Microextraction
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Microextraction techniques are extraction methods that use very small volumes of extracting solvent. This document discusses various microextraction techniques including solid phase microextraction (SPME), single-drop microextraction (SDME), and dispersive liquid-liquid microextraction (DLLME). SPME uses a coated fiber to extract analytes from samples, while SDME uses a single drop of solvent and DLLME uses a mixture of solvents to extract analytes. These microextraction techniques provide advantages over traditional extraction methods like reduced solvent usage and higher enrichment of analytes.
Microextraction
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- 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
- 16. 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 16
- 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
- 19. Different steps in dispersive liquid-liquid microextraction 19
- 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
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