According to some aspects, a spectrometer is provided, the spectrometer configured to receive molecules of a plurality of metabolites including one or more molecules of a first metabolite, filter the received molecules to retain molecules of the first metabolite including a plurality of different mass isotopomers of the first metabolite, fragment molecules of a first mass isotopmer of the retained molecules to produce a first plurality of daughter ions, measure abundances of the first plurality of daughter ions as a function of daughter ion mass, fragment molecules of a second istopomer, different from the first mass isotopmer, of the retained molecules to produce a second plurality of daughter ions, and measure abundances of the second plurality of daughter ions as a function of the daughter ion mass.