sulfuric acid blank for very low ash levels; repeat weighings until two successive masses differ by ≤ 1.0 mg.
• Precision: repeatability and reproducibility statistics are provided; reporting precision varies by ash level (e.g., results reported to 0.001 % for <0.02 %).

Applications and who uses it

• Lubricant and additive manufacturers for product formulation control and batch release.
• Quality control (QC) and testing laboratories performing routine sulfated ash content assays.
• R&D teams evaluating additive concentrations and interactions (e.g., zinc or phosphorus effects).
• Regulatory and certification bodies assessing compliance with product specifications.
• Useful for estimating metal-containing additive concentration in new oils and for comparative quality assessment.

Safety and notes

• Procedure involves hazardous reagents (concentrated sulfuric acid), flammable solvents, and high-temperature furnaces - appropriate safety controls are required.
• Some elements (e.g., magnesium, molybdenum, zinc) can give atypical results; interpret results with caution when these are present.

Related standards

• ISO 6245 (ash in non-additive oils), ISO 3170 / ISO 3171 (sampling), ISO 3696 (water for analysis), EN 14213 / EN 14214 (FAME references).