Table 3.

Ratio of ¹⁵N/¹⁴N peaks for key ions

species	amino acid	set 1A labeled	set 1B labeled	set 1B unlabeled	set 1C labeled	set 1C unlabeled	set 2 labeled	set 2 unlabeled
NH4+	all	0.65±0.04	0.24±0.03	0.009±0.001	0.15±0.02	0.013±0.001	0.016±0.003	0.0058±0.0001
CH4N+	all	0.25±0.01	0.14±0.01	0.012±0.0007	0.087 ±0.01	0.0132±0.001	0.054±0.01	0.0081±0.0001
* CH3N2+	arg	2.12±0.13	0.80±0.09	0.12±0.05	0.51±0.06	0.14±0.03	0.035±0.003	0.028±0.001
C2H6NO+	ser	3.76±0.12	0.89±0.12	0.045±0.009	0.58±0.08	0.051±0.008	0.047±0.006	0.0304±0.001
C2H7N3+	arg	4.63±0.18	0.79±0.11	0.064±0.002	0.51±0.07	0.085 ±0.02	0.053±0.008	0.052±0.006
C5H10N+	lys	1.20±0.05	0.63±0.04	0.21±0.006	0.44±0.03	0.24 ±0.05	0.20±0.01	0.21±0.002
C4H10N3+	arg	0.61±0.12	0.26±0.02	0.15±0.007	0.21±0.02	0.18 ±0.03	0.15±0.01	0.15±0.001

^*this ratio uses the sum of the CH₃¹⁴N¹⁵N and CH₃¹⁵N₂ intensities since both will arise from the ¹⁵N labeled arginine.