Fluorimetry by Dr. MONIKA SINGH as per PCI Syllabus

Dr. MONIKA SINGH (Pharmaceutical Chemistry) 03-10-2020
BP701T Instrumental Method of Analysis Unit-I 1
FLUORIMETRY
Dr. Monika Singh
CONTENTS
Principle
Factors affecting fluorescence intensity
Instrumentation
Applications
Conclusion
References.
BP701T InstrumentalMethod of Analysis Unit-I 2

FLUORESCENCE
It is a phenomenon of emission of
radiation when the molecules are exited by
radiation at certain wavelength.
FLUORIMETRY:- It is measurement
of fluorescence intensity at a particular
wavelength with the help of a filter
fluorimeter or a spectrofluorimeter.
 PRINCIPLE:- Molecule contains electrons,
electrons and non bonding (n) electron.
 The electrons may be present in bonding molecular
orbital. It is called as highest occupied molecular
orbital (HOMO).It has least energy and more
stable.
 When the molecules absorbs radiant energy
from a light source, the bonding electrons may be
promoted to anti bonding molecular orbital (LUMO).
It has more energy and hence less stable.BP701T InstrumentalMethod of Analysis Unit-I 4

 The process of promotion of electrons from HOMO
to LUMO with absorption of energy is called as
excitation.
 Singlet Ground state (S0):-a state in which all
the electrons in a molecule are paired 
 Doublet state:- a state in which un paired
electrons is present  or 
 Triplet state (T1) :- a state in which unpaired
electrons of same spin present 
 Singlet excited state (S1) :- a state in which
electrons are unpaired but of opposite spin like 
(un paired and opposite spin)
Ground singlet
states
• Spin: paired
• S0
• no net mag.field
• Stable
Excited singlet
state
• Spin: paired
• S1
• no net mag.field
• Unstable
• S1 energy is more
Triplet state
• Spins: unpaired
• T1
• net mag.field
• More stable
• T1energy is less
Singlet/ Triplet State

Light emitting at once sourcestarts& stops
whensource stops
Jablonski Energy Diagram explaining the Principle:

FIGURE 1
 When light of appropriate wavelength is
absorbed by a molecule the electrons are
promoted from singlet ground state to singlet
excited state. once the molecule is in this
excited state relaxation can occur via
several process. For ex by emission of
radiation . The process can be the following
1) Collisional deactivation
2) Fluorescence
3) Phosphorescence.

 Collisional de activation :- In which entire energy lost
due to collision de activation and no radiation
emitted.
 Fluorescence:-excited singlet state is highly unstable.
Relaxation of electrons from excited singlet to singlet
ground state with emission of light.
 Phosphorescence:-At favorable condition like low
temperature and absence of oxygen there is transition
from excited singlet state to triplet state which is called
as inner system crossing or Inter state conversion (ISC).
The emission of radiation when electrons undergo
transition from triplet state to singlet ground state is
called as phosphorescence.
1. Concentration
2. Intensity of incident light
3. Adsorption
4. Oxygen
5. pH
6. Temperature
7. Viscosity
8. Photodecomposition
9. Electron Donating Group
10.Electron Withdrawing Group
11.Scatter
12.Quenchers
Factors affecting fluorescent intensity:

CONCENTRATION:-
Fluorescence intensity is directly proportional
to concentration of substance only when the
absorbance is less than 0.02
A=log IoIt or A= abc
Io= intensity of incident light
It = intensity of transmitted light
a= absorptivity of constant
b= Pathlength
c= concentration
 INTENSITY OF INCIDENT LIGHT: Increase in the Intensity
of Incident Light on the Sample, Fluorescence Intensity also
Increases (luminescence also increases).
 ADSORPTION: Adsorption Of Sample Solution In The
Container May Leads ToA Serious Problem. (strong solutions must be
diluted)
 OXYGEN:- Oxidation of fluorescent species to a non
fluorescent species, quenches fluorescent substance.
 pH:- Alteration of pH of a solution will have significant effect
on fluorescence. Neutral and Alkaline solution show
fluorescence. E.g Aniline in alkali medium gives visible fluorescence.
 Temperature :- Temperature Increases Can Increase the
collisional de activation, and reduce fluorescent intensity.BP701T InstrumentalMethod of Analysis Unit-I 14

 Viscosity:- If viscosity of solution is more the frequency of
collisions are reduced and increase in fluorescent intensity.
 Photochemical decomposition:- Absorption of intense
radiation leads to photochemical decomposition of a
fluorescent substance to less fluorescent or non fluorescent
substance.
 Electron Donating group: increases fluorescence (Amino
group, Hydroxylic group)
 Electron withdrawing group: decreases fluorescence
(Nitro group, Carboxylic group)
 Scatter: Scatter is mainly due to colloidal particles in
solution. Scattering of incident light after passing through
the sample leads to decrease in fluorescence intensity.BP701T InstrumentalMethod of Analysis Unit-I 15
 Quenchers:-
 Quenching is the reduction of fluorescence intensity
by the presence of substance in the sample other
than the fluorescent analyte.
 Quenching is following types:-
 INNER FLUORESCENT EFFECT:- Absorption Of Incident (uv) Light Or Emitted
(fluorescent) Light By Primary And Secondary Filters Leads To Decrease In
Fluorescence intensity.
 SELF QUENCHING:-At Low Concentration Linearity Is Observed, At High
Concentration Of The Same Substance Increase In Fluorescent Intensity Is
Observed. This phenomena is called self quenching.
 COLLISONAL QUENCHING:- Collisions between the fluorescent substance and
halide ions leads to reduction in fluorescence intensity.
 STATIC QUENCHING:- This occurs because of complex formation
between the fluorescent molecule and other molecules.
Ex: caffeine reduces fluorescence of riboflavin.

INSTRUMENTATION
FIGURE 2

INSTRUMENTATION
• SOURCE OF LIGHT
• FILTERS AND MONOCHROMATORS
• SAMPLE CELLS
• DETECTORS
 1)SOURCE OF LIGHT:-
 mercury vapour lamp: Mercury vapour at high pressure give
intense lines on continuous background above 350nm.low
pressure mercury vapour gives an additional line at 254nm.it is
used in filter fluorimeter.
FIGURE 3

 Xenon Arc Lamp: It give more intense
radiation than mercury vapour lamp. it is used
in spectrofluorimeter.
FIGURE 4
 Tungsten lamp:- If excitation has to be done in
visible region this can be used. It is used in low cost
instruments.
FIGURE 5BP701T InstrumentalMethod of Analysis Unit-I 21
 2) FILTERS AND MONOCHROMATORS:-
 Filters: these are nothing but optical filters works on the
principle of absorption of unwanted light and
transmitting the required wavelength of light. In
inexpensive instruments fluorimeter primary filter and
secondary filter are present.
Primary filter:-absorbs visible radiation
 and transmit UV radiation.
Secondary filter:-absorbs UV
radiation and transmit visible
radiation.
FIGURE 6

 Monochromators: they
convert polychromatic
light into monochromatic
light. They can isolate a
specific range of
wavelength or a particular
wavelength of radiation
from a source.
 Excitation
monochromators:-provides
suitable radiation for
excitation of molecule .
 Emission monochromators:-
isolate only the radiation
emitted by the fluorescent
molecules.
 3) Sample cells: These are ment for holding liquid samples.
These are made up of quartz and can have various shapes
ex: cylindrical or rectangular etc.

 Barrier layer cell/Photo voltaic cells
Photomultiplier cells
FIGURE 8
 4) Detectors: Photometric detectors are used they are

1. Barrier layer /photovoltaic cell:
 it is employed in inexpensive instruments. For ex: Filter
Fluorimeter.
 It consists of a copper plate coated with a thin layer of cuprous
oxide (Cu2o). A semi transparent film of silver is laid on this plate
to provide good contact.
 When external light falls on the oxide layer, the electrons
emitted from the oxide layer move into the copper plate.
 Then oxide layer becomes positive and copper plate becomes
negative.
 Hence an emf develops between the oxide layer and copper plate
and behaves like a voltaic cell. So it is called photovoltaic cell..
 A galvanometer is connected externally between silver film and
copper plate and the deflection in the galvanometer shows the
current flow through it. The amount of current is found to be
proportional to the intensity of incident light
BARRIER LAYER CELL
FIGURE 9

2. Photomultiplier tubes:
 These are incorporated in expensive instruments like
spectrofluorimeter. Its sensitivity is high due to measuring weak
intensity of light.
 The principle employed in this detector Is that, multiplication
of photoelectrons by secondary emission of electrons.
 This is achieved by using a photo cathode and a series of anodes
(Dyanodes). Up to 10 dyanodes are used. Each dyanode is
maintained at 75- 100Vhigher than the preceding one.
 At each stage, the electron emission is multiplied by a factor of 4
to 5 due to secondary emission of electrons and hence an overall
factor of 106 is achieved.
 PMT can detect very weak signals, even 200 times weaker than
that could be done using photovoltaic cell. Hence it is useful in
fluorescence measurements.
 PMT should be shielded from stray light in order to have
accurate results. BP701T InstrumentalMethod of Analysis Unit-I 27
FIGURE 10

INSTRUMENTS
The most common types are:-
 Single beam (filter) fluorimeter
 Double beam (filter )fluorimeter
 Spectrofluorimeter(double beam)
 Instruments:-
It contains tungsten lamp as a source of light and
has an optical system consists of primary filter.
 The emitted radiations is measured at 900 by using
a secondary filter and detector. Primary filter absorbs
visible radiation and transmit uv radiation which excites
the molecule present in sample cell.
 In stead of 90 if we use 180 geometry as in colorimetry
secondary filter has to be highly efficient other wiseboth
the unabsorbed uv radiation and fluorescent radiation will
produce detector response and give false result.

 Single beam instruments are simple in construction
cheaper and easy to operate.

FIGURE 11
It is similar to single
beam except that the two incident beams from a single
light source pass through primary filters separately and
fall on the another reference solution. Then the emitted
radiations from the sample or reference sample pass
separately through secondary filter and produce
response combinly on a detector.

SPLITTER
 In spectrofluorimeter:-
 In this primary filter in double beam fluorimeter is
replaced by excitation monochromator and the
secondary filter is replaced by emission
monochromator.
 Incident beam is split into sample and
reference beam by using beam splitter.

APPLICATIONS
1) Determination of Uranium Salt in Nuclear Research
2) Determination of inorganic substances from Fluorescent
chelates. Al3+,Li+,Zn2+
3) Determination of vitamin B1 (Thiamine HCl).
4) Determination of Vitamin B2 (Riboflavin).
5) Detemination of phenytoin.
6) Determination of indoles, phenols, & phenothiazines.
7) Determination of napthols, proteins, plant pigments
and steroids.
8) Fluorimetry ,nowadays can be used in detection of
impurities in nanogram level better than absorbance
spectrophotometer with special emphasis in
determining components of sample at the end of
chromatographic or capillary column.

 Determination of ruthenium ions in presence of other
platinum metals.
 Determination of boron in steel, aluminum in alloys,
manganese in steel.
 Determination of boron in steel by complex formed with
benzoin.
 Estimation of cadmium with 2-(2 hydroxyphenyl)
benzoxazole in presence of tartarate .
 Respiratory tract infections.
Identification test as per IP2007 , Vol 3, Page no1173: Dissolve about 20 mg in
10 ml of water, add 1 ml of 2 M acetic acid and 1.6 ml of 1 M sodium hydroxide,
heat on a water-bath for 30 minutes and allow to cool. Add 5 ml of 2 M sodium
hydroxide, 10 ml of potassium ferricyanide solution and 10 ml of 1-butanol and
shake vigorously for 2 minutes. The upper layer exhibits an intense light blue
fluorescence, particularly in ultraviolet light at 365 nm. Repeat the test but adding
0.9 ml of 1 M sodium hydroxide and 0.2 g of sodium sulphite in place of the 1.6 ml
of 1 M sodium hydroxide; practically no fluorescence is produced.
Vitamin B1 (Thiamine) Determination
Principle: Thiamin (vitamin B1) is analyzed quantitatively by fluorometric
methods.
• The method of choice is the thiochrome procedure, which involves treatment
of thiamin with an oxidizing agent (ferricyanide or hydrogen peroxide or
Potassium permagnate) to form a fluorescent compound (thiochrome).
• The thiochrome formed is ex- tracted with isobutanol, and, when irradiated
with ultraviolet light, emits a blue fluorescence which can be read visually or
in a fluorophotometer.
• The intensity of fluorescence is proportional to the thiamine concentration.
Vitamin B1 has neurological benefits. Vitamin B1 is found in many foods
including yeast, cereal grains, beans, nuts, and meat. Thiamine is also used for
boosting the immune system, digestive problems, diabetic pain, heart disease etc.

Assay as per IP2007 , Vol 3, Page no1043-1044: Weigh accurately about 65 mg and
transfer to an amber-glass 500-ml volumetric flask, suspend in 5 ml of water, ensuring
that it is completely wetted. Dissolve in 5 ml of 2 M sodium hydroxide. As soon as
dissolution is complete add 100 ml of water and 2.5 ml of glacial acetic acid and dilute
to 500.0 ml with water. To 20.0 ml of this solution add 3.5 ml of a 1.4 per cent w/v
solution of sodium acetate and dilute to 200.0 ml with water. Measure the absorbance of
the resulting solution at the maximum at about 444 nm. Calculate the content of
C17H20N4O6 taking 328 as the specific absorbance at 444 nm.
Vitamin B2 (Riboflavin) Determination
Riboflavin (vitamin B2) is usually assayed fluorometrically by measuring its characteristic
yellowish green fluorescence.
Identification test as per IP2007 , Vol 3, Page no1043-1044: Dissolve about 1 mg in 100
ml of water. The solution has a pale greenish yellow colour by transmitted light and an
intense yellowish green fluorescence by reflected light, which disappears on addition of
mineral acids or alkalis.
It can also be assessed microbiologically, using Lactobacillus casei, where the growth of
this riboflavin-dependent microorganism correlates with the amount of vitamin in the
sample. The growth response of the organism is measured either by titration or by
measuring turbidity.
Vitamin B2 helps break down proteins, fats, and carbohydrates. It plays a vital role in
maintaining the body’s energy supply. vitamin B2 helps maintain proper eyesight.
S.No Name of the
compound
Experimental
conditions/ PH
Emission
wavelength
1 Adrenaline 1 335
2 Cynacobalamine 7 305
3 Riboflavin 6 520
4 Morphine 7 350
5 Hydrocortisone Acidic 520
6 Pentobarbitone 13 440
7 Amylobarbitone 14 410
Table 1

Conclusion :
 Fluorimetric methods are not useful in qualitative
analysis ,and much used in quantitative analysis.
 Fluorescence isthe most sensitive analytical
techniques.
 Detection studies will increase the development of
fluorescence field.
References :
 SKOOG ,Principles of InstrumentalAnalysis.
 Practical pharmaceutical chemistry by A.H.
BECKETT& J.B.STENLAKE ,volume 2,
 B.K.Sharma Instrumental methods of
chemical analysis.
 A textbook of pharmaceutical analysis by
Dr.S.RAVISANKAR.

Fluorimetry by Dr. MONIKA SINGH as per PCI Syllabus

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