Graduate Presentations Flashcards
What is accelerated solvent extraction?
type of solid-liquid extraction;
automated technique using high pressure (200C) and temperature (1500psi)
Accelerated solvent extraction is also known as_____ and used as an alternative to: _____
pressurized liquid extraction
maceration, soxhlet, sonication, etc
2 types of accelerated solvent extraction:
static
dynamic
what is the purpose of high pressure and temperature in ASE?
high temp => accelerate extraction kinetics (faster)
high pressure => keeps solvent in liquid state above boiling pt
advantages of ASE: (3)
Uses less solvent (50-90% less than hot water extraction)
fast (12-20 min)
allows mixing of up to 3 solvents
In ASE, the sample is loaded and ____ is added in the extra volume
sand
What are examples of applications of ASE?
extracting polysaccharides
extract/determine organic contaminants in sludge/soil/other waste
analyze nutritional/bioactive compounds
analyze organic contaminants in feed/food
extract benzoylecgonine, cocaine from coca leaves
limitations of ASE:
expensive
high temp/pressure affects selectivity
extract volume not reproducible
What does QuEChERS stand for?
Quick, Easy, cheap, effective, rugged, safe
What is the QuEChERS method?
simple sample prep method:
- extraction (SLE or salting)
- cleanup (dispersive SPE)
QuEChERS was originally developed for:
multi-class pesticides in fruit/veg
Why would QuEChERS need to be optiimized?
different matrices!
obtain high recovery %
diminish matrix effects
avoid analyte degradation
The _____ method (QuEChERS) is effective for determination of pesticide residues, mycotoxin, PAHs, etc…in complex matrices
multi-toxin
What are the components needed for QuEChERS?
solvent (ACN usually) extraction salt buffer centrifuge sorbent (for dispersive SPE)
Can QuEChERS be done without a buffer?
Yes (original method); can be used for nonbase sensitive compounds
The AOAC QuEChERS method uses ____ as buffer.
What does the CEN mthod use?
AOAC: Na acetate
CEN: NaCl, Na citrate, Na citrate sesquihydrate
What does the dSPE step in QuEChERS achieve?
cleans extract (remove impurities)
What are common sorbents for dSPE?
MgSO4 (almost always used); remove excess water
C18: remove fat/nonpolar compounds
PSA: remove sugar, FA, carbs, pigment
GCB: remove pigment, sterol
PSA stands for:
primary sorbent amine
GCB stands for:
graphitized carbon black
applications of QuEChERS:
mycotoxin multi-class pesticides PAHs food additives pharmaceuticals acrylamide
advantages of QuEChERS: (5)
reduced matrix effects less solvents/materials less time, less work lower cost versatile and modifiable
disadvantages of QuEChERS: (3)
not appropriate for all chemicals
non acid pH can affect recovery
ACN is $$$, toxic, low volatility, can interfere with detectors
What is an eco-friendly, GRAS extractant that is an alternative to organic solvents?
supercritical fluid extraction
most common SCF
CO2 (sometimes modified by ethanol, methanol)
extraction conditions for supercritical CO2:
above critical temp of 31C, critical pressure 7.4MPa
Properties of SCF:
single homogenous fluid;
heavy like liquid, penetration power like gas
4 basic steps of SCFE:
liquid heated to supercrit. conditions
go to extraction vessel, diffuse into solid matrix and dissolves material to be extracted
goes into separator (lower pressure) -> extracted material settles out
Cool, reuse, or discharge CO2
Why are co-solvents added to Supercritical CO2?
adjust polarity (affinity)
what parameters must be considered for SCFE? (6)
density (pressure) polarity of solvent matrix porosity particle size temp flow rate
Applications of SCFE:
cholesterol in eggs caffeine in coffee/tea microalgae oil flavor compounds bioactive compounds pesticides
advantages of SCFE:
high selectivity and yield lower temp can be automated nontoxic, nonflammable (safe) low cost eco-friendly
limitations of SCFE:
not good for highly polar compounds
many parameters
high pressure
cost
SPME stands for:
solid phase microextraction
what is the principle of SPME?
partitioning analyte between fibre coating (on microfibre) and the sample matrix to reach equilibrium;
amount extracted is proportional to concentration in sample
basic procedure for SPME:
push plunger to expose fibre into sample
adsorption of analytes -> wait until attains equilibrium
withdraw needle
put needle in chromatograph machine (GC or LC)
extraction modes for SPME:
direct
headspace (for volatile)
membrane
Applications of SPME:
aroma/volatiles analysis (wine) PAHs in fish pharmaceuticals biological samples (even living animals!) environmental contaminants
advantages of SPME
simple fast cheap little to no solvent needed limited manipulation sufficiently sensitive/accurate/precise small sample volumes adaptable
disadvantages of SPME:
each protocol needs optimizing parameters must be controlled/kept constant for all samples analyte carry-over (error) limited sensitivity in complex matrices low repeatability (fibre is damaged)
