The Secrets of
Elemental Composition Revealed
Introduction
http://www.youtube.com/watch?v=xYNFxOgCcsI
When the Earth was forming 4.5 billion years ago, certain elements were available for the “construction” of Earth. These “ingredients” have been the determining factors for everything that occurs on Earth today, from the average annual rainfall in the Northern Hemisphere to the average ice melting in the Antarctic. Studying what’s happening to Earth’s climate today means understanding the mechanisms that controlled climatic changes thousands or millions of years ago. Finding sediment or ice core samples that are old enough to test is one of the hard parts. The Earth is constantly recycling its tectonic plates from the hard exterior crust you and I walk on every day into viscous liquid magma layers beneath us, then in the form of volcanoes fresh magma is brought to the surface. This cyclical process is called the “Conveyor Belt” (Spero). This mechanism is great for thermal equilibrium but not so great if a scientist wants to look back at climate data one billion years ago. Even when a suitable sample is procured to be tested in the GVI Isoprime Mass Spectrometer (See Figure 1), the ancient oxygen “residue” that was absorbed by the sample is very fragile and requires extremely sensitive machines to detect it. These machines can identify the slightest elemental changes in a substance.
http://www.youtube.com/watch?v=xYNFxOgCcsI
When the Earth was forming 4.5 billion years ago, certain elements were available for the “construction” of Earth. These “ingredients” have been the determining factors for everything that occurs on Earth today, from the average annual rainfall in the Northern Hemisphere to the average ice melting in the Antarctic. Studying what’s happening to Earth’s climate today means understanding the mechanisms that controlled climatic changes thousands or millions of years ago. Finding sediment or ice core samples that are old enough to test is one of the hard parts. The Earth is constantly recycling its tectonic plates from the hard exterior crust you and I walk on every day into viscous liquid magma layers beneath us, then in the form of volcanoes fresh magma is brought to the surface. This cyclical process is called the “Conveyor Belt” (Spero). This mechanism is great for thermal equilibrium but not so great if a scientist wants to look back at climate data one billion years ago. Even when a suitable sample is procured to be tested in the GVI Isoprime Mass Spectrometer (See Figure 1), the ancient oxygen “residue” that was absorbed by the sample is very fragile and requires extremely sensitive machines to detect it. These machines can identify the slightest elemental changes in a substance.
Image A: How do you take a part a
molecule? (Image created by Savannah Lisle) (Adapted from “NASA”)
Description:
The basic idea of Mass Spectroscopy can be explained by an
experiment that you probably have done either with your own curiosity or in an
elementary school science class setting. I’m sure you know that a magnet
has two ends: a positive end and a negative end. I am also sure you know that
the negative end of a magnet will repel any other negative end of any other
magnet anywhere on Earth. But did you know that this basic phenomeno, amplified
by very powerful and sensitive equipment, can also allow you to gaze into the
deeper and more mysterious characteristics and relationships of the building
blocks of life: the secrets of elemental composition? Have you ever pushed a
magnet across the smooth surface of a table? If you have, you know the joy and
“magic” of making a solid object move along without ever touching it with
another object.
You may have also noticed that the size of the magnet affected the speed at which you were able to move it. This observation is an exciting and clear example of how magnetic fields work. Two negative, or positive, ends of two magnets repel each other, conversely a positive end attracts a negative end. This is probably the source of the archetypal catchphrase, “opposites attract.”
You may have also noticed that the size of the magnet affected the speed at which you were able to move it. This observation is an exciting and clear example of how magnetic fields work. Two negative, or positive, ends of two magnets repel each other, conversely a positive end attracts a negative end. This is probably the source of the archetypal catchphrase, “opposites attract.”
Background:
All elements are essentially made up of
three things: protons, neutrons, and electrons.
The more of these parts the more mass an atom has. The more mass an atom
has, the less force a magnetic field will have on it, opposed to, for example,
a lighter atom. What makes one element so different from the other is the
number of these essential building blocks.
By controlling the general path an atom takes requires very accurate instrumentation but also provides very accurate data.
By controlling the general path an atom takes requires very accurate instrumentation but also provides very accurate data.
Purpose:
Mass spectrometry allows chemists to precisely
“weigh” atoms and molecules. As you can imagine atoms are far too small to
actually use a balance. What mass spectrometry does is to apply a constant
force in the form of magnetic fields to measure how far ions travel. The
distance traveled is directly related to the mass. By accelerating and
deflecting ions with magnetic fields, the reactions of the ions tell us a great
deal about the atom or molecule. Data is recorded in the form of mass and
abundance.
Steps
in Experiment:
When
charged particles come in contact with other charged particles, a directional
change inevitably occurs. This in itself is a simple concept, but applying and
observing this at the molecular level gets slightly more complicated. Atoms are
so small that one would think that the normal techniques for moving matter would
be not applicable. However, it is very
similar. At first this may seem like an improbable and impossibly small task,
but it can actually be quite simple. One
of the ways that a molecule can be controlled is to give it a charge. This
charge reacts and interacts with its environment differently depending on the
charge of the environment. With the right mechanisms, the mass spectrometer can
detect if a molecule loses an electron and if it has a positive charge. This
charged atom then is directed by various types of charged fields. This process
is very similar to what occurs in the Earth’s atmosphere.
Earth’s environmental mechanisms can be observed in a controlled and measurable setting using the Mass Spectrometer. Molecules are bombarded by Solar ions every day in the form of Solar radiation on Earth. Both the Sun and the Earth have electromagnetic fields that also direct ion paths. To better understand Earth, and because the Earth is so massive, scientists have to observe parts of Earth’s mechanisms in smaller scale experiments. The Mass Spectrometer is almost like a tiny Earth atmosphere. Liquids or solids are changed into gases that are ionized then directed by magnetic fields into detectors.
Earth’s environmental mechanisms can be observed in a controlled and measurable setting using the Mass Spectrometer. Molecules are bombarded by Solar ions every day in the form of Solar radiation on Earth. Both the Sun and the Earth have electromagnetic fields that also direct ion paths. To better understand Earth, and because the Earth is so massive, scientists have to observe parts of Earth’s mechanisms in smaller scale experiments. The Mass Spectrometer is almost like a tiny Earth atmosphere. Liquids or solids are changed into gases that are ionized then directed by magnetic fields into detectors.
Figure 1: GVI
Isoprime Mass Spectrometer, Stable Isotope Laboratory, Earth and Physical
Science Department, UC Davis (Photo by Savannah Lisle)
The GVI
Isoprime Mass Spectrometer is desktop sized and is about 4 x 2 ft, not
including the computer and printer that read and printed the result (See Figure
1). The sample is placed in small copper “boats” (See Figure 2) (usually 1-2 grams) placed in
the carrying tray (See Figure 3.1) then dropped into an acid bath to create a chemical reaction with
a molecular gas phase (usually CO2) product in the input tray.
Figure 2: Copper sample cartiridges,
3-4mm wide, 2-3mm deep. (Photo by Savannah
Lisle)
Figure 3.1: Carrying tray for boats
with samples, to be carried to input tray in GVI
Isoprime Mass Spectrometer (see next figure). (Photo by Savannah Lisle)
Figure 3.2: Input tray, mechanical arm
programed to drop .1 ml of acid (type of acid depending on sample, Hydrochloric
Acid, Carbonic Acid etc) into each boat, then sucks gas up into GVI Isoprime Mass Spectrometer. (Photo by Savannah
Lisle)
Figure 4: Mass Spectrometry Steps
(Image created by Savannah Lisle) (Adapted from “Chem Survival”)
Description of Automated Internal
Processes of Mass Spectrometer (detailed description of above image):
Step 1 is to Ionize Molecules:
In the Ionization chamber the sample is
ionized. Ionization means that molecules consisting of linked atoms are broken
up into smaller individual charged atoms, allowing for elemental analysis of
substance.
Once molecules are broken up into individual elemental atoms in the gas phase of the elements, the magnetic fields “push” them along an arcing electrical current. (“Encyclopedia”) (See Figures 5.1-5.4)
Once molecules are broken up into individual elemental atoms in the gas phase of the elements, the magnetic fields “push” them along an arcing electrical current. (“Encyclopedia”) (See Figures 5.1-5.4)
Types of
Ions Produced after Electron Impact ionization: (See Figures 5.1 – 5.4, Images created by Savannah Lisle)
Figure 5.1 One electron knocked out of
molecule, producing an intact molecular radical cation. (Image created by
Savannah Lisle) (Adapted from “Chem Survival”)
Steps 1 and 2 remain similar for other
molecular ionization types, so just a description for Step 3 will be explained
in the following images.
Figure 5.2 After electron knocked out,
molecule fragmented: The larger fragment is the radical and the small fragment
is the charge. (Image created by Savannah Lisle) (Adapted from “Chem Survival”)
Figure 5.3: Large fragment is the
charge, and the smaller is the radical. (Image created by Savannah Lisle) (Adapted
from “Chem Survival”)
Figure 5.4: Many impacts are occurring simultaneously,
generating many different ions and fragments creating a large collection of
ions in different sizes. (Image created by Savannah Lisle) (Adapted from “Chem
Survival”)
Step 2 is to filter the ions by mass.(See Figures 6.1-6.2)
Then the ions are shot with a high
powered ion beam
Figure 6.1: Ion Path (Image from “Royal”)
The amount of deflection from the
magnetic field (See Figure 6.2) depends on mass of cation (positively charged
atom) and strength of field. Heavier ions will not be deflected as much,
magnetic fields are increased to allow cations of gradual density to be
detected.
Figure 6.2: Magnetic field (created
magnet, usually about 10x10in), the greater the mass, the lesser the force
acting the ion, therefore larger ions will travel farther. (Image from “Royal”)
Step
3 is to detect number of ions present. (See Figure 7)
Then the ions in the order they arrive
are detected by dynodes. Dynodes are sensitive bars that are programed to
generate one or more electrons when an impact of a cation is detected (“Encyclopedia”). There are several dynodes that generate enough electrons that can be measured.
The results appear as graphs on a computer with the X-axis being "% Abundance" and Y-axis being "Mass" (Atomic Mass Units). (See Figure 7)
Figure
7: Mass Spectrometry Results. Example is Mass Spectrometry analysis of Limonene).
(Image from “Royal”)
Conclusion:
Conclusion:
As the need to combat and even just to
understand climate change increases, understanding Earth’s past climates will
become an important part of the conversation in the scientific analysis and
predictions of what kinds of atmospheric changes we expect to see. “The problem in climate change control is that
we have not seen these problems before in Earth’s history and the solution is
studying the Earth’s climate history to uncover the mechanisms responsible for
climate shifts and the rate at which such changes could occur” (Spero). Knowing
how to look deeper into an atom is only half the battle. Understanding what you
see is an integral part of science. Mass spectrometry may be the hardware that
provides you the specifications of a molecule or atom, but it is up to the
educated scientist to determine the probable reasons for, for example, high
abundance of Delta Oxygen 18 values. There is no one machine that if you push
a button the history of the Earth comes printed out on a sheet of 8 ½ x 11
sheet of paper. But the statistics of elemental composition and abundance are
terrific guides for future scientific breakthroughs.
Works Cited:
ChemSurvival. “A Brief Introduction to Mass Spectrometry.”
Youtube.com. April 17 2013.
http://www.youtube.com/watch?v=NuIH9-6Fm6U
Encyclopedia Britanica. “Mass
Spectrometry”. 2013.
Lisle, Savannah. “Image
1” and “Figures 1, 2, 3.1, 3.2 4, 5.1-5.4.” Created by author. April 15 2013.
NASA. “The
Molecule Dissector - Mass Spectrometry.” Youtube.com. April 20 2013. http://www.youtube.com/watch?v=_L4U6ImYSj0.
Royal Society of
Chemistry. “Modern Instrumental
Techniques for schools and colleges DVD”. United Kingdom. Sep 27, 2008.
Spero, Howard. Gel 108. Geology
Lecture. April 20 2012. UC Davis.
