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Extraction

It is the sample separation technique. It has various types – liquid-liquid extraction,

liquid-solid extraction, Solid phase extraction etc.

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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

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• Consumption of large volumes of expensive and toxic solvents

2.• Difficult phase separations

3.• Low concentration factor 3

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 operation4

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

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Solid phase microextraction (SPME)

SPME is a simple and efficient technique, whicheliminates 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-steeltubing that is used to provide additional mechanicalstrength to the fiber assembly for repeated sampling.

This stainless-steel tubing is connected to a speciallydesigned syringe-like instrument.

A small volume of extraction phase (usually less than1 μL) coated on fused silica support is mounted in amodified syringe.

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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.

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SPME can be performed in two ways

1. Direct immersion SPMEFiber is directly immersed in liquid samples.

2. Headspace SPMEFiber needle is placed above the headspace of the sample.

volatile analytes

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Factors affecting SPME Fiber coating selection

Microextraction temperature

Microextraction time

Desorption temperature and time

Sample agitation

Salting out effect

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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

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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 thanhundreds 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 (donorphase).

Types of liquid phase microextraction

Single-drop microextraction (SDME)

Dispersive liquid–liquid microextraction (DLLME)

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Single-drop microextraction (SDME)

In this technique, extraction solvent has the form of onedrop (1 -8 μL) hence called single-drop microextraction.

The SDME method can be used for liquid and gaseoussamples.

After extraction, the micro drop is retracted back into thesyringe and transferred for further analysis.

Compatible with GC & HPLC, AAS & ICP It can be performed in two ways1. Direct immersion SDME2. Headspace SDME

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a) Direct immersion (DI)-SDME A drop of a water-immiscible organic

solvent is suspended directly from thetip of a micro syringe needle immersedin the aqueous sample.

Two liquid phases are in direct contactbetween each other, & the transfer ofanalytes from the water solution to theextraction drop lasts untilthermodynamic balance is achieved.

DI-SDME requires the use of a mixingorganic solvent and analytes, which arecharacterised by higher solubility in theorganic solvent than in the samplesolution

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b) Headspace SDME A micro drop of appropriate solvent is

placed in the headspace of the samplesolution or in a flowing air samplestream to extract volatile analytes.

Gaseous analytes from the liquidphase, dissolve in the solvent drop.

After the extraction, the microdrop iswithdrawn back into the syringeneedle and then it is injected to thedetector for quantitativedetermination of analytes

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Factors affecting SDME Kind and volume of extraction solvent

Extraction time

Extraction temperature

Salt addition

pH Adjustment

Sample agitation

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Advantages

cheap technique

simple equipment

Use of minimum amounts of solvents

Disadvantages

instability of the drop

small surface of the drop

slow kinetics of extraction

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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

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Dispersive liquid-liquid microextraction (DLLME)

This technique uses μL volume of extraction solvent along with a few mL ofdispersive solvents.

A cloudy solution is formed when an appropriate mixture of extraction anddispersive solvents is injected into an aqueous sample containing theanalytes of interest.

Solutes are enriched in the extraction solvent, which is dispersed into thebulk aqueous solution.

After centrifugation, analytes in the settled phase can be determined byusing conventional analytical techniques.

Extraction solvent must be immiscible with aqueous sample solution anddisperser solvent must soluble in both of the extraction solvent and aqueoussample solution.

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Different steps in dispersive liquid-liquid

microextraction

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Factors affecting DLLME

Kind and volume of extraction solvent

Kind and volume of dispersion solvent

Extraction temperature and time

Salting out

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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 centrifugation21

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

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References

Pourya Biparva and Amir Abbas Matin, Chapter 4 Microextraction Techniques as aSample 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 BiologicalSamples, 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 Organomercuryand Organotin Compounds in Environmental Samples, Molecules, Pg. No. 7581 –7609, 2014.

Ali Sarafraz-Yazdi, Amirhassan Amiri, Liquid-phase microextraction, Trends inAnalytical Chemistry, Vol. 29, No. 1, Pg. No. 1 – 14, 2010.

David Harvey, Chapter 7 Obtaining & Preparing Samples for Analysis, ModernAnalytical Chemistry, Pg. No. 212 – 213, 2000.

James W. Robinson, Eileen M. Skelly Frame, George M. Frame II, Chapter 1Concepts of Instrumental Analytical Chemistry, Undergraduate InstrumentalAnalysis, 6th Edition, Pg. No. 44 – 51, 2005. 23

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