Overview
EN ISO 13759:1996 - Petroleum products - Determination of alkyl nitrate in diesel fuels - Spectrometric method specifies a laboratory procedure to measure alkyl nitrate additives in diesel fuel over the volume-fraction range 0.03 % to 0.30 % (v/v). The method quantifies alkyl nitrate by converting the additive to nitric acid, forming a coloured derivative and measuring absorbance spectrometrically at 452 nm. Results are reported as % (v/v), either for the specific alkyl nitrate present or, when unknown, relative to 2‑ethylhexyl nitrate (reference).
Key topics and technical requirements
- Scope and limits: Target concentration 0.03–0.30 % (v/v). Interferences include nitrate esters, inorganic nitrate ions and nitrogen oxides.
- Analytical principle: Alkyl nitrate is hydrolysed in strong sulfuric acid, releasing nitric acid that reacts with 2,4‑dimethylphenol to form a nitroxylenol; this product is extracted, converted to a yellow salt with sodium hydroxide, and measured at 452 nm.
- Calibration: Requires reference solutions of the same alkyl nitrate as the sample. If the specific additive is unknown, use 2‑ethylhexyl nitrate (≥97 %) to build the calibration curve. Prepare multiple standard points, correct absorbance by subtracting blank fuel, and derive a slope (C) or use a best‑fit curve for non‑linear responses.
- Reagents and materials: Glacial acetic acid, concentrated sulfuric acid, 2,4‑dimethylphenol, sodium hydroxide, propan‑2‑ol, 2,2,4‑trimethylpentane and a clean diesel fuel blank.
- Apparatus: Matched absorption cells (10.00 mm path), spectrometer (452 nm ± 5 nm), separating funnels, automatic shaking machine, Class A volumetric glassware.
- Performance: Precision from interlaboratory tests - repeatability (r) = 0.017 % (v/v) and reproducibility (R) = 0.036 % (v/v).
- Reporting: State the alkyl nitrate identity (or basis on 2‑ethylhexyl nitrate), value to nearest 0.001 % (v/v), test date and any deviations from the standard procedure.
Applications and users
- Quality control laboratories in refineries, fuel blending facilities and distribution terminals for monitoring alkyl nitrate anti‑knock/cetane‑improver additives.
- Additive manufacturers for product verification and formulation control.
- Regulatory and compliance testing where accurate determination of nitrate-based additives is required.
- Research and development teams studying additive effects on cetane number and combustion performance.
Related standards
- ISO 5165 - Diesel fuels - Determination of ignition quality (cetane engine method) (referenced for cetane effects).
- ISO 4264 - Calculation of cetane index (background on cetane index vs additives).
- ISO 3696 - Water for analytical laboratory use (grade requirements).
- Glassware standards: ISO 385‑1, ISO 835‑1, ISO 1042 (normative references).
Keywords: EN ISO 13759:1996, alkyl nitrate, diesel fuels, spectrometric method, 2‑ethylhexyl nitrate, calibration curve, 452 nm, sulfuric acid hydrolysis, fuel additive analysis, cetane number.
