Extraction by ajizai

VIEWS: 64 PAGES: 5

									                         Extraction
Dissolution              Extraction                Chromatography

   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:
1. Roger M Smith. (2003) Before the injection – modern methods of
   sample preparation for separation techniques J. Chromatography A,
   1000, 3-27.
2. Kathy Ridgway et. al.(2007) Sample Preparation techniques for the
   determination of trace residues and contaminants in food. J.
   Chromatography A, 1153, 36-53.


                                                         Created with MindGenius Business 2005®
          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


                                                                 Created with MindGenius Business 2005®
               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



                                                            Created with MindGenius Business 2005®
              Solid-Phase Extraction
   Adsorbent coated on               Most chromatographic phases
        packed powder                 available
        fibre/capillary                  C18
        beads                            ion exchange
        stirrer bar                      size exclusion
   Advantages include                    chiral, immunoaffinity and
        low waste
                                           molecular imprinted
        automatable
        effective concentration      Requires desorption post
        May be “in-line”              extraction
   Performance is affected by             by solvent
        flow rate                        thermally (GC injection port)
        preconditioning
        Brand
        matrix



                                                            Created with MindGenius Business 2005®
               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


                                          Created with MindGenius Business 2005®

								
To top