I recently created a new VOC method EPA 624. The method looks good for all compounds, including the 7-point calibration curve fits with linear regression. The only issue is that the lowest cal level (@ 0.5 ppb) is quantitating closer to the 1.0 ppb level for most compounds. I'm not sure how important this is compared to having good curve fits. I have been using the general integrator for building this method although it looks like agile2 might be better for this? Somewhat related - I use a Purge and Trap unit with some carryover (mainly ion 44) that might affect the quantitation regardless of what is done in method building. It definitely shows up as most abundant in the few minutes after solvent delay where many of these compounds are having trouble staying around 0.5 ppb. I understand that 44 or CO2 can manifest in other ways but feel confident it is mostly coming from the P&T process.