Graduate Presentations

Question 1

What is accelerated solvent extraction?

Answer 1

type of solid-liquid extraction;

automated technique using high pressure (200C) and temperature (1500psi)

Question 2

Accelerated solvent extraction is also known as_____ and used as an alternative to: _____

Answer 2

pressurized liquid extraction

maceration, soxhlet, sonication, etc

Question 3

2 types of accelerated solvent extraction:

Answer 3

static

dynamic

Question 4

what is the purpose of high pressure and temperature in ASE?

Answer 4

high temp => accelerate extraction kinetics (faster)

high pressure => keeps solvent in liquid state above boiling pt

Question 5

advantages of ASE: (3)

Answer 5

Uses less solvent (50-90% less than hot water extraction)

fast (12-20 min)

allows mixing of up to 3 solvents

Question 6

In ASE, the sample is loaded and ____ is added in the extra volume

Answer 6

sand

Question 7

What are examples of applications of ASE?

Answer 7

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

Question 8

limitations of ASE:

Answer 8

expensive
high temp/pressure affects selectivity
extract volume not reproducible

Question 9

What does QuEChERS stand for?

Answer 9

Quick, Easy, cheap, effective, rugged, safe

Question 10

What is the QuEChERS method?

Answer 10

simple sample prep method:

1. extraction (SLE or salting)
2. cleanup (dispersive SPE)

Question 11

QuEChERS was originally developed for:

Answer 11

multi-class pesticides in fruit/veg

Question 12

Why would QuEChERS need to be optiimized?

Answer 12

different matrices!

obtain high recovery %
diminish matrix effects
avoid analyte degradation

Question 13

The _____ method (QuEChERS) is effective for determination of pesticide residues, mycotoxin, PAHs, etc…in complex matrices

Answer 13

multi-toxin

Question 14

What are the components needed for QuEChERS?

Answer 14

solvent (ACN usually)
extraction salt
buffer
centrifuge
sorbent (for dispersive SPE)

Question 15

Can QuEChERS be done without a buffer?

Answer 15

Yes (original method); can be used for nonbase sensitive compounds

Question 16

The AOAC QuEChERS method uses ____ as buffer.

What does the CEN mthod use?

Answer 16

AOAC: Na acetate
CEN: NaCl, Na citrate, Na citrate sesquihydrate

Question 17

What does the dSPE step in QuEChERS achieve?

Answer 17

cleans extract (remove impurities)

Question 18

What are common sorbents for dSPE?

Answer 18

MgSO4 (almost always used); remove excess water
C18: remove fat/nonpolar compounds
PSA: remove sugar, FA, carbs, pigment
GCB: remove pigment, sterol

Question 19

PSA stands for:

Answer 19

primary sorbent amine

Question 20

GCB stands for:

Answer 20

graphitized carbon black

Question 21

applications of QuEChERS:

Answer 21

mycotoxin
multi-class pesticides
PAHs
food additives
pharmaceuticals
acrylamide

Question 22

advantages of QuEChERS: (5)

Answer 22

reduced matrix effects
less solvents/materials
less time, less work
lower cost
versatile and modifiable

Question 23

disadvantages of QuEChERS: (3)

Answer 23

not appropriate for all chemicals
non acid pH can affect recovery
ACN is $$$, toxic, low volatility, can interfere with detectors

Question 24

What is an eco-friendly, GRAS extractant that is an alternative to organic solvents?

Answer 24

supercritical fluid extraction

Question 25

most common SCF

Answer 25

CO2 (sometimes modified by ethanol, methanol)

Question 26

extraction conditions for supercritical CO2:

Answer 26

above critical temp of 31C, critical pressure 7.4MPa

Question 27

Properties of SCF:

Answer 27

single homogenous fluid;

heavy like liquid, penetration power like gas

Question 28

4 basic steps of SCFE:

Answer 28

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

Question 29

Why are co-solvents added to Supercritical CO2?

Answer 29

adjust polarity (affinity)

Question 30

what parameters must be considered for SCFE? (6)

Answer 30

density (pressure)
polarity of solvent
matrix porosity
particle size
temp
flow rate

Question 31

Applications of SCFE:

Answer 31

cholesterol in eggs
caffeine in coffee/tea
microalgae oil
flavor compounds
bioactive compounds
pesticides

Question 32

advantages of SCFE:

Answer 32

high selectivity and yield
lower temp
can be automated
nontoxic, nonflammable (safe)
low cost
eco-friendly

Question 33

limitations of SCFE:

Answer 33

not good for highly polar compounds
many parameters
high pressure
cost

Question 34

SPME stands for:

Answer 34

solid phase microextraction

Question 35

what is the principle of SPME?

Answer 35

partitioning analyte between fibre coating (on microfibre) and the sample matrix to reach equilibrium;
amount extracted is proportional to concentration in sample

Question 36

basic procedure for SPME:

Answer 36

push plunger to expose fibre into sample

adsorption of analytes -> wait until attains equilibrium

withdraw needle

put needle in chromatograph machine (GC or LC)

Question 37

extraction modes for SPME:

Answer 37

direct
headspace (for volatile)
membrane

Question 38

Applications of SPME:

Answer 38

aroma/volatiles analysis (wine)
PAHs in fish
pharmaceuticals
biological samples (even living animals!)
environmental contaminants

Question 39

advantages of SPME

Answer 39

simple
fast
cheap
little to no solvent needed
limited manipulation
sufficiently sensitive/accurate/precise
small sample volumes
adaptable

Question 40

disadvantages of SPME:

Answer 40

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)