In multi-syringe flow systems it is not feasible to introduce
the sample into the system through one of the available
syringes, as it would take a long time of washing steps to
avoid carry-over between consecutive samples. Hence, other
devices (selection or commutation valves) must be incorporated
to the manifold to provide access to these solutions.
Therefore, valves V5 and V6 were included in the present
manifold. The tubing connecting these two valves (Fig. 1A,
L1) defined the volume of sample to be introduced into the
flow system. Moreover, the tubing L2 (Fig. 1A) was placed
in the flow manifold to allow previous reduction of Fe(III) to
Fe(II) prior to the colour reaction