Table 2. Overview of m/z values for the analysis of amino acids, N^ε-(carboxymethyl) lysine, metformin, and their internal standards.

ID	Compounds	m/z	Internal standards	m/z
1	Alanine	90	Alanine-13C3	93
2	Arginine	175	Lysine-13C6, 15N2	182
3	Asparagine	134	Asparagine-13C4, 15N2	137
4	Aspartic Acid	134	Aspartic acid-2, 3, 3-d3	137
5	Cystine	241	Cystine-3, 3', 3'-d6	245
6	Glutamic Acid	148	Glutamic acid-13C5, 15N	154
7	Glutamine	147	Glutamine-13C5, 15N2	154
8	Glycine	76	Glycine-13C5, 15N	79
9	Histidine	156	Histidine-13C6, 15N3	165
10	Isoleucine	132	Isoleucine-13C6, 15N	139
11	Leucine	132	Leucine-5, 5, 5-d3	135
12	Lysine	147	Lysine-13C, 15N2	155
13	Methionine	150	Mehionine-13C5, 15N	156
14	Phenylalanine	166	Phenylalanine-13C9, 15N	176
15	Proline	116	Proline-13C5, 15N	122
16	Serine	106	Serine-13C3, 15N	110
17	Threonine	120	Threonine-13C4	124
18	Tryptophan	205	Tryptophan-13C11, 15N2	218
19	Tyrosine	182	Tyrosine (Ring-13C6)	188
20	Valine	118	Valine-13C5, 15N2	124
21	Anserine	241	Histidine-13C6, 15N3	165
22	Carnosine	227	Histidine-13C6, 15N3	165
23	Citrulline	176	Citrulline-4, 4, 5, 5-d4	180
24	Cystathionine	223	Citrulline-4, 4, 5, 5-d4	180
25	Hydroxylysine	163	Ornithine-13C5	138
26	Hydroxyproline	132	Proline-13C5, 15N	122
27	Monoethanolamine	62	Monoethanolamine-1, 1, 2, 2-d4	66
28	Nτ-Methylhistidine	170	Nτ-methyl-d3-histidine	173
29	Nπ-Methylhistidine	170	Nτ-methyl-d3-histidine	173
30	Ornithine	133	Ornitine-13C5	138
31	Sarcosine	90	Alanine-13C3	93
32	α-Amino butyric Acid	104	Glutamic acid-13C5, 15N	154
33	α-Aminoadipic Acid	162	Alanine-13C3	93
34	β-Alanine	90	Alanine-13C3	93
35	γ-Aminobutyric Acid	104	Alanine-13C3	93
36	Nε-(Carboxymethyl)lysine	205>84	Lysine-13C, 15N2	155
37	Metformin	130>60	Aminoguanidine	75>45