Dual-wavelength spectrophotometry

Shibata, S., Furukawa, M., and Goto, K., Dual-wavelength spectrophotometry. II. Determination of (components of) mixtures. Anal. Chim. Acta 53, 369-377 (1971). 

Ohnishi ST. Characterization of the murexide method dual-wavelength spectrophotometry of cations under physiological conditions. Anal Biochem 1978 85 165-79. 

In general, different radiation wavelengths correspond to slightly different indices of refraction. The main consequence of this aberration is that the refraction angle is wavelength dependent [80]. This aspect is very important for minimising the Schlieren effect by dual-wavelength spectrophotometry (see also 4.23.5). 

As mirrors are involved, wavelength-independent reflective phenomena are more likely to occur. Compensation of this effect can efficiently be accomplished by dual-wavelength spectrophotometry (see 4.2.3.5). 

FIGURE 4.13 Schlieren signals recorded for different solutions with the same refractive index. Carrier stream = water coiled reactor length = 100 cm a. b, c, d = 2.0 mol L-1 HC1,11.2% (m/v) sucrose, 14% (m/v) glycerol, and 24.13% (m/v) ethanol respectively. Other conditions are as in Fig. 4.13. Reprinted from Anal. Chim. Acta 234 (1990) 153, E.A.G. Zagatto, M.A.Z. Arruda, A.O. Jacintho, I.L. Mattos, Compensation of the Schlieren effect in flow-injection analysis by using dual-wavelength spectrophotometry, with permission from Elsevier (Ref [28]). 

TABLE 4.4 Minimisation of the Schlieren Effect by Dual-Wavelength Spectrophotometry. Data Refer to Analytical Signals, in Arbitrary Units. Dye Solutions [Buffered Bromocresol Green (BCG) Solutions] Inserted into the Buffer Carrier Stream of a Single line Flow Injection Manifold. For Experimental Details, see Ref. [28], ... 

E.A.G. Zagatto, M.A.Z. Arruda, A.O. Jacintho, I.L. Mattos, Compensation of the Schlieren effect in flow-injection analysis by using dual-wavelength spectrophotometry, Anal. Chim. Acta 234 (1990) 153. 

Classical transducers such as the photomultiplier tube and the photodiode have been used in most the flow systems [96,97], Since the 1980s, the tendency to use diode array spectrophotometers has increased, mainly for simultaneous determinations [98] and/or for implementing dual wavelength spectrophotometry [99], the latter being more exploited in segmented flow analysis. 

S. Honda, T. Konishi, and H. Chiba, Evaluation of Dual-Wavelength Spectrophotometry for Drug Level Monitoring. Anal. Chem., 56 (1984) 2352. 

Derivative and dual-wavelength spectrophotometry have also proved particularly useful for extracting ultraviolet-visible absorption spectra of analytes present in turbid solutions, where liglitscatleringobliterates the details of an absorption. spectrum. For example. 

Dual-wavelength spectrophotometry has also proved useful for determination of an analyte in the presence of a spectral interference. Here, the instrument is operated in the nonscanning mode with absorbances being measured at two wavelengths at which the interference has identical molar absorptivities. In contrast, the analyte must absorb radiation more strongly at one of these wavelengths than the other. The differential absorbance is then directly proportional to the anaivte concentration. 

Ferreira et al.(43] developed an FI spectrophotometiic method for the determination of zinc in plant ash extracts using zincon. The zinc chlwo-complex was retained on an anion-exchange column and subsequently eluted by dilute sodium hydroxide. Schlieren effects were overcome using dual-wavelength spectrophotometry. A sampling frequency of 45 h was achieved with an r.s.d. better than 2%. 

From the above it Is clear that dual wavelength spectrophotometry provides information from two wavelengths per unit time. All other factors being equal, the resultant data should be more useful than data from a double beam spectrophotometer. 

Section 3E-4). Another technique uses mechanical oscillation of a refractor plate to sweep a wavelength interval of a few nanometers repetitively across the exit slit of a monochromator while the spectrum is scanned, a technique known as wavelength modulation. Alternatively, the spectrum can be scanned using two wavelengths offset by a few nanometers, which is called dual-wavelength spectrophotometry. 

Liu, H., P. K. Dasgupta, Flow injection extraction without phase separation based on dual wavelength spectrophotometry. Anal. Chim. Acta, 1994,288,237-245. 

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