Download - Chromatographic Theory 2014-03-27
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Quiz (Previous lecture: Sample Prep+Concentration Calculation)
1. A sample is said to be homogeneous if
a) the sample is the same throughout.
b) the sample has a different composition in different parts of the sample.
c) the sample can be separated into the individual components by filtering the sample.
2. In a random heterogeneous material,
a) differences in composition occur randomly and on a fine scale.
b) large regions have obviously different compositions.
c) the composition of the sample is evenly distributed throughout the sample
3. In discussing quantitative and qualitative analysis one could say
a) the two terms are commonly used interchangeably.
b) quantitative analysis deals with determining what materials may be present in a sample.
c) quantitative analysis deals with the amount of a material present in a sample.
4. Which extraction method uses a small volume of a stationary phase?
a) microwave assisted extractionb) supercritical-fluid extraction
c) solid-phase extraction
5. Interference occurs
a) when a species other than the analyte causes an analysis to be inaccurate.
b) when the analyte is precipitated from a non-homogeneous solution.
c) when two or more methods used for separating species interfere with each other.
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6. Which statement is correct?
a) Sampling is the process of selecting a bulk sample from the representative lot, and
sample preparation is the process that converts a bulk sample into a heterogeneous
laboratory sampleb) Sample preparation is the process of selecting a representative bulk sample from the lot,
and sampling is the process that converts a bulk sample into a homogeneous laboratory
sample
c) Sampling is the process of selecting a representative bulk sample from the lot, and
sample preparation is the process that converts a bulk sample into a homogeneous
laboratory sample
7. Calculate the formal concentration of a sodium acetate solution prepared by diluting 45.0
mL of a solution containing 25.0 ppm sodium acetate (NaC2H3O2, MW 82 g/mol) to a total of
0.500 L of solution.
a) 6.10 x 10-4Molar
b) 1.37 x 10-6Molar
c) 2.75 x 10-5Molar
8. A 250.0 mL sample is concentrated for analysis to 25.0 mL. What is the correct
expression for the new concentration?
a) [sample] x (25.0 mL/250.0 mL)
b) [sample] x (250.0mL/25.0 mL)
c) [sample] x 100
Quiz (Previous lecture: Sample Prep+Concentration Calculation, cont.)
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Chromatographic theory
(2014-03-27)
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Learning objectives
Identify and define the majorcharacteristics of chromatographicseparation
Define the concept of chromatographicseparation
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History behind
Tswett's Experiment (1900)
Column packed with sorbent Distribution on the coloured zones
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Schematic chromatographic process
Chromatographic column
Mixture (1+2+3)
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Mechanism of chromatographic separation
Important parametes:
1. Surface adsorption
2. Solubility
3. Charge
Mechanism:
1. Solute moves down by being
replaced by more highly retained
solute2. A solute partinions between two
phases
3. Separation is based on relative
retention
Forces:
1. Polar Forces
i) Dipole-dipole interactions
ii) Dipole-induced dipoleiii) Ionic forces
2. Hidrophobic / Hydrophilic
3. Dispersive
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Chromatographic peak
Baseline
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Resolution
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Separation theories
1. Plate theory
1941, Martin and Synge
- Theoretical plates (actual in distillation)
- Assumes that equilibrium is immediate (fast)
2. Rate theory
1956, van Deemter
- More realistic
- Takes into account time which is needed for
solute to equilibrate between phases
A Multiple path (eddy diffusion)
B - Longitudinal diffusion
C - Resistance to mass transfer
u - Linear velocity of the mobile phase
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Band broadening
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Tailing of chromatographic peak
1. Symmetric peak happens at
ideal isotherm sorption2. Tailing is the most typical
case
3. Overloading happens not
so often
Anti-tailing protection