Chromatography

Question 1

Define chromatography

Answer 1

Separation of mixtures using a mobile phase (solvent) and a stationary phase (column packing material)

Question 2

Define adsorption

Answer 2

Adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. Takes place on surface of substrate

Question 3

Define absorption

Answer 3

Phenomenon involving atoms or molecules of bulk properties of a solid, liquid or gas crossing the surface and entering the volume of material

Question 4

Define desorption

Answer 4

Release of 1 substance from another, wither from the surface or through the surface. Occurs when equilibrium state of substance/system under investigation is altered

Question 5

What is chromatography based on?

Answer 5

A physical equilibrium that results when solute is transferred between mobile and stationary phases

Question 6

What is the distribution factor or partition ratio?

Answer 6

Calculation of amount sitting on solvent in stationary phase. K=Cs/Cm (conc stationary/ conc mobile)

Question 7

What do sharp narrow peaks mean?

Answer 7

Sharp means good separation and narrow means efficient system

Question 8

What does k mean in regards to the separation?

Answer 8

When k=1 the separation is poor, when k is bigger than 30 separation is slow and when k is between 2-10 separation is optimum

Question 9

What are the types of Liquid chromatography and what is it generally used for?

Answer 9

Thin layer chromatography, high performance liquid chromatography and column. It is used for compounds not volatile enough for GC

Question 10

What is thin layer chromatography?

Answer 10

Solid stationary phase and liquid mobile phase. Presumptive for illicit drugs or explosives and sample comparisons of dyes/inks. Process is inert material covered in thin film of silica gel for stationary. Requires a chamber and mobile phase (eluent), sample dissolved in volatile solvent and then dried to put on gel. Immerse plate in eluent without eluent covering spots

Question 11

What is HPLC?

Answer 11

Very fine and tightly packed stationary phase (more polar than mobile), uses a pump to increase speed of separation. Reverse phase is used more which refers to the mobile phase more polar than stationary phase

Question 12

What is rf?

Answer 12

IT is the distance travelled by component/distance travelled by mobile phase

Question 13

What are some types of HPLC detectors?

Answer 13

UV/VIS, electrochemical, photoconductivity, RI, mass spec, fluorescence

Question 14

Name the 4 attractive forces

Answer 14

Adsorption, partition, Size exclusion (big particles move out first and small take more time) and Ion exchange (polar mobile liquid containing salts and stationary phase with either acidic or basic fixed sites. Separated based upon attractive ionic forces. Use on explosives and GSR)

Question 15

What is Ion chromatography?

Answer 15

Separation of ions and polar molecules based on charge properties of analytes. Used for anion and cation analysis

Question 16

What are the 2 types of gas chromatography?

Answer 16

Gas solid and Gas liquid

Question 17

What is gas;liquid chromatography?

Answer 17

A chromatographic process in which a volatilised sample is eluted from a column containing liquid stationary phase using a gaseous mobile phase. For volatilised samples but need to be thermally stable. Mobile phase usually H, He or N as need to be inert

Question 18

What are the components of a GC?

Answer 18

Carrier gas, injector, column, detector and computer

Question 19

What does the liquid stationary phase for GC need to be?

Answer 19

High bp, low volatile and chemically unreactive

Question 20

What are the 2 types of injectors?

Answer 20

Split less mode and split mode

Question 21

What is split less mode?

Answer 21

Entire volatilised sample is swept into the column by the carrier gas

Question 22

What is split mode?

Answer 22

Only a portion of sample is taken into column, excess mixture is exhausted to atmosphere through split vent

Question 23

What is a SPME?

Answer 23

Solid Phase Microextraction Injector. It is a thin silica needle that is coated with extracting phase

Question 24

What is the capacity factor inversely proportional to?

Answer 24

Column temperature ie low temp= more time in stationary phase. Easiest parameter to control

Question 25

What is the resolution?

Answer 25

How close 2 peaks are whilst still being separate

Question 26

What is the molecular ion in mass spec?

Answer 26

The total mass thats calculated, molecular weight

Question 27

What is the base peak in mass spec?

Answer 27

Most intense peak in spectrum

Question 28

What are the 3 types of isotopes include examples

Answer 28

A- single and own eg F, I
A+1- varies by 1 number eg H, C, N
A+2- varies 2 numbers eg CL, O, S

Question 29

What is GC pyrolysis?

Answer 29

Breakdown using inert gases. Non-volatile, absence of O2 and extremely destructive. Used for textiles