Question

1.635 L of water were concentrated on a solid phase extraction device in order to determine the concentration of dibutyl phthalate on the shoreline of a reservoir in northern Canada (T = 13.5 °C). If the technique was previously shown to have a recovery of 85%, and the analysis returned a value of 23.7 ng, what is the concentration of DBP (in parts-per-billion w/w) on the shoreline, based on this analysis?