Impurities definition Sources of impurities Effect/ type of impurities Limit test definition Limit test Importance, Principle & procedure of Limit test for iron, chloride, sulphate, arsenic & heavy metals.

1. Impurities in Pharmaceuticals
By,
Miss. Shalini N. Barad,
Lecturer,
Appasaheb Birnale College of Pharmacy, Sangli

2.  Impurity-
It is define as foreign particle that affects
the purity of the substance.
 Sources of Impurities-
1. Raw Material in Mfg.
2. Manufacturing process.
3. Chemical Process and plant material
employed in process
4. Inadequate Storage conditions-
a) Filth
b)Decomposition of the product during
storage

3. 5. Manufacturing hazards
a) particulate contamination
b) Process error
c) Cross contamination
d) Microbial contamination
e) Packing errors
6. Accidental substitution/ Deliberate Adulteration
with Spurious or useless material.

5. 2) Manufacturing Process:
 Tap water is invariably used in various
process which contain chloride, calcium,
magnesium ions which contaminate
manufactured substance. So limit to these
impurities have been prescribed.
 Due wide use of strong acids in the
manufacture of medicinal substances,
chloride & sulphate ions are very commonly
occurring impurities. So tests of anions are
generally included in pharmacopoeias.

6. 3) Material of the plant:
 The equipment/ utensils used in
manufacturing process are made of metals
like copper, aluminum, iron, zinc, nickel &
tin/ stainless steel.
 Due to action of solvents on material of
equipment, traces of metals are introduced
as impurities in the compound.
 Water pipe & steam pipe contain lead &
heavy metal pharmacopoeias prescribed
limit test for lead & heavy metal.

7. 4) Inadequate storage and their effects are as
follows:
a) Filth: Stored products may become contaminated
with dust, bodies of insects, animal and insect excreta.
b) Chemical instability/ decomposition of product:
decomposition because of light, traces of acid oral
alkali, air oxidation, water vapour, CO2 and traces of
metallic ions.
e.g light sensitive materials should be stored in amber
colored bottles.
c)Reactions with container materials :
e.g salicylic acid ointment must not be stored in metal
tubes.
d)Physical changes: The occurrence of changes in the
physical form of drug like change in crystal size can
lead to change in efficiency of product.
e)Temperature effect: Chemical and physical changes
occur if materials are not stored at proper

9. 5) Accidental substitution or
deliberate adulteration with spurious
or useless materials:
 Accidental substitution can take place if the
toxic substances are stored together with
other compounds, it can be avoided by
storing toxic substances separately or in a
locked cupboard.
 Many pharmaceutical chemicals are
adulterated with cheaper substances.
 E.g The expensive potassium may be
adulterated with sodium bromide.

10. 6) Manufacturing hazards:

11. i) Microbial contamination:
 Parenteral preparations and ophthalmic preparations
require special care against microbial contamination.
 Many liquid preparations and creams are liable to
bacterial and fungal contamination. So care should
be taken.
Eg. Acacia, senna, tragacanth They should be
controlled for Salmonellae.

12. ii) Packing errors:
 Products of similar appearance such as
tablets of same size, shape, colour packed
in similar containers can cause danger
through mislabeling.

13. iii) Process error:
Error arise from incomplete solution of
solute in liquid preparation should
probably be detected by normal analytical
control procedure.
iv) Cross contamination:
 The handling of powders, granules, and
tablets in large bulk creates air-borne
dust, which leads to cross contamination
of the product.
 E.g penicillin preparation requires special
handling during its manufacture.

15. e) Particulate contamination:
 The presence of unwanted particulate matter
can arise due to dirt, dust, glass, porcelain or
plastic fragments from sieves, granulating or
tableting machines or from product
containers.
 Ware and tare of equipment or improperly
cleaned equipment may also cause
particulate contamination.
 E.g Metal particles which have been found in
eye ointments packed in metal tubes.

16. •Types of Impurities or Effect of
Impurities-
1) Toxic impurities. Impurities even when present in
trace amount may show a cumulative toxic
effect.
 Eg – lead & arsenic impuities
2) Harmless impurities but are present in large
proportion beyond the limit in pharmaceutical
substances than, it lowers active strength of
drug.
 Eg- impurities of sodium salt in Potassium salt
3) Impurities if present beyond the limit affect the
storage capacity of pharmaceutical.
 Eg- moisture beyond limit –activate free flowing
property of substance / decompose it.
4) Impurities may form technical difficulties in
formulation.

17. 5. Impurities bring incompatibility with other
sub.
6. Impurities may lowers shelf life of drug.
7. Impurities though harmless in nature they
may bring about changes in colour, odour
& taste thus making the sub unaesthic and
unhygenic.
Eg- phenolic impurity- in Sodium salicylate –
alters colour

18.  Limit= certain/ fix value/ amount
Test= to examine/ investigate
 Limit test- Is an quantitative or semi
quantitative test used to detect small amount of
impurities which are likely to be present in
substance.
 It is performed to find impurity
 impurity = foreign organic matter
 Types-
1. Test in which there is no visible reaction.
2. Comparison Method
3. Quantitative determination.
•Limit Test

19. Importance of limit test
1. Limit test is generally carried out to
determine the inorganic impurities
present in compound.
2. It is used to check the quality / purity
of pharmaceutical substance.

20. Nessler's cylinder
Made up of =
Borosilicate
glass

21. 1) Limit test for Chloride
 Principle-
 This test is based on reaction in
between soluble chloride as an impurity
& silver nitrate which result in formation
of a ppt of insoluble silver chloride in the
presence of dil. HNO3 giving an
opalescence to final solution.
 Reaction-
Cl- + AgNO3 AgCl + NO3
Dil. HNO3

22.  Role of Nitric acid(HNO3): It is used to
dissolve other impurities like carbonates &
Phosphate, which otherwise ppt along with AgCl &
unecessarily intensify the opalesence of the test
solution.
 2 HNO3 + CHO3
-- H2CO3 + 2 NO3
-
 3 HNO3 + PO3
-- H3PO4 + 3 HNO3
-
 The extent of opalescence produced depends
upon the- concentration of silver chloride form,
 which in turn depend upon concentration of
chloride ion impurities present in the sample to be
tested.
 The opalescence produced by given amount of
subs compared with opalescence produced by std.
solution of impurities  which is produced by
adding AgNO3 solution to std as well as test

23.  Procedure-
A) Std Sol-
1ml of std Chloride solution + 10ml Dil.HNO3
in Nessler’s cylinder mark with ‘S’ dilute this
solution upto 50 ml with H2O + 1ml of 0.1N
AgNO3 solution. Stir it immediately with glass
rod & allow to stand for 5 min.
B) T.S-
Weighed sub in Nessler’s cylinder mark with ‘T’
+10ml dil.HNO3 dilute this solution upto 50 ml with
DW + 1ml of 0.1 N AgNO3 solution. Stir it immediately
with glass rod & allow to stand for 5 min.

24.  Protect the opalescence from the light & view it
against black background & compare the
opalescence produced by test with that of std
opalescence
1. If the test opalescence is less than or equal
to std. opalescence, then limit test for Cl ion
for given sample complies/ passes with the
official std of IP.
2. If the test opalescence is
more than std. opalescence,
then limit test for Chloride ion
for given sample doesn't
complies/ fails with the official std. of IP.

25. 2) Limit test for sulphate-
 Reaction-
 BaCl2 + Na2SO4 BaSO4 +
2NaCl
Barium chloride sodium sulphate Barium sulphate
impurity (ppt)
 Principle—
 It is based on the reaction of soluble sulphate
(as impurity) with barium chloride in presence
of dil. HCl to form barium sulphate (insoluble),
which appears as solid particles (turbidity) in
the solution.
Dil HCl

26.  Procedure-
 T.S- Weighed sub in Nessler's cylinder mark as
‘T’ +2ml dil HCL --- Solution is diluted with 45 ml
D.W+ 5ml BaSO4 reagent. Stir it immediately with
glass rod & allow to stand for 5 min.
 Std- 1 ml of alc. K2SO4 solution + 2ml dil HCl in
Nessler's cylinder mark as ‘S’ ---it is diluted with
45 ml D.W + 5 ml BaSO4 reagent. Stir it
immediately with glass rod & allow to stand for 5
min.

27.  Observation: Protect the turbidity from the light
& view it against black background & compare the
turbidity produced by test with that of std opalescence
1. If the test turbidity is less than or equal to std.
turbidity, then limit test for Cl ion for given sample
complies/ passes with the official std of IP.
2. If the test turbidity is more than std. turbidity, then
limit test for Chloride ion for given sample doesn't
complies/ fails with the official std of IP.

28. 3) Limit test for Iron
 Principles:
 Reduction of ferric impurities to ferrous & formation of
the color complex.
 It is based on the reaction of iron with thioglycollic
acid in presence of strong ammonical solution & citric
acid to form iron thioglycolate which is pale pink to
deep reddish purple in color.
 Reaction 

29.  Role of Thioglycolic acid  It acts as a
reducing agent in the conversion of ferric to
ferrous impurities.
 Role of Ammonia solution It is used to
maintain alkaline media.
 Role of Citric acid It is used to prevent the
formation of ferric impurities in presence of
ammonia (alkaline media).

30. •Procedure-
 T.S- Weighed sub + 40ml D.W +2ml citric
acid + 0.1ml thioglycollic acid + 2ml of citric
acid made alkaline with ammonia sol &
diluted with DW. upto 50 ml ------ stir,
stand for 5 min.
 Std sol- 2ml Iron std sol + 40 ml DW +2ml
citric acid + 0.1ml thioglycollic acid make it
alkaline with NH3 solu. + dil upto 50 ml
DW.------ stir, stand for 5 min.

32.  Observation
 If the intensity of color (violet/purple)
produced in the sample preparation is less
than that of the standard preparation, then
the sample passes the limit test for iron.
 If the intensity of color (violet/purple)
produced in the sample preparation is more
than that of the standard preparation, then
the sample fails the limit test for Iron.

33. 4) Limit test for Heavy metals
 Principal-
 It is based upon reaction between certain
heavy metals like lead, Bi, Antimony, Ni, Sn,
Ag, resulting in formation of sulphides of
respective metal.
 Reaction
 M + H2S MS + H2
metal

34.  It is performed by 3methods-
 Method A- Sub that yield clear colourless
solution. (acidic medium)
 Method B- Sub that yield colourled solution or
for those sub whose nature is complex (acidic
medium)
 Method C- Sub that yield clear colourless sol
with NaOH
1) Method A-
 2ml lead std + 25ml DW + adjust pH bet 3-4 with
dil acetic acid / dil NH3 than---- dilute it upto 35
ml DW & mix.
To it add10 ml H2S sol and dil it upto 50 ml with
DW  & mix & stand for 5 min
T.S- 25ml of solution + rem same

35. Std solution- Test Solution
2ml lead std + 2ml sample/ test substance +
25ml DW  25ml DW
adjust PH bet 3-4 with dil acetic
acid
adjust PH bet 3-4 with dil acetic
acid
 dilute it upto 35 ml DW  dilute it upto 35 ml DW
+ add10 ml H2S sol add10 ml H2S sol
+ Dil. it upto 50 ml with DW Dil. it upto 50 ml with DW
mix & stand for 5 min mix & stand for 5 min
Procedure- Method A

36. 2) Method B-
Std- same method A
Test- test sub (sample) + H2SO4 in porcelain
dish till wet  Ignite at low temp till charred
+ HNO3 + drops of H2SO4  heat it till carbon
burnt off cool
+ 4ml HCl  digest on water bath for 2 min till
dryness.
 moisten the residue with HCl & H2O 
neutralize with NH3 solution
+ dilute it with 25ml DW  again make it
acidic with acetic acid by making the PH bet 3-
4

37. Std solution- Test Solution
2ml lead std + filter the solution adjust the filtrate
with 35 ml DW
25ml DW
adjust PH bet 3-4 with dil acetic
acid
 dilute it upto 35 ml DW  dilute it upto 35 ml DW
add10 ml H2S sol add10 ml H2S sol
Dil. it upto 50 ml with DW Dil. it upto 50 ml with DW
mix it & allow to stand for 5 min mix it & allow to stand for 5 min
Procedure- Method B

38.  Method C-
 Std -2ml lead std sol+5ml dil NaOH
making volume 50 ml
 Test- sub+20ml D.W+5ml NaOH dil
with 50ml of D.W
 To both these add 5 ml of Sodium
sulphide reagent.

39. Std solution- Test Solution
2 ml lead std Sample + 25ml DW  dissolve
+5ml dil NaOH 5ml dil NaOH
 dilute it upto 50 ml with DW  dilute it upto 50 ml with DW
+ Add drop of Sodium sulphide
(Na2S)
Add drop of Sodium sulphide
(Na2S)
+ Dil. it upto 50 ml with DW Dil. it upto 50 ml with DW
 mix it & allow to stand for 5 min mix it & allow to stand for 5 min
Procedure- Method C
Compare the intensity by viewing downward over white surface.

40. 5) Limit test for Arsenic
Cork
Glass
tube
opening
Glass tube
H= 200 mm
I.D= 6.5 mm
•Sample + SnCl2
+ H2SO3
•Granulated Zn +
KI
•Conc. HCl
•H2O
Trap H2S
gas
Gutzeit test

41.  Construction of Gutzeit's apparatus
1. Consists of a wide mouthed glass bottle fitted
with a rubber bung.
2. A glass tube (20cm length, 8mm outer diameter.
6.5mm internal diameter) consists of two open
ends passed through a rubber bung.
3. A hole (2mm diameter) is present on the glass
tube from the lower open end for passage of
hydrogen sulfide gas.
4. Place a cotton plug which is moistened with
lead acetate solution just above the hole from
the lower open end.
5. The top open end of the glass tube consists of
two rubber bungs holding mercuric chloride
paper as shown in the figure.
6. The two rubber bungs are held together by a
clamp.

42.  Principle –
• It is based on Reduction of pentavalent
arsenic to trivalent arsenic.
• Formation and Passage of arsine gas.
• Development of yellow color strain with
HgCl2 paper.

43.  Stannous chloride is used for complete
evolution of arsine gas.
 Zinc, potassium iodide and stannous chloride
are used as reducing agents.
 Hydrochloric acid is used to make the solution
acidic.
 Lead acetate cotton plug is used to trap
hydrogen sulphide gas impurities which may
be evolved along with arsine gas.

44. Pentavalent Trivalent

45. Reaction

46. Procedure
Std Solution Test Solution
• Std Solution • Sample
• + 1gm KI + 5 ml SnCl2 • 1gm KI + 5 ml SnCl2
• + 10 gm Zn • 10 gm Zn
• + Sulphurous acid ( H2SO3) • Sulphurous acid ( H2SO3)
• + Conc. HCl
Wait for 40 min
• Conc. HCl
Mercuric chloride paper  compare color intensity

47.  Observation
 If the intensity of yellow color produced in the
sample preparation is less than that of the
standard preparation, the sample passes the
limit test for arsenic.
 If the intensity of yellow color produced in the
sample preparation is more than that of the
standard preparation, the sample fails the limit
test for arsenic.

48. Thank You