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PHAR 20100 > UV/ Vis spectroscopy > Flashcards

UV/ Vis spectroscopy Flashcards

1
Q

What are the components of a UV/VIS spectrophotometer?

A 
UV—> deuterium lamp 
Vis—> tungsten lamp 
Monochromator 
Optics- direct light to detector 
Director
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2
Q

How does a spectrophotometer work?

A

Polychromatic light enters monochromator- prism splits light into various wavelengths
Light leaves exit slit with selected wavelength and passes through sample
Sample absorbs certain intensity of light

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3
Q

What is a dual beam instrument?

A

2 cuvettes- light entering spilts into two- 1 passes through sample and 1 thought reference

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4
Q

Why use reference sample?

A

Compensated for other factors affecting abs such as solvents

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5
Q

How does Single beam instrument avoid detecting other factors?

A

Tared to 0- calibrated

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6
Q

What solvent is the sample dissolved in?

A

A solvent with minimum abs in the wavelength range used

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7
Q

What cuvettes are used for Vis?

A

Plastic

Glass

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8
Q

Cuvettes used for UV?

A

Quartz

Silica

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9
Q

cuvettes should be handled with which side?

A

From frosted side- to avoid fingers proteins being detected

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10
Q

Which drugs have abs in UV?

A

Drugs with aromatic rings and double bonds

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11
Q

What should be the maximum abs of a sample?

A

Below 1.5- need dilution otherwise

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12
Q

What is difference spectrometry

A

Taking spec of one sample- making a change and calc abs again to see how this change affects abs

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13
Q

What is derivative spectrophotometer?

A

If there is a big change- amplify it

If small change- flatten it

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14
Q

What is the process of luminescence?

A

1- excitation- electron excited to higher energy state by light abs
2- excited state lifetime- the time E stays up before returning
3- luminescence- emission of photons- E return to ground state

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15
Q

Why is fluorescence emitted at a diff wavelength?

A

As E- return to ground state- some energy lost- as energy changes so does wavelength

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16
Q

What does a jablonski diagram show?

A

Energy diagram that describes the process of photon emission

17
Q

What is stokes shift?

A

The difference in wavelength between abs and emission

18
Q

Are drugs with longer stokes shirtfront easier to understand?

A

YES

19
Q

What is a fluorophore?

A

A molecule that is fluorescent

20
Q

Is fluorescence more than UV for detection of analytes?

A

YES

21
Q

What is the instrument used to measure fluorescence?

A

Spectrofluorometer

22
Q

Components of a spectrofluorometer?

A

Xe lamp/ laser
Cell holders- 4 sided and transparent
Monochromator
Detector

23
Q

Fluorescence spectrum x and y axis?

A

X axis- wavelength

Y axis- fluorescence intensity

24
Q

Does sample need to be diluted and why?

A

YES- conc 10-100x less than abs spec

Very sensitive —> better for potent drugs

25
Q

Can you have solid particles in your sample?

A

NO- cause light scattering- excitation light can enter detector

26
Q

Maximum abs of solution for fluorescence?

A

Ideally less than 0.05

27
Q

Pros of fluorescence?

A

Very sensitive- higher selectivity than UV-Vis

Less expensive than NMR or MS

28
Q

Cons of fluorescence?

A

Don’t all drugs are fluorescent

Changes in conditions affect fluorescent properties

29
Q

Eg of drugs analysed by fluorescence?

A

Phenobarbitone
Adrenaline
Chlorpromazine
Procaine

30
Q

What is the BP standard for quantitative analysis?

A

Dissolve substance in solvent
Set excitation wavelength
Measure intensity of light emitted
Calc Conc on substance in solution

31
Q

What is the formula to calc conc of substance?

A

Cx = Ix (intensity of light) x ACS (conc of standard sol) / Is ( intensity of light emitted by standard sol)

32
Q

The method calc conc of substance is only valid if….?

A

Fluorescence linear with conc

33
Q

Factors affecting fluorescence intensity?

A 
PH
Viscosity and temp 
O2 
Photonleaching 
Solvents 
Structural effects 
Substituents

PHAR 20100 (14 decks)

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