When running the EPA 525.2 method by GCMS, the relative response factors for each analyte consistently increase with increasing standard concentration. According to the methodology, I should be able to achieve an RSD less than 30. However, with the wide range in RRFs I see from low to high standards, many of my compounds have RSD greater than 50. The strange thing is that I can demonstrate good linearity, so I feel confident in my standard preparation.

Standard concentrations range from 0.1ppm to 10ppm, with a constant I.S. concentration of 2ppm. Final volumes are all 100ul in ethyl actetate.

Am I doing something wrong?