help with high EMV value

[emma2009]

Hi everyone, i have a question about high EMV values I keep getting in my GC-MS.

I had high EMV volts values (2600 to 2800) no matter what. I tried clean the source, replaced the filaments with new ones. There is no leaks in the system as indicated by the water/air check. Right now, the GC/MS still works, but I am not sure if the high EMV means any damage done to the system or if there is any thing we have done wrong that caused it.

I am wondering what could cause a high EMV values. I have another student in the lab who always runs gas samples with very high VOC concentrations in it on this GC/MS. I am wondering if that actually contributes to this high EMV value..

By the way, we are using HP5972A MS.

Is there any solution to this problem? Any suggestion/help will be really appreciated...Bow...

Emma

[nkg]

do you have copies of previous tune reports?

If so you can see whether there is a trend happening with the emv or if something has occurred at one time causing this high value, as you have cleaned the source and are happy that the system is leak free I would be changing the multiplier, these can be purchased locally from most suppliers at a reasonable cost, you are looking at a couple of hours down time to change this and then hopefully you should be ok. when was the multiplier last changed anyway?

when you say your student runs samples with high concentrations, are they still getting correct peak shape or are they getting flat top peaks? ie detector saturation, what are the levels of the peaks being obtained?

[emma2009]

I do not think we have change the multiplier for a long time...And the student was happy with the peaks and she was able to get her thing calibrated and samples analyzed...So I assume that did not saturate the detector...

I guess a multiplier might be a good possibility that caused problem coz the EM volts increased a lot but with time...Not a sudden thing...

Thanks!

[nkg]

dont go direct to agilent unless you have money to burn, do a quick search online and you should be able to save some money

[thohry]

May be the student did not turn off the EM when the solvent eluted.
I used to use a 5972 and normally the EM horn lasts quite long (about 1 year or more)

[carras]

As nkg noted before, my guess is that the multiplier needs changing. I should point that mine died suddenly after working at about 2400 eV for a long time. The last one I had to change was working OK for more than 10 years . I tend to have very long solvent delays and shut off the filaments as soon as feasible at the end of the runs (MSOff). Probably that helps to ensure a long life to multipliers and filaments (they last me for years).

[Uros]

Check on surce if the screw is not over tightened, it can create crack in the plastic surrounding it, so the electricity could jump through (sorry don't know the right english word)