pesticides in water samples. The extraction and analysis procedure, is shown as a block diagram in figure 66. It is seen that the herbicide peaks are clearly and unambiguously revealed. The individual mass spectra of Atrazine (retention time 16.30 minutes) and Simazine (retention time 16.36 minutes) are shown in figures 65, C and D, The spectra are clear and more than adequate to confirm the identity of the two herbicides.   Okumyura et al., (27) also developed an alternative type of extraction procedure to determine carbamate pesticides in water samples. The extraction and analysis procedure, is shown as a block diagram in figure 66. Figure 66. Extraction Procedure for Determining Carbamate Pesticides in Water   The modus operandi was as follows. A sample of water 1 litre in volume was extracted for a period of 5 minutes with a 100 ml portion of dichloromethane for. This was repeated three times and the extracts combined and concentrated on a water bath at 70-80ûC.

This type of extraction system is useful for biotechnology samples. An example of the use of solid phase extraction to determine trace amounts (5 ppb) of some chlorinated pesticides in drinking water is shown in figure 36. The extraction tube was designated as the Novo-Clean C18. It was 47 mm tube long which included the membrane manifold. The materials were removed from the water sample by dispersive interactions between the solutes and the C18 reversed phase. The tube was conditioned before use with

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,

that diluting a known weight of sample with mobile phase or be much more complex including an extraction procedure followed by derivatization and then dilution. For some samples the preparation can be the most time consuming and difficult part of the whole analysis. Details of sample preparation is the subject of Book 18 but an example of one of the more complex sample preparation methods will be given to illustrate some of the procedures that may be necessary.   Liquid extraction is a clumsy procedure, particularly when used on the micro scale which is often necessary in sample preparation. An alernative procedure is solid phase extraction. The procedure is relatively simple and involves the use of a short tube packed with an appropriate adsorbent such as silica, reversed phase silica or, for some applications, macro porous polymer beads. The adsorbent must be capable of removing the substances of interest from the liquid medium. Extracting trace

nbsp; 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

was carried out using an LC-PCN column packed with a bonded phase carrying cyanopropylmethyl moieties on the surface. Thus, in contrast to the extraction process, which appears to be based on ionic interactions with the weak ion exchange material, the LC separation appears to be based on a mixture of interactions. There will be dispersive interactions of the drugs with the hydrocarbon chains of the bonded moiety and also weakly polar interactions with the cyano group. It is seen that the extraction procedures are very efficient and all the tricyclic antidepressant drugs are eluted discretely.   Courtesy of Supelco Inc.   Figure 43 Chromatogram of the Tricyclic Antidepressant Drugs from Blood Serum