Real-Time Reaction Monitoring with the VERAXVERAXVERAXVERAXVERAXTM

and VizRamanTM Software

Technical Note #17

Why Raman?

Raman spectroscopy continuesto emerge as an important toolfor monitoring reactions in real

time. Raman scattering providescomplementary information to tradi-tional FT-IR (mid-IR) and NIRspectroscopy, and has advantages overboth:

• Raman measures fundamentalvibrational modes that are easilyattributed to molecular structure.

• Measurements can often be madethrough glass reaction vessels.

• Immersible fiber optic probes can bemanufactured with inexpensive silicafibers and quartz or sapphire optics.

• Water is a weak Raman scatterer, soaqueous solutions do not pose anyadditional difficulties.

• Most Raman bands are not sensitiveto minor temperature fluctuations.

The VERAX System

The VERAXTM Raman system combines a high quality spectrometer,

wide array of fiber optic probes, andVizRamanTM software to enable moni-toring of experiments in real time. Atthe heart of the system is the high-throughput spectrometer providingexcellent data in the “fingerprint” re-gion of the spectrum. High resolution(4 cm-1) ensures that small spectralchanges can be clearly discriminated.The VERAX is available with a varietyof RamanProbeTM fiber optic probes

for through-vessel or immersion mea-surements. Various diameters ofprobes are available to fit into lab-scalereaction glassware or an ALR (Auto-mated Laboratory Reactor). Becausesilica fiber optics are highly transmis-sive, laboratory results are readilytransferrable to on-line process moni-toring.

Real-time spectral display with VizRaman and theVERAX spectrometer.

Real-Time Display

VizRaman software provides asimple but powerful interface for

setting up and running reaction moni-toring experiments. The ExposureTime (or measurement time) can be set

on the main control panel enablingeither single spectra or a set of succes-sive spectra to be collected. Large datasets are not a problem, and the overallreaction time does not need to be de-fined prior to data collection. The“Stop” button can be pressed at anytime to halt the data acquisition andsave all data. An interactive 3D displayallows the full visualization of thespectral data while the reaction is stillin progress. An optional second win-dow can be added to show the mostrecent spectra, or a trend line of theheight of a selected peak versus time.All individual spectra, and any calcu-lated trendlines, are stored for laterdetailed analysis.

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ReactionViewTM, VizRamanTM, and RamIRTM are trademarks of Remspec Corp.Copyright 2004, InPhotonics, Inc.

Combined FT-IR and Raman

FT-IR and Raman are complementary vibrational spectroscopic

methods. The selection rules for thetwo techniques are quite different: FT-IR is very sensitive to changes in polarfunctions such as carbonyl and nitrilegroups, whereas Raman is particularlyuseful for observing molecular linkagesinvolving multiple bonds and heavieratoms. FT-IR is an absorbancetechnique and is inherently moresensitive to dilute constituents. Ramanis a scattering technique with a largersample volume, and can detect changesin phase and morphology in additionto molecular properties. In a crystalli-zation study, for example, an FT-IRsystem equipped with an ATR (attenu-ated total reflectance) probe willprovide information about the liquidphase, while the Raman spectra willinclude morphological informationabout the crystals that are forming.Mixing information about multi-phasesystems and emulsions is also acces-sible using Raman spectroscopy.

The VERAX Raman system coupledwith a ReactionViewTM fiber-optic FT-IR spectrometer provide a wealth ofchemical information in real time. TheRamIRTM multichannel reactionmonitoring software can be used tocontrol both systems simultaneously,resulting in complete vibrationalspectroscopic characterization of agiven system. The FT-IR data extendsthrough the R-H stretching regionsbeyond 3000 cm-1, while the Ramandata spans below 300 cm-1, enablingmonitoring of low-frequency bendingmodes and halogen-containing vibra-tions. Together, the VERAX andReactionView form a completesolution for monitoring reactionchemistry, phase changes, and crystalli-zation.

The VERAX and ReactionView combined FT-IR and Ramanreaction monitoring system with RamIR software.