2.3. Preconcentration procedure
The systemrepresented in Fig. 1 was used for on-line preconcentration
and determination of Mn content. At the beginning of a cycle, both
valves are in the positions shown in the figure. In this situation, the
solution of manganese ions (S) fills the sample loop (L1). The peristaltic
pump P2 is turned off. Then the position of valve 2 (V2) is changed and
the pump P2 is turned on. In this step, the solution of Mn (II) is
transported to the confluence (T) by the carrier (H2O). Fromthis point,
the solutions of Mn (II) and reagent–surfactant (R) are mixed. The
mixture flows through the reaction coil (L2),maintained in a bathwith a
thermostat (B). After passing the coil (45s), the position of the valve V1
is changed, and the mixture passes through a minicolumn (C), where
the ions Mn (II) are retained. The other components of the mixture
followed to thewaste (W). Finally, the pump P2 is again turned off, and
the positions of the two valves V1 and V2 are both changed. In this
condition, a flow of eluent passes through the column, removing the
ions Mn (II) and carrying them to the nebulizer of FAAS. The analytical
signal is measured as the height of the peak in absorbance. At the same
time, the solution (S) completes the loop L1 to the next cycle. Thewhole
process for one cycle (120 seconds) resulted in an analytical frequency
of 30 cycles per hour.