2. Extraction
It is the sample separation technique.
It has various types – liquid-liquid extraction,
liquid-solid extraction, Solid phase extraction
etc.
2
3. Liquid-Liquid Extraction (LLE)
LLE is based on establishment of
distribution equilibrium of the analytes
between two immiscible phases, an
aqueous and an organic phase.
Apparatus for LLE is a separating
funnel.
Important disadvantages
1.
• Consumption of large volumes of
expensive and toxic solvents
2.
• Difficult phase separations
3.
• Low concentration factor 3
4. Solid Phase Extraction (SPE)
SPE process is based on distribution of
analytes between solid sorbent packed in
a cartridge and liquid sample which moves
through the solid phase. Solid phase
usually consists of small porous particles
of silica with or without bonded organic
phase, organic polymers and ion
exchangers.
Limitations :
1. Clogging the pores of the solid phase
2. SPE needs at least 100 μL of the solvent
3. Time consuming method due to several steps of operation
4
5. Microextraction
Microextraction is defined as an extraction
technique where the volume of the extracting
phase is very small and extraction of analytes
is not exhaustive. In most cases only a small
fraction of the initial analyte is extracted for
analysis.
Microextraction
Solid Phase
Microextraction
Liquid Phase
Microextraction 5
6. Solid phase microextraction (SPME)
SPME is a simple and efficient technique, which
eliminates the necessity of using solvents.
SPME Device
Modified syringe-like instrument.
The fused silica fiber, having a small size and
cylindrical shape, is connected to stainless-steel
tubing that is used to provide additional mechanical
strength to the fiber assembly for repeated sampling.
This stainless-steel tubing is connected to a specially
designed syringe-like instrument.
A small volume of extraction phase (usually less than
1 μL) coated on fused silica support is mounted in a
modified syringe.
6
7. Extraction phase - high molecular weight
polymeric liquid or a solid porous sorbent
with high surface area.
SPME fiber is quite sensitive to complex
matrix such as plasma.
With pulling the syringe plunger in, the
fiber is protected in the needle and with
pulling out; the fiber is exposed to the
sample.
7
8. SPME can be performed in two ways
1. Direct immersion SPME
Fiber is directly immersed in
liquid samples.
2. Headspace SPME
Fiber needle is placed above the
headspace of the sample.
volatile analytes
8
9. Factors affecting SPME
Fiber coating selection
Microextraction temperature
Microextraction time
Desorption temperature and time
Sample agitation
Salting out effect
9
10. Rapid, simple, solvent free
and sensitive method
It is compatible with analyte
separation and detection by
GC & HPLC
It provides linear results for
a wide range of
concentrations of analytes
It gives highly consistent,
quantifiable results from
very low concentrations of
analytes
Their relatively low
recommended operating
temperature (generally in
the range 240 – 280o C)
Fiber breakage
Stripping of coatings
Bending of needles and
their expense
DisadvantagesAdvantages
10
11. Liquid Phase Microextraction (LPME)
LPME is a solvent-minimized procedure, in which only several μL of solvent
are required to concentrate analytes from various samples rather than
hundreds of mL needed in traditional LLE.
Compatible with GC, CE & HPLC.
Extraction normally takes place into a small amount of a water-immiscible
solvent (acceptor phase) from an aqueous sample containing analytes (donor
phase).
Types of liquid phase microextraction
Single-drop microextraction (SDME)
Dispersive liquid–liquid microextraction
(DLLME)
11
12. Single-drop microextraction (SDME)
In this technique, extraction solvent has the form of one
drop (1 -8 μL) hence called single-drop microextraction.
The SDME method can be used for liquid and gaseous
samples.
After extraction, the micro drop is retracted back into the
syringe and transferred for further analysis.
Compatible with GC & HPLC, AAS & ICP
It can be performed in two ways
1. Direct immersion SDME
2. Headspace SDME
12
13. a) Direct immersion (DI)-SDME
A drop of a water-immiscible organic
solvent is suspended directly from the
tip of a micro syringe needle immersed
in the aqueous sample.
Two liquid phases are in direct contact
between each other, & the transfer of
analytes from the water solution to the
extraction drop lasts until
thermodynamic balance is achieved.
DI-SDME requires the use of a mixing
organic solvent and analytes, which are
characterised by higher solubility in the
organic solvent than in the sample
solution
13
14. b) Headspace SDME
A micro drop of appropriate solvent is
placed in the headspace of the sample
solution or in a flowing air sample
stream to extract volatile analytes.
Gaseous analytes from the liquid
phase, dissolve in the solvent drop.
After the extraction, the microdrop is
withdrawn back into the syringe
needle and then it is injected to the
detector for quantitative
determination of analytes
14
15. Factors affecting SDME
Kind and volume of extraction solvent
Extraction time
Extraction temperature
Salt addition
pH Adjustment
Sample agitation
15
17. Selection of the extractant is very flexible & its solubility in the sample solution need
not be considered.
Wide range of extractable analytes & analytical methods that can be coupled to
SDME.
Provides excellent clean up for samples .
HS-
SPME
HS-
SDME
Advantages of HS-SDME over DI-SDME
Comparison of HS-SPME & HS-SDME
17
18. Dispersive liquid-liquid microextraction (DLLME)
This technique uses μL volume of extraction solvent along with a few mL of
dispersive solvents.
A cloudy solution is formed when an appropriate mixture of extraction and
dispersive solvents is injected into an aqueous sample containing the
analytes of interest.
Solutes are enriched in the extraction solvent, which is dispersed into the
bulk aqueous solution.
After centrifugation, analytes in the settled phase can be determined by
using conventional analytical techniques.
Extraction solvent must be immiscible with aqueous sample solution and
disperser solvent must soluble in both of the extraction solvent and aqueous
sample solution.
18
20. Factors affecting DLLME
Kind and volume of extraction solvent
Kind and volume of dispersion solvent
Extraction temperature and time
Salting out
20
21. Advantages
low cost
operation simplicity
high recovery
high enrichment factor
very short extraction time
Disadvantages
Low selectivity
Requires the use of three solvents
Limited solvent choice
Requires centrifugation
21
22. Summary
Microextraction is defined as an extraction technique
where the volume of the extracting phase is very small
and extraction of analytes is not exhaustive. In most
cases only a small fraction of the initial analyte is
extracted for analysis.
It has types such as LPME & SPME
LPME is further types such as SDME & DLLME
22
23. References
Pourya Biparva and Amir Abbas Matin, Chapter 4 Microextraction Techniques as a
Sample Preparation Step for Metal Analysis, Atomic Absorption Spectroscopy, Pg.
No. 61 – 88, January 2012.
Mohammad Mahdi Moein, Rana Said, Fatma Bassyouni, and Mohamed Abdel-
Rehim, Solid Phase Microextraction and Related Techniques for Drugs in Biological
Samples, Journal of Analytical Methods in Chemistry, Pg. No. 1 – 25, 2014.
Małgorzata Rutkowska, Kinga Dubalska, Piotr Konieczka and Jacek Namieśnik,
Microextraction Techniques Used in the Procedures for Determining Organomercury
and Organotin Compounds in Environmental Samples, Molecules, Pg. No. 7581 –
7609, 2014.
Ali Sarafraz-Yazdi, Amirhassan Amiri, Liquid-phase microextraction, Trends in
Analytical Chemistry, Vol. 29, No. 1, Pg. No. 1 – 14, 2010.
David Harvey, Chapter 7 Obtaining & Preparing Samples for Analysis, Modern
Analytical Chemistry, Pg. No. 212 – 213, 2000.
James W. Robinson, Eileen M. Skelly Frame, George M. Frame II, Chapter 1
Concepts of Instrumental Analytical Chemistry, Undergraduate Instrumental
Analysis, 6th Edition, Pg. No. 44 – 51, 2005. 23
