Raman caffeine

Examples of solvent-mediated transformation monitoring include the conversion of anhydrous citric acid to the monohydrate form in water [235,236], CBZ with water [237] and ethanol-water mixtures [238,239], and cocrystallization studies of CBZ, caffeine, and theophylline with water [240]. Raman spectroscopy was used to monitor the crystallization rate and solute and solvent concentrations as griseofulvin was removed from an acetone solution using supercritical CO2 as an antisolvent [241]. Progesterone s crystallization profile was monitored as antisolvent was added [242]. 

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... 

A typical example of the characterization of a polymorphic system by FT Raman spectroscopy has been given by Gu and Jiang (1995) while an application of the technique with near infrared excitation to the polymorphic cimetidine system has been described by Tudor et al. (1991). The FT Raman technique has been compared to infrared diffuse reflection spectroscopy in the study of the polymorphs of spironolactone (Neville et al. 1992), and the pseudopolymorphic transition of caffeine hydrate (i.e. loss of solvent) has been monitored using the technique (de Matas et al. 1996). 

Unsupervised analyses are often performed on unknown samples in order to obtain qualitative results. The results shown in Figure 11.9 can be considered the final results here, the sample consisted of at least four chemical components-caffeine, acetaminophen, aspirin and cellulose-and their distributions were visualized in Raman images. 

When a number of adjacent spectra (or points or pixels) are classified as one chemical component, they can be termed as a domain. These could be particles, agglomerates or simply a continuous area of the same chemical component. However, when they form discrete areas, they are more likely to be from particles or agglomerates, and it is viable to determine their sizes and distributions. The Raman image (Figure 11.13, left) shows the spatial distribution of caffeine the white areas are caffeine-rich. A binary image isolating these areas is created by assigning 1 to all points above a threshold, and 0 to all below. The threshold... 

Figure 11.13 A Raman image and a binary image showing caffeine chemical domains in red.

In this analysis, three Raman maps of an OTC analgesic tablet were mapped (Figure 11.14) the areas are caffeine-rich (red), aspirin-rich (green) and acetamino-phen-rich (blue). 

Figure 4.68 The analysis of a common multicomponent pharmaceutical tablet by Raman spectroscopy with spectral subtraction. The top spectmm is the entire tablet. The spectra for acetylsali-cylic acid and caffeine were subtracted, resulting in the spectmm of the third component, identified as 4-acetamidophenol. [Courtesy of ThermoNicolet, Madison, WI (www.thermonicolet.com).]...

Theoretical and pH dependent surface enhanced Raman spectroscopy study on caffeine. Biopolymers, 72, 25-37. 

On the basis of IR and Raman spectroscopy (Table 5.2, Figure 5.12), which are relatively cheap, fast, and easy for technical operation and interpretation of data, and do not require sample dissolution methods, we presented the quantitative determination of the six binary mixtures with the studied cephalosporins in solid state, which was reported for the first time in the literature. The IR-LD analysis of oriented colloids as a liquid crystal suspension was applied for experimental IR band assignment and selection of appropriate bands for quantitative determination. This method gives additional supramolecular solid-state structural information at room temperature and atmospheric pressure. It also avoids the phase transition and guarantees the study of different forms without polymorph transitions. This approach has been applied recently for caffeine as a matrix compound and for studying the polymorphs of Paracetamol, Aspirin, Phenacetin , and Salophen. The spectroscopic data were... 

Koleva, B.B., T.M. Kolev, D.L. Tsalev, and M. Spiteller. 2008. Determination of phenacetin and salophen analgetics in solid binary mixtures with caffeine by infrared linear dichroic and Raman spectroscopy. J. Pharmaceut. Biomed. Analys. 46 267-273. 

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