Extraction And Sample Preparation Methods Flashcards
Outline some steps in sample extraction and preparation
Comminution Add Menstrum Incubation Remove Marc Adjust Volume
Describe percolation
Maceration then a flow of fresh solvent flowing over ground material at a specified rate
Describe continuous hot extraction
Repeated infusion of hot solvent
Describe how the permeability of cell walls can be controlled so it doesn’t limit the rate
Add alcohol or other solvent
Define the term liquid extract
1 part by mass or volume is equivalent to 1 party by mass of the dried herbal drug or animal matter
1:1 ratio
Amines
Typical pKa
At low pH and high pH they are positive or negative?
pKa >9
Low pH: positive
High pH: neutral
Define the term tincture
1 part herbal drug/animal matter and 10 parts extraction solvent (1:10)
OR
1 part herbal drug/animal matter and 5 parts of extraction solvent (1:5)
If a galenical is from a natural source, what processes can it undergo when the menstrum is water?
Infusion
Decoction
Why is the menstruum in a decoction boiling water and not cold water?
Allows for better penetration
Describe continuous hot extraction process
Perlocation
Flask heated and extraction occurs
Percolate drops in outer tube
Solvent will rise and reach condenser at the top
Solvent falls back down though cotton pad
Extract runs through it and down to the flask
Repeat
Define the term dry extract
Solid preparations obtained by evaporation of the solvent used for their product.
Dry extracts have a loss of not greater than 5% m/m, unless on drying with a different limit or test on water is prescribed in the monograph
Phenols
Typical pKa
At low pH and high pH they are positive or negative?
8-10 = pKa
Low pH: neutral
High pH: negative
What are the names of the three main steps in extraction and sample preparation?
Separation
Incubation
Comminution
How is pH utilised for suitable extraction?
Describe an example
Most drugs are weak acids/weak bases
Ionised drug is charged usually in the form of a salt soluble in water
The neutral (unionised) drug is soluble in other organic solvents
E.g. Phenobarbital is an acidic drug. Lowering pH leads to increased solubility in organic solvents.
Procaine is a basic drug. Increasing pH leads to increased solubility in organic solvents
Name some liquid phase extraction techniques for immiscible and miscible liquids
Mobile phases
Solvent-solvent
Immiscible:
Separating funnel
Counter current distribution
Miscible:
Crystallisation
Fractional distillation
Define the term soft extract
Semi-solid preparation obtained by evaporation or partial evaporation of solvent used for extraction
How can one justify or reduce costs?
Need to justify therapeutic value
Can reduce cost by using solvents that can be reused
How does SPE work? Briefly describe instrumentation
Selectively removes impurities
Has an SPE tube with a syringe barrel-like body, usually polypropylene, sometimes glass
Has SPE packing between two frits (20um pores usually polyethylene, sometimes teflon or stainless steel)
Luer tip is exit (bottom of SPE tube)
Advantages of SPE over LLE
Quick (few mins) Higher thorough-put Less labout Better recovery Less solvent (<20mL, low disposal cost) Easier to automate More selective - broader choice of bonded phases and solvents
Common organic solvents used in sample preparation/extraction
Ether Hexane Ethyl acetate Chloroform Note: pH will protonate/deprotonate the species, making it polar and removable in the water layer
Purpose of purification methods
Isolate pure drug from crude (synthetic or natural) forms
Remove interfering constituents (e.g. Excipients) for analysis
What factors must be considered when decided with method of galenical preparations to use?
- pharmacognosy - nature of natural source
- if material is soft or hard
- if it is unstable to heat or highly volatile
- cost/labour
- environmental responsibility
Describe infusion
State when it should be used by
Extracts from soluble constituents of crude drugs
Prepared by diluting infusion in 1 in 10 (v/v) with water
Should be used within 12 hours of their preparation
Name 4 basic techniques that would allow you to separate drugs from miscible phases
- Rotary evaporation - vacuum and heat - high surface area
- Distillation (fractional) - different boiling points (differ by 25 degrees Celsius or less)
- crystallisation (fractional) - different solubility
- sublimation - e.g. Freeze drying (solid to gas)
What gives a useful indication of the likely success of extracting a drug from an aqueous medium into organic solvent?
LogP (for unionisable compounds)
Most organic solvents are lighter (expect the chlorinated ones) than water so float to the top
Name some solid phase extraction techniques
Stationary and mobile phases:
SPE/SPME
Filtration
Chromatography
Why is the concentration in infusions adjusted but in decoctions it is not adjusted?
In infusions, plants vary in drug content so you mix different batches
In decoctions, you try to get as much out as possible, so the concentration/volume is not adjusted
In SPE, describe the interactions with the stationary phase that happen
- Non-polar van der waals forces 20KJ/mol: e.g. Reverse phase silicia
- polar: dipole/dipole bonds 40KJ/mol e.g. Normal phase silicia
- electrostatic: ionic: 600KJ/mol e.g. Ion exchange
What is SPME
Solid phase micro extraction
Similar principle to SPE but using tiny volumes of solvent
Describe the separation step
Separate off marc and active principles
E.g. Filtration, decantation (pouring out), expression (squeezing material)
Describe the below conditions/parameters for infusion:
- menstruum
- solid material
- active principles
- concentration (volume)
- thermal degradation
- menstruum: cold or boiling water
- solid material: soft
- active principles: volatile or non-volatile
- concentration: adjusted
- thermal degradation: can be used cold
Define marc
Insoluble materials (waste) remaining after extraction
Define a base
Proton acceptor
What is SPE used for?
Solid phase extraction is used for sample preparation to:
- remove interferences from the sample
- give more reliable results
- concentrate analytes to improve sensitivity e.g. In forensics
What process does a soxhlet extractor do?
Name two advantages of this equipment
Perclocation
Can go unattended for a long time
High efficiency as each time new solvent goes up
Describe the process of SPE
Capture: Sample is filtered through sorbent particles
Analytes captured from the liquid matrix
Elute: concentrated analytes eluted with solvent. Eluted sample collected
Describe how the wetting of the surface can be controlled so it doesn’t limit the rate
Increase comminution
Change solvent
Describe maceration
Prolonged infusion (e.g. Days) often in aqueous alcohol and a closed container
carboxylic acids
Typical pKa
At low pH and high pH they are positive or negative?
At <6 pKa
Low pH: neutral
High pH: Negative
What is the need to sample preparation?
- to derivatize the analyte
- to isolate (purify) drugs of interest from complex matrices
- to concentrate the analyte
- to stabilise the analyte from undue degradation
Which method would you use for an extract that is unstable to heat or highly volatile?
Cold infusion
Describe the incubation step
Incubate with menstrum
Penetration and dissolution
Describe the lyophilisation process
Freezing sample (below the triple point i.e. Temperature at which solid, liquid and gas phases can coexist)
So mixture becomes solid/ice
Must be all frozen.
Pressure lowered so sublimation occurs, structure preserved
(Apply vacuum to sublimate the ice into water vapour)
Keep drawing off water vapour (usually collected as waste)
Solid product recovered in flask
Acid-base extractions require…
pH change of the aqueous phase
Define galenical
Medicinal extract or tincture (concoctions) derived mainly from natural sources, especially vegetables or herbs
Describe the process of a Soxhlet extractor
Solvent heated to reflux
Floods into the chamber housing the thimble (contains drug)
Solid material slowly fills with warm solvent
If a galenical is from a natural source, what processes can it undergo when the menstrum is aqueous or organic solvent?
Maceration
Percolation
Counter current matter
Define menstrum
Solvent(s) used in the extraction process
Which method would you use for a hard material?
Percolation or decoction
Name 5 methods of galenical preparations
Infusion Decoction Maceration Percolation Continuous hot extraction
With method would you use for a soft material?
Maceration
Rate limiting factors of extraction and sample preparation
Wetting on the surface of particles
Permeability of cell walls
Rate of dissolution of cell content
Outward diffusion of the solution
Describe the comminution step
Physically reduce plant material to a specified size e.g. By grinders/cutters
Describe decoction
Extraction of soluble constituents by simmering (boiling) plant material in water for a specified time
Define D
Distribution ratio
Solute conc in organic phase/solute conc in water phase
Describe the below conditions/parameters for decoction:
- menstruum
- solid material
- active principles
- concentration (volume)
- thermal degradation
Menstruum: boiling water Solid material: hard Active principles: non-volatile Concentration: not adjusted Thermal degradation: not for heat labile
Describe how the rate of dissolution of the cell content can be controlled so it doesn’t limit the rate
Stirring/agitation
Why must the active principle in a decoction be non-volatile?
To prevent evaporation
Advantage of lyophilisation
Good for heat labile compounds, particularly biologicals, proteins, viruses, bacteria plasma, vaccines etc.
Define an acid
Proton donor
Describe infusion
Drug stood in hot/cold water for a short time
