Hello,

I am very sorry to notice your question on the forum so late.

I think pLink's pConfig default BS3 crosslinker mass are right. Maybe your 
calculations are wrong.

BS3 linker after reaction has 10 hydrogen atoms, and the added mass is 138. 
Monolink by H2O has 12 hydrogen atoms, and the added mass is 156. As you said, 
monolink will probably lose an H, adding a mass of 155 also exists. There is a 
lot of literature(https://doi.org/10.1016/j.ijms.2019.116184) and the Thermo 
product documentation(https://assets.fishersci.com/TFS-
Assets/LSG/manuals/MAN0011542_BS3_d0d4_BS2G_d0d3_UG.pdf) that support these mass 
values.

BS3_heavy is replacing four hydrogen atoms with four deuterium atoms, which is 
2H.

Regards,
Pengzhi Mao