Determination of phthalic,terephthalic, and isophthalic acids in the presence of each other by gas chromatography

A procedure was developed for the simultaneous determination of phthalic acid isomers; the procedure includes the preparation of diisoamyl esters by reaction with isoamyl alcohol in a benzene solution in the presence of sulfuric acid with the distillation of an azeotrope mixture of benzene with water, the neutralization of acid with triethylamine, and the separation of esters by gas-liquid chromatography on a steel column (1 m × 3 mm) filled with Chromaton N-AW-HMDS with 5% Apiezon L in the temperature programming mode with flame-ionization detection. The time of separation is 13 min. The time of the sample preparation step is 2–2.5 h. The lower determination limit is 20 ng. The procedure allows the determination of phthalic acids in the concentration range from 0.02 to 2 mg/L in liquid samples and from 0.03 to 3 mg/m³ in air.