| Limit Test for Iron |
| 1.0 Apparatus: >50ml Nessler’s cylinder >50ml cylinder >Glass Funnel >5ml bulb pipette >50ml conical flask >2ml graduated pipette 2.0 Reagent: Limit Test for Iron >20%w/v solution of iron free citric acid >Nitric acid AR grade >Citric acid AR grade >Thioglycollic acid AR grade >Iron free ammonia solution >20 ppm Iron standard solution >Dilute ammonia solution 3.0 Preparation of Reagents: >20%w/v solution of iron free citric acid: >Dissolve about 5.0 g of iron free citric acid to 25 ml with purified water. >Dilute ammonia solution: >Dilute 4.2 ml of strong ammonia solution to 10 ml with purified water. >Iron free ammonia solution: >Evaporate 5 ml dilute ammonia solution nearly to dryness on a water bath, add 40 ml of purified water, 2 ml of 20% w/v solution of iron free citric acid and 0.1 ml of thioglycollic acid, mix make alkaline with iron free ammonia solution, and dilute to 50 ml with purified water; no pink colour should produce. >20 ppm iron standard solution: Dilute 1 volume of a 0.1726 % w/v solution of ferric ammonia sulphate in 0.05M sulphuric acid to 10 volumes with purified water. 4.0 Method: Sample preparation: Dissolve the specified quantity of the substance being examined in purified water, or prepare a solution as directed in the STP, and transfer to a Nessler cylinder. Add 2 ml of 20% w/v solution of iron-free citric acid and 0.1 ml of thioglycolic acid, mix make alkaline with iron-free ammonia solution, dilute to 50 ml with purified water and allow to stand for 5 minutes. Standard preparation: In a 50ml Nessler cylinder pipetting 2.0 ml of iron standard solution (20 ppm Fe) and add 2 ml of 20 % w/v solution of iron-free citric acid and 0.1 ml of thioglycolic acid, mix make alkaline with iron-free ammonia solution, dilute to 50 ml with purified water and allow to stand for 5 minutes. |