Ultraviolet
Spectroscopy
Purpose: It will be the
purpose of this experiment to investigate the utility of
ultraviolet spectroscopy for qualitative and quantitative
analysis and the effect of instrumental slit width on
spectrophotometric measurements.
References: Skoog, Holler,
Nieman, Principles of Instrumental Analysis; Gillam and Stern, Electronic
Absorption Spectroscopy
Apparatus: Hitachi spectrophotometer,
1 set silica cuvettes with caps
Reagents: 4 standard benzene
solutions in iso-octane covering the range 0.1 to 0.5 g/L, o-xylene, p-xylene,
and m-xylene in iso-octane each at 0.5 g/L
Procedure
- Place one drop of benzene in
a 1 cm cuvette, insert the stopper, and let stand for 10
minutes. Scan versus an empty cuvette from 220 nm to 280
nm with each of the 4 slit settings.
- Scan the 0.5 g/L benzene
solution versus an iso-octane blank from 220 nm to 280 nm
using the 0.2 nm slit setting.
- For each of the benzene
solutions scan only the strongest peak with each of the 4
slit settings.
- Scan each of the xylene
solutions versus the iso-octane blank from 220 nm to 280
nm using the 0.5 nm slit setting.
Results and
Questions
- Describe and explain any
change in the observed spectra with a change in slit
width.
- Account for any change in the
spectrum on going from vapor to solution.
- Using the data of part 3,
plot absorbance versus concentration (g/L) for each of
the slit settings. Label each curve with the spectral
band width of the instrument.
- What is the potential utility
of ultraviolet spectrophotometry for the determination of
percentages of the respective isomers of xylene?