Determination of low levels of an antioxidant in polyolefins by large-volume injection temperature-programmed packed capillary liquid chromatography

Sub-ambient column temperatures, promoting strong interactions between the analyte and the stationary phase material, were utilized to focus large vol umes of the polyolefin antioxidant Irganox 1076 [benzenepropanoic acid, 3,5 -bis(1,1-dimethylethyl)-4-hydroxy-, octadecyl ester] on the column inlet, u sing pure acetonitrile as sample solvent and mobile phase. Injection volume s up to 100 mu l were successfully employed on a 50 cm x 320 mu m I.D. capi llary column packed with 5 mu m Kromasil 100 ODS particles. Irganox 1076 wa s eluted after completed injection: by temperature programming, using a tem perature program from 7 to 90 degrees C, in 3 degrees C min(-1). UV detecti on,:using a low-dispersion "U"-shaped flowcell, was performed at 280 nm. Th e method was applied for the determination of Irganox 1076 that was extract ed from low-density polyethylene (0.6 ppm, w/w). Both Soxhlet and microwave -aided solvent extractions were performed, using chloroform and acetonitril e as solvents, respectively. The microwave-aided extraction with acetonitri le was found to give approximately the same:yield as the standard Soxhlet r eference method. Consequently, small volumes of acetonitrile could be used both as extraction solvent, sample solvent and mobile phase, simplifying th e analysis process. The mass limit of detection of the method was found to be 3.3 ng, corresponding to a concentration limit of detection of 33 ng ml( -1), utilizing an injection volume of 100 mu l. The within and between day precision of retention times displayed relative standard deviations below 1 .2%. (C) 1999 Elsevier Science BN. All rights reserved.