Separation of polyethylene glycol oligomers using inverse temperature programming in packed capillary liquid chromatography.

Inverse temperature programming in packed capillary liquid chromatography coupled to evaporative light-scattering detection has been used to resolve native polyethylene glycol (PEG) oligomers. The model compound, PEG 1000, was separated on a 300 mm x 0.32 mm I.D. capillary column packed with 3 microm Hypersil ODS particles with acetonitrile-water (30:70, v/v) as mobile phase. The retention of the PEG oligomers increased with increasing temperature, different from what is commonly observed in liquid chromatography. The retention times of the oligomers were approximately doubled for each 25 degrees C increment of the column temperature in the temperature range 30-80 degrees C. The oligomers were almost unretained and co-eluted at a column temperature of 30 degrees C. At 80 degrees C a baseline separation of more than 22 peaks was obtained, but the last eluting peaks were severely broadened and all oligomers did not elute. When a negatively sloped temperature ramp from 80 to 25 degrees C at -1.5 degrees C/min was applied, the peak shapes were improved, additional peaks were detected and the analysis time was reduced by 48%. In the temperature programming mode, the intra-day precision of the retention times ranged from 0.5 to 5.8% (n=5).

Hindered amine stabilizers investigated by the use of packed capillary temperature-programmed liquid chromatography. I. Poly((6-((1,1,3,3-tetramethylbutyl)-amino)-1,3,5-triazine-2,4- diyl)(2,2 ,6,6-tetramethyl-4-piperidyl)imino)-1,6-hexanediyl ((2,2,6,6-tetramethyl-4-piperidyl)imino)).

Three different trademarks of a hindered amine stabilizer with the IUPAC name poly((6-((1,1,3,3-tetramethylbutyl)-amino)-1,3,5-triazine-2,4-d iyl)(2,2,6,6-tetramethyl-4-piperidyl)imino)-1,6-hexanediyl(( 2,2 ,6,6-tetramethyl-4-piperidyl)imino)), have been analyzed and compared to each other by the use of non-aqueous packed capillary temperature-programmed liquid chromatography and light scattering detection. The analysis by this method has shown that the products contained almost 40 different homologues and other components. This is in contrast to what has been assumed earlier based on results achieved with size exclusion chromatography. The method demonstrated significant differences between the products from different manufacturers.

Hindered amine stabilizers investigated by the use of packed capillary temperature programmed liquid chromatography. II: Poly-(N-beta-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidyl succinate).

Three different trademark products of a hindered amine stabilizer with the IUPAC name poly-(N-beta-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidyl succinate), have been analyzed and compared to each other by the use of packed capillary temperature programmed liquid chromatography and light scattering detection. The analysis by this method has shown that the products contained approximately 50 different homologues and/or other components. The method also demonstrated its potential in purity control of products from different manufacturers.

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 volumes of the polyolefin antioxidant Irganox 1076 [benzenepropanoic acid, 3.5-bis(1,1-dimethylethyl)-4-hydroxy-, octadecyl ester] on the column inlet, using pure acetonitrile as sample solvent and mobile phase. Injection volumes up to 100 microl were successfully employed on a 50 cm x 320 microm I.D. capillary column packed with 5 microm Kromasil 100 ODS particles. Irganox 1076 was eluted after completed injection by temperature programming, using a temperature program from 7 to 90 degrees C, in 3 degrees C min(-1). UV detection, using a low-dispersion "U"-shaped flowcell, was performed at 280 nm. The method was applied for the determination of Irganox 1076 that was extracted from low-density polyethylene (0.6 ppm, w/w). Both Soxhlet and microwave-aided solvent extractions were performed, using chloroform and acetonitrile as solvents, respectively. The microwave-aided extraction with acetonitrile was found to give approximately the same yield as the standard Soxhlet reference method. Consequently, small volumes of acetonitrile could be used both as extraction solvent, sample solvent and mobile phase, simplifying the 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 microl. The within and between day precision of retention times displayed relative standard deviations below 1.2%.