Spectrophotometric methods with speciation

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

The spectrophotometric methods for the determination (and speciation) of phosphorus in natural waters have been compared with other analytical techniques [144]. 

Spectrophotometric methods applicable to speciation analysis for V in different oxidation states have been reviewed [12]. Attempts to speciation of V(IV) and V(V) with Eriochrome Cyanine R in natural waters by solid-phase spectrophotometry has been described... 

The advantages of SIA methodology indicated above and the commercial availability of such instrumentation generated wide interest in it and led to the development of numerous different applications in various fields of chemical analysis. They are most commonly used with spectrophotometric detection but numerous electrochemical detections were also employed (Barnett et al., 1999 Perez-Olmos et al., 2005). Sequential injection analysis methods with various detections were developed for environmental analysis (Cerda et ah, 2001 Miro and Hansen, 2006 Mesquite and Rangel, 2009), and also for speciation analysis (Van Staden and Stefan, 2004). These are considered a useful tool for clinical and biochemical analysis (Economou et ah, 2007), and even as an alternative approach to process analytical chemistry (Barnett et ah, 1999). 

Direct speciation of dissolved americium and plutonium is possible only for solutions with appreciable concentration ([Am(DI)] > 10-6 M and [Pu(VT)] s 10-5 M) using a spectrophotometer with cumulative data recording (21). Typical spectra measured for the Am3+ ion at pH = 6.5 are shown in Figure 5 for 1, 5, 10, and 40 times cumulation at 503 nm. With this method it is shown that only trivalent americium ions are present in both equilibrium solutions from Am02 and Am(0H)3>nH20 solids. For plutonium solutions, the spectrophotometric study indicates the presence of polymers as shown in Figure 4. 

Spectrophotometric techniques combined with flow injection analysis (FIA) and on-line preconcentration can meet the required detection limits for natural Fe concentrations in aquatic systems (Table 7.2) by also using very specific and sensitive ligands, such as ferrozine [3-(2-bipyridyl)-5,6-bis(4-phenylsulfonic acid)-l,2,4-triazine], that selectively bind Fe(II). Determining Fe(II) as well as the total Fe after on-line reduction of Fe(III) to Fe(II) with ascorbic acid allows a kind of speciation.37 A drawback is that the selective complexing agents can shift the iron redox speciation in the sample. For example, several researchers have reported a tendency for ferrozine to reduce Fe(III) to Fe(II) under certain conditions.76 Most ferrozine methods involve sample acidification, which may also promote reduction of Fe(III) in the sample. Fe(II) is a transient species in most seawater environments and is rapidly oxidized to Fe(III) therefore, unacidified samples are required in order to maintain redox integrity.8 An alternative is to couple FIA with a chemiluminescence reaction.77-78... 

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