Extractions and sample preparation

Question 1

What is a Galenical?

Answer 1

Medicinal extract or tincture (concoctions) derived mainly from natural sources esp. vegetables or herbs

Question 2

What is a Menstrumm?

Answer 2

Solvent(s) used in the extraction process (water is commonly used as a solvent)

Question 3

What is a Marc?

Answer 3

Insoluble materials (waste) remaining after extraction

Question 4

What types of extracts are there?

Answer 4

Liquid extracts
Tinctures
Soft extracts
Dry extracts

Question 5

What is a liquid extract?

Answer 5

1 part by mass or volume is equivalent to 1 part by mass of the dried herbal drug or animal matter (quite concentrated)

Question 6

What is a tincture?

Answer 6

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)

Question 7

What is a soft extract?

Answer 7

semi-solid preparations obtained by evaporation or partial evaporation of the solvent used for extraction. (very concentrated)

Question 8

What is a dry extract?

Answer 8

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

Question 9

What are the 3 main steps of extraction?

Answer 9

1. Comminution: Physically reduce the plant material (barks, roots etc) to a specified size e.g. with grinders or cutters
2. Incubation with Menstruum – penetration & dissolution
3. Separating off the Marc and active principles – e.g. Filtration, decantation (when you have ‘big stuff’), expression

Question 10

What are the rate limiting factors?

Answer 10

1. Wetting of the surface of the particles
2. Permeability of cell walls (cell walls hard to break)
3. Rate of dissolution of cell contents
4. Outward diffusion of the solution

Question 11

What are the 5 methods of galenical preparations?

Answer 11

1. Infusion: Drug stood in water (hot or cold) for a short time.
2. Decoction: Extraction of soluble constituents by simmering (boiling) plant material in water for a specified time
3. Maceration: Prolonged infusion (e.g. days) often in aqueous alcohol and a closed container
4. Percolation: Maceration and then flow of fresh solvent passing over ground material at a specified rate
5. Continuous hot extraction: Repeated infusion with hot solvent

Question 12

What are the conditions for infusion extracts?

Answer 12

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.

Question 13

Describe maceration

Answer 13

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.

Question 14

Describe Percolation

Answer 14

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

Question 15

What is a soxhlet extractor?

Answer 15

(industrial scale)
• The solvent is heated to reflux
• Floods into the chamber housing the thimble
• The solid material slowly fills with warm solvent

Question 16

What are the aims of sample preparation?

Answer 16

• To isolate (purify) drugs of interest from complex matrices
• To concentrate analyte
• To derivatise the analyte
• To stabilise the analyte from undue degradation

Question 17

What is the purpose of purification methods?

Answer 17

• Isolate pure drug from crude (synthetic or natural) forms

* Remove interfering constituents (e.g. excipients) for analysis

Question 18

What technique can be used to separate substances?

Answer 18

Using immiscible liquid phases (water and organic solvent) and a separating funnel

Question 19

What is the distribution ratio?

Answer 19

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

Question 20

What are the common problems with using immiscible liquids?

Answer 20

• Emulsions – due to vigorous shaking
• Where is the boundary?
• Mixed layers?
• Venting a separating funnel safely?

Question 21

What do acid-base extractions require?

Answer 21

Requires pH change of the aqueous phase

Question 22

What are ionizable groups?

Answer 22

Carboxylic acids, phenolic protons, amines

Question 23

How is pH utilized for selective extraction?

Answer 23

1. Most drugs are weak acids or weak bases
2. Ionised drug is charged usually in the form of salt soluble in water
3. The neutral drug is soluble in other organic solvents

Question 24

What leads to increased solubility in organic solvents for ACIDIC drugs?

Answer 24

LOWERING pH e.g. phenobarbital

Question 25

What leads to increased solubility in organic solvents for BASIC drugs?

Answer 25

RAISING pH e.g. Procaine

Question 26

What are techniques to remove solvent (separating drugs from miscible phases)

Answer 26

1. Rotary evaporation – vacuum & heat 2. Distillation (Fractional) – diff boiling points 3. Crystallisation (Fractional) – diff solubility 4. Sublimation – e.g. freeze drying (solid to gas) - LYOPHILISATION - From solid to the vapour stage

Question 27

What is the process of sublimation?

Answer 27

* Freezing the sample so that the mixture becomes solid/ice; * Apply vacuum to sublimate the ice directly into water vapour * Keep drawing off the water vapour; Usually collected as waste * Solid product recovered in the flask Key advantage: Good for heat labile compounds particularly biologicals: Vaccine, proteins, Viruses, bacteria plasma

Question 28

What is solid phase extraction?

Answer 28

Used for Sample preparation to 1. Remove interferences from sample 2. More reliable results 3. Concentrating analytes to improve sensitivity

Question 29

What are the advantages of solid phase extraction?

Answer 29

* Quick (few minutes) * Less labour * Less solvent (<20ml) , low disposal cost) * Better recovery * Easier to automate * More slecetive - broad choice of bonded phases and solvents

Question 30

How does SPE work?

Answer 30

Capture Sample is filtered through absorbent particles Analytes captured from the liquid matrix Elute Concentrated analytes eluted with solvent. Eluted sample collected

Question 31

What interactions are there with the stationary phase in SPE?

Answer 31

Non polar: VanderWaals (reverse phase silica) Polar: Dipole/dipole, H bond: normal phase silica Electrostatic: Ionic: ion exchange

Question 32

What is SPME?

Answer 32

Solid Phase Micro Extraction is similar principle but using tiny volumes of solvent