detecting parent molecules with LC-MS

[shannie]

hello,

may i request input from all the gurus here if you have encountered this situation:

the molecule seems to dissociate in 0.1% formic acid system and an acetyl group was removed before entering the MS, thus it's always the daugther molecules being detected. is there any other solvent system we can try to minimize the dissociation?

thank you in advance for your comments and reply!

shan

[james little]

use a few mmolar ammonium acetate in 50/50 mix of water/acetonitrile or just don't add any salts or acid.

Another mix is 0.1 mmolar potassium acetate in a mix of methanol in water or 0.1 mmolar potassium acetate in mixture of 50/50 methylene chloride/methanol, get usually M+K adducts..

[ym3142]

if you have evidence showing that a acetyl group was lost before sample gets into the LC/MS, why don't you report it and report the MS of the remaining fraction of the molecule?

Does deacetylation happen under basic condition where you can get enough ionization? If so, added some TEA instead of the acid.

IF TEA also helps the deacetylation, try diluent with pH close to 7 or
straight 7.

Good Luck

[shannie]

thank you all for your helpful hints!

to answer part of the query, the acetyl group can be detected when it's manually injected into the MS. once it passes through the column, the mass of the compound detected is reduced.