LC-MS IONISATION

[maheshthirupathigari]

Dear all,

I am the user of LC-MS.

Can i inject KBr and SOCl2 compunds into lc-ms?

i am waiting for ur precious response. :

[Mannich Adorer]

If you want to ruin your instrument - why not?
On KBr - it has a melting point of > 700 C and boiling point of > 1400, so is not volatile at all, and only volatile salts can be used in
chromatography employing MS detection.
On SOCl2- if you use water-containing eluents, you'll get at least a nice hydrolysis reaction.

[James_Ball]

Are you injecting a few microliters of sample containing these into your mobile phase flow for analysis or are you wanting these to be a component of your mobile phase? It will be a huge difference between the two options.

[orcicdejan]

KBr (and any non-volatile salt, for that matter) will form deposits in your ion source. In addition, unwanted [M+K]+ and [M+Br]- adducts will form.

SOCl2 reacts with water giving HCl, I recall. HCl is generally not too welcome in either LC or MS, as it can (if the concentration is high enough) damage the hardware. Also, you'll get some nice [M+Cl]- adducts.

Of course, as James_Ball said, it depends on the concentration - small amounts may not be a problem.

[Camisotro]

And not to mention, if you are injecting lots of such samples, you can divert the LC flow to waste while these generally polar matrix compounds elute, sparing the ion source, and then switch back to MS for your peaks to come out.

If the samples are corrosively acidic, adjust the pH by adding an appropriate amount of ammonium hydroxide.

But yes I'd agree that for small injection volumes it's not a big deal. If a 10 uL plug of a sample containing "undesirables" goes through the ion source, followed by several mL of LC solvents, you're probably going to flush out most of the contamination.

[James_Ball]

And not to mention, if you are injecting lots of such samples, you can divert the LC flow to waste while these generally polar matrix compounds elute, sparing the ion source, and then switch back to MS for your peaks to come out.

If the samples are corrosively acidic, adjust the pH by adding an appropriate amount of ammonium hydroxide.

But yes I'd agree that for small injection volumes it's not a big deal. If a 10 uL plug of a sample containing "undesirables" goes through the ion source, followed by several mL of LC solvents, you're probably going to flush out most of the contamination.

I completely forgot about the diverter valve. I used it when I was analyzing some very nasty tobacco extracts for preservatives to keep the junk off the source, it worked rather well. I diverted to waste until just before and after each peak was to elute, switched to the source to capture the peak then back to waste. Just need to make sure to give yourself just enough capture window to account for any retention time fluctuations if any.

[Camisotro]

I completely forgot about the diverter valve. I used it when I was analyzing some very nasty tobacco extracts for preservatives to keep the junk off the source, it worked rather well. I diverted to waste until just before and after each peak was to elute, switched to the source to capture the peak then back to waste. Just need to make sure to give yourself just enough capture window to account for any retention time fluctuations if any.

If salts and very small ions are the matrix components of concern, then at least in an RPLC context it suffices to choose a time somewhere between the void and the start of the first analytical peak to switch back to MS.