Table 2.

Summary of the identified characteristic signals with formula and exact mass for each organic capping agent on Au and Ag NPs in the stock and purified suspension in the positive mode

Capping agent	Detected ion	Exact mass [m/z]	S/N ratios
			Au NPs		Ag NPs
			Stock	Purified	Stock	Purified
CA	[CA + H]+	193.034	17*	28	---	35
TA§	[TA-C62H46O38 + H]+	303.014	32	32	---	---
LA	[LA-C2H4 + H]+	179.019	36	37	---	---
PVP	[VP + H]+	112.076	190	263	104	118
	[VP + C2H2 + H]+	138.091#	74	122	118	146
BPEI	[EI + H]+	44.049	239	100	617	559
	[EI + C2H2 + H]+	70.065#	113	63	250	237
m-PEG-SH	[EG + H]+	45.033	161	259	1356	1432
	[EG + C2H4 + H]+	73.065#	63	114	90	94

*This value for Au-CA in the stock suspension was manually readout due to the overlapping signal at m/z 192.86

^#These additional identified polymeric fragment ions are referred to as “monomer+C₂”

^§The TA fragment ion was also detected as the corresponding anion on Au NPs

“---” denotes not assigned signals due to S/N < 5