FLAME EMISSION SPECTROSCOPY

Presented by

K.Gopalasatheeskumar

I M.Pharm., Pharmacology

CONTENTS

INTRODUCTION

HISTORY

PRINCIPLE

INSTRUMENTATION

APPLICATIONS

INTERFERENCES

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INTRODUCTION

• Flame emission spectroscopy is so named

because of the use of a flame to provide the

energy of excitation to atoms introduced into

the flame.


HISTORY

Early- detect the presence of metal elements in samples aspirated

into a flame.

Modern analytical FES- Lundegardh- 1934,

(flame- air-acetylene, Prism spectrograph, densitometer for

spectral line )

First "flame photometer" -1945- Barnes.(Na, K detection, Poor

detection of Ca, Mg)-Meeker burner

1948- total-consumption burner.


PRINCIPLE


Desolvation: The metal particles in the flame are dehydrated by theflame and hence the solvent is evaporated

Vapourisation: The metal particles in the sample are dehydrated. Thisalso led to the evaporation of the solvent.

Atomization: Reduction of metal ions in the solvent to metal atoms bythe flame heat.

Excitation: The electrostatic force of attraction between the electronsand nucleus of the atom helps them to absorb a particular amount ofenergy. The atoms then jump to the exited energy state.

Emission process: Since the higher energy state is unstable the atomsjump back to the stable low energy state with the emission of energy inthe form of radiation of characteristic wavelength, which is measuredby the photo detector.


The basic components for flame photometer are as follows

Burner(source)

Atomizer

Monochromators

Detector

Read out device

INSTRUMENTATION


BURNERS

The FLAME used in the flame photometer should possess following

functions:

The flame should have ability to evaporate the liquid droplets from

the sample solution in the formation of solid residue

The flame should decompose the compounds in the solid residue

resulting in the formation of atoms.

The flame must have the capacity to excite the atoms formed and

cause them to emit radiant energy.


FLMES IN FES

Name of the element

Emitted

wavelength range

(nm)

Observed colour of

the flame

Potassium (K) 766 Violet

Lithium (Li) 670 Red

Calcium (Ca) 622 Orange

Sodium (Na) 589 Yellow

Barium (Ba) 554 Lime green


TYPES OF BURNERS

Mecker Burner

Total Consumption Burner

Laminar Flow (premix) Burner

Lundergraph Burner.

Shielded Burner

Nitrous Oxide –Acytelene Flame.


MECKER BURNER

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This burner employed natural gas and

oxygen.

Produces relatively low temp. and

low excitation energies.

This are best used for ALKALI

metals only.

Nowadays it is not used.

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Total consumption burner

In this burner the fuel andoxidant are hydrogen andoxygen gas respectively.

In this the sample solution isaspirated through a capillary bythe high pressure. fuel andoxidant are burnt at the tip ofthe burner.

The name “total consumptionburner” is used because all thesample that enters the capillarywill enter the flame regardlessof the droplet size.


Advantage

Design is simple and entire sample is consumed.

Disadvantage

Uniform and homogeneous flame is not obtained. Since

droplet size vary, leading to fluctuations in the flame

intensity.

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LAMINAR FLOW BURNER


LAMINAR FLOW (PREMIX) BURNER.

In this type of the burner, aspirated sample, fuel and oxidant are

thoroughly mixed before reaching the burner opening and then

entering the flame.

Important feature of this is that only a small portion (about 5%) of the

sample reaches the flame in the form of small droplets and is easily

decompose.

ADVANTAGES:

Premix burner is non-turbulent ,noiseless and stable.

Easy decomposition which leads to high atomization.

Can handle solution up to several % without clogging.

DEMERITS

When it contains 2 solvents, the more vol. will evaporate and lesser

will remain undissociated.


MONOCHROMATORS AND FILTERS

In simple flame photometers, the monochromators is the prism.

QUARTZ is the material most commonly used for making prisms

because quartz is transparent over entire region .

FILTERS: the filter is made up of such material which is

transparent over a narrow spectral range.

When a filter is kept between the flame detector, the radiation of

the desired wavelength from the flame will be entering the

detector and be measured. The remaining undesired wavelength

will be absorbed by the filter and not measured.

In flame photometry, the wavelength as well as intensity of

radiation emitted by the element has to be monitored. Hence a

filter or monochromatore is used.9/22/2017 KMCH College of Pharmacy 16

DETECTORS

Photovoltic cell

Phototubes

photomultiplier tubes.


APPLICATIONS

FES has found wide application in agricultural andenvironmental analysis, industrial analyses of ferrous metals andalloys as well as glasses and ceramic materials, and clinicalanalyses of body fluids.

FES can be easily automated to handle a large number ofsamples. Array detectors interfaced to a microcomputer systempermit simultaneous analyses of several elements in a singlesample

They are also used to determine the metals present in Chemicals,Soil, Cements, Plant materials, Water, Air pollutants andOceanography


INTERFERENCES

Matrix interference

Chemical interference

Ionization interference

Spectral Interferences


Matrix interference

When a sample is more viscous or has different surface tension

than the standard it can result in differences in sample uptake rate

due to changes in nebulization efficiency.

Such interferences are minimized by matching as closely as

possible the matrix composition of standard and sample.


Chemical interference

If a sample contains a species which forms a thermally stable

compound with the analyte that is not completely decomposed by

the energy available in the flame then chemical interference

exists.

Refractory elements (Ti, W, Zr, Mo and Al) may combine with

oxygen to form thermally stable oxides.

Analysis of such elements can be carried out at higher flame

temperatures using nitrous oxide – acetylene flame instead of air-

acetylene to provide higher dissociation energy.

Alternately an excess of another element or compound can be

added e.g. Ca in presence of phosphate produces stable calcium

phosphate which reduces absorption due to Ca ion.

If an excess of lanthanum is added it forms a thermally stable

compound with phosphate and calcium absorption is not affected.


Ionization interference

Ionization interference is more common in hot flames. The

dissociation process does not stop at formation of ground state

atoms.

Excess energy of the flame can lead to excitation of ground state

atoms to ionic state by loss of electrons thereby resulting in

depletion of ground state atoms.

In cooler flames such interference is encountered with easily

ionized elements such as alkali metals and alkaline earths.

Ionisation interference is eliminated by adding an excess of an

element which is easily ionized thereby creating a large number

of free electrons in the flame and suppressing ionization of the

analyte.

Salts of such elements as K, Rb and Cs are commonly used as

ionization suppressants.9/22/2017 KMCH College of Pharmacy 22

FLAME EMISSION SPECTROSCOPY

Education

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