Fig. 6.

Results of glyphosate (a) and AMPA (b) standard addition experiments in Durham, NC, tap water, Duke University stormwater retention pond water, Sri Lankan well water, and Ellerbe Creek (Durham, NC) water samples. Measurements of samples via internal standard quantitation (black bars, [EDTA] = 10 μM and [Analyte]spiked = 0 μg L⁻¹) and via standard addition (pattern bars, [EDTA] = 10 μM and [Analyte]spiked = 20 μg L⁻¹) are shown. Dashed and dotted lines represent LOD and LOQ of the analytes, respectively. Error bars represent standard deviation among triplicate analyses of samples. Standard addition and internal standard quantified concentrations of analytes agreed within error except for the Creek 4 samples which were significantly different (p value ≤ 0.05) as denoted by the asterisk. Glyphosate was measured above the LOD in all environmental samples except the tap water, while AMPA was found only in Ellerbe creek samples with most of the samples below the LOQ of the method