Spectrophotometer Flashcards
measurement of light intensity in a much
narrower wavelength.
Spectrophotometry
It uses a device
(prisms and/or gratings) to disperse the
source of light into a continuous spectrum.
Spectrophotometry
2 Dispersing element or monochromator
prism (triangle) and grating
Basic component device
Light source
Entrance slit
Dispersive elements
Exit slit
Sample
Detector
Basic
Components
Light source
Device to isolate light of a desired wavelength
Cuvet
Photodetector
Read-out device
Data system
Different light sources
Continuum source
Line source
emits radiation that changes in
intensity/ Immites radiation wide source
Continuum source
type of light Source
Tungsten iodine lamp
Quartz halide lamp
Deuterium discharge lamp
Infrared energy source
Most commonly used light source
Tungsten iodine lamp
contains small amounts of
halogen such as iodine to prevent the decomposition
of the vaporized tungsten from the very hot filament.
Quartz halide lamp
provides energy source
with high output in the UV range (down to 165 nm).
Deuterium discharge lamp
used above 800 nm.
Infrared energy lamp
It is a device more sophisticated it isolates the narrow band of wavelengths from visible and ultraviolet sources
Monochromator
monochromator is made up of three parts:
Entrance slit
Dispersive elements
Exit slit
is a small circular or rectangular hole cut in an otherwise opaque plate,
such as a black metal plate.
Slit
is where light enters the monochromator from the source. Its
purpose is to create a unidirectional beam of light of appropriate intensity
from the multidirectional light emanating from the source
Entrance Slit
After passing through the entrance slit, the beam
encounters a ______________
Disperse element
The narrow band of the spectrum is then selected by the ______________
Exit slit
is rotated, the spray of colors moves
across the exit slit such that a different narrow wavelength range
emerges from the exit slit at each position of rotation.
Disperse element
is a three-dimensional triangularly shaped glass or quartz
block. When the light beam strikes one of the three faces of the
prism, the light emerging through another face is dispersed.
Prism
is like a highly polished mirror that has a large
number of precisely parallel lines or grooves scribed onto its
surface. Light striking this surface is reflected, diffracted, and
dispersed into the component wavelengths-
Diffraction grating
Type of Detectors:
Photomultiplier and photodiodes
are
used as detectors in UV-VIS
spectrophotometers
Photomultiplier tubes or
photodiodes (light sensors)
is a light sensor combined with
a signal amplifier. The light emerging from the sample
compartment strikes the photosensitive surface and
the resulting electrical signal is amplified.
Photomultiplier
The photomultiplier tube consists of a
Photocathode, anode, and dynodes
This amplified signal is then sent on to the
readout
Photomultiplier
Photodiodes Utilizes materials such as
Silicon
Silicon can be doped with impurities to make it either electron rich
BORAN n- type semiconductor
electron poor
p-type semiconductor
used for UV-VIS spectrophotometry must be transparent to all wavelengths of
light for which it is use
Cuvette
If visible light is used, the material must ideally be completely clear and colorless, which
means that inexpensive materials, such as
Colorless glass or plastic
For visible light spectrophotometry, the cuvettes must be made of
Colorless glass or plastic
For ultraviolet spectrophotometry, the cuvettes must be made of
Quartz
Warm
Up spectrophotometry
20 mins
is a contaminating
substance that gives an absorbance
signal at the same wavelength or
wavelength range selected for the
analyte.
Interference
- can be high or low because of it
Interference
