UNIT I_History of pharmacopoeia and limit test

Impurities in Pharmaceutical
Substances
By…
Prof. Sonali R. Pawar
Assistant Professor, Pharmaceutical Chemistry Department,
Pharmaceutical Inorganic Chemistry
1
UNIT I

Content:
1) History of Pharmacopoeia
2) Sources and types of impurities
3) Principle involved in the limit test for
 Chloride
 Sulphate
 Iron
 Arsenic
 lead and
 Heavy metals
 Modified limit test for chloride and sulphate
IMPURITIES IN PHARMACEUTICAL SUBSTANCES
2

 Pharmaceutical chemistry deals with the structure, chemical
nature, composition, preparation, studies of physical and chemical
properties, methods of quality control and conditions of their uses.
The subject is further sub-divided into various branches like:
 Inorganic chemistry . Biochemistry
 Organic chemistry
 Analytical chemistry
 Physical chemistry
 Phytochemistry
 Medicinal chemistry
3

 Now a days compounds of various metals like iron, arsenic, lead,
mercury & copper were used for medicinal purpose.
 Hence, a sound knowledge of chemistry is required for
understanding and following the recent developments in
medicine and pharmacy.
 Pharmaceutical chemistry thus plays an important role in
deciding the physiochemical properties, conditions for the
storage and dispensing of drugs.
4

PHARMACOPOEIA
 Pharmacopoeia: the word derives from the ancient Greek
“pharmakopoiia” from pharmako- ″drug″, followed by the verb-
stem poi- ″make″ and finally the abstract noun ending -ia.
 These three elements together can be rendered as ″drug-mak-
ing″ or ″to make a drug″.
A pharmacopoeia, pharmacopeia, or pharmacopoea
is a legally binding collection (legal document, monograph, official
publication/book), prepared by a national or regional authority, of
standards and quality specifications for medicines used in that
country or region (e.g., IP, BP, USP).
quality specification: such as
identity
strength or amount
and purity of medicines
5

• Pharmacopoeia is the official book of standards for drugs prepared
by any country or regulatory body to specify the standards of
identity, purity and strength for the drugs imported, manufactured
or distributed throughout the country or a specific region.
• It is a book containing collection of monographs and published by
an authorized body like government or Pharmaceutical society.
• The term Pharmacopoeia comes from the Greek
word “Pharmakon” meaning drug and “Poieo”
meaning make, and the combination means any
formula or standards required to make a drug.
PHARMACOPOEIA
6

Organization, region or
country
Name of pharmacopoeia
World Health Organization
The International Pharmacopoeia (Ph.
Int.)
India Indian Pharmacopoeia (IP)
European Union European Pharmacopoeia (Ph. Eur.)
United Kingdom (UK) British Pharmacopoeia (BP)
China
Pharmacopoeia of the People's Republic of
China
Japan The Japanese Pharmacopoeia (JP)
United States of America United States Pharmacopeia (USP)
 In addition to these some other documents prescribing standards are:
 British Pharmaceutical Codex (B.P.C.) & National Formulary in America
(U.S.N.F.) 7

• A monograph is a collection of detailed
information on a particular drug, its dosage forms
and methods of analysis.
•
 Main title/synonyms
 Chemical formula/formula
weight
 Therapeutic category
 Dosage
 Description
 Solubility
 Minimum standards of
purity
• Identification tests
• Tests for purity/limit tests for
impurities
• Methods of assay
• Storage condition
• Packaging and labeling
8

IMPORTANCE OF PHARMACOPOEIA
9
1. To maintain the uniformity and control
the standards of the drugs available in
market.
2. Avoid adulterated drugs.
3. Complete information on drugs and
their dosage forms.
4. Reference for laboratory, industry
and academic institutions.

FORMULARY
10
• Formularies are the list of drugs or collections of
formulas for the compounding of
medicinal
•
•
preparations.
Formulariescontains more comprehensive details
on therapeutics.
Collectively these books are known as drug
compendia.
Pharmacopoeias + Formularies = Drug
Compendia

Drug compendia
1. Official compendia
• Official compendia are the compilation of drugs and other
substances recognized as legal standards of purity, quality and
strength by
government agency of respective countries.
British Pharmacopoeia (BP)
British Pharmaceutical Codex (BPC) United
States Pharmacopoeia (USP) Indian
Pharmacopoeia (IP) Japanese pharmacopoeia
(JP)
11

2. Non-official compendia
• The books other than official drug
compendia which are used as secondary
reference sources for drugs and other
related substances are known as non-official
drug compendia.
Merck Index
Martindale (The extra Pharmacopoeia)
12

PHARMACOPOEIA
The term Pharmacopoeia first appears as a distinct title in a work
published in Basel, Switzerland in 1561 by Dr A. Foes.
But does not appear to have come into general use until the beginning of
the 17th century.
Today’s pharmacopoeias focus mainly on assurance of quality of
products by various tools of analytical sciences.
Drugs & Cosmetic Act 1949 and Rules 1945.
IP is published by the Indian Pharmacopoeia
Commission, the Standards Setting Institution for
Drugs.
It is an autonomous body under the Ministry of
Health & Family Welfare.
To keep pharmacopoeia up-to-date,
pharmacopoeial commissions constantly update
pharmacopoeia Once in every four years.
13

INDIAN PHARMACOPOEIA (IP)
14
• Indian Pharmacopoeia is the official book of
standards for drugs to define identity, purity
and strength for the drugs imported,
manufactured for sale, stocked or distributed
in India.
• In 1946 Government of India Published Indian
Pharmacopoeial List which served as
supplement to BP.
• Indian Pharmacopoeia was prepared by Indian
Pharmacopoeia Committee formed in 1948.

INDIAN
PHARMACOP
OEIA
15
Year of
Publicatio
n
1st Edition 1955 986 monographs
Supplement to 1st Edition 1960
2nd Edition 1966 890 monographs
Supplement to 2nd
Edition
1975
3rd Edition 1985 1. Consists of 2 Volumes
2. IUPAC system of nomenclature
3. Analytical Techniques were
included e.g: Electrophoresis,
Fluorimetry
4. Instrumental Analysis were
included e.g: UV spectroscopy
5. Dissolution of 6 tablets included
6. Limit tests for microbial
contamination
Addendum to 3rd Edition 1989
Addendum to 3rd Edition 1991
Content
s

Indian Pharmacopoeia Year of
Publication
Contents
4th Edition 1996 1. Consists of 2 Volumes
2. Included 1149 monographs
3. Included new monographs
e.g: cream, gels, eye drops
4. Included method of preparation and
analytical methods like HPLC
5. Include In Process Quality control
Addendum to 4th Edition 2000
Supplement to 4th Edition 2000 Veterinary Products
5th Edition 2007 Consists of 3 Volumes
6th Edition 2010 Consists of 3 Volumes
7th Edition 2014 Consists of 4 Volumes with DVD
16

Indian National Formulary
• It is a reliable reference book on drugs
formulations for the practicing
physicians/clinicians, pharmacists, clinical
pharmacists, nurses and others engaged in
healthcare profession.
Indian Pharmaceutical Codex 1953
• It is a book containing detailed information
on indigenous drugs of India.
17

BRITISH PHARMACOPOEIA (BP)
• British Pharmacopoeia is the source of official
standards of drugs in UK and other parts of the
world.
• Commission.
• Since then Pharmacopoeial commission is
reconstituted from time to time and new editions
of British Pharmacopoeia are published.
18
• It was first published by General Medicine
Council and was later done by Pharmaceutical

BRITISH
PHARMACOPOEIA
19
Year of
Publication
Contents
First Publication 1864 extracts, crude drugs, galenicals
14th Edition 1988 2100 monographs
Contains 2 Volumes
Volume I: monographs of medicinal
and pharmaceutical substances
Volume II: formulations, blood
products, appendices
It is now published annually and consists of 6 volumes.

BRITISH PHARMACEUTICAL CODEX
(BPC)
20
• British Pharmaceutical Codex was prepared as
a reference book to physicians and dispensing
pharmacists in 1907 as per the Council of
Pharmaceutical Society.
• Since then subsequent revisions of these books
are published.
• The decision of medicine commission stated
that there should be only one book of
standards of medicine, so BPC was
discontinued.
• Later BPC was published as “The
Pharmaceutical Codex” and plans to be
encyclopedia.

THE BPC DIFFERS FROM BP IN:
21
• BPC contains more drugs and preparations.
• It contains additional information on
standard of drugs, surgical dressing,
pharmaceutical preparations, etc
• It provides action and uses of drugs.
• It contains formula and preparation
methods of some other formulations.

BRITISH NATIONAL FORMULARY (BNF)
22
• British National Formulary is a source of
essential information on drugs and medicines
published by pharmaceutical society of Great
Britain and British Medical Association.
• Pharmacological classification of drugs are
given.
• It includes preparations as per Pharmaceutical
forms.
• It provides information about actions, uses,
dosage & adverse reactions.

UNITED STATES PHARMACOPOEIA (USP)
23
• The United States Pharmacopoeia and the National Formulary
(USP-NF) are recognized as the official compendia and are used as
reference books for determining the strength, quality, purity,
packaging and labeling of drugs and other related articles.
•
•
First USP was published in 1820 by US Pharmaceutical
Convention in English and Latin. It consists of 272 drugs.
USP contains over 3400 monographs for drug substances and
products, together with over 160 general chapters that describe
•
specific procedures to support monograph tests and other
information as well.
USP also contains 16 monographs and 9 general chapters on
nutritional supplements.

NATIONAL FORMULARY (NF)
24
• First National Formulary of US was published in 1888
by American Pharmaceutical Association.
• USP and NF was combined as a single book of drug
standards as USP-NF.
• USP-NF represents 25threvision of USP & 20th revision of
NF official on 2002. From then USP-NF was published
annually.
• NF covers over 3800 monographs for excipients and
dietary supplements.

INTERNATIONAL PHARMACOPOEIA
25
• The International Pharmacopoeia is
published by the WHO and is practically
used in developing countries.
• It was prepared to meet the international
uniformity and standardization of drugs.
• International Pharmacopoeia was first
published in 1951 in multilanguages (
English, French, German, Japanese, etc.).

EUROPEAN PHARMACOPOEIA (PH. EUR.)
26
•
•
• The European Pharmacopoeia (Ph. Eur.) is the legal
document for the standards of drugs and related
substance prepared by the Council of Europe.
European Pharmacopoeia Volume I was published
in 1969 as first European Pharmacopoeia.
It includes more than 2000 specific and general
monographs, including various chemical
substances, antibiotics, biologicals, vaccines,
herbal, immunosera, radiopharmaceuticals,
homeopathic preparations.
,

JAPANESE PHARMACOPOEIA (JP)
27
• Japanese Pharmacopoeia is established and
published to regulate the properties and
quality of drugs by Ministry of Health,
Labour and Welfare of Japan.
• It consists of general notices, rules for crude
drugs, rules for preparations, general tests,
processes, apparatus and official
monographs.
• First published in 1886, JP has been revised
many times.

Introduction
Pure Chemical Compound: Having no Foreign matter that is Impurity
Chemical Purity means freedom from foreign matter.
28

29
 Presence of Impurities in the pharmaceutical substances may
produce toxic effects on the body and may also lower down the
active strength of the pharmaceutical substance.
 Impurities commonly in chemical substances include small
quantities of lead, Arsenic, Iron, Chloride and sulphate.

Sources of
Impurities
Raw
Material
Method of
Manufactu
ring
Delibrate
Adulterati
on
Atmospheri
c
Contaminat
ion
Improper
Storage
Manufact
uring
Hazards
Sources of Impurities
Improper Storage
Deliberate Adulteration
Atmospheric
Contamination
Manufacturing Hazards
Raw Material
Method of Manufacturing
30

Types of
Impurities
Toxic
Impurities
Harmless
Impurities
Affect
Quality
Create
Incompatibil
ity
Technical
difficulties
Organic
Impurity
Types of Impurities
31
Analytically 100 % pure substances are not available and traces of impurities must be
present. Normally undesirable foreign materials are present in the pharmaceutical
substances.

SOURCES & TYPES OF IMPURITIES
• Raw material
• Method of manufacturing
(Reaction Vessels, Reagent used, Solvent used, intermediates)
• Manufacturing hazards
(Particulate contamination, process error, packaging error,cross
contamination, microbial contamination)
• Improper storage (Filth, temperature effect, reaction with container)
• Atmospheric contamination
• Delibrate adultrance
32

TEST FOR PURITY
a) Washing
b) Drying
c) Recrystallization of solid substances from water
d) Sublimation
METHODS USED TO PURIFY THE INORGANIC SUBSTANCE
a) Colour, Odour And Test
b) Physico-chemical constants
c) Acidity, alkalinity and PH
d) Moisture content
e) Anions and cations
a) Ash value
b) Loss of ignition
c) Loss on drying
33

Impurities:
• A compound is said to be impure if it is having foreign matter i.e.,
impurities.
• Pure chemical compound refer to that compound which is having no
foreign matter!
• Purification of chemicals is an expensive process, substances should
not be purified more than required as it brings about waste of time,
material and money.
• In such cases, if it is not possible to eliminate out these impurities
completely, attempts have to be made to at-least minimise their
concentration!
34
Since the drug and pharmaceutical products concern with health and life of
people and animal
The prime consideration behind every formulation is that the product should
be:
 Pure as much as possible (absolute purity).
 Satisfactory clinically.
 Homogenecity.
 Safety in its use.

• Pharmacopoeia prescribe limits for physiologically harmful
compound(s)/impurities present in substances/formulations.
Impurities commonly found in Medicinal preparations:
1. Activity depressing impurities. e.g., presence of water in hard soap.
2. Due to colouring or flavouring substances, e.g., Sodium Salicylate is
discoloured due to phenolic compounds.
3. Humidity – may cause many substances to oxidize.
4. Decrease shelf life.
5. Physical and chemical properties.
6. Impurities due to which substances become incompatible or unfit for
medicinal use. (Physical, Chemical & Therapeutically).
7. Toxic impurities. E.g. Lead and arsenic salts.
35

SOURCES OF IMPURITIES: RAW, SOLVENTS, MFG, ETC
1. RAW MATERIALS Employed in the Manufacturing of the
Pharmaceutical Substance:
• It is essential to verify the identity of the source (natural e.g. mineral
sources, plants, animals, microbes or synthesized from chemicals) of
raw materials.
• In nature minerals rarely occurs in a reasonably pure from. Almost
always mixtures of closely related substances occur together
1. Rock salt used for the preparation of sodium chloride is
contaminated with small amounts of calcium and magnesium
chlorides
36

e.g.,
1. Barium and Magnesium impurities are found in calcium minerals.
2. Magnesium or Iron compounds are found in zinc.
3. Lead and Heavy metals are found as impurities in many sulphide ores.
4. Chlorides, bismuth salts contains silver copper and lead as impurities.
37

SOURCES OF
IMPURITIES
2. METHOD OF MANUFACTURE:
(A)Reagents used/employed in the manufacturing process:
Calcium carbonate contains ‘soluble alkali’ as impurity which arises from
the sodium carbonate (Na2CO3) employed in the process of Calcium
carbonate.
CaCl2 + Na2CO3 → CaCO3 ↓ + 2 NaCl
Soluble Soluble Precipitate Soluble
• Anions like chlorides and sulfates are common impurities in many
substances because of the use of tap water, hydrochloric acid and
sulphuric acid respectively in processing.
• Hydrogen peroxide can contaminate the final product with barium ion.
(B) Regents used to eliminate other impurities:
Barium is used in the preparation of potassium bromide to remove sulphate
38

SOURCES OF
IMPURITIES
(C) Solvents: Water!
(i) Tap water: Containing impurities of Ca2+, Mg2+, Na+, Cl–, CO3–2 and
SO4–2 in trace amounts. The use of tap water on large scale will lead to
the contamination of the final product with these impurities because
the impurities will remain in the product even after washings.
(ii) Demineralized water: is free from above ions. It may have pyrogens,
bacterias and organic impurities. So, discourage its use on large scale.
(iii) Distilled water: It is free from all organic and inorganic impurities and is
therefore the best as a solvent but it is quite expensive.
(iv) Softened water: It is almost free from divalent cations (Ca2+, Mg2+ ) but
contains more of Na+ and Cl– ions as impurities.
39

SOURCES OF
IMPURITIES
D) Reaction vessels:
The reaction vessels used/employed in the
manufacturing process may be metallic such as:
copper, iron, cast iron, galvanized iron, silver, aluminium, nickel,
zinc, lead, glass and silica.
• Some solvents and reagents used/employed in the process may
react with the metals of reaction vessels, leading to their corrosion
and passing traces of metal impurities into the solution &
contaminating the final product.
• Similarly, glass vessels may give traces of alkali to the solvent.
40

SOURCES OF
IMPURITIES
(E) Intermediates:
Sometimes, an intermediate substance produced during the
manufacturing process may contaminate the final product
e.g., Sodium bromide is prepared by reaction of sodium hydroxide and bromine
in slight excess.
6NaOH + 3Br2 → NaBrO3 + 5NaBr + 3H2O
The sodium bromate an intermediate product is reduced to sodium bromide
by heating the residue (obtained by evapourating the solution to dryness)
with charcoal.
NaBrO3 + 3C → NaBr + 3CO
Sodium bromate Sodium bromide
• If sodium bromate is not completely converted to the sodium bromide then
it is likely to be present as an impurity.
41

SOURCES OF
IMPURITIES
(F) Atmospheric contamination during the manufacturing
process:
• Atmosphere may contain:
dust of aluminum oxide, sulphur, silica etc. And
• some gases like carbon dioxide, sulphur dioxide and hydrogen
sulphide etc.
• These may contaminate the final product.
e.g., sodium hydroxide readily absorbs atmospheric carbon dioxide when
exposed to atmosphere.
2NaOH + CO2 → Na2CO3 + H2O
Calcium hydroxide solutions can absorb carbon dioxide from the
atmosphere to form calcium carbonate.
Ca(OH)2 + CO2 → CaCO3 + H2O
42

SOURCES OF
IMPURITIES
(G) Manufacturing hazards:
Contamination from the particulate matter:
• from sieves, granulating, tabletting and filling machines and the product
container.
• From dirty or improperly maintained equipments.
• From Cross-contamination of the product.
Contamination by microbes:
• products intended for parenteral administration and
ophthalmic preparations are liable to contamination by
microbes from the atmosphere
• sterility testing - provides an adequate control for microbial contaminations
in such preparations.
• Microbial contamination can be controlled by adding suitable antimicrobial
and antifungal agents.
43

SOURCES OF
IMPURITIES
Errors in the packaging: Similar looking products, such as tablets
of the same size, shape and colour, packed in similar containers
can result in mislabeling of either or both of the products.
Adequate care should be taken to avoid the handling of such
products in the close proximity.
Errors in the manufacturing process
Cross contamination
Microbial Contamination
44

3. Instability of the Product
(A) Chemical instability/decomposition:
Impurities can also arise during storage when storage
conditions are inadequate.
• This chemical decomposition is often catalyzed by:
Light , traces of acid or alkali, traces of metallic
Impurities, air oxidation, carbon dioxide and water
Vapours.
• It can easily be predicted from the knowledge of
chemical properties of the substance.
• It can be minimized or avoided by using proper storage
procedures & conditions.
45

• Improper storage: ex. Ferrous sulphate slowly gets changed into
insoluble ferric oxide by air and moisture.
• a)Filth : Contaminated with dust
• b)Temperature Effects: The rate at which chemical decomposition
and physical changes occure in stored products depend upon it.
• c) Reaction with container material: container material and
content .
• d)chemical instability
• Atmospheric contamination during the manufacturing process.
• Deliberate adulteration
46

• The photosensitive substances should be protected
from light by storing them in darkened glass (amber
glass bottles) or metal containers thereby inhibiting
photochemical decomposition.
• Materials susceptible to oxidation by air or attack by
moisture should be stored in sealed Containers and if
necessary the air from the containers can be
displaced by an inert gas such as Nitrogen or by
adding suitable antioxidants (like in food products
ascorbic acid, tocopherol and sodium citrate.
47

(B) CHANGES IN PHYSICAL PROPERTIES:
• changes in crystal size and shape,
sedimentation, agglomeration and caking of the suspended particles.
• Particle size and surface area is a critical factor in determining the
bioavailability of the low solubility drug.
E.g: under dosage and later to over dosage of the drugs (suspensions).
& Injectable emulsions on storage may lead to fat embolism.
48

(C) REACTION WITH CONTAINER MATERIAL:
• e.g., salicylic acid ointment must not be packed in metal tubes.
• alkali-sensitive e.g., atropine sulphate injection must be packed in
glass ampoules must not be packed in containers made from soda
glass.
• Plastic containers - plasticizers, particularly in the presence of non-
aqueous solvents.
• Rubber closures are more susceptible to absorb medicaments
• Temperature: The rate of chemical decomposition and physical
changes of stored products depends upon the temperature.
49

TYPES OF ERRORS OR IMPURITIES
1. Determinate Errors (Systematic errors): Definite value and
underlying (undisclosed/hidden) cause.
• Can measure & account for these errors.
Sources:
Impurities in the crude material.
Excess of reagent used.
Salts from the water used when the preparation is
carried out in aqueous solutions.
Metallic contamination.
Contamination from exposure to the atmosphere.
50

TYPES OF ERRORS OR IMPURITIES
2. Indeterminate errors:
• Result from extending a system of measurements to its maximum.
• Neither identify the sources of these errors nor predict the
magnitudes of individual errors.
51
The International Council for Harmonisation of Technical
Requirements for Pharmaceuticals for Human Use (ICH)

PERMISSIBLE LIMITS OF
IMPURITIES
• Impurities are always present in the Pharmaceutical products.
• The following points are considered to permit the impurities in
these substances:
1. A level of harmful substances is to be determined.
2. A permissible limit, based on the amount to be tolerated of the
toxic substances is prescribed.
e.g., Heavy metal (Toxic impurities) limits in India
52
P.T.O

HEAVY METAL LIMITS
53
Permissible Limits of Impurities

PERMISSIBLE LIMITS OF IMPURITIES
Acceptance criteria for impurities in drug substances:
Each identified specified impurity
(Determinate errors)
Not more than 0.5 per cent
Each unidentified impurity
(Indeterminate errors)
Total impurities Not more than 1.0 per cent
54
Provided it has been determined that the impurities are not toxic. Higher limits may
be set if scientifically justified.
Acceptance criteria for degradation products in drug products:
Each identified degradation
product
Each unidentified degradation
products
Total degradation products Not more than 2.0 per cent
Provided it has been determined that the impurities are not toxic. Higher limits may be
set if scientifically justified.

the limit for harmless impurities are also prescribed depending
upon the nature, type and usefulness of the substances.
e.g., colouring substances
flavouring agents
preservatives are the harmless compounds added to the
pharmaceutical preparations.
55
Permissible Limits of Impurities
Intermediate
By-product
Transformation product
Interaction products
Related products
Degradation products

If there is no emphasis on
impurities in kilogram(s)
and liters of food taken by
an individual in a day
56
Then how come it is a
so serious issue for few milligrams
of drug(s) consumed in a tiny pill
daily?

CONTENTS
1
• Introduction of Limit test
2
• Importance of Limit test
3
• Limit test of Chloride
4
• Limit test of Sulphate
5
• Limit test of Iron
6
• Limit test of Arsenic
7
• Limit test of Lead
8
• Limit test of Heavy Metal
9
• Modified limit test of
Chloride and Sulphate
57

LIMIT TEST
58
“Limit test is defined as quantitative or semi quantitative test
designed to identify and control small quantity of impurity
which is likely to be present in the substance.”
Importance of Limit Test
 To find out the harmful amount of impurities
 To find out the avoidable/ unavoidable amount of impurities
Limit Test Invoves
 The simple comparison of opalescence, turbidity or colour produced in
test with that of fixed slandered.
 limit test for inorganic compound is carried out so that the amount of
inorganic impurity present in the drug/required material do not exceed
is prescribed limit test.
Limit tests: Tests being used to identify the impurity.
Tests being used to control the impurity.

59
Factors affecting limit tests:
1. Specificity of the tests
2. Sensitivity
3. Control of personal errors (Analyst errors)
• Test in which there is no visible reaction
• Comparison methods
• Quantitative determination
Types:
 Tests in which there is no visible reaction
 Comparison methods
 Quantitative determinations

60
The limit test involve simple comparisons of opalescence,
turbidity, or colour with standard.
These are semi-qualitative reactions in which extent of impurities
present can be estimated
by comparing visible reaction response of the test and standard.
By this way, extent of reaction is readily determined by direct
comparison of test solution with standard. So pharmacopoeia prefers
comparison methods.

62
The test is used to limit the amount of Chloride as an impurity in
inorganic substances.
LIMIT TEST FOR CHLORIDE
Principle: Limit test of chloride is based on the reaction of soluble chloride
with silver nitrate in presence of dilute nitric acid to form silver chloride,
which appears as solid particles (Opalescence) in the solution.
Soluble chloride present as impurity
The silver chloride produced in the presence of dilute Nitric acid makes the test
solution turbid, the extent of turbidity depending upon the amount of Chloride present
in the substance is compared with the standard opalescence produced by the addition
of Silver nitrate to a standard solution having a known amount of chloride and the
same volume of dilute nitric acid as used in the test solution.
Cl- + AgNO3 AgCl + NO3 –

64
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
Take1 ml of 0.05845 % W/V
solution of sodium chloridein
Nessler cylinder
Add 1 ml of nitric acid Add 1 ml of nitric acid
Dilute to 50 ml in Nessler cylinder Dilute to 50 ml in Nessler cylinder
Add 1 ml of AgNO3 solution Add 1 ml of AgNO3 solution
Keep aside for 5 min Keep aside for 5 min
Observe the Opalescence/Turbidity Observe the Opalescence/Turbidity
PROCEDURE

65
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.
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 as Dilute HNO3 is insoluble inAgCl.

67
The Sulfate Limit Test is designed to determine the allowable limit of
sulfate contained in a sample.
Principle:
Limit test of sulphate is based on the reaction of soluble sulphate
with barium chloride in presence of dilute hydrochloric acid to
form barium sulphate which appears as solid particles (turbidity)
in the solution.
LIMIT TEST FOR SULPHATE

68
 Then comparison of turbidity is done with a standard turbidity
obtained from a known amount of Sulphate and same volume of
dilute Hydrochloric acid have been added to both solutions.
 The barium chloride test solution in the IP has been replaced by
Barium sulphate reagent which is having barium chloride,
sulphate free alcohol and a solution of potassium sulphate.
Potassium sulphate has been added to increase the sensitivity of the
test.

69
Specific weight of compound is
dissolved in water or solution is
prepared as directed in the
pharmacopoeia and transferred
in
Nessler cylinder
Take 1 ml of 0.1089 % W/V solution of potassium
sulphate in Nessler cylinder
Add 2 ml of dilute hydrochloric acid Add 2 ml of dilute hydrochloric acid
Dilute to 45 ml in Nessler cylinder Dilute to 45 ml in Nessler cylinder
Add 5 ml of barium sulphate reagent Add 5 ml of barium sulphate reagent
Observe the Turbidity Observe the Turbidity
PROCEDURE

70
OBSERVATION
The turbidity produce in sample solution should not be greater than standard
solution. If turbidity produces in sample solution is less than the standard
solution, the sample will pass the limit test of sulphate and vice versa.
REASONS
 Hydrochloric acid helps to make solution acidic.
 Potassium sulphate is used to increase the sensitivity of the test by giving
ionic concentration in the reagent.
 Alcohol helps to prevent super saturation and so produces a more uniform
opalescence.
Barium sulphate reagent contains barium chloride, sulphate free
alcohol and small amount of potassium sulphate.

S.N. Chemical Quantity Apparatus Quantity
1 Ferric Ammonium Sulphate
[NH4Fe(SO4)2]
0.17 gm Nessler Cylinder 2
2 0.1 N Sulphuric Acid (H2SO4) 10 ml Beaker (100 ml) 2
3 Iron Free Citric Acid (C6H8O7) 2 gm Glass rod 2
4 Thioglycolic Acid (C2H4O2S) 0.5 ml Pipette 2
5 Ammonia Solution (NH4OH) 20 ml Stand 1
•Standard Solution: Accurately weighted 0.1726 gm of ferric ammonium sulphate
dissolved in 10 ml of 0.1 N sulphuric acid (H2SO4) and volume make up to 1000 ml
with distilled water. Each ml of solution contains 0.02 mg of iron.
•Citric acid (20%): Dissolve 20 g of iron free citric acid in 100 ml of distilled water.
•Iron free ammonia solution: Dilute ammonia solution i.e. 10 % ammonia (10 ml
dissolve in 100 ml in distilled water).
REAGENT PREPARATION
72

PRINCIPLE
 Iron, in ferrous or ferric condition, is non-toxic when taken orally or administered
parental. The limit test of iron is based on reaction of iron in ammonical solution, in
presence of citric acid with Thioglycolic gives purple colour. The colour produce by test
solution is compared with standard iron solution (ferric ammonium sulphate).
 Citric acid form a soluble complex with iron and prevent precipitation by ammonium
as ferrous hydroxide. Ferrous thioglycolate is colorless in nature & acid solution.
 The colour develop only in presence of alkali. It is unstable in presence of air due to
oxidation to the ferric compound; therefore colour should be compared immediately
after the time allowed for food development of colour is over.
 Thioglycolic acid also reducing agent, hence any ferric ions present are converted to
ferrous ions, which form thioglycolate.
73

PRINCIPLE………(Continue)
 It is believed that the thioglycolic acid that has been more sensitive than the
ammonium thiocynate test. Hence, ammonium thiocynate is replaced by thioglycolic
acid. Interferences of other metal cation is eliminate by making the use of 20% citric
acid, whic forms a complex with other metal cation.
 Limit test of Iron is based on the reaction of iron in ammonical solution with
thioglycollic acid in presence of citric acid to form iron thioglycolate, which is pale
pink to deep reddish purple in color.)
 Earlier aamonium thiocyanate reagent was used for the limit test of iron. Since
thioglycolic acid is more sensitive reagent, it has replaced ammonium thiocyanate in
the test.
74

75
Reasons:
 Citric acid helps precipitation of iron by ammonia by forming a complex with it.
 Thioglycolic acid helps to oxidize iron (II) to iron (III).
 Ammonia to make solution alkaline
 The color of the Ferrous thioglycolate complex fades in the presence of air due to
oxidation.
 Also, the color is destroyed in presence of oxidizing agents and strong alkalis.
 The purple color is developed only in alkaline media. So ammonia solution is used.
 But ammonia reacts with iron, forms precipitate of ferrous hydroxide.
 Thus citric acid is used which prevents the precipitate of iron with Ammonia by forming
a complex with iron as iron citrate.

Sample is dissolved in specific
amount of water and then volume is
made up to 40 ml
2 ml of standard solution of iron
diluted with water up to 40ml
Add 2 ml of 20 % w/v of citric acid
(iron free)
Add 2 ml of 20 % w/v of citric acid
(iron free)
Add 2 drops of thioglycollic acid Add 2 drops of thioglycollic acid
Add ammonia to make the solution
alkaline and adjust the volume to
50 ml
Add ammonia to make the solution
alkaline and adjust the volume to 50
ml
Color developed is viewed
vertically and compared with
standard solution
Color developed is viewed vertically
and compared with standard
solution
PROCEDURE
76

REACTION
(Purple colour)
OR
Fe+2 + 2 CH2COO-HS Fe (SCH2COO-)-2
Iron ion Thioglycolic acid Ferrous thioglycolate
OBSERVATION
The purple color produce in sample solution should not be greater than standard
solution. If purple color produces in sample solution is less than the standard
solution, the sample will pass the limit test of iron and vice versa. Means; the
intensity of colour produced by sample is less than that of standard solution colour,
it passes the test.
77

S.N. Chemical Quantity Apparatus Quantity
1 Lead acetate solution (10%
w/v) Pb (C2H3O2)2
Q.S. Arsenic apparatus (Gutzeit
Apparatus)
02
2 Potassium iodide (KI) 2 gm Beaker (100 ml) 02
3 Zinc (Zn) 20 gm Glass Rod 01
4 HgCl2 Paper Q.S. Stand 01
To perform limit test for Arsenic for given unknown sample
79
REAGENT PREPARATION
1.Preparation of the test solution: The solution of water soluble substance is
prepared with water and stanneted HCl AsT. The solution of substance such as
metallic carbonates, which effervesces with acids, is obtained with brominated HCl
AsT. The substances, which are insoluble, e.g.: BaSO4, bentonite or kaolin are
diffused in water.

1.Stanneted Chloride solution : It is prepared by adding Stannous Chloride solution
to an equal volume of HCl AsT, reducing the original volume by boiling and filtering
through a fine-grain filter paper.
2.Stannated Hydrochloric acid : It is prepared by adding 1 ml of stannous chloride
solution AsT to 100 ml of HCl AsT.
3.Preparation of standard arsenic solution (10 ppm As): Dissolved 0.330 g of
arsenic trioxide in 5ml of 2 M sodium hydroxide and dilute to 250.0 ml with water.
Dilute 1 volume of this solution to 100 volumes with water.
4.Zinc : It is the granulated zinc which complies with the following additional test:
-To 10 gm of the granulated zinc adds 15 ml of the stannous chloride solution AsT and
5 ml of 0.1 M potassium iodide.
-Apply the general test but allow the reaction to continue for one hour.
-NO visible stain should be produced on the mercuric chloride paper.
-Repeat the test by adding 0.1 ml of standard arsenic solution (10 ppm As); a faint but
distinct yellow stain is produced.
80

PRINCIPLE
Arsenic is harmful due to its toxic nature.
Pharmacopoeia method is based on ‘Gutzeit Method’.
Concentration of arsenic beyond 0.01 mg/L in pollutant by the World Health
Organization (WHO).
All arsenic present converted into arsenic gas (AsH3) by reduction with
zinc and Hydrochloric acid.
Based on the reaction of arsenic gas with hydrogen ion to form yellow
stain on mercuric chloride paper in presence of reducing agents like
potassium iodide.
British Pharmacopoeia suggest the use of mercuric chloride paper
instead of mercuric bromide paper.
The standard stain prepared from a definite quantity of arsenic is
used for comparison and provide the limit,
81

1
• REACTION:
2
• The sample dissolved in acid where by the arsenic present as impurity
in sample
3
• Converted into arsenic acid (Arsenic, present as arsenic acid in the
sample )
4
• Is reduced to Arsenious acid by reducing agents like potassium
iodide, stannous acid, zinc, hydrochloric acid, etc.
5
• Arsenious acid is further reduced to arsine (gas)
6
• By hydrogen and reacts with mercuric chloride paper to give a yellow
stain.
The depth of yellow stain on mercuric chloride paper will depend upon the
quality of arsenic present in the sample,
which is compared with that of standard stain
produced from
known amount of arsenic.
82

83
PRINCIPLE:
Limit test of Arsenic is based on the reaction of arsenic gas with hydrogen ion to
form yellow stain on mercuric chloride paper in presence of reducing agents like
potassium iodide. It is also called as Gutzeit test and requires special apparatus.
 Arsenic, present as arsenic acid (H3AsO4) in the sample is reduced to arsenious
acid (H3AsO3) by reducing agents like potassium iodide, stannous acid, zinc,
hydrochloric acid, etc. Arsenious acid is further reduced to arsine (gas) (AsH3)
by hydrogen and reacts with mercuric chloride paper to give a yellow stain.
Substance + dil HCl ------------------------- H3AsO4
(containsArsenic impurity) Arsenic acid
 H3AsO4 +
Arsenic acid
H2SnO2 -------------------→ H3AsO3 +H2SnO3
Arsenious acid
H3AsO3 + 6[H] ---------------------→ AsH3 +3H2O
Arsenious acid nascent hydrogen Arsine gas
The depth of yellow stain on mercuric chloride paper will depend upon the quantity
of arsenic present in the sample.

84
 When the sample is dissolved in acid, the Arsenic present in the sample
gets converted to Arsenic acid.
 By action of reducing agents like Potassium iodide, stannous acid etc.,
Arsenic acid gets reduced to arsenious acid.
 The nascent hydrogen formed during the reaction, further reduces
Arsenious acid to Arsine gas, which reacts with mercuric chloride paper,
giving a yellow stain.

85
Use of stannated Hydrochloric acid:
If pure zinc and HCl are used, the steady evolution of gas does not occur. This produces
improper stain (e.g slow evolution produces short but intense stain while rapid evolution of
gas produces long but diffused stain.)
So, to get steady evolution of gas, stannated hydrochloric acid is used.
Use of Lead Acetate solution:
H2S gas may be formed during the experiment as zinc contains sulphides as impurities. It
gives black stain to HgCl2 paper and so will interfere the test.
Hence, gases evolved are passed through cotton wool plug moistened with lead acetate,
where H2S gas is trapped as PbS.
Use of Potassium iodide:
KI is converted to HI which brings about reduction of unreacted pentavalent arsenic to
trivalent Arsenic. Thus, reproducible results can be obtained. If it is not used then some
pentavalent Arsenic may remain unreacted.

 Stannous chloride is used for complete
evolution of arsine.
 Zinc, potassium iodide and stannous chloride is
used as a reducing agent.
 Hydrochloride acid is used to make the
solution acidic.
Reasons
 Lead acetate pledger or papers are used to
trap any hydrogen sulphide, which may be
evolved along with arsine. 86

SN Standard Test
1 A know amount of dilute arsenic
solution is kept in the wide mouthed
bottle of the apparatus.
The test solution is prepared by dissolving
specific amount in water and stannated
HCl (arsenic free) and kept in a wide
mouthed bottle.
2 To this solution 1 gm of KI, 5 ml of
stannous chloride acid solution and 10
gm of zinc is added (all this reagents
must be arsenic free)
To this solution 1 gm of KI, 5 ml of
stannous chloride acid solution and 10 gm
of zinc is added (all this reagents must be
arsenic free)
3 Keep the solution aside for 40 min Keep the solution aside for 40 min
4 Compare the stain obtained on
mercuric chloride paper with
standard solution.
Compare the stain obtained on mercuric
chloride paper with standard solution.
PROCEDURE
Take 250 ml of the arsenic LT apparatus bottles. Labelled one is ‘Test’ and
other is ‘standard’.
87

Regular arsenic apparatus with alternate device (a) and (b) for fixing
mercuric chloride paper.
Diagram
88

Assembly for Limit Test
of Arsenic
Sample Preparation
Preparation of Mercuric
Paper
Standard (S) & Test (T)
Attachment of Paper During Reaction Yellow stain observed after reaction completion
Answer for How to Performed?
89

OBSERVATION
If the stain produced by test is no deeper than standard stain,
then sample complies limit test for arsenic.
CONCLUSION
After 40 minutes, if the intensity of the yellow stain produced in
the standard is more that in the test, the sample complies with
the limit test of arsenic.
RESULT
Limit test of arsenic passes the test.
90

LIMIT TEST FOR HEAVY METALS
92
 The limit test for heavy metals is designed to determine the content of metallic
impurities that are coloured by hydrogen sulphide or sodium sulphide under the
condition of the test should not exceed the heavy metal limits given under the individual
monograph.
 The heavy metals (metallic impurities) may be iron, copper, lead, nickel, cobalt, bismuth,
antimony etc.. The limit for heavy metals is indicated in the individual monograph
in term of ppm of lead i.e. the parts of lead per million parts of the substance being
examined
 In substances the proportion of any such impurity (Heavy metals) has been expressed as
the quantity of lead required to produce a color of equal depth as in a standard
comparison solution having a definite quantity of lead nitrate.
 The quantity is stated as the heavy metal limit and is expressed as parts of lead
(by
weight) per million parts of the test substance.
 These remain distributed in colloidal state, and give rise to a brownish coloration.

 I.P limit for heavy metals in 20 ppm.
 The test solution is compared with a standard prepared using a lead solution (as the
heavy metal).The metallic impurities in substance are expressed as parts of lead per
million parts of substance.
 IP has adopted 3 methods for this:
 Method I: The method is applicable for the samples which give clear colourless
solutions under specified conditions of test.
 Method II: The method is applicable for the samples which DO NOT give
clear colourless solutions under specified conditions of test.
 Method III: Used for substances which give clear colourless solutions in
sodium hydroxide medium.
93
 The limit test for heavy metals has been based upon the reaction of the metal ion with
hydrogen sulphide, under the prescribed conditions of the test causing the formation
of metal sulphides.

LIMIT TEST FOR LEAD
95
Lead Is A Most Undesirable Impurity In Medical Compounds and comes through use of
sulphuric acid, lead lined apparatus and glass bottles use for storage ofchemicals.
Principle
Limit test of lead is based on the reaction of lead and diphenyl thiocabazone
(dithizone) in alkaline solution to form lead dithizone complex which is red in color.
 Dithizone in chloroform, is able to extract lead from alkaline aqueous
solutions as a lead dithizone complex (Red in colour)
 The original dithizone is having a green colour in chloroform while the
lead- dithizone is having a violet color. So, resulting color at the end of the
process is read.

 The intensity of the color of complex is dependant upon the amount
of lead in the solution.
 The color of the lead-dithizone complex in chloroform has been
compared with a standard volume of lead solution, treated in the same
manner.
 In this method, the lead present as an impurity in the substances, gets
separated by extracting an alkaline solution with a dithizone extraction
solution.
 The interference and influence of the other metal ions has been
eliminated by adjusting the optimum pH for the extraction by
employing Ammonium citrate/ potassium cyanide.
96

Method:
• Sample solution is transferred to a separating funnel.
• Toit 6 ml of ammonium citrate, 2 ml potassium cyanide and 2 ml of
hydroxalamine HCl are added.
• 2 drops of phenol red
• Solution is made alkaline by adding ammonia solution.
• This is then extracted with 5 ml portions of dithizone solution until it becomes
green.
• The combined dithizone extracts are shaken for 30 seconds with 30 ml of
nitric acid and chloroform layer is discarded.
• Tothe acid solution 5 ml of standard dithizone solution is added and 4 ml
ammonium cyanide and solution is shaken for 30 sec.
• Similarly prepare standard. 97

 Observation:
The intensity of the color of complex, is depends on the amount of lead in
the solution. The color produced in sample solution should not be greater
than standard solution. If color produces in sample solution is less than the
standard solution, the sample will pass the limit test of lead and vice versa.
98
Reasons: Ammonium hydrochloride, citrate, potassium cyanide,
hydroxylamine is used to make pH optimum so
interference and influence of other impurities have been eliminated.
 Phenol red is used as indicator to develop the color at the end of process
Lead present as an impurities in the substance, gets separated by
extracting an alkaline solution with a dithizone extraction solution.

A known quantity of sample solutionis
transferred in a separating funnel
A standard lead solution is prepared equivalentto
the amount of lead permitted in the sample under
examination
Add 6ml of ammonium citrate Add 6ml of ammonium citrate
Add 2 ml of potassium cyanide and 2 ml of
hydroxylamine hydrochloride
Add 2 ml of potassium cyanide and 2 ml of
hydroxylamine hydrochloride
Add 2 drops of phenol red Add 2 drops of phenol red
Make solution alkaline by adding ammonia solution. Make solution alkaline by adding ammonia solution.
Extract with 5 ml of dithizone until it becomes
green
Extract with 5 ml of dithizone until it becomes green
Combine dithizone extracts are shaken for 30 mins
with 30 ml of nitric acid and the chloroform layer is
discarded
Combine dithizone extracts are shaken for 30 mins
with 30 ml of nitric acid and the chloroform layer is
discarded
Tothe acid solution add 5 ml of standard dithizone
solution
Tothe acid solution add 5 ml of standard dithizone
solution
Add 4 ml of ammonium cyanide Add 4 ml of ammonium cyanide
Shake for 30 mins Shake for 30 mins
Observe the color Observe the color
Esha Shah 99

Aq. Ammonia is added in limit test of lead:
Pb+ S------------- PbS
In limit test of lead, PbS is produced by addition of standard H2S , to
the solution containing lead.
pH 3-4 is necessary for the precipitation of PbS. So aq.
Ammonia/ acetic acid is added to maintain that pH.
100

LIMIT TEST FOR MODIFIED
LIMIT TEST
101

MODIFIED LIMIT TEST FOR CHLORIDES
102
Depending upon the nature of the substance, some modifications have
to be adopted for the preparation of the solution.
(a)Alkaline substances have to be dissolved in acid so that effervescence ceases and
much of the free acid is left in the solution as is prescribed in the test.
(b)Insoluble substances are generally extracted with water and then filtered, and
the filtrate is used for the test, because the presence of insoluble substance
modifies the opalescence and colour.

Esha Shah 103
(a)Salts of organic acids like sodium benzoate, sodium salicylate, etc. liberate
free water insoluble organic acid during acidification which is filtered off and
the filtrate is employed for the test.
(b) Coloured substances like crystal violet, malachite green, etc. are
carbonised and the
ash so produced is extracted in water.
(e)Deeply coloured substances have to be decolourised before test e.g.,
potassium permanganate is reduced by boiling with alcohol and the filtrate is
used.
(f)Reducing substances like hypophosphorus acid, which react with silver
nitrate in the limit test for chlorides should be oxidized with nitric acid or
some other oxidizing agents before carrying out the test.

104
Aim: To perform the limit test for chloride in potassium permanganate sample
(according to IP’96)
Requirement:
Nessler’s cylinder, measuring cylinder, pipette, spatula, distilled water, dilute nitric acid,
0.1 M silver nitrate solution, potassium permanganate sample
Principle:
The limit test for chloride based on the reaction between soluble chloride impurities
present in the substance and silver nitrate solution to give white precipitates of silver
chloride. These white precipitates are insoluble in dilute nitric acid and hence give
turbidity or opalescence to the test solution. The extent of the turbidity produced
depends upon the amount of the chloride present in the substance which is compared
with a standard opalescence produce by addition of silver nitrate to a standard solution
having known amount of chloride and the same volume of the dilute nitric acid as the
use in the test solution.

When potassium permanganate solution is treated with ethanol in presence of heat
the redox reaction will take place, i.e. potassium permanganate gets reduced to
manganese dioxide (precipitates). The filtrate of the reaction is colorless that is
subjected to proceed for limit test for chloride.
105
If the turbidity developed in the sample is less than the standard turbidity, the
sample passes the limit test for chloride and vice-versa. As potassium
permanganate gives purple color aqueous solution that interferes in the
comparison of opalescence or turbidity, therefore the aqueous solution
must first be decolorized. Potassium permanganate is oxidizing agent
while ethanol is reducing agent.

Chemical Reaction:
2 KMNO4 + 3 C2H5OH---------- 2 MNO2 + 2 KOH + 2 CH3CHO + 2 H2O
106
S.N. STANDARD SOLUTION S.N. TEST SOLUTION
1
Take 10 ml chloride standard solution (25
ppm
chloride) and add 5 ml water in a Nessler’s
cylinder.
1
Transfer the prepared test solution in
Nessler’s
cylinder
2
Add 10 ml of dilute nitric acid and dilute to
50 ml
with distilled water
2
Add 10 ml of dilute nitric acid and dilute to
50
ml with distilled water
3
Add 1ml of 0.1 M silver nitrate solution and
stir
immediately with glass rod and allow
standing for 5 minutes protected from light.
3
Add 1ml of 0.1 M silver nitrate solution and
stir immediately with glass rod and allow
standing for 5 minutes protected from light.
Compare the turbidity or opalescence produced in test solution with respect to
standard solution and report the result and conclusion.

Observation and conclusion:
Observation and conclusion will be of two types:
If the intensity of turbidity or opalescence appears to be more in test
solution than the standard solution then conclusion is impurities of
chloride in given sample is over the limit as per IP’96. Hence, sample do
not passes the limit test for chlorides.
If the intensity turbidity or opalescence appears to be less or equal in
test solution than the standard solution then conclusion is impurities of
chloride in given sample is under the limit as per IP’96. Hence, sample
passes the limit test for chloride
107

ToPerform The Limit Test For Sulphate In Potassium
Permanganate Sample (According To IP’96)
108
Principle:
It is a comparison method. It involves the comparison of opalescence or turbidity of
test sample verses standard sample which contain the definite amount of sulphate
impurities.
The limit test of sulphate is performed on the basis of reaction between the barium
chloride reagent (containing barium chloride, sulphate free alcohol and solution of
potassium sulphate (K2SO4) and soluble sulphate in the sample with formation of
barium sulphate (BaSO4) white precipitates.
Sulphate free alcoholic potassium sulphate is added to increase the sensitivity of the
test. Very small amount of barium sulphate present in the reagents acts as a seeding
agents for precipitation of barium sulphate, if sulphate is present in the sample under
the test.

109
Ethanol is added to prevent the super saturation i.e. the crystallization of sulphate
with any other ion.
As potassium permanganate gives purple colored aqueous solution that interferes
in the comparison of opalescence or turbidity, therefore it requires to be
decolorized. Potassium permanganate is oxidizing agent while ethanol is reducing
agent. When potassium permanganate solution is treated with ethanol in
presence of heat the redox reaction takes place, i.e. potassium permanganate gets
reduced to manganese dioxide (precipitates) and ethanol gets oxidized to form
ethanal. The filtrate of the reaction is colorless that is subjected to proceed for
limit test for sulphate.
Reaction
2 KMnO4 + 3 C2H5OH 2 MnO2 + 2 KOH + 2 CH3CHO + 2 H2O

Sr.
No.
STANDARD SOLUTION
SR.
NO
TEST SOLUTION
1
Take 1 ml 25% w/v barium chloride
in Nessler’s cylinder and add 1.5 ml
of ethanolic sulphate standard
solution (10 ppm SO4
-2). Mix and
allow to stand for 1 minutes
1
Take 1 ml 25% w/v barium chloride
in Nessler’s cylinder and add 1.5 ml
of ethanolic sulphate standard
-2). Mix and
allow to stand for 1 minutes
2
Add 15 ml of standard sulphate
-2) and 0.15 ml
of 5M acetic acid.
2
Transfer prepared test solution and
add 0.15 ml of 5 M acetic acid.
3
Add sufficient distilled water to
produced 50 ml. Stirred it
immediately and allow standing for 5
minutes.
3
Add sufficient distilled water to
produced 50 ml. Stirred it
immediately and allow standing for 5
minutes.
110
Compare the turbidity or opalescence in the test solution by
viewing transversely both solutions against black background.

UNIT I_History of pharmacopoeia and limit test

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UNIT I_History of pharmacopoeia and limit test