GC/MS - Testing your System

[Absolutdude]

Hello,

i want to test my GC/MS (Agilent GC 78990A + MS5975c) because I think that it doesn't work as sensitiv as it should.

How can I test it? Should I order standards to check it or are there certain methods where you can easily check?

What is a normal detection limit for this GC/MS or fo GC/MS in generall?

THanks for the Help,

Dude

[Don_Hilton]

There is a sensitivity test used by the vendor on installation.

Before running sensitivity tests, be sure all the preventative maintanance tasks are up to date. And, to test the instrument, you would do well to install a new column - as column age can affect background and peak shape on the run of the test sample.

With the mass spectrometer, the tune check gives you an indication of the sensitivity of the mass spectrometer itself. As the detector ages, the voltage requried to maintain signal increases. If you run the instrument at a particular voltage relative to tune, the sensitivity of the mass spectrometer will be close to the same - the same measured signal for the level of PFTBA delivered during the tune check.

Because you often move away from the instrument configuration used by the vendor for running the sensitivity test, it is not a bad idea to measure signal to noise on a low level standard for the method you run and then to monitor the signal to noise measurement on that standard (make it up fresh every now and again...) to monitor system performance. This becomes part of your daily, weekly, or whenever instrument qualificaiton.

[R13]

Page 76 of "Agilent 5975 Series MSD Operation Manual"

[Absolutdude]

Thanks for you help...

I am still working on the problem with the sensivity-check.
It I want to verify the tune performance. I become an Error... "Error 8 - There is no Emission"
Same Error if I do "GainTune" or any other Tune (except of TuneMSD).

But I don't understand it, because I can do the "TuneMSD" and I can run real Samples an get Chromatogramms with Spectrums. So the filament is okay and there is actually emission.

If I start verifying the sensifity performance (as written on page 76 in the manual) I get an Error about the "frontinlet-pressure" which I don't get as well. Because the Frontinlet is directly connected to an Thermodesorber. And there shouldn't be any pressure problems.

Do you know what is going wrong there?

[AICMM]

Absolutdude,

1) Can you post a tune?

2) Can you tune on both filaments?

Best regards,

AICMM

[R13]

You did not mention thermodesorber before - I do not have experience with them.
Does all carrier gas supply go trough thermodesorber? Generaly "Front inlet - pressure" error means that with the selected column flow and split values there is not enough entrance pressure available- it should be increased.

[Absolutdude]

hello,

1) I would like to post a tune. I just made one and safed the data .But I haven't found out how to post a picture in this forum. (I also could mail it to you if you want)

2) No, I can't tune on Filament1. I think this is not working anymore. I still can do the "Tune MSD" on Filament2. I have to change Filament1 in the next days. But I don't understand why I can't do all the offer types of tunes with filament 2.


The Thermodesorber is connected to the front inlet. But I do not work with it at the moment (it is switched off).
I work with a split/splitless at the back Inlet. So I thought I can do a sensivity check without caring whats at the frontinlet.

[Don_Hilton]

If there is no column mounted in the front inlet, set the gas flow to the front inlet to "off" then there will not be a failure on being able to maintain pressure.

Do you, by chance have both inlets connected to the analytical column with a "Y" connector or two columns connected with a "Y" connector going into the mass spectrometer? If so, there are a couple of pathways for gas flow (which can include air sucked into an "unused" inlet), which can give an excess of gas flow into a mass spec - and loss of sensitivity.

[Absolutdude]

Yes, I have both inlets connected to a column, connected with an "Y" to the mass spectrometer.

At the moment I do maintaince. (Cleaning Ion source, changing Liner, trimming Column) to see if this maybe will solve the probem.

I just noticed that in my tuning reports that the values for the PFTBA are not were they should be.
I read the schould be for the autotune about
m/z 69 = 100% ; 219=35-85% ; 502= 1-5%

mine are 69=100% ; 219= 130% ; 502= 15%

What can that mean?

[tlahren]

Yes, I have both inlets connected to a column, connected with an "Y" to the mass spectrometer.

At the moment I do maintaince. (Cleaning Ion source, changing Liner, trimming Column) to see if this maybe will solve the probem.

I just noticed that in my tuning reports that the values for the PFTBA are not were they should be.
I read the schould be for the autotune about
m/z 69 = 100% ; 219=35-85% ; 502= 1-5%

mine are 69=100% ; 219= 130% ; 502= 15%

What can that mean?

If you have both columns connected with a "Y" then make sure in your method you have the front inlet set up with some flow (I use constant pressure @ 1 psi for my application). This will keep He going through the column and prevent air from getting through the column and into the MS.

I think the pressure issues are at least half your problem.

Try to disconnect the columns and install a plug at the MS interface. Now run your Autotune etc. and see what the values are. This will tell you if your MS is the problem or your GC.

[Don_Hilton]

Assuming that the MS looks good when plugged off, I would strongly suggest installing only one column and not using the Y connector to check out the operation of the instrument. These types of systems are great when they work - but can be a pain when they don't. Leaving the Y out of the system while checking things out keeps it as simple as possible. Add the complexity back in after you are sure that simple works.

When eliminating the Y connector, the best option is a column from the inlet all the way through the transfer line. If you have to join column segments, be sure to leak test the union between column segments.