A sample of pure water was spiked with 0.475 ng/mL silver ion. Ten replicate determinations of the spiked water sample gave 0.485 , 0.465 , 0.442 , 0.428 , 0.469 , 0.449 , 0.453 , 0.457 , 0.435 , and 0.420 ng/mL silver ion. Determine the mean percent recovery of the spike and the detection limit of the analytical method used for the silver ion determination.