Abstract
Any method developed hitherto was not satisfactory in view of reproducibility for determining such small amounts of As as up to about 0.05%. So the author made some studies to get a rapid and accurate photometric method, and found the following procedure most suitable: Dissolve 0.5 g of the sample in 20 mL of HNO3 (1+1), add 7 mL of MnSO4 (5%) and about 100 mL of water, heat to boil, add 2 mL of KMnO4 (3%), continue to boil, and when MnO2 begins to separate, add 1 mL of KMnO4 (3%), and boil gently until all MnO4′ is decomposed. Filter the hot solution, wash well with hot water, place the paper above the original beaker, dissolve the MnO2 with 7 mL of hot H2SO4 (3N) and a few mL of H2O2 (3%), wash with hot water and boil off the excess of H2O2. Transfer the cooled solution to a separating funnel, add 8 mL of (NH4)2MoO4 (1%), dilute to about 50 mL with water and add 5 mL of amylalcohol. Shake vigorously about 50 times, draw off the lower layer into a 100 mL volumetric flask, add 6 mL of H2SO4 (3N), add 10 mL of N2H4·H2SO4 (1%) and dilute to the mark with water. Warm for 3 to 4 minutes in boiling water, cool immediately in cold water, and measure the absorbancy with a photoelectric photometer using a S66 filter (820 mμ). Si up to 4.2% and P up to 1% have no effects. The time required for the analysis is 25 to 35 minutes and 0.005 to 0.07% of As in iron, steel and iron ore can be determined with the reproducibility of ±0.001% by this method.
