Chromatography

Question 1

How do you calculate the Retardation factor?

Answer 1

Rf= Distance the component travelled from the origin ÷ Distance the solvent front travelled from the origin.

Question 2

What is the Rf value

Answer 2

-The retardation factor is a measure of how far substances of a mixture travel in comparison to the mobile factor.
-it is compared to those of known substances
-furtherest travelled=most polar
-Are always less than 1 as the component cannot travel further than the solvent.

Question 3

What is absorption?

Answer 3

The attraction of 1 substance to the surface of another.

Question 4

What is desorption?

Answer 4

• The breaking of the attraction between a substance and the surface to which the substance is absorbed.

Question 5

What is a polar molecule?

Answer 5

A molecule that acts as a dipole; it has 1 or more polar covalent bonds, with the charges being distributed assymetrically.

Question 6

What is the mobile phase?

Answer 6

The solvent(usually a liquid or gas) that moves over the stationary phase in chromatography.

Question 7

What is the stationary phase?

Answer 7

-The components of a mixture undergo absorption to mobile phase.
-typically a solid, eg paper or powder.
-molecules in this phase cannot move.

Question 8

What are 4 principles of chromatography?

Answer 8

• Technique used to separate and identify the components in a mixture.
• All chromatography techniques involve a mobile and stationary phase.
• Rf values are used to identify components within a substance.
• can be used for drugs in blood or powder containment in water and toxic gases in the air.

Question 9

What is column chromatography used for?

Answer 9

• Used for separating substances

Question 10

What is high performance liquid chromatography used for?

Answer 10

• can be used to analyse the presence and concentration of dioxins, insecticides, and oil spills in water.
• Can be used to determine the presence of pesticides in food and detect the presence of drugs in alcohol.

Question 11

What is a standard?

Answer 11

• is a mixture where the concentration and identity of each component is already known.
• They provide us with data that we can use to analyse unknown mixtures - through finding similar comparisons we can identify the possible components and their concentrations within a mixture.

Question 12

Qualitative analysis

Answer 12

-uses the retention time to determine the chemicals present in a sample.
-measured on the x-axis. Where samples are measured against a standard.

Question 13

Quantitative Analysis

Answer 13

-used to determine the concentration of a substance by taking known concentrations and measuring their peak areas.
- we can transfer this information to a line graph and use that graph to determine unknown concentrations (=calibration curve)
- Measured on the Y-axis, against a standard solution.
-concentration of a substance = peak areas

Question 14

Main differences between HPLC and column chromatography

Answer 14

-The particles in the solid used in the HPLC are often 10-20x smaller than those used in column chromatography, allowing more frequent absorption and desorption of the components=much better separation of the similar components.
- the small particle size used in HPLC creates a considerable resistance to the flow of the mobile phase=the solvent is pumped by high pressure unlike in column chromatography that uses gravity.

Question 15

Foundations ( things that are constant)

Answer 15

• will always be a stationary and mobile phase, and the mixture that’s being analysed and / or separated.
• Any technique used to analyze the composition of a mixture, will use standard.

Question 16

What are components?

Answer 16

• the different compounds in the mixture, which can be separated by chromatography.

Question 17

Types of chromatography

Answer 17

• Thin layer/paper
• High Performance Thin Layer(HPTLC)
• column
  Advanced Aplications of chromatography:
• High performance liquid(HPLC)
• Gas (GC)

Question 18

What’s the difference between adsorb and absorb?

Answer 18

-absorb: Atom/molecules are taken into the material.
-adsorb: Atom/molecules accumulate and bond weakly to the surface of a solid/liquid.

Question 19

Why is it important to measure the peak areas produced by a no. Standard solutions when performing quantitative analysis in HPLC?

Answer 19

-Because HPLC doesn’t directly produce measures on concentration.
-Standard solutions are used to find the relationship between peak area and concentration.

Question 20

5 steps of the analytical process in HPLC.

Answer 20

-Obtain chromatograms of the stream water and of standard solutions of the herbicide.
-use Rt values to identify the herbicide peak on chromatograms of the standard solutions and the stream water sample.
-Construct a calibration curve and mark the herbicide peak area from the stream water sample on it.
-Determine the herbicide concentration in the stream water sample.