Chromatography Forum

Normally we run a full QuEChERS clean up on all samples, following EU method, but for a new study on Apples and Pears the dispersive salts interfere with target analytes and we get a very low recovery, <10%. So after some quick tests, we are not doing any dispersive salt clean up and are only using C18 SPE cartridges to clean up the samples after extraction solvent (1% Formic Acid in MeOH) has been added. These samples are analyzed on a Waters LC-MS/MS system, should I be worried about sugar content of samples ruining the instrument? What if I clean front end of MS/MS (cone assembly, ion block, and stepwave (maybe)) after every sample set (roughly 50 injections), would that prevent contamination of the MS from the "dirtier" samples?

Any and all thoughts are appreciated! Thank you!

How much sugar are you getting after SPE? If your target analytes are things that bind to the C18 SPE and are eluted off it prior to analysis, then you shouldn't have much sugar because it should go straight through.

There are many worse things to put in a mass spec than sugars. I've shared an instrument with a group who analysed samples sufficiently sugary that the spray chamber smelt like a toffee-apple and was covered in brown caramel whenever I came to it. The good news is that it washes off really easily, and it didn't seem to cause major problems to the instrument. Sugars, at least, don't ionise very strongly, so they won't cause serious background peaks.

I have run tobacco samples looking for preservatives and Tobacco Specific Nitrosamines and after even a set of 20 samples the cones would be nearly black from the tars in the tobacco. I have never found more than a barely visible trace of anything on the inner cone and almost nothing on the first one inside the vacuum. (ABI3200 LCMSMS) As long as you have a good purge flow between the cones(I assume the other instruments have this also) it should keep out most of the non-ionized material which will just build up on the outer cone surfaces.

lmh

spray chamber smelt like a toffee-apple and was covered in brown caramel

That is exactly what I see after I run a set! I was also very happy that it washed off quite easily, I have to admit - I was quite scared when I first saw how dirty it was Our target analyte does bind to the C18 so we could elute it off the cartridge and not collect the intial load. This will also give us the same sample concentration before and after clean up, only makes it easier.

James_Ball

As long as you have a good purge flow between the cones(I assume the other instruments have this also) it should keep out most of the non-ionized material which will just build up on the outer cone surfaces.

Yes we have a constant Cone Gas flow on our instrument, we are actually considering increasing the flow as we are having issues with contamination inside mass analyzer (quads & coll cell). Current flow is set at 150L/hr, how does that compare to your setting?

James_Ball

As long as you have a good purge flow between the cones(I assume the other instruments have this also) it should keep out most of the non-ionized material which will just build up on the outer cone surfaces.

Yes we have a constant Cone Gas flow on our instrument, we are actually considering increasing the flow as we are having issues with contamination inside mass analyzer (quads & coll cell). Current flow is set at 150L/hr, how does that compare to your setting?[/quote]

I am not sure what the flow is from our API3200 it only list the flow a 5, 10, 20, ect with no units. The tech from AB Sciex told me to set it to the highest setting I could without loosing too much sensitivity and that would keep the insides cleaner.

Hello; I haven't read all the comments posted here; but I remember that Quechers use PSA in order to retain Sugars; so that could be a way to remove sugar using PSA or Amino sorbentconbined with C18; I do not know if this could affect the recovery of your analyte.

I am not sure what the flow is from our API3200 it only list the flow a 5, 10, 20, ect with no units. The tech from AB Sciex told me to set it to the highest setting I could without loosing too much sensitivity and that would keep the insides cleaner.

The Waters tech told me the same thing, use highest flow rate without loosing too much sensitivity. Interesting that AB Sciex doesn't have units on the flow, would be nice to compare flows between instruments.

Hello; I haven't read all the comments posted here; but I remember that Quechers use PSA in order to retain Sugars; so that could be a way to remove sugar using PSA or Amino sorbentconbined with C18; I do not know if this could affect the recovery of your analyte.

Yes PSA would help retain sugars, but since this is only a short study and I don't expect it to become a regular one we are not looking into it. But if this does become a regular study, I would defintely try PSA and see how it affects the recovery of our target analyte.

I don't know the Waters Instrument, but our Agilent has a switch valve. I usually pump the first 1-2min of each run into waste before switching to the ESI when analyzing sugar-containing samples.

I don't know the Waters Instrument, but our Agilent has a switch valve. I usually pump the first 1-2min of each run into waste before switching to the ESI when analyzing sugar-containing samples.

Waters instrument has this as well, need to ensure its set up for this new method - I completely forgot about it, thank you!

And for those of you wondering about the smell of residue left on cone exterior - yes it really does smell like caramel yummy!