Table 2.

Measured percentages of Q in peptide mixtures spiked into tryptic protein digests (BSA, CytC and collagen) analysed using either ESI or MALDI

Biological matrix	[peptide spike] (ppm)	Known % Q	ESI		MALDI
			Measured % Q	SD	Measured % Q	SD
BSA	5	31	34	2.98	58	2.21
BSA	10	31	34	1.63	60	0.83
BSA	5	50	64	3.63	74	0.42
BSA	10	50	56	0.59	74	0.42
BSA	5	69	85	1.41	85	1.28
BSA	10	69	77	1.65	87	0.73
CytC	5	31	29	0.29	56	3.00
CytC	10	31	31	3.78	61	0.46
CytC	5	50	47	2.21	57	1.13
CytC	10	50	45	0.56	61	0.46
CytC	5	69	65	0.61	88	0.63
CytC	10	69	65	2.27	88	0.29
Collagen	2.5	31	34	0.69	61	1.6
Collagen	5	31	32	1.26	61	3.04
Collagen	2.5	50	52	1.25	74	1.67
Collagen	5	50	52	1.03	75	0.91
Collagen	2.5	69	73	1.08	86	0.85
Collagen	5	69	70	0.38	86	0.48

SD: standard deviation