Spiking with a Agilent 7890 with SCD

[hobbes922]

I am trying to figure out why the online signal of my GC is showing large peak looking spikes every minute. We tried turning off the ozone generator, changing the septum/liner, and switching power outlets. Does anyone have any ideas?

[tkubowicz]

Hello

If you have FID detector probably those spikes come from graphite (small particles from ferrules). So I'd recommend:
1. Put new ferrule to the column nut
2. Trim your column a bit - make sure that tip of the column is not covered with graphite from ferrule (sometime you can see grey collar around column and it comes from ferrule)
3. Install your column as it should be in FID - about 1-2mm below the tip of FID jet.

It should do the trick.
Good luck

Regards

Tomasz Kubowicz

[hobbes922]

Hi Tomasz,

Thanks for the advice, but we are using a SCD, not a FID.

Hello

If you have FID detector probably those spikes come from graphite (small particles from ferrules). So I'd recommend:
1. Put new ferrule to the column nut
2. Trim your column a bit - make sure that tip of the column is not covered with graphite from ferrule (sometime you can see grey collar around column and it comes from ferrule)
3. Install your column as it should be in FID - about 1-2mm below the tip of FID jet.

It should do the trick.
Good luck

Regards

Tomasz Kubowicz

[tkubowicz]

Hello

So why don't you give us all information than? Methods parameters, chromatogram?

Do you want us guessing?

Regards

Tomasz Kubowicz

[hobbes922]

Here is a picture of the online signal from the 355 SCD:

http://postimg.org/image/p3jncqsd7/

We have tried turning off the ozone, baking out the GC, changing septums/liner, and checking connections.

We are seeing these signals despite not running any sample.

[antonk]

Probably
* Water in gas supply lines
* Try to disconnect SCD from AIB - do spikes appear? If so - check the GC electronics
* Phase (not properly bond to column) so your current condition wash the phase remnants to detector
* You have non-proper plumbing which periodically "whistles" and drops pressure
* EPC/APC is dirty, try to select another channel

[hobbes922]

Hi Antok,

Thanks for the reply! I wanted to give an update.

1 and 4 - The gas plumbing is good and there is no water.
2 - I disconnected the SCD from the AIB and the signal became steady - with no noise or spiking. This returns once I plug it back in.
3 - Hard to tell, but we did trim the column a little and make sure it wasn't clogged.

It seems as though the problem is lying with the SCD itself, not the GC based on this test.

Probably
* Water in gas supply lines
* Try to disconnect SCD from AIB - do spikes appear? If so - check the GC electronics
* Phase (not properly bond to column) so your current condition wash the phase remnants to detector
* You have non-proper plumbing which periodically "whistles" and drops pressure
* EPC/APC is dirty, try to select another channel

[muGC]

How old is the SCD?

This looks like electronic noise from the PMT, likely indicating that the PMT has failed and needs replacement.

[hobbes922]

Its pretty old - from 2010. It could be very likely that the electronics are causing the issue.

How old is the SCD?

This looks like electronic noise from the PMT, likely indicating that the PMT has failed and needs replacement.

[hobbes922]

Follow up for those who may have the same issue.

The problem was with the power supply board inside the SCD. It was humming, and when it was replaced, the signal stabilized.

[muGC]

what was the Part Number for your replacement?