Pyrolysis-gas chromatography–isotope ratio mass spectrometry of polyethylene

• Polyethylene pyrograms consist of n-alkane, α-alkene and α,ω-alkanediene triplets.
• Saturated chains were found consistently deuterium depleted (low δD).
• Fractionation occur during pyrolysis with tertiary carbons acting as 2H concentrators.
• This reflects structural aspects depend on polymerization process and conditions.
• First report of Py-CSIA application to the characterization of a synthetic polymer.

Polyethylene is probably the most used plastic material in daily life and its accurate analysis is of importance. In this communication the chemical structure of polyethylenes is studied in detail using conventional analytical pyrolysis (Py-GC/MS), bulk stable isotopic analysis (IRMS) and pyrolysis compound specific stable isotopic analysis (Py-CSIA) to measure stable isotope proportions (δ13C, δ15N and δD) of polyethylene pyrolysis compounds. Polyethylene pyrolysis yields triplet peaks of n-alkanes, α-alkenes and α,ω-alkanedienes. No differences were found for bulk δ13C among different polyethylene types. However, conspicuous differences in δD were evident. It was possible to assign structure δ13C and δD values to specific polyethylene pyrolysis products in the range 12–18 carbon chain length. Conspicuous differences were found for the pyrolysis products with unsaturated moieties showing significant higher δD values than saturated chains (alkanes) that were deuterium depleted. In addition, a full isotopic fingerprinting (δ13C, δ15N and δD) for a dye (o-chloroaniline) contained in a polyethylene is reported. To the best of our knowledge this is the first application Py-CSIA to the study of a synthetic polymer. This hyphenated analytical technique is a promising tool to study synthetic materials, providing not only a fingerprinting, but also allowing the traceability of the polymerization process and the origin of the materials.