Flame photometry for M.pharmacy 1st year

1. dsss
Chetan Sharma
Quality control department

2. Introduction
 Flame photometry (more accurately called flame atomic
emission spectrometry)
 It is a branch of atomic spectroscopy in which the species
examined in the spectrometer are in the form of atoms
 Based on measurement of intensity of the light emitted when a
metal is introduced into flame
• The wavelength of color tells what the element is .
• The color's intensity tells us how much of the element present.

3. History
 The history of spectroscopy starts
with the use of the lens by
Aristophanes about 423 B.C.; and
the studies of mirrors by Euclid (300
B.C.) and Hero (100 B.C.).
 Seneca (40 A.D.) observed the light
scattering properties of prisms.
 In 100 A.D. Ptolemy studied
incidence and refraction.

4.  Fraunhofer , about 1814-15, observed diffraction phenomena and
was able to measure wavelength instead of angles of refraction.
 Herschel (1823) and Talbot (1825) discovered atomic emission
when certain atoms were placed in a flame.
 Wheatstone concluded in 1835 that metals could be distinguished
from one another on basis on the wavelengths of this emission.
 In 1848, Foucault observed atomic emission from sodium and
discovered that the element would absorb the same rays from
an electric arc.

5.  In the later 1800, scientists such as Kirchoff, Bunsen,
Angstrm, Rowland, Michelson and Balmer studied the
composition of the sun based on their emissions at
different wavelengths.
 Kirchhoff summarized the law which states that,
"Matter absorbs light at the same wavelength at
which it emits light". It is under this law that atomic
absorption spectroscopy works.

6.  Woodson was one of the first to apply this principle to
the detection of mercury.
 In 1955, Walsh suggested the use of cathode lamps to
provide an emission of appropriate wavelength; and
the use of a flame to produce neutral atoms that would
absorb the emission as they crossed its path

7. Principle
 Liquid sample contaning
metal salt solution
introduced into a flame:
 Solvent is vaporised , leaving
particles of solid salt
 Salt is vaporised into gaseous
state
 Gaseous molecule dissociate
to give neutral atoms

8.  Neutral atoms are excited by thermal energy of flame
 The unstable excited atoms emit photons while
returning to lower energy state
 The measurement of emitted photons forms the basis
of flame photometry.

9. Structure of flame
 As seen in the figure, the
flame may be divided into the
following regions or zones.
i) Preheating zones
ii) Primary reaction zone or
inner zone
iii) Internal zone
iv) Secondary reaction zone

10.  preheating zone- In this combustion mixture is heated to
the ignition temperature by thermal conduction from the
primary reaction zone.
 primary reaction zone- This zone is about 0.1 mm thick at
atmospheric pressure
There is no thermodynamic equilibrium in this zone and the
concentration of ions and free radicals is very high.
This region is not used for flame photometry.
 interconal zone – It can extend up to considerable height.
The maximum temperature is achieved just above the tip of
the inner zone.
This zone is used for flame photometry.

11.  secondary reaction zone - In this zone, the products
of the combustion processes are burnt to stable
molecular species by the surrounding air.

12. Instrumentation
1. Sample Delivery
2. Source
3. Monochromator
4. Detector
5. Read out device

13. Schematic diagram showing the layout of various components of a flame photometer

14. Sample delivery
There are three components for introducing liquid
sample.
 Nebulizer – it breaks up the liquid into small
droplets
 Aerosol modifier – it removes large droplets from the
stream and allow only smaller droplets than a certain
size to pass
 Flame or Atomizer – it converts the analyte into free
atoms

15. Sample Introduction Techniques
Liquid:
 Pneumatic Nebulization
 Ultrasound Nebulization
 Electro thermal Vaporization
Solid:
 Direct Insertion
 Electro thermal Vaporization
 Laser Ablation

16. Types of sample introduced

17. Nebulization
 Nebulization: is conversion of a sample to a fine mist of
finely divided droplets using a jet of compressed gas.
The flow carries the sample into the atomization region.
 Pneumatic Nebulizers: (most common)
Four types of pneumatic nebulizers:
 Concentric tube
 Cross flow
 Fritted disk
 Babington

19. • Concentric tube - the liquid sample is sucked through
a capillary tube by a high pressure jet of gas flowing
around the tip of the capillary.
-This is also referred to aspiration. The high
velocity breaks the sample into a mist and carries it to
the atomization region.
• Cross-flow -The jet stream flows at right angles to the
capillary tip. The sample is sometimes pumped through
the capillary.
• Fritted disk -The sample is pumped into a fritted disk
through which the gas jet is flowing. Gives a finer
aerosol than the others.

20. • Babington - Jet is pumped through a small orifice in a
sphere on which a thin film of sample flows. This type is
less prone to clogging and used for high salt content
samples.
 Ultrasonic Nebulizer-The sample is pumped onto the
surface of a vibrating piezoelectric crystal.
-The resulting mist is denser and more homogeneous
than pneumatic nebulizers.
 Electro-thermal Vaporizers (Etv)-An electro thermal
vaporizer contains an evaporator in a closed chamber
through which an inert gas carries the vaporized sample
into the atomizer.

21. Source

22. Source
Burner-which are used to spray the sample solution
into fine droplets.
Several burners and fuel – oxidant combinations have
been used to produce analytical flame
 Premixed burner
 Mecker burner
 Total consumption burner
 Lundergarh burner
 Shielded burner
 Nitrous oxide-acetylene flames

23. Premixed burner
 widely used because
uniformity in flame intensity
 In this energy type of burner ,
aspirated sample , fuel and
oxidant are thoroughly mixed
before reaching the burner
opening.

24. Total consumption burner
 In this fuel and oxidant are
hydrogen and oxygen gases
 Sample solution is aspirated
through a capillary by high
pressure of fuel and Oxidant
and burnt at the tip of burner
 Entire sample is consumed.

25.  Mecker burner - Generally used for study of alkali
metals only.
 Lundergarh burner-In this sample must be in liquid
form
• Large droplets condense on the side or drain away
• Small droplets and vaporised sample are swept into the
base of flame in form of cloud
• Devices such as ultrasonic vibrators are used to
enhance the nebulization stage in this burner.

26. Shielded Burner
• In this flame was shielded from the ambient
atmosphere by a stream of inert gas.
• Shielding is done to get better analytical sensitivity.
• Following results are obtained with shielded burner
Element Sensitivity(ppm)
Ba 0.05
Ca 2
Cr 0.002
Pb 0.05
Mg 0.3

27. Nitrous oxide-Acetylene flame
• These flames were superior to other flames for
effectively producing free atoms
• Eg.-metals with very reflective oxides such as
aluminium and titanium.
 The drawback of it is:
• the high temperature reduces its usefulness for the
determination of alkali metals as they are easily
ionized
• Intense background emission, which makes the
measurement of metal emission very difficult

28. Monochromator
Converts a polychromatic light into monochromatic
light.
 It is of two types:
1. Prism : Quartz material is used for making prism, as
quartz is transparent over entire region
2. Grating : it employs a grating which is essentially a
series of parallel straight lines cut into a plane
surface

29. Prism monochromator

30. Grating monochromator

31. Detectors
 Photomultiplier tubes
 Photo emissive cell
 Photo voltaic cell

32. Flame Photometric detector

33. Photovoltaic cell
• It has a thin metallic layer coated with silver or gold act
as electrode , also has metal base plate which act as
another electrode
• Two layers are separated by semiconductor layer of
selenium, when light radiation falls on selenium layer.
• This creates potential diff. between the two electrode
and cause flow of current.

34. Read Out Device
 It is capable of displaying the absorption spectrum as well
absorbance at specific wavelength
 Nowadays the instruments have microprocessor
controlled electronics that provides outputs compatible
with the printers and computers thereby minimising the
possibility of operator error in transferring data.

35. Applications
 Qualitative application:
• used for the determination of alkali and the alkaline
earth metals
• elements can be detected visually by the colour in the
flame, e.g. sodium produces yellow flame

36. • In this flame photometer with a filter or
monochromator of separate radiation with the
wavelength characteristic of the different metals are
used . If the radiation of the characteristic wavelength
is detected, it will indicate the presence of the metal in
the sample.

37.  The table below gives details of the measurable atomic
flame emissions of the alkali and alkaline earth metals
in terms of the emission wavelength and the colour
produced.
Elements Emission
Wavelength(nm)
Flame Colour
Sodium(Na) 589 Yellow
Potassium(k) 766 Violet
Barium(Ba) 544 Lime green
Calcium(Ca) 422 Orange
Lithium(li) 670 Red

38. Quantitative application
 It is done by determining the concentration of various
alkali and alkaline earth metals
 It is done by two methods:
I. Standard addition method
II. Internal standard method

39. Elements, their characteristic emission
wavelengths and detection
limits
Element wavelengt
h
Detection
limit
Element wavelengt
h
Detection
limit
Al 396 0.5 Pb 406 14
Ba 455 3 Li 461 0.067
Ca 423 0.07 Mg 285 1
Cu 325 0.6 Ni 355 1.6
Fe 372 2.5 Hg 254 2.5

40. Other applications
 Useful in determination of Na , K , Al, Ca , B:
• In biological fluids and tissues
• In soil analysis
 Used for natural and industrial waters, glass , cement ,
petroleum products.

41. INTERFERENCES IN QUANTITATIVE
DETERMINATIONS
 The interferences encountered can be classified as
follows.
• Spectral interferences
• Ionised interferences
• Chemical interferences

42. Spectral interferences
 The first type of interference arises when two
elements exhibit spectra, which partially overlap, and
both emit radiation at some particular wavelength.
eg. - the Fe line at 324.73 nm overlaps
with the Cu line at 324.75 nm.
• It can overcome either by taking measurements at an
alternative wavelength which has no overlap, if
available, or by removing the interfering element by
extraction.

43.  The second type of spectral interference deals with
spectral lines of two or more elements which are close
but their spectra do not overlap.
• It can be reduced by increasing the resolution of the
spectral isolation system.
 A third type of spectral interference occurs due to the
presence of continuous background which arises due
to high concentration of salts in the sample, especially
of alkali and alkaline earth metals
• This type of interference can be corrected by using
suitable scanning technique.

44. Ionisation interferences
 high temperature flame may cause ionisation of some
of the metal atoms, e.g. sodium
Na Na+ + e_
The Na+ ion possesses an emission spectrum of its
own with frequencies, which are different from those
of atomic spectrum of the Na atom.

45. • The addition of potassium salt suppresses the
ionisation of sodium, as the potassium atom itself
undergoes ionisation due to low ionisation energy.
Chemical Interferences:
 The chemical interferences arise out of the reaction
between different interferents and the analyte . These
are of different types:

46. Cation-anion interference
• The presence of certain anions, such as oxalate,
phosphate, sulphate , in a solution may affect the
intensity of radiation emitted by an element, resulting
in serious analytical error.
• For example, calcium in the presence of phosphate ion
forms a stable substance, as Ca3(PO4)2 which does not
decompose easily, resulting in the production of lesser
atoms.

47. Cation-cation interferences
• Due to mutual interferences of cations
• These interferences are neither spectral nor ionic in
nature
• Eg. aluminum interferes with calcium and magnesium.
Interference due to oxide formation:
It arises due to the formation of stable metal oxide if
oxygen is present in the flame

48. Limitations
 The temperature is not high enough to excite
transition metals, therefore the method is selective
towards detection of alkali and alkaline earth metals.
 The relatively low energy available from the flame
leads to relatively low intensity of the radiation from
the metal atoms.
 The low temperature renders to interference and the
stability of the flame and aspiration conditions.
 Interference by other elements is not easy to be
eliminated.

49. New technology in flame
photometry
BWB XP Flame Photometer
It is the first and only 5 channel
flame photometer
 Simultaneous detection and
display of all 5 elements like
potassium (K), Sodium (Na),
Lithium (Li), Calcium (Ca) and
Barium (Ba).
 A high quality and high
performance flame photometer,
which improve both accuracy and
stability while significantly
reducing analysis time.