Unit 2

Question 1

what are the most common separation techniques in the lab?

Answer 1

extractions

Question 2

describe extractions

Answer 2

• allows for the transfer of the analyte(s) of interest from the sample (liquid or solid) to another phase not miscible with the first one

Question 3

what is the principle behind extractions

Answer 3

based on the partition/distribution of the analyte between the two phases

depends on affinity with both phases

Question 4

what are 2 major types of extractions?

what techniques are an example of these?

Answer 4

solvent extraction:

• liquid-liquid
• solid-liquid
• SFE
• LPME

solid-phase

• SPE
• SPME

Question 5

brewed coffee is an example of what type of extraction?

Answer 5

solid-liquid extraction

Question 6

describe liquid-liquid extraction (LLE)

Answer 6

occurs when a solute is partitioned between 2 immiscible liquids and the system is allowed to attain a thermodynamic equilibrium

Question 7

in LLE, the chemical of interest is ____

Answer 7

solute

Question 8

in LLE, what is left after the extraction?

Answer 8

raffinate

Question 9

what are the two phases in LLE?

Answer 9

phase 1: raffinate

phase 2: extractant

Question 10

what relationships describe the distribution of the solute between the 2 phases in LLE?

what type of constants are these?

Answer 10

1. partition constant
2. partition ratio/distribution constant

they are thermodynamic constants

Question 11

define solvent

Answer 11

substances (usually liquids) that acts as a medium for the dissolution of solvents

Question 12

define solvation

Answer 12

when a solute is dissolved in a solvent and the solvent molecules arrange themselves around molecules of the sulte

Question 13

what does solvation involve?

Answer 13

• bond formation
• H bonding
• vander Waals forces

Question 14

how does solvation affect entropy and thermodynamic stability of the solution?

Answer 14

increases entropy and thermodynamic stability

Question 15

describe non-polar solvents

Answer 15

solvents that consist of molecules with low or no net dipole moments

Question 16

describe polar solvents

Answer 16

solvents with large dipole moments

Question 17

how are dipoles derived

Answer 17

from chemical bonds between atoms with large differences in electronegativity

results in a molecule with uneven distribution of the bonding electron cloud about nuclei in the molecule

Question 18

in LLE, the ____ (larger/smaller) the interface area is, the faster the extraction will take place

Answer 18

larger interface area = faster extraction

Question 19

how can you increase the interface for the mass transfer (ie. create a faster extraction)

what should you be careful of

Answer 19

vigorous shaking of the spearatory funnel

be careful of pressure build up

Question 20

k’ is what?

Answer 20

capacity factor

Question 21

beta is what?

Answer 21

phase ratio

Question 22

what is the fundamental equation for separation methods driven by equilibrium?

Answer 22

Kd = k’ x beta

Question 23

what is distribution ratio (D)?

Answer 23

the ratio of total analytical concentration of a solute in the extract (regardless of its chemical form) to its total analytical concentration in other phases

D = C(A phase 2) / C (A phase 1)

Question 24

describe dominant chemical species

Answer 24

when pH < pKA

efficiently extracted in organic solvent

Question 25

what is the non-dominant species

Answer 25

when pH > pKa less efficiently extracted in organic solvent

Question 26

what is LPME?

Answer 26

liquid phase microextraction

Question 27

what are 3 types of LPME?

Answer 27

1. single drop microextraction 2. hollow fiber LPME 3. dispersive liquid-liquid mic

Question 28

what was the soxhlet extraction first used for? by who?

Answer 28

determination of milk fat by Franz von Soxlet

Question 29

describe soxhlet extraction

Answer 29

- method which minimizes the use of extraction solvent by circulation - thermally labile volatile analytes may be lost - potential interference from contaminants from extraction thimbles; may necessitate a blank extraction prior to actual sample extraction

Question 30

describe pressurized liquid extraction (PLE)

Answer 30

- involves use of pressurized liquids/fluids for extraction - uses elevated temp and pressures - allows extraction solvent to penetrate sample matrix, thus enhancing solvation of solute to be extracted

Question 31

in PLE, what are 2 types of extraction?

Answer 31

1. solubility controlled | 2. diffusion controlled

Question 32

what are 3 factors affecting extraction in PLE?

Answer 32

1. solvent type 2. temp 3. time

Question 33

in PLE, what are 3 extraction enhancers?

Answer 33

1. drying agents 2. dispersing agents 3. other additives

Question 34

how is microwave energy used in microwave assisted solvent extraction

Answer 34

to heat molecules in the sample (notably water) by ionic conduction and dipole rotation

Question 35

how does microwave assisted solvent extraction (MASE) work?

Answer 35

within in closed vessel systems: - heated water expands and generates pressure within the sample - increased pressure disrupts sample matrix from inside - analytes escape the matrix and be dissolved in the extraction solvent

Question 36

how does the use of solvent in MASE compare with conventional extraction methods?

Answer 36

- MASE uses less solvent | - solvent used maybe be microwave absorbing or non-microwave absorbing

Question 37

what is SFE?

Answer 37

supercritical fluid extraction

Question 38

how is a supercritical fluid formed?

Answer 38

- when a substance is heated above its critical temp/point | - fluid would have new properties different from the gas and liquid state

Question 39

how can the "solvent power" of a supercritical fluid be tuned?

Answer 39

by varying T and P

Question 40

what is the most commonly used supercritical fluid? what are some properties?

Answer 40

CO2 properties - low Tc (critical temp) - non-polar - non-toxic, non-flammable, non-explosive - relatively cheap - easily accessible in high purity