Measuring Absorbance Part 2 Flashcards
What is different in IR spec than absorance spec
The light sources are low powered
The sample and its holder (cuvette) needs to transmit IR
Water vapour acts as an interferent
The detectors aren’t very sensitive to changes (they’re bad)
What should the ir sample holder be made out of
What shouldn’t it be
Should be salt or plastic
No glass or water
What is attenuated total reflectance
The IR light is sent into the machine at a sharp oblique angle,
the light then bounces on the walls of the diamond window in the machine and interacts with the outside material as much as possible
This allows the light to remain intense and be reflected this is called the evanescent wave
What is FTIR stand for
Fourier transform IR
What is Fourier transform IR
You use this type of spectrum to take a complex signal and transform it to see all of the frequencies that make up the signal
What is an interferogram
The thing used in FTIR to make the absorbance spectrum
A graph of signal vs retardation
What are the agvantages to IR spec
The weak light and detector makes it so that they get used as much as possible
It’s fast (result after a few seconds)
Get lost of spectra quickly
What is the Michelson interferometer
It’s a way to interpret complex waves for IR, it’s used instead of a monochromater
One light beam is sent in, and beam splitter (or half silvered mirror) splits the light beam
What two beams are made when the beam splitter his in the michealson interferometer
Light 1: the light from this gets reflected on a fixed position mirror (so the light travels down a fixed path to the detector) (s for stationary mirror)
Light 2: the light gets sent and reflected from a mirror that can move and make a varied light path to the detector (it can slow the beam)
What is the pin t of the stationary and the movable beam in the michealson interferometer
One beams is out of phase with that other so this creates destructive and constructive interference depending on the position of the moveable mirror
What is random noise and how do you fix it
White noise
Each data point is affected differently for each run (data is higher or lower)
We can Average many runs to smooth out the random noise (ex. Rolling averages)
What is rolling averages
Taking the average of four data point at a time , moving over one data point and doing it again
What are the four sources of noise
Drift and flicker
Thermal
Line
Scattered light/stray light
What is Drift and flicker noise
The Drift and flicker of a lamp and detector
The p and p0 are affected
Can fix by warming up the machine or zeroing the machine often (blank) or using a double beam
What is thermal noise
Caused by vibrations of molecules and varying energy
Affected by temp because energy is higher at higher temp
So keep a cool temp
