Ex4 General Chromatography

Wed, 06/05/2013 - 08:41 -- sewm02

Ex4 General Chromatography

 

Exam On chromatography.

1. Define the following terms and explain how each functions

  • Absorption chromatographyLSC

1. A solid stationary phase and a liquid or gaseous mobile phase are used. Solute is absorbed on the surface of the solid particles.

  •  Partition chromatography LLC

1. A liquid stationary phase is bonded to a solid surface which is typically the inside of the silica (SiO2) chromatography column in gas chromatography. Solute equilibrates between the stationary liquid and the mobile phase.

  • Ion-exchange chromatography IEC

1. Anions or cations are covalently attached to the stationary solid phase with a resin. The solute ions of the opposite charge are attached to the stationary phase by electrostatic forces.

  • Molecular exclusion chromatographyEC

1. A gel or a porous stationary phase is used to separate the solute solely based on size in, an ideal state.

  • Affinity chromatographyBC

1. The use of biochemical mixtures to selectively separate one kind solute molecule from a mixture. The process is so effective it requires the changing of the pH to dislodge the selected solute.

2. Give a basic mathematical definition of resolution. Be sure to identify all variables.

Also called the degree of separation (resolution)

W  base widths

tr  retention times

3. Describe the physical process (in terms of equilibria) that is responsible for separation as a mixture moves down a column.

The physical process that is occurring is the solute is moving through a column that is made up of a solid or liquid. The solute is also being sweep along with the mobile phase. Both the mobile phase and the solute interact with the column thus slowing down the time in which the solute reaches the detector.

4. Define the following terms

  • Retention time Is the characteristic time it takes for a particular analyte to pass through the column to the detector.
  • Retention volume  Retention volume is the volume of mobile phase passed through the column between the injection point and the peak maximum
  • Adjusted retention time  The adjusted retention time is the time a compound spends in the stationary phase. The adjusted retention time is the difference between the dead time and the retention time for a compound
  • Relative retention time: The ratio of the adjusted or net retention volume(time) or retention factor of a component relative to that of a standard obtained under identical conditions.

http://goldbook.iupac.org/R05277.html

  • Capacity factor: The capacity factor is the ratio of the mass of the compound in the stationary phase relative to the mass of the compound in the mobile phase. The capacity factor is a unitless measure of the column’s retention of a compound.

5. Give the equation used to determine plate height (Douglas A. Skoog)

H=plate height   L= length of the column packing N= number of plates

6. Give the relationship between plate height and resolution and describe each variable and clearly state how each factor effects the resolution <http://www.mems.utah.edu/Papers/Himanshu%20ElFFF%20Scaling%20Paper.pdf> (Bernie)

7. Give the van Deemter equation and define each variable and their physical meaning. (you mighe want to consider other books) to give a clear explanation.

Plate Height (cm) = H

u = linear velocity

A = multiple flow paths  

B = longitudinal diffusion

CM = The mobile phase Mass- Transfer term

Cs = The stationary phase Mass-Transfer term

the rate at which the analyte can move in and out of the mobile phase and stationary phase

8.  Describe how nonlinear partition isotherms lead to non-Gaussian band shapes. Also draw the isotherm and the associated non-Gaussian band shape.

Draw graph

Overloading is when concentration is too high

Trailing is when concentration is too low

http://classes.uleth.ca/200801/chem3410a/Chemistry_3410Test5_Answers.pdf (Bernie)

9.  Why is it that the larger the partition coefficient the longer it takes a solute to be eluted. Be sure to give the mathematical definition of a partition coefficient in your explanation.

It takes a solute longer to be eluted because the solute is spending more time in the stationary phase

Good webpage with lots of detailed information on Chromatography <http://www.chromatography-online.org/index.html> (Bernie)

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