WEF Discussion Forums
Laboratory Management and Technical Issues
Ammonia Issues Again
We do ammonia by ISE. We were having slope issues so we tried some old probes, same problem. We bought a new probe, it worked one day and then same issues. We tried it on another meter, same problems. Both meters work for ISE for nitrates with no slope issues. We've used new/old ISA (10N NaOH we make up) and new/old calibration standards. Any suggestions...I'm running out of scientific method choices.
From past headaches, are you determining the slope following the procedure outlined in the manual or the meter output from running standards? When we were pushing the lower limit of the probe with our standards, the meter generated slope was beyond the anticipated range. In talking to tech service, they suggested following the method to determine slope outlined in their manual. It worked. They later explained that the slope variability is more when you're using the meter's slope and low level standards.
Plan B....check with the manufacturer's technical support. To facilitate the call, you may want to systematically go through probe troubleshooting procedures and have the answers handy when you make the call.
Please let us know the final resolution. We'll all get stuck there sometime.
Are you standards preserved. They will loose strength with time and the the slope is not correct as all the standards are low. It would be impossible to get results then.
What do all of the probes have in common? Same lot of ammonia membranes? Same filling solution? Do you have another lot that you can try?