Hello,

My standard is (Tyr[SO3H]27)Cholecystokinin 8 from Sigma. (molecular isotopic mass: 1142.35)

I make stock solution in 0.05M aqueous NH4OH as COA. I have tried many solvent for the stock like methanol, methanol-water, water

When I do MS infusion in LCMS system (API 3200 System - Sciex), I can not see any adduct ion of sulfated CCK8 but only the unsulfated form.

My question is: what does happen with sulfated CCK8 in NH4OH? Is it degraded and looses -SO3H?

If that is true, what should I do to keep my standard stable for the analysis?

Thank you for your help!