Limit test for chlorides alok sharma

Limit tests are quantitative or semi-quantitative tests designed to identify and control small quantities of impurity, which are likely to be present in the substance. The quantity of any one impurity in an official substance is often small, and consequently the visible reaction response to any test for that impurity is also small. The design of individual tests is therefore important if errors are to be avoided in the hands of different operators.

1. Limit test for chlorides Mahakal Institute of Pharmaceutical Studies, Ujjain Behind Air strip , Datana , Dewas road, Ujjain Given by Alok Sharma Asst. Professor Pharmaceutical chemistry Presentation on

2. Introduction Limit tests are quantitative or semi-quantitative tests designed to identify and control small quantities of impurity, which are likely to be present in the substance. The quantity of any one impurity in an official substance is often small, and consequently the visible reaction response to any test for that impurity is also small. The design of individual tests is therefore important if errors are to be avoided in the hands of different operators.

3. Specificity of the test Any test used as a limit test must, of necessity, give some form of selective reaction with the trace impurity. Many tests used for the detection of inorganic impurities in official inorganic chemicals are based upon the separations involved in inorganic qualitative analysis.

4. Sensitivity of the test The degree of sensitivity required in a limit test varies enormously according to the standard of purity demanded by the monograph. The sensitivity of most tests is dependent upon a number of variable factors concentration of the solute, precipitating reagent, duration of the reaction, temperature, and the nature and concentration of other substances unavoidably present in solution.

5. Comparison methods: Tests of this type require a standard containing a definite amount of impurity, to be set up at the same time and under the same conditions as the test experiment. In this way the extent of the reaction is readily determined by direct comparison of the test solution with a standard of known concentration. E.g. limit test of chlorides and sulphate e.t.c Method use for Limit tests

6. Limit test for chlorides Principle Limit test of chlorides is based on the reaction of soluble chlorides with silver nitrate in presence of dilute nitric acid to form silver chloride, which appears as turbidity (Opalescence). Reasons : Nitric acid is added in the limit test of chloride to make solution acidic and helps silver chloride precipitate to make solution turbid at the end of process.

7. Apparatus & chemicals Apparatus Required Nessler cylinders Glass rod Stand Chemicals Required Dilute Nitric acid (10%) Silver nitrate (5%) Sodium chloride

8. Nessler Cylinder Nessler cylinders are laboratory tubes with a fixed volume, made of glass with optically plane bottom. On the walls there are marks of the nominal stroke volume (usually 100 ml) and possibly one half-way mark (then usually 50 ml).

9. Procedure for Chloride limit test Test sample Standard compound Specific weight of compound is dissolved in water or solution is prepared as directed in the pharmacopoeia and transferred in Nessler cylinder Take 1ml of 0.05845 % W/V solution of sodium chloride in Nessler cylinder Add 1ml of nitric acid Add 1ml of nitric acid Dilute to 50ml in Nessler cylinder Dilute to 50ml in Nessler cylinder Add 1ml of AgNO3 solution Add 1ml of AgNO3 solution Keep aside for 5 min Keep aside for 5 min Observe the Opalescence/Turbidity Observe the Opalescence/Turbidity

10. Observation The opalescence produce in sample solution should not be greater than standard solution. If opalescence produces in sample solution is less than the standard solution, the sample will pass the limit test of chloride and visa versa.

11. Results & conclusion If the opalescence in the sample is less than the standard, it passes the test. If it is more than the standard, it fails the test. For comparison of turbidity for different substances with varying amount of impurity, the amount of substance to be used is varied, and not the standard turbidity. Pharmacopoeias do not give a numerical value to the limits, as is not practicable as its content will be influenced to great extent, by large quantities of other substances present.