Masking separation techniques based

Flow injection analysis is based on the injection of a liquid sample into a continuously flowing liquid carrier stream, where it is usually made to react to give reaction products that may be detected. FIA offers the possibility in an on-line manifold of sample handling including separation, preconcentration, masking and color reaction, and even microwave dissolution, all of which can be readily automated. The most common advantages of FIA include reduced manpower cost of laboratory operations, increased sample throughput, improved precision of results, reduced sample volumes, and the elimination of many interferences. Fully automated flow injection analysers are based on spectrophotometric detection but are readily adapted as sample preparation units for atomic spectrometric techniques. Flow injection as a sample introduction technique has been discussed previously, whereas here its full potential is briefly surveyed. In addition to a few books on FIA [168,169], several critical reviews of FIA methods for FAAS, GF AAS, and ICP-AES methods have been published [170,171]. 

Fig. 7.11 Photos of a PANl-based flexible electrochromic display device containing 25 pixels. The display region and the connections were made by depositing gold on a plastic sheet using an appropriate mask and an evaporation technique. Each pixel can be driven separately. Left. PANI is in its oxidized state in all pixels. Right. PANI is reduced in two pixels (the bleached ones)...

While in most cases the color reactions used are not specific, numerous procedures can be made selective by the proper choice of pH and the addition of masking agents. Recent developments - in double-wavelength spectrophotometry have further increased the specificity of many direct methods. Separation and preconcentration techniques can be applied, but these impose a restriction on the detection limit based on the reproducibility and magnitude of the blank. Theoretical and practical considerations presently set the limit of detection on the most sensitive spectrophotometric methods at 5-20 ng. 

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