FLAME EMISSION SPECTROMETRY

Principle M.Shalini

Dept of ChemicalAdhiyamaan college of Engg,hosur

Relationship Between Atomic Absorption and Flame Emission Spectroscopy

•Flame Emission -> it measures the radiation emitted by the excited atoms that is related to concentration.

• Atomic Absorption -> it measures the radiation absorbed by the unexcited atoms that are determined.

Atomic absorption depends only upon the number of unexcited atoms, the absorption intensity is not directly affected by the temperature of the flame.

The flame emission intensity in contrast, being dependent upon the number of excited atoms, is greatly influenced by temperature variations.

COMPARISON OF FES AND AAS1.FES is better for determinations of alkali, alkaline-earth and rare earth elements as well as Ga, In and Ti.

2.Flame AAS permits Ag,Al,Au,Cd,Cu,Hg,Pg,Te,Sb,Se and Sn to be detected with high sensitivity.

3.FES permits quantitative multi-element analysis.

4.Flame noise is greater in FES than AAS.

INSTRUMENTATION FOR FLAME

EMISSION EPECTROMETRI

C METHODS:

THE BASIC COMPONENTS ARE

PRETREATMENT OF SAMPLE BOTH FLAME AAS AND FES REQUIRES THE SAMPLE( ANALYTE) TO BE DISSOLVED IN SOLVENT TO UNDERGO NEBULIZATION. THE ANALYST MUST BE CAREFUL TO CHOOSE THE SOLVENT WHICH HAS LESS INTERFERENCE PROBLEMS.

SAMPLE DELIVERYTHE MOST POPULAR SAMPLING METHOD IS THE NEBULIZATION OF THE LIQUID SAMPLE TO PROVIDE A STEADY FLOW OF AEROSOL INTO FLAME.FOR LIQUID SAMPLES:3 COMPONENTS(1). A NEBULIZER(2). AN AEROSOL MODIFIER(3). THE FLAME OR ATOMIZER

NEBULIZATION- Pneumatic nebulizer

THE ABOVE PNEUMATIC NEBULIZER FUNCTION AS FOLLOWS:•THE SAMPLE AND THE NEBULIZING GAS MEETS AT RIGHT ANGLE AND CONVERTED INTO AEROSOL•THE AEROSOL THEN STRIKES AN IMPACT BEAD ( NOT SHOWN) WHICH SEPERATES THE AEROSOL INTO SIZE•THE SMALLER SIZE DROPS ENTER THE FLAME•THE LARGER DROPS ARE DRAINED

Pneumatic nebulizer

In the above nebulizer• THE SAMPLE IS SUCKED IN THROUGH THE CAPILLARY BY THE FLOW OF NEBULIZING GAS ( HERE ARGON)•THE AEROSOL GENERATED IN THE SPRAY CHAMBER IS SEPERATED INTO SIZE.•THE SMALLER DROPS ARE CARRIED TO THE FLAME AND THE LARGER DROPS ARE DRAINED

ATOMIZATIONFLAME ATOMIZERS

The Functions of Flame

1. To convert the constituents of liquid sample into the vapor state.

2. To decompose the constituents into atoms or simple molecules:

M+ + e- (from flame) -> M + hn

3. To electronically excite a fraction of the resulting atomic or molecular species

M -> M*

FLAMES ARE NOT UNIFORM IN COMPOSITION, LENGTH AND CROSS-SECTION. THE STRUCTURE OF A PREMIXED FLAME , SUPPORTED ON A LAMINAR FLOW BURNER IS SHOWN ABOVE.

THE CONCENTRATION OF UNEXCITED AND EXCITED ATOMS IS DETERMINED BY FUEL/OXIDANT RATIO

IN FES, THE ACETYLENE/AIR IS USED PRACTICALLY FOR ALL PURPOSES IN DETERMINING THE AMOUNTS OF ALKALI METAL ELEMENTS.THE HOTTER FLAMES PROVIDE HIGH SENSITIVITY.SHIELDING A FLAME WITH A SHEATH OF INERT GAS, BLOWN AROUND OUTSIDE OF THE FLAME , CAUSES AN ELONGATION OF THE INTERCONAL ZONE THUS REDUCING FLAME NOISE.

Other Applications

The flame photometer is especially useful in the determination of an alkali and similar metals because of the scarcity of other good quantitative methods for these substances. Suggested applications are in the study of the co-precipitation of sodium ion with colloidal ferric hydroxide (other precipitates or ions might also be used), in the study of equilibrium constants involving ion-exchange resins, in the determination of lithium in the presence of magnesium or other alkaline earth or alkali elements, in the determination of Ca(II) and Mg(II) in cement, and in the analysis of a high-detergency motor oil for barium.