Page 319 - Multidimensional Chromatography
P. 319

Industrial and Polymer Applications                             309





















                           Figure 12.4 Chromatograms of a styrene–isoprene–styrene triblock copolymer sample:
                           (a) microcolumn SEC trace; (b) capillary GC trace of the introduced section ‘x’. Peak identi-
                           fication is as follows: 1, ionol; 2, not identified; 3, Irganox 565. Reprinted with permission
                           from Ref. (12).


                           of emulsion polymerized acrylonitrile–butadiene–styrene–(ABS) copolymer, igni-
                           tion-resistant high-impact polystyrene, and styrene–isoprene–styrene triblock
                           copolymer. The following conditions were used in these three analyses. LC: UV
                           detection at 254 nm; injection volume of 200 nL; fused-silica capillary column
                           (30 cm   250  m i.d.) with an Ultrastyragel 10 000 (styrene/divinylbenzene) poly-
                           meric packing; mobile phase, THF at a flow rate of 3  L min. GC: DB-1 column
                           (15 m   0.32 i.d., 0.25  m film thickness); He carrier gas; column connected to an
                           uncoated deactivated inlet (5m   0.32 mm i.d.), with the latter being connected to a
                           10-port valve, which was used to transfer components from the SEC system to the
                           capillary GC–MS system.
                              The coupling of SEC with GC has also been used for the analysis of polymer
                           additives from a polystyrene matrix (13). The transfer technique in this case includes
                           concurrent solvent evaporation using a loop-type interface, early vapor exit and
                           co-solvent trapping. The latter allowed recoveries of almost 100% for solutes as
                           volatile as n-tridecane.  The adaptation made to the standard loop-type interface by
                           the addition of an extra valve between the LC detector and the LC–GC transfer
                           valve led to improved quantitative results by avoiding the problem of mixing within
                           the injection loop and also improved the recovery of n-alkanes from the mixture.
                           Since the sample pretreatment incorporated dissolving the sample instead of extract-
                           ing it, quantitative results were obtained. In addition, the effects of shifting the reten-
                           tion time window for the transfer were investigated and demonstrated that
                           recoverabilities of C 13 –C 38 compounds of up to almost 100% could be obtained.
                           The fraction obtained from 4.25–5.25 min, shows the greatest recovery, as can be
                           seen in Figure 12.5.
                              The coupling of SEC to GC is not an easy process and in order to avoid additional
                           LC interactions that could effect the predominate size exclusion separation relatively
                           polar solvents such as  THF are usually employed.  The drawback is that polar
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