Fig. 5.

Results of a matrix fortification study with standard addition of glyphosate (a) and AMPA (b) in Haw River samples. Results from analyte-spiked and EDTA-amended samples (white bars, [EDTA] = 10 μM and [Analyte]spiked = 20 μg L⁻¹) and analyte-spiked samples without EDTA amendment (black bars, [EDTA] = 0 μM and [Analyte]spiked = 20 μg L⁻¹) are shown. The dashed line represents the spiked analyte concentration of 20 μg L⁻¹. Error bars represent standard deviation among triplicate analysis of samples. Location CCB was the only river sample with background glyphosate measured at 1.5 μg L⁻¹ (gray bar in panel A), which contributed to the elevated measured concentration of glyphosate in the standard addition sample (22 ± 1 μg L⁻¹). No background AMPA levels were detected in these samples