DIFFERENTIAL FLOW-INJECTION POTENTIOMETRY WITH DOUBLE SENSITIVITY USING ONE ION-SELECTIVE MEMBRANE

Differential now-injection potentiometric determinations of nitrate wi th one ion-selective membrane fixed in a symmetrical flow-through cell and one reference electrode on each side of the membrane are describe d. The measured potential depends on the difference of the measuring i on activity on both sides of the membrane only. By connecting both sid es of the now-through cell with a tube and the sample contacting both sides of the membrane subsequently, double sensitivity is achieved. By varying the length of the connecting tube either separate or overlapp ing peaks are observed. As only the difference of the peak maxima is n ecessary for the determination of the concentration, this analytical m ethod shows good reproducibility and is independent from drift or nois e of the baseline. In this way, the nitrate content of tap water and s pinach is determined and compared to ion-chromatography.