Topics - Solid State Extraction

Solid State Extraction Solid state extraction is an extremely efficient method for isolating and concentrating solutes from relatively large volumes of liquid. This technique can be very effective, even when the solutes are present at extremely dilute concentrations (e.g. ppb). Materials extracted in this way can be used for subsequent chromatographic separation, spectroscopic examination, or biological assessment. The apparatus consists of a simple tube, which may be 2-4 mm I.D. and 2-4 cm long and is usually, but not necessarily, made from stainless steel or a suitably inert polymer. The extraction tube is usually packed with an appropriate bonded phase. The most effective for extracting dispersive materials (e.g. hydrocarbons, chlorinated hydrocarbons, pesticides etc) from water being long chain hydrocarbon bonded phases. This system can extract many liters of water (e.g. 2 l) if necessary and all the solutes accumulate at the front of the packing. The solutes can then be displaced from the adsorbent by 0.5 1 ml of methanol or acetonitrile (usually by reverse flow techniques to minimize extract dilution. The result would indicate a concentration factor of 2000-4000. Providing the right adsorbent is chosen, the extraction process can be very efficient, e.g.>99%. The choice of adsorbent can be quite critical. A contrasting example of the previous type of extraction would be the removal of polar materials (e.g. alcohols) from dispersive solvents (e.g. gasoline). This would best be achieved using a silica gel as the adsorbent, the alcohols being held on the adsorbent by strong polar interactions with the silica gel hydroxyl groups., Again the solutes might be desorbed with acetonitrile or an acetonitrile-water mixture