Download Lab-1

Name:
ID:
Group:
Calcium Carbonate capsules
For 6th Semester
Students
Lab. 1
1
Methods of Quantitative drug analysis
1. Titrimetric (volumetric) analysis:
Acid base
Involves neutralization reactions using acid-base indicator. Detection of end point depends on sharp
change in pH.
Can be divided to: - Aqueous titration (used for strong acids or bases)
- Non aqueous titrations (used for weak acids or bases)
Preciptimertic titrations:
These methods are based on formation of a precipitate.
e.g Mohr’s, Volhard’s & Fajan’s method
Complexometric titrations:
These methods are based on formation of complex between the metal ions and complexing agent
using metallochromic indicator.
Redox titrations:
These methods involve a change in the oxidation number of the reactants
e.g. Bromometry, Iodometry & Iodimetry.
2. Instrumental analysis:
Determination of the concentration of the active constituents via measuring its properties using
instruments.
e.g. spectrophotometer analysis which has two main classes: absorption spectroscopy and emission
spectroscopy.
Classification of methods of drug analysis according to functional groups
(Functional group analysis)
Aim: prediction how you can make an assay of any drug according to the functional group(s) present.
2
Complexometry

Complexometric titrations: are methods of volumetric analysis which involve complex
formation reaction between the sample and the standard. The formed complexes are very
slightly ionizable compounds.

A complex: is a compound formed of a metal ion and a complexing agent (ligand).

A complexing agent (ligand): is any donor ion or molecule which by its ability to form coordinate covalent bond with the metal, produces a complex which differ in properties from the
ion.
Ligands are classified according to the number of points of attachment to the
metal into:



Uni-dentate: NH3, CN-, ClBi-dentate : NH2 – CH2 – CH2 – NH2 “ethylene diamine”
Tri-dentate : NH2 – CH2 – CH2 – NH – CH2 – CH2 – NH2 “di-ethylene triamine”
When the complex is between:
 Mn+ and unidentate complexing agent this is known as Co-ordination compound.
 Mn+ and mutidentate ligand that form a cyclic structure is known as Metal chelate and the
complexation reaction is called chelation.
The most common complexing agent in quantitative analysis is the EDTA “Ethylene Diamine Tetraacetic Acid disodium salt (Na2H2Y).”
It is a sequestering agent (which forms a water soluble chelate with di- and polyvalent metal ions.)
EDTA reacts with the different cations (metals) in 1:1 ratio irrespective of the valence of the cation and
always 2H+ are liberated.
M2+ + H2Y2M3+ + H2Y2M4+ + H2Y2-
MY2- + 2H+
MY- + 2H+
MY + 2H+
3
Metallochromic indicators:
These are organic dyes which form colored chelates; the color of the free dye (indicator) varies greatly
from the color of the metal chelate. They also change their color according to the PH of the medium.
e.g.
Meruxide, EBT (Erichrome Black T)
For EBT
H2In(Below PH 6)
“Wine red”
HIn2(PH 8-12)
“Blue”
In3(Above PH 12)
“orange”
At PH 10
MgIn- + H2Y2Wine red
MgY2- + HIn2- + H+
blue
Why do we use buffer in EDTA titration?
1. To avoid the drop of pH and the accumulation of the H+ liberated from the EDTA. And so make
the reaction go forward “towards the formation of complex”.
2. To avoid change of the color of the indicator with the change of PH.
3. By adjusting pH we can increase the selectivity of EDTA.
4
Calcium Carbonate Capsules (Calcimate Capsules)
Each tablet contains 500 mg CaCO3 (Mwt = 100.0869 g/mol)
Uses:
Calcium supplements are used to prevent and to treat calcium deficiencies.
Principle of the assay
Back titration of EDTA may be used if the reaction between the analyte and the titrant is slow or
to make the end point clearer.
Procedure:
1. Weigh the content of 2 Capsules (group of two).
2. To a quantity of the powder containing the equivalent of 0.25 g of calcium Carbonate, add 50 ml of
water and 5 ml of hydrochloric acid.
3. Heat the dispersion gently to boiling and continue to boil for about 2 minutes.
4. Allow to cool, add sufficient water to produce 250 ml (using a 250 ml volumetric flask).
5. To 25 ml of this solution, add 25 ml distilled water.
6. Add 25 ml of 0.05M disodium edetate VS.
7. Neutralize the solution using 2M sodium hydroxide (1 ml) and ammonia buffer (10 ml) pH 10.9.
8.Titrate the excess of disodium edetate with 0.05M zinc chloride VS using EBT as indicator (end point:
from full blue to purple).
5 ml of hydrochloric acid.
50 ml of water
Heat the dispersion gently to
boiling and continue to boil for
about 2 minutes.
Y g powd. tab
Allow to cool
Add specks EBT
Neutralize the
solution using
2M NaOH (1 ml)
NH3 buffer (10
ml) pH 10.9 and
25 ml of water.
Add 25 ml of 0.05M
EDTA
Transfer 25 mL of
a flask
Transfer to
a volumetric
flask 250 mL
Add sufficient water to
produce 250 ml
5
Calculations
Recovery % 
Rec % 
Practical Value
 100
Labeled Value
(mL of EDTA X f - mL of Zinc chloride X f) X F X100
g
0.025
1 Mole EDTA = 1Mole CaCO3
1L 1M EDTA = Mwt CaCO3
1mL 1M EDTA = (1/1000) Mwt CaCO3
1mL 0.05 M EDTA = (1/1000X20) Mwt CaCO3
Calculation:
Calculate the Equivalent factor between 0.05M EDTA and calcium, and then calculate the recovery
percent.
Start point
End point
mL’s consumed
Average
Recovery % =
6