Does anyone have a copy of this book who can view the mercury procedure and tell me where they are getting 0.5ppb from when adding 10ng of standard and then 1ppb when they add 20ng of standard to the 2nd flask... I thought standard addition method meant that whatever standard you add to a flask is decreased by the amount of solution you have in the end. For example, if I add a ml of a 500ppb standard to a 100mL volumetric flask and then add 20grams of my unknown and then raise up to 100ml with water, I should be left with a 5ppb standard, respectively.