Analysis of Caffeine by Liquid Chromatography-Mass Spectrometry - Caffeine: Chemistry, Analysis, Function and Effects - page 114

7.2.3 Biological Matrices

7.2.3.1 Urine, Plasma and Saliva
The first reports of the use of LC-MS for the analysis of caffeine in biological
samples date back to the end of the 1980's. Setchell et al (1987) reported the
development of an LC-MS method employing thermospray ionization for the
analysis of caffeine in human serum and saliva. In the following year, Sakairi
and Kambara (1988) published a paper on the first use of atmospheric pressure
ionization (API) for the analysis of drugs, including caffeine in human serum.
In 1995, Hieda et al (1995) established a sensitive and reliable analytical
procedure for the detection of theophylline, theobromine and caffeine in
human plasma and urine by gradient capillary HPLC-frit-fast atom
bombardment (FAB) MS. FAB is a relatively soft ionization technique and
produces primarily pseudomolecular ions. The material to be analyzed is
mixed with a non-volatile chemical protection environment called a matrix and
is bombarded under vacuum with a high energy beam of electrons (4 to 10
keV). The nature of its ionization products places FAB close to ESI.
In the background of assessing the exposure of restaurant and hotel workers
to environmental tobacco smoke, Tuomi et al (1999) reported a method for the
simultaneous analysis of nicotine and its metabolites, together with caffeine, in
urine by HPLC-MS n . Identification and quantification were performed using
ESI on a quadrupole ion trap mass analyzer. Caffeine detection limit of the
whole procedure was 5 mgL -1 , with a 92% recovery.
Many analytical methods were reported over the following years, usually
including improvements in aspects such as sample preparation, selectivity,
sensitivity and speed.
Recently, Arinobu et al (2009) established an automated on-line method for
ultra-fast determination (2 min) of caffeine and theophylline with backflush
column-switching and with a monolithic separation column. Serum sample

d n 0 t 2 n g | 3

Figure 7.6

Diagrams of a backflush column-switching system employed by Arinobu
et al (2009).