Introduction to Applied Medical Science
(AMS 110)
‫مقدمة العلوم الطبية التطبيقية‬
Part I: Introduction to Chemical Analyses
Analytical chemistry deals with methods for the identification of one or more
of the components in a sample of matter and the determination of the relative
amounts of each. The identification process is called a qualitative analysis
while the determination of amount is termed a quantitative analysis.
Some Medical Applications of Quantitative Analysis:
1. Determination of the concentration of ionized calcium in blood serum is
an important method for the diagnosis of hyperparathyroidism in
human patients.
2. Determination of the blood sugar levels is very important for the
diagnosis of diabetes.
3. Monitoring of the serum cholesterol level is very important to follow
the coronary disease.
4. Determination of albumin, urea, creatinin and some elements such as
copper, zinc, and iron is very important for the diagnosis of many
diseases.
5. Quantitative data on nitrogen in breakfast cereals and other foods are
directly related to their nutritional qualities.
6. Measuring the conduction of nerve signals in humans and the
contraction or relaxation of muscles involves the transport of sodium
and potassium ions across membranes.
7. Studies concerned with the mechanism by which oxygen and carbon
dioxide are transported in blood have required methods for continually
monitoring the concentration of these and other compounds within a
living organism.
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Performance of Quantitative Analysis:
The results of a typical quantitative analysis are based upon two
measurements:
1. The quantity of sample taken.
2. The quantity of analyte in that sample.
The chemist who has need for analytical data usually finds himself faced with
an array of methods which could be used to provide the desired information.
His choice among these will be based on such considerations as speed,
convenience,
accuracy,
availability
of
equipment,
number
of
analyses, amount of sample that can be sacrificed, and concentration
range of the analyte.
Analytical chemistry is a sub discipline of chemistry that has the broad
mission of understanding the chemical composition of all matter and
developing the tools to elucidate such compositions. This differs from other
sub disciplines of chemistry in that it is not intended to understand the
physical basis for the observed chemistry as with physical chemistry and it is
not intended to control or direct chemistry as is often the case in organic
chemistry and it is not necessarily intended to provide engineering tactics as
are often used in materials science. Analytical chemistry generally does not
attempt to use chemistry or understand its basis; however, these are
common outgrowths of analytical chemistry research. Analytical chemistry has
significant overlap with other branches of chemistry, especially those that are
focused on a certain broad class of chemicals, such as organic chemistry,
inorganic chemistry or biochemistry, as opposed to a particular way of
understanding chemistry, such as theoretical chemistry. For example the field
of Bioanalytical chemistry is a growing area of analytical chemistry that
addresses all analytical questions in biochemistry, (the chemistry of life).
Analytical chemistry and experimental physical chemistry, however, have a
unique relationship in that they are very unrelated in their mission but often
share the most in common in the tools used in experiments.
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Analytical chemistry is particularly concerned with the questions of "what
chemicals are present, what are their characteristics and in what quantities
are they present?" These questions are often involved in questions that are
more dynamic such as what chemical reaction an enzyme catalyzes or how
fast it does it, or even more dynamic such as what is the transition state of
the reaction. Although analytical chemistry addresses these types of questions
it stops after they are answered. The next logical steps of understanding what
it means, how it fits into a larger system, how can this result be generalized
into theory or how it can be used are not analytical chemistry. Since analytical
chemistry is based on firm experimental evidence and limits itself to some
fairly simple questions to the general public it is most closely associated with
hard numbers such as how much lead is in drinking water.
Modern analytical chemistry
Modern analytical chemistry is dominated by instrumental analysis. Many
analytical chemists focus on a single type of instrument. Academics tend to
either focus on new applications and discoveries or on new methods of
analysis. The discovery of a chemical present in blood that increases the risk
of cancer would be a discovery that an analytical chemist might be involved
in. An effort to develop a new method might involve the use of a tunable
laser to increase the specificity and sensitivity of a spectrometric method.
Many methods, once developed, are kept purposely static so that data can be
compared over long periods of time. This is particularly true in industrial
quality assurance (QA), forensic and environmental applications.
Analytical chemistry plays an increasingly important role in the pharmaceutical
industry where, aside from QA, it is used in discovery of new drug candidates
and in clinical applications where understanding the interactions between the
drug and the patient are critical.
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Types of analytical chemistry:
Traditionally, analytical chemistry has been split into two main types,
qualitative and quantitative:
Qualitative

Qualitative inorganic analysis seeks to establish the presence of a given
element or inorganic compound in a sample.

Qualitative organic analysis seeks to establish the presence of a given
functional group or organic compound in a sample.
Quantitative

Quantitative analysis seeks to establish the amount of a given element
or compound in a sample.
Approaches
Most modern analytical chemistry is categorized by two different approaches
such as analytical targets or analytical methods. Analytical Chemistry (journal)
reviews two different approaches alternatively in the issue 12 of each year.
By Analytical Targets

Bioanalytical chemistry

Material analysis

Chemical analysis

Environmental analysis

Forensics
By Analytical Methods

Spectroscopy

Mass Spectrometry

Spectrophotometry and Colorimetry

Chromatography and Electrophoresis

Crystallography

Microscopy

Electrochemistry
4
Traditional analytical techniques
Although modern analytical chemistry is dominated by sophisticated
instrumentation, the roots of analytical chemistry and some of the principles
used in modern instruments are from traditional techniques many of which
are still used today. These techniques also tend to form the backbone of most
undergraduate analytical chemistry educational labs. Examples include:
Titration
Titration involves the addition of a reactant to a solution being analyzed until
some equivalence point is reached. Often the amount of material in the
solution being analyzed may be determined. Most familiar to those who have
taken college chemistry is the acid-base titration involving a color changing
indicator.
There
are
many
other
types
of
titrations,
for
example
potentiometric titrations. These titrations may use different types of indicators
to reach some equivalence point.
Gravimetry
Gravimetric analysis involves determining the amount of material present by
weighing the sample before and/or after some transformation. A common
example used in undergraduate education is the determination of the amount
of water in a hydrate by heating the sample to remove the water such that
the difference in weight is due to the water lost.
Inorganic qualitative analysis
Inorganic qualitative analysis generally refers to a systematic scheme to
confirm the presence of certain, usually aqueous, ions or elements by
performing a series of reactions that eliminate ranges of possibilities and then
confirms suspected ions with a confirming test. Sometimes small carbon
containing ions are included in such schemes. With modern instrumentation
these tests are rarely used but can be useful for educational purposes and in
field work or other situations where access to state-of-the-art instruments are
not available or expedient.
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Instrumental Analysis:
Block diagram of an analytical instrument
Spectroscopy
Spectroscopy measures the interaction of the molecules with electromagnetic
radiation.
Spectroscopy consists of many different applications such as:

Atomic Absorption Spectroscopy (AAS)

Atomic Emission Spectroscopy (AES)

Ultraviolet-visible Spectroscopy (UV/VIS)

X-ray

Fluorescence Spectroscopy

Infrared Spectroscopy (IR)

Raman Spectroscopy

Nuclear Magnetic Resonance Spectroscopy (NMR)

Photoemission Spectroscopy

Mass Spectrometry (MS)
Crystallography
Crystallography is a technique that characterizes the chemical structure of
materials at the atomic level by analyzing the diffraction patterns of usually xrays that have been deflected by atoms in the material. From the raw data
the relative placement of atoms in space may be determined.
6
Electrochemical Analysis
Electroanalytical methods measure the potential (volts) and/or current (amps)
in an electrochemical cell containing the analyte. These methods can be
categorized according to which aspects of the cell are controlled and which
are measured. The three main categories are:

Potentiometry (the difference in electrode potentials is measured)

Coulometry (the cell's current is measured over time)

Voltammetry (the cell's current is measured while actively altering the
cell's potential).
Chromatographic Analysis:
Chromatographic analysis includes two different types according to the mobile
phase; gas or liquid.

Gas Chromatograph (GC)

High Performance Liquid Chromatograph (HPLC)
Electrophoresis
Separation processes are used to decrease the complexity of material
mixtures. Chromatography and electrophoresis are representative of this field.
Hybrid Techniques:
Combinations of the above techniques produce "hybrid" or "hyphenated"
techniques. Several examples are in popular use today and new hybrid
techniques are under development.
Hyphenated separation techniques refer to a combination of two (or more)
techniques to detect and separate chemicals from solutions. Most often the
other technique is some form of chromatography. Hyphenated techniques are
widely used in chemistry and biochemistry. A slash is sometimes used instead
of hyphen, especially if the name of one of the methods contains a hyphen
itself.
7
Examples of hyphenated techniques:
GC-MS
HPLC-MS
GC-IR
Lab-on-a-chip
Devices that integrate (multiple) laboratory functions on a single chip of only
millimeters to a few square centimeters in size and that are capable of
handling extremely small fluid volumes down to less than pico liters.
Standard Curve
A standard method for analysis of concentration involves the creation of a
calibration curve. This allows for determination of the amount of a chemical in
a material by comparing the results of unknown sample to those of a series
known standards. If the concentration of element or compound in a sample is
too high for the detection range of the technique, it can simply be diluted in a
pure solvent. If the amount in the sample is below an instrument's range of
measurement, the method of addition can be used. In this method a known
quantity of the element or compound under study is added, and the
difference between the concentration added, and the concentration observed
is the amount actually in the sample.
Internal Standards
Sometimes an internal standard is added at a known concentration directly to
an analytical sample to aid in quantitation. The amount of analyte present is
then determined relative to the internal standard as a calibrant.
Trends
Analytical chemistry research is largely driven by:

Performance which includes: sensitivity, selectivity, linear range,
accuracy, precision, and speed.

Cost which includes: purchase, operation, training, time, and space.
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Among
the
main
branches
of
contemporary
analytical
atomic
spectrometry, the most widespread and universal are optical and mass
spectrometry. In the direct elemental analysis of solid samples, the new
leaders
are
laser-induced breakdown
and laser ablation mass
spectrometry, and the related techniques with transfer of the laser ablation
products into inductively coupled plasma. Advances in design of diode lasers
and optical parametric oscillators promote developments in fluorescence and
ionization spectrometry and also in absorption techniques where uses of
optical cavities for increased effective absorption path length are expected to
expand. Steady progress and growth in applications of plasma- and laserbased methods are noticeable.
A lot of effort is put in shrinking the analysis techniques to chip size. Although
there are few examples of such systems competitive with traditional analysis
techniques, potential advantages include size/portability, speed, and cost.
(micro Total Analysis System (µTAS) or (Lab-on-a-chip). Microscale
chemistry reduces the amounts of chemicals used.
Much effort is also put into analyzing biological systems. Examples of
rapidly expanding fields in this area are:

Genomics - DNA sequencing and its related research. Genetic
fingerprinting and DNA microarray are very popular tools and
research fields.

Proteomics - the analysis of protein concentrations and modifications,
especially in response to various stressors, at various developmental
stages, or in various parts of the body.

Metabolomics - similar to proteomics, but dealing with metabolites.

Transcriptomics- mRNA and its associated field

Lipidomics - lipids and its associated field

Peptidomics - peptides and its associated field
9

Metalomics - similar to proteomics and metabolomics, but dealing
with metal concentrations and especially with their binding to proteins
and other molecules.
Analytical chemistry has played critical roles in the understanding of
basic science to a variety of practical applications such as:

Biomedical applications

Environmental monitoring

Quality control of industrial manufacturing

Forensic science
The
recent
developments
of
computer
automation
and
information
technologies have innervated analytical chemistry to initiate a number of new
biological fields. For example, automated DNA sequencing machines
were the basis to complete human genome projects leading to the birth of
genomics. Protein identification and peptide sequencing by mass
spectrometry opened a new field of proteomics.
Also,
analytical
chemistry
has
been
an
indispensable
area
in
the
development of nanotechnology. Surface characterization instruments,
electron microscopes and scanning probe microscopes enables scientists to
visualize atomic structures with chemical characterizations.
Analytical chemistry is pursuing the development of practical applications and
commercial instruments rather than elucidating scientific fundamentals. This
may be an arguable difference from overlapping science areas such as
physical chemistry and biophysics, although there isn't any distinct boundaries
among disciplines in contemporary science and technology. However, this
aspect may attract many engineers' interest; thus, it is not difficult to see
papers from engineering departments in analytical chemistry journals.
10
Among active contemporary analytical chemistry research fields, micro total
analysis system is considered as a great promise of revolutionary
technology. In this approach, integrated and miniaturized analytical systems
are being developed to control and analyze single cells and single
molecules. This cutting-edge technology has a promising potential of leading
a new revolution in science as integrated circuits did in computer
developments.
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SPECTROSCOPY
Spectroscopy
is
the
study
of
the
interaction
electromagnetic radiation (EMR) and matter.
Electromagnetic radiation
The Shape of wave motion
12
between
radiation
Spectrometry is the measurement of these interactions and a machine
which performs such measurements is a spectrometer or spectrograph.
A plot of the interaction is referred to as a spectrogram, or, informally, a
spectrum.
A spectrometer is an optical instrument used to measure properties of light
over a specific portion of the electromagnetic spectrum, typically used in
spectroscopic analysis to identify materials. The variable measured is most
often the light's intensity.
A spectrometer is used in spectroscopy for producing spectral lines and
measuring their wavelengths and intensities. Spectrometer is a term that is
applied to instruments that operate over a very wide range of wavelengths,
from gamma rays and X-rays into the far infrared.
Basic units for any spectrometer Instrument are:

Energy source

Monochromator

Sample container

Detector

Recorder
Tungsten lamp
As a source of visiple light
UV lamp
as a source of ultraviolet light
13
Light filters
Monochromators
used in photometres
used in spectrophotometers
14
Prism
Grating
Sample containers
15
Detector (vl)
Photomultiplier tube (uv)
Recorders
16
Single beam spectrophotometer
Double beam spectrophotometer
17
Photometer
S-D Curve
18
C-D curve
Concentration (μg/ml) = Absorbance/specific extinction coefficient (K)
19
Ultraviolet-visible spectroscopy
UV/VIS- Spectrophotometer
UV/ VIS spectrometer involves the spectroscopy of photons in the UV-visible
region. It uses light in the visible and adjacent near ultraviolet (UV) and near
infrared (NIR) ranges.
In this region of the electromagnetic spectrum, molecules undergo electronic
transitions. This technique is complementary to fluorescence spectroscopy, in
that fluorescence deals with transitions from the excited state to the ground
state, while absorption measures transitions from the ground state to the
excited state.
20
Applications
UV/Vis spectroscopy is routinely used in the quantitative determination of
solutions of transition metal ions and highly conjugated organic compounds.

Solutions of transition metal ions can be coloured (i.e., absorb visible
light) because d electrons within the metal atoms can be excited from
one electronic state to another. The colour of metal ion solutions is
strongly affected by the presence of other species, such as certain
anions or ligands. For instance, the colour of a dilute solution of copper
sulfate is a very light blue; adding ammonia intensifies the colour and
changes the wavelength of maximum absorption (λmax).

Organic
compounds,
especially
those
with
a
high
degree
of
conjugation, also absorb light in the UV or visible regions of the
electromagnetic spectrum. The solvents for these determinations are
often water for water soluble compounds, or ethanol for organicsoluble compounds. (Organic solvents may have significant UV
absorption; not all solvents are suitable for use in UV spectroscopy.
Ethanol absorbs very weakly at most wavelengths.) Solvent polarity
and pH can effect the absorption spectrum of an organic compound.
Tyrosine, for example, increases in absorption maxima and molar
extinction coefficient when pH increases from 6 to 13 or when solvent
polarity decreases.

While charge transfer complexes also give rise to colours, the colours
are often too intense to be used for quantitative measurement.
The absorbance of a solution is directly proportional to the solution's
concentration. Thus UV/VIS spectroscopy can be used to determine the
concentration of a solution.
21
UV spectrum
It is necessary to know how quickly the absorbance changes with
concentration. This can be taken from references (tables of molar extinction
coefficients), or more accurately, determined from a calibration curve.
22
CHARACTERISTIC
ABSORPTION
BANDS
FOR
COMMON CHROMOPHORES.
Chromophore
Compound
types
Example
Solvent
Absorption Band
max
Alkene
RCH=CHR
Ethylene
Vapor
Alkyne
R-CC-R
2-octyne
Heptane
Ketone
R2 - C=O
Acetone
Hexane
Aldehyde
R-COH
Carboxyl
R-COOH
Acetaldehy
de
acetic acid
Amido
Nitro
R-C(O)-NH2
RNO2
vapor,
hexane
95%
ethanol
Water
methanol
Nitrate
R-ONO2
Nitroso
R-N=O
Nitrile
Sulfoxide
Sulfone
Azo
-CN
-S=O
O=S=O
R-N=N-R
Acetamide
Nitrometha
ne
n-butyl
nitrate
Nitroso
butane
95%
ethanol
ethyl ether
alcohol
Azomethan
e
23
95%
ethanol
(m)
max
165
193
195
223
189
270
180
290
208
15,000
10,000
2,100
160
900
15
10,000
17
32
220
201
63
5,000
270
17
300
665
< 160
210
<180
338
100
20
4
ATOMIC ABSORPTION SPECTROSCOPY
Atomic absorption spectrometer
24
In analytical chemistry, atomic absorption spectroscopy is a technique for
determining the concentration of a particular metal element in a sample.
Atomic absorption spectroscopy can be used to analyze the concentration of
over 62 different metals in a solution.
Principles
The technique makes use of absorption spectrometry to assess the
concentration of an analyte in a sample. It relies therefore heavily on BeerLambert law.
In short, the electrons of the atoms in the atomizer can be promoted to
higher orbitals for an instant by absorbing a set quantity of energy (i.e. light
of a given wavelength). This amount of energy (or wavelength) is specific to
a particular electron transition in a particular element, and in general, each
wavelength corresponds to only one element. This gives the technique its
elemental selectivity.
As the quantity of energy (the power) put into the flame is known, and the
quantity remaining at the other side (at the detector) can be measured, it is
possible, from Beer-Lambert law, to calculate how many of these transitions
took place, and thus get a signal that is proportional to the concentration of
the element being measured.
Instrumentation
In order to analyze a sample for its atomic constituents, it has to be
atomized. The sample should then be illuminated by light. The light
transmitted is finally measured by a detector. In order to reduce the effect of
emission from the atomizer (e.g. the black body radiation) or the
environment, a spectrometer is normally used between the atomizer and the
detector.
25
Single beam AAS
Double beam AAS
26
Types of Atomizer
The technique typically makes use of a flame to atomize the sample, but
other atomizers such as a graphite furnace or plasmas, primarily inductively
coupled plasmas, are also used.
When a flame is used, it arranged so that it is laterally long (usually 10 cm)
and not deep. The height of the flame above the burner head can be
controlled by adjusting the flow of the fuel mixture. A beam of light passes
through this flame at its longest axis (the lateral axis) and hits a detector.
Mixing of feul and oxidizing agent
27
Analysis of liquids
A liquid sample is normally turned into an atomic gas in three steps:
1. Desolvation – the liquid solvent is evaporated, and the dry sample
remains
2. Vaporization – the solid sample vaporises to a gas
3. Atomization – the compounds making up the sample are broken into
free atoms.
Light Sources
The light source chosen has a spectral width narrower than that of the atomic
transitions.
Hollow cathode lamps
In its conventional mode of operation, the light is produced by a hollow
cathode lamp. Inside the lamp is a cylindrical metal cathode containing the
metal for excitation, and an anode. When a high voltage is applied across the
anode and cathode, the metal atoms in the cathode are excited into
producing light with a specific wavelength. The type of hollow cathode tube
depends on the metal being analyzed. For analyzing the concentration of
copper in an ore, a copper cathode tube would be used, and likewise for any
other metal being analyzed.
Hollow Cathode lamp
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X-RAY SPECTROMETER
X-radiation (composed of X-rays) is a form of electromagnetic radiation. Xrays have a wavelength in the range of 10 to 0.01 nanometers. They are
longer than gamma rays but shorter than UV rays. In many languages, Xradiation is called Röntgen radiation after one of its first investigators,
Wilhelm Conrad Röntgen.
X-rays are primarily used for diagnostic radiography and crystallography. As a
result, the term "X-ray" is metonymically used to refer to a radiographic
image produced using this method, in addition to the method itself. X-rays
are a form of ionizing radiation and as such can be dangerous.
X-rays span 3 decades in wavelength, frequency and energy. From about 0.12
to 12 keV they are classified as soft x-rays, and from about 12 to 120 keV as
hard X-rays, due to their penetrating abilities.
29
Medical uses:
30
Since Röntgen's discovery that X-rays can identify bony structures, X-rays
have been developed for their use in medical imaging. Radiology is a
specialized field of medicine. Radiographers employ radiography and other
techniques for diagnostic imaging. This is probably the most common use of
X-ray technology.
X-rays are especially useful in the detection of pathology of the skeletal
system, but are also useful for detecting some disease processes in soft
tissue. Some notable examples are the very common chest X-ray, which can
be used to identify lung diseases such as pneumonia, lung cancer or
pulmonary edema, and the abdominal X-ray, which can detect ileus (blockage
of the intestine), free air (from visceral perforations) and free fluid (in
ascites). In some cases, the use of X-rays is debatable, such as gallstones
(which are rarely radiopaque) or kidney stones (which are often visible, but
not always). Also, traditional plain X-rays pose very little use in the imaging of
soft tissues such as the brain or muscle. Imaging alternatives for soft tissues
are computed axial tomography (CAT or CT scanning), magnetic resonance
imaging (MRI) or ultrasound. Since 2005, X-rays are listed as a carcinogen by
the U.S. government.
Radiotherapy, a curative medical intervention, now used almost exclusively
for cancer, employs higher energies of radiation.
The efficiency of X-ray tubes is less than 2%. Most of the energy is used to
heat up the anode.
31
NMR SPECTROSCOPY
900MHz NMR instrument
Nuclear magnetic resonance spectroscopy, most commonly known as
NMR spectroscopy, is the name given to a technique which exploits the
magnetic properties of certain nuclei. This phenomenon and its origins are
detailed in a separate section on nuclear magnetic resonance. The most
important applications for the organic chemist are proton NMR and carbon-13
NMR spectroscopy. In principle, NMR is applicable to any nucleus possessing
spin.
Many types of information can be obtained from an NMR spectrum. Much like
using infrared spectroscopy to identify functional groups, analysis of a 1D
NMR spectrum provides information on the number and type of chemical
32
entities in a molecule. However, NMR provides much more information than
IR.
The impact of NMR spectroscopy on the natural sciences has been
substantial. It can, among other things, be used to study mixtures of
analytes, to understand dynamic effects such as change in temperature and
reaction mechanisms, and is an invaluable tool in understanding protein and
nucleic acid structure and function. It can be applied to a wide variety of
samples, both in the solution and the solid state.
Basic NMR techniques
The NMR sample is prepared in a thin-walled glass tube - an NMR tube.
When placed in a magnetic field, NMR active nuclei (such as 1H or
13C)
absorb
at a frequency characteristic of the isotope. The resonant frequency, energy
of the absorption and the intensity of the signal are proportional to the
strength of the magnetic field. For example, in a 21 tesla magnetic field,
protons resonate at 900 MHz. It is common to refer to a 21 T magnet as a
900 MHz magnet, although different nuclei resonate at a different frequency
at this field strength.
33
In the Earth's magnetic field the same nuclei resonate at audio frequencies.
This effect is used in Earth's field NMR spectrometers and other instruments.
Because these instruments are portable and inexpensive, they are often used
for teaching and field work.
Chemical shift
Depending on the local chemical environment, different protons in a molecule
resonate at slightly different frequencies. Since both this frequency shift and
the fundamental resonant frequency are directly proportional to the strength
of the magnetic field, the shift is converted into a field-independent
dimensionless value known as the chemical shift. The chemical shift is
reported as a relative measure from some reference resonance frequency.
(For the nuclei 1H,
13C,
and
29Si,
TMS (tetramethylsilane) is commonly used as
a reference.) This difference between the frequency of the signal and the
frequency of the reference is divided by frequency of the reference signal to
give the chemical shift. The frequency shifts are extremely small in
comparison to the fundamental NMR frequency. A typical frequency shift
might be 100 Hz, compared to a fundamental NMR frequency of 100 MHz, so
the chemical shift is generally expressed in parts per million (ppm).
By understanding different chemical environments, the chemical shift can be
used to obtain some structural information about the molecule in a sample.
The conversion of the raw data to this information is called assigning the
spectrum. For example, for the 1H-NMR spectrum for ethanol (CH3CH2OH),
one would expect three specific signals at three specific chemical shifts: one
for the CH3 group, one for the CH2 group and one for the OH group. A typical
CH3 group has a shift around 1 ppm, a CH2 attached to an OH has a shift of
around 4 ppm and an OH has a shift around 2–3 ppm depending on the
solvent used.
Because of molecular motion at room temperature, the three methyl protons
average out during the course of the NMR experiment (which typically
34
requires a few ms). These protons become degenerate and form a peak at
the same chemical shift.
The shape and size of peaks are indicators of chemical structure too. In the
example above—the proton spectrum of ethanol—the CH3 peak would be
three times as large as the OH. Similarly the CH2 peak would be twice the size
of the OH peak but only 2/3 the size of the CH3 peak.
Modern analysis software allows analysis of the size of peaks to understand
how many protons give rise to the peak. This is known as integration—a
mathematical process which calculates the area under a graph (essentially
what a spectrum is). The analyst must integrate the peak and not measure its
height because the peaks also have width—and thus its size is dependent on
its area not its height. However, it should be mentioned that the number of
protons, or any other observed nucleus, is only proportional to the intensity,
or the integral, of the NMR signal, in the very simplest one-dimensional NMR
experiments. In more elaborate experiments, for instance, experiments
typically used to obtain carbon-13 NMR spectra, the integral of the signals
depends on the relaxation rate of the nucleus, and its scalar and dipolar
coupling constants. Very often these factors are poorly understood therefore, the integral of the NMR signal is very difficult to interpret in more
complicated NMR experiments.
35
MAGNETIC RESONANCE IMAGING
(MRI)
Magnetic resonance imaging (MRI), or Nuclear magnetic resonance
imaging (NMRI), is primarily a medical imaging technique most commonly
used in radiology to visualize the structure and function of the body. It
provides detailed images of the body in any plane. MRI provides much
greater contrast between the different soft tissues of the body than computed
tomography (CT) does, making it especially useful in neurological (brain),
musculoskeletal, cardiovascular, and oncological (cancer) imaging. Unlike CT,
it uses no ionizing radiation, but uses a powerful magnetic field to align the
nuclear magnetization of (usually) hydrogen atoms in water in the body.
Radiofrequency fields are used to systematically alter the alignment of this
magnetization, causing the hydrogen nuclei to produce a rotating magnetic
field detectable by the scanner. This signal can be manipulated by additional
magnetic fields to build up enough information to construct an image of the
body.
MRI is a relatively new technology, which has been in use for little more than
30 years (compared with over 110 years for X-ray radiography).
Magnetic resonance imaging was developed from knowledge gained in the
study of nuclear magnetic resonance. In its early years the technique was
referred to as nuclear magnetic resonance imaging (NMRI). However, as the
word nuclear was associated in the public mind with ionizing radiation
exposure it is generally now referred to simply as MRI. Scientists still use the
term NMRI when discussing non-medical devices operating on the same
principles. The term Magnetic Resonance Tomography (MRT) is also
sometimes used.
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How MRI works
Brief lay explanation of MRI physics
When a person lies in a scanner, the hydrogen nuclei (i.e., protons) found in
abundance in the human body in water molecules, align with the strong main
magnetic
field.
A
second
electromagnetic
field
(which
oscillates
at
radiofrequencies and is perpendicular to the main field) is pulsed to push a
proportion of the protons out of alignment with the main field. These protons
then drift back into alignment with the main field, emitting a detectable
radiofrequency signal as they do so.
Since protons in different tissues of the body (e.g., fat vs. muscle) realign at
different speeds, the different structures of the body can be revealed.
Contrast agents may be injected intravenously to enhance the appearance of
blood vessels, tumors or inflammation. Contrast agents may also be directly
injected into a joint, in the case of arthrograms, MR images of joints. Unlike
CT scanning MRI uses no Ionizing Radiation and is generally a very safe
procedure. Patients with some metal implants and cardiac pacemakers are
prevented from having an MRI scan due to effects of the strong magnetic
field and powerful radiofrequency pulses.
MRI is used to image every part of the body, but is particularly useful in
neurological conditions, disorders of the muscles and joints, for evaluating
tumors and showing abnormalities in the heart and blood vessels
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Sagittal MR image of the knee
Para-sagittal MRI of the head
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41
GENERAL QUESTIONS
Choose the best answer of the following:
The identification process is termed:
1. Qualitative analysis
2. Quantitative analysis
3. Spectrometric analysis
The determination of amount is termed:
1. Qualitative analysis
2. Quantitative analysis
3. Photometric analysis
The performance of quantitative Analysis is based upon:
1. The quantity of sample taken.
2. The quantity of analyte in that sample only .
3. Both of them.
The modern analytical chemistry is dominated by:
1. Instrumental analysis.
2. Volumetric analysis.
3. Gravimetric analysis.
The study of the interaction between radiation electromagnetic
radiation (EMR) and matter is called:
1. Spectroscopy.
2. Spectrometer.
3. Spectrum.
The
machine
used
to
measure
the
interaction
electromagnetic radiation and matter is called:
1. Spectroscopy.
2. Spectrometer.
3. Spectrum.
Imaging alternatives for soft tissues are:
1. Computed axial tomography (CAT or CT scanning)
2. Magnetic resonance imaging (MRI)
3. Ultrasound.
4. all
42
between
MRI provides detailed images of the body in
1. vertical position
2. horizontal position
3. any plane
MRI is very useful in
1. neurological (brain) imaging.
2. cardiovascular imaging
3. oncological (cancer) imaging.
4. All answers are correct.
The plotting of the interaction between electromagnetic radiation
and matter is called:
1. Spectroscopy.
2. Spectrometer.
3. Spectrum.
Complete the following statements:
1. Basic units for any spectrometer Instrument are ……………………………….
, …………………………………………………, ………………………….…………………,
…………………………………………, and ……………………………………………
2. S-D curve shows the relationship between …………………. and ……………
3. ……………………. curve shows the relationship between absorbance and
concentrations.
4. Tungsten lamp is a source of ……………. While ……. ……… is a source
of ultraviolet light.
5. Light filters used in ………………… instrument while ……………………… used in
spectrophotometers.
6. UV/Vis spectroscopy is used in the quantitative determination of
………………………………….and ………………………..
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7. Atomic absorption spectroscopy is a technique for determining the
concentration of ………………………………………...
8. ……………………………. are primarily used for diagnostic radiography
and crystallography.
9. X-rays are a form of ……………………. radiation and as such can be
………………………..
10.
X-rays are classified as …………………………………………. and
………………………………. due to their penetrating abilities.
11.
X-rays are especially useful in the detection of pathology of the
skeletal system, but are also useful for detecting some disease
processes in soft tissue such as ………………………………………………………
12.
Magnetic resonance imaging (MRI) is primarily a medical
imaging technique used in radiology to visualize the ………………. and
………….. of the body.
13.
MRI uses no ionizing radiation, but uses a powerful magnetic
field to align the nuclear magnetization of (usually) ………….. atoms in
water in the body.
14.
MRI provides much greater contrast between the different soft
tissues of the body than …………………….. does.
15.
……………………may be injected intravenously to enhance the
appearance of blood vessels, tumors or inflammation.
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Select the correct name for each item:
Hollow cathode
lamp
UV lamp
Tungesten lamp
Filters
Grating
Prism
detector used in
visible light
Single beam
spectrometer
Sample
containers
UV/VL
Spectrometer
MRI machine
X-ray image
NMR
Photomultiplier
tube
Atomic
Absorption
Spectrometer
magnetic
resonance
image
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Double beam
spectrometer
X-ray
Spectrometer
Single beam
AAS
x-ray source
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