Instrumental Analytical Methods Lab Report 2013 Anastazija Ristovska Ristovska Experiment 1 Flame Photometric Analysis
The purpose of this experiment was to determine the concentrations of sodium and potassium ions in solution through flame-photometric analysis. When excited in flame i.e. at the high temperature of the flame, potassium and sodium elements emit light at a few characteristic and specific wavelengths unique for these two elements. The intensity of the light emitted, i.e. the number of photons emitted by each element at the particular wavelength is the basis for determining the concentration of potassium and sodium in solution. As the name of the technique suggests, flame photometric analysis counts the number of photons emitted per unit time and at one particular wavelength from the flame in which a solution containing potassium and sodium ions is dispersed in aerosol spray form. The instrument does this by utilizing photon-sensors and photomultipliers. This simple concept is the basis for designing complex instruments that function on the same photometric idea such as atomic emission spectroscopy.
sodium
potassium
Flame photometer reading (FLM)
Sodium concentration (µg/ml)
Flame photometer reading (FLM)
Potassium concentration (µg/ml)
76,9
20
78,8
20
61,7
16
81,7
16
45
12
69,2
12
35
8
43,2
8
21,8
4
25,5
4
We were given given 6 solutions of unknown unknown concentration, concentration, and, using the linear fit for the FLM readings of the solutions of known concentration, we were supposed to find, or calculate to best approximation, the concentration of sodium and potassium of these 6 solutions. The first solution contained contained sodium only. It had a reading of 23.9 FLM. Using Using the equation of the first plot y=0,2901x-1,9504, y=0,2901x-1,9504, where y is the solution concentration and x is the FLM reading, [Na+ ] in this solution was calculated to be 4,983 µg/ml, or almost 5 µg/ml. The fifth solution solution contained potassium potassium only. The flame-photometer flame-photometer reading of of it was 25.1 FLM. FLM. Using the equation of the second plot, y = 0,2438x - 2,5481, where y is the solution concentration and x is the FLM reading, [K + ] in this solution was found to be 3,571 µg/ml, or almost 3,6 µg/ml.
1
The composition and reading of all solutions, solutions, and their calculated calculated concentrations concentrations are given in this table: # Composition
Na+ FML Reading
K + FLM Reading
µg/ml) [Na+ ] ( µg/ml)
µg/ml) [K + ] ( µg/ml)
µg/ml) Approx. ( µg/ml)
1
Na+
23.9
n/a
4,983
n/a
[Na + ]=5
2
Na+ + K +
31.4
27.8
7.159
4.230
[Na+ ]=7, [K + ]=4
3
Na+ + K +
24.8
47.1
5.244
8.935
[Na + ]=5, [K + ]=9
4
Na+ + K +
27.1
38.2
5.911
6.765
[Na + ]=6, [K + ]=7
5
K +
n/a
25.1
n/a
3,571
[K + ]=3.5
6
K +
n/a
33.0
n/a
5.497
[K + ]=5.5
We were able to determine the concentration concentration of sodium sodium and potassium in in a mixture with a high high enough precision and accuracy as if they were not in a mixture but in two separate solutions by themselves. We did not use a blind sample in this experiment. experiment. Blind samples samples are often used used to control for the quality of emission analysis. In our experiment we only wanted to determine the concentration of samples with known composition composition and identity. identity. The purpose of of a blind sample is to to determine the identity identity of the solutes through emission analysis. Even though though it is possible to do this for alkaline metals as they give of characteristic emission colors in the flame-photometer, yellow for sodium and purple for potassium, it would had been hard to to determine with accuracy accuracy what the elements elements are in a mixture mixture of sodium and potassium where the colors were blurred. Although originally an old technique for qualitative identification of select metallic elements, we did not use blind samples with flame-photomet flame- photometry ry in our experiment. The instrument displayed greater sensitivity in measuring measuring the concentration concentration of sodium sodium than that of potassium. In the case of potassium the model we obtained explained for 88.4% of the variance in the system, whereas the model for determining sodium concentration through through linear fit explained for 99.3% of the variance in system. Because it was able to more accurately detect and describe the concentration of sodium than that of potassium, we say that the instrument was more sensitive in measuring the concentration of sodium.
2
25 y = 0,2901x - 1,9504 R² = 0,993
) l m r 20 e p s m a r g o r 15 c i m ( n o i t a r t 10 n e c n o c m u i 5 d o s
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FLM reading
25 y = 0,2438x - 2,5481 R² = 0,8843
) l m r e 20 p s m a r g o r c i 15 m ( n o i t a r t n e 10 c n o c m u i s s 5 a t o p
Series1 Linear (Series1)
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Axis Title
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