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Principles of Analysis > Spectrophotometry > Flashcards

Spectrophotometry Flashcards

1
Q

what does electromagnetic radiation comprise of?

A

radiant energy extending from cosmic rays (λ 10^-9nm) to radio waves (λ km)

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2
Q

what does visible light describe?

A

radiant energy in the visible portion of spectrum where our eyes work ranges from 380-750 nm

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3
Q

what is wavelength

A

the distance between 2 peaks

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4
Q

UV has a…

A

slightly shorter wavelength

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5
Q

Infrared has a …

A

slightly longer wavelength

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6
Q

what is the speed of light equivalent to?

A

186,000 miles per second

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7
Q

wavelength is inversely proportional to a…

A

given frequency
V = c / λ
V = frequency of light (cycles per second [Hz])
C = speed of light in a vacuum (3x1010cm/s)
λ = wavelength in cm

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8
Q

energy is proportional to…

A

frequency.
- the relationship between the energy of photons and their frequency is proportional
- it makes sense that the more times a wave wobbles in a second then the more energy required to make that happen
E=hv
E=energy (ergs)
H= plank’s constant (6.62x1027 erg s)
V = frequency of light (cycles per second (Hz))

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9
Q

energy is inversely proportional to…

A

wavelength
- λ is inversely proportional to v
- v is directly proportional to E
- therefore λ is inversely proportional to E
- E = hc / λ
- For example UV radiation at 200nm possesses greater energy than IR radiation at 750nm

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10
Q

light hitting matter may be

A

absorbed
transmitted
scattered
reflected

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11
Q

where does absorbed light go?

A

electrons in the ground state are promoted to higher energy orbitals
energy absorbed corresponds to the difference between those orbitals
energy is then lost vibrationally (non-radiative) or radiatively (e.g. fluorescence)

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12
Q

organic molecules

A

what are are interested in in a clinical lab
often have conjugated double bond systems, so easy for electrons to move around (delocalise)
conjugated double bond systems have fairly low energies for absorption
since colour occurs with absorption many organic compounds are coloured

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13
Q

why are some chemicals coloured?

A
  • The wavelength of light absorbed will depend on the chemical structure of the compound in the solution
  • Since white light is a spectrum, only certain parts of the spectrum will be absorbed. The remainder produces the colour observed.
  • Chlorophyll gives leaves their green colour
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14
Q

what is absorbance calculated from

A

intensity

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15
Q

what intensity does incident light have

A

I0

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16
Q

What intensity does light reaching the detector have?

A

I

17
Q

what is transmittance?

A

the fraction of incident light reaching the detector

18
Q

what is the equation for transmittance

A

T=I/I0
%T = IX100/I0

19
Q

The relationship between concentration and transmittance is…

A

non-linear
we can calculate the absorbance from transmittance and convert the absorbance, which is the logarithm or the reciprocal of T
A=log10/T
A=2-log10%T

20
Q

when is light absorbed

A

when a photon collides with a molecule

21
Q

what does the amount of light absorbed depend on?

A

the concentration of the compound in a soltuion

22
Q

the concentration of a substance is…

A

directly proportional to the amount of light absorbed

23
Q

what is the equation for absorbance?

A

A=ɛcl

24
Q

what do A, ɛ, c and I mean in the equation for absorbance?

A

A= absorbance
ɛ= molar absorptivity (molar extinction coefficient)
c= concentration mol/l
I = path length (cm)

25
Q

what is molar absorptivity?

A

a proportionality constant for any given compound at any given wavelength of light ɛ=A/cl. most cuvettes have a path length of 1cm, so the equation can be simplified to ɛ=A/c and this equation can be rearranged to calculate concentration =C=A/ ɛ

26
Q

why is absorbance an ideal analysis

A

quick and easy
relatively cheap
readily integrated into automation
reproducible

27
Q

most big chemistry analysers are…

A

spectrophptometers

28
Q

spectrometry

A

measurement of interactions between light and matter, and the reactions and measurements of radiation intensity and wavelength

29
Q

spectrophotometry

A

measures the colour produced - how much light a chemical substance absorbs

Principles of Analysis (8 decks)

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