Table 3: Measurements, limit of detection (LOD) on pure standards by LC/MS/MS (ESI) with LC/MS system no. 2.

Buffer/pH modifier (obtained pH)TFA (~2)Without buffer/pH-modifierNH4OAc (~7)NH3 (~9)
PositivePositiveNegativePositiveNegativePositiveNegative

FTH-MeVal (LOD, nM)2.0230268.27.22.40.5
DABTH-MeVal (LOD, nM)1420020031245.129
DNTH-MeVal (LOD, nM)54550560560130,0002709,400
PTH-MeVal (LOD, nM)4,10019,0004707,5003,400310470