Sorry for the delay in getting back to you.
So I came across an error message that I had gotten on May 31st on the instrument in question, that said” NO3 Failure- Restart
If problem persist call technical support” I restarted the instrument at that time, and things seemed ok right after that. This was on a Thursday, and I didn’t have any samples on Friday and then tried to get things going on the following Monday, and that is when things seemed to start going south. I had forgotten about his message by that time, and was distracted with the method not running, so sorry for not mentioning it. Things seemed to have settled down right now, And I haven’t gotten this message again. Hopefully it was just a computer glitch and turning the instrument off and restarting it has gotten rid of it. in answer to your question though:
Yes we run efficiency checks for the Cd coil daily to ensure efficiency between 90-110%.
The tubes for the instrument in question were changed on April 2, 2018. I make sure the tubes are at that length, but the company sent replacement tubes that are 4” in length, so they need to be cut.
The pH of the reagent is at 8.5 and is tested on a meter, which is calibrated before use. We have never used the pH at 9.1 for the acid preserved samples, and after reading you message I made up the ammonium chloride-EDTA at that pH and ran a calibration for this method. It was a mess, so not sure what is going on with that. Could be the settings on the instrument (?) I remember when we first got the instrument (2006) we were adding ammonium hydroxide to the samples before running them, but somewhere along the way this was stopped and I really don’t remember why. Seems like we started using SO4 in the reagent water and diluent. I think through the years, when there is an issue, we call in and get someone who gives advice and then things get changed and they continue that way. Anyway we are currently using the same reagents as the NO3 method for drinking water for the acid preserved samples.
Color reagent is stored in foil wrapped bottle in a fridge. We just bought new chemicals to make this to ensure no contamination.
I tried running on the other smartchems in our lab. We have 3, but didn’t get a calibration to pass, but I think that is due to not running the method consistently on the other instruments. By the time I got the Cd coils reactivated/reconditioned things seemed to clear up on the one that was giving me problems.
I do have one other question, what is it method for de-chlorination of samples with sodium thiosulfate? We tried this and it seemed to deactivate the Cd coil. The same thing for the addition of EDTA, there are no amounts listed in the Smartchem method