5. UV-Vis Spectroscopy5.1 Introduction
Objective
Review basic analytical chemistry skills, including solution making, transferring and linear diluting. Understand the error involved and error propagation.
Materials:
Methylene Blue C16H18ClN3S, MW 319.85.Also called Swiss blue. One gram dissolves in about 1000 ml of water. Peak absorption at 369 nm
5.2 Create Calibration Curve from standard solutions
Procedures:
solution
Table 5-1 Preparation of standard solutions
PPM |
STD |
||
Stock |
DI water |
Total Volume |
|
20 |
0.2 |
9.8 |
10ml |
50 |
0.5 |
9.5 |
10ml |
100 |
1 |
9 |
10ml |
200 |
2 |
8 |
10ml |
500 |
5 |
5 |
10ml |
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PPM |
Wavelength |
Absorbance |
||
1 |
2 |
Average |
||
20 |
||||
50 |
||||
100 |
||||
200 |
||||
500 |
1 0.8 0.6 0.4 0.2 0
UV/VIS
0 50 100 150 200 250 300 350 400 450 500
Concentration (ppm)
Figure 5-1 Calibration curve from standard solutions
5.3 Two steps of a serial dilution and measure the concentrations of unknown samples
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Absorbance
Figure 5-2 Serial Dilution of unknown samples Table 5-3 Absorbance of unknown samples
Instrument Use
Serial Dilution |
Absorbance |
Wavelength |
||
1 |
1/10 |
1/100 |
||
Sample 1 |
||||
Sample 2 |
||||
Sample 3 |
a.
b.
Choose Abs (absorbance).
Replicate is 2on ‘Standard’.
unit : mg/L
number of standard and concentration of standard solutionon ‘Sample’ and enter sample number
‘OK’
on Zero icon after insert Blank cuvette into UV slot.
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Lab report requirement
o Calculate solution concentration by ppm for all solutions
o Discuss source of data errors
o How do you improve your skill to get better accuracy and precision of solution makingo Describe the key steps of the experiment
o Attach all the original data and spectrum
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