Single interface flow system with potentiometric detection for the determination of nitrate in water and vegetables

In this work a single interface flow system (SIFA) with potentiometric detection was for the first time implemented and applied to the determination of nitrate in waters and plant extracts. The analytical potential of the SIFA system was exploited not only to transport the sample towards detection but also to carry out, in a reproducible and automated way, the tasks associated with sample pre-treatment, namely ionic strength, pH adjustment and interfering species suppression. The advantageous aspects of combining a SIFA system with potentiometry with enhanced simplicity, ease of implementation and automation were further discussed and emphasised. The obtained results showed relative deviations lower than 5%, for both types of samples, with sampling rates of about 40h(-1). In addition, an innovative and straightforward process for constructing plastic membrane ion selective electrodes with a tubular configuration able to be coupled to flow-based analytical systems is also proposed. The developed approach, consisting of assembling the electrode inside a flow tubing connector is very simple to implement, robust, particularly adequate to be combined with flow methodologies and maintains all dynamic and analytical characteristics exhibited by previous assembling processes.