Spectrophotometric determination of Irgafos 168 in polymers after different sample preparation procedures

Different sample preparation methods on the basis of the oxidation of Irgafos 168 (a phosphite ester used as a secondary antioxidant in polymers) to phosphate ion are presented for its determination in polymers. Different reagents such as perchloric acid and sodium hydroxide or heat were used to convert analyte to phosphate ions. In final step, a standard method (vanadomolybdophosphoric acid method) was used to determine the phosphate ions produced. The method is simple, reliable and relatively rapid. The repeatability was evaluated using a 20 mg·L⁻¹ solution of analyte and it is found that the relative standard deviation is less than 5% for all procedures. Accuracy of the method was tested by applying the spectrophotometric method along with gas chromatography to three commercial polymers. The results in all cases are in good agreement. In nine other polymers Irgafos 168 was not detected using both methods. The procedure in case of real samples (polyolefins) is: dissolution/precipitation of polymer, filtration, evaporation, dissolving residue in acetone and performing digestion procedures using HClO₄ or NaOH. In the case of the pyrolytic method, the polymer was burned in an electrical furnace at 500 °C and the residue was dissolved in HCl.