Evaluation of acid digestion methodology in poly (ethylene terephthalate) resin for elementary determination by ICP OES

Poly (ethylene terephthalate)-PET is a thermoplastic polymer that occupies a significant place in the food and medicine market, where PET pellets are used in the manufacturing of packages. One-quality criterium for PET is the control of inorganic contaminants, which is indispensable for quality control and the safety of the final plastic product. The present study proposes a microwave-assisted decomposition methodology using diluted acid mixtures, for better quantification of boron (B), barium (Ba), calcium (Ca), cadmium (Cd), cobalt (Co), magnesium (Mg), sodium (Na), phosphorus (P), and lead (Pb) in pellets of PET resin, purchased in Pernambuco, Brazil, and analyzed by inductively coupled plasma optical emission spectrometry (ICP OES). In order to overcome the difficulties faced in the pellet’s decomposition and the detection of the inorganic content by ICP OES, an experimental design was carried out, using the strategy of polar coordinates as a statistical tool for the simultaneous analysis of mixing and processing variables. The following optimal parameters were established after full factorial design: 100 mg of resin and 10 mL of a digesting mixture composed of 40% water, 54% of nitric acid and 6% of sulfuric acid, digestion time of 20 min with heating at 220 ºC. The resins analyzed in this study showed higher levels of Ba (0.79 µg g −1 ) and Pb (1.64 µg g −1 ), compared to other studies in the literature.