... while K, Ca, Mg, and Na (M3-K, M3-Ca, M3-Mg, and M3-Na, respectively) areremoved by the action of ammonium nitrate and nitric acid. The Cu, Zn, Mn, and Fe (M3-Cu,M-Zn, M3-Mn, and M3-Fe) are extracted ... color-developing solution in a 50 0 mLflask as follows: add 250 mL of 2 .5 M H2SO4,followedby75mLofammo-nium molybdate solution, 50 mL of ascorbic acid solution, and 25 mL of antimony potassium tartrate ... 0 .5 mL Brij- 35 and mix.4 Standar d solutions : prepa re stock standa rd A by diss olving 1000 mg B (5 : 7 15 g H3 BO 4 ) in 1 L deionized water and prepar e stock standa rd B by taki ng 50 ...