Table 2

HPLC retention times (tR) of amino acid conjugates of VPA with different mobile phases.

LC-MS/MS Method 1 (tR = min)LC-MS/MS Method 2 (tR = min)LC-MS/MS Method 3 (tR = min)
VPA-GLN22.9714.707.86
VPA-GLU30.7023.2010.53
VPA-GLY30.3024.011.99
VPA-ASP23.999.93
FVPA-GLN9.33

Mobile phase for LC-MS/MS 1: methanol/water (43:57, 0.05% TFA). Mobile phase for LC-MS/MS 2: acetonitrile/water (30:70, 0.05% TFA). Mobile phase for LC-MS/MS 3: acetonitrile/water (40:60, 0.05% TFA).