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Chemistry > HPLC & GC > Flashcards

HPLC & GC Flashcards

1
Q

What are the typical samples used in GC?

A
  • water
  • gases
  • foods
  • drugs
  • biological samples
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2
Q

What are the typical substances tested in GC?

A
  • low molecular mass organic compounds e.g. acetone, asprin
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3
Q

What is HPLC commonly used for?

A
  • commonly used for the separation and identification of complex mixtures of similar compounds e.g. drugs in blood
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4
Q

In GC & HPLC what tool is used to identify the components in a mixture?

A

-Retention Time

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5
Q

In GC & HPLC what tool is used to determine the concentration of an individual sample?

A
  • peak area
    (of the sample is then compared to peak areas of known samples with known concentrations of the same chemical)
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6
Q

What are some advantages of GC & HPLC?

A
  • high sensitivity and precise
  • small sample size
  • readily automated
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7
Q

What are some disadvantages of GC & HPLC?

A
  • moderately expensive instrument
  • trained technician needed to operate
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8
Q

What are the typical substances tested in HPLC?

A
  • medium to high molecular mass organic compounds e.g. pesticides and enzymes
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9
Q

What are the typical samples used in HPLC?

A
  • food
  • drugs
  • biological samples
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10
Q

What are the two main differences between HPLC and column chromatography?

A
  • the particles in the solid used in HPLC are often 10-20 times smaller, allowing more frequent adsorption and desorption to give a better separation of similar compounds
  • the small particles size used in HPLC creates a considerable resistance to the flow of the mobile phase and so the solvent is pumped through the column under high pressure
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11
Q

What solids can be used in HPLC?

A
  • a wide range of solids, some with chemicals specially bonded to their surfaces to improve the separation of particular classes of compounds
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12
Q

How are components detected in HPLC?

A
  • components are usually detected by passing the eluent stream through a beam of UV light
  • organic compounds absorb the UV light so when an organic compound passes in front of the light a reduced signal is picked up by the detector
  • the amount of light received by the detector is recorded on a chart that moves slowly at a constant speed or sent to a computer
  • a chromatogram is then formed
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13
Q

How little of a component is GC capable of detecting?

A
  • it is capable of detecting as little as 10^-12g of a component
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14
Q

What components is gas chromatography limited to?

A
  • it is limited to components that can be readily vaporised without decomposing
  • such elements have a relative molecular mass of less than 300
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15
Q

What relative molecular mass of a component can HPLC separate?

A
  • HPLC can separate compounds with relative molecular masses that are as high as 1000 or more
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16
Q

What is the mobile phase in GC?

A
  • the mobile phase is an unreactive gas, often nitrogen, called a carrier gas
17
Q

How does GC work?

A
  • a small amount of the sample is injected into the top of the column through an injection port
  • the injection port is heated to vaporise the sample which is swept into the column by the carrier gas
  • the column is a series of loops of glass or metal that has an internal diameter of about 4mm and is about 2-3m long in total.
  • It is heated.
  • as the sample passes through the instrument, the components of the sample repeatedly interact with the stationary phase and are swept forward by the carrier gas.
  • components that adsorb least strongly to the stationary phase are swept out first by the gas
  • as the components emerge from the end of the column, they are sensed by the detector
18
Q

What is the stationary phase is GC?

A
  • the column can be packed with a porous solid coated with an ester or liquid hydrocarbon with a high boiling point, or it can be packed with an adsorbent solid such as silica gel or alumina.
  • the solid acts as the stationary phase
19
Q

What is retention time?

A
  • the time taken for a component to pass through the HPLC or GC column
  • it is characteristic of the component for the conditions of the experiment
20
Q

What is a standard solution?

A
  • a solution with an accurately known concentration

Chemistry (3 decks)

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