The Chemistry of Caffeine - Caffeine: Chemistry, Analysis, Function and Effects - page 47

The pure product is claimed to be stable but will decompose in the presence of
alkali (WHO-IARC 1991) and by heating (HSDBank 2011). Polymerization of
caffeine does not occur. No data is available concerning caffeine reactivity
towards other substances, however it has been reported as non-corrosive to
glass by the manufacturers in the product MSDS - Material Safety Data
Sheet (Sciencelab 2010). The product must be stored in airtight containers
(HSDBank 2011).

d n 0 t 2 n g | 1

3.3 Spectral Data
Caffeine presents a maximum absorption in the UV-Vis range at 276 nm,
which is the wavelength used in most official UV-Vis analytical methods
(Ohnsmann et al 2002; Belay et al 2008). The spectrum obtained by infrared
spectroscopy (FT-IR) shows bands between 1800 and 1500 cm 21 ,an
additional band at 1050 cm 21 , and the most intense bands at 1710 (carbonyl
group), 1659 (carbonyl group) and 1554 cm 21 , respectively (Garrigues et al
2000).
The mass spectra of caffeine after electron impact (EI) ionization and
collision-induced dissociation, under vacuum conditions, will present the
typical molecular ion at m/z 194.0 and fragments at m/z 108.9; 67.0; 82.0; 137.0;
165.0 (Verenitch and Mazumder 2008). Ionization at atmospheric pressure
using an electrospray source (ESI) will generate typically m/z of 195.0
(molecular ion plus a proton, [M+H] + ) and m/z 138.0 and m/z 110.0 as most
intense fragment ions after collision in a quadrupole cell (Carvalho 2011).

3.4 Technical Substance, Identification and Impurities
Caffeine can be obtained in many commodities and forms, related to its
various uses. For medical and cosmetic purposes, specifications are described
for either the anhydrous form or the monohydrate by the national
pharmacopoeias, as well as the European Pharmacopoeia (European
Pharmacopoeia 2008). The anhydrous form of caffeine must obey the
following specifications: contain not less than 98.5% and not more than the
equivalent of 101.5% (m/m, by dry weight) of the active ingredient, i.e. caffeine.
The first identification is made by the melting point (must be within 234 uC
and 239 uC), by infrared spectrophotometry referenced to a caffeine certified
reference material (CRM) (e.g. Fluka TraceCERT 1 56396) or by the test of
loss on drying (0.5% max. weight loss when drying 1.000 g in an oven at 105 uC
for 1 hour).
For the second identification, three tests are described in the European
Pharmacopoeia including a selective precipitation reaction and a specific
reaction on xanthines (European Pharmacopoeia 2008).
The most relevant impurity described for caffeine technical material is
theophylline. Other relevant impurities are N-[6-amino-1,2-dimethyl-