[kamiyu]

Curious about the impurities present in methyl iodide. Sure it contains iodine.

But how about hydroiodic acid??? I think this is also likely because of hydrolysis of CH3I.

Recently doing a reaction and the product is slightly impure. Wondering if the impurity in CH3I is the culprit

[TheUnassuming]

Depends on the bottle (how old, exposed to moisture ect).
MeI exposed to water or moisture in the air will form MeOH and HI.  This is especially a problem in areas with higher humidity (east coast).
If you think its a problem, distilling the MeI before use is a good idea.