Chromatography Forum

Anybody seen this before? I'm unsure if it's a gas issue or electrical interference from another instrument on the same circuit. Just swapped out gas filters and the problem persists. Bench set up is as follows: Two Agilent 6890 dual ECDs on one bench with an agilent Dual FID in the middle. Bench three feet away has the reverse, with two 6890 dual FIDs, and one 6890 dual ECD. The problem has been escalating for some time, but now it is interfering with analysis. It seems that it is a timed event, leading me to believe that it's electrical, though it could be gas. The interference is on both ECDs on the southern bench, but is signifcantly smaller on the northern bench. Mantaining doesn't help. First graphic is an expanded c-gram of the interference in a degradation check on the primary column. Second graphic is both columns, note the times of the interference between 23 - 25 mins on both columns. Any help would be appreciated.

If the interference is synchronised between different instruments (i.e. not only between the two detectors on one instrument) and is not appearing at the same time each time on the chromatogram then it pretty much has to be electrical.

Peter

Stunt,

Two GC's that are running at the same time or just sitting there? Couple of things you could try. Turn off every
other instrument on the bench and see if the noise goes away. (Way less demand on that circuit, way easy to do.) Or, put one of the instruments on an isolation
transformer.

Best regards,

AICMM

I have seen something similar to this, just not as extreme. One thing to check would be your neutral to ground voltage. There should be 0 volts when you connect a voltmeter between the neutral and ground on an outlet. If you are getting anything above 1 volt there, then you need better ground on that circuit, or there is just too much on that circuit. We has a bench in out old building that had 12-15v neutral to ground because someone had stuffed so many different circuits into one conduit that there literally wasn't room for a thread to pass through that conduit, and it contains positive, neutral and ground wires and the positive and neutral wires were inducing currents in the ground wires.

Yes, it could be electrical, but do not rule out flow changes due to pressure changes in your lab. It could be air conditioning. Do you have vent lines on your ECd's? If yes, where do these vant lines go. Many years ago I was called out out to a lab in London where the customer complained about a noisey ECD. The day of my visit, no problems were evident. A few days later the customer called in with the same problem and I was able to visit on the same day. The lab was in a high rise building, several floors up. It was a windy day and the customer had the ECd vent line stuck out of the window. The pressure of the wind on the side of the building was enough to cause the flow to fluctuate, causing the baseline noise. Remember that the ECD is flow sensitive.

Gasman

This is why I love this forum. So many great ideas in three hours. Interference appears sporadic, but affects both columns on three instruments. I dont see the issue on FIDs. The ECDs are significantly more sensitive than the FIDs in terms of concentration values, so the interference could be lost in the baseline if it's quite small in height. The interference does not seem to happen at the same time on diff inst Peter, so I am inclined to agree with you on the electrical thing. All GCs are on, but not necessarily running at the same time, although both of the GCs affected ran overnight, and the interference is in both, just not at the same time or sensitivity. I will check the neurtal to ground voltage James, good idea. GasMan, I pulled our lines out of a duct that feeds our fume hoods. There is quite a large vaccuum there, but I'm unsure if the hoods are on all night, I think they may be turned off.

I will let you all know what happens after each attempt at your suggestions below for your own troubleshooting notes, and thanks again,

Stunt.

Haven't checked the neutral / ground yet with a volt meter, but the other suggestions didn't work. Problems persist, and appear sporadic.

I'll keep you posted,

Stunt.