Transcript Beakers & Tubes III

Chapter 5 and 6
Organic and
Inorganic
Chemical Analysis
Phase Changes: (physical state changes)
• Melting: from solid directly into liquid
• Freezing: from liquid directly into solid
• Vaporization: from liquid directly into gas
• Condensation: from gas directly into liquid
• Sublimation: from solid directly into gas
• Deposition: from gas directly into solid
Phase Diagrams:
Matter
Can be separated
by physical methods
No
Yes
Pure Substance
Mixture
Uniform Composition?
Yes
Homogeneous
(solution)
No
Heterogeneous
Can it be broken down further ?
Yes
Compound
No
Element
Selecting an Analytical Technique
• Organic: a substance composed of carbon
(often contain hydrogen and smaller amounts of oxygen,
nitrogen, chlorine, or phosphorus)
• Inorganic: a chemical compound not
based on carbon
Questions to consider in choosing an analytical
(chemical) method:
•
•
•
•
•
•
•
Quantitative or qualitative required
Sample size and sample preparation requirements
What level of analysis is required (ex. ± 1.0% or ± 0.001%)
Detection levels
Destructive or non-destructive
Availability of instrumentation
Admissibility
What Is Chromatography?
• Laboratory technique for separating mixtures
into their component compounds
• Uses some version of a technique in which two
phases (one mobile, one stationary) flow past
one another
Chromatography Review
• Chromatographic systems have a stationary phase and a
mobile phase (usually liquid or gas)
• The mixture to be separated is placed on the stationary phase
• The mobile phase then “pushes” the components of the
mixture through the system
• Each component adsorbs on the stationary phase with a
different strength (stronger means moves more slowly through
the system)
• Each component comes out the end of the system at a different
time (retention time)
• When the molecules reach the far end of the surface, they are
detected or measured one at a time as they emerge
• Chromatography is non-destructive
• Separation of components depends on both their solubility in
the mobile phase and their differential affinity to the stationary
phase.
Street Drugs in Real Time
RT: 2.80 - 7.43
100
SM: 9G
NL:
7.91E6
m/z=
43.50-44.50
F: MS
level4
80
60
Amphetamine
40
20
0
100
NL:
1.18E7
m/z=
57.50-58.50
F: MS
level4
80
60
40
Methamphetamine
and MDMA
20
0
100
NL:
5.92E5
m/z=
298.50299.50 F:
MS level4
80
60
Hydrocodone
40
20
0
100
NL:
2.17E6
m/z=
81.50-82.50
F: MS
level4
80
60
Cocaine
40
20
0
100
NL:
2.40E5
m/z=
314.50315.50 F:
MS level4
80
60
40
20
0
3.0
3.5
4.0
4.5
5.0
5.5
Time (min)
6.0
6.5
7.0
Oxycodone
Types of Chromatography
• Paper Chromatography
• Thin-Layer Chromatography (TLC)
• Liquid Chromatography (HPLC)
• Gas Chromatography (GC)
Paper Chromatography
• Stationary phase
 a sheet or strip of paper
• mobile phase
 a liquid solvent
• Sample mixture spotted onto the paper
• Capillary action moves mobile phase
• Components appear as separate spots spread
out on the paper after drying
Thin Layer Chromatography (TLC)
• Stationary Phase
 a thin layer of adsorbent coating on a sheet of
plastic or glass
• Mobile Phase
 a liquid solvent
• Sample mixture spotted onto the adsorbent
- Solids must first be dissolved
- Liquids can be directly applied
• Some components bind to the adsorbent
strongly; some weakly
• Components appear as separate spots after
development
TLC
Retention Factor (Rf)
• An indication of how far a
compound travels in a particular
solvent
• Good gauge of whether an
unknown and a known compound
are similar
• Rf = distance the solute (D1) moves
divided by the distance traveled by the
solvent front (D2)
• Rf = D1
D2
Gas Chromatography
• Stationary phase
 a solid or very “syrupy” liquid in a tube (column)
• Mobile phase
 an inert gas (carrier gas)
• Usually nitrogen or helium
Analysis Using the GC
• Retention time can be used as an identifying
characteristic of a substance
 retention times may not be unique
• An extremely sensitive technique
 area under a peak is proportional to the quantity of
substance present
 allows quantitation of sample
Retention time: time between when the sample is injected
and when it exits the column reaching the detector
Retention Time
Tm is the time it takes for the mobile phase to pass through the column
High Performance Liquid Chromatography (HPLC)
• Stationary phase
 fine solid particles which are chemically treated
• Mobile phase
 a liquid
• Advantage: takes place at room temperature
Used for organic explosives that are heat sensitive
as well as heat sensitive drugs
Mass Scale
Atomic and Molecular Weights
• Atomic Mass Scale - based upon 12C isotope. This
isotope is assigned a mass of exactly 12 atomic mass units
(amu) and the masses of all other atoms are given relative
to this standard.
• Most elements in nature exist as mixtures of isotopes
(atoms of an element that have different numbers of
neutrons but same number of protons).
Mass Spectrometry (MS or mass spec)
Basic Ideas
Creates charged particles (ions) from gas phase molecules.
The Mass Spec analyzes ions to provide information
about the molecular weight of the compound and its
chemical structure.
Mass Spectrometer (MS)
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As the sample leaves the GC or HPLC, it
enters the Mass spec.
Within the MS, a beam of electrons is shot
at the substance breaking it down into
fragments
These fragments pass through an electric
field which separates them by their masses
The fragment masses are then recorded
Each substance breaks down into its own
characteristic pattern
Mass Spectrometer
Atomic Spectra
Mass
Spectrum
Cl
Int.
Mass
Spectrum
Int.
C
35
Mass
Spectrum
P
12
37
mass number (amu)
35Cl:
75% abundant
37Cl: 24% abundant
Int.
31
13
mass number (amu)
12Cl:
98.9% abundant
13Cl: 1.11% abundant
mass number (amu)
31P:
100% abundant
• The unique feature of mass spectrometry is that
under carefully controlled conditions, no two
substances produce the same fragmentation
pattern
• Allows for identifying chemical substance
• Each mass spectrum is unique to each drug and
so serves as specific test for identifying the
substance
Mass Spectrometer
Unknown white powdery substance ingested by
unconscious patient.
What do you do? Is it Heroin, Cocaine, Caffeine?
Intensity
Mass Spectrum of Unknown Compound
Mass 25
50
75
100
125 150 175 200
225 250 275
300
Mass Spectrometer
Intensity
MS Library
43
Intensity
Mass 25
50
75
67
55
42
50
other peaks at
327 and 369
268
204
215
94
Mass 25
Heroin
Heroin
146
100 125 150 175 200 225 250 275
194
Caffeine
300
109
82
75
MS of Unknown
100 125 150 175 200 225 250 275
300
Mass Spectrometer
Intensity
82
MS
Library
182
303
42
122
25
Intensity
Mass
Cocaine
Cocaine
Mass 25
50
75
67
55
42
50
150
272
100 125 150 175 200 225 250 275
194
Caffeine
300
109
82
75
MS of Unknown
100 125 150 175 200 225 250 275
300
Mass Spectrometer
Intensity
MS Library
Intensity
Mass 25
Mass 25
67
55
109
75
67
55
42
50
Caffeine
Caffeine
82
42
50
194
100 125 150 175 200 225 250 275
194
Caffeine
300
109
82
75
MS of Unknown
100 125 150 175 200 225 250 275
300
Mass Spectrometer
Unknown white powdery
substance ingested by
unconscious patient.
What do you do?
O
H 3C
N
Mass Spectrum
Mol. Wgt
= 194
N
CH 3
Caffeine
Intensity
Mass 25
N
N
O
CH 3
50
75
100
125 150 175 200
225 250 275
300
Electrophoresis
• Separates materials
based on their migration
rates on a stationary solid
phase
• Passes an electrical
current through the
medium and allows for
classification of proteins
(DNA)
Most useful applications of Electrophoresis
• Characterization of proteins and DNA in dried blood
• Proteins migrate at speeds
that vary according to their
electrical charge and size
resulting in characteristic
band patterns
Spectroscopy and Spectrophotometry
• Study of absorption of light by chemical substances
• Used for identification of various organic materials
or for presence of trace elements
• Electromagnetic spectrum – entire range of “light
waves”
• Colors – absorption or reflection of various
wavelengths of visible light
• Ultraviolet or infrared radiation (either side of visible
region)
• X-ray – high energy, short wavelength
• Incoherent light – light comprised of
waves that are out of step with each other
• Coherent or laser light – light whose waves
are pulsating in unison
– Laser (light amplification by the simulated
emission of radiation)
• Photon – small packet of
electromagnetic radiation energy.
• Each photon contains a unit of energy
E = hν
E = energy of photon
ν = frequency of radiation
h = Plank’s constant (6.626 X 10-34 J•s)
The Spectrophotometer
• Instrument used to measure and record
the absorption spectrum of a chemical
substance
UV Spectrophotometry
• Measures absorbance of UV and visible light as a
function of wavelength or frequency
• Allows tentative identification
Ex. White powder with UV spectrum
comparable to that of heroin results in a
tentative identification
UV Spectrum
Infrared Spectrophotometry
• Different materials always have distinctively
different infrared spectra
• Each IR spectrum is therefore equivalent to
a “fingerprint” of that substance and no
other
• Extensive catalogue of IR spectra of
organic compounds allows for identification
of organic substances
IR Spectrum
Atomic Emission Spectroscopy (AES)
• Used to detect the types of elements present in a sample
• Can use measurement of the emissions from excited atoms to
determine concentration.
• Frequency of light given off
The Hydrogen Discharge Tube
• H2 molecules are
excited by an
electric discharge
• As the atoms return
to lower energy
states, light is
emitted
Flame Tests
Atomic Emission
Atomic Absorption Spectroscopy (AAS)
• Sample heated and atoms absorb radiation
• Atoms become excited
• The amount of radiation absorbed is recorded
• Can be used to quantitate amounts based on a calibration curve
• Beer’s Law (Absorption is proportional to concentration)
Example:
• Determination of the wavelength of light absorbed
by a sample of grape soda
Absorption of Grape Soda
Example:
• Determination of the amount of dilution of a sample of
grape soda
Neutron Activation Analysis (NAA)
• Used for determining the concentrations of elements
Process:
• Neutrons interact with a target nucleus to form a nucleus in an
excited state.
• The excited nucleus will decay immediately into a more stable
configuration through emission of gamma rays
• This new configuration may yields a radioactive nucleus which
continues to undergo decay but at a much slower rate (depending on
the unique half-life of the sample). This decay is also measured.
• Allows quantitation in parts per billion but requires a nuclear
reactor
Neutron Activation Analysis
• Rate depends on half-life
– Prompt gamma ray formation
• measurement taken during irradiation
– Delayed gamma ray formation
• measurements taken after irradiation
• more common
• About 70% of elements have properties
suitable for measurement by NAA
Gamma-ray Spectra
Continuation of medium & long-lived elements