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Extraction

Extraction. Dissolution. Chromatography. Extraction. Purification based on relative affinity for extracting media May isolate analyte from solid, liquid or gaseous matrices Can involve extraction to solvent or solid phase media

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Extraction

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  1. Extraction Dissolution Chromatography Extraction • Purification based on relative affinity for extracting media • May isolate analyte from solid, liquid or gaseous matrices • Can involve extraction to solvent or solid phase media The following are readable reviews of this stage of sample preparation: • Roger M Smith. (2003) Before the injection – modern methods of sample preparation for separation techniques J. Chromatography A, 1000, 3-27. • Kathy Ridgway et. al.(2007)Sample Preparation techniques for the determination of trace residues and contaminants in food. J. Chromatography A, 1153, 36-53.

  2. Analytes in Solid Samples • Particle size is important – so may need pre-extraction homogenisation • Solvent is chosen to enhance selectivity • May also require • Recycling (Soxhlet) • Heating (boiling, or superheating under pressure) • Supercritical fluids • Microwave and sonic radiation (difficult to automate) • Aqueous pastes (eg meat or plant tissue) require special care – sometimes using powdered matrix • Insoluble analytes may be pyrolysed (to produce soluble fragments) • Volatile analytes may be “thermally desorped” and then treated as for gases

  3. Analytes in Solution • Biphasic (aqueous/organic) liquid-liquid extraction but has problems • Costly in solvent • Waste/environmental concerns increae cost • Concentration of solvent gives loss of volatile analytes and concentration of solvent impurites • Purge and Trap (volatile analyte flushed out by gas) • Dialysis • Uses a membrane to separate layers / increase selectivity • Solid phase extraction/microextraction

  4. Adsorbent coated on packed powder fibre/capillary beads stirrer bar Advantages include low waste automatable effective concentration May be “in-line” Performance is affected by flow rate preconditioning Brand matrix Most chromatographic phases available C18 ion exchange size exclusion chiral, immunoaffinity and molecular imprinted Requires desorption post extraction by solvent thermally (GC injection port) Solid-Phase Extraction

  5. Gaseous Analytes • Problems • low concentration • difficult to store • Sample preparation focuses on trapping • cooling • bubbling through solution • adsorbing to fibre • Need to control for misting and desolvation

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