Ammonia Gas-Sensing Electrode (501)

Product Description

Type 501Ammonia Gas-sensing Electrode

This electrode is an electrochemical sensor used for measuring the dissolved ammonia and ammonium salt in aqueous solution. It maybe as well used for the determination of nitrate-nitrogen, total nitrogen, organic nitrogen etc. Its construction is shown in figure 1. A gas-permeable membrane is fitted on the base of tube. In tube the middle electrolyte (internal electrolyte) is filled. The internal sensitive elements consist of a glass electrode with flat head and a silver/silver chloride electrode. The pH sensitive glass membrane on the flat head is screwed down on to the membrane so that it sandwiches a thin film of the middle electrolyte against the membrane. When ammonia gas-sensing electrode is immersed in alkaline determinant solution contained NaOH, ammonium salt in solution converts to ammonia, which diffuses into the middle electrolyte through the membrane and undergoes the following reaction: NH3+H2O=NH4+OH-

The concentration of NH4 present originally in the middle electrolyte is probingly more than the quantity of NH4 formed by the above reaction, therefore its change may be negligible. But the pH of middle electrolyte in the thin film rises due to the OH- formed. The activity of Cl- in middle electrolyte is constant. The potential of AG/AgCl reference electrode therefore is constant. When the temperature is constant, thus the potential of the electrode couple consisted of pH glass electrode and AG/AgCl electrode varies only with the change of pH in middle electrolyte. That is to say, the potentials measured would be similarly a Nernst relation with concentrations of ammonia in external test solution.
2.3 RT
E=Const - ---------log(NH3)
F
The blank potential is about +80mV.
The linear range (when measuring ammonia) is 1*10-5---1*10-1mol/l. Its limit of detection is about 5*10-6mol/l. It is suitable for room temperature not above 40oC.

This electrode consists of outer tube (gas-permeable membrane has been fitted on but middle electrolyte has not been filled yet) and internal electrode. Additionally the gas-permeable membrane is included.