Raman spectroscopy Tests

Intensity enhancement takes place on rough silver surfaces. Under such conditions, Raman scattering can be measured from monolayers of molecular substances adsorbed on the silver (pyridine was the original test case), a technique known as surface-enhanced Raman spectroscopy. More recendy it has been found that sur-fiice enhancement also occurs when a thin layer of silver is sputtered onto a solid sample and the Raman scattering is observed through the silver. 

Raman spectroscopy s sensitivity to the local molecular enviromnent means that it can be correlated to other material properties besides concentration, such as polymorph form, particle size, or polymer crystallinity. This is a powerful advantage, but it can complicate the development and interpretation of calibration models. For example, if a model is built to predict composition, it can appear to fail if the sample particle size distribution does not match what was used in the calibration set. Some models that appear to fail in the field may actually reflect a change in some aspect of the sample that was not sufficiently varied or represented in the calibration set. It is important to identify any differences between laboratory and plant conditions and perform a series of experiments to test the impact of those factors on the spectra and thus the field robustness of any models. This applies not only to physical parameters like flow rate, turbulence, particulates, temperature, crystal size and shape, and pressure, but also to the presence and concentration of minor constituents and expected contaminants. The significance of some of these parameters may be related to the volume of material probed, so factors that are significant in a microspectroscopy mode may not be when using a WAl probe or transmission mode. Regardless, the large calibration data sets required to address these variables can be burdensome. 

Identifying pharmaceuticals, whether APIs or excipients used to manufacture products, and the end products themselves is among the routine tests needed to control pharmaceutical manufacturing processes. Pharmacopoeias have compiled a wide range of analytical methods for the identification of pharmaceutical APIs and usually several tests for a product are recommended. The process can be labor-intensive and time-consuming with these conventional methods. This has raised the need for alternative, faster methods also ensuring reliable identification. Of the seven spectroscopic techniques reviewed in this book, IR and Raman spectroscopy are suitable for the unequivocal identification of pharmaceuticals as their spectra are compound-specific no two compounds other than pairs of enantiomers or oligomers possess the same IR... 

Bannister, D.J., Andrews, M.C., Cervenka, A.J. and Young, R.J. (1995). Analysis of the single fiber pullout test by means of Raman spectroscopy. Part 11. Micromechanics of deformation for an aramid/ epoxy system. Composites Sci. Technol. 53, 411—421. 

Experimental systems without irradiation of the reactor, but with (i) Raman spectroscopy with UV or VIS sources (ii) UV-VIS and ECD spectroscopy and (iii) fluorescence spectroscopy, represent special cases. It is possible, even perhaps probable, that the chemistry observed in the sample cell is dissimilar to the chemistry in the CSTR fluid elements. This is particularly worrisome in the cases were UV exposure occurs. Having said that, a test can be performed using exact replicate catalytic runs. For example, in the first mn, the sample cell can be irradiated for the full duration [to < t < tf]. In the second and third case, the sample cell can be irradiated for 50 % and 10 % of the duration. If the same set of observable species are found, and the time dependences of all the observable species are the same between runs, then, to a first approximation, the spectroscopy has not affected the system. In conclusion, cases (i) to (iii) should be treated with caution by the experimentalist. 

Hester and Sloan (2005) extended the size-structure correlations for double hydrates. A simple scheme of guest size-structure boundaries was proposed to predict the sl/sll structural transitions for double hydrates consisting of si hydrate formers (Figure 2.16). Raman spectroscopy and neutron diffraction measurements were performed to test the limits of these structural transitions. 

The methoxylation can be carried out by reacting silica with methanol vapor at 300-400°C, or by refluxing silica in methanol (21,36). Because the infrared spectrum of the modified surface is well understood (36) we chose to use this system as a model to test the feasibility of using Raman spectroscopy (21 ) for studying such surface modification procedures. 

Savolainen et al. investigated the role of Raman spectroscopy for monitoring amorphous content and compared the performance with that of NIR spectroscopy [41], Partial least squares (PLS) models in combination with several data pre-processing methods were employed. The prediction error for an independent test set was in the range of 2-3% for both NIR and Raman spectroscopy for amorphous and crystalline a-lactose monohydrate. The authors concluded that both techniques are useful for quantifying amorphous content however, the performance depends on process unit operation. Rantanen et al. performed a similar study of anhydrate/hydrate powder mixtures of nitrofurantoin, theophyllin, caffeine and carbamazepine [42], They found that both NIR and Raman performed well and that multivariate evaluation not always improves the evaluation in the case of Raman data. Santesson et al. demonstrated in situ Raman monitoring of crystallisation in acoustically levitated nanolitre drops [43]. Indomethazine and benzamide were used as model... 

Typical analysis of blood and urine is based upon chemical reactions, one per chemical species (or analyte ) of interest. Low-accuracy, single-analyte tests such as for blood glucose can be performed using at-home kits comprehensive blood tests at hospitals are performed using dedicated analyzers that suck in a sample and pump portions of it to various sensor modules. The purpose of this chapter is to explore the possibility of using Raman spectroscopy to replace conventional present tests in certain circumstances. 

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