Evaluation of sample preparation methods for polymerdigestion and trace elements determination by ICPMS and ICPOES

Abstract

In this work, sample preparation methods for polymer digestion based on microwave-induced combustion (MIC) and microwave-assisted acid digestion (MW-AD) were evaluated for further As, Bi, Cd, Co, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Sr, Ti, V and Zn determination by inductively coupled plasma mass spectrometry (ICPMS) and inductively coupled plasma optical emission spectrometry (ICPOES). Samples of low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET, colorless and green), polyetheretherketone (PEEK) and nylon 6,6 were digested using MIC and MW-AD in closed quartz vessels. The type and concentration of acids used for MIC were investigated and better results were achieved using a 4 mol l⁻¹ HNO₃ + 4 mol l⁻¹ HCl solution. Microwave-assisted acid digestion was also evaluated for polymer digestion using concentrated acids. Both sample preparation methods were considered suitable for polymer digestion but MIC was preferable in view of the possibility of using diluted acids as absorbing solution and allowing higher sample mass to be digested and consequently better limits of detection. Residual carbon content in digests of polymers obtained by MIC was lower in comparison with the values obtained after MW-AD. Accuracy for all the analytes determined by ICPOES and ICPMS after MIC digestion was better than 95% (analysis of certified reference materials and by neutron activation analysis). It was possible to digest up to 8 samples by MIC in less time (in 25 min) in comparison with MW-AD (more than 50 min) and also using diluted acids (4 mol l⁻¹ HNO₃ and HCl) instead of concentrated acids.