One of these samples was spiked with the reference standard mixture (Table .2) and the other was used for a three-point dilution series with a constant dilution factor of two and diluting with the extraction solvent. The QCs and process blank were measured in triplicate during the LC-HRMS acquisition sequence. Features were removed during data analysis if they were not present in all three replicates of the QC, had a relative standard deviation greater than 30% in the QC measurements, or had an average chromatographic peak area in the process blank sample greater than 1/3 of the average area in the QC . Finally, features that did not have a Spearman correlation coefficient greater than 0 in the QC dilution series were removed.