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What are food examples of hydrophilic substances?
Simple sugas, oligosaccharides, amino acids, some small proteins and peptides, some vitamins
What are some food examples of hydrophobic substances?
fats, phospholipids, sterol, vitamins, carotenoids
what are some examples of volatile food substances?
essential oils, LMW fatty acids, flavor compounds, pesticides
what are some examples of food substances that are sensitive to acids and bases?
proteins, amino acids, color compounds
What are some important considerations to include when doing sample prep?
- qualitative or quantitative
- quantity range of analyte
- size of sample material
- nature of impurities
- desired level of accuracy
- instrumentation required
what are the primary goals of sample prep?
- remove interfering impurities
- selective enrichment of analyte
- increased [analyte]
- conversion of analyte into other forms for analysis (derivatization)
what are the 6 steps of sample prep?
- 1. drying
- 2. grinding
- 3. solvent extraction
- 4. separation of extract from residue
- 5. cleanup
- 6. derivatization, concentration, etc.
what is drying of the sample?
- remove water which is the main component of food matrices
- lyophilization (freeze drying), oven drying, vacuum oven drying
what does separation of extract from residue include?
filtration, centrifugation, membrane separation (molecular sieve)
what does sample cleanup include?
remove extracted impurities that can potentially interfere with further analysis
what are some examples of solvent extraction?
what is ASE/PSE/PFE?
- accelerated solvent extraction
- pressurized liquid extraction
- pressurized fluid extraction
what is MAE?
what is UE?
what is SPE?
what types of analytes can be lost to Soxhlet extraction?
thermally labile volatile analytes
what is a pro of Soxhlet extraction?
minimizes the use of extraction solvent by circulation (continuous process)
what is a con of Soxhlet extraction?
can be interference from contaminants from the extraction thimble used, so always need to do a blank extraction prior to actual
what is accelerated solvent extraction?
- involves the use of pressurized liquids or pressurized fluids for extraction
- elevated temperatures and pressures are used in these techniques
- this allows the extraction solvents to penetrate the sample matrices, thus enhancing solvation of desired solute
what is the most popular ASE technique?
super-critical CO2 extraction
How is microwave-assisted extraction done?
- water in sample is heated by microwave
- the expansion of the heated water generated pressure from within the sample
- increased pressure disrupts sample matrix from the inside and allows analyte to escape and to be dissolved in extraction solvent
- requires less solvent compared to conventional extraction methods
- the solvent used may be microwave absorbing or non-microwave absorbing
How is solid-phase extraction done?
- analytes suspended or dissolved in a liquid mixture are passed over a sorbent material, which selectively binds the solute of interest
- weakly bound impurities are washed out with a weak solvent and the desired analyte(s) are eluted with a strong solvent
- can be used as primary method or just for cleanup step
- several types of sorbent materials are available, depending on the physicochemical properties of the desired analyte (reversed phase, normal phase, ion exchange, affinity)
how do you ensure you get just the desired analyte during a SPE process?
- condition the column
- load sample into column, some impurities leave immediately by not attaching to the solid phase
- wash the column, more weakly bound impurities leave
- selectively elute the desired sample, leaving behind the last of the impurities in the column
how do molecular sieves work?
- membrane filtration techniques use specialized materials to achieve separation of particles or molecules based on their size
- the membrane is selectively permeable which allows preferential transport of matter through its pores