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

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.