Transcript Flam photometry

ATOMIC SPECRTOSCOPY
Atomic spectroscopy
 It’s a class of spectroscopic method in which
the species examined in the spectrometer are
in the form of atoms.
Flame
spectroscopy
Atomic absorption
spectrophotometry
Flame emission
spectroscopy
Flam emission
Atomic absorption
phenomenon
emission
absorption
Source of excitation
flame
Hallow cathode lamp
Role of flame
1-Evaporation.
2-Atomisation.
3-Excitation.
4-Emission of radiation
1-evaporation.
.2-atomisation.
No. of determined
elements
Alkali and alkali earth
Metal (Na,K,Li)
All elements
Flame emission
Definition:
 determination of the concentration of an
element by measurement of light emitted
when the element is excited by energy in the
form of heat.
Why flame emission is used for
limited no of elements?
 Because most elements except ( Na ,k.Li)
needs high energy for excitation, & in flame
spectroscopy only relatively cool flame are
used(natural gas-air flame 1800-200o c)
applications
 Rapid determination of Na ions in the blood.
 In organic and inorganic analysis of alkali and
alkali earth metals
 Flame emission can be used :
- qualitative and quantitative .
1- qualitative (the substance emitted radiation at
characteristic λ).
2- quantitative depend on the intensity of
emission. Emission concentration .
 .
instrument
 The instrument consist of two parts:
1- burner and atomizer system ( pressure
regulator, flow meter , nebulizer and burner)
2- optical system ( monochromator , detector,
amplifier , recorder, in addition to mirrors )
1-Atomizer and burner:
Atomizer : produce a fine and uniform spray of
the sample solution ( mist)
N .b : only liquid samples are used in this
method.
2- burner:
a- total consumption burner.
b- pre mix chamber burner.
Total consumption burner:
A-Total consumption burner
 The sample is aspirated through a capillary to
the tip of it where its break down into a fine
mist by the stream of the oxidant.
 The mist + fuel & supporting gases are mixed
in the flame .
 It is called total consumption cause the entire
aspirated sample enters the flame.
Premix chamber burner:
 Aspiration of sample in to the nebulizer .
 In the nebulizer the sample is sprayed into very
fine droplet ( mist).
 Large droplet will be drain out
 the fuel and the oxidant are mixed in the mixing
chamber before they enter the flame head
where the combust.
 only fine droplets remains and mixed with the
Gases and enters the flame( 2-10% of the sample
get atomized)
 At the flame evaporation , melting,
atomization and excitation of the atoms
takes place.
 The excited atom emit radiation in which its
intensity α concentration of the determent
elements. The emitted radiation is filtered
→D→R
 Why a mirror is placed behind the flame :
Cause the radiation from the flame is emitted
in different directions & so the mirror will
increase the amount of radiation falling on
the detector.
Determination of Na & K
1- Determination of Na :
Stock = 100 ppm. ( Nacl)
mls
Conc.
% emission
2
cxv = c-xv-
25
4
35
6
60
8
80
10
100
unkown
67
Calibration curve
Determination of K
 Stock 100 ppm
mls
conc
% emission
1
Cxv = c-xv-
11
3
30
5
51
7
72
10
100
unknown
62
Standard addition method
Radiation intensity
Sample alone
5.1
Sample +0.1 ppm
standard Ca
6.2
Sample + 0.2 ppm
standard Ca
7.3
Sample + 0.5 ppm
standard Ca
10.6
Flame alone
0.7
Radiation intensity after
correction
Standard addition curve
%E
c
Atomic absorption
 It is a type of flame spectroscopy in which the
absorption caused by atoms when
introduced into the flame is studied , it is a
method of elemental analysis.
 The process of atomic absorption
spectroscopy (AAS) involves two steps:
 1. Atomization of the sample
 2. The absorption of radiation from a light
source by the free atoms
spectroscopy
Atomic absorption
principle
Molecular absorption
Atomic absorption
Source of light
Tungsten , deuterium
Hallow cathode lamp
Rang of λ
Wide rang
Narrow rang
Absorption spectrum
Broad absorption
spectrum
Line absorption spectrum
Applications
 Poisoning of heavy metals e.g Hg,Pb s of
 Analysis of certain drugs which contains
metal e.g vit B12 .
 In organic chemistry , its used for
determination of all the elements in the
periodic table
instrument
1- hollow cathode lamp.
2- burner ( as in flame emission).
3-optical system
Hollow cathode lamp
 It consists of:
1- a cylindrical metal cathode made of the same
elements to be determined .
2- anode.
3- the lamp is filled with an inert gas ex: Ar or
He.
.
 Why The cathode is hollow ?
to allow the atoms to deposit back on the
cathode , thus increasing the life time of the
lamp
hollow cathode lamp
Steps of atomic absorption:
 The sample is aspirated , aerosolized and mixed
with the combustible gases.
 The role of flame here is atomization.
 When a light beam from a cathode ( which is
made from the same element to be determined )
passes through the flame the free atoms will
absorb it.
 The light passing through the flame is received
by the monochromator , transmitted to the
detector which measures the reduction of the
beam of light as absorbance
Determination of Zn
stock = 10 ppm
Conc. ppm
unknown
by AAS
mls
absorption
4
0.21
5
0.29
7
0.4
10
0.58
12
0.7
0.46