Electromagnetic Radiation Flashcards
The principles that govern the analytic techniques and instrumentations in the lab fall into four basic areas:
Spectrophotometry
Luminescence
Chromatography
Electroanalytic Methods
a particle of electromagnetic radiation is known as
photon
is described as photons of energy traveling in waves
Electromagnetic radiation
Electromagnetic radiation is spread in the form of
electromagnetic waves
Electromagnetic radiation energy comes from the
SUN
The sun gets its energy from the process called______.
Nuclear Fusion
Distance between identical points on consecutive waves
Wavelength
Distance between origin and crest (or trough)
Amplitude
Number of waves that pass a point per unit time
Frequency
Speed
Formula
= wavelength x frequency
Wavelength is______ proportional to the frequency of the light wave
inversely
Energy is_____ proportional to the wavelength of light
inversely
T or F
The closer the two peaks are, the shorter the wavelength.
The shorter the wavelength, the larger number of photons will be contained in a given distance.
TRUE
More photons represents more energy, hence,_____ wavelengths represent____ energy
shorter
higher
: is a wave of alternating electric and magnetic fields
Light
Light: is a wave of alternating ______ and ______
electric and magnetic fields
2 types of light
Visible
Invisible
Invisible light
UV
Ifrared
- wavelength falls below the visible region (190-340 nm)
Ultraviolet
Ultraviolet nm
(190-340 nm)
Infrared, Microwaves, Radio Waves nm
More than 700
Visible light Wavelength falls within
340-700 nm
■ also called as “transmitted light”
■ the one that our eyes can see
Reflected light
White light
■ also called as “________light”
polychromatic
■ composed of all the visible colors
■ made up of all colors of the rainbow because it contains all wavelengths
■ Ex: Ray of the sun
White light
■ Produces only one color
■ Ex: Laser
Monochromatic
What is the color absorbed and the color emitted
Wavelength (nm) - 350-400
Violet
Yellow
What is the color absorbed and the color emitted
Wavelength (nm) - 400-450
Indigo
Yellow
What is the color absorbed and the color emitted
Wavelength (nm) - 450-500
Blue
Orange
What is the color absorbed and the color emitted
Wavelength (nm) - 500-550
Green
Red
What is the color absorbed and the color emitted
Wavelength (nm) - 550-600
Yellow
Indigo
What is the color absorbed and the color emitted
Wavelength (nm) - 600-650
Orange
Blue
What is the color absorbed and the color emitted
Wavelength (nm) - 650-700
Red
Green
In spectrophotometry, what we’re after is not the light that is_____ by the solution, but the light that is_____ by the solution
reflected
absorbed
If the solution is red, the wavelength that is being absorbed is ______
green
A hemolyzed (red) solution containing hemoglobin will absorb
green light at 540 nm
● States that “ The concentration of a substance directly proportional to the amount of light absorbed and inversely proportional to the logarithm of the light transmitted”.
BEER-LAMBERT’S LAW
The relative amount of light passing through the sample is known as_______
Transmittance (T)
Percent Transmittance (%T)
T
—- x 100
I
○ also called as “Optical Density”
Absorbance (A)
is the measurement of the light transmitted by a solution to determine the concentration of the light-absorbing substance in the solution
Spectrophotometry
Internal components of Spectrophotometer
- Light source
- Entrance slit
- Monochromator
- Exit slit
- Cuvette
- Photodetector
○ “Exciter lamp”
○ Provide the electromagnetic radiation as visible infrared or ultraviolet light
○ Provides energy that the sample will modify by absorption
Light source
Types of light sources
■ Tungsten/Tungsten-iodide lamp or Halogen Quartz lamp
■ Mercury Vapor Lamp
■ Deuterium Discharge Lamp
■ Infrared Energy Source
most common light source at visible, near UV and near IR
Incandescent tungsten/
Tungsten-iodide lamp or Halogen
Quartz lamp
Fluorometry
Mercury/ hydrogen lamp/
Xenon arc
AAS (Atomic absorption spectrophotometry)
Hollow cathode lamp
UV range; continuous light emission down to 165nm
Deuterium
Infrared light
Merst Glower
Globar
uses an electrically heated rod of rare earth element oxides
Merst glower
uses silicon carbide heated to 1200 degrees Celsius
Globar
○ Reduce stray light
○ Prevents scattered light from entering the monochromator
Entrance Slit
the____ light is allowed to pass through the analytical cell, it would cause a deviation from the readings
stray
○ Device that produces light of specific wavelengths from a light source
Monochromator
▪ light radiation of a single wavelength
Monochromatic light
• defines the range of wavelengths transmitted
• Determines the efficiency of monochromator
BANDPASS
Generally, the narrow range of wavelength is the most desirable
Prisms & gratings = <5 nm
Interference filters = 10-20 nm
Bandpass
Types of monochromator
- Prism
- Diffraction Gratings
- Interference Filters
Wedge-shaped piece of (3) or some other material that allows transmission of light
Prism
glass, quartz, or sodium chloride
Prism is based on_____ of light
refraction
§ aluminized surfaces that has been cut into tiny grooves that can act as a prism and a slit
Diffraction Grating
Diffraction Grating
Based on the principle that_____ bend as they pass a sharp corner.
The degree of bending depends on the______
wavelengths
§ based on the principle of constructive interference of waves
§ Only light with desired wavelength which is reflected twice will be in phase and come out of the filter
Interference Filter
It is constructed by using two parallel glass plates, which are silvered internally and separated by thin film of dielectric material (CaF2 , SiO, MgF2 ) of different refractive index
Interference Filter
○ Exclusion of unwanted light from entering the monochromator
Entrance Slit
○ allows only a narrow beam of the spectrum to pass through the cuvette
○ narrows down the light coming from the monochromator
○ Entering to the cuvette
Exit Slit
● Analytical cell/sample holder
● Used to hold the solution in the instrument whose concentration is to be measured
● Made of material that does not absorb light in the wavelength range of interest
CUVETTE
Types of cuvettes
Borosilicate
Quartz/ plastic
Alumina silica
Soft glass
For alkaline solutions cuvette
Borosilicate glass
For wavelength below 320 nm cuvette
Quarts or plastic
Good at visible regions cuvette
Alumina Silica Glass
Preferable for acidic solutions cuvette
Soft Glass
● Converts transmitted light energy into an equivalent amount of electrical energy
PHOTODETECTORS
Types of Photodetectors
- Barrier-Layer cell
- Photoemissive/phototube
- Photomultiplier
○ Photocell or Photovoltaic
○ composed of light-sensitive materials (e.g. selenium on iron plate with transparent layer of silver)
Barrier-Layer cell
○ when exposed to light, electrons in the light-sensitive material are excited and are released into the highly conductive silver
○ LEAST EXPENSIVE
○ NO NEED FOR POWER SOURCE
Barrier-Layer cell
○ Similar to barrier-layer cell that it has photosensitive material that gives of electrons when light energy strikes it
○ Composed of positively charged anode and negatively charged cathode enclosed in a glass
Photoemissive/ Phototube
○ Light strikes cathode → cathode emits electrons → electrons accelerate towards anode
○ Flow of electrons = current = no. of photons
○ Requires an external source of energy
Photoemissive/ Phototube
○ Once light strikes the coated electron, electrons are emitted.
○ The electrons are attached to a series of anodes known as_____
Photomultiplier (PM) tube
dynodes
The_____ tube can amplify the amount of light energy therefore it can measure even the very low light waves
Photomultiplier
○ displays the amount of light transmitted
Read-Out device
Read-out devices
- Meter
- Digital
- Recorder
