I am performing TOC and I need some troubleshooting help for NPOC analysis on pharmaceutical grade water. I can't seem to get my blank (environmental water) consistent and at an acceptable level. According to my previous cal curve it is calculated at about 150 to 230 ppb carbon. This is a brand new unopened bottle that comes from a reputable company with certifications(stating around 20ppb). I have tried multiple lots. I don't know where else to turn. All and any advice is appreciated.