I have used nitrate ion selective electrode and they are a handful to work with in particular in high salinities. With freshwater it would probably be somewhat simpler. Ammonia electrodes I haven't used personally, but most people do not recommend it as it is based on ammonium gas rather than ammonia cation (for the most part) and with a gas selective membrane which do not always work well (I have experience with a similiar electrode type, the CO2 and it is very difficult to calibrate).

I have used both electrodes in the past with no problem. They worked well in freshwater, despite of the high organic load. I used the Orion brand and prepared the ionic strength solutions my self which save me lots of money. I did not have problems with the gas membrane. You need to take care of them though...

Dear Mrs Kondrlova, I have experience in the manufacturing of ISE. ISE-NH4+ can be manufactured using nonactin as ionophore and PVC membrane. The selectivity is not good in the presence of potassium ions, but is possible to minimize this problem applying multivariate calibration or a system based on flow injection analysis. It is not necessary to use electrode for ammoniun gas. ISE-NO3- can be also manufactured of similar manner.

Use the Ammonium ISE to measure levels of ammonium ions introduced from fertilizers in soil. It can also indicate aqueous ammonia levels if sample solutions are acidified to convert NH3 to NH4+ and its interfering ion is K+

The Ammonium ISE has a combination-style, non-refillable, gel-filled electrode. Like all other PVC ISE membranes, the membrane on the ISE has a limited life expectancy.

Like as ammonium ISE, the Nitrate ISE also has a combination-style, non-refillable, gel-filled electrode and membrane on the that ISE has a limited life expectancy. The interfering ions of nitrate are: CIO4-, I-, ClO3-, CN-, BF4-

Thank you all for reply. Up till now, our laboratory is more physical than chemical, so we do not have many experiences with chemical analyses. Recently we have started to measure pH and determine Cox. We have bought electrodes from Czech manufacturer Elektrochemicke detektory spol. s.ro., so I do not expect, that you have used the same one. We would like to determine NO3- and NH4+ in fresh soil samples. Do you have any experience how to prepare soil suspension for this kind of analysis?

Dear Mrs Kondrlova, below follow 2 articles about subject. Unfortunately, I don't have acess to Journals, but I believe that you, may to print in any library of your country. The articles use ISE and FIA. Then, I think that they explain the procedure for soil analysis.

1) THE RAPID-DETERMINATION OF NITRATE AT LOW CONCENTRATIONS IN SOIL EXTRACTS - COMPARISON OF ION-SELECTIVE ELECTRODE WITH CONTINUOUS-FLOW ANALYSIS; LI, S; SMITH, KA COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS; 15 (12), 1437-1451, 1984.

2) FLOW-INJECTION ANALYSIS OF NITRATE IN SOIL EXTRACTS - EVALUATION OF A NITRATE-SELECTIVE FLOW ELECTRODE METHOD; SCHALSCHA, EB; CHIRADO, T; VERGARA, I; SOIL SCIENCE SOCIETY OF AMERICA JOURNAL; 45 (2) 446-448; 1981.