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Pharmacy Year 2 Semester 1 > Extraction And Sample Preparation Methods > Flashcards

Extraction And Sample Preparation Methods Flashcards

1
Q

Outline some steps in sample extraction and preparation

A 
Comminution 
Add Menstrum 
Incubation
Remove Marc
Adjust Volume
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2
Q

Describe percolation

A

Maceration then a flow of fresh solvent flowing over ground material at a specified rate

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3
Q

Describe continuous hot extraction

A

Repeated infusion of hot solvent

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4
Q

Describe how the permeability of cell walls can be controlled so it doesn’t limit the rate

A

Add alcohol or other solvent

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5
Q

Define the term liquid extract

A

1 part by mass or volume is equivalent to 1 party by mass of the dried herbal drug or animal matter
1:1 ratio

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6
Q

Amines
Typical pKa
At low pH and high pH they are positive or negative?

A

pKa >9
Low pH: positive
High pH: neutral

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7
Q

Define the term tincture

A

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)

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8
Q

If a galenical is from a natural source, what processes can it undergo when the menstrum is water?

A

Infusion

Decoction

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9
Q

Why is the menstruum in a decoction boiling water and not cold water?

A

Allows for better penetration

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10
Q

Describe continuous hot extraction process

A

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

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11
Q

Define the term dry extract

A

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

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12
Q

Phenols
Typical pKa
At low pH and high pH they are positive or negative?

A

8-10 = pKa
Low pH: neutral
High pH: negative

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13
Q

What are the names of the three main steps in extraction and sample preparation?

A

Separation
Incubation
Comminution

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14
Q

How is pH utilised for suitable extraction?

Describe an example

A

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

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15
Q

Name some liquid phase extraction techniques for immiscible and miscible liquids

A

Mobile phases
Solvent-solvent

Immiscible:
Separating funnel
Counter current distribution

Miscible:
Crystallisation
Fractional distillation

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16
Q

Define the term soft extract

A

Semi-solid preparation obtained by evaporation or partial evaporation of solvent used for extraction

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17
Q

How can one justify or reduce costs?

A

Need to justify therapeutic value

Can reduce cost by using solvents that can be reused

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18
Q

How does SPE work? Briefly describe instrumentation

A

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)

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19
Q

Advantages of SPE over LLE

A 
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
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20
Q

Common organic solvents used in sample preparation/extraction

A 
Ether
Hexane 
Ethyl acetate 
Chloroform 
Note: pH will protonate/deprotonate the species, making it polar and removable in the water layer
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21
Q

Purpose of purification methods

A

Isolate pure drug from crude (synthetic or natural) forms

Remove interfering constituents (e.g. Excipients) for analysis

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22
Q

What factors must be considered when decided with method of galenical preparations to use?

A
  • pharmacognosy - nature of natural source
  • if material is soft or hard
  • if it is unstable to heat or highly volatile
  • cost/labour
  • environmental responsibility
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23
Q

Describe infusion

State when it should be used by

A

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

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24
Q

Name 4 basic techniques that would allow you to separate drugs from miscible phases

A
  • 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)
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25
Q

What gives a useful indication of the likely success of extracting a drug from an aqueous medium into organic solvent?

A

LogP (for unionisable compounds)

Most organic solvents are lighter (expect the chlorinated ones) than water so float to the top

26
Q

Name some solid phase extraction techniques

A

Stationary and mobile phases:
SPE/SPME
Filtration
Chromatography

27
Q

Why is the concentration in infusions adjusted but in decoctions it is not adjusted?

A

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

28
Q

In SPE, describe the interactions with the stationary phase that happen

A
  • 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
29
Q

What is SPME

A

Solid phase micro extraction

Similar principle to SPE but using tiny volumes of solvent

30
Q

Describe the separation step

A

Separate off marc and active principles

E.g. Filtration, decantation (pouring out), expression (squeezing material)

31
Q

Describe the below conditions/parameters for infusion:

  • menstruum
  • solid material
  • active principles
  • concentration (volume)
  • thermal degradation
A
  • menstruum: cold or boiling water
  • solid material: soft
  • active principles: volatile or non-volatile
  • concentration: adjusted
  • thermal degradation: can be used cold
32
Q

Define marc

A

Insoluble materials (waste) remaining after extraction

33
Q

Define a base

A

Proton acceptor

34
Q

What is SPE used for?

A

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
35
Q

What process does a soxhlet extractor do?

Name two advantages of this equipment

A

Perclocation

Can go unattended for a long time
High efficiency as each time new solvent goes up

36
Q

Describe the process of SPE

A

Capture: Sample is filtered through sorbent particles
Analytes captured from the liquid matrix

Elute: concentrated analytes eluted with solvent. Eluted sample collected

37
Q

Describe how the wetting of the surface can be controlled so it doesn’t limit the rate

A

Increase comminution

Change solvent

38
Q

Describe maceration

A

Prolonged infusion (e.g. Days) often in aqueous alcohol and a closed container

39
Q

carboxylic acids
Typical pKa
At low pH and high pH they are positive or negative?

A

At <6 pKa
Low pH: neutral
High pH: Negative

40
Q

What is the need to sample preparation?

A
  • to derivatize the analyte
  • to isolate (purify) drugs of interest from complex matrices
  • to concentrate the analyte
  • to stabilise the analyte from undue degradation
41
Q

Which method would you use for an extract that is unstable to heat or highly volatile?

A

Cold infusion

42
Q

Describe the incubation step

A

Incubate with menstrum

Penetration and dissolution

43
Q

Describe the lyophilisation process

A

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

44
Q

Acid-base extractions require…

A

pH change of the aqueous phase

45
Q

Define galenical

A

Medicinal extract or tincture (concoctions) derived mainly from natural sources, especially vegetables or herbs

46
Q

Describe the process of a Soxhlet extractor

A

Solvent heated to reflux
Floods into the chamber housing the thimble (contains drug)
Solid material slowly fills with warm solvent

47
Q

If a galenical is from a natural source, what processes can it undergo when the menstrum is aqueous or organic solvent?

A

Maceration
Percolation
Counter current matter

48
Q

Define menstrum

A

Solvent(s) used in the extraction process

49
Q

Which method would you use for a hard material?

A

Percolation or decoction

50
Q

Name 5 methods of galenical preparations

A 
Infusion
Decoction
Maceration
Percolation
Continuous hot extraction
51
Q

With method would you use for a soft material?

A

Maceration

52
Q

Rate limiting factors of extraction and sample preparation

A

Wetting on the surface of particles
Permeability of cell walls
Rate of dissolution of cell content
Outward diffusion of the solution

53
Q

Describe the comminution step

A

Physically reduce plant material to a specified size e.g. By grinders/cutters

54
Q

Describe decoction

A

Extraction of soluble constituents by simmering (boiling) plant material in water for a specified time

55
Q

Define D

A

Distribution ratio

Solute conc in organic phase/solute conc in water phase

56
Q

Describe the below conditions/parameters for decoction:

  • menstruum
  • solid material
  • active principles
  • concentration (volume)
  • thermal degradation
A 
Menstruum: boiling water 
Solid material: hard
Active principles: non-volatile
Concentration: not adjusted 
Thermal degradation: not for heat labile
57
Q

Describe how the rate of dissolution of the cell content can be controlled so it doesn’t limit the rate

A

Stirring/agitation

58
Q

Why must the active principle in a decoction be non-volatile?

A

To prevent evaporation

59
Q

Advantage of lyophilisation

A

Good for heat labile compounds, particularly biologicals, proteins, viruses, bacteria plasma, vaccines etc.

60
Q

Define an acid

A

Proton donor

61
Q

Describe infusion

A

Drug stood in hot/cold water for a short time

Pharmacy Year 2 Semester 1 (32 decks)

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