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Spectroscopy > Polarity and basic chromatography > Flashcards

Polarity and basic chromatography Flashcards

Forensic Chemistry

1
Q

Define dipole moment

A

The sum of individual bond polarities and lone pair contributions within a molecule.

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2
Q

What are polar molecules?

A
  • They are hydrophilic (love water)
  • An uneven distribution of electrons.
  • can be dissolved in a polar solvent but unable to in a non-polar solvent.
  • Has an asymmetrical structure.
  • Have a higher boiling and melting point compared to non-polar molecules.
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3
Q

What is a dipole-dipole interaction?

A
  • When there are different electrostatic attractions between different molecules.
  • A permanent delta negative and a permanent delta positive come into contact.
  • The greater the strength of the dipole- dipole interaction the higher the boiling and melting point.
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4
Q

What is bond polarity?

A

The distribution of electric charge across a bond between two atoms.

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5
Q

What is electronegativity?

A

The tendency of an atom to attract a bonding pair of electrons.

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6
Q

What does D stand for in polar molecules?

A

D stands for Debeyes.
The lower the D the lower the boiling point and results in weaker bonds between atoms in a molecule.

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7
Q

Describe hydrogen bonds

A
  • They are one of the strongest type of intermolecular forces and a lot of energy is required to break them.
  • Hydrogen bonds are formed between a hydrogen atom being attached to an oxygen , nitrogen or fluorine group.
  • Hydrogen bonding occurs between highly electronegative molecules.
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8
Q

What are the four types of intermolecular forces and put them in order from strongest to weakest.

A
  1. Ion- dipole (strongest)
  2. Hydrogen bonding
  3. Dipole- dipole
  4. Van der Waals (weakest)
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9
Q

What are non-polar molecules?

A
  • They are hydrophobic (water hating)
  • They can be dissolved in non-polar solvents but unable to in soluble solvents.
  • Low boiling and melting points due to weak forces.
  • Only London forces are found between molecules
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10
Q

What is extraction?

A
  • It is when a compound is extracted from a solid or liquid and is transferred to another phase/ solvent.
  • Compounds need to be extracted so they can be analysed by using chromatography.
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11
Q

What is a drawback of extraction?

A
  • It can be difficult extracting a sample that contains small amounts of different samples.
  • When extracting a sample from a small group of samples you may lose some sample which can result in large or gross loss.
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12
Q

Name the four types of extractions.

A
  1. Liquid-solid
  2. liquid- liquid
  3. Solid phase
  4. Solid phase Micro extraction
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13
Q

What does Log p value determine?

A
  • It determines how hydrophobic or hydrophilic a drug is.
  • Is done in liquid- liquid extraction.
  • Determines how early a drug will cross a lipid membrane and reach the site to action.
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14
Q

Describe a liquid-solid extraction.

A

When a solid powder is being extracted into a liquid.

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15
Q

Describe a liquid- liquid extraction.

A
  • A separating funnel is used.
  • There is two layers formed and the bottom layer is composed of an aqueous solution and the top layer is formed of a non-polar layer.
  • The two layers do not mix together , however yo do shake the funnel for usually ten times and then you release the pressure that has been obtained in the funnel by opening the valve.
  • Separate the two layers by putting them in two conical flasks and then you evaporate them to dryness by using nitrogen.
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16
Q

What does amphoteric mean?

A

Drugs have acidic and basic functionalities.

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17
Q

What happens to acidic and basic drugs when they are added to water?

A

Acidic drugs will lose a proton when they are added to water.
Basic drugs will gain a proton when they are added to water.

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18
Q

What does protonated and deprotonated mean?

A

Protonated is when a molecule gains a proton and deprotonated is when a molecule loses a proton.

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19
Q

What are disadvantages of liquid-liquid extraction?

A
  • It is time consuming
  • A large amount of solvents are used.
  • Very expensive
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20
Q

What is TLC?

A

-It stands for thin layer chromatography.
- A technique that separates components of a mixture.
- The mobile phase is the solvent phase.
- The stationary phase is the plate.

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21
Q

What type of action is used in TLC to draw the solvent up the plate?

A

Capillary action

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22
Q

What are the steps to TLC?

A
  1. Equilibrate the TLC tank by pouring 2.5cm of mobile phase in it and adding the lid on for ten minutes.
  2. Draw a line in pencil 1cm from above the bottom of the plate.
  3. Add small crosses to the line all at the same distances.
  4. Get an open end capillary tube and add the samples to the crosses.
  5. Open the TLC tank and add the plate and allow the mobile phase to move up the stationary phase.
  6. Once development has been completed, a pencil line should be drawn to where the solvent reached on the plate and this is known as the solvent front.
  7. Calculate the Rf values of the samples.
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23
Q

What is the equation for Rf value?

A

Rf value= distance moved by the sample/ distance moved by the mobile phase.

The Rf value should be less than the value of 1.

24
Q

What are the types of backings used in TLC?

A

Aluminium and glass.

25
Q

What are the four types of stationary phases used in TLC and their applications.

A
  1. Hydrocarbon modified silica’ Non-polar compounds.
  2. Cellulose; amino acids and carbohydrates.
  3. Alumina; Hydrocarbons, alkaloids, lipids.
  4. Sephadex gel- polymer and proteins.
26
Q

Define gas chromatography.

A
  • It is a separation technique and its based on the boiling points and the affinity for the stationary phase.
  • The sample is injected into an injector and then its carried by a carrier gas to the column where the stationary phase is located.
  • When the components of the sample have been eluted from the column and have been detected by the detector a chromatogram will produce to show the absorbance against retention time.
27
Q

What is the relationship between the stationary phase and the sample in gas chromatography?

A
  • If the sample has a high affinity for the stationary phase compared to the mobile phase it will spend a longer length of time in the column.
  • If the sample has got a lower affinity for the stationary phase but has a higher affinity for the stationary phase it will elute from the column more quickly.
28
Q

What are the two types of columns used in GC?

A
  1. Capillary column.
  2. Packed column.
29
Q

Which gases can be used in the capillary and packed column?

A

Capillary= helium and nitrogen.
Packed column= hydrogen.

30
Q

What are the non polar stationary phases used in GC?

A
  1. Methyl polysiloxane
  2. Methly and phenyl polysiloxane.
31
Q

What are the polar stationary phases used in GC?

A
  1. Polyethylene glycol
    2.Cyanopropylpolysiloxae
  2. Phenyldimethylsilicone
32
Q

What type of injector is used for a capillary column?

A

Split/ splitless injector

33
Q

What is the percentage of the sample that reaches the column when a split injection is used?

A

2%

34
Q

What type of detector is used when a packed column is used?

A

Split packed injector

35
Q

What is a flash vaporisation injector?

A

It is when a sample has ben injected into a hot zone that is 20-50 degrees hotter than the column temperature.
This allows the sample to be broken down and become volatilized immediately.

36
Q

What does volatile mean?

A

A substance can become easily evaporated at normal temperatures.

37
Q

What are three differences between a capillary and a packed column?

A
  1. A capillary column is made out of quartz and a packed column is made out of glass.
  2. capillary columns are longer and narrower compared to packed columns.
  3. Capillary columns are more efficient compared to packed columns.
38
Q

Define an ISO thermal method in GC.

A

When the temperature of the oven remains constant.

39
Q

Define a temperature programming method in GC?

A

When the temperature changes in GC.

40
Q

What are represented on the X and Y axis of a chromatogram?

A

X= retention time (mins)
Y= relative abundance

41
Q

Define retention time.

A

The amount of time for a component to move through the column.

42
Q

Define thermal conductivity detector.

A

Detects changes in thermal conductivity of the carrier gas.

43
Q

Define flane ionisation detector.

A
  • The carrier gas elutes from the column and its mixed with air and hydrogen.
  • Results in ions that are collected at the negative electrode and a current will be produce which is directly proportional to the concentrarion of the sample.
44
Q

What is a nitrogen and phosphorous detector?

A
  • Its a modified flame ionisation detector.
  • Has a ceramic bead which is made out of caesium and rubidium salts.
  • Heated up to 800 degrees.
45
Q

What is an electron capture detector?

A

It is specific for electronegative elements such as Group 7 elements.

46
Q

What is a mass spectrometer detector?

A
  • When the samples are broken down in the GC and they are eluted from the column, they are broken down into ions and fragments.
  • The ions and fragments have specific masses and this allows for the components that make up the sample to be identified.
47
Q

What is HPLC?

A
  • A mixture is separated into its components at room temperature.
  • The sample is transported to the column by a liquid mobile phase.
  • The stationary phase is solid and its located in the column.
  • When the sample is in the column it is separated into its different components based on the affinity for the stationary phase.
  • if the components have a high affinity for the stationary phase it will spend a longer mount of time in the column.
  • if the components of the sample have a low affinity for the stationary phase it will elute from the column in a shorter amount of time.
48
Q

What is normal phase separation in HPLC?

A
  • Mobile phase in non-polar.
  • Stationary phase is polar.
  • Stationary phase is a unmodified silica.
  • The non-polar components have a low affinity for the stationary phase.
49
Q

What is the reverse phase in HPLC?

A
  • The mobile phase is polar.
  • The stationary phase is non-polar.
  • Modified silica is used in the stationary phase and non-polar compounds love.
  • More commonly used than normal phase separation.
50
Q

Mobil phase in HPLC.

A
  • The polarity of the stationary phase and the mobile phase need to be different, if they are the same there will be no separation of the sample.
  • The sample needs to be the same polarity as the stationary phase; the mobile phase polarity needs to be different.
51
Q

Define HPLC injection.

A
  • A valve with a sample loop.
  • The sample loop is filled with the sample and it can hold between 1-100 micro litres.
  • Controlled by a computer.
52
Q

Define the conventional column in HPLC.

A
  • Made out of stainless steel.
    Different mobile phases can be used.
  • Flow rate of 500-3000 psi.
  • Jas a flow rate of 1-3 ml min-1.
53
Q

Define the micropore column in HPLC.

A
  • Made out of stainless steel.
  • Flow rate of 10-100 micrometers.
  • Has an operating pressure of 1000-5000 psi.
54
Q

Name the four types of HPLC detectors.

A

-Mass spectroscopy.
- UV-Visible, absorbance detector.
- Fluorescence detector.
- Refractive index detector.

55
Q
A

Spectroscopy (2 decks)

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