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Separation Techniques > Solvent Extractions > Flashcards

Solvent Extractions Flashcards

1
Q

What is the principle of extraction?

A

the partitioning of the analyte between 2 phases, due to its respective affinity for each (more goes into the one it has more affinity for)

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2
Q

What does extraction achieve?

A

transfers analyte out from sample into another phase (not miscible with the phase containing the sample matrix)

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3
Q

major types of extraction (2):

A

Solvent extraction (liquid-liquid, solid-liquid, SFE, LPME)

Solid phase extraction (SPE, SPME)

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4
Q

Are coffee and tea preparation considered extraction?

A

yes; example of solid-liquid extraction (extracting compounds from coffee grains or tea leaves)

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5
Q

What is a liquid-liquid extraction?

A

solute partitioned between 2 immiscible liquids (system allowed to attain equilibrium)

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6
Q

The phase in liquid-liquid extraction that EXTRACTS the analyte is called the _____

A

extractant

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7
Q

the phase in liquid-liquid extraction that contains the matrix the solute is extracted from is called the _____

A

raffinate

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8
Q

The names of the 2 phases in liquid liquid extraction:

A

extractant

raffinate

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9
Q

The compound 2-pentanethiol in guava can be extracted with liquid liquid extraction, using ____ and _____

A

pentane

dichloromethane

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10
Q

What is KoD? What is KD?

A

KoD (partition constant): ratio of ACTIVITY of analyte in phase 2 vs phase 1

KD (distribution constant/partition ratio): ratio of CONCENTRATION of analyte in phase 2 vs phase 1

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11
Q

True/False: A very low KD value means very little has been extracted

A

True (much less analyte in phase 2 than phase 1)

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12
Q

Describe the process of ‘dissolving’ in a solvent:

A

Solvation:
solvent molecules arrange themselves around solute molecules

bond formation, H bonds, VDW forces

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13
Q

The process of solvation will (increase/decrease) entropy and (increase/decrease) thermodynamic stability)

A

increase

increase

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14
Q

True/False: molecules are usually soluble in solvents with similar polarity

A

True

Like dissolves like

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15
Q

hydrophobic molecules are usually soluble in what type of solvents?

A

hydrocarbons
chlorinated solvents

(nonpolar, non-dissociating solvents)

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16
Q

Describe the molecular structure that makes a solvent nonpolar

A

low or no net dipole moments

no charges, electrons equally distributed (cancel’s out), or atoms have similar electronegativity

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17
Q

What makes hydrocarbons very nonpolar?

A

Made of CH (non polar bonds); C and H have similar electronegativity, share electrons equally

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18
Q

T/F: CO2 is nonpolar. Why or why not?

A

True

The O on each side of the C will balance out (nullify) the charges

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19
Q

What makes a molecule polar?

A

large dipole moment

chem bonds have large electronegativity difference; unequal distribution of electron cloud -> net charge

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20
Q

Chem bonds with large dipole moments:

A

OH

C-Cl

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21
Q

T/F: C-Cl has a large dipole moment, so CCl4 is a polar solvent

A

False

due to arrangement (tetrahedral), all the dipoles cancel out; net dipole is null!

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22
Q

Polar protic solvents: (4)

A

water
acetic acid
methanol
ethanol

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23
Q

Polar aprotic solvents (3)

A

dichloromethane
tetrahydrofuran
acetone

24
Q

nonpolar solvents (4)

A

hexane (and other hydrocarbons)
benzene
chloroform
diethyl ether

25
Q

hexane has a dipole moment of _____

A

0

26
Q

_____ is the most polar of the common solvents used

A

water

27
Q

How can a liquid-liquid extraction be sped up?

A

increase INTERFACE AREA between 2 phases (interaction)

  • do this by shaking vigorously
28
Q

a liquid liquid extraction aims to reach what point?

A

thermodynamic equilibrium

29
Q

When performing a liquid liquid extraction manually, a _____ is used. What precaution must be taken?

A

separatory funnel

pressure buildup

30
Q

What is an alternative to a separatory funnel?

A

continuous liquid liquid extractor

solvent is boiled in closed system, continuously evaporate and mix in with sample -> collected and repeats

31
Q

True/False: the same continuous liquid-liquid extractor set up can be used for all solvent types

A

False; will need to adjust depending is solvent is heavier or lighter than water (or whatever phase 1 is)

32
Q

Can LLE procedures be automated?

A

Yes; can have robots that do the adding of solvents, vortexing, drydown, and redissolution

33
Q

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

A

KD = k’ x B

34
Q

What is k’?

A

capacity factor = m2/m1

analyte mass in phase 2)/(analyte mass in phase 1

35
Q

what is the phase ratio?

A

B = v1/v2

36
Q

What is the Distribution ratio, and what does it ignore?

A

ratio of TOTAL analyte concentration (all chemical forms) in phase 2 vs phase 1

ignores the diff. chemical species in solution (all considered the same)

37
Q

When pH < pKa -1, log D = ?

A

log D = log KD (approximation)

38
Q

When pH >pKa + 1, log D = ?

A

log D = log KD + pKa - pH

39
Q

How does pKa affect the relationship between D and KD?

A

D assume all chem species are the same (total concentration)

above pKa => dissociation => different species in solution

below pKa => no dissociation => same species

40
Q

T/F: the pH the extraction takes place at will not affect the results

A

False
pH above pKa (+1) => dissociation => becomes charged
(will affect affinity and solubility)

41
Q

an uncharged compound is being extracted by an organic solvent. Its pKa is 4.5, and the pH is neutral. How will this affect results?

A

less efficient extraction

dissociation -> becomes charged, less affinity for organic solvent

42
Q

How can we increase extraction yield with the same solvent? (2) What is the better way?

A

increase solvent amount

consecutive extractions (better; less solvent needed, more efficient)

43
Q

What is LPME?

A

liquid phase microextraction

single drop microextraction, hollow fibre LPME, dispersive LLME

44
Q

Soxhlet extraction was proposed for determination of ______. What type of extraction is it?

A

milk fat

solid-liquid extraction

45
Q

What is a soxhlet extraction?

A

closed loop for solvent evaporation, condensation, and extraction (repeats)

designed to minimize amount of solvent needed (continues circulating and extracting)

46
Q

problems with soxhlet extraction:

A

may lose thermally labile and volatile analytes

interference (contaminants) from extraction thimbles
*should correct with blank

47
Q

What is pressurized liquid extraction?

A

use pressurized liquid/fluids for extraction; high temperature (better penetration) => accelerated process

48
Q

factors to consider for optimizing pressurized liquid extraction?

A 
matrix parameters
extraction type
extraction mode
factors affecting extraction (solvent, temp, time)
extraction enhancers
49
Q

T/F: microwaves can be used to enhance extraction

A

True: use to heat molecules by ionic conduction/dipole rotation (mostly water) => generate pressure from within => allow analytes to escape into solvent

50
Q

advantage of microwave assisted extraction:

A

less solvent needed

51
Q

T/F: the analyte in microwave assisted extraction must be microwave absorbing

A

false; can be absorbing or non-absorbing

52
Q

CO2 is often used in ____ ____ extraction

A

supercritical fluid extraction

53
Q

What is a supercritical fluid?

A

formed when substance heated above critical temperature

54
Q

advantages of using CO2:

A 
nontoxic
nonflammable
nonexplosive
cheap
readily available in high purity
relatively lower temperature/pressure needed to reach supercritical
55
Q

___ and ____ can be adjusted to vary the properties of a supercritical fluid

A

temperature

pressure

Separation Techniques (12 decks)

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