IP 631: Determination of the contamination level of fatty acid methyl esters in middle distillate and residual fuels using Flow Analysis by Fourier Transform Infrared Spectroscopy - Rapid Screening Method

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  • Method adopted/last revised:
  • Method reapproved: 2023
  • Status: Current
  • First printed in STM books: July 2021

This standard specifies a rapid screening method using flow analysis by Fourier transform infrared (FA-FTIR) spectroscopy with partial least squares (PLS) processing for the quantitative determination of the fatty acid methyl ester (FAME) contamination of middle 
distillates, in the range of 29.11 mg/kg to 989.97 mg/kg, and of middle distillates and residual fuels, following dilution, for levels up to 49.76 %.

NOTE 1 – Annex B describes a dilution procedure to significantly expand the measurement range above 1000 mg/kg for distillates and to enable measurement of residual oils.

NOTE 2 – This method detects all FAME components, with peak IR absorbance at approximately 1749 cm−1 and C8 to C22 molecules, as specified in standards such as EN 14214. The accuracy of the method is based on the molecular mass of C16 to C18 FAME species; the presence of other FAME species with different molecular masses could affect the accuracy.

NOTE 3 – Additives such as antistatic agents, antioxidants and corrosion inhibitors are measured with the FAME by the FTIR spectrometer. However any potential interference effects of these additives are eliminated by the flow analysis processing.

NOTE 4 – The scope of this method does not include aviation turbine fuel which is addressed by test method IP 583.

NOTE 5 – Marine fuels meeting the requirements of ISO 8217 are covered by the scope of this method.

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