Hi all,
The practical problems are:
1. that they are difficult and fiddly to calibrate, (you have to take into account any chloride ions in solution) http://www.nico2000.net/Book/Guide7.html
and
2. The nitrate (or ammonia) content of the sample is changing all the time, so you need to "fix" the sample immediately, from the link for nitrate "must be treated to prevent bacterial activity reducing the nitrate concentration before measurement. Boric acid is used as a preservative to prevent this and should be added to your samples at the time of collection. The amount recommended is 2 mL of 1M boric acid to 100 mL of sample".
3. Even a fixed sample gives you a "snapshot", and a leak of silage liquor or ammonium nitrate spillage may pass as a relatively rapid pulse down stream, leaving clean water before and behind it. This is why biotic indices (basically a scale calibrated using the amphibious invertebrate assemblage) and B.O.D tend to be more useful.
You can use ion selective electrodes (and they are used by the EA etc.) for continual monitoring, but you still have the problems of drift and calibration.
There are also newer "cheap" ion specific meters, but I've not tried these. http://www.alanaecology.com/acatalog/Nitrate_Meter.html
cheers Darrel
The practical problems are:
1. that they are difficult and fiddly to calibrate, (you have to take into account any chloride ions in solution) http://www.nico2000.net/Book/Guide7.html
and
2. The nitrate (or ammonia) content of the sample is changing all the time, so you need to "fix" the sample immediately, from the link for nitrate "must be treated to prevent bacterial activity reducing the nitrate concentration before measurement. Boric acid is used as a preservative to prevent this and should be added to your samples at the time of collection. The amount recommended is 2 mL of 1M boric acid to 100 mL of sample".
3. Even a fixed sample gives you a "snapshot", and a leak of silage liquor or ammonium nitrate spillage may pass as a relatively rapid pulse down stream, leaving clean water before and behind it. This is why biotic indices (basically a scale calibrated using the amphibious invertebrate assemblage) and B.O.D tend to be more useful.
You can use ion selective electrodes (and they are used by the EA etc.) for continual monitoring, but you still have the problems of drift and calibration.
There are also newer "cheap" ion specific meters, but I've not tried these. http://www.alanaecology.com/acatalog/Nitrate_Meter.html
cheers Darrel
