Analysis of Caffeine and Related Compounds by Automated Flow Methods - Caffeine: Chemistry, Analysis, Function and Effects - page 201

d n 0 t 2 n g | 3

Figure 11.5 Determination of caffeine in tea samples by the quasi-FI method.

Typical chromatograms of (A) PVPP (50 mg) cartridge-treated and (B)
non-treated samples of (a) oolong and (b) black tea by the quasi-FIA
system; (i) Due to the low separation efficiency of the short column
pretreatment with PVPP is critical and (ii) caffeine (3) and theobromine
(1) are adequately resolved for quantitative analysis. Other peaks: 2,
(2)-epigallocatechin; 4, (2)-epigallocatechin gallate; 5, (2)-epicatechin;
6, (2)-epicatechin gallate. (With permission from Elsevier, Yamauchi
et al 2008).

drink, coffee) has been proposed by coupling of FI to capillary electrophoresis
(CE) (Pu and Fang 1999). CE offers the critical advantages of minimum waste
generation, aqueous running buffers and high separation efficiency of both
organic and inorganic compounds. On the other hand, typical injection modes
in CE (electrokinetic or hydrodynamic) are performed in a batch way limiting
the potentials of automated sample preparation. A viable solution was the on-
line coupling of FI to CE (Kuban and Karlberg 2009). Pu and Fang separated
the three xanthines by FI-CE with a simple background electrolyte of borate
buffer (30 mmol L 21 ,pH5 10) and precision of better than 6% in all cases.
The recoveries from the analysis of real samples ranged between 91.6 and
105.8%.

11.4 Determination of Caffeine and Related Compounds
by Flow Optosensors
A major drawback of application of direct UV-Vis measurements in analytical
chemistry is the lack of sufficient sensitivity and selectivity. A viable solution