Table 4.

Comparison of the most common mass differences in observed and random metabolite networks

Observed metabolite network				Random metabolite network
Mass difference	Frequency	Formula	Exact mass	Mass difference	Frequency
2.01595	382	H2	2.01565	92.70975	7
21.98312	326	Na–H	21.98194	205.30491	7
1.00320	284	13C isotope	1.0033	52.82462	7
24.00000	260	C2	24	193.60014	6
26.01629	237	C2H2	26.01565	243.29213	6
28.03188	218	C2H4	28.03130	254.75355	6
4.03201	197	H4	4.03130	6.46724	6
1.01259	164	H2−13C isotope	1.01229	52.69339	6
3.01910	148	H2+13C isotope	3.01900	21.98649	6
22.99695	140	C2−13C isotope	22.99664	22.12482	6
Total	25,370 (in 2472 clusters of >5 members)			Total	115 ± 22 (in 19 ± 4 clusters of >5 members)