Newton 7

Question 1

What are five types of liquid chromatography?

Answer 1

Liquid liquid chromatography (partition)

Liquid solid chromatography (adsorption)

Ion exchange chromatography

Size exclusion chromatography

Affinity chromatography

Question 2

Why increasing pressure or using vaccum for liquid chromatography is not recomended?

Answer 2

Because you see an increase in plate height, this reduces resolution.

Question 3

What is high pressure liquid chromatography?

Answer 3

When the mobile phase needs to be pumped through the analytical column at much greater pressure.

Question 4

How do we increase column efficiency of LC?

Answer 4

By reducing the plate height by having more plates per unit length of stationary phase and by reducing the size of the particles that are used in the stationary phase.

Question 5

Why using smaller particles for LC can be disadvantage?

Answer 5

Because sample can move very slowly and if you apply pressure it will develop large backpressures.

Question 6

What is the purpose of solvent reservoirs in LC?

Answer 6

To control flow and concentration of different solvents.

Question 7

What is the reason of havin two reciprocating pumps in LC?

Answer 7

To give a smooth flow, with no pilsing. It is very important when it comes to the separation of the system within the comumn.

Question 8

What are charecteristics of pumps in LC?

Answer 8

They need to generate pressure up to 6000 psi, have a large range of flow rates (0.1-10 mL/min), provide reproducible flow (within 0.5%) and smooth flow, have high resistance to corrosion.

Question 9

What are charecteristics of injector in LC?

Answer 9

When it introduces sample into mobile phase there must not be bubbles of gas, sample loop size can be changed (0.5-500 μL), injection needs to be reproducible and rapid, it can be automated (autosampler)

Question 10

What are characteristics of columns?

Answer 10

Column is constructed from stainless steel to withstand high pressure,

packed with stationary phase (3-10μm), usually silica particles,

interval volume 0.5-50 mL,

often use a guard column containing large particles before the analytical column.

Question 11

What is chromophore?

Answer 11

The part of a molecule responsible for its color

Question 12

What are charecteristics of UV detector?

Answer 12

It require the analyte to contain chromophone,

has dual wavelength

can have multi wavelength detectors

can be diode array detectors

Question 13

What are two types of partition chromatography?

Answer 13

Liquid- liquid partition,

liquid- bonded phase partition

Question 14

In liquid-liquid partition what holds stationary phase?

Answer 14

It is held by physical adsorption on to the solid support

Question 15

In liquid-bonded partition what holds stationary phase?

Answer 15

Stationary phase is covalently bonded to the solid support

Question 16

In general, how bonded-phase packings are prepared?

Answer 16

By the reaction of organochlorosilaned with hydroxil functionalities on the surface of silica particles in hot dilute HCl.

Question 17

What are advantages of using bonded-phases?

Answer 17

They are very stable, no requirement to re-coat the solid support periodically

Question 18

What is disadvantage of using bonded-phases?

Answer 18

Limited sample capacity as we have large chemical modification on the surface

Question 19

On what depends in we use normal or reverse phase?

Answer 19

Depends upon the polarity of the mobile and stationary phases

Question 20

When do we have normal phase?

Answer 20

When we have polar stationary phase like water and non-polar mobile phase like hexane. The least polar component is eluted first, meaning increasing the polarity of the mobile phase decreases the elution time

Question 21

When do we have reverse phase?

Answer 21

When we have non-polar stationary phase like hydrocarbons and polar mobile phase like MeOH. Most polar component eluted first, meaning increasing the polarity of the mobile phase increases the elution time.