Dispersive spectrometry, modulated

Ferri D, Kumar MS, Wirz R, et al. First steps in combining modulation excitation spectroscopy with synchronous dispersive EXAFS/DRIFTS/mass spectrometry for in situ time resolved study of heterogeneous catalysts. Phys Chem Chem Phys. 2010 12 5634. 

Although these are the most important considerations in designing a parallel reactor module, another important point is the analysis. While in principle each analytical instrument is suitable and can be connected to the exit of such a multiple-pass reactor, one must ensure that the instrument works with relatively small amounts of sample, as well as low flow rates. For the model reaction under investigation in our reactor, the CO-oxidation, non dispersive IR is used. As C02 concentrations are relatively high under our conditions, the analysis chamber can be kept short, and purge times are therefore also short. Analysis times are around 4 minutes, this being determined mainly by the purge times of the tubes and the sample chamber. However, any analytical techniques, such as mass spectrometry, GC, etc., can in principle be used in connection with this set-up. 

Now, in order to employ a locked-in detection system, as in EMIRS, the modulation frequency of the potential at the electrode would have to be at least an order of magnitude greater than F(i). Thus, the potential modulation would have to be between 70 and 100 KHz, too great to allow sufficient relaxation time for most electrochemical processes to respond. As a consequence, lock-in detection has not been employed in in-situ FTIR studies and the sensitivity of SNIFTIRS is less than that of EMIRS. Nevertheless, the FT method does have the sensitivity necessary to detect monolayers, and submonolayers, of adsorbed species [55, 56]. This arises out of the very large improvements in S/N ratio available to FT (compared with dispersive) infrared spectrometry by the Jacquinot and Fellgett advantages. 

Another area in which PIMs show considerable promise is chemical analysis. The use of PIMs in the construction of ISEs and optodes is well established, but their potential use in analytical separation is only starting to be explored. PIMs are particularly useful in solid-phase extraction (SPE) for preconcentration of analytes [17,18]. Also, Eonths et al. have used a PIM containing Aliquat 336 as the carrier for the preconcentration of Cr(VI) prior to its determination in the membrane by energy-dispersive X-ray fluorescence spectrometry [47]. Flat-sheet PIMs can also be conveniently incorporated into separation modules for use in online analytical techniques such as flow injection analysis. For example, a D2EHPA-based PIM has been used in a separation module incorporated into a flow injection analysis system for the determination of Zn(II) [35]. This new approach has interesting implications for use in automated analysis, particularly in held instruments for the continuous monitoring of pollutants. 

EDXRF (energy dispersive x-ray fluorescence) spectrometry works without a ciystal. An EDXRF spectrometer includes special electronics and software modules to take care that all radiation is properly analyzed in the detector. It provides a lower cost alternative for applications where less precision is required. The high-end uses the 3D EDXRF techniques featuring a 3-dimensional, polarizing optical geometry. 

Chester, T. L. Winefordner, J. D., Evaluationof the Analytical Capabilities of Freqnency Modulated Sources in Multielement Non-Dispersive Flame Atomic Flnorescence Spectrometry , Spectrochimica Acta 1976,3IB, 21-29. 

---