Chromatography Forum

Hi all,

I just reinstalled the GC column in the GC-MS in the lab and have run in to a few issues. The ion source temperature is quite higher than the setpoint of 45 degree celsius. It does not go below 67 degree celsius, even when the transfer line temperature is set very low, say 50 degrees. Additionally, m/z of 18 seems to be the most abundant ion during auto tune, higher than that of the calibration gas. I did not want to increase the source temperature or tthe temperature of the GC oven prior to seeing a decrease in water detected by the mass spec. The instrument was turned off for a couple of weeks before column replacement, and I had taken care to block the entrance to the mass spec off with an old nut and column to prevent accumulation of moisture.

What can be the issue here ? Can anyone help ? Thanks!

Hello

First of all provide information about GC/MSD (vendor)
Secondly...I don't know where you have method from but normal (recommended/most common) temperatures for ion source is 230 and 150 for Quad (Agilent)

Regards

Tomasz Kubowicz

If the vacuum was off then moisture can get into the analyzer even with everything capped off, simply because nothing is 100% leak proof.

Cool temperatures will cause the water to be trapped inside the metal and insulators of the source and will need to be baked out. You should probably set the source to at least 105C for a while to help bake out water.

As for the higher than 45c temp, just turning on the filaments will heat up the source and is probably what is causing it to be 65C, bump it up to 105c and see if it holds temp better. You won't damage the source until you are well above 100C even if you have some air and water in the system.

If the vacuum was off then moisture can get into the analyzer even with everything capped off, simply because nothing is 100% leak proof.

Cool temperatures will cause the water to be trapped inside the metal and insulators of the source and will need to be baked out. You should probably set the source to at least 105C for a while to help bake out water.

As for the higher than 45c temp, just turning on the filaments will heat up the source and is probably what is causing it to be 65C, bump it up to 105c and see if it holds temp better. You won't damage the source until you are well above 100C even if you have some air and water in the system.

Thanks James! I have started heating up the ion source to 105 degrees and increased the helium flow a bit. Hopefully it gets rid of the water. I don't see a lot of air in the system, compared to water, so I am keeping my fingers crossed. The manual says that precise temperature control of the ion source is for 100-320 degrees range. However, the lowest possible steady source temperature, prior to the column change, was 45 degrees. I am not sure why it increased after the installation though.

Hello

First of all provide information about GC/MSD (vendor)
Secondly...I don't know where you have method from but normal (recommended/most common) temperatures for ion source is 230 and 150 for Quad (Agilent)

Regards

Tomasz Kubowicz

The instrument is a Varian 300 MS connected to a Bruker 450 GC. Generally we set the ion source at 280 degrees. I just did not want to heat it up as I was not sure if heating it up with water could damage the system. Thanks Tomasz!