Extraction of the time taken is needed

Extraction is aprocess which used to remove a desired compound from a solid or a liquidmixture using a suitable solvent, or it can also be defined as removal of thesoluble material from an insoluble residue, either it is solid or liquid bytreatment with suitable solvent.

There will be left behind a little amount ofimpurities after extraction because it is never possible to completely extractor remove a compound from a given solvent ideally. 1                For the analyticalprocess, 60% of the time taken is needed for the sample preparation. Therefore,it is important to choose the correct sample preparation technique andunderstand the underlying separation mechanisms to fully maximize the processto give optimum results.2            Thereare many types of extraction methods including Solid phase extraction (SPE),Liquid-liquid extraction (LLE), Solid phase micro extraction (SPME), Microextraction by packed sorbent (MEPS) and Stir bar sorptive extraction (SBSE).However, in the processing of medicinal plants, significant advances have beenmade such as microwave-assisted (MAE), ultrasound-assisted extraction (UAE) andsupercritical fluid extraction (SFE). Increasing yield at lower cost is the aim of these advances. 3Solid Phase Extraction            Solid-phaseextraction (SPE) is one of the sample preparation technique which is sensitive.

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SPE has same principles of column chromatography and it is also generally usedin analytical laboratories for the extraction experiment such as extraction ofanalytes from a complex mixture. Besides, prior to the quantification, SPE enables the clean-up, extraction and concentration of analytes. Most ofthe problems that have encountered with liquid-liquid extraction has beenprevented by solid phase extraction. In addition, quantitative recovery yieldscan be improved by SPE.

BY using SPE technique, the most extraction is in lessthan 30 minutes, so it is a rapid and easy to perform. In addition, automationcan be used in this technique. Moreover, SPE is only needed to handle lowamount of solvents. However, whensolid phase extraction is compared to other sample preparation techniques, forexample, protein precipitation, QuEChERS (quick, easy, cheap, effective,rugged, and safe) or liquid–liquidextraction (LLE) , SPE is often requires more effort toward method developmentand is considerably more time consuming. However, the rewards are certainlyworth it, with highly selective extractions typically producing very puresamples.2,4             Besides,SPE sorbent phases fall into four primary categories which are nonpolar, polar,ion exchange (cation and anion), and mixed mode.2Procedure of Solid phase extraction            Solid phase extraction depends on the difference ofaffinity between an analyte and interferents, which is present in a liquidmatrix, for a solid phase (sorbent). The separation of the target analyte fromthe interferents depends on the affinity.

4 Besides, retained orunretained analytes are found. For retained analyte, it is while matrixinterference is washed through. For unretained, it is while the matrixinterference is adsorbed.

Solid phase extraction involves four steps: Conditioning: It must be exposed to a common solvent and solution for the material in the cartridge to be solvated and effective. Loading: The loading solution containing the analyte is percolated through the solid phase. Ideally, the analyte and some impurities are retained on the sorbent. Washing: A solvent or solution is used to wash the interferents from SPE material without removing the analytes of interest. Elution: During this elution step, the compound of interest is collected.Applications           Solid-Phase Extraction (SPE) is asample preparation step which is important in determination of specificcompounds in foods. SPE offers many opportunities not only for analysis of alarge diversity of food samples but also for optimization and advances. 5           Besides, in recent years, SPEtechnique enables a high-throughput DNA extraction.

Moreover, in food analysis, SPE technique is widelyused for clean-up. Classical gravity column chromatography has been largelyreplaced by SPE. 6           Furthermore, the applications of SPEare determination of sympathomimetic amines in blood, urine and tissues,Benzodiazepines screening in urine, determination of cocaine and cocainemetabolites and anabolic steroids in urine and Lysergic acid diethylamide (LSD)in blood, serum or plasma.Liquid-liquid Extraction          Liquid – liquid extraction is also known as solvent extraction.

It is aseparation process which is based on the different distribution of thecomponents to be separated between two liquid phases. It depends on the masstransfer of the component to be extracted from a first liquid phase to a secondone. For instance, the isolation of trimyristin form nutmeg is an example ofsolid-liquid phase extraction. It is also possible to partition the componentsof a mixture between two immiscible liquids such as liquids that will notdissolve in each other and form two distinct phases when combined.7            There are two general types ofliquid-liquid extractions which are organic solvent extraction and acid-baseextraction. For an organic solvent extraction, an organic solvent with highaffinity for the desired compound is used to extract the compound from anothersolution. For an acid-base extraction, in which an organic acid or base isextracted from an organic solvent by using an aqueous solution of an inorganicbase or acid, respectively.

A neutralization occurs which converts the compoundinto an ionic, water-soluble salt, causing it to transfer from the organicphase to the aqueous phase.7Extraction with organic solvents            Liquid-liquidextractions normally involve an organic solvent and water. Organic solvent isimmiscible in water and the most common organic solvents are diethyl ether,ethyl acetate, toluene and methylene chloride. If 50 mL of ethyl acetate and 50mL of water are placed in a flask and the solution is stirred to mix it, ahomogeneous solution will not be obtained. After stirring, if the solution canstand, two distinct liquid phases will form in the flask: the lower layer isthe denser solvent and the upper layer is less dense solvent.

7            Mostorganic solvents are much less polar than water. Polar compounds are moresoluble in polar solvents than in nonpolar solvents, and non-polar is moresoluble in non-polar solvent. Depending on the selective solubility ofdifferent compounds in polar versus nonpolar solvents, separation by LLE iscarried out.7            Themain principle of liquid-liquid extraction is the distributioncoefficient or the partition coefficient, Kd,where7 K is the ratio of solubility of solutedissolved in the organic layer to the solubility of material dissolved in theaqueous layer.   Applications            Liquid– liquid extraction is primarily applied where direct separation methods suchas distillation and crystallization cannot be used or are too costly. Liquid –liquid extraction is also employed when the components to be separated areheat-sensitive such as antibiotics or relatively non-volatile, for example, mineralsalts.9            Liquid– liquid extraction is used in industry for the many purposes. First,separation of systems with similar boiling points such as separation ofaromatics from aliphatic hydrocarbons.

Second, separation of high boilers andlow-concentration solutes from aqueous solutions such as phenol. Third,separation of mixtures with high boiling points such as vitamins. Fourth,separation of temperature-sensitive compounds such as acrylates andbiotechnology. Fifth, separation of azeotropic mixtures, for example, extractionof acetic or formic acid from aqueous media using MTBE as solvent. Sixth,extraction of organic compounds from salt solutions such as caprolactam.

Seventh, extraction of salts from polymer solutions such as ketone resins andpolyols. Eighth, extraction of metal salts from low-grade ores such as copper.Ninth, extraction of metal salts from wastewater such as copper and lastly,recovery of nuclear fuels such as Purex process.9Solid Phase Microextraction (SPME)            SolidPhase Microextraction (SPME) is a solvent-free adsorption or desorption technology.

It is rapid, economical, and versatile. A fibre coated with a liquid which is polymeror a solid which is sorbent, or a combination of both is used by SPME. Thefibre coating extracts the compound of interest from the sample by absorptionin the case of liquid coatings or solid coatings. Then, insert the fibredirectly into the chromatograph for desorption and analysis is done.

10            Inaddition, the concept of SPME may have been derived from the idea of animmersed GC capillary column. The SPME apparatus is a very simple device. Itlooks like modified syringe consisting of a fibre holder and a fibre assembly,the latter containing a 1–2 cm long retractable SPME fibre. The SPME fibreitself is a thin fused-silica optical fibre, coated with a thin polymer film(such as polydimethylsiloxane (PDMS)), conventionally used as a coatingmaterial in chromatography.

11There are three basic modes which can beperformed by Fibre SPME which are direct extraction, in a headspaceconfiguration, and in a membrane-protected approach. For directextraction, dip the fibre coating into the aqueous sample and the analytes canpartition between the coating and the matrix. For headspace extraction, placethe fibre in the headspace above the aqueous matrix during extraction.

Extractingthe volatile analytes only, but this method is advantageous for high molecularweight interfering samples. When a sample contains both high molecular weightinterfering and non-volatile compounds, such as proteins, it is quite difficultto applied direct or headspace SPME. In such cases, restricted-access materialsor membrane-protected SPME is used and a better reproducibility and accuracyresult will be produced.12 First, the fibre is drawn into the needle.

Then, the needle is passed through the septum which seals the vial. Next, theplunger is depressed to expose the fibre to the sample or headspace that abovethe sample. Then, the organic analytes are adsorbed to the coating on thefibre. After adsorption equilibrium is attained, which can be anywhere from 2minutes to 1.5 hours, the fibre is then drawn back into needle and is withdrawnfrom the sample vial.

Lastly, the needle is introduced into the GC injector orSPME/HPLC interface, where adsorbed analytes are thermally desorbed and deliveredto the instruments column. Besides, there are two type of extraction which arefibre extraction and in-tube extraction. Applications            Inenvironmental applications, HS-SPME is used for analysing volatile and semivolatile compounds in solid samples such as soils sediments and sludges.HS-SPME has been used to determine aromatics and PAHs in spiked sand and claymatrices, volatile organic compounds in landfill soils, organometalliccompounds in sediments in soil, and in plasma samples and inorganic mercurysamples in soil. It has also been used for the determination of odorants,chloro- and nitrobenzene and chloro- and nitroanilines in a broad variety ofsoils. SPME extraction is also can be applied for the direct determination ofdifferent components of air samples, which is analogous to the conventional HSextraction. 11            Forapplication in food chemistry, SPME extraction technique became commerciallyavailable it has been used for the analysis of different foods and foodmaterials. Various SPME methods have been applied to the analysis of variouscomponents and contaminants in a range of different food samples.

Besides,HS-SPME is used popularly for the characterization of different alcoholicdrinks based on their volatile composition or to extract specific tracecomponents from the HS. In addition, SPME is also used for hair analysis. 11Microextraction by Packed Sorbent (MEPS)            MicroExtraction by Packed Sorbent (MEPS) is a new development in the fields ofsample preparation and sample handling. MEPS is the miniaturization ofconventional SPE packed bed devices from millilitre bed volumes to microlitervolumes. The MEPS approach to sample preparation is suitable a few phases suchas reversed phases, normal phases, mixed mode or ion exchange chemistries. 13            MEPSis worked with much smaller samples which as small as 10 ?L than full-scaleSPE. It can be fully automated where the sample processing, extraction andinjection steps are performed on-line using the same syringe. MEPS reduces thevolume of sample and also solvent needed.

In MEPS the sorbent, 1–2 mg, iseither inserted into the syringe of 100–250 ?L barrel as a plug or between theneedle and the barrel as a cartridge. The cartridge bed can be packed or coatedto provide selective and suitable sampling conditions. Any sorbent materialsuch as silica-based material, for example, C2, C8, C18, SCX, restricted accessmaterial (RAM), carbon, polystyrene-divinylbenzene copolymer (PS-DVB) ormolecular imprinted polymers (MIPs) can be used. Besides, a liquid polymercoating can be provided.

14 Procedure of MEPS First, the sample is pumped through the MEPSBIN which some volumes may be taken. Next, the MEPS BIN is washed once bypumping 20 µL to 50 µL of wash solution through the BIN in order to removeinterferences. Then, the analyte is eluted by drawing solvent through the BINinto the syringe barrel.

Finally, the analyte is injected directly into theinjector. 50 µL solvent is pumped and followed by 50 µL wash solution toprepare BIN for the next sample.13Applications            MEPS has been successfully appliedin many fields. First, in environmental application, it is used to determineorganic priority pollutants. In addition, MEPS is also used in determining emergingcompounds in snow samples and wastewater too. Besides, MEPS is also used inforensics industry. For example, contribution of miroextraction in packedsorbent for analysis of cotinine in human urine by GC-MS.

Moreover, MEPS iswidely used in pharmaceutical industry. For instance, liquid chromatographicanalysis of oxcarbazepine and its metabolites in plasma and saliva. MEPS isused in determination of 2,4,6-trichloroanisole and 2,4,6-tribromoanisole inwine. Lastly, MEPS is useful in life science industry.

For example, rapid andsensitive method for determination of cyclophosphamide in patients’ plasmasamples. 13Stir Bar Sorptive Extraction (SBSE)            Stirbar sorptive extraction (SBSE) is a solvent-free extraction technique. Mostconventional extraction techniques such as solid phase extraction, liquid-liquidextraction and so forth are slower than SBSE. There is more sorbent volume canbe taken by the stir bar. Besides, due to the efficient stirring, SBSE can alsoextract and concentrate analytes from a sample volume which is large. Hence, SBSEis more sensitive than SPME which is up to 1000x.

The Twister might be lookalike a conventional magnetic stirring rod, but while stirring the samples,such as water, or other beverages, it will absorb and concentrate organiccompounds into its sorbent coating. By using multi-position stir plates, extractionof many samples can be carried out simultaneously. The result of this is highproductivity. By using SBSE, some preparation steps are eliminated such as labour-and resource-intensive sample preparation steps. By using thermal desorption,desorption of analytes from the Twister is taken place. If the analytes arevery high-boiling, thermally labile, or when they must be determined by HPLC,liquid desorption using a solvent is performed.15            Inaddition, the basic concept of SBSE is based upon sorption, which is a form ofpartition based upon the analyte’s dissolution in a liquid-retaining polymerfrom a liquid or vapor sample, thus, originating a bulk retention.

The mainadvantages of sorption are related to high inertness of PDMS, which givesbetter performance for labile, polar, or reactive compounds; absence ofcatalytic degradation reactions; analyte recovery mechanism based upon awell-known chromatographic process; and linearity of sorption isotherms, which isfundamental for quantitative analysis.16Applications            Byusing PDMS Twister, the application are pesticides in water, PAH in marinetissue, determination of 2,4,6-TCA in wine and flavor compounds in food.Furthermore, by using Silicone Twister, the application is analysis the flavorcompounds in beverages. 15            Besides,SBSE is also in production of ultra-pure water, heavy metal recovery, recoveryof organic acids from salts and in oil emulsion and pulp mill waste treatment.In addition, it also used in the enzyme and pharmaceutical preparation. Recent Advances/ Development            Arecent advance in the application of HS-SPME is an internally cooled coatedfibre device (CCF). It is also called as cold fibre HS-SPME device.

The main purposefor developing CCF is there is lots of improved release of analytes from theinterfering phases in complex matrices.17            Itis used to increase the temperature of extraction for desorption of the analytesfrom solid particles. However, exothermic process is carried out when theabsorption of analytes by the fibre coating. Thus, a decrease of the partitioncoefficients will be caused by the process. The objective is to increase themass transfer process, by this, it increases the distribution constants ofanalytes too. For that purpose, an internally cooled coated fibre device whichis known as CCF was developed which the sample matrix is heated at the sametime while the fibre coating is cooled down. CCF is used for the matrices especiallyit is high viscosity or for volatiles with low partition coefficients. Theextraction of analytes from various environmental matrices was successfullydone by this method.

In addition, the application of CCF is food analysis too. Besides,a cold-fibre HS-SPME is more sensitive and having higher sample throughput thanconventional HS-SPME. But, there is a drawback which is increased fibrecapacity through this cooled coated fibre leads to the loss of selectivity. Itis not only the analytes, the interferences are also affected which areextracted exhaustively onto the coating.17 


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