December 5, 2011
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs
The explanation offered herein covers one possible scenario to a complicated situation. Please note that other explanations are possible.
The LC/MS data shows an unknown at 1.8 minutes exhibiting an [M+H]+ at m/z 260 and an [M-H]- at m/z 256. The difference of 4 mass units lends itself into a scenario of conflicting data.
One potential explanation for the differing LC/MS data is the unknown is a really comprised of a mixture of two compounds ionizing under separate ion modes and differing by 2 mass units. The short column run (< 2.5 minutes) done under UPLC conditions appears not to be adequate to separate out the mixture as they elute.
Thanks Graham M. for your assistance.