APEC Youth Scientist Journal Vol. 3
ANALYTICAL CHEMISTRY
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Hoang Le Thanh
Hanoi-Amsterdam Specialized high school for the gifted, Hoang Minh Giam Rd.,
Cau Giay district. Hanoi, Vietnam
ABSTRACT
Analytical chemistry is the study of the separation, identification, and quantification of the
chemical components of natural and artificial materials. Qualitative analysis gives an
indication of the identity of the chemical species in the sample and quantitative analysis
determines the amount of one or more of these components. The separation of components is
often performed prior to analysis.
Analytical methods can be separated into classical and instrumental. Classical methods (also
known as wet chemistry methods) use separations such as precipitation, extraction, and
distillation and qualitative analysis by color, odor, or melting point. Quantitative analysis is
achieved by measurement of weight or volume. Instrumental methods use an apparatus to
measure physical quantities of the analyte such as light absorption, fluorescence, or
conductivity. The separation of materials is accomplished using chromatography or
electrophoresis methods.
Analytical chemistry is also focused on improvements in experimental design, chemo metrics,
and the creation of new measurement tools to provide better chemical information. Analytical
chemistry has applications in forensics, bioanalysis, clinical analysis, environmental analysis,
and materials analysis.
1. PURPOSE
The main purpose of this research is to show the overview of analytical chemistry- a method
which many scientists have developed it and took it to the apex of chemistry. With this
research, we can know what analytical chemistry is and how the scientists apply it to their
study? The simplest way to interact with analytical chemistry is to investigate what
∗
Correspondence to : Hoang Le Thanh ([email protected])
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spectroscopy is and some spectroscopic methods. I hope it will be useful with the students
who is working for chemistry as well as other scientific fields
2. INTRODUCTION
2.1. What is analytical chemistry?
Analytical chemistry is a branch of chemistry-a popular subject in all school. It study the
properties of materials or develop tools to analyze materials about:
Qualitative Identify WHAT materials is present in a sample
Example: Is there any Lead in a sample?
Quantitative Identify HOW MUCH of a material is present in a sample.
Example: How much Lead in a sample?
1) What is spectroscopy?
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The most simple and popular method in analytical chemistry is spectroscopy
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Method where interaction of electromagnetic radiation with chemical molecules is
measured and visualized in order to obtain characteristics, properties and quantity of
an element in one object.
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We can decide which tool to use by specific wavelength of sample (Figure 1: If the
sample has long wavelength, it will have low energy. If the sample has short
wavelength, it will have high energy)
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Figure 1. Wavelength
2) UV-Vis Spectroscopy
Figure 2. Light source
The diffraction grating is able to rotated so a specific wavelength is selectable. The light
intensity after going through sample cuvette will be detected at detector
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Uv-Vis Spectroscopy measure the relative light intensity of the beam before and
after a test sample is inserted and then compares the fraction of light that passes
through a reference solution and a test solution
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The Beer-Lambert law is the linear relationship between absorbance and
concentration of an absorbing species.
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•
Experimental measurements are usually made in terms of transmittance (T), which
is defined as:
T = I / Io
(Where I is the light intensity after it passes through the sample and Io is the initial
light intensity)
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The relation between A and T is:
A = -log T = - log (I / Io)
(Where A is the measured absorbance)
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This method is used to determined DNA and food color
3) Atomic Absorption Spectroscopy(AAS)
There are 2 types of AAS. Both of them have similar method. At first, we have to put
sample in compatible condition (with flame or graphite furnace). And then it will absorb
light we shine. Our final task is to measure the lost energy of light, and compare result
with reference sample.( figure 3 and 4)
With AAS we can detect small amounts of metal elements such as zinc or iron
a) flame atomization absorption spectrometry
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High sensitivity (especially for elements like Pb, Cd, Cu and Cr)
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Used for liquid and dissolved sample
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Low detection limit
Figure 3. Flame atomization absorption spectrometry
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b) graphite furnace absorption spectrometry
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Highly sensitive that provides excellent detection limits for measuring concentrations
of metals in aqueous and solid samples.
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Capable of simultaneous and automatic determinations for more than one element
Figure 4. Graphite furnace absorption spectrometry
4) Atomic Emission Spectroscopy(AES)
Not like AAS, with AES, we can detect oil and waste water
-First, we convert them into gas and then excite them by flame, electrical discharge
(arc or spark), laser, or measurement criteria
-And then, when they return to relax stated, energy is released in the form of light
which can be separated into characteristic spectral lines by a monochromator.
-the final step is to measure it and compare the result with reference sample (figure
Figure 5. Atomic Emission Spectroscopy
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5) Atomic Fluorescence Spectroscopy (AFS)
There are 2 types of AFS are Dispersive and Non-dispersive. We use AFS to determine the
concentration of elements in samples.AFS is the combination of emission and absorption
spectroscopy
Figure 6. Definition of AFS
Figure 7. Atomic Fluorescence Spectroscopy
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6) Raman spectroscopy
Scattering is redirection of light due to its interaction with matter, and may or may
not occur with transfer of energy.
Stokes Raman scattering occur if the molecule is promoted from a ground to a
virtual state and then drops back down to a (higher energy) vibrational state then
the scattered photon has less energy than the incident photon, and therefore a longer
wavelength.
Anti-Stokes scattering occur if the molecule is in a vibrational state to begin with
and after scattering is in its ground state then the scattered photon has more energy,
and therefore a shorter wavelength.
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Sir Raman discovered this when he used sunlight as the source and a telescope as the
collector; the detector was his eyes
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Now we can apply Raman Effect in detecting explosive/drug, Uncovering artistic
techniques, even discover Life on Mars
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1.
2.
3.
4.
5.
6.
Laser source
Scatter light ( include Rayleigh and Raman)
Sample
Filter ( remove Rayleigh scatter)
Raman Scattered light
Diffraction Grating ( diffract scatter light into spectrum)
7) Non-dispersive infrared spectroscopy(NDIR)
How can we detect CO2?
NDIR is the answer. Below is a diagram of a simple NDIR. When the light source
(IR) goes through the sample gas, it is absorbed. The color filter eliminates all light
except the wavelength that the selected gas molecules can absorb (figure 10)
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As you can see, the width and length of these flames are not equal through time, in the other
way, they are very different
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I see that when the length decrease, the width increase so they must have connection
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The deviation of the length is much more than the width (as you can see Relative
Standard Deviation)
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The average value is near the length more than the width so the length is more
trustable than the width
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Apparently, it has some reasons:
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May be I didn’t keep the same distances when I took pictures
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The digital camera can’t give absolutely right images
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Problems when measuring
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The deviation of the flame is noticeable
Note: The experiment of the candle is the simplest way to handle the data we took when we
use analytical chemistry. As I mention in the opening: The main purpose of analytical
chemistry is qualitative and quantitative analysis, So when we analyze the graph and the table,
we can have an overview of the candles’ characteristics such as length, width, volume,
chemistry interactions, affection of nature to an experiments,...At that time the sample is the
candle and the detector is the eyes. I don’t want to give you the thought that analytical is so
abstruse, however, I want you to know that we can work with analytical chemistry anywhere,
anytime
3. CONCLUSION
Future of Analytical chemistry
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In the near future, I think all old analytical chemistry method will be replaced
by automated analyzer.
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The advantage of this method is to decrease costs, save time, conserve
reagents and materials, minimize errors, and improve productivity
4. REFERENCES
1. Royce W. Murray (1929) Analytical chemistry, ACS Publications (United States)
2. Some documents and images from internet
3. David Harvey (1956), Modern analytical chemistry
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