TM24-03 Characterization of bias and variability in Total Organic Carbon attributable to change in preservation from chilled to sulfuric acid preservation

This technical memorandum alerts data users to potential shifts in measured concentration and variability due to the correction of a deviation from the Total Organic Carbon (TOC) source method (Standard Method 5310B; Lipps and others, 2018, revised 2022) and provides validation data for a preservation change from chilled and unacidified (hereafter referred to as “unacidified”; 4°C) to chilled with acidification to pH<2 by sulfuric acid (hereafter referred to as “acidified”) in samples analyzed for TOC. Results from a paired sample study are provided to allow data users the ability to compare results from the previous and new procedures. The National Water Quality Laboratory will begin requiring TOC samples be preserved to pH <2 using sulfuric acid beginning January 1, 2025.