Extraction and purification methods of plant samples Flashcards
What are some different drying methods?
Air drying – takes a few days to a year depending on type of sample, plant leaves with stem are tied together and hang to expose the plant to air. Not using high temperatures therefore heat-liable compounds are preserved. May be liable to contamination
Microwave drying – electromagnetic causes collisions between molecules resulting in fast heating of samples. Reduces drying time but may cause degradation
Oven drying – uses thermal energy to reduce moisture in samples, easy and rapid method that preserves phytochemicals, no major effect on antioxidant activity but may affect other activities e.g. rosmarinic acid content (has anti-inflammatory, antiviral, antibacterial, pain releaving and antioxidant properties)
Freeze-drying – lyophilisation, samples frozen for 12 hours and then lyophilised avoiding melting, sample may be lost by splattering into freeze-flask, most phytochemicals are preserved, complicated and expensive method used for delicate and heat-sensitive materials
Why does grinding take place as a pre-extraction process?
Lowering particle size increases surface area and contact with extraction solvents. Coarse particles are less homogeneous than powder particles
Particle size of 0.5 mm or less is ideal
What is Maceration?
An extraction method -
Soaking plant material in a container with a solvent at room temperature for 3 or more days with frequent shaking. Breaks cell wall and releases the soluble phytochemicals, used solvent will determine type of compound extracted
What is percolation?
An extraction method -
Using a percolator (like a coffee machine), boiling water is added to dried powder and macerated for 2 hours at a moderate rate (drops of water/min). When extraction is complete, samples are evaporated to obtain a concentrated extract
What is decoction?
An extraction method -
Suitable for heat-stable compounds and hard plant material (bark or roots), more oil-soluble compounds are extracted compared to maceration
Percolator is also used in process packed of dried powdered samples that are macerated with boiling water for 2 hours
What is liquid-liquid extraction?
Solvent extraction – used for separating compounds in mixtures based on their relative solubilities in 2 different liquid phases (water and organic solvent)
Extract the solvent with high solute concentration.
K (distribution coefficient) = conc of solute in organic phase/conc of solute in aqueous phase
What is hot continuous extraction?
Soxhlet extraction – ground sample is placed in thimble (strong filter paper tube) placed in thimble chamber, solvent is heated and evaporated before passing in condenser and dripping on thimble then emptied with dissolved phytochemicals into bottom flask again in a continuous process
Only small quantities of solvent is used, but the exposure to toxic and flammable organic solvents during the extraction is bad for health and environment
High purity solvents should be used in this system (expensive)
Ideal for dry and finely ground samples
What is microwave-assisted extraction?
Microwave induced rotation disrupts the hydrogen bonding and enhances migration of ions and helps solvent penetration into sample (damages sample tissues)
Poor heating occurs in non-polar solvents (poor extraction), it is a selective method for polar molecules and solvents
Short extraction time and less solvent consumed with risk of thermal degradation
Limited to small molecule phenolics (gallic acid and ellagic acid), quacertin, isoflavin and trans-resveratrol but additional cycles decrease the yield of phenolics and flavanones due to oxidation
What is ultrasound-assisted extraction?
Increase yield with lower cost, ultrasound from 20-2000kHz, increases contact between solvent and samples
Simple fast and low cost, but may lead to damage of compound looking to extract
Energy more than 20 kHz may affect active phytochemicals due to formation of radicals
What is supercritical fluid extraction?
Used in many good manufacturing, very efficient and clean, can be low cost
Dense-gas under pressure becomes oil-like, changes characteristics from non-polar to polar
SFF such as CO2 (above 31.1°C and 7380 kPa) is more like a gas but has solvating properties as a liquid
what is accelerated solvent extraction (ASE)?
Efficient liquid solvent extraction, minimal amount of solvent, large scale extraction
Sample is packed with inert material like sand in stainless steel extraction to prevent sample sedimentation
Fast automated technology that can control temperature and pressure for individual samples
What is column chromatography?
Efficient separation method used to purify individual compounds from mixture in crude extract (silica on top of column, then add sample then solvent), often used for large scale, time consuming and solvent consuming
Polar solvent for polar compound, non-polar solvent for non-polar compound
What is TLC?
a purification method -
Thin-layer – separation using thin stationary phase
Thick-layer – plates with thick layers of silica for larger scale separation
Simple and sensitive method with low cost and quick separation
what is paper chromatography?
Separate coloured chemicals or substances (cellulose paper), used mainly as teaching tool for other methods
Retention factor – distance travelled by solute by the distance travelled by solvent
What is HPLC?
An instrumental chromatography method.
more info*
What is Gas chromatography?
Analytical chromatography technique for separating compounds that can be vaporised without decomposition
10-20% of known compounds are analysed by GC
