Molecular speciation, control sample

The principal difficulty with the previous approaches to molecular speciation has been less with what was attempted and more with the inability to control the sample surface. A recent study of RF plasma treated surfaces has shown that the surface composition can change on exposure to laboratory air and water vapor (91,92). The development of a sample isolation/ treatment/... 

In its reversed mode, FIA is fully adaptable to Industrial process control [49-51], and to studies of the speciation of various elements In waters [102]. One of the most promising developments in the latter area is the speciation of chromium by means of the configuration depicted in Fig. 6.20. This uses a combined giass-calomel microelectrode incorprorated in the sample stream prior to the simultaneous injection of the reagents (Ce and 1,5-diphenylcarbazide for Cr3+ and Cr(VI). The data obtained for the concentration of these two species, together with the sample pH and the constants corresponding to the equilibria in which both oxidation states are involved, allow the calculation of the concentration of up to nine different chromium species aquo complexes and hydroxylated forms of Cr(III) and ionic, molecular and dimeric forms of Cr(VI) [103]. 

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