Pharmaceutical Inorganic Chemistry -B Pharmacy First Year -First semester - PIC PPT 3-Limit tests for chloride and sulphate

1. Pharmaceutical Inorganic Chemistry
Lecture 3
Unit I
Limit Tests
 By Manjusha SK
 Associate professor

2. Limit tests –
 Limit tests are the quantitative/semiquantitative tests designed to identify
and control the small amount of impurities which are likely to be present in
the substance.
 These tests are carried out to determine the inorganic impurities present in
the compound.eg limit test for chloride,sulphates,iron,heavy metals,lead
and arsenic.
 Limit tests are carried out in Nessler cylinder which is made up of the
borosilicate glass.
 As shown in above image the two Nessler cylinder are used to perform the
limit tests,one for the preparation of test solution and one for the standard
solution.
 The presence of opalescence,turbidity and change in colour is an indication
for the presence of impurity in the given substance.

3. 1.Limit tests for Chloride --
 Principle --
 The limit test for chloride is based on the simple reaction between the
silver nitrate and soluble chloride ions to obtain silver chloride.
 The silver chloride is produced in the presence of dilute nitric acid due to
which the solution becomes turbid.
 The extent of turbidity/opalescence depends upon the presence and
amount of chloride ions in the test solution is compared with the standard
solution.
 The precipitated silver chloride formed is insoluble in dilute nitric acid,gives
 turbidity/opalescence.

4. 1.Limit tests for Chloride -- Procedure
For Test Solution For Standard Solution
Dissolve the specific amount of
sample(1gm) in 10ml of distilled water.
Transfer the above content to Nessler
cylinder and label it as TEST.
Dissolve the 10ml standard chloride
solution (25ppm) in 10ml of distilled
water.
Transfer the above content to Nessler
cylinder and label it as STANDARD.
To this add 1ml of dil.nitric acid and
dilute with water upto 50ml of mark on
Nessler cylinder.
To this add 1ml of dil.nitric acid and
dilute with water upto 50ml of mark on
Nessler cylinder
Now add 1ml of (0.1M) silver nitrate
solution.
Now add 1ml of (0.1M) silver nitrate
solution.
Stir it and with glass rod and allowed to
stand for 5 mins and observe the
turbidity/opalescence.
Stir it and with glass rod and allowed to
stand for 5 mins and observe the
turbidity/opalescence.

5. 1.Limit tests for Chloride --
 Observation -Now compare the presence of turbidity/opalescence in
the test solution with standard by keeping the Nessler cylinder
vertically against the black background.
 If the turbidity/opalescence in test solution should be less than
standard solution,the sample will pass the limit test.
 It indicates the sample complies with the standards of pharmacopoeia

6. 2.Limit tests for Sulphates –
 Principle –
 The limit test for Sulphate is based on the simple reaction between the
barium chloride and soluble sulphates in the presence of dil.hydrochloric
acid.
 BaCl2 + SO4
2- → BaSO4 + 2Cl-
 Now the hydrochloric acid is replaced by dil.acetic acid so the barium
sulphate precipitate formed and produces turbidity/opalescence.
 Ethanol is used to prevent supersaturation and form the uniform
turbidity/opalescence.
 Supersaturation- A super saturated solution contains more dissolved solute
than the saturated solution.

7. 2.Limit tests for Sulphates –
 Procedure -
For Test Solution For Standard Solution
Dissolve the specific amount of sample
(1gm) in 10ml of distilled water.
Transfer the above content to Nessler
cylinder and label it as TEST.
Dissolve the 1mlof barium chloride
(25%w/v) in 10ml of distilled water.
Transfer the above content to Nessler
cylinder and label it as STANDARD.
To this add 1ml of ethanolic sulphate
standard solution and mix it.
To this add 1ml of ethanolic sulphate
standard solution and mix it.
To the above solution add 0.15ml of (5M)
acetic acid.
To the above solution add 15ml of
standard sulphate solution and 0.15ml of
(5M) acetic acid.
Now add sufficient water to make upto
50ml mark on Nessler cylinder.
Now add sufficient water to make upto
50ml mark on Nessler cylinder.
Stir it and with glass rod and allowed to
stand for 5 mins and observe the
turbidity/opalescence.
Stir it and with glass rod and allowed to
stand for 5 mins and observe the
turbidity/opalescence.

8. 2.Limit tests for Sulphates –
 Observation -Now compare the presence of turbidity/opalescence in the
test solution with standard by keeping the Nessler cylinder vertically
against the black background.
 If the turbidity/opalescence in test solution should be less than standard
solution,the sample will pass the limit test.
 It shows that the sample complies with the standards of pharmacopoeia.

9. THANK YOU