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. Author manuscript; available in PMC: 2016 Nov 3.
Published in final edited form as: Eur J Mass Spectrom (Chichester). 2015;21(3):183–190. doi: 10.1255/ejms.1374

Figure 1.

Figure 1

EI mass spectra of methyl esters of N-trifluoroacetyl- derivatives of N-methyl-l-phenylalanine (a),15N-methyl-l-phenylalanine(b), N-trideuteromethyl-l-phenylalanine (c), N-ethyl-l-phenylalanine (d), N-methyl-l-alanine (e), and 2-13C-N-methyl-l-alanine (f).