1. hn1 hn2 optical l selector source sample detector signal processor
Instrument components: UV-VIS
hn1
hn2
optical
source
l selector
sample
detector
signal
processor

2. a liquid sample is usually contained
Instrument components: UV-VIS
sample containers
a liquid sample is usually contained
in a cell called a cuvet that has a
flat
material
fused silica
glass  only Vis
quartz

3. Common cuvets for visible and ultraviolet spectroscopy.
Instrument components: UV-VIS
Common cuvets for visible and ultraviolet spectroscopy.

4. Wavelength selectors 1. Filter 1.1 Absorption filter
Instrument components: UV-VIS
Wavelength selectors
1. Filter
1.1 Absorption filter
1.2 Interference filter
2. Monochromators

5. “a wavelength selector that uses either
Instrument components: UV-VIS
Filter
“a wavelength selector that uses either
absorption, or constructive and destructive
interference to control range of selected
wavelengths”
the simplest method for isolating a
narrow band of radiation

6. work by selectively absorbing radiation from a narrow region
Instrument components: UV-VIS
Absorption filters
work by selectively absorbing radiation
from a narrow region
Interference filters
use constructive and destructive
interference to isolate a narrow range
of wavelengths

7. effective bandwidths, range 30-250 nm
Instrument components: UV-VIS
Absorption filter
coloured glass
effective bandwidths, range nm

8. Colour of visible light
Instrument components: UV-VIS
Colour of visible light
Wavelength of maximum
Absorption (nm)
Colour
absorbed
Colour
observed
violet green-yellow
violet-blue yellow
blue orange
green purple
yellow-green violet
yellow violet-blue
orange blue
red blue-green
purple green

9. Instrument components: UV-VIS

10. Two filters can produce narrower band.

11. Interference filters
consist of a transparent dielectric
(CaF2 or MgF2 that occupies the space
between two semitransparent metallic films

12. Monochromators: components
entrance slit
lens or mirror to produce a parallel beam
dispersion elements (prism or grating)
to disperse the radiation into its components
wavelength
focusing lens or mirror
exit slit

14. Prism: (many older instruments)
shaped like a bar with a triangular cross section
disperse incident radiation according to
wavelength (see figure)
the degree to which light is bent depends on
the refractive index of light passing (in a glass
prism) and form glass to air
the refractive index varies with wavelength;
hence different wavelength can be separated

16. Diffraction Grating: (most modern instrument)

17. it is coated with aluminum to make it reflective
on top of the aluminum is a thin protective layer
of silica (SiO2) to prevent the metal surface from
oxidizing, which would reduce its reflectivity
when the light is reflected from the grating, each
groove behaves as a source of radiation
when adjacent light rays are in phase, they
reinforce one another
when they are not in phase, they partially or
completely cancel one another

19. Path of light
diffracted by
a grating

20. Resolution required to separate two lines of different wavelength
the ability to disperse radiation is called
resolving power
Ex:
In order to observe an absorption band at nm
without interference from an absorption band at
600.1 nm, we must be able to resolve, or separate,
the two bands.  resolving power (R) =?

22. R = nN Resolution of grating
The resolving power of a grating is given by
R = nN
where
n = the order
N = the total number of grooves in the
grating

23. Ex:
Suppose that we can obtain a grating with 500
line/cm. How large a grating would be required
to separate the sodium D line at and 589.0
nm in first order?

24. But the grating contains 500 lines/cm
Soln.
R = nN ; n = 1
R = N =
But the grating contains 500 lines/cm
Thus, long of grating = /500 = cm

25. Ex:
How many lines per centimeter must be cut on
a grating 3 cm long to resolve the same sodium
D lines?
The required resolution is
nN =
If n = 1, N = lines
Thus, N/cm = /3 = = 393 lines/cm
or 1179 lines on the entire grating

26. Detectors (UV-VIS) (lecture notes)
Photo cell

27. Photomultiplier tube

28. Photodiode
Array
(PDA)

29. Spectrophotometers