LC/MS questions

[firework1]

Our lab is going to purchase an LC/MS system. Our boss would like to have a PDA detector as well, so it will be LC/PDA/MS. Of course, a PDA would be helpful with regard to peak identification, etc, but he wants this system function as a backup of the other heavily used LC system, which means, even if people do not need MS detector, they will still come to this LC/PDA/MS system if the other LC system is in use.

I do not know how commonly this is practiced in other labs. Is this a good idea at all? In my previous experience, LC/MS system is strickly for MS samples only, I really do not want all sorts of dirty stuffs contaminate the ionization source. But I also understand that we might not have money to purchase another LC/PDA.

Would someone give any idea?

[Kostas Petritis]

Well, if someone does not want to use the MS part then do not direct his sample to MS after the PDA (i.e. sent it to the waste). Especially if people use non-volatile salts (which must be the case for all the other LC/PDA systems) then you must make sure that the mobile phase does not go through the MS after the PDA...

[firework1]

Thanks.

But that would need a lot of cleaning after using non-volatile salts with PDA, is that practical?

Well, if someone does not want to use the MS part then do not direct his sample to MS after the PDA (i.e. sent it to the waste). Especially if people use non-volatile salts (which must be the case for all the other LC/PDA systems) then you must make sure that the mobile phase does not go through the MS after the PDA...

[Kostas Petritis]

Not really other than purging the lines and column with a high water low methanol solution, and as I said you do not direct the non-volatile salts to the electrospray source when using the PDA only approach...

[sassman]

It has been my experience that LC/MS systems are always in high demand once installed. In the past we have purchased PDA detectors with our LC/MS systems, but the PDA was basically never used. If you think that there may be MS downtime in your lab, then maybe it is a good idea. I don’t see many logistical problems with having a dual system. Just be sure to divert samples run on just the PDA to waste before they go into the mass spec and rinse the system well after using non-volatile salts.

[sindhu]

In my opinion many labs are having the same concept of buying a LC-PDA-MS systems for dual usage purpose.

When you use only LC-PDA then you need not worry about contamination in the MS ionization source as we never allow the flow to go to MS system.

You can buy LC-PDA-MS and use for dual purposes.