EM spectrum & spectrometry laws Flashcards
Describe the relationship between energy, wavelength & frequency?
Wavelength increases= frequency decreases= energy decreases
Equation that links speed of light to frequency and wavelength?
C = frequency X wavelength
C–> speed of light
which part of the spectrum is most useful in pharm analysis?
UV / Vis / IR- in increasing wavelength
Equation that links energy to frequency?
E = hf
E = hc/wavelength
h–> planks constant
What are photons?
A quantum of light or electromagnetic radiation which compromises EMR waves
What happens when photon hits mater?
The energy can be absorbed, emitted or scattered
When does absorption occur?
When e- promoted from low energy state to higher
When does excitation occur?
When excited particles return to ground state
Change in energy must = to?
Change in energy= E1 - Eo
Function of a spectrophotometer?
Recordds absorbance at different wavelengths
Most drugs absorbs which range of wavelengths?
UV- except coloured drugs
Are the absorbance peaks sharp?
Not sharp- broad due to vibrational levels being present with each electronic level- its of jumps–> converted to broad band
What are sigma bonds?
Single bonds
What are pi bonds?
Double/ triple bonds
Uses of UV absorption?
- ID of drugs
- measuring reactions such as pKa, solubility, ionisation
- quantification of drugs
What is the right shift called?
Bathochromic- red
What is left shift?
Hypsochromic shift- blue
What is up shift?
Hyperchromic
What is down shift?
Hypochromic
What is conjugation?
Alternating single double bonds
Presence of conjugation shifts absorbance to?
Bathochromic- longer wavelength
What is the correlation between Abs & conjugation?
No conjugation = weak absorption
what is an Auxochrome
A funtioonal soup with lone pairs e.g. OH / NH2
They do not absorb much light on their own
What shift do Auxochromes cause?
Bathochromic, Hyperchromic
What is a chpormophore?
A part of the molecule which absorbs UV/ Vis light- double bonds or groups with lone pairs of e-
Usual distance of cuvette?
1cm- path length- distance that a light travels
How to calc amount of light transmitted?
T = I / Io OR %T= 100XT T= transmission I = coming out Io= going in
What is the correlation between conc, abs & transmission?
As conc increases, absorption increases & transmission decreases
Equation linking abs & T?
A = log(1/T) = log Io/I
What is the Beer- Lambert Law?
A = Ebc e= molar extinction coefficient - mcm- b= path length - usually 1cm c= conc- mol/L
Equation linking Conc & Abs?
C = A / A1%1cm
conc- g/100ml
Is the relation between abs & conc linear?
A directly proportional to C until A < 1.5- after that very little transmission and dilution is required- can multiply with dilution factor
