Essential idea A variety of analytical techniques is used for detection identification isolation and analysis of medicines and drugs Drug detection IR mass spectrometry and 1 H NMR can be used to detect banned or illegal chemicals such as ID: 679854
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Slide1
Drug detection and analysis
Essential idea
A variety of analytical techniques is used for detection, identification, isolation and analysis of medicines and drugs. Slide2
Drug detection
IR, mass spectrometry and
1
H
NMR can be used to detect banned or illegal chemicals such as
steroids (hormones)
in sport as they function as performance-enhancing drugs
.
Steroids: lipids found in sex hormones (
e.g
testosterone) that promote muscle growth (anabolic steroids). Examples:
nadrolone
.Slide3
Detection of steroids in sport
Gas chromatography
Mass spectrometrySlide4
Gas chromatography
U
sed
to separate and identify the components in a mixture such as blood and urine.
R
elies
on the different components in the mixture
having
different affinities for two different phases, a mobile phase (a gas medium) and a stationary phase (made up of a liquid).
The different affinities depend
on its boiling point/volatility and its solubility in both the gas and the
liquid
Affinities determine
the rate at which it passes through the stationary phase. Slide5
Gas chromatography: how?
The mixture sample is heated (boiling point) and mixed with the gas phase (solubility) and injected in the gas chromatography column.
Each
component travels though the column at a rate depending on their volatility and solubility in both
phases (affinity). The components partitions itself between both phases.
A detector measures the
time - retention time -
this is
the amount
of time between injection time (t=0 on the gas chromatogram) and the time a component is
eluted (=removed or extracted using a solvent).
The
retention
time of a component
is recorded
as a
peak on the gas chromatogram.
The
area underneath the peak indicates the concentration of the
component.Slide6
Gas chromatography apparatusSlide7
Gas chromatography
The retention times for a variety of compounds are known and the component can
therefore
be identified although identification can also be completed using the fragmentation pattern obtained using mass
spectrometry (=more accurate).
(
see 11.3
)Slide8
Gas chromatogramSlide9
Gas chromatographySlide10
Extraction and purification
Many
synthesis reactions in the pharmaceutical industry produce a mixture that contains the drug but often also excess or unreacted reactants and solvent. The next step is then to isolate or extract the drug from the mixture and increasing its purity
.
Often the extraction and purification use differences in solubility in different solvents and/or volatility between the product and other substances in the mixture. Slide11
Organic structure and solubility
P
olarity
of the structure of molecules
determines
their solubility in polar and non-
polar
solvents.
Non
-polar molecules have very low solubility in
polar solvents such as water
but higher solubility in other non-polar solvents
. (London forces interactions)
Molecules with a polar structure
and ionic compounds (salts) are
very soluble in
water (ionic, dipole-dipole, hydrogen bonding interactions)
but have low solubility in non-polar solvents.
The longer the carbon chain, the less the effect of the polarity, the lower the solubility.
Molecules
that can hydrogen bond have the highest
solubility in polar solvents.Slide12
Organic structure and solubility
low solubility
(non-polar molecules)
soluble
(dipoles)
high solubility
(hydrogen bonding)
alkanes/
alkenes
aldehydes/ketones
alcohols
carboxylic
acids
halogenoalkanes
amines/amides Slide13
Solvent extraction
Solvent extraction refers to the process in which a suitable solvent is selected that dissolves the organic compound (=solute) to be extracted or isolated from
a
solution.
The
solvent used to extract the drug (e.g. cyclohexane if the drug is a non-polar molecule in an aqueous solvent) is immiscible with the solvent in which the solute is in (e.g. water).
The
solute is partitioned between both solvents but a lot more in one than in the other.
In the case of organic compounds usually more soluble in non-polar solvent. Slide14
Solvent extraction
Example:
Extraction of penicillin using
trichloromethane
.
A separating funnel is used to remove the most dense solvent layer and the solute or drug can be obtained pure by crystallization Slide15
Fractional distillation: main ideas
Vapour
pressure refers to the pressure when a
vapour
is in equilibrium with a liquid or solution
.
The weaker the intermolecular forces, the more volatile a compound, the lower its boiling point, the higher its
vapour
pressure.
Raoults
’ law applies to ideal solutions and states that
the partial
vapour
pressure of each component in a solution is equal to the product of the
vapour
pressure of that component when pure multiplied by the mole fraction of that component in the solution
.
Ideal solution = completely miscible liquids that behave in the same way as when they are pure e.g. in terms of
vapour
pressure, e.g. octane
and hexane
.Slide16
Fractional distillation: main ideas
This means that the total
vapour
pressure of a solution is equal to sum of the partial pressure of each component. For a solution consisting of 2 components A and B:
P
total
= P
A
+
P
B
Partial
pressure of P
A
=
vapour
pressure A when pure x mole fraction A in solution.
Partial
pressure of P
B
=
vapour
pressure B when pure x mole fraction B in solution
.
Mole
fraction A = moles of A/moles of A +
B.
M
ole
fraction B = moles of B/moles of A + B.Slide17
Fractional distillation: main ideas
G
raph from your book shows
Raoult’s
law. It shows the
vapour
pressure of a solution of 2 components of different compositions.
Component B is more volatile as it has a higher
vapour
pressureSlide18
Fractional distillation: main ideas
Component B is the
more
volatile, has a higher
vapour
pressure and a lower
boiling
point
.Slide19
Fractional distillation: main ideas Slide20
Detection of ethanol:
breathalyser
Only used for detection of ethanol in breath.
Ethanol is sufficiently volatile to pass into the lungs from the bloodstream which is why it can be detected using a breathalyzer which contains acidified potassium dichromate(VI), an oxidizing agent.
There is a direct relationship between the alcohol content in exhaled air and the alcohol content in the blood
.
In a positive result (i.e. presence of ethanol) the potassium dichromate changes form orange (Cr
(VI)
or +6) to green (Cr
(III)
or
+3
) as the chromium in the
chromate ion
is reduced by the ethanol
(C = ) and
the ethanol itself oxidized to
ethanal
(C= -1) and
ethanoic
acid (C=0) .
The
extent of the
colour
change corresponds to a particular
ethanol concentration
.Slide21
Detection of ethanol:
breathalyser
Symbol equations
:
oxidation:
C
2
H
5
OH
+ H
2
O → CH
3
COOH + 4H
+
+ 4e
−
reduction:
Cr
2
O
7
2−
+ 14H
+
+ 6e
−
→ 2Cr
3+
+
7H
2
O
Overall:
3C
2
H
5
OH+16H
+
+2Cr
2
O
7
2
−
→ 3CH
3
COOH+2Cr
3+
+ 11H
2
O Slide22
Detection of ethanol in breath: fuel cell
Cell = 2 platinum electrodes and an acid electrolyte; uses electrochemistry.
Breath is passed over cell.
Ethanol
is oxidized to
ethanoic
acid and H
2
O at the anode releasing electrons that produce an electrical
current between the electrodes.
At cathode oxygen reduced to water.
Overall equation: C
2
H
5
OH + O
2
→ CH
3
COOH + H
2
O
The
voltage of the current can be used to measure the
ethanol concentration
.Slide23
Detection of ethanol in
breath using a fuel cell: reactions
Anode:
C
2
H
5OH
(g) + H
2
O(l
)→
CH
3
COOH(l) + 4H
+
(
aq
)+
4e
–
Cathode:
O
2
(g) + 4H
+
(
aq
) + 4e
–
→ 2H
2
O(l)
Current flows from anode to cathode