limit test for iron

LIMIT TEST FOR IRON

1. LIMIT TEST FOR IRON BY PROF. TAUFIK MULLA ASSISTANT PROFESSOR DEPARTMENT OF PHARMACEUTICS SPBC COLLEGE OF PHARMACY.

2. Limit test for IRON The iron Limit Test is designed to determine the allowable limit of iron contained in a sample. Principle: This test is based on the formation of purple colour by reaction of iron with thioglycolic acid to form ferrous thioglycollate in the presence of ammonium citrate. Iron present as an impurity in the sample reacts with thioglycollic acid to form ferrous thioglycollate which is responsible for the appearance of purple colour in the solution. This reaction will only occur if the given sample contains iron as an impurity even in trace amount. The intensity of colour produced by test solution is compared with the standard soluton obtained by taking standard iron solution containing 0.04 mg of iron.

3. Note: Citric acid reacts with ammonia solution giving ammonium citrate, which act as a buffer. The citrate ion also prevents the precipitation of iron by ammonia by forming a complex with it. Thioglycolic acid not only react with ferrous ions, but it also reduces ferric ions to ferrous ions.

4. PROCEDURE TEST SAMPLE STANDARD SAMPLE REASON Dissolve 1gm of sample in 40 ml of distilled water and transfer in Nessler cylinder and marked it as ‘T’ Take 2ml of standard iron solution in Nessler cylinder and marked it as ‘S’ and add 40 ml of distilled water The aqueous solution will leach out all iron present in sample Add 2ml of 20%w/v iron free citric acid Add 2ml of 20%w/v iron free citric acid Citric acid prevents the p recipitation of iron with ammonia and keeps iron in solution even in presence of ammonia by forming complex with iron as iron citrate. Add 0.1 ml thioglycolic acid Add 0.1 ml thioglycolic acid To convert ferric ion to ferrous ion. And further react with ferrous ion and form ferrous thioglycolate Add ammonia to make alkaline solution Add ammonia to make alkaline solution Ferrous thioglycolate give color only in alkaline media Make volume with distilled water to 50 ml Make volume with distilled water to 50 ml Equal volume of sample and standard is needed to identify intensity of color

5. conclusion The purple color produced in the sample solution should not be greater than standard solution. If purple color produced in the standard is more than that of test, the sample complies with the limit test of sulphate as per I.P. 1996