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Volumetric and Gravimetric Analysis 67
2.31 PURITY OF PRECIPITATE
When the precipitate is separated from the solution, it is constantly not pure and may be
contaminated even after washing. The impurities in precipitates come from the solution
constituents that are not normally soluble, causing the precipitate to become contaminated.
2.31.1 Co-precipitation
Co-precipitation is the process of precipitation in which soluble compounds in a solution are
removed from solution during precipitate formation. There are mainly four types of
co-precipitation:
➢ Occlusion and Inclusion
➢ Surface Adsorption
➢ Isomorphous Replacement
➢ Post-precipitation
Occlusion and Inclusion
It is a type of co-precipitation in which the soluble impurity is enclosed or entrapped within
the crystal structure of the solid. Occlusion causes when an adsorbed impurity gets physically
trapped inside the crystal as it grows. Occlusion co-precipitation generally occurs when ions, of
large size or charge, are trapped within the crystal lattice. Digestion is effective in reducing the
quantity of entrapped contaminant.
Surface Adsorption
In surface adsorption, the soluble impurity is concentrated only at the surface and does not
penetrate through the surface to the bulk of the adsorbent. Contamination in the surface
adsorption will be important only when dealing with colloidal precipitates. Colloidal particles
adsorbed on their surfaces, one of the constituent ions of the precipitate. The adsorption of
impurities at the surface can be eliminated by using hot solution followed by digestion.
Isomorphous Replacement
If two compounds have the same formula and crystallize in similar geometric forms, they are
said to be isomorphous compound. Due to their similar lattice dimension, one ion can replace
another in a crystal resulting in a mixed crystal. This process is called isomorphous replacement.
This type of replacement is very significant and hardly can be done about it.
Post-precipitation
Post precipitation is a type of contamination where the impurities occur after the formation of
the precipitate of the desirable compound. Post precipitation arises on the surface of the first
precipitate. This kind of precipitation occurs if the solution is allowed to stand too long before
being filtered.
68 Text Book of Pharmaceutical Chemistry
2.32 EXERCISE
A. Long Answer Type Questions
1. What types of solvents are used in non-aqueous titration?
2. Differentiate between qualitative and quantitative analysis.
3. Write a note on scope of analytical chemistry.
4. Write a short note on principle/fundamentals of volumetric analysis.
5. Classify acid-base titrations and write a note on strong acid-strong base titration.
6. Write about the methods used in detection of end-point in non-aqueous titration.
7. What are Ionizing Solvents? Write the classification of ionizing solvents.
8. Discuss the advantages and disadvantages of gravimetric analysis.
9. What is Lewis Concept of Acid and Base? Write the limitations of Lewis theory.
10. Enumerate the various types of indicators used in non-aqueous titration.
11. What is Volhard’s method? Write the advantages and disadvantages of Volhard’s
method.
12. What is Co-precipitation? Explain the types of co-precipitation.
B. Short Answer Type Questions
1. What is pH and pOH?
2. Write a short note on buffer solution.
3. Define Arrhenius theory of acids and bases.
4. Write a short note on Bronsted-Lowry’s theory with example.
5. What are the limitations of Lewis Concept of Acid and Base?
6. What is Acidimetry? Explain the method of acidimetry with examples.
7. Write the assay of sodium benzoate.
8. Write a short note on masking and demasking agents.
9. Explain the method of alkalimetry with examples.
10. Differentiate between oxidizing and reducing agents.
11. What is Fajan’s method? Write about the types of adsorption indicators used in this
method.
12. Explain digestion and ignition process in gravimetric analysis.
13. What types of filters are used for the filtration of the precipitates?
14. What do you mean by an Indicator?
15. Differentiate between test solution and standard solution.
16. What do you mean by the term titration?
Volumetric and Gravimetric Analysis 69
C. Fill in the Blanks
1. ______________ states that color change as a result of ionization of the
acid-base indicator.
2. Fajan’s method was introduced by ______________ in 1923.
3. Formation of a colored complex is used to indicate the end-point in ______________.
4. Full form of EDTA is ______________.
5. Adsorption indicator is ______________.
6. According to Arrhenius theory, an acid ______________.
7. Lewis theory was proposed by ______________.
8. pH is a measure of ______________ concentration.
9. pOH scale represent acidic values from ______________.
10. Volhard’s method was given by ______________ in 1874.
11. In Mohr’s method, brick red precipitate is formed due to ______________.
12. ______________ is a self-indicator.
Answers:
1. Ostwald Theory
2. Kazimierz Fajans
3. Complexometric titration
4. Ethylene diamine tetraacetate
5. Eosin
6. Produces H
+
ion when dissolved in water
7. G.N. Lewis
8. hydrogen (H
+
) ion
9. 8 to 14
10. Volhard
11. Silver chromate
12. KMnO
4
Chapter
3
INORGANIC PHARMACEUTICALS
STRUCTURE
3.1 Haematinics
3.2 Gastrointestinal Agents
3.3 Topical Agents
3.4 Dental Products
3.5 Medicinal Gases
3.6 Exercise
OBJECTIVES
Inorganic Pharmaceuticals: Pharmaceutical formulations, market preparations, storage
conditions and uses of:
➢ Haematinics: Ferrous sulphate, Ferrous fumarate, Ferric ammonium citrate, Ferrous
ascorbate and Carbonyl iron.
➢ Gastrointestinal Agents: Antacids: Aluminium hydroxide gel, Magnesium hydroxide,
Magaldrate, Sodium bicarbonate, Calcium Carbonate, Acidifying agents, Adsorbents,
Protectives and Cathartics.
➢ Topical Agents: Silver Nitrate, Ionic Silver, Chlorhexidine Gluconate, Hydrogen
peroxide, Boric acid, Bleaching powder and Potassium permanganate.
➢ Dental Products: Calcium carbonate, Sodium fluoride, Denture cleaners, Denture
adhesives and Mouthwashes.
➢ Medicinal gases: Carbon dioxide, Nitrous oxide, Oxygen
3.1 HAEMATINICS
Haematinics are the substances that are required in the formation of blood and are used to
treat anemia. These are the nutrients necessary for the production of blood cells during the
hematopoiesis process. Folic acid, Vitamin B
12
, and iron are all the examples of haematinics.
Inorganic Pharmaceuticals 71
Anemia is a condition in which the blood does not contain enough healthy red blood cells to
transport oxygen to the body’s tissues. It is caused when the balance between the production and
destruction of RBCs is disrupted by the following factors:
(i) Blood loss (acute or chronic)
(ii) Impaired red cell formation due to:
➢ Deficiency of iron
➢ Vitamin B
12
and folic acid
➢ Bone marrow depression (hypoplastic anemia)
➢ Erythropoietin deficiency
(iii) Increased destruction of RBCs (hemolytic anemia)
Iron
Iron is a major component of hemoglobin, a type of protein in red blood cells that carries
oxygen from the lungs to all parts of the body. A lack of iron is called iron-deficiency anemia.
The recommended dietary allowance (RDA) of iron for individuals aged between 19 to 50 years
is 8 mg for men, 18 mg for women and 27 mg for pregnant women.
Classification
➢ Iron and its compound: e.g., Ferrous sulfate, Ferrous succinate, Ferrous gluconate, etc.
➢ Maturation factor: e.g., Cynocobalamine, Hydroxocobalamin, etc.
➢ Miscellaneous: e.g., Copper, Cobalt, Riboflavin, etc.
3.1.1 Ferrous Sulphate
Molecular Formula: FeSO
4
.7H
2
O
Molecular Weight: 278.0
Synonym: Green vitriol, Iron vitriol, Copperas
Brand Names: Feosol, Fer-In-Sol, Ferrousal, Slow Fe, Slow Release Iron
Ferrous sulphate contains not less than 98.0% of FeSO
4
.7H
2
O.
Ferrous sulfate exists most commonly as the hepta hydrate and denotes a range of salts with
the formula FeSO
4
·xH
2
O.
72 Text Book of Pharmaceutical Chemistry
Preparation:
1. Ferrous sulphate is prepared by adding slight excess of iron to dilute sulphuric acid.
When reaction is complete, the liquid is concentrated by boiling. Then the solution is
filtered and allowed to cool. The crystals are separated and dried, then recrystallizes
from water.
Fe + H
2
SO
4
→ FeSO
4
+ H
2
2. Ferrous sulfate is also produced commercially by oxidation of pyrites in heap leaching
process.
2FeS
2
+ 7O
2
+ 2H
2
O → 2FeSO
4
+ 2H
2
SO
4
Properties: Ferrous sulfate occurs as anhydrous greenish or yellow-brown crystalline solid. It is
odorless, melting point is 60-64°C (heptahydrate) and loses the seven waters of hydration at 90°C,
and density is 1.895 g/cm
3
. It is soluble in water. Salt dissolves in 1-5 times of its weight of water
at 25°C and about less than half of its weight of boiling water to form solution and negligible in
alcohol.
Uses of Ferrous Sulphate – FeSO
4
:
➢ It is used therapeutically at higher doses to cure or avoid iron-deficiency anemia.
➢ It is used in the prophylaxis for iron deficiency in pregnancy.
➢ It is used as a precaution if sedation or general anaesthesia is required; risk of the
hypotensive episode.
➢ It is also used with chlorine. This treatment is normally known as chlorinated copper as
treatment.
➢ It is used for treating iron chlorosis in horticulture (condition in which leaves produce
insufficient chlorophyll).
➢ It is used as hematinic and in the preparation of oral iron formulation.
➢ It is used to enhance food item for treating and avoiding anaemia.
➢ It is used in the textile industry for centuries as a dye fixative.
➢ Industrially, ferrous sulfate is mostly useful as a precursor to other iron compounds.
Pharmaceutical Formulations: Ferrous Sulphate is available in the following different
formulations:
➢ Oral delayed release tablet – 324 mg; 325 mg
➢ Oral elixir – 220 mg/5 ml
➢ Oral liquid (as elemental iron) – 15 mg/mL; 300 mg/5 ml
➢ Oral tablet – 200 mg; 325 mg
➢ Oral tablet, extended release (as elemental iron) – 45 mg; 160 mg
Inorganic Pharmaceuticals 73
Dosage Forms:
1. Ferrous Sulphate Tablet – 325 mg
Dried ferrous sulfate USP – 325 mg (65 mg of elemental iron)
Elemental Iron – 65 mg (equivalent to 325 mg of Ferrous Sulphate)
Excipients – q.s.
2. Ferrous Sulphate Tablet BP – 200 mg
Each tablet contains 200 mg Dried Ferrous Sulphate Ph. Eur. Equivalent to 65 mg elemental
iron.
Excipients – Also contains glucose, sucrose and lactose.
Treatment of iron-deficiency anaemias.
130-195 mg ferrous iron (2-3 tablets) daily in divided doses.
Ferrous sulphate + Folic acid capsules (Ferro Folic) 200 mg.
Marketed Preparations of Ferrous Sulfate
Brand Name
Dosage Form
Company
Eleron F
Dried Ferrous Sulphate capsule
150 mg
Geno Pharmaceutical Limited
➢ Folic acid (Vitamine B
9
) – 1.5 mg
➢ Zinc sulphate – 61.8 mg
➢ Cyanocobalmin – 15 mcg
Ferroealth
Ferrous Sulfate Tablets – 200 mg
Livealth Biopharma Pvt. Ltd.
Fervit capsules
Ferrous Sulfate, folinic acid, vitamins
Stanlet
3.1.2 Ferrous Fumarate
Molecular Formula: C
4
H
2
FeO
4
or FeC
2
H
4
(CO
2
)
2
Molecular Weight: 169.91
Synonym: Iron II fumerate
Brand Names: Aurovela Fe, Concept Ob, Generess
Ferrous fumarate contains not less than 93.0% of C
4
H
2
FeO
4
and not more than the equivalent
of 101.0% of iron (II)(E)-butenedioate, calculated with reference to the dried substance.
74 Text Book of Pharmaceutical Chemistry
Properties: It occurs as reddish orange to reddish brown color powder, tasteless or slightly
astringent, odorless or with slight odor. It is slightly soluble in water and very slightly soluble in
alcohol. Its melting point is 280°C. It is a granular form and it is stable even at 200°C.
Preparation: Ferrous fumarate is prepared by the interaction of hot, aqueous solution of ferrous
sulfate and sodium fumarate. Here, sodium fumarate is generally added to the ferrous sulfate.
FeSO
4
+ Na
2
C
4
H
2
O
4
→ FeCH
2
O
4
+ Na
2
SO
4
The precipitate of ferrous fumarate is removed by filtration. Then it is washed, dried and reduced
to a powder.
Pharmaceutical Formulations:
1. Ferrous Fumarate Syrup BP 200 ml
➢ Ferrous fumarate BP – 140 mg (Equivalent to 45 mg of iron)
2. Ferrous Fumarate Tablet 210 mg
➢ Ferrous fumarate – 210 mg (Equivalent to 65-70 mg of iron)
3. Ferrous Fumarate with Multivitamin Capsule
➢ Ferrous – 106 mg (Iron)
➢ Vitamin C (Sodium Ascorbate) – 200 mg
➢ Vitamin B
1
(Thiamine mononitrate) – 10 mg
➢ Vitamin B
2
(Riboflavin) – 6 mg
➢ Vitamin B
6
(Pyridoxin HCl) – 5 mg
➢ Vitamin B
12
– 30 mg
➢ Folic acid – 15 mcg
➢ Niacinamide Pantothanic acid 10 mg – 30 mg
➢ Zinc (Zinc sulphate) – 18.2 mg
➢ Magnesium (Magnesium sulphate) – 6.9 mg
➢ Copper (Copper sulphate) – 0.8 mg
➢ Manganese (Manganese sulphate) – 1.3 mg
4. Ferrous Fumarate and Folinic Acid Tablet
➢ Ferrous Fumarate – 152 mg
➢ Folic acid – 1.5 mg
Inorganic Pharmaceuticals 75
Marketed Preparations of Ferrous Fumarate:
Brand Name
Dosage Form
Company
Centratex
Ferrous fumarate with multivitamin capsule
➢ Ferrous fumarate (Iron) – 106 mg
➢ Vitamin C (Sodium Ascorbate) – 200 mg
➢ Vitamin B
1
(Thiamine mononitrate) – 10 mg
➢ Vitamin B
2
(Riboflavin) – 6 mg
➢ Vitamin B
6
(Pyridoxin HCl) – 5 mg
➢ Vitamin B
12
– 30 mg
➢ Folic acid – 15 mcg
➢ Niacinamide – 30 mg Pantothanic acid 10 mg – 30 mg
➢ Zinc (Zinc sulphate) – 18.2 mg
➢ Magnesium (Magnesium sulphate) – 6.9 mg
➢ Copper (Copper sulphate) – 0.8 mg
➢ Manganese (Manganese sulphate) – 1.3 mg
Centurion labs
ECOFER
Tablet – Ferrous Fumarate Folinic Acid Tablet:
Ferrous Fumarate 152 mg + Folic Acid 1.5 mg Tab.
Tanishq Life Care
ECOFER
Syrup:
Folic Acid 0.5 mg + Vitamin B12 5 mcg + Ferrous
Fumarate 100 mg/5 ml Susp.
Tanishq Life Care
Storage: Protect from light. It should be stored in a cool place below 25°C. Stable under normal
conditions of use.
Uses: Ferrous fumarate is a medicine used to treat and prevent iron-deficiency anemia. Iron helps
the body to make healthy red blood cells which carry oxygen around the body. Some things such
as blood loss, pregnancy or too little iron in the diet decrease the iron supply and leads to anemia.
3.1.3 Ferric Ammonium Citrate
Molecular Formula:
(NH
4
)
5
[Fe(C
6
H
4
O
7
)
2
]
Molecular Weight: 261.98
Synonym: Ammonium Iron (III) Citrate
Brand Name: Auryxia
76 Text Book of Pharmaceutical Chemistry
Preparation: Ferric ammonium citrate is prepared by the reaction of ferric hydroxide with citric
acid, followed by treatment with ammonium hydroxide, evaporating, and drying. The resulting
product occurs in two forms depending on the stoichiometry of the initial reactants.
Fe(OH)
3
+ CH
2
COOH-C(OH)COOH-CH
2
COOH + NH
4
OH → C
4
H
8
FeNO
7
+ H
2
O
Properties: Ferric ammonium citrate occurs as a yellowish brown to red or as green crystals or
powder, with a faint odor of ammonia. A distinguishing feature of this compound is that it is very
soluble in water, in contrast to ferric citrate which is not very soluble. It is stable under ordinary
conditions of use and storage. It may reduce to ferrous salt by exposure to light. Very
deliquescent; forms a solution on prolonged exposure to air.
Uses of Ferric Ammonium Citrate:
➢ Ferric ammonium citrate is used as a Haematinic.
➢ It is added to foods as an acidity regulator and anticaking agent.
➢ It is used in medical imaging; ferric ammonium citrate is used as a contrast medium.
➢ It is used as a reducing agent of metal salts of low activity like gold and silver.
➢ Ferric ammonium citrate is used with folinic acid in folic acid deficiency.
➢ It is used with potassium ferricyanide as part of the cyanotype photographic process.
Pharmaceutical Formulations: Ferric ammonium citrate is available in the following
formulations:
➢ Oral tablet : 210 mg ferric iron (equivalent to 1 g ferric citrate)
➢ Syrup : 200 mg (equivalent to elemental iron 41 mg)/5 ml
160 mg (equivalent to elemental iron 32.8 mg)/5 ml
1. Ferric Ammonium Citrate Syrup with Folic Acid and Cyanocobalmin 200 ml
➢ Ferric Ammonium Citrate – 200 mg (equivalent to elemental iron 41 mg)
➢ Folic Acid – 1.5 mg
➢ Cyanocobalamin (Vitamin B
12
) – 50 mcg
➢ Syrup base – q.s.
2. Ferrous Ammonium Citrate Syrup I.P. with Folinic Acid and Cyanocobalamin 200 ml
➢ Ferric Ammonium Citrate I.P. – 160 mg
➢ Folinic acid – 0.5 mg
➢ Cyanocobalamin (Vitamin B
12
) – 7.5 mcg
➢ Alcohol (95%) I.P. – 0.87 ml
➢ Color: Erythrocin, caramel – q.s.