⛽ Determination of the oxidation stability of fatty acid methyl esters (FAME, biodiesel) by the accelerated oxidation test — purified air at 10 l/h flows through the sample at 110 °C, volatile oxidation acids are absorbed in water, and the end of the induction period is marked by a rapid increase of its conductivity (up to 48 h), PN-EN 14112

Petrochemistry PN-EN 14112

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN 14112:2021-05 (English version), in full (our translation): “This document specifies a method for the determination of the oxidation stability of fatty acid methyl esters (FAME) at 110 °C, by means of measuring the induction period up to 48 h. For induction periods higher than 8,5 h the precision is not covered by the precision statement of this method. NOTE 1 EN 15751 [1] describes a similar test method for oxidation stability determination of pure fatty acid methyl esters and of blends of FAME with petroleum-based diesel containing 2 % (V/V) of FAME at minimum. NOTE 2 Limited studies on EN 15751 with EHN (2-ethylhexyl nitrate) on FAME blends indicated that the stability is reduced to an extent which is within the reproducibility of the test method. It is likely that the oxidation stability of pure FAMEs is also reduced in the presence of EHN when EN 14112 is used for testing. NOTE 3 For the purposes of this document, the term “% (V/V)” is used to represent the volume fraction”. We read the text of the standard in the sample of SIST EN 14112:2021 (the text of EN 14112:2020 without changes) from the cover to 9.5.1 (automatic instruments record and process the data); we do not have the rest of the measurement (9.5.2 onwards), the calculation (10 — automatic and manual evaluation), expression of results, precision (repeatability r and reproducibility R), the test report or Annexes A (background of the method) and B (results of the interlaboratory study).

ACCORDING TO THE TEXT OF EN 14112:2020 (foreword, Clauses 1–9.5.1, table of contents). The standard was prepared by CEN/TC 307 “Oilseeds, vegetable and animal fats and oils and their by-products — Methods of sampling and analysis” (secretariat AFNOR); it supersedes EN 14112:2016. Changes from 2016: Figure 2 changed (dimension between air inlet and heating block removed), introduction removed, editorial revision. Scope (1) — as on the card. References (2): EN ISO 3170 (manual sampling of petroleum liquids), EN ISO 3171 (automatic pipeline sampling). Terms (3): induction period — the time between the start of the measurement and the moment when the formation of oxidation products begins to increase rapidly; oxidation stability — the induction period determined according to this standard, in hours. Principle (4): a stream of purified (dried) air passes through the sample heated to the target temperature, usually 110 °C; volatile compounds from oxidation are carried with the air into a vessel with demineralized or distilled water with a conductivity electrode connected to a measuring and recording device; the end of the induction period is indicated by a rapid increase of conductivity due to dissociation of volatile carboxylic acids absorbed in the water (background — Annex A). Chemicals (5): analytical grade, distilled or demineralized water; ternary solvent mixture methanol/toluene/acetone 1:1:1 (V/V); alkaline laboratory glass cleaning solution; 2-propanol. Apparatus (6): device for determination of oxidation stability (footnote: Rancimat — Metrohm, OSI — Omnion; equivalent products permitted): air filter with molecular sieve at the pump suction, gas membrane pump with adjustable flow rate (10 ± 1,0) l/h, borosilicate glass reaction vessels with a sealing cap with gas inlet and outlet tubes, closed measuring cells of about 150 ml with an air inlet tube to the bottom and ventilation holes at the top, electrodes for conductivity 0–300 µS/cm, amplifier and recorder for the signal of each electrode, contact thermometer graduated in 0,1 °C or Pt 100 sensor (range 0–150 °C), heating source — aluminium block adjustable to (150 ± 0,1) °C with holes for the vessels, or an oil bath up to 150 °C adjustable to 0,1 °C; calibrated thermometer or Pt100 sensor up to 150 °C, graduated in 0,1 °C; measuring pipettes or cylinders; oven up to (150 ± 3) °C; hoses of inert material (PTFE or silicone); molecular sieve with moisture indicator, pore size 0,3 nm, dried at 150 °C and cooled in a desiccator; balance accurate to ± 0,1 g or better. Sampling (7): according to EN ISO 3170 or EN ISO 3171 or national regulations; container filled to the top to minimize contact with air; storage in the dark, measurement as soon as possible after receipt, for longer storage 4 °C is recommended. Preparation (8.1): homogenize the sample carefully and analyse immediately after preparation. Cleaning (8.2.1): disposable reaction vessels, tubes and hoses are recommended; caps, cells and electrodes are cleaned with 2-propanol, rinsed with tap and demineralized water, dried at 80 °C for at least 2 h (not higher than 80 °C because of the elastomers; 2 h removes volatile residues); reusable vessels are purged at least three times with the ternary mixture (the last portion colourless), 2-propanol and water, filled with alkaline cleaning solution overnight, rinsed and dried at least 2 h at 80 °C; in case of doubt a run without sample under standard conditions — conductivity increase not more than 10 µS/cm within 5 h. Temperature correction (8.2.2): any difference between the temperatures of the sample and the block has a significant effect on the result; ΔT = Tblock − Tsensor is determined with a calibrated external sensor in a vessel with 5 g of thermo-stable oil (sensor touching the bottom, kept away from the air inlet, air connected); the block is set to Tblock = Ttarget + ΔT (example: ΔT = +2 °C → block 112 °C for 110 °C); the correction is repeated whenever the test temperature changes. Measurement (9.1–9.5.1): set up the apparatus (for commercial equipment — according to the manufacturer); set the air flow to (10 ± 1) l/h (dedicated instruments usually have automatic flow control); bring the block to the temperature giving the required temperature in the test tubes (usually 110 °C, with the 8.2.2 correction); fill the measuring cells with 60 ml of distilled or demineralized water; if recommended by the manufacturer, check and adjust the electrode signals; automatic instruments record and process the data.

STATUS (PKN catalogue cards as of 02.10.2026). The card of PN-EN 14112:2021-05 (English version, published 06-05-2021, 20 pages, price group K) has no “Withdrawn” header: Food, Agriculture and Forestry Sector, KT 92 Oilseeds, Vegetable and Animal Fats and their By-products, ICS 67.200.10, “Introduces: EN 14112:2020 [IDT]”, “Replaces: PN-EN 14112:2016-10 – English version”. The card of PN-EN 14112:2016-10 (22 pages) has the “Withdrawn” header: withdrawal date 06-05-2021, “Replaced by: PN-EN 14112:2021-05”; its scope stated that the precision was determined for induction periods up to 8,5 h, which corresponds to the limit value in EN 14214. The PKN search engine (query “PN-EN 14112”, 02.10.2026) shows the 2004 (Polish version), 2016-10 and 2021-05 editions. What changed for the result: according to the foreword of EN 14112:2020 the changes are editorial (Figure 2, introduction removed) — procedure and conditions (110 °C, 10 l/h, 60 ml of water) unchanged.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 14112 appears in 7 records of 6 laboratories: AB 009, AB 098, AB 391, AB 484, AB 1668, AB 1679. In the current scopes on the PCA website (read 02.10.2026, issues from 19.09.2025 to 30.07.2026) AB 391, AB 484, AB 1668 and AB 1679 cite the 2021-05 edition, AB 009 and AB 098 — the designation alone without a date. The “Laboratories” tab (“PN-EN 14112”) shows the same 6 laboratories — checked with a query of the tab on the labcoda.pl production server on 02.10.2026.

WHAT THE LABORATORIES TEST (PCA entries). “Oxidation stability” of liquid fuels — bio-components (FAME) and biodiesel — by the “conductometric method”; one record gives the range (4,0–24,0) h.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With temperature: the difference between the block temperature and the sample has a significant effect on the result — without a ΔT correction determined with a calibrated sensor a block at “110 °C” does not give 110 °C in the sample (8.2.2). With cleanliness: fuel and solvent residues in the elastomers of caps and hoses shorten the induction period of the next sample — hence drying for 2 h at 80 °C and the blank check (≤ 10 µS/cm in 5 h) (8.2.1). With the sample: contact with air and light before the test oxidizes FAME — full container, darkness, measurement as soon as possible (7); the sample is analysed immediately after homogenization (8.1). With additives: EHN may reduce the stability of pure FAME (Note 2). With the range: induction periods above 8,5 h are measured, but the precision of the method does not cover them (scope) — a comparison of two laboratories at results of around 20 h has no criterion from the standard.

WHAT WE DO NOT GIVE. We do not have 9.5.2–13 or the annexes: the sample mass, the method of automatic and manual evaluation of the conductivity curve, rounding of the result, the values of repeatability r and reproducibility R and the results of the interlaboratory study — so we give none of these values.

Method principle

A FAME sample heated to 110 °C is purged with purified, dried air (10 l/h); volatile oxidation products pass into a cell with distilled or demineralized water and a conductivity electrode; the rapid increase of conductivity from dissolved volatile carboxylic acids marks the end of the induction period, which in hours is the oxidation stability.

Applications

• Fatty acid methyl esters (FAME, biodiesel, fuel bio-components) — oxidation stability in quality control; 6 laboratories in PCA scopes
• Assessing compliance of FAME with the requirements of EN 14214 (limit value 8,5 h according to the card of the 2016 edition)
• Blends with diesel fuel — with a similar method according to EN 15751 (Note 1 of the scope)

Key parameters

Standard

Standard number

PN-EN 14112:2021-05 (wersja angielska; EN 14112:2020 IDT)

Title (PL)

Produkty przetwarzania olejów i tłuszczów — Estry metylowe kwasów tłuszczowych (FAME) — Oznaczanie stabilności oksydacyjnej (test przyspieszonego utleniania)

Title (EN)

Fat and oil derivatives — Fatty Acid Methyl Esters (FAME) — Determination of oxidation stability (accelerated oxidation test)

Step-by-step procedure

1. Sample

   Take according to EN ISO 3170 or 3171; container full, in the dark, measure as soon as possible (longer — 4 °C); homogenize and analyse immediately after preparation. PN-EN 14112:2021-05 current (PKN cards as of 02.10.2026).

2. Cleaning

   Preferably disposable vessels; others — ternary mixture, 2-propanol, alkaline solution overnight, drying at least 2 h at 80 °C; in case of doubt a blank run (≤ 10 µS/cm in 5 h).

3. Temperature correction

   Determine ΔT with a calibrated sensor in a vessel with 5 g of thermo-stable oil with the air connected; set the block to Ttarget + ΔT (e.g. 112 °C for ΔT = +2 °C).

4. Measurement

   Air flow (10 ± 1) l/h; 110 °C in the sample; cells with 60 ml of water; record conductivity until the rapid increase (further procedure according to 9.5–10 — we do not have the content).

5. Result

   Induction period in hours as oxidation stability; for results above 8,5 h remember that the precision of the method does not cover them.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The ternary mixture contains methanol and toluene (flammable, toxic) — work in a fume hood, away from ignition sources; the standard contains no separate warnings in the part we read
• The heating block operates up to 150 °C — risk of burns when inserting vessels

Frequently asked questions