Experimental procedures. Experimental studies on
the development of procedures for determining purine
alkaloids, based on the photometric measurements of
the reaction of their joint oxidation with MBTH, were
conducted in flow systems schematically shown in
Figs. 1 and 2. When developing the FIA procedure, we
use a threechannel system (Fig. 1a), in which the
sample microvolumes (V) are injected into a continu
ous carrier (water) flow that then is mixed with flows of
the oxidant (potassium periodate) and reagent
(MBTH) solutions. After the indicator reaction is
completed, the reaction zone enters the flowthrough
cell of the spectrophotometric detector, and the absor
bance of solution is continuously recorded at a prese
lected wavelength of 630 nm. A jump in the absor
bance of the reaction zone relative to the absorbance
of the mixture flow of the oxidant and MBTH solu
tions (the baseline) served as an analytical signal.