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Chemistry > 29 - Chromatography and Spectroscopy > Flashcards

29 - Chromatography and Spectroscopy Flashcards

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1
Q

What can chromatography be used in?

A

Analysis of drugs, plastics, flavourings, air samples and has applications in forensic science

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2
Q

What is thin layer chromatography (TLC) ?

A

Quick and inexpensive analytical technique that indicates how may components are in a mixture
Uses a TLC plate

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3
Q

What is a TLC plate?

A

A plastic sheet of glass, coated with a thin layer of adsorbent substance - usually silica

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4
Q

What is the stationary phase in TLC?

A

The adsorbent

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5
Q

How do the different components act on the TLC plate?

A

Different components in the mixtures have different affinities for the absorbent and bind with differing strengths to its surface

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6
Q

What is adsorption?

A

Process by which the solid silica holds the different substances in the mixture to its surface.

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7
Q

How do you carry out TLC?

A
  1. Use a pencil to draw a line across the TLC plate about 1cm from the base (baseline)
  2. Using a capillary tube, spot a small amount of a solution of the sample on to the baseline
  3. prepare a chromatography tank for the TLC plate - pour solvent into a small beaker to about 0.5 cm depth
  4. Place prepared TLC plate upright in the beaker, making sure the solvent does not cover the spot.
  5. Leave to stand and allow solvent to rise up the TLC plate.
  6. Once solvent has reached about 1cm from top of plate, remove from beaker and immediately mark the end of the solvent with a line (solvent front)
  7. Circle any visible spots with a pencil
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8
Q

What is a locating agent?

A

A chemical such as iodine that is sprayed over the TLC plate to show the position of spots that may be colourless

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9
Q

How do you calculate the retention factor, Rf Value?

A

Rf = distance moved by component/distance moved by solvent front

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10
Q

What is gas chromatography?

A

Used for separating and identifying volatile organic compounds present in a mixture

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11
Q

What is the stationary phase in gas chromatography?

A

a high boiling point liquid adsorbed on to an inert solid support

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12
Q

What is the mobile phase in gas chromatography/

A

An inert carrier gas such as helium or neon

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13
Q

How is gas chromatography carried out?

A
  1. Small amount of mixture is injected into the apparatus called a gas chromatograph
  2. Mobile carrier gas carries the components in the sample through the capilalry column whihc contains the liquid stationary phase adsorbed on to the solid support
  3. Components of the mixture are separated depending on thier solubility in the liquid bstationary phase
  4. Compunds in the mixture reachb the detector at different times depending on their intreactions with the stationary phase in the column
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14
Q

Which compound is detected first in gas chromatography?

A

The compound retained in the column for the shortest amount of time (lowest retention value)

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15
Q

What is the retention time?

A

Time taken for each component to travel through the column

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16
Q

What two pieces of information can be obtained from a gas chromatogram?

A 
Retention times 
Peak integrations (areas under each peak)
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17
Q

What can retention times be used for?

A

Identify the components present in the sample by comparing them to retention times for known components

18
Q

What can peak integrations be used for?

A

Determine the concentrations of components in the sample

19
Q

How are the concentrations of components determined?

A

By comparing its peak integration (peak area) with values obtained from standard solutions of the components

20
Q

What is the chemical test for alkenes?

A
  • Bromine water

Decolourised from orange to colourless

21
Q

What is the chemical test for haloalkanes?

A

-Silver nitrate and ethanol and warm to 50 degrees in water bath
Cl = white precipitate
Br = cream precipitate
I = yellow precipitate

22
Q

What is the chemical test for carbonyls?

A
  • 2,4 - DNP

yellow/orange precipitate

23
Q

What is the chemical test for aldehydes?

A
  • Tollens reagent and warm

silver mirror

24
Q

What is the chemical test for primary and secondary alcohols and aldehydes?

A
  • Acidified potassium dichromate (VI) and warm in water bath
    Colour change from orange to green
25
Q

What is the chemical test for carboxylic acids?

A 
Add Na2CO3 (aq) 
effervescence
26
Q

When is nuclear spin significant?

A

If there is an odd number of nucleons (protons and neutrons)

27
Q

For what isotopes of organic compounds is NMR relevant for?

A

13C and 1H

28
Q

What can NMR spectroscopy be used for?

A

Detect isotopes of other elements with odd numbers of neutrons

29
Q

What are the most common forms of NMR analysis used?

A

1H and 13C

30
Q

What is 1H NMR usually referred to as?

A
  • proton NMR

- nucleus consists of just a proton

31
Q

What is nuclear magnetic resonance?

A
  • Both the nucleus and an electron have two different spin states with different energies
  • With the right combination of magnetic field and radio frequency radiation, the nucleus can absorb energy and rapidly flip between the two spin states
32
Q

What is the difference between radio frequency radiation and infrared radiation?

A
  • radio freq. radiation has much less energy
  • freq. required for resonance is proportional to the magnetic field strength
  • small quantity of energy can only be detected in strong and uniform magnetic fields
33
Q

Where are NMR spectrometers commonly found?

A

MRI body scanners

34
Q

What is meant by chemical shift?

A

fhgfyh

35
Q

What is the standard reference chemical?

A

Tetramethylsilane (TMS), (CH3)4Si

36
Q

What is the chemical shift value given to TMS?

A

0ppm

37
Q

How is NMR spectroscopy carried out?

A
  1. Sample dissolved in a solvent and placed in a narrow NMR sample tube, with a small amount of TMS
  2. Place placed inside the NMR spectrometer where it is spun to even out any imperfections in the magnetic field within the sample
  3. Spectrometer is zeroed against the TMS standard and the sample is given a pulse of radiation containing a range of radio frequencies, whilst maintaining a constant magnetic field
  4. Any absorptions of energy resulting from resonance are detected and displayed
38
Q

How is a sample recovered after NMR spectroscopy analysis?

A

evaporation of the solvent

39
Q

When is a deuterated solvent used?

A

When the 1H atoms in 1H NMR spectra have been replaced by 2H atoms (deuterium, D)
- Produces no NMR signal in the frequency in the frequency ranges used in 1H and 13C NMR spectroscopy?

40
Q

What is a common deuterated solvent?

A

Deuterated trichloromethane, CDCl3

Chemistry (26 decks)

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