Recent Issues in Analytical Chemistry

7/27/2019 Recent Issues in Analytical Chemistry

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Recent issues in

analytical chemistry

Pretreatment method and emerging contaminant


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Background

One of the biggest challenges facing the

chemical and pharmaceutical industry today is

the need to replace current environmentally

unsustainable and often polluting processes

with cleaner ones. The transition to these new

green processes will be easier if these

technologies are more efficient and less costly

than the current ones.


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Background

Anastas and Warner in their book (Green

Chemistry: Theory and Practice) describe 12

principles of green chemistry.

That principles are mainly for chemical

synthesis applications, but they can also be

applied to other processes, such as extraction.


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Background

What can be demanded from a modern

extraction technique today?

Safe to the environment Non-toxic Fast and automated

Robust Highly sensitive

Cost -efficient


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Background

Some of the more promising extraction

techniques are :

Supercritical Fluid Extraction (SFE)

Pressurized Liquid Extraction (PLE)

Pressurized Hot Water extraction (PHWE)

Microwave Assisted Extraction (MAE)

Membrane-Assisted Solvent Extraction (MASX)

Solid Phase Micro Extraction (SPME)

Stir-Bar Sorptive Extraction (SBSE)


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Supercritical Fluid Extraction

A liquid or gas becomes supercritical as you

increase the temperature and the pressure

above its critical point (defined by Tc

and Pc

in

the figure)


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SFE is simply performed by pumping the SF

through a vessel filled with sample, and

further down the line depressurize the SF for

collection of extracted component.


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Several parameters have to be optimized in SFE:

Temperature and pressure of the SF

Extraction time

Flow rate

Addition of cosolvent

Collection mode Furthermore, the methods are generally matrix-

dependent, (a method developed for a particular target-molecule(s) cannot be directly applied to other types ofsamples than the one(s) it was optimized for.


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Pressurized Liquid Extraction

The principle of PLE, fast extraction are obtainedbecause of higher diffusivity, improvedsolubilization capability and more efficientdisruption of analyte-matrix interactions in aliquid solvent at temperature above its boilingpoint.


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PLE is performed by filling a sample-vessel with solventand then heat the vessel to dessired temperature andpressurizing the vessel to maintain the solvent as aliquid. Several static extraction are commonlyperformed with nitrogen-purging in between. Thesolvent containing the extracted solutes is collected inan empty vessel.


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An advantage of PLE is that the same solvents canbe used as the ones typically used in conventionalsolvent extraction methodologies.

Two important parameters in PLE aretemperature and extraction time (usually given bystatic extraction time and number of extractioncycles).


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Pressurized Hot Water Extraction

For polar to medium polar target compounds itmay be feasible to use water as a solvent atelevated temperature.

PHWE is based on the same principle as PLE, butusing only water as extraction solvent.

As shown in the figure, the dielectric constant ofwater decreases at elevated temperature. Hence,water behaves more like an organic solvent athigher temperatures.


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Microwave Assisted Extraction

Microwave assisted extraction is also anextraction technique based on heating anorganic solvent.

The principle is roughly that a sample and anappropriate solvent or solvent mixture are putin a vessel, which is then pressurized and

heated by microwaves.


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Microwave Assisted Extraction

In general, method development in MAE involves

optimization of

Solvent composition

Solvent volume

Extraction temperature and time


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Membrane-Assisted Solvent Extraction

Non-porous membrane can be used for extractionof polar and non-polar compounds from liquidsamples using only minimal amount of organicsolvent.

A non-porous membrane is a liquid or a solidphase sandwiched between two other phases

One of these phases contains the components tobe extracted (donor phase). On the other side of

the membrane is the acceptor phase, where theextracted components are collected.


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Membrane-Assisted Solvent Extraction

The driving force for the extraction processover the membrane is in most cases aconcentration gradient.

High enrichment factors of the extractedcomponents can be obtained if a small volume,stagnant acceptor phase is used.


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Solid Phase Micro Extraction

SPME uses a fused silica fiber

that is coated commonly on

the outside with an

appropriate stationary phase.

The small size of the SPME

fiber and its cylindrical shape

enables it to fit inside theneedle of a syringe like

device.


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SPME extraction modes

[A] Direct extraction mode

[B] Headspace extraction mode

[C] Membrane protected mode


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Several parameters in SPME :

Extraction mode

Type and thickness of fiber coating

Extraction time and temperature

Analyte concentration

pH, buffer Agitation

Analyte desorption


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Stir Bar Sorptive Extraction

SBSE has many similarities to SPME, as it is alsoa solventless sample preparation technique andit uses similar sorbents (based on PDMS).

In SBSE, an aqueous sample is extracted by

stirring for a certain time with a PDMS-coatedstir bar.

The stir bar is thereafter removed from thesample and the absorbed compounds are theneither thermally desorbed and analyzed by GC-

MS, or desorbed by means of a liquidinterfacing to a LC system.

The parameters to optimize in SBSE also similarto those in SPME.


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Emerging Contaminant

Pharmaceuticals and Personal Care Products (PPCPs),

are a diverse groups of environmental chemicals that

have captured the attention of scientist and the

public. There are more than 3000 different substance used

as a medicines.

The greatly escalating use of prescription drugs and a

bewildering variety of personal care products has

resulted in the manufacture literally ten thousands of

new and complex chemicals that enter the

environment in large quantities


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PPCPs are excreted as human or animal waste or are

rinsed from our bodies and washed down drains and

sewer systems to be released into the environment

in staggering quantities around the world. Many PPCPs have persistent chemicals and

compounds that remain biologically active after they

leave the body or are disposed in landfills and water.


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Prescription and over-the counter therapeutic drugs

Veterinary drugs

Fragrances

Cosmetics

Sun-screen products

Diagnostics agents

Nutraceuticals

PPCPs include :


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Human activity

Residues from pharmaceutical manufacturing

Residues from hospitals

Illicit drugs

Veterinary drug use, especially antibiotics and

steroids

Agribusiness

Source of PPCPs :


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The effects of PPCPs are different from conventional

pollutants. Drugs are purposefully designed to

interact with cellular receptors at low concentrationsand to elicit specific biological effects. Unintended

adverse effects can also occur from interaction with

non-target receptors.

Effects may be subtle because PPCPs in the

environment occur at low concentrations. Theres a

need to develop tests that detect more subtle end-

points

Health effects of PPCPs:

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Recent Issues in Analytical Chemistry