Extractions and sample preparation Flashcards
What is a Galenical?
Medicinal extract or tincture (concoctions) derived mainly from natural sources esp. vegetables or herbs
What is a Menstrumm?
Solvent(s) used in the extraction process (water is commonly used as a solvent)
What is a Marc?
Insoluble materials (waste) remaining after extraction
What types of extracts are there?
Liquid extracts
Tinctures
Soft extracts
Dry extracts
What is a liquid extract?
1 part by mass or volume is equivalent to 1 part by mass of the dried herbal drug or animal matter (quite concentrated)
What is a tincture?
1 part of herbal drug or animal matter and 10 parts of extraction solvent, or 1 part of herbal drug or animal matter and 5 parts of extraction solvent (more diluted)
What is a soft extract?
semi-solid preparations obtained by evaporation or partial evaporation of the solvent used for extraction. (very concentrated)
What is a dry extract?
solid preparations obtained by evaporation of the solvent used for their production. Dry extracts have a loss on drying of not greater than 5 per cent m/m, unless a loss on drying with a different limit or a test on water is prescribed in the monograph
What are the 3 main steps of extraction?
- Comminution: Physically reduce the plant material (barks, roots etc) to a specified size e.g. with grinders or cutters
- Incubation with Menstruum – penetration & dissolution
- Separating off the Marc and active principles – e.g. Filtration, decantation (when you have ‘big stuff’), expression
What are the rate limiting factors?
- Wetting of the surface of the particles
- Permeability of cell walls (cell walls hard to break)
- Rate of dissolution of cell contents
- Outward diffusion of the solution
What are the 5 methods of galenical preparations?
- Infusion: Drug stood in water (hot or cold) for a short time.
- Decoction: Extraction of soluble constituents by simmering (boiling) plant material in water for a specified time
- Maceration: Prolonged infusion (e.g. days) often in aqueous alcohol and a closed container
- Percolation: Maceration and then flow of fresh solvent passing over ground material at a specified rate
- Continuous hot extraction: Repeated infusion with hot solvent
What are the conditions for infusion extracts?
Infusions extracts from soluble constituents of crude drugs. Prepared by diluting concentrated Infusion 1 in 10 (v/v) with Water. For dispensin : should be used within 12 hours of their preparation.
Describe maceration
Orange Peel Infusion Extemporaneous preparation
The following directions apply.
Macerate the Dried Bitter-Orange Peel in a covered vessel for 48 hours with 1000 mL of the Ethanol (25 per cent) and press out the liquid. To the pressed marc add 350 mL of the Ethanol (25 per cent), macerate for 24 hours, press and add the liquid to the product of the first pressing. Allow to stand for not less than 14 days and filter.
Describe Percolation
BP : Appendix XI F. Continuous hot Extraction
A = Outer glass tube of certain defined dimensions
B= open glass tube contain solvent moistened drug
D= glass coil
G= cotton pad
F= condenser
The flask is heated and the extraction continued as directed.
percolate drops into the outer tube
What is a soxhlet extractor?
(industrial scale)
• The solvent is heated to reflux
• Floods into the chamber housing the thimble
• The solid material slowly fills with warm solvent
What are the aims of sample preparation?
- To isolate (purify) drugs of interest from complex matrices
- To concentrate analyte
- To derivatise the analyte
- To stabilise the analyte from undue degradation
What is the purpose of purification methods?
- Isolate pure drug from crude (synthetic or natural) forms
* Remove interfering constituents (e.g. excipients) for analysis
What technique can be used to separate substances?
Using immiscible liquid phases (water and organic solvent) and a separating funnel
What is the distribution ratio?
Liquid phase extraction
D is distribution ratio =[Solute] in the organic phase/[Solute] in the water phase
• For unionizable compounds log P can be useful indication of the likely success of extracting a drug from an aqueous medium into an organic solvent.
• Organic Solvent: most are lighter (except chlorinated) than water so float to the top. Common use: hexane, DCM, ethyl acetate, ether, chloroform
What are the common problems with using immiscible liquids?
- Emulsions – due to vigorous shaking
- Where is the boundary?
- Mixed layers?
- Venting a separating funnel safely?
What do acid-base extractions require?
Requires pH change of the aqueous phase
What are ionizable groups?
Carboxylic acids, phenolic protons, amines
How is pH utilized for selective extraction?
- Most drugs are weak acids or weak bases
- Ionised drug is charged usually in the form of salt soluble in water
- The neutral drug is soluble in other organic solvents
What leads to increased solubility in organic solvents for ACIDIC drugs?
LOWERING pH e.g. phenobarbital
