Determination of soap in refined vegetable oils by atomic-absorption spectrophotometry

Soap has been determined, as sodium, in alkali-refined vegetable oils by atomic-absorption spectrophotometry. The oil is treated with absolute ethanol, the mixture dissolved in ethyl methyl ketone and the solution then aspirated. Oil solutions have been compared with standards containing virgin olive oil and known amounts of sodium oleate. Concentrations of sodium oleate in the range 3 to 1000 p.p.m. in oil show a linear absorption. The method is rapid and accurate and can also be applied to the detection of adulteration of virgin olive oil with refined olive or other vegetable oils.