A 200 µL autosampler vial from lot 22-1147 gave a certified concentration of 10.02 mg/L on the CoA and 9.61 mg/L by our own ICP-MS check, a 4.1% low bias that repeated across six vials from the same case. The standard came from a vendor with a NIST-traceable certificate. The balance was calibrated that morning. The pipette had a current calibration certificate. Everything in the chain looked documented, and yet the number was wrong. What the paperwork could not show was the polypropylene of...