With the ever increasing number of samples to be assayed in agronomical laboratories and servicing stations, fertilizer and food industries, sugar factories, water treatment plants, biomedical laboratories, drug quality control, and environmental research, the interest for automated chemical analysis has been increasing. In this context, flow analysis is very attractive, as they the flow-based procedures are characterized by enhanced analytical figures of merit. Moreover, the flow analysers do not usually require sophisticated and expensive instrumentation, are amenable to full automation...