I could use some help from experienced users of this method. We have a policy that requires us to prepare our standard in duplicate and check the %relative difference between the two. The %RD must be <2.0% for the analysis to be acceptable.

The analytes are iodomethane and iodopropane for this method. We have no trouble with the iodopropane, but are have a very difficult time meeting the %RD requirement with the iodomethane. It is much more volatile and much more reactive.

The vials also contain hydroiodic acid, xylene, and adipic acid. The xylene and HI form two layers, with the analytes going into the xylene (top) layer. We have tried several techniques to try and control volatility, so I don't think that is the entire problem.

Does anyone have any insight into this method? Would stabilized HI vs. unstabilized HI make a difference? We've tried both, but don't have any conclusive results on that.

If anyone out there has any thoughts on this analysis, I'd appreciate the help. It's a big headache right now.