Species of arsenic found in drinking water include AsO3^3- (arsenite), AsO4^3- (arsenate), (CH3)2AsO2^- (dimethylarsinate), and (CH3)AsO3^2- (methylarsonate). Pure water containing no arsenic was spiked with 0.40 µg arsenate/L. Seven replicate determinations gave 0.39, 0.40, 0.38, 0.41, 0.36, 0.35, and 0.39 µg/L. Find the mean percent recovery of the spike and the concentration detection limit (µg/L).