Chromatography Forum

We recently moved our two 5890 Series II GCs to a new building and ever since the move sharp signal dips have occasionally popped up in our FID and PID runs (both use split columns). They occur more often on the FID chromatograms, but when they do occur on the PID side it is usually at the exact same time as the FID dips. The columns are new since the move, we have appropriate filters/traps installed on all of our gas lines and we have cleaned out both of our FIDs. The dips are much more frequent (i.e. almost every run) during working hours and rare during non-working hours, making me think it must be electrical-related. Any advice on what I can do to troubleshoot or fix the problem?

Thanks!

Make sure each GC is on it's own 120V/20 amp circuit with their own ground. Have the PC's, autosamplers, etc. on different circuits. If you have a multimeter with min/max, you can install that to one of the GC circuits and see if there are voltage fluctuations that co-inside with the spikes. If you really want to find out if something else is attached to the circuit, turn off the circuit breaker during the day and see who complains of no power. The other thing that could be happening is with your air supply. If it is being used for anything other than a detector gas (like actuating a valve or solenoid on an autosampler, or something else, it can cause a drop in air pressure causing a spike. Good luck and please let us know what you find.

Sometimes a sudden change in pressure or a gas leak can look like electrical noise. I sometimes see sharp negative peaks during a run if a column is not connected properly at an inlet or a union between two columns.

Also, I have seen very regular "waves" in the baseline that was caused by a leak in the piping from the gas flow block on the left side of a 5890.

I guess the test is that if you only see the dips during runs then it wouldn't be electrical. If you turn the unit on and have gas flowing, FID lit, and the baseline is stable then you are good. But when your temp/pressure ramps during a run and things start to change, it is most likely due to the column installation or gas lines.

Sounds like something jiggled loose during the move...

It is not exactly clear if the problem occurs just on one GC or on both? I agree that this is most likely electric problem, do not think it is gas flow related.

It seems some equipment periodically activating itself "sends a signal" - fridge/freezer, compressor, oven, water bath (it is swithched on also overnight which should help locating the offender)? Was any of that kind equipment not present at old lab now placed close to GC/shares electrical circuit?