Comparison of methods for quantitative analysis of additives in low-density polyethylene using supercritical fluid and enhanced solvent extraction

Abstract

On-line supercritical fluid extraction–supercritical fluid chromatography (SFE–SFC) with cryogenic trapping was used to extract and separate five additives from a low-density polyethylene (LDPE) sample. A glass tube filled with glass wool afforded excellent collection efficiency for the extracted analytes. Additive spiked sand was employed to optimize the various parameters of the on-line SFE–SFC system. Calibration curves from the spiked sand studies for on-line SFE–SFC were obtained with good linearities for quantitation. Results obtained on additives in LDPE from on-line SFE–SFC were comparable to those from off-line SFE–HPLC and off-line enhanced solvent extraction (ESE)–HPLC for all additives except Irganox 1076. However, the precision obtained with on-line SFE–SFC was lower than that from off-line SFE–HPLC and off-line ESE–HPLC due to the small sample size employed in the on-line system. Considerable clean-up of the ESE extract was required prior to chromatographic analysis. On-line SFE–SFC minimized the sample handling and eliminated the use of organic solvent. Despite the lower than expected precision, the on-line SFE–SFC method for quantitation of polymer additives appears to be reliable and robust for application in routine quality control analysis.