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Logic Puzzle #24: Conflicting Masses? … Solution

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.