Extraction And Sample Preparation Methods Flashcards Preview

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

Flashcards in Extraction And Sample Preparation Methods Deck (61):
1

Outline some steps in sample extraction and preparation

Comminution
Add Menstrum
Incubation
Remove Marc
Adjust Volume

2

Describe percolation

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

3

Describe continuous hot extraction

Repeated infusion of hot solvent

4

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

Add alcohol or other solvent

5

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

6

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

pKa >9
Low pH: positive
High pH: neutral

7

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)

8

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

Infusion
Decoction

9

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

Allows for better penetration

10

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

11

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

12

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

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

13

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

Separation
Incubation
Comminution

14

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

15

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

16

Define the term soft extract

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

17

How can one justify or reduce costs?

Need to justify therapeutic value
Can reduce cost by using solvents that can be reused

18

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)

19

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

20

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

21

Purpose of purification methods

Isolate pure drug from crude (synthetic or natural) forms
Remove interfering constituents (e.g. Excipients) for analysis

22

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

23

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

24

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)

25

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

26

Name some solid phase extraction techniques

Stationary and mobile phases:
SPE/SPME
Filtration
Chromatography

27

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

28

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

29

What is SPME

Solid phase micro extraction
Similar principle to SPE but using tiny volumes of solvent

30

Describe the separation step

Separate off marc and active principles
E.g. Filtration, decantation (pouring out), expression (squeezing material)

31

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

32

Define marc

Insoluble materials (waste) remaining after extraction

33

Define a base

Proton acceptor

34

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

35

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

36

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

37

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

Increase comminution
Change solvent

38

Describe maceration

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

39

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

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

40

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

41

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

Cold infusion

42

Describe the incubation step

Incubate with menstrum
Penetration and dissolution

43

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

44

Acid-base extractions require...

pH change of the aqueous phase

45

Define galenical

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

46

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

47

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

48

Define menstrum

Solvent(s) used in the extraction process

49

Which method would you use for a hard material?

Percolation or decoction

50

Name 5 methods of galenical preparations

Infusion
Decoction
Maceration
Percolation
Continuous hot extraction

51

With method would you use for a soft material?

Maceration

52

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

53

Describe the comminution step

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

54

Describe decoction

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

55

Define D

Distribution ratio

Solute conc in organic phase/solute conc in water phase

56

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

57

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

Stirring/agitation

58

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

To prevent evaporation

59

Advantage of lyophilisation

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

60

Define an acid

Proton donor

61

Describe infusion

Drug stood in hot/cold water for a short time