YSI 9600 - Manual (Page 71)

8.2 EFFECT OF PH
The pH of the solution reacting with the copper activated Cd can have a major impact on reduction
efficiency and the lifetime of the Cd/Cu particles. Hydrogen ions are required for the reduction of nitrate to
nitrite, but if the hydrogen ion concentration is too high, additional reduction of the nitrite will occur. At
the other extreme, if the pH is too high, cadmium hydroxide can precipitate in the column causing rapid
degradation in performance (1). For natural water samples, YSI has observed the longest cadmium column
life using the ammonium chloride solution (1.6 M) (not truly a buffer) which is characterized by a pH of 6.
YSI has found higher pH solutions to significantly reduce column life for natural water samples.
8.3 FLOW SYSTEM DETAILS
The above chemistry is achieved using flow injection analysis. A manifold of 7 pumps delivers sample and
reagents in sequences defined by preset schedules in the instrument as shown in the diagram below.
First, the environmental water sample is pumped to fill the entire system – the purpose of this is mainly to
purge the inlet filter so that a representative sample resides at the inlet. Next, four pumps operate
simultaneously until the reagents reach a steady-state concentration at the detector. Two pumps push
sample and buffer through line A and the cadmium column while another two pumps push sulfanilamide
YSI Environmental 71 Model 9600 Nitrate Monitor