Chromatography Forum

Hi,
I have been using an HPLC/ELSD system for quite some time now, wtihout any problem. Accidentally, a collegue of mine who is also using the HPLC (but with UV detection) forgot to switch the valve from ELSD to waste and has passed her PBS + NaN3 solution through the ELSD. Now I get only half the signal than before. Could this have something to do with the PBS? I have flushed the ELSD for several hours, changed the column, used new sample solution etc - with the same outcome. Is there something else I could try to get the sensitivity up to the "usual" level?

Thank you!

try to wash the HPLC system with water. It can take some days before the system is clean.

G'day Monika

Can you let me know what PBS is? Your ELSD flushing, what flow, solvent and temperatutrre setting are you cleaning at? It may also pay to remove the nebuliser and sonicate it in a suitable solvent.

Our cleaning regime for ELSD involved water at 3ml/min, tube at 120C for around 2 hours, plus sonication of the nebuliser unit. We mainly analyse sugars from wine and grapes.

hope that helps some.

Regards
Greg

Hi Greg

PBS is Phosphate Buffered Saline (80.0g NaCl, 2.0g KCl,14.4g Na2HPO4,
2.4g KH2PO4 ad 1000 ml with water, pH 7.4 with HCl).
Usually I clean the ELSD by heating the nebulizer to 100°C and the evaporator to 250°C and using air (instead of nitrogen) to oxidize the impurities. I'll try and sonicate the nebulizer unit - hopefully this will solve my problem! Thank you for your input!
I analyse Polysorbate 80 and phospholipids from products manufactured from blood plasma.


Regards

Monika

Hello Monika,

I worked for more than Two years for a ELSD manufacturer (but I think it is a competitor of yours).

At first try to wash your nebulizer, this is the first thing to do.

Then if it is not resolved, consider that the contanimation is more or less located to the drift tube.
Using high temperature may not be the best thing to do (250°C is not enough to oxidize or pyrolyse anything). What I would suggest is to use lower temperatures in order to really flush the drift tube.
The best is maybe to use cycle temperture washing, i mean increase to 250°C and decrease to 50°C, and increase...

I don't know which ELSD brand you use, please let me know, maybe could I be more helpful.

Good Luck!

Salut Rodolphe

This heating procedure is what the manufacturer (Polymer Lab, PL-ELS-1000) recommends as routine maintenance in the case of contaminations.
At the moment, I'm trying to clean the nebulizer...

Monika

Hello Monika,

Let us know if that solve your problem.

Be sure that in most cases, such contaminations are located in the nebulizer. You should be able to work after neb wash.

Monika,

When you say that you get half the signal, do you literarly mean it or is it just the signal to noise ratio? I would expect that if your system is really poluted with phosphate, your background noise would have gone up. Otherwise, it could just be a different ELSD parameter (??).

If it is really a pollution, in addition with what everyone else said you can also try to clean with HPLC water the beginning of the drift tube.

Hi,

the signal-to-noise isn't the problem; the chromatogram looks as good as ever (no impurity "noise"), but the hight and the area of the peaks are only half of what I expect.
The cleaning of the nebulizer hasn't changed anything...help!!!

Is there anything else I could try?

Monika

If your background noise is the same, then it is probably not a pollution. Especially if the signal to noise ratio is better than before (i.e. 2 times better) I would search for something much more simpler such as the parameters of the photomuliplier (gain) etc. I do not beleive that a pollution in your system would just decrease your signal by half without affecting your background noise (assuming that the LC conditions are all identiical as before (i.e. flow rate etc))...