Hi,

To answer your first question, it is likely to get isotopic pattern which is usually distinguishable. Are these m/z species singly charged? Are you able to see other isotopic species like at m/z 450.306x? Also, is any one of these two species more abundant than the other? If you can not identify them as isotopes, I would assume m/z 451.3069 and m/z 452.3060 are two different species. It is possible to get two separate compounds within this much close retention time.

To answer your second question, No. Same compound would not elute at 2 different retention time. So these would be two different species.

Remember, 2 compounds can elute at the same retention time but one compound would not elute at two separate retention time, unless there is some modifications (which would again give you two separate m/z values).

Hope this helps.

question 1: very likely isotopes. But as pointed out by Noel, there might be other atoms that influence the mass difference between the two ones. if it was just a C13, it would have been +1.00335 (while yours is + 0.9991). Without the original spectrum, it is difficult to say what it could be, many are possible. how to deal with that: check the spectrum, look for other isotopes, the ratio between the isotopes and their mass distance.

question 2 - 3 options:

1) double peak of the same compound (the compound gets different forms in specific gredients and so it splits during the chromatographic run, giving two close but distinct peaks)

2) isomer of your compound of interest. same formula, and very similar structure except for the position of one atom.

3) unrelated compound (unlikely but still possible). btw if it is an unrelated compound, the isotopic pattern or the fragmentation pattern should be different from your compound of interest.

hope this helps.

CORRECTION: The examples of m/z in question 1 are 451.3069 and 452.3102 instead of 452.3060. I've corrected it in the question.

C13 isotope with (almost) no doubt then...