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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