Nitrogen Phosphorus Detector NPD - conditioning frequency ?

[jeddallebach]

I’ve been working with an NPD. I'm still trying to optimize the method and I realize that the air is consuming extremely fast (one tank in a week), so I thought that it may had a leak but I checked all the connections and did not detect any outside leak. Since I have had to turn off the gases to save gas every day and therefore the instrument I am conditioning the bead every day and I don't know if that is bad for the instrument. Another thing that I noticed is that after the bead is conditioned the chromatograms are pretty good based on base line but after about the fifth run the baseline starts getting bad (wavy and with negative peaks). Any way to improve this?  Also the peak does not look clean at the tip, it actually has several tiny peaks so when I integrate the peak is actually integrating all of those little dips at the top of the peak. Do you have any suggestions, possibly? Thank you for any help. Cheers, J

[AICMM]

jeddallebach,

An NPD does not take more air than an FID so I would guess that something is wrong with your air situation. Typically about the same air flow but much less hydrogen. What is your flow set at for the air?

The presence of little peaks on your peak makes me wonder if you are working near the detection limit of the detector and the top of the chromatogram is actually noise. Can you post more about the parameters of your analysis like the flow rates, sample concentrations, etc.... that might help us troubleshoot the problem.

Finally, you might consider contacting DET in California for help setting up your NPD.

Best regards,

AICMM