Raman confocal dispersive

Breitenbach, J., W. Schrof, and J. Neumann. 1999. Confocal Raman spectroscopy Analytical approach to solid dispersion and mapping of drugSiarm ReSl6 1109-1113. 

Laser-source confocal Raman spectroscopy was used to analyze solid dispersions to evaluate the physical properties and determine the distribution of ibuprofen in extrudates of polyvinylpyrrolidone (PVP). As is shown in Figure 14, a shift in the Raman spectra occurs when the crystalline form of ibuprofen is compared to a solution or a PVP extrudate containing ibuprofen. For comparison purposes, ibuprofen was completely dissolved in dimeric... 

Breitenbach, J., Schrof, W, and Neumann, J. Confocal Raman spectroscopy analytical approach to solid dispersions and mapping of drugs. Pharm. Res. 16(7) 1109-1113, 1999. 

The interaction between zinc oxide and stearic acid in a medium suitable to simulate a vulcanized system has been investigated [65] experimentally using vibrational spectroscopic technique. Confocal Raman micro spectroscopy revealed that at ambient temperature both components are phase-separated in the form of microcrystals. When the reaction temperature (SO C and above) is reached only zinc oxide is present in the form of particles while the stearic acid melts and gets molecularly dispersed within the rahher matrix. The analysis points to a core-shell structure of the reacting system stearic acid diffuses to the surface of zinc oxide domains causing the shrinkage of the zinc oxide core and the formation of a shell of increasing thickness made of zinc stearate. 

Although the Raman effect was discovered in 1928 by Sir Chandrasekhara Venkata Raman, it has not until recently been applied to food adulteration problems (Baeten et al., 1996 Li-Chan, 1994 Ozaki et aL, 1992 Sadeghi-Jorabchi et al., 1990, 1991). Baeten et al. (1996) used FT-Raman which, they claim, produces fluorescence-free spectra, using a 1.064 pm laser. They were able to detect adulteration with soybean, corn and olive pomace with 100% accuracy down to 1% adulterant. In fact 780 nm excitation in a confocal instrument (Williams, 1994 Williams et al., 1994) produces excellent dispersive Raman spectra from olive oils in a wholly non-invasive fashion (N. Kaderbhai and the authors, unpublished observations). Baeten et al. (1996) comment that at present liquid and gas chromatography is the most accurate technique to determine adulteration, and it is this method that is the European Union adulteration standard (EC, 1991), but that FT-Raman has the potential for detecting adulterants beyond the limits of liquid and gas chromatography. 

There are other modern spectroscopic methods such as X-ray photoelectron spectroscopy (XPS), small angle neutron scattering (SANS), Raman spectroscopy (RS), electron spinning resonance (ESR) and nuclear magnetic resonance (NMR). These techniques are well known in the membrane field. Static secondary ion mass spectrometry (SSIMS), energy dispersive X-ray spectroscopy (EDS), laser confocal scanning microscopy (FCSM) and environmental scanning electron microscopy (ESEM) can also be added to new microscopic methods to characterize the membranes [84]. 

Figure 2. Diagram of a confocal Raman detection system. A Helium-Neon laser is focused onto a sample through a microscope objective. Raman signals are epi-detected and sent to either an avalanche photodiode detector (APD) for imaging or dispersed onto a CCD camera in the spectrometer.

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