Caffeine spectroscopy

Nishio, J., Yonetani, I., Iwamoto, E., Tokura, S.,Tagahara, K., and Sugiura, M., Interaction of caffeine with 1-tryptophan study of 1H nuclear magnetic resonance spectroscopy, J. Pharm. Sci., 79,14,1990. 

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... 

Various organomercury complexes of theophylline and theobromine have been characterized by IR, H, and 13C NMR spectroscopy <87JCR(S)186> and similar products with theophylline, 6-thioguanine and 6-thiolpurine, and caffeine were prepared <92IJC(A)972>. 

Using the same reaction route, N-coordination and subsequent acid catalysed isomerisation to the C-coordinated carbene complex, Taube and coworkers could synthesise a broad range of purine derived ruthenium carbene complexes [80,81]. The structure of a caffeine carbene complex could be determined with X-ray aystallography (see Figure 6.34). Most of the compounds were characterised with spectroscopic methods, mainly UV-Vis spectroscopy. 

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). 

Fig. 5 Comparison of mid-infrared spectra of caffeine obtained by diffuse reflectance and transmission spectroscopy. (A) Diffuse reflectance spectrum of the pure powdered substance with transformed intensity data in K-M units. (B) Same diffuse reflectance spectrum, but using —log(i ) transformation (top trace), the lower spectral range was limited by the cut-off of the MCT detector used the bottom trace shows a transmission spectrum using the conventional KBr pellet technique transformed into absorbance, i.e., —log(transmittance).

About 2 to 3 g of coffee are placed in the sublimator, the pressure is reduced to 50 to 60 torr, and the temperature of a slow flow of entrainer air is raised to 170 to 180 "C. The entrainer gas is heated because, if cold gas passes over a hot sample, the caffeine will condense as a fog. Many of these particles then will be pumped through the system and not collected, thus causing low results. The caffeine will separate as white crystals in the cooled downwind side. These crystals are dissolved in chloroform and verified as being caffeine by infrared spectroscopy. 

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).]...

A similar method to PVM and FBRM is BVI (bulkvideo imaging), wherein a video camera is used through an observation window of the reaction vessel or a process endoscope employed. Simon et al. [26] used this technique coupled with UV-vis spectroscopy, FBRM, and calorimetry to monitor the crystallization of caffeine and palm oil. UV-vis spectroscopy and calorimetry were used for validation. BVI was shown to detect the boundaries of the metastable zone with comparable or better performance than FBRM and UV-vis probes. 

Table 3.2 Calibration data for caffeine solutions (cf. SAQ 3.3). From Stuart, B., Biological Applications of Infrared Spectroscopy, ACOL Series, Wiley, Chichester, UK, 1997. University of Greenwich, and reproduced by permission of the University of Greenwich...

In some cases, small amount of caffeine is added to soft drinks. Caffeine has a classic bitter taste that enhances other flavors. UV spectrometry, HPLC, and CE are used for the determination of caffeine in beverages. All of the above methods require sample preparation. FTIR spectroscopy with chemometrics, using partial least squares first derivative spectrum in the region between 2800 and 3000 cm have been developed to directly determine the caffeine in soft drinks. 

Of particular interest are the solubilities of cobalt-, nickel- and copper-halide complexes in dense supercritical aqueous phases. Aquo- and halide complexes have higher coordination numbers at higher density. Several of gaseous solutions are highly coloured (for example dark blue cobalt-II solutions). Visible and UV-spectra, which permit to determine the stability ranges of various complexes have been reported by us up to 500 °C and 6000 bar [43-45]. The results may have interest for hiture catalyst developments. We have used near-UV spectroscopy to determine the solubility of organic solids in various dense gases. Examples are anthracene [46] and caffeine [47] to 200 °C and 2000 bar. Supercritical extraction has become a widely applied procedure in the food, pharmaceuticals and other industries. 

The caffeine obtained from tea or coffee can be purified by sublimation using the procedure described in Experiment 13A. At your instructor s option, you may combine your sample with another student s sample for sublimation. After sublimation, determine the weight of caffeine recovered and calculate the weight percentage recovery of the caffeine. Compare this value to the amount of crude sample obtained. At the instructor s option, determine the melting point of the purified caffeine. The melting point of pure caffeine is 236°C however, the observed melting point will be lower. Submit the sample to the instructor in a labeled vial unless it is to be used for infrared spectroscopy (recommended) or mass spectroscopy (also recommended). 

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