LC/MS/MS Analysis of N-Terminal Protein Adducts with Improved Sensitivity: A Comparison of Selected Edman Isothiocyanate Reagents

Table 2

Measurements, limit of detection (LOD) on pure standards, data obtained by LC/MS system no. 1.

Buffer/pH modifier (obtained pH) ionization method	TFA (~2) ESI	Without buffer/pH-modifier ESI		NH4OAc (~7) ESI		NH3 (~9) ESI		TFA (~2) APCI
	Positive	Positive	Negative	Positive	Negative	Positive	Negative	Positive
FTH-Val (LOD, nM)	15	5,200	750	47	21	61	10	8.4
FTH-MeVal (LOD, nM)	51	5,900	660	210	180	14	2.7	4.6
DABTH-MeVal (LOD, nM)	350	5,000	5,100	790	590	130	730	55
DNTH-MeVal (LOD, nM)	1,200	12,000	13,000	12,000	2800,000	6,100	210,000	110
PTH-MeVal (LOD, nM)	100,000	48,000	12,000	130,000	87,000	7,800	12,000	10,000