UV-VIS SPECTROPHOTOMETRY Flashcards
• Technique used to measure the absorption of ultraviolet and visible light by molecules in a sample
• it provides information about the concentration and structure of molecules based on their absorbance characteristics in the uv invisible regions of the electromagnetic spectrum
UV-Vis spectrophotometry
Basic principle:
____ and ____ comprise only a small part of the electromagnetic spectrum which includes such other forms of radiation as a radio, infrared, cosmic, and x-rays
Ultraviolet and visible radiation
The energy associated with electromagnetic radiation is defined by the equation of:
e = hv, where
e - energy in joules
h- plank constant (6.62 x 10 ^ -34) joul-hertz or joule-second
v- is frequency in seconds
Ultraviolet and visible radiation compromise only a small part of the electromagnetic spectrum which includes such other forms of radiation as radio, infrared, cosmic, and x-rays
THE ELECTROMAGNETIC SPECTRUM
Electromagnetic radiation can be considered as a combination of alternating electric and magnetic fields that travel through space with a wave motion because radiation acts as a wave it can be classified in terms of either ____ or ___
Wavelength or frequency
Wavelength and frequency are related by the equation:
v = c/λ, where
v - frequency in seconds
c - the speed of light (3 * 10 ^ 8 ms-1)
λ- wavelength in meters
Electromagnetic radiation can be considered a combination of alternating electric and magnetic fields that travel through space in a wave motion.
Wavelength and frequency
In general when measuring uv visible spectra we want only ___ to occur. Because light is a form of energy absorption of light by matter causes the energy content of the molecules to ___
Absorbance
Increase
When light passes through or is reflected from a sample the amount of light absorbed is the difference between the ___ __ and ___ ___
incident radiation (Io) and the transmitted radiation (I)
Transmittance equation
T=I/Io or T=I/Io x 100
Absorbance equation
A=-logT
Many spectrophotometers depending on the wavelength setting alternate between a halogen lamp for visible range and the deuterium lamp for the ultraviolet region
Light source
Light source:
Many spectrophotometers depending on the wavelength setting alternate between a ____ lamp for visible range and the ___ lamp for the ultraviolet region
halogen
deuterium
A device that disperses monochromatic from polychromatic light
Monochromator
Monochromator is a device that disperses ___ from ____ light
monochromatic
polychromatic
is the process of breaking down light into its constituent wavelengths in a manner similar to rainbow
Dispersion
Tool used to separate the spectral lines
Diffraction grating
Quartz __ are frequently used for ultraviolet measurement since many plastics and glass absorb uv light and cause interference
Cuvette (sample holder)
The incoming light is transformed by ___ into a measurable electrical current
Detector
General components
Light source
Monochromator
Cuvette
Detector
Journal article
Determination of sun protection factor by uv-vis spectrophotometry
Objective of the study
To determine the real spf value of the chemical or physical sunscreen through uv visible spectroscopy
• Quartz is highly ____ to UV light, meaning it does not absorb UV wavelengths.
• This property allows the UV light to pass through the quartz cuvette without significant attenuation or interference
Transparent
polychromatic light contains ___ wavelengths (colors) of light.
Multiple
Inside the monochromator, there is a dispersive element, such as a:
prism
diffraction grating
separates the different wavelengths of light based on their different angles of refraction
Prism
separates the different wavelengths of light based on their different angles of diffraction
diffraction grating
After the light is dispersed, it passes through an ____ ___. By moving the slit, the monochromator can isolate a specific wavelength of light, effectively selecting a narrow band of wavelengths (monochromatic light) from the dispersed spectrum.
Adjustable slit
• the initial amount of light that strikes the sample.
• It represents the intensity of the light source before any interaction with the sample occurs.
Incident Radiation (I₀)
• the amount of light that passes through the sample and emerges on the other side.
• It represents the intensity of light that is not absorbed by the sample.
Transmitted Radiation (I)
