This presentation provide a complete note of Heavy metals limit Test in pharmaceutics.

1. LIMIT TEST FOR HEAVY
METALS
BY
SONU PATEL
M PHARM
(PHARMACEUTICS)
UTTARAKHAND TECHNICAL UNIVERSITY
DEHRADUN

2. LIMIT TEST FOR HEAVY METALS
• The limit for heavy metals is indicated in the individual
monographs in terms of ppm, i.e., the parts of lead, Pb, per
million parts (by weight) of the substance under examination.
• According to Indian pharmacopoeia (IP) Limit Test of Heavy metal
induced four different methods.
• Method A:. For colourless substances.
• Method B:. For coloured substances.
• Method C:. For substances which form coloured and colourless
with Sodium hydroxide.
• Method D:. For remaining substances.

3. METHOD A
•Principle:. It is based on reaction between Heavy metals and
Hydrogen sulphide (H2S) in acidic medium to produce metal
sulphide.
•. Pb + H2S H+. PbS. +. H2
. (Hydrogen. (Lead
Sulphide) sulphide)
Note:
•Here PbS produce brown colour.
•PH should be maintained at 3 to 4 with Acetic acid or

4. PROCEDURE
“TAKE TWO 50 ML NESSLER CYLINDER AND MARK ONE AS TEST AND OTHER AS
STANDARD”
Test Standard
Place 25ml of solution prepared for the test as
directed in the individual monograph or dissolve
the specified quality of the substance under
examination in sufficient water to produce
25ml.
Pipette 1.0ml of lead standard solution (20 ppm
Pb) and dilute with water to produce 25 ml.
Adjust PH between 3 to 4 with Dil. Acetic acid or
Dil. Ammonia solution and dilute with water to
produce 35ml and mix.
Adjust PH between 3 to 4 with Dil. Acetic acid or
Dil. Ammonia solution and dilute with water to
produce 35ml and mix.
Add 10ml of freshly prepared Hydrogen
sulphide solution, mix and dilute to 50ml with
water.
Allow to stand for 5 minute.
Add 10ml of freshly prepared hydrogen
sulphide solution,mix and dilute to 50ml with
water.
Allow to stand for 5 minute.

5. OBSERVATION: THE COLOUR PRODUCED WITH THE TEST SOLUTION
IS NOT MORE INTENSE THAN THAT PRODUCE WITH THE STANDARD
SOLUTION.
Method B
Principle:. This method is also depends upon reaction between Heavy
metal and Hydrogen sulphide in acidic medium to produce metal sulphide
and Hydrogen gas.
Pb. +. H2S. H+ PbS +. H2
• Note:
• PbS produce brown colour.
• PH should be maintained at 3 to 4 with Dil. Acetic acid or Dil Ammonia
solution.

6. PROCEDURE :.
“TAKE TWO 50 ML NESSLER CYLINDERS AND MARK ONE AS TEST AND
OTHER AS STANDARD.”
Test Standard
Weigh in a suitable crucible the quantity of the
substance specified in the individual
monograph, add sufficient sulphuric acid to wet
the sample, ignite carefully at low temperature
until thoroughly charred.
Pipette 1ml of lead standard solution (20ppm
Pb) and dilute with water to 25ml.
After charred add 2ml of nitric acid and 5 drops
of sulphuric acid and heat cautiously until white
fumes are no longer evolved.
Adjust PH with Dil. Acetic acid or Dil.ammonia
solution to 3to 4 and dilute to 35ml with water.
Ignite preferably in a muffle furnace at 500 to
600 c until the carbon is completely burnt off.
Add 10ml of freshly prepared hydrogen sulphide
solution, mix and dilute to 50 mL with water.
Allow to stand for 5 minute.

7. Cool,and add 4ml of HCl , cover and digest on a
water bath for 15 minutes. Uncover and
evaporate to dryness.
Moisten the residue with 1drop of HCl add 10 ml
of hot water and digest for 2 minutes.
Add ammonia solution dropwise until the
solution is just alkaline to litmus paper and
dilute to 25ml with water and adjust PH at 3 to 4
with dil.acetic acid. And filter it.
Add filtrate and washing in 50ml Nessler
cylinder and dilute to 35ml with water. And mix.
Add 10ml of freshly prepared hydrogen sulphide
solution, mix and allowed to stand for 5 minute.

8. OBSERVATION:. THE COLOUR PRODUCED IN TEST SOLUTION IS NOT
MORE INTENSE THAN STANDARD.
Method C
Principle:. This method is based Upon reaction
between sodium sulphide and heavy metal to form
metal sulphide In alkaline medium.
Pb. +. NaS. OH. PbS. + 2Na
Here lead sulphide produce brown colour.

9. PROCEDURE
“TAKE TWO 50 ML NESSLER CYLINDERS AND MARK ONE AS TEST AND
OTHER AS STANDARD”
Test Standard
Place 25ml of the solution prepared for the test
as directed in the individual monograph, or
dissolve the specified quality of the substance
under examination in a mixture of 20 ml of
water and 5ml of Dil. NaOH and dilute to 50 mL
with water.
Pipette 1.0ml of lead standard solution (20ppm
Pb) add 5ml of Dil NaOH . Dil. With water to
produce 50ml.
Add 5 drops of sodium sulphide solution and
mix it.
Add 5 drops of sodium sulphide solution and
mix it.
Allow to stand for 5 minute. Allow to stand for 5 minute.

10. OBSERVATION:. THE COLOUR PRODUCED WITH THE TEST
SOLUTION IS NOT MORE INTENSE THAN THAT PRODUCE WITH
THE STANDARD SOLUTION.
Method D
Principle:. This method is based on the reaction between
Thioacetamide and heavy metal in acidic medium.
Pb. + CH3CSNH2. H+. Brown colour
(Thioacetamide)

11. PROCEDURE
“TAKE TWO 50 ML NESSLER CYLINDERS AND MARK ONE AS TEST
AND OTHER
AS STANDARD”.
Test Standard
Prepared a solution as directed in the individual
monograph and pipette 12ml into a Nessler
cylinder.
Pipette 10.0ml of either lead standard solution
(1ppm Pb) or lead standard solution (2ppm Pb)
into a Nessler cylinder.
Add 2ml of acetate buffer pH 3.5 and mix. Add 2ml of acetate buffer pH 3.5 and mix.
Add 1.2ml of thioacetamide reagent and allow to
stand for 2 minutes. And observe it.
Add 1.2ml of thioacetamide reagent and allow to
stand for 2 minutes and observe it.

12. OBSERVATION:. THE COLOUR PRODUCED IN TEST SOLUTION IS NOT
MORE INTENSE THAN THAT PRODUCE WITH THE STANDARD SOLUTION.