Does somebody have experience with the new Agilent's NPD (for 6890GC? I am trying to use it for analysis of pesticides but I am not very satisfied with it, so far. It happened a few times that the signal fell down to 3-4 during analysis and later raised to normal operating value (between 30-40). Gas flows are as follows: hydrogen 3 ml/min, air 60, no makeup, carrier helium 4 (constant flow, detector temperature is 320. Are these conditions good or can be optimised? What lifetime can I expect from this type NPD? How to extend its lifetime?
By Anonymous on Monday, June 18, 2001 - 07:38 am:
Did the signal drop after an injection and not recover or did it drop during the middle of a run. If the signal does not recover after the solvent "peak", you may need to turn the hydrogen off at the time of the injection then turn it back on after the solvent has passed through the detector. The manual also states that adding makeup gas at 5 mL/min or running the detector at a higher offset may be used to eliminate this problem.
As far as extending the lifetime, if you use the auto adust function, we have found that setting the bead voltage to zero before you turn it off seems to help. On our unit, we found that if we did not set the voltage to zero on shutdown, when we started it back up with the automatic adjust offset function, the bead voltage would immediately jump to the last value entered before it was turned off. Starting from zero resulted in more gradual adjustments which should extend bead life. Putting a value of zero for the bead voltage before starting the auto adjust may work the same but I haven't tried it.
By MBSetzer on Tuesday, July 24, 2001 - 10:40 am:
check the latest edition of the newsletter *DET Report* No. 41, June 2001.
Very advanced newsletter when it comes to thermionic detection.
Their phone # is 925-937-4203, their email: firstname.lastname@example.org
I am not affiliated with them, I just read the newsletter . . .
Hope this helps,
By Rolandas Plausinaitis on Wednesday, July 25, 2001 - 02:37 am:
Be aware, that there are two types of beads - original white (G1534-60570) and black (5183-4647). Black is claimed to be more longliving, and to have less tailing on phosphorus compounds, but less "sensitive".
My first white bead I used about 1 year (not many analyses). At the end of life except voltage increase it started to show "bumps" (don't remember exactly, around 5-10 pA for 0,2-3 mins)on the baseline, mostly positive, but sometimes also negative. Second bead was dead wery fast (in about 12 weeks) and Agilent agreed to replace it. Next one I installed was black type and I'm still using it (15 months).
On the newer instruments there is change of firmware preventing jump of bead voltage to the last used value, instrument increases it slowly (There is a message "NPD bead sleeving").
By recai on Monday, July 12, 2004 - 06:58 am:
We want to analyse pesticides in foods.
We willl buy a new GC but we can't make an election between agilent and varian.
Is there anyone who has experiences these two trademarks.
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