How to analyse for sodium nitrate

A. Tony,

If your only source of sodium and nitrate in the bath is from this compound then you could measure either one of those using ion chromatography equipment.

A. I guess one of the many commercial test kits for nitrate in well water or drinking water will do the job.
The analysis method would than be something like this:
- make a 1 : 1000 dilution (commercial kits will normally measure in 0 - 100 mg/l range)
- fill a 5 ml test tube
- put test tube in photocell
- read concentration of nitrate or nitrate-N
- convert tot sodium nitrate

Check with the local supplier of these test kits for unwanted side reactions from other components in your application.

A. There is a titrimetric procedure.

A portion of the sample is added to 100 ml of concentrated sulfuric acid. This is then cooled to 0 degrees C. While maintaining this temperature, the mixture (with continuous stirring) is titrated with standard ferrous sulphate ferrous sulphate [affil links] solution. A good titer to use is 0.25 N. The ferrous sulphate ferrous sulphate [affil links] solution must be standardized vs. a standard solution of nitric acid on the day of the analysis.
The endpoint is a rose color that persists in the acid titration mixture for at least 60 seconds.

You could also run it via nitrate selective electrode, or if you have a UV spectrophotometer, there is a direct reading method. Neither of those things are cheap, but the titration I describe is not easy to do and you might decide to spring for one of them after you do it a few times.

Good luck!