Stable isotope shifted matrices enable the use of low mass ion precursor scanning for targeted metabolite identification

Table 1 List of low mass target ions in native and stable isotope labelled peptides

Residue	Native Immonium ion	Related native ions	¹⁵N Immonium ion
Alanine, A	44		45
Arginine, R	129	59,70,73,87,100, 112	133
Asparagine, N	87	70	89
Apartic acid, D	88	70	89
Cysteine, C	76		77
Glutamic acid, E	102		103
Glutamine, Q	101	56,84,129	103
Glycine, G	30		31
Histidine, H	110	82,121,123, 138,166	113
Isoleucine, I	86	44,72	87
Phenylalanine, F	120	91	121
Proline, P	70		71
Leucine, L	86	44,72	87
Lysine, K	101	70,84,112,129	103
Methionine, M	104	61,70	105
Serine, S	60		61
Threonine, T	74		75
Tryptophan, W	159	77,117,130,132, 170,171	161
Tyrosine, Y	136	91, 107	137
Valine, V	72	41,55,69	73
Insulin tryptic peptides		Target ions used for precursor scanning
FVNQHLCGSHLVEALYLVCGER		120 (F), 70 (P/R/N), 86 (L/I), 72 (V)
GFFYTPKT		120 (F), 70 (P/R/N)
GIVDQCCTSICSLYQLENYCN		72 (V), 86 (L/I), 70 (P/R/N)

(Top) List of immonium and related ions for the 20 naturally abundant amino acids and the expected isotopic shifts of immonium ions when 15N labeled. (Bottom) Tryptic Insulin digest peptides and the potential target ions to be used for information dependant MS/MS acquisition (IDA) targets during a precursor ion scan.

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