Solvent Extractions Flashcards by Nancy He

What is the principle of extraction?

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)

How well did you know this?

Not at all

Perfectly

What does extraction achieve?

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

How well did you know this?

Not at all

Perfectly

major types of extraction (2):

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

Solid phase extraction (SPE, SPME)

How well did you know this?

Not at all

Perfectly

Are coffee and tea preparation considered extraction?

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

How well did you know this?

Not at all

Perfectly

What is a liquid-liquid extraction?

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

How well did you know this?

Not at all

Perfectly

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

extractant

How well did you know this?

Not at all

Perfectly

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

raffinate

How well did you know this?

Not at all

Perfectly

The names of the 2 phases in liquid liquid extraction:

extractant

raffinate

How well did you know this?

Not at all

Perfectly

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

pentane

dichloromethane

How well did you know this?

Not at all

Perfectly

What is KoD? What is KD?

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

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

Describe the process of ‘dissolving’ in a solvent:

Solvation:
solvent molecules arrange themselves around solute molecules

bond formation, H bonds, VDW forces

How well did you know this?

Not at all

Perfectly

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

increase

How well did you know this?

Not at all

Perfectly

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

True

Like dissolves like

How well did you know this?

Not at all

Perfectly

hydrophobic molecules are usually soluble in what type of solvents?

hydrocarbons
chlorinated solvents

(nonpolar, non-dissociating solvents)

How well did you know this?

Not at all

Perfectly

Describe the molecular structure that makes a solvent nonpolar

low or no net dipole moments

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

How well did you know this?

Not at all

Perfectly

What makes hydrocarbons very nonpolar?

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

How well did you know this?

Not at all

Perfectly

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

True

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

How well did you know this?

Not at all

Perfectly

What makes a molecule polar?

large dipole moment

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

How well did you know this?

Not at all

Perfectly

Chem bonds with large dipole moments:

C-Cl

How well did you know this?

Not at all

Perfectly

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

False

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

How well did you know this?

Not at all

Perfectly

Polar protic solvents: (4)

water
acetic acid
methanol
ethanol

How well did you know this?

Not at all

Perfectly

Polar aprotic solvents (3)

dichloromethane
tetrahydrofuran
acetone

nonpolar solvents (4)

hexane (and other hydrocarbons)
benzene
chloroform
diethyl ether

hexane has a dipole moment of _____

_____ is the most polar of the common solvents used

water

How can a liquid-liquid extraction be sped up?

increase INTERFACE AREA between 2 phases (interaction) - do this by shaking vigorously

a liquid liquid extraction aims to reach what point?

thermodynamic equilibrium

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

separatory funnel pressure buildup

What is an alternative to a separatory funnel?

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

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

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

Can LLE procedures be automated?

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

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

KD = k' x B

What is k'?

capacity factor = m2/m1 | analyte mass in phase 2)/(analyte mass in phase 1

what is the phase ratio?

B = v1/v2

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

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)

When pH < pKa -1, log D = ?

log D = log KD (approximation)

When pH >pKa + 1, log D = ?

log D = log KD + pKa - pH

How does pKa affect the relationship between D and KD?

D assume all chem species are the same (total concentration) above pKa => dissociation => different species in solution below pKa => no dissociation => same species

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

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

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?

less efficient extraction | dissociation -> becomes charged, less affinity for organic solvent

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

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

What is LPME?

liquid phase microextraction | single drop microextraction, hollow fibre LPME, dispersive LLME

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

milk fat solid-liquid extraction

What is a soxhlet extraction?

closed loop for solvent evaporation, condensation, and extraction (repeats) designed to minimize amount of solvent needed (continues circulating and extracting)

problems with soxhlet extraction:

may lose thermally labile and volatile analytes interference (contaminants) from extraction thimbles *should correct with blank

What is pressurized liquid extraction?

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

factors to consider for optimizing pressurized liquid extraction?

``` matrix parameters extraction type extraction mode factors affecting extraction (solvent, temp, time) extraction enhancers ```

T/F: microwaves can be used to enhance extraction

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

advantage of microwave assisted extraction:

less solvent needed

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

false; can be absorbing or non-absorbing

CO2 is often used in ____ ____ extraction

supercritical fluid extraction

What is a supercritical fluid?

formed when substance heated above critical temperature

advantages of using CO2:

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

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

temperature | pressure