This part of ISO 10540 specifies a method for the quantification of phosphorus in oil, which is limited to oils with low phosphorus content, without any turbidity or visible sediment.

Depending on the dilution solvent used, most types of vegetable oils can be analysed (crude, degummed, refined, bleached, deodorized and hardened oils) and nearly all types of lecithins and phosphatides. This method is only suitable when phosphorus is present in a solubilized form. When it is present as fine particles, such as bleaching earth, ICP-OES analysis results in poor recovery as a result of nebulization and atomization problems. The only suitable non-ashing direct method for these samples is graphite furnace atomic absorption spectrometry.

ISO 10540-1 is the reference (colorimetric) method for the determination of the phosphorus content in fats and oils.