Determination of phenolic antioxidants in polypropylene by derivative ultraviolet spectroscopy

Abstract

A method has been developed for the determination of two phenolic antioxidants exhibiting virtually identical ultraviolet absorption spectra (2,6-di-tert-butyl-4-methylphenol and 4-substituted 2,6-xylenol, denoted by AO-4K and Chemantox AO-49, respectively). The absorption coefficient of AO-4K is an order of magnitude higher than that of Chemantox AO-49. The anti-oxidants can be distinguished in alkaline medium, where the latter forms phenolate readily, thus allowing the utilisation of the bathochromic shift for its determination. The use of derivative spectroscopy reduces light scattering and matrix interferences when extracts from polypropylene samples are measured.