SPECTROSCOPY 55
scattering arising from bubbles or immiscible phases can be affected by flow, temperature and mixing parameters. In liquids applications, turbidity is undesirable since it can attenuate the Raman signal but these effects are minimised in a small-volume backscattered Raman probe immersed into the reaction or flow. Additional benefits of using a small-volume immersion Raman probe are its compatibility with reactive or corrosive chemistries, in situ measurements, and real-time process knowledge and control. Successful applications of small sampling volume probes include flowing streams, slip-streams or directly in the reaction vessel. In-process Raman measurements involving solids or turbid media are established in pharmaceutical and polymer applications. Successful examples can be found in real-time release testing, tablet coating and in understating formation of spatially heterogeneous polymers, elastomers or composites. In solids and turbid media sampling, the effects of optical scattering are harnessed and representative sampling is achieved because multiple
collection fibres collect signal from the surface and subsurfaces.
Raman hybrid sampling
Coupling multiple probes with different sampling volumes to a single analyser is a powerful tool because it provides a multi-scale examination of the process. A Raman hybrid sampling approach improved understanding during polymerisation of a spatially heterogeneous material.3
feedback on stirring rate, reactant addition rate or temperature in order to consistently achieve the target copolymer morphology. Embodiment of the principles described by Brun et al can be easily incorporated into a process environment using a Kaiser Raman hybrid system. Raman spectroscopy
High-
impact polystyrene preparation involves multiple steps and the end product is a spatially heterogeneous graft copolymer. Micro-scale and macro- scale Raman measurements were collected during the polymerisation process. An immersion probe measured an approximate volume of 1 µm3
and was used to measure
styrene polymerisation on the micro-scale. A non-contact sampling probe measured an approximate volume of 100 µm3
and was sensitive to
changes macro-scale changes in the copolymer’s morphology arising from phase changes and formation of nodules. Raman can provide real-time process
is a valuable technique for process monitoring and control, with applications in reaction monitoring and solids manufacturing. Flexibility in fibre optic sampling probes expands the utility of Raman spectroscopy in order to meet current and future application needs. A hybrid Raman approach, using a micro-scale and a macro-scale probe, is powerful for understanding hierarchical properties of materials. Raman spectroscopy provides increased process knowledge that enables advanced process monitoring, improved product quality and real-time process control.
For more information ✔ at
www.scientistlive.com/eurolab
Karen Esmonde-White is with Kaiser Optical Systems.
www.kosi.com
Raman spectroscopy substrates launched O
cean Optics has introduced a new substrate for Raman spectroscopy applications. The new Ram-SERS- SP Surface Enhanced Raman Spectroscopy substrates use a gold-silver nanosponge alloy to produce highly sensitive, trace-level Raman spectroscopy measurements. The applications for SERS range from detection of explosives and narcotics, to food safety, anti-counterfeit tagging and biological research.
SERS substrates amplify very weak Raman
signals by many orders of magnitude. Fast, repeatable measurements of SERS-active analytes are possible even to parts-per-trillion levels. Silver-only SERS substrates work best with 532nm Raman excitation, and gold substrates are better suited to 785nm
Raman systems. By combining the silver and gold on one substrate, the new SERS nanosponge substrates perform well with either wavelength. Also, when used with 638nm Raman excitation, the nanosponge substrates are enhanced to an even higher level of sensitivity.
Ram-SERS-SP nanosponge substrates are
more robust than other options and handle the deposition of sensitive samples more effectively. The higher sensitivity of these substrates opens up new opportunities for SERS applications - particularly in addressing the growing need for fast, effective detection of explosives and pesticides. The new substrates work with the whole
range of Ocean Optics Raman instruments. For users to take full advantage of the Ram- SERS-SP nanosponge substrates’ sensitivity, Ocean Optics now offers 638nm modular Raman solutions and 638nm versions of its mini handheld IDRaman spectrometers.
For more information visit
www.oceanoptics.com
www.scientistlive.com
REFERENCES 1
Li, B.; Calvet, A.;
Casamayou-Boucau, Y.; Morris, C.; Ryder, A. G. Anal. Chem. 2015, 87 (6), 3419–3428. 2
Shin, K.; Chung, H.
Analyst 2013, 138 (12), 3335–3346. 3
Brun, N.; Chevrel, M.-C.;
Falk, L.; Hoppe, S.; Durand, A.; Chapron, D.; Bourson, P. Chem. Eng. Technol. 2014, 37 (2), 275–282.
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