Chromatography Forum

we have dionex ultimate 3000 series hplc-multiple wavelength UV detector ,the baseline exhibits unusual zigzag noise during monitoring baseline at certain wavelengths eg. 210nm, 220 nm , 360nm ,at other wavelengths the baseline is normal, plz i need ur help what may be the causes and how to solve the problem, thanks in advance

Almost sounds electrical. Be sure the electricity is 'clean' and you have a 'good' ground.

But we have ups connected to the HPLC device

That's a diode-array type of detector. Are you seeing the baseline problem *only* at the 10 nm increments? and are you seeing it at *all* the 10 nm increments? If both conditions are true, it's more likely to be a software/firmware artifact than anything else. Probably best to contact Thermo (Dionex) for service.

You might try changing the bandpass and see if that has any effect.

No, i didn't encounter the problem at 10 nm increments ,i just gave an examples of wavelengths at which the baseline developed the problem, the baseline is also noisy at wavelength 360nm but good at wavelength 340 nm for example, finally it is multiple wavelength detector not a photodiode array and this is a new problem i encountered recently, the baseline used to be very steady except lately

Nobody running a 'drill' or other piece of electrical equipment nearby? The EMF generated can affect your equipment.

nothing changed, the same environment i used to work in on my HPLC device

A picture of the baseline at the affected wavelengths would be a big help.

Is the zig-zag still there if the pump is turned off ?

Peter

What is the age of the deuterium lamp ?
The wavelenghts mentioned are low energy regions of the deuterium lamp , so it may need replacing.

we brought this HPLC device a year ago, i checked the effectiveness of the lamp it was well, the zigzag baseline noise happened also not only at high energy wavelengths but also at wavelength 360 nm, at the rest of wavelengths the baseline is good eg 230,280,350 nm......ect

i don't think the pump or the mixer is the cause of problem because the displayed pressure is very steady and has no fluctuation

We need full details - mobile phase, flow rate, column and guard column, gradient, etc etc etc.

Also, if the baseline zig-zags at 360 and not at 350 does it zigzag at 355, 359 ?

The more you don't tell us, the more we can't help.

Peter

mobile phase water,acetonitrile, glacial acetic acid (89:10:1) (mobile phase A)
actonitrile (mobile phase B)
the gradient is 100 mobile phase A 0-4 minutes
then 70 mobile phase A 30 mobile phase B 4-14 minutes
then 100 mobile phase B for 2 minutes
and finally 100 mobile phase A for another 2 minutes
but i once was working isocratic(phospate buffer pH 7: acetonitrile 60:40) and encountered the same problem
in both methods the flow was 1 mL/min
column in the first method prontosil c18(250 x4.6mm,particle size 3um
the second isocratic method the column was phenomenex luna 2(250 x4.6mm,particle size 5 um)

yes the zigzag noise happened at certain wavelengths eg 210,215,220 but at 225 nm the baseline is good also at 360 nm the baseline is noisy and at 355 nm it is good

From your first post; "during monitoring baseline" - is baseline monitoring a specific procedure with your instrument ?, or do you see the zigzags during ordinary analytical runs ?.

Are you sure that there is no autozeroing going on during the monitoring ? does the baseline rise slowly tand then drop suddenly ? - a picture of the baseline would help, there is a sticky on how to post pictures somewhere.

Peter