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noisy baseline
Posted: Fri Jul 03, 2015 3:09 pm
by kaavie0801
Mobile phase: water, on-line degassing
Column temperature: 30 C
Detection: UV 227 nm
flow rate = 1 ml/min:
flow rate = 1.5 ml/min:
flow rate = 2 ml/min：
What can be the causes of the noisy baseline at 2 ml/min?
Thanks for any help
Re: noisy baseline
Posted: Fri Jul 03, 2015 4:15 pm
by Fernando
Hi kaavie0801
What is the height of your peaks?. If you inject an amount of sample that is for example 200 mAu of height your noisy baseline is not that important. Your lamp is new? Or is old, that is a very important fact, you may need to replace it.
A certain amount of noise is unavoidable, check your equipment manual for limits and evaluate the noise.
Best luck!
Fernando
Re: noisy baseline
Posted: Fri Jul 03, 2015 7:27 pm
by M Farooq
It seems that whoever made those method, also changed the sampling frequency and time constants. At high flow rates, you need high sampling frequency and small time constants to capture narrow peaks eluting at high speed. Check the detector settings in all 3 methods.
Re: noisy baseline
Posted: Fri Jul 03, 2015 8:34 pm
by Peter Apps
Rather a wild guess, but the very high frequency of the noise points strongly to electrical or electronics rather than anything to do with fluid flows, and at 2 ml/min the pump is working harder, so mayber you have some kind of electrical interference between pump and detector ??
Peter
Re: noisy baseline
Posted: Sat Jul 04, 2015 5:28 am
by kaavie0801
It seems that whoever made those method, also changed the sampling frequency and time constants. At high flow rates, you need high sampling frequency and small time constants to capture narrow peaks eluting at high speed. Check the detector settings in all 3 methods.
Thank you for your suggestion.
(1) The detector settings were not changed at all three flows (sampling frequency= 6.25 Hz; time constant=0.16 s).
(2) At higher flow, higher sampling frequency and smaller time constant may be needed for the narrower peak, but the baseline would go more noisy.
Re: noisy baseline
Posted: Sat Jul 04, 2015 5:42 am
by kaavie0801
Rather a wild guess, but the very high frequency of the noise points strongly to electrical or electronics rather than anything to do with fluid flows, and at 2 ml/min the pump is working harder, so mayber you have some kind of electrical interference between pump and detector ??
Peter
Thank you very much. Could you say more about the "electrical interference?"
Re: noisy baseline
Posted: Sat Jul 04, 2015 5:52 am
by kaavie0801
Hi kaavie0801
What is the height of your peaks?. If you inject an amount of sample that is for example 200 mAu of height your noisy baseline is not that important. Your lamp is new? Or is old, that is a very important fact, you may need to replace it.
A certain amount of noise is unavoidable, check your equipment manual for limits and evaluate the noise.
Best luck!
Fernando
Thank you for your reply.
(1) The noisy baseline at 2 ml/min flow was unacceptable to my analysis in which the detection of very small peaks was required.
(2) The lamp is old but it seems that the noise level at 1-1.5 mL/min flow is acceptable. I'm curious about the >five-fold increase in noise level at 2 mL/min flow.
Re: noisy baseline
Posted: Sat Jul 04, 2015 8:27 am
by kaavie0801
Rather a wild guess, but the very high frequency of the noise points strongly to electrical or electronics rather than anything to do with fluid flows
Peter
Peter, I noticed the noise level is not affected by the pump flow as long as the detector flow cell is not flushed through.
Re: noisy baseline
Posted: Sat Jul 04, 2015 12:22 pm
by Peter Apps
Rather a wild guess, but the very high frequency of the noise points strongly to electrical or electronics rather than anything to do with fluid flows
Peter
Peter, I noticed the noise level is not affected by the pump flow as long as the detector flow cell is not flushed through.
So if you disconnect the detector from the column the noise is reduced ?
If the tubing between the column and detector is metal, try replacing it with PEEK.
What instrument are you using ?
Check that you have a good earth connection on all the components.
Peter
Re: noisy baseline
Posted: Sat Jul 04, 2015 2:14 pm
by kaavie0801
Thank you for your informative advice, Peter.
So if you disconnect the detector from the column the noise is reduced ?
Yes
If the tubing between the column and detector is metal, try replacing it with PEEK.
A stainless steel tubing is used between the column and detector. Did you mean the steel tubing led to an "electrical interference?"
What instrument are you using ?
An HPLC system from SHIMADZU: LC-20AB (pump), SIL-20A (autosampler), CTO-20A (oven), SPD-M20A (DAD), and CBM-20A (Communications bus module)
Re: noisy baseline
Posted: Sat Jul 04, 2015 5:14 pm
by Peter Apps
Thank you for your informative advice, Peter.
So if you disconnect the detector from the column the noise is reduced ?
Yes
If the tubing between the column and detector is metal, try replacing it with PEEK.
A stainless steel tubing is used between the column and detector. Did you mean the steel tubing led to an "electrical interference?"There is a possibility that a stainless tube would conduct electrical interference as well as carrying mobile phase. To check this you need to allow mobile phase to flow, but stop electrical conduction by using a non-conductive tube. I have to admit that this is a long shot
What instrument are you using ?
An HPLC system from SHIMADZU: LC-20AB (pump), SIL-20A (autosampler), CTO-20A (oven), SPD-M20A (DAD), and CBM-20A (Communications bus module)