spiky baseline

[chemwipe]

Hello-

I have a rather spiky baseline. I have done all routine maintenance (trimmed column from injector side, changed liners and septa, cleaned out injection port with acetone) and I have also baked out the ECD at 400C (with flow) for a few hours. There doesn't seem to be much of a change in the way the baseline looks.

Could this possibly be an electrical issue? I don't think there's anything more that I can do.

CW

[KC]

you say spikey baseline, these would not be a bunch of negative spikes are they? What is you signal when you set your detector to about 300 for awhile?

[chemwipe]

you say spikey baseline, these would not be a bunch of negative spikes are they? What is you signal when you set your detector to about 300 for awhile?

I guess I mean noisy...when you zoom in on the baseline it looks really spiky though.

My signal is between 400 and 1000 when the detector is at 325; unfortunately I'm not sure where it was before I had this problem.

CW

[KC]

I ask because we have an ECD that I performed very similiar maintence to the injector recently due to a spikey baseline and high signal. Spikes are primarily negative and signal runs around 170 which is extremely high to me but I am only familiar with the 5890. I do not know if that translates to other instruments. We have 4 and with detector at about 300C a signal of 15-30 is typical. I think I have pretty well ruled out everything but the detector and thats about as far as I can take it (not yet resolved).
If your baseline is uniformly spikey (if thats possible), it does not sound as though you have the same problem. I will assume you are sure you have no leaks, the right flows, the right column length past the ferrule inserted into the detector (I know what a pain this is) and are not looking too close at that baseline. The electrical spikes I have seen can be repetitive but are also obvious, super sharp almost vertical lines separated by flat baseline. Much sharper than you could ever hope your peak to be.

[Peter Apps]

Hi Chemwipe

Check whether or not a cylinder of carrier gas or makeup gas was changed just before the problem appeared, could be you have a bottle of dirty gas. You might alos have an exhausted gas scrubber.

KC

Spikes that sharp are almost certainly electrical or electronic - about the only thing that you can do is to pull out and reinsert all the plugs, and remove and reinsert the boards (mayber clean the edge contacts if your boards have them).

Peter

[KC]

Thanks Pete but how about my ECD with the high signal. I'm relatively certain if I can get the signal to come back down, my negative spikes will go away. One analyst said she knew how to take apart and clean the detector but that it was against the law due to the radioactivity. I suggested we not go that route.

[Peter Apps]

Hi KC

A high background might also be electronics - since you have other GC-ECDs would it be possible to swap some boards between instruments ?

Peter

[KC]

Not a bad idea. If nothing else it will it will rule out one more possiblity, thanks

[pi3832]

Check whether or not a cylinder of carrier gas or makeup gas was changed just before the problem appeared, could be you have a bottle of dirty gas. You might alos have an exhausted gas scrubber.

Or you might have a leak at the cylinder or somewhere along the gas supply lines.

Be sure to to also check for leaks around where the gauges screw into the regulator body, and the pressure relief device and any plugs.

Found a leak myself on the PRD of one of my regulators a couple of weeks ago. Wasn't effecting my analysis, but it did explain why I was losing cylinder pressure even when the gas wasn't in use.

Mike

[rekuci]

Just based on my own experience, I had an extremely noisy baseline (by FAR drowned out any real signal), seemed worse when the oven was on, and after a couple weeks trying everything in the books, called some repair companies and was told it sounded like either a bad detector or a detector board (I use a TCD).

Since the board was far cheaper than repairing the detector, the company sent it to me to try out - and the noise was completely gone! This is an HP 5890, so quite old.

The previous user of the instrument spoke of "stability problems" a couple years earlier that made him have to 'equilibrate' the system for 2 hours every day he used it - apparently this had been the early signs of the bad electronics problem.