2. Experimental
2.1. Apparatus
The multi-pumping flow system was constructed with five solenoid micro-pumps (Biochem Valve Inc., Boonton, NJ, USA) of 8 L (P2and P3) and 10 L (P1, P4and P5) nominal volumes; onethree-way solenoid valve (NResearch, West Caldwell, NJ, USA); polyethylene tubes (0.8 mm i.d.) and acrylic joint points.
All micro-pumps were operated at 5 Hz, except P4 that worked at 1 Hz in the sampling step.
The active devices were controlled by a Pen-tium I microcomputer equipped with a parallel interface, through a current drive based on an ULN2803 integrated circuit.
The control software was developed in Microsoft Visual Basic 6.0.