Gas Chromatography - Quantitative Analysis > Page 53


Courtesy of Supelco Inc.


Figure 34 A Solid Phase Extraction Tube


The extraction tubes are usually made of an inert plastic such as polypropylene and have a range of capacities of 1, 2, or 5 ml. The tube is one fifth filled with adsorbent and contained by plastic frits at either end. The upper part of the tube, above the packing, acts as a funnel or container for the liquid to be extracted. The liquid sample is allowed to percolate through the adsorbent bed. Sometimes the lower end of the tube is connected to a vacuum or the top to a gas supply to increase the flow of sample through the bed. The adsobed material is then desorbed with an appropriate solvent, the sample diluted to a known volume and an aliquot used for analysis. If necessary the extract can be concentrated by evaporation and the total concentrate employed for analysis.

To avoid breakdown of labile materials, a totally inert extraction apparatus can be constructed from Teflon. A diagram of such an apparatus, produced by Alltech, is shown in figure 35 which even includes a Teflon hypodermic needle.

Figure 35 An All–Teflon Solid Phase Extraction Apparatus