Table 3.

Experimental atomic composition and O/C ratio obtained by XPS analysis for ONC, ONC-Trp, ONC-Phe, ONC-EMP, and ONC-WRF. Errors in determination ± 1%.

Sample	Atomic content (%)			O/C
	C	O	N
ONC	63.8	36.2	0	0.57
ONC-Trp	64.4	34.2	1.4	0.53
ONC-Phe	64.0	33.9	1.1	0.53
ONC-EMP	67.2	31.3	1.5	0.47
ONC-WRF	67.1	31.2	1.7	0.46