Determination of polyethylene glycol in low-density polyethylene by large volume injection temperature gradient packed capillary liquid chromatography

Polyethylene glycol (PEG) 20 000 in low-density polyethylene has been determined using column switching and inverse temperature programming in reversed-phase packed capillary liquid chromatography with evaporative light scattering detection. PEG 20 000 was extracted into water from the polyethylene dissolved in toluene and PEG 35 000 was added as an internal standard (I.S.). The samples in aliquots of 100 μl were reconcentrated on the enrichment column using a loading mobile phase of acetonitrile–water (3:97, v/v) at a flow-rate of 75 μl/min for 3 min, then back-flushed and separated on the analytical column with acetonitrile–THF–water (40:5:55, v/v) as mobile phase. The column temperature was reduced from 68 to 55 °C with a ramp of −1.5 °C/min, held constant for 3 min and then reduced further to 45 °C with a −1.5 °C/min ramp and kept constant for 1 min. The analysis runtime was 20 min. The recovery of PEG 20 000 was determined to 65.1% with 2.8% RSD and the mass limit of detection of PEG 20 000 was 1.25 μg. The within-assay and between day precision of the retention times of both PEG 20 000 and PEG 35 000 displayed RSD of less than 1.1% (n=9), while the overall area ratio RSD of 100 μg/ml PEG 20 000 over PEG 35 000 was 1.3% (n=9). The method was linear within the investigated concentration range 25–125 μg/ml (R2=0.9983). In addition, a mixture of PEG 4000, 8000, 10 000, 20 000 and 35 000 was analysed on the system to demonstrate the possibility of analysing several PEGs in a sample with the use of temperature gradient elution.