Principles of Non-Aqueous Titration &
Application in Pharma Industries
Content
 Introduction – Volumetric analysis
 Non- Aqueous Titration
 Acid Base Theory
 Solvents for NAT
 End Point Detection
 Indicators
 Potentiometric End Point
 Acid & Base Titration
 Pharmacopeia USP <541>
 PotentiometricAnalysis
 Precaution To Be Taken
 Estimation Of Errors And Elimination Of Errors
 References
Introduction
Tirtimetric / Volumetric analysis:
Volumetric analysis is performed for Quantitative determination of
assay / content. It is simple and commonly used technique in Chemical
Industries.Analysis conducted in Aqueous and non-aqueous medium.
◦ Simple and easy
◦ Fast and can be done on site
◦ Less expensive
◦ Estimation of content or Assay of chemical
◦ Precise and accurate - depends on method and specificity
Limitation in Aqueous Titration
Titration in water solutions has limitation:

To titrate week acids or weak bases

To titrate separately for a mix of acids (bases) with near
dissociation constants.

To determine the substances which are insoluble in
water.

The substances, which are either to weakly acidic or too
weakly basics to give sharp end point in water

The above can be overcome by non-aqueous to
perform easily and with accuracy
Non-Aqueous Titration (NAT)
Non aqueous titration: Titration performed in
solvent medium which does not contain water.
Substance is dissolved in a solvent and titrated
using acid or base as titrant.
 Theory is same as Acid-Base titration
 Reaction carry out in non-aqueous medium
 Extensively used for organic acids and bases
Principle is based on Brønsted-Lowry Theory
Where to use NAT
NAT is applied where;
◦ To titrate week acid or weak bases
◦ To titrate separately for a mix of acids (bases) with
near dissociation constants.
◦ To determine the substances which are insoluble in
water.
◦ The substances, which are not give sharp end point in
aqueous solutions, can be titrated non-aqueous solvent
( eg too weakly acidic or basic)
Advantages of NAT






Organic acids and bases that are insoluble in water can be tested
using appropriate solvents
Principle of NAT is same as aqueous titration.
Very week acid and bases can be analysed in NAT
Mixture of week acids can be tested in single or mixture of
solvents.The individual acid can give separate end point in different
solvent.
Biological ingredients of a substance whether acidic or basic can be
selectively titrated using proper solvents.eg Nitrogen containing
compounds
Non aqueous titrations are simple and accurate, examples of non
aqueous titration are;
◦ Ephedrine , codeine phosphate, tetracycline, piprazine Anti- histamines etc
What are Acids & Bases
Acids:
Arrhenius acid: Any substance that, when dissolved in
water, increases the concentration of hydronium ion
(H3O+)
Bronsted-Lowry acid: A proton donor; conjugate base
Lewis acid: An electron acceptor
Bases:
Arrhenius base: Any substance that, when dissolved in
water, increases the concentration of hydroxide ion (OH-)
Bronsted-Lowery base: A proton acceptor ; conjugate
acid
Lewis acid: An electron donor
Brønsted-Lowry Theory
The conjugate acid of a base is the base plus the attached proton and
the conjugate base of an acid is the acid minus the proton
proton
receiver
.. ,r.g·
e
n
QI ~00.f.1'.,,.,'I!_••
H-
_,
I
acid
proton
source
proton
source
proton
receiver
Qu
o:
I
+
N-H
- A+- base
HB+
B - HA
base
+- acid
H
H
Base
Acid
Acid
of
·~
:61
1
1
-
••
_
- •
. .
H
.
-+
£:.·~
·
··
._.
_•
!
I
H-·:
Copy
I
ht@
Conjugate acid
water
Conjugate
of acetic
~l -~ 1']
+
+
H
2005
Poarson
Pr. nUcm, Ha.II,
Inc.
Bae
base
acid
Equilibrium constant Ka and Kb
The equilibrium constant for a Brønsted acid is
represented by Ka, and base is represented by Kb.
CH3COOH(aq) + H2O(l)
Notice that H2O is not
included in either
equilibrium expression.
NH3(aq) + H2O(l)
pH of 1M ACOH =2.4
H3O+(aq) + CH3COO–(aq)
[H3O+][CH3COO–]
Ka = –––––––––––––––––
[CH3COOH]
NH4+(aq) + OH–(aq)
[NH4+][OH–]
Kb = –––––––––––––
[NH3]
Solvents used in NAT
Solvent which are used in non aqueous titration are called
non aqueous solvent.
Classified as four types:
1. Aprotic solvents: Chemically neutral
2. Protogenic solvents: Acidic nature readily donate
protons,
3. Amphiprotic solvent: Which are sly ionize and
donate and accept protons,
4. Protophilc solvents: Posses high affinity for protons.
Aprotic Solvents:
Aprotic Solvents:
◦ Solvents are chemically neutral,
◦ un-reactive under the titration conditions; do not
undergo reactions with acids and bases
◦ they possess low dielectric constants,
◦ do not cause ionization in solutes and
◦ Aprotic solvents are frequently used to dilute reaction
mixture.

Eg. Toluene, carbon tetrachloride , acetonitrile,
benzene, and chlorinated hydrocarbons
Protogenic Solvents

Protogenic Solvents: ( protogenic – proton producing)

Also called as Acidic solvents are acidic in nature and
readily donate protons.

solvents which are more acidic than water,

strength and ability to donate protons, they enhance the
strength of weak bases.

these solvents have a more acidic character and tend to
have a leveling effect on the bases they come in contact
with.

Eg . Anhydrous Hydrogen fluoride , Sulphuric acid,
Formic acid , acetic acid etc.
Protophilic Solvents
Protophilic Solvents: (philic- affinity)

solvents which are more basic than water,

They will react with an acidic solute with the formation
of a solvated proton and the conjugate base of the acid :

which possess a high affinity for protons.
Eg. Liq ammonia, Amine , Ketones, ethers etc.
Weak acids are normally used in the presence of
strongly protophilic solvents as their acidic strengths are
then enhanced and then it behave like strong acids; this
is known as the levelling effect.
Amphiprotic Solvents:
Amphiprotic Solvents:

Solvents have properties which are protophilic as well as
protogenic.

Similar to water possesses both acidic and basic
properties (donating and accepting of protons)

Which are slightly ionize and donate or accept protons,
◦ Eg Alcohols (Methanol, Ethanol, etc.) , weak
organic acids ( Acetic acid)
◦ Acetic acid makes weak acid into storing base
Acetic Acid
Acetic acid slightly ionise and combine both protogenic and
protophilic propertiesamd able to donate and to accept protons

Acetic acid is slightly ionize and dissociate to produce protons
CH3COOH ↔ CH3COO- + H+

But in the presence of perchloric acid, a far stronger acid, it
will accept a proton:
CH3COOH + HClO4 ↔ CH3COOH2+ + ClO4 –
The CH3COOH2+ ion can very readily give up its proton to
react with a base, so basic properties of a base is enhanced, so
titrations between weak base and perchloric acid can often be
accurately carried out using Acidic acid .
Levelling Solvents:
LevellingSolvents:
In general, strongly protophilic solvents are important to force
equilibrium equation to the right.
CH3COOH + HClO4 ↔ CH3COOH2+ + ClO4 –
This effect is so powerful that, in strongly protophillic solvents, all
acids act as of similar strength.
HB
)
(
B- + H+
The converse occurs with strongly protogenic solvents, which cause
all bases to act as they were of similar strength.
Solvents, which act in this way, are known as Levelling Solvents.
Properties of a solvents
The choice and Properties of a solvent for the particular
titration is very critical.
◦ the solvent should dissolve the substance to be titrated,
◦ should not introduce interfering side reactions with either
the substance to be titrated or the titrant,
◦ should permit a large change in the solvated proton
concentration near the equivalence point,
◦ should be easily purified, and
◦ preferably should be less expensive.
If the solvent is to be used for a differentiating titration it
should be neither strongly acidic nor strongly basic to avoid
"LEVELING" effects.
Titration Of Bases

The titrant should be a very strong acid. Ie Perchloric
acid in Dioxane

The solvent should not be basic properties

Aprotic solvents, such as benzene, chloroform, carbon
tetrachloride, chlorobenzene, either alone or mixed with
glacial acetic acid may sometimes be used for titration
with acetous perchloric acid

To determine primary , secondary , tertrary amines,
heterocyclic amines
Titration Of Acids

The titrant should be a solution of a strong base
◦ Solutions of quaternary ammonium hydroxides in organic solvents,
e.g. tetra-butylammonium hydroxide in benzene - methanol or IPA
or triethyl-n-butylammonium hydroxide in benzene – methanol.
◦ Solution of sodium or potassium methoxide in benzene - methanol

Solvent (s):
◦ A mixture of benzene and methanol
◦ very weak acids (e.g., many phenols) usually require a more
strongly basic solvent, such as DMF, anhydrous ethylenediamine or
butylamine

To determine week organic acids.
Precaution: Amine may absorb carbon dioxide from the atmosphere
Selection of Solvents for NAT

Acetic acid used for titration of weakbases,Nitrogen
containingcompounds

Acetonitrile / with ACOH: Metalethanoates

Alcohols (IPA, nBA) : Soapsandsaltsoforganic
acids,

DMF: Benzoicacid,amidesetc
Titrants for NAT

Perchloricacid in acetic acid
◦ Amines, amine salts, amino acids, salts of acids

PotassiumMethoxide in Toluene-Methanol
◦ Week organic acid

Quaternaryammoniumhydroxide in
acetonitrile- pyridine
◦ Acids, enols, imides & sulphonamides
Endpoint Detection
End point detection is critical for titration, it is to
know the completion of reaction and accurate
determination.
1) Visual indicators:
• Observe a colour change or precipitation at the endpoint.
– Reaction progress checked by addition of external or self
indicator
2) Electrochemistry:
• Potentiometry - measure voltage change ( pH electrode)
• Amperometry - measure change in current between
electrodes in solution
• Conductance – measure conductivity changes of solution
Latertwousedforcoloured,turbid&accurateendpoint
Improvement of end point

The end points may often be improved by the addition of aprotic
solvents in order to depress the solvolysis of the neutralisation product.

Potentiometric titrations are used for coloured solutions and
also for compounds which remain feebly acidic or basic
notwithstanding the levelling effect of the solvent.

Visual indicators may be employed for compounds which behave as
sufficiently strong acids or bases in appropriate non-aqueous solvents.

The suitability of a visible indicator for a particular titration must be
determined by performing a potentiometric titration and observing the
colour change of the indicator simultaneously.

Temperature of standardization and test shall be same since
coefficients of expansion and dissociation constant may vary
Indicators for NAT
1. Crystal violet is used as a 0.5% (w/v) solution in glacial
acetic acid. Its colour change is from violet through
blue, followed by green, then to greenish-yellow,
2. Methyl red is used as a 0.2% (w/v) solution in dioxane
with a yellow to red colour change.
3. I-Naphthol benzein 0.2% (w/v) solution in acetic acid
gives a yellow to green colour. It gives sharp end points
in Nitromethane containing acetic anhydride for
titrations of weak bases against perchloric acid.
Indicators for NAT
4. Oracet blue B is used as a 0.5 % (w/v) solution in acetic
acid and is
considered to be superior to crystal violet for titrations of
bases in acetic acid with standard perchloric acid. The end
point : from blue to pink.
5. Thymol blue 0.5 % (w/v) in methanol is used for titrations
of substances acting as acids in dimethylformamide
solution. The end point: change from yellow to blue
6. Methyl violet 0.2% (w/v) in chlorobenzene, violet to blue.
Preparation of 0.1N Perchloric Acid

Preparation of 0.1N Perchloric Acid in Glacial Acetic
Acid
◦ Mix 8.5 ml 70% of perchloric acid with 500 ml of
glacial acetic acid and 21 ml of acetic anhydride, cool,
and add glacial acetic acid to make 1000 ml.
◦ Allow the prepared solution to stand for 1 day for the
excess acetic anhydride to be combined, and
determine the water content 0.02% and 0.5% (if >
0.5%, add acetic anhydride).
Precaution for Perchloric acid preparation

Perchloric acid (70 to 72%) addition in solvent contain water is
exothermic and may decompose, handle carefully,.

Conversion of acetic anhydride to acetic acid requires 15-45 min

Allow to cool to room temperature before adding glacial acetic acid

Avoid adding an excess of acetic anhydride especially when
primary and secondary amines are to be assayed, because it may
react and convert acetylation .
Standardization of Perchloric Acid
Standardization of 0.1N perchloric acid

Accurately weigh about 700 mg of potassium biphthalate,
previously crushed lightly and dried at 120° for 2 h, and dissolve it
in 50 mL of glacial acetic acid in a 250-mL flask. Add 2 drops of
crystal violet TS, and titrate with the perchloric acid solution until
the violet color changes to blue-green.

Standardization: perform potentiometrically as specified

Sample shall be tested the same type of end point determination (
visual or potentometry) followed for standardization
Note: Use benzoic acid as primary standard where required as
specified in USP
Blank correction

Blank correction is usually obtained by means of a
residual blank titration, wherein the required procedure
is repeated in every detail except that the substance
being assayed is omitted.

An appropriate blank correction shall be included in
calculation

difference between the volume consumed in the residual
blank titration and that consumed in the titration can be
considered for assay

If blank is high or suspected, repeat the analysis
Calculation
o
Normality: Eq.wt/1000ml or meq/mL
o
Morality: Mole/1000ml
o
V1 N1 = V2N2
o
N1 = V2N2/V1

Normality = Wt of sample x 1000 / Eq. Wt x V

Wt of sample (mg) = V x N x Eq. wt

Assay = Qty estimated in sample x 100/ wt of sample

Assay = V x N x Eq. wt x 100/ wt of sample x 1000
Thank You