Negative Peaks on ELSD

[Paladin]

Folks,

I have two ELSD issues:

#1 One of the chemists keeps getting negative peaks on the ELSD. Since he is the only one seeing this, I assume it is due to his compounds. Which brings me to the second issue.

#2 One of the compounds being run by the above mentioned chemist is dissolved in a solvent with a little NaOH. Is this bad for the ELSD if only run occassionally?

Thanks

[Kostas Petritis]

It is extremely difficult to get negative peaks in ELSD so I would look on something else as an explanation on this (such as inverse cable polarity etc).

Negative peaks would mean that the volatility of the eluted compounds is higher that the mobile phase but even in this case the background noise is pretty high not allowing to see such subtle differences. The NaOH should be interefering (at least not giving negative peaks)...

[Sallybeetle]

NaOH should be causing a higher baseline mV value and higher baseline noise. I wonder about the NaOH getting cleaned out of the ELSD thoroughly.

[Kostas Petritis]

In this case the NaOH is just used in the injection solvent (and not as part of the mobile phase) and thus shouldn't create any problems...

[Paladin]

As it turns out, he was running his samples on the wrong ELSD method. He was using one that was for a highly organic isocratic mobile phase rather than one I had for highly aqueous gradient methods. I'm still not sure why we were getting negative peaks but the problem is solved so its time to move on to other lab issues. I can spend time cogitating on the reason for negative peaks during a more tranquil moment.

Thanks for the responses.

[Sallybeetle]

Now we're talking. . . . When are there tranquil moments in lab work?