inconsistent responses

Hell all,

I run VOCs (EPA method 524.2) on GC/MS (6890N/5973) using Teledyne Tekmar ATOMIX P&T. I have issues with some early eluters, mostly Vinyl Chloride, having very inconsistent IS response factors during calibrations. I am consistently having to drop my two lowest calibration levels in order to meet RSD criteria. For normal client work, this does not pose too big of an issue but it is causing issues with QC studies (LOQ, MDL, etc). Any thoughts would be greatly appreciated. Specs are as follows 

Column: Agilent J&W DB-VRX 20mx0.18x1.0um

Split ratio: 50/1

Total flow: 28.4 mL/min

Initial temp: 30C for 3  min

Ramp 15 @ 190C then 20 @ 225 for 2 min

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