Chromatography Forum

Hi !

Recently I met a problem : noise on baseline.
I never had problem before.
It seems that noise follows pressure. For example I get a wave when pressure increases.


Equipmemnt information : Waters Alliance e2695 - Column : Symmetry C18, 75x4.6mm; 3.5um - Detector ELSD (waters 2424).
Dilution slovant is 60/40 water/acetronitril with 0,05% TFA. We use a gradiant of Acetronitrile and water during analysis.
Flow rate is 1mL/mn.

Any suggestion?

Thank!

Please check your pump heads, the check valves respectively. You need to clean and/or replace the seals. Typical pump problem!
Good luck

Oh that sounds bad...

I will check on manual how to do it.

Regardless pump, can it be another problem?

Moreover, when flow rate is 0, detector shows a -300 (about) LSU. Is that normal?

If the check valves are not working properly it means that your mobile phase composission is not constant. that can cause such a problem with your detector.
Hope that other colleagues have better ideas.
Good luck.

One of the main reasons for noisy baseline for ELSD is switching from ammonium buffer to TFA and TFA to ammonium buffers. It literally takes a day to wash it off. Each of our ELSD is dedicated either to TFA or ammonium acetate/ammonium formate. Wash your ELSD and all channles with water overnight. Set up ELSD temperature at 100*C.

We only use TFA so it cannot be the problem.
But thank for information!

We clean the drift tube. It seems to stay noisy.

Gerhard Kratz may be right!

Il seems we also have variations when flow rate is 0...

Thus it may be not a pump problem....

Il seems we also have variations when flow rate is 0...

Thus it may be not a pump problem....

That sounds like "not a pump issue" to me as well.

base-line noise is in no way related to proportional valve with ACN/water/TFA. You might observe this with ammonium formate or acetate if you are running high concentrations of the buffer and ELSD temperature is not high enough. It might be some electrical problem in the instrument or interference coming from somewhere.

After new tests, the higher is the pressure, the noisier is the baseline...

I am scared, even when I clean the column with Acetonitril, the detector signal increases to 1000 LSU (like a standard peak...but for longtime).

You need to clean everything with water not ACN.

We have cleaned with water 4 hours, without improvement.

Moreover we have cleaned the drift tube and the nebulizer of our ELSD

When 100% ACN and flow rate 1mL/mn, LSU= ~ 400
When I stop flow, LSU= ~ -400
That makes sense???

This is our baseline after 9 minutes of equilibration (same result for 30 mn...)
(A = water grade HPLC + 0,05% TFA, B= acetonitril grade HPLC + 0,05% TFA)

This, to me at least, looks like one of two situations:

1. Your nebulizer temperature is too low to evaporate all of your solvent off efficiently (or your N2 pressure is on the low side).

2. Your mobile phase is slightly contaminated with some non-volatile material, which is causing noise. Water is frequently the culprit there.

Also, I've never had significant difficulty changing back and forth between ammonium acetate and TFA based mobile phases in reversed phase systems with either a Waters 2420 or 2424, both of which I've used for nearly 10 years. I have however seen MP switch over issues when using more polar supports. Perhaps the phenomenon Vlad has observed is related to the nature of the columns in use?

Hope this helps! Let us know how things turn out, please.

I don't think this is ue to low nebulizer temperature because it has worked well for 3 mounths...

We also have changed water and ACN and noise stay without flow...

A Waters' Engineer will come monday. I will give you the diag back !