Analysis of Caffeine by Liquid Chromatography-Mass Spectrometry - Caffeine: Chemistry, Analysis, Function and Effects - page 109

d n 0 t 2 n g | 3

Figure 7.3

Schematic diagram of the DAPCI source used by Chen et al (2007) for
direct analysis.

analyze tea infusions, it would require an extra step to make the tea brew. On
the other hand, desorption chemical ionization (DAPCI) has been demon-
strated for direct surface analysis with enhanced sensitivity, thus enabling the
analysis directly on tea leaves (Figure 7.3). The DAPCI-MS and mass-mass
spectrometry (MS-MS) spectra of tea products were recorded in a linear ion
trap mass spectrometer (LTQ-MS). Caffeine was detected from tea samples as
protonated molecules at m/z 195. In the collision induced dissociation (CID)
experiments, caffeine ions generated two major fragments of m/z 138 and 110
by the loss of CH 3 NCO and CO, successively. This fragmentation pattern was
in agreement with previous observations in the literature (Ford et al 2005;
Venzie et al 2007) and with the data obtained using the standard compound,
thus confirming the assignment of caffeine.
Lin et al (2008) applied a LC-DAD-ESI-MS method to establish the profile
of phenolic compounds and purine alkaloids of 41 green and 25 fermented
teas. These samples could be organized in five distinct groups according to
their profiles; (1) high-grade teas, consisting of the younger buds and leaves
harvested in the early leaf-growing stage; (2) green teas; (3) partially fermented
oolong, tikuanyin and puerh teas; (4) fully fermented black teas; (5) highly
overfermented tou and chitsebenng black teas.
Wang et al (2008) used an HPLC-DAD-ESI-MS-MS method to analyze the
polyphenols and purine alkaloids in 22 different tea cultivars, from three
distinct origins (Fujian Province, Guangdong Province and Taiwan). Their
method, which was adapted from that of del Rio et al (2004), entailed
ultrasonic extraction in acetonitrile-water (1 : 1, v/v) and chromatographic
separation on an octadecylsilane (ODS) column with linear gradient elution by
the mobile phase consisting of acetonitrile and 1% formic acid aqueous