Determination of aniline in vegetable oils by diazotization and coupling in a microemulsion medium

A microemulsion containing sodium dodecyl sulphate and n-pentanol in a mass ratio of 1 : 4, water and a vegetable oil was investigated using pseudo-tenary phase diagrams. The medium can co-solve important amounts of vegetable oils and aqueous solutions over a wide range of ionic strengths. A procedure for the determination of 1.4–140 μg ml^?1 of aniline in vegetable oils using ionic diazotization and coupling reactions was developed. The absorbance was measured in an optically clear microemulsion containing 4% or 20% of oil. The procedure is much simpler and rapid than the official chromatographic methods and gives almost the same limits of detection (ca. 05 μg ml^?1) using no more than 1 ml of sample. The repeatability for 30 μg ml^?1 aniline was 2%. Acid-base titrations in the microemulsion medium permitted the evaluation of the protonation constant of the dye.