Solvent Extractions Flashcards
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)
What does extraction achieve?
transfers analyte out from sample into another phase (not miscible with the phase containing the sample matrix)
major types of extraction (2):
Solvent extraction (liquid-liquid, solid-liquid, SFE, LPME)
Solid phase extraction (SPE, SPME)
Are coffee and tea preparation considered extraction?
yes; example of solid-liquid extraction (extracting compounds from coffee grains or tea leaves)
What is a liquid-liquid extraction?
solute partitioned between 2 immiscible liquids (system allowed to attain equilibrium)
The phase in liquid-liquid extraction that EXTRACTS the analyte is called the _____
extractant
the phase in liquid-liquid extraction that contains the matrix the solute is extracted from is called the _____
raffinate
The names of the 2 phases in liquid liquid extraction:
extractant
raffinate
The compound 2-pentanethiol in guava can be extracted with liquid liquid extraction, using ____ and _____
pentane
dichloromethane
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
True/False: A very low KD value means very little has been extracted
True (much less analyte in phase 2 than phase 1)
Describe the process of ‘dissolving’ in a solvent:
Solvation:
solvent molecules arrange themselves around solute molecules
bond formation, H bonds, VDW forces
The process of solvation will (increase/decrease) entropy and (increase/decrease) thermodynamic stability)
increase
increase
True/False: molecules are usually soluble in solvents with similar polarity
True
Like dissolves like
hydrophobic molecules are usually soluble in what type of solvents?
hydrocarbons
chlorinated solvents
(nonpolar, non-dissociating solvents)
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
What makes hydrocarbons very nonpolar?
Made of CH (non polar bonds); C and H have similar electronegativity, share electrons equally
T/F: CO2 is nonpolar. Why or why not?
True
The O on each side of the C will balance out (nullify) the charges
What makes a molecule polar?
large dipole moment
chem bonds have large electronegativity difference; unequal distribution of electron cloud -> net charge
Chem bonds with large dipole moments:
OH
C-Cl
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!
Polar protic solvents: (4)
water
acetic acid
methanol
ethanol
Polar aprotic solvents (3)
dichloromethane
tetrahydrofuran
acetone
nonpolar solvents (4)
hexane (and other hydrocarbons)
benzene
chloroform
diethyl ether
hexane has a dipole moment of _____
0
_____ 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
