chromatography - unit 4 AOS 2

Question 1

principles of chromatography

Answer 1

• In chromatography, a solvent of known polarity – the mobile phase – is passed through a mixture over a medium of known polarity – the stationary phase. - - As the mobile phase passes through the mixture over the stationary phase, the components
  in the mixture undergo a continual process of adsorption to and desorption from the stationary phase.

Question 1

chromatography

Answer 1

• Chromatography is the process of separating components in a mixture based on their solubility.

Question 2

absorption and desorption

Answer 2

• Adsorption refers to a substance sticking/adhering to the surface of another.
• Absorption is one substance being taken within another; for example, water being drawn into a sponge.
• Since the components of a mixture vary
  in their relative attraction to the mobile and stationary phase, they are separated as they travel at different speeds through the column.

Question 3

factors affecting the speed that a component will move through the HPLC

Answer 3

• affinity to mobile phase: a higher affinity to the mobile phase means it will travel faster
• molar mass - lower molar mass will travel faster
• length of column: shorter column = faster
• temp: higher temp = faster
• stationary phase surface area: increase = faster

Question 4

HPLC

Answer 4

• High performance liquid chromatography (HPLC) is another sensitive application of chromatographic principles. In HPLC, a column or coil is packed tightly with a stationary phase and a solvent is allowed to pass through

Question 5

retention time

Answer 5

• the time taken to travel through the column
• Retention time can be used to identify a component, by comparing the retention time for an unknown substance with those for known substances under the same operating conditions.

Question 6

chromatograms

Answer 6

• The output of high performance liquid chromatography is a chromatogram of
  absorbance peaks
• the number of peaks is the number of compounds in the mixture
• The peak area – the area under a peak in an HPLC chromatogram – is proportional to the amount of the substance responsible for the peak present in the sample

Question 7

chromatograms axes

Answer 7

vertical: absorbance
horizontal: retention time

Question 8

calibration curves

Answer 8

• concentration graphed against peak area
• Several solutions of the component at known concentrations are run through the
  same HPLC column under identical conditions.
• The resulting peak areas are then plotted against concentration and a calibration curve is drawn.
• The concentration of the component in the sample is interpolated from the calibration curve using construction lines

Question 9

calibration curves axes

Answer 9

vertical: peak area
horizontal: known concertation (mg L-1)