separation techniques - phase extractions Flashcards
(25 cards)
what is the purpose of separation techniques?
to determine what substances are in a sample and how much of each is present
analyte definition
the target species
matrix definition
number of materials mixed in with analytes
interferants definition
any substance that interferes with the analysis
selective method definition
a technique that responds only to analyte of interest
give the 3 types of separation technique
isolation
purification
removal of compounds
when would a simple separation be used?
for samples with few analytes or for more complex samples as a coarse reparation step, often for separating 2 phases
give the 5 types of phase separations
gas-liquid
liquid-liquid
gas-solid
liquid-solid
supercritical fluid-solid
what techniques would be used for a gas-liquid separation?
(l->g) distillation
(g->l) denuders, bubblers, condensation
what techniques would be used for a liquid-liquid separation?
liquid liquid extraction via separating funnel
what techniques would be used for a gas-solid separation?
(g->s) adsorption tubes
(s->g) sublimation, lyophilisation, filtration
what techniques would be used for a liquid-solid separation?
(s->l) dissolution, soxhlet extraction
(l->s) precipitation, filtration
what techniques would be used for a supercritical fluid-solid separation?
(s->scf) supercritical fluid extraction
what is raoults law?
the vapour pressure of each component of a mixture is proportional to its mole fraction
Pa = xa*Pa^o
azetropic mixture definition
a mixture of 2 or more liquids with a similar boiling point and composition in vapour phase
- this mixtures have either lower or higher b.p. than their components - this is related to raoults law, solutions showing large +ve/-ve deviations may have a b.p. lower/higher than pure components
what is necessary for liquid-liquid extraction to occur?
the 2 liquids must be immiscible - form 2 distinct phases (e.g. aqueous and organic layers)
what property determines positioning of the layers?
density - higher density means the phase will be below/on the bottom
partition coefficient Kp equation
Kp = [X]raffinate/[X]extractant
- this depends on thermodynamics of dissolving X in 2 phases
how is Kp often found in databases?
as log P
if logP < 0 compound has a higher affinity for aq phase
if logP = 0 compound is equally partitioned between phases
if logP > 0 compound has a higher affinity for organic phase
if logP = 1 then partitioning is 10:1 org:aq
what is the rule of thumb for solubility?
like dissolves like
how is logP altered for ionisable compounds?
logD which = logP as a function of pH
how does polarity of the particular organic solvents/analytes change Kp values?
less polar org solvents give very high Kp values for non polar analytes, and smaller Kp values for analytes of a higher polarity
in terms of Kp, what makes extraction easier?
ideally analyte and interferant should have vastly different Kps e.g. analyte has very low Kp and interferant has very high Kp
what determines mole fraction of compound extracted?
Kp and volume of phases
