Flame Emission Spectroscopy : FES
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1. Optimization of fuel-air ratio for sodium determination by Flame
2. Investigation of some factors affecting accuracy of sodium
3. Analysis of sodium in sample
Atomic emission spectroscopy (AES) employing flames, also called flame
emission spectroscopy (FES) or flame photometry has found widespread
application in elemental analysis. Its most important uses have been in
the determination of sodium, potassium, lithium and calcium,
particularly in biological fluids and tissues. For reasons of
convenience, speed, and relative freedom from interferences, flame
emission spectroscopy has become the method of choice for these
otherwise difficult to determine elements. The method has also been
applied, with varying degree of success, to determine of perhaps half
the elements in the periodic table.
Flame photometry is an analytical technique based on the spectrum of an
element when a solution containing it is aspirated into a flame (e.g.
propane/air, acetylene/air) which is hot enough to cause the element to
emit its characteristic radiation. The spectrum is normally relatively
simple, consisting of only a few lines, and measurement of the
intensity of one or more of these provides a highly sensitive measure
of the concentration in the sample. When several elements are present,
the required sprectral line is isolated either by passing the light
from the flame into the entrance slit of a monochromator by means of a
lens or mirror or by a system of optical filters. The intensity of the
isolated radiation is measured by a photosensitive detector coupled to
an amplifier and recorder.
In the analysis of sodium and potassium in the presence of calcium,
some interference by the latter due to spectral overlap occurs. The
addition of a sufficient quantity of aluminium ions to the analyte
solution tends to reduce the emission due to calcium and hence minimize
Potassium determination by flame emission is affected mainly by
ionization of potassium at the high temperatures associated with
air/acetylene or hotter flames, especially at low concentrations of the
elements. This effect is however, neglible for the air/propane flame as
used by the flame analyser in this experiment. Therefore, addition of
radiation buffers is not required.
A. Optimization of the fuel/air flow rate for determination of
(1) Prepare a calibration series containing 1.25, 2.5, 5.0, and 10 ppm
sodium in deionized distilled water (50 mls each) from the 50 ppm standard stock
sodium solution provided.
(3) Set the sodium filter in position before the photocell and set the
air pressure to the burner as recommended (~20 psi)
(4) Depress ignition switch to light the flame and slowly and slowly
increase the fuel flow rate. Once the flame is lit, observe the flame,
and carefully adjust the fuel flow rate until a non-luminous flame is
obtained. Allow the temperature to equilibrate for about 3-5
(5) Aspirate the 2.5 ppm sodium standard and adjust the sensitivity
knob to obtain about an emission reading of about 0.3. Re-zero the
instrument while aspirating deionized distilled water
(6) Aspirate again the 2.5 ppm solution, and carefully change the fuel
flow rate until a maximum signal is obtained, but avoid using a
(7) Re-zero with deionized distilled water again. The instrument is now ready for
B. The effect of aspiration rate on sensitivity of detection of
(1) Into each of four 25 ml volumetric flasks, pipette the required
volume of standard 100 ppm sodium standard to give a final
concentration 2.5 ppm. Add to the flasks 2.5, 5.0, 7.5, and 10.0 mls
respectively of methanol and make up to the mark with deionized
(2) Aspirate the 2.5 ppm sodium made up in distilled water only and
note the emission reading.
(3) Using deionised distilled water, zero the instrument and then
determine the emission of the distilled water standards.
(4) Aspirate the methanol samples in order of increasing methanol
content, and note the corresponding readings.
(5) Plot emission vs methanol (0-40%) content of the solution.
What precautions should be taken when determining sodium in alcoholic
C. Interference of sodium emission by calcium and the countering
effect of aluminium
(1) Into five 25 ml volumetric flasks, add the required volume of the
100 ppm sodium standard stock solution that will give respective final
concentration values of 1.25, 2.5, 5.0, and 10 ppm. To each flask add
10 ml of the 1000 ppm calcium standard stock solution provided and make
up to the mark with deionized distilled water.
(2) Prepare a blank solution containing 10 ml of the 1000 ppm calcium
stock solution in 25 ml volume solution.
(3) Into five other 25 ml volumetric flasks, add similar quantities of
sodium and calcium solutions. Then add to each 5 ml of the aluminium
solution provided and make uo to the mark with distilled water.
(4) Prepare a blank containing 10 ml 1000 ppm calcium standard stock
solution and 5 ml of the aluminium solution in 25 ml volume
(5) Aspirate the standard solutions in distilled water, with distilled
water as blank, then the sodium-calcium solutions, and then the
sodiun-calcium-aluminium solutions, and note the emission/sodium
(6) Note and comment on the change of color of the flame.
(7) Aspirate the respective blanks and subtract their emission values
from the sample solution values to provide blank-corrected emission
(8) Plot corrected emission values vs sodium concentration of each set
of solutions on the same sheet of graph paper, or using a
Comment on coincidence of the calibration curves, and
the effectiveness of the Al+3 in suppressing Ca+2
D. Analysis of sodium in sample
(1) Place triplicate, accurately weighed or measured quantities of the
sample provided into separate boiling tubes
(2) To each tube add 5 ml pure nitric acid and allow to predigest for
at least one hour in a fume hood.
(3) Prepare an acid blank simultaneously
(4) Reflux the material gently on dry heating block for one hour in a
fume hood, ensuring that fumes are properly vented.
(5) Cool and dilute with 10 ml distilled water
(6) Filter through a Whatman fifter paper No. 1 into 100 ml volumetric
flasks and rinse the boiling tube and filter paper with 25 ml distilled
(7) To each flask add 10 ml of Aluminium stock solution and make up to the mark with distilled water.
(8) Aspirate your sample solutions along with the solutions of section
D (5) and determine the mean sodium content of the samples.
1. Flame Emission and Atomic Absorption Spectroscopy, Vols 1, 11, 111.
Dean, J.A., Rains,T.C. Eds. Marcel Decker, NY. 1969-75
2. Analyst 77 430-436 (1952)
3. Analyst 82 200 (1957)