Note:
6.3 Calibration curve
Transfer by pipette, 0,5, 10, 15.20 and 25 ml standard molybdenum solution (3.5.2) into a series of 125 ml separating funnels. To each funnel add 1 ml ammonium ferrous sulphate solution (3.6) and 25 ml of 2 N hydrochloric acid (3.2); dilute to 50 ml with water where necessary and proceed as described at 6.2.1, commencing at “then add 1 ml potassium thiocyanate solution (3.7) and mix ... ... ... ...”. Plot a calibration curve of the absorbance of the solutions against the corresponding amounts of molybdenum (μg).