Table 1.

Purine compounds identified in our residues.

Species	Formula	Molecular mass (Da)	Rt (GC-MS) (min)a	M* GC-MS peak (Da)b	Abundance in nmol (% deposited purine)
Purine	C5H4N4	120	9.31	192	–
Hypoxanthine	C5H4N4O	136	12.29	280	120 (5.7%)
Xanthine	C5H4N4O2	152	14.43	368	1.5 (0.07%)*
Adenine	C5H5N5	135	12.71	279	31 (1.5%)
2-Aminopurine	C5H5N5	135	13.20	279	42 (2.0%)
2,6-Diaminopurine	C5H6N6	150	15.46	366	0.11 (0.0052%)
Isoguanine	C5H5N5O	151	14.82	367	0.58 (0.028%)
Guanine	C5H5N5O	151	15.21	367	0.25 (0.012%)

^*The abundance of xanthine could not be determined accurately because it eluted between two more abundant compounds that may be interfering with the integration. This value should be thus taken as an upper limit.