Spectrometry Flashcards
- Meas. light intensity in a much narrower WL using a device (prism/grating) to
disperse the light source into a cont. spectrum
Spectrophotometry
Quantitation of subs of spectrophotometry
meas. amt of light absorbed after appropriate treatment
spectrophotometry advantage
- Therefore, it gives a relatively high sensitivity, greater ease of rapid meas.
compared to visual colorimetry
-High degree of specificity reacts the subs of interest w/ proper rgts = diff colors
(analytical separation prior to color formation rxns)
Filter Photometry
- meas light intensity of multiple WL
- uses filter to isolate part of spectrum
Parts of Spectrophotometer:
Source→(EnS)→monochromator→(ExS)→cuvet→detector→meter/read out device(Galvanometer)
provides radiant energy to monochromator—separates into discrete WL
Light Source
is a form of electromagnetic energy Transmitted via electromagnetic waves Characterized by frequency and wavelength
Light
is the distance of 2 successive waves (nanometers). Waves are measured by nanometers (wavelength).
Wavelength
is number of vibrations of wave motions per second;
Frequency
Wavelength is _______ proportional to the frequency and energy.
inversely
Shorterwavelength,
↑Freq,↑Energy
LongerWavelength
↓Freq,↓Energy
Visible spectrum – wavelength
400-700 nm
Invisible spectrum ranges below 400 nm
UV Region
Invisible spectrum ranges below 700 nm
Infrared Region
below 400 nm
- Gamma Rays
- X-Rays
- UV
greater 700 nm
Infrared and Radio Waves
Spectrum of energy from a short wavelength
of Gamma Rays and X-rays to a longer wavelength of Infrared and Radio waves
Between the invisible Region, the Visible light falls in those regions
Spectrum of energy from a short wavelength
of Gamma Rays and X-rays to a longer wavelength of Infrared and Radio waves
Spectrophotometric measurement is related to the principle of beer’s law
Beer’s Law
The concentration of a substance is Beer’s Law
o Directly proportional to amount of light
absorbed
o Inversely proportional to amount of transmitted
light
The amount of light absorbed, which is proportional to concentration
Not directly measured by spectrophotometer; derived from percent transmittance
Absorbance
measures amount of
transmitted light or percent transmittance
Spectrophotometer
Directly proportional to the inverse logarithm of
percent transmittance
Absorbance
-Ratio of transmitted light through the sample
(aka the light that is not absorbed by the sample) and the intensity of light striking the sample (from the light source) multiplied by 100
-As light passes through the sample, some of them are absorbed while the remainder passes through
- Light strikes the light detector and is converted to an electrical signal (% transmittance)
% T r a n s m i t t a n c e