1) Are your compounds of the general type CH2=CH-CH2-Si-R3 (NOT Si-O-Si siloxanes) ??
2) Is your mobile phase MeCN/water or other ??
3) Do you see hydrolysis products ??
Suggest you use non-protic solvents (e.g. MeCN) with a small amount of silver tetrafluorborate (ca. 10 mg/100 mL) to generate [M + Ag]+ ions; these are very obvious due to the Ag 108/110 doublet (~1:1 intensity)
Also possibly run in CH2Cl2 in -ve mode, see [M + Cl]- ions; again, very obvious due to Cl 35/37 doublet (~3:1 intensity).
You are ONLY allowed to act on these options if you report back the results---whether they are successful or not. Seriously, we all learn from the negative results as well as
the positive.
Good Luck !!