INSTRUMENTATION PROPER Flashcards
Measurement of the wavelength and the intensity of electromagnetic radiation in the visible region of the
spectrum.
COLORIMETRY
Used for identification and determination of concentrations of substances that absorb light.
COLORIMETRY
relies on visual acuity to determine end-point
Visual Colorimetry
measurement of light intensity in a much narrower wavelength
SPECTROPHOTOMETRY
Makes use of prisms and/or diffraction gratings as monochromator to disperse the radiant energy into a
continuous spectrum & isolate radiant energy of desired wavelength
SPECTROPHOTOMETRY
Makes use of prisms and/or ___________ as _________ to disperse the ______ into a
continuous spectrum & isolate radiant energy of desired wavelength
diffraction gratings
monochromator
radiant energy
measurements of light intensity of multiple wavelength
FILTER PHOTOMETRY
It makes use of filters (interference or transmission) to isolate part of the spectrum
FILTER PHOTOMETRY
PRINCIPLE of SPECTROPHOTOMETRY (LAW of COLORIMETRY):
______ passes through a __________ to provide a selection of the desired region of the spectrum
to be used for measurements.
Light
Monochromator
PRINCIPLE of SPECTROPHOTOMETRY (LAW of COLORIMETRY):
____ are used to isolate a __________ and to improve its __________.
Slits
narrow beam of light
chromatic purity
The _____next passes through an __________ where a portion of the ________ is absorbed, depending upon the nature and concentration of the solution.
light
absorption cell
radiant energy
Any light not absorbed is transmitted to a _______, which converts the light energy to _________ that can be registered on a _____
detector
electrical energy
meter or a digital read-out.
The concentration of the solution is directly proportional to the amount of light absorbed and inversely proportional to the logarithm of transmitted light
BEER’S LAW
BEER’S LAW
The _______ of the solution is __________ to the amount of __________ and ________proportional to the __________
concentration
directly proportional
light absorbed
inversely
logarithm of transmitted light
ratio of the radiant energy transmitted, divided by the radiant energy incident on the sample
%T
Absorbance is directly proportional to the length of light path
BOUGUER’S LAW or LAMBERT’S LAW
BOUGUER’S LAW or LAMBERT’S LAW:
___________ is _____ proportional to the _________
Absorbance
directly
length of light path
What is Lambert’s Law formula?
A = abc
the concentration of a solution for the known path length is directly proportional to its absorption of light.
BEER- LAMBERT LAW
BEER- LAMBERT LAW
the _______ of a solution for the ________ is ____ proportional to its __________
concentration
known path length
directly
absorption of light.
In the formula of Lambert’s law:
What ‘a’ stands for?
proportionality constant or molar absorptivity or extinction coefficient
In the formula of Lambert’s law:
What ‘b’ stands for?
length of light path in cm
In the formula of Lambert’s law:
What ‘c’ stands for?
molar concentration of absorbing substance
provides a continuous spectrum of white light which can be separated at different wavelengths
LIGHT SOURCE
produces energy wavelength from 340 – 700 nm (visible region); used
for moderately diluted solution
Tungsten Iodide 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 source
an electrically heated rod of rare earth element oxides
Merst glower
uses silicon carbide
Globar
– emits narrow bands of energy at well-defined places in the spectrum
(UV and visible)
Mercury Vapor lamp
consists of a gas-tight chamber containing anode, a cylindrical
cathode, and inert gas such as helium or argon
Hollow Cathode lamp
isolates a narrow beam of radiant energy; prevents stray light from entering the monochromator
ENTRANCE SLIT
wavelength selector; isolates radiant energy of desired wavelength and
excluding that of other wavelengths
MONOCHROMATOR
the range of wavelengths transmitted and is calculated as width at
more than half the maximum transmittance.
Monochromator bandpass
used to hold the solution whose concentration is to be measures
ANALYTICAL / ABSORPTION CELL / CUVETTE
for solutions that do not etch glass
Borosilicate glass
does not absorb UV radiation at wavelength below 320 nm
Quartz or plastic
good for 340 nm and above (visible region)
Alumina silica glass
✓ wedge-shaped pieces of glass, quartz, NaCl, or some other material that allows transmission of light
✓ Disperses white light into a continuous spectrum of colors by refraction
✓ Produces a non-linear spectrum. The longer wavelengths are close to each other and those of shorter
wavelengths are widely spaced.
✓ Glass prisms are for visible region while quartz prisms are for the UV region
Prism
✓ consist of a thin layer of aluminum-copper alloy on the surface of a flat glass plate that has many small
parallel grooves ruled into the metal coating
✓ Rays of radiant energy bend (refract) around the sharp edges of the grooves
✓ Extent of refraction varies with the wavelength
Diffraction Gratings
✓ colored glass or colored gelatin sandwiched between two glass plates
✓ Light outside the transmission band are absorbed by the colored material
✓ Band pass is 35 – 50 nm or more
Transmission Filters
✓ Produce monochromatic light based on the principle of constructive interference of waves.
✓ dielectric material (e.g. NaF) sandwiched between two half-silvered pieces of glass
✓ The thickness of the layer determines the wavelength of energy transmitted.
✓ Band pass is 10 – 20 nm
Interference Filters
measure light intensity by converting light signal into electrical signal
DETECTORS
Composed of a film of light sensitive material (e.g. Selenium) on an iron plate with a transparent layer of silver
Barrier-Layer cell (Photocell or Photovoltaic cell)
Barrier-Layer cell (Photocell or Photovoltaic cell):
When light passing through the _____________ falls upon the Selenium surface, ________
are released in proportion to the intensity of light and are collected to the ______ to produce a
__________
semi-conductive metal layer
electrons
silver layer
negative charge
Has photosensitive material that gives off electrons when light energy strikes it
Photoemissive tube or Phototube
Consists of 2 electrodes (cathode and anode) sealed in an evacuated glass
Photoemissive tube or Phototube
A device whose electrical resistance decreases as the level of incident light is raised
Photoconductive tube or Photoresistive tube
Cadmium sulfide or cadmium selenide are the light-sensitive materials typically used for the
visible region
Photoconductive tube or Photoresistive tube
Does not require an external power source
Photoconductive tube or Photoresistive tube
Capable of significantly amplifying a current
Photomultiplier tube
The cathode is a negative light-sensitive metal that absorbs light and emits electrons in
proportion to the radiant energy that strikes the surface
Photomultiplier tube
- Electrons go to the dynodes, where electrons produce 4 – 6 additional electrons
- The electrons are collected at a final electrode, the positive anode
Photomultiplier tube
