Gas Chromatography - Tandem Techniques - Examples of GC/MS Spectrometry Applications > Analysis of Waxes and Lipid Type Materials > Page 79

 

Figure 64. Total Ion Current Chromatogram Showing the Simultaneous Determination of 60 Pesticides (after ref..24).

 

Two types of polymer coating were used on the fibre, polydimethylsiloxane (100 mm thick) and polyacrylate (95 mm thick). The fibers were prepared by heating the fibers in the injection port at about 250C until no peaks could be detected on a blank run. A Varian Model 3400 gas chromatograph coupled to a Varian Saturn ion-trap mass spectrometer was used for the analysis. The capillary column was 30 m long, 250 mm I.D. and carried a film of SPB-5 stationary phase, 0.5 mm thick. The column was held at 40C for 5 minutes, heated to 100C at 50/min., then to 275C at 5/min. and finally heated to 300C at 30/min. where it was held for 2 min. The injector and transfer lines were held at 250C. the mass range scanned was 45-400 mu. A chromatogram showing the separation of 60 pesticides, using the polyacrylate fiber for extracting the sample, is shown in figure 64. The concentration of each pesticide in the water was 100 ng/liter indicating a very high sensitivity and a very efficient extraction procedure. The authors claimed a linearity range of 0.1 to 1 mg per liter and demonstrated there was little difference in the extraction efficiency between the two types of polymer coated fibers.

 

Vreuls et al. (26) employed a similar technique using an extraction system involving a tube packed with polymeric material. A 1 ml sample was collected in an LC sample loop and an internal standard added. The sample was then displaced through a short column, 1 cm long, 2 mm I.D., packed with 10 mm particles of PLRP-S polymer (styrene-divinylbenzene copolymer) by pure water. The extraction column was then dried in a stream of nitrogen and the adsorbed materials displaced into the gas chromatograph with 180 ml of ethyl acetate. To remove the solvent, the sample was firstly passed through a short retention gap column before entering the actual analytical column. The oven was maintained at 70C so that the ethyl acetate was eluted through the retaining column and then released to waste. At this temperature the solutes of interest were held in the retaining column while the ethyl acetate was removed. After the ethyl acetate had been removed, the column temperature was increased and the components in the residue separated on the analytical column using an appropriate temperature program. The solutes eluted from the analytical column passed to a QMD 1000 mass spectrometer.