A student prepares a combined standard solution by weighing out 252.6 mg of KNO3 and 148.5 mg of NaHPO43HO, dissolving in deionized water to a final mass of 102.234 g. After through mixing, 1.022 g of this solution were transferred to a clean dry container and diluted with deionized water to a final mass of 250.654 g. Calculate the final concentration NO3-N and PO4-P in ppb. Strategy: This question involves a series of gravimetric dilutions. Since we are asked for the final concentrations as mass ratio (i.e., ug/kg of nitrate-nitrogen and phosphate- phosphorus, respectively), we can convert the mass of solids dissolved into a corresponding mass of the elements N and P. Dividing by the mass of solution and taking into account the dilutions yields the final result.