Noise

[nellermann]

I need help please!

I run a method that has a very low detection limit. Lately, the noise has gotten really bad. I've changed the lamp, the column and degassed my MP.

How possible is it that it could be my DI water in the mobile phase? My mobile phase is 85%water/15%MeOH.

Any other suggestions for getting rid of noise? If nothing works, I guess I'll have to start using a larger injection loop. It just sucks, that after running this method for the last 5 years, this is happening and I don't know why.

Thanks!
Natalie

[Consumer Products Guy]

More information needed, like (1) what is your wavelength? (2) what is your water source, like purchased, purifier, whatever? (3) what is your methanol source, same lot as used before, same supplier? (4) what happens if you shut off the pump - does the baseline stabilize? (5) what happens if you just pump methanol 100% (6) does this happen with a "no injection" and with an injection of just methanol as well? (7) isocratic or gradient? (8) what has changed recently, think carefully: different sample filters, different lot of solvent, different lot of water or methanol, etc.

[Mark Tracy]

A picture is worth a thousand words. Can you post a blank chromatogram?

[Noser222]

Another possibility, perhaps your flow cell is dirty. I replaced mine and was amazed at the difference in noise. This will be more likely at low UV wavelength.

[Jumpshooter]

Do you use MilliQ water at 18 ohms? Do you use methanol manufactured by Burdick & James? Have you changed your guard column recently? Flow cell cleaned recently? Check out these variables--and if possible post up a 'gram pic for us. This is a problem that does NOT have a mysterious cause--there is a purely rational reason why you're havin noise in your signal

[Metrologist]

I know this is simple, but is your signal cable draped over an outlet? This could be a source of noise, however, it would be cyclical (60 Hz).

[nellermann]

Thanks for all your replies.

It turns out that the problem was our DI water. When our micro dept. checked it, the conductivity was off the charts!

Anyways, thanks for all the brilliant advice.