22 Spectroscopy 22(4)
w w w. s p e c t r o s c o p y o n l i n e . c o m
April 2007
Mass Spectrometry Forum
Jelly Beans and Mass
Spectrometry for K–4 Students
Each column in “Mass Spectrometry Forum” follows a stick-to-the-basics approach so
that it can be used as a stand-alone introduction for the topic. Column content doesn’t
become overly dated, even as the photo that appears in the ending biography documents
the advancing age of the author. Even with this “basics” approach, though, “Forum”
columns are usually too lengthy and complex when a scientist needs to explain mass
spectrometry (MS) to a student audience, using elementary concepts or simple science,
within the space of maybe 20 minutes. When might such short explanations be necessary? From the author’s direct experience, short, cogent presentations can explain gas
chromatography coupled with MS to a class of fidgety third-graders. Explanations using
more-sophisticated analogies can be used in explaining forensic analysis using MS to a
larger group of high-school students, or in describing instrumentation for MS to company
managers who were wondering why the instrument purchase was so expensive. Or perhaps just explaining to family what you actually do for a living.
Kenneth L. Busch
G
as chromatography–mass spectrometry (GC–MS) is
an example of a “complicated” analytical method
that nevertheless can be explained in simple terms
and in a short time. GC–MS is known to the mature general
public in venues such as forensic and environmental analyses,
and even to younger children through multiple shows on television (even cartoons touch on analytical instrumentation).
GC–MS instruments themselves are small and not overly expensive, and the data produced, while sophisticated, still can
be displayed and manipulated by a personal computer in a
manner most folks can understand. The single topic of
GC–MS and how it is used actually can fill a series of talks
and demonstrations. But even within a single presentation,
the basis of GC–MS can be highlighted. At the end of 20
minutes, the kids in my third-grade class understood the
concepts of the chromatographic separation, the measurement of mass, and the principles of fragmentation as a structural fingerprint. The teacher, a bit more old-school perhaps,
wondered why I, as a chemist, did not bring beakers and test
tubes as part of my demonstration. I retreated quickly once
the kids began chanting “GC–MS” as part of a catchy limerick about what to ask for at Christmas. The students in that
class are just now graduating from high school, and I hope a
few of them developed a spark for science.
This column discusses some simple analogies to describe
GC–MS to an elementary-school student audience. The
analogies used can be made more sophisticated for an older
group of school students, or for audiences of senior citizens.
Remember that a detailed and technically correct explanation
might seem more satisfying to you as a scientist, but your audience will remember simple, direct analogies and your skill
in linking them to the points you are trying to explain. If you
have similar experiences to share, I look forward to hearing
from you. The contact information is in the biography at the
end of the column. I divide the “GC–MS” explanation into
four parts, the latter three of which are the mass spectrometer
instrument itself. The section on the gas chromatograph can,
with appropriate changes, be applied to most any chromato-
24 Spectroscopy 22(4)
w w w. s p e c t r o s c o p y o n l i n e . c o m
April 2007
graphic separation. Similarly, the MS
analogies can be extended (with some
modifications) to most mass spectrometers, and not just GC–MS instruments. I admit to some difficulty in
putting together an elementary analogy
for Fourier-transform MS (FT-MS); I
hope to use a sound effect to demonstrate different frequencies of different
ion masses trapped in the cell.
Gas Chromatography
The basis of a GC separation is a differential interaction of mixture components with the stationary phase of
the column. Because there is a physical
transport and a time involved, the differential interaction shows up as an
elution time difference. The GC analogy is fairly easy to set up in a classroom setting. For elementary-school
students, I use a cafeteria-line analogy.
For older folks, I use a wedding receiving line to outline the situation. With
the former, create a cafeteria food line
in the classroom by rearranging chairs
and recruiting three volunteers — call
them Curly, Larry, and Moe. Each volunteer has a different behavior, which
you explain clearly to the classroom,
and which is rooted in jelly bean selection. Curly is hungry and stops at each
station in the cafeteria line for only the
time needed to grab some jelly beans
— any jelly beans. Larry only likes red
and pink and orange jelly beans, so he
has to spend more time at each station
to get only the jelly beans he likes. Moe
is the picky eater and spends a long
time at each stop trying to find the
blue jelly beans, which are the only
ones that he will eat. Start all three volunteers at the same time, encourage
them to stay true to behavior, and the
differential partitioning process becomes clear. The students are immediately able to determine the order of
elution time as Curly, Larry, and then
Moe. You can even repeat the “play” to
show how retention times, given a constant set of behaviors and number of
stations, remain the same, and even
with more or less stations, in the same
order. If the class is a bit more sophisticated, you can change the behaviors by
“offering” different foods at the stops;
this is the equivalent of a different sta-
tionary phase. You can then explain the
reasons for subsequently different values and different orderings of retention times. The analogy to different
food offerings in the cafeteria line (of
more or less attractiveness to the students) is a rationale for chemical selectivity of different stationary phases.
The students will remember the science because the analogy is simple,
valid, and straightforward. They will be
eager to participate because — well, because the analogy involves food (it’s a
bribe, I admit). My demonstration bag
is packed with jelly beans of different
sizes and colors. Different color jelly
beans represent the food that elicits different behaviors of Curly, Larry, and
Moe — who demonstrate different
fondness for the various flavors. And
once your volunteers have worked
through your first aliquot of jelly beans,
you have the attention of the class to
segue into some elementary concepts of
MS. With jelly beans, of course.
MS — Ionization
Elementary-school students seem to
have a basic idea of atomic structure,
possibly from cartoons. (“Captain
Proton” searched on Google provides
links to both classic and modern science fiction escapades.) A web search
also reveals many suggested elementary-school level demonstrations of
atomic structure, using atomic particle
surrogates of colored marshmallows,
clay, or jelly beans. Jelly beans, in different colors and different sizes, will be
used in each of the three different
parts of the MS demonstration, and a
polite guest lecturer leaves an ample
supply in the classroom so that the
students recall your demonstration for
the next few weeks. NASA suggests
using jelly beans and chocolates and
raisins for the different atomic particles (1), and Matthew Besman describes an “edible atom lab” (2). Interestingly, the use of jelly beans to model
atomic structure and reactivity extends through Grade 12, as described
in state of Ohio standards (3).
Explain to the students that, for purposes of simplicity, atoms will substitute for more complicated molecules
that represent the compounds eluted
from the gas chromatograph. They will
grasp that molecules are collections of
atoms, and atoms are collections of
subatomic particles. Set up and explain
an atomic-particle scheme, such as big
black jelly beans for neutrons, big blue
jelly beans for protons, and smaller
white jelly beans for electrons. Choose
your own easy-to-see colors, but remember that some students might be
color-blind to red. (How many mass
spectrometrists remember that Dalton
was color-blind, did research in this
field (4), and that an early term for
color-blindness was Daltonism?) If you
can prepare ahead of time, you can
string white jelly beans along a nylon
fishing line, and depending upon your
dexterity, you might actually venture to
show electrons in orbit around a jellybeans-in-your-hand nucleus! Choose
your student volunteers to assemble
their own several-different-jelly-bean
nuclei to match the number of electrons you pre-prepared on white jelly
bean strings. The salient points are the
presence of the protons and neutrons
together in the nucleus, the balanced
numbers of protons and electrons in
the neutral atom, and the proclaimed
lack of interaction of a “balanced” proton–electron atom with external forces
such as a magnetic or an electric field.
These main issues suffice to introduce
the concept of atomic structure, and
then ionization. If you have time (and
the class has interest), the concept of
isotopes can be introduced with the use
of a different number of black jelly
beans (neutrons).
This simple demonstration works
best for electron ionization of atoms;
molecular ionization involves an ensemble of jelly bean atoms that is
more difficult to assemble and explain.
Protonation (such as occurs in chemical ionization) raises issues of chemical bonding that surpass most elementary student levels of understanding.
The third point listed earlier — that
an atom with a balanced number of
protons and electrons is indifferent (to
an elementary approximation) to external forces such as a magnetic or an electric field — is crucial to the understanding of ionization. Introduce ionization
as a process through which we put a
26 Spectroscopy 22(4)
w w w. s p e c t r o s c o p y o n l i n e . c o m
April 2007
Figure 1: Jelly beans can be used to
demonstrate some basic principles of MS. The
direct size comparison between jelly beans and
a quadrupole mass filter and an electron
multiplier invites discussions of the true
differences in size scales.
handle on the atom so that we can
move it around at will, and perform a
mass analysis with electric or magnetic
fields. Students might recall common
demonstrations of magnetic field interactions that rely on classic metallic or
nonmetallic items, showing a presence
or absence of the attractive force. But
this effect is based upon the magnetic
properties of the material, rather than
the relevant fact in mass spectrometry
that the ion carries a charge. It is best to
avoid the analogy based upon a correct
but somewhat irrelevant underlying
premise; concentrate on the charge!
How to achieve ionization in a jelly
bean atom? Find a student group
whose jelly bean atom has the same
number of protons as the number of
electrons on your chosen jelly bean
string. Then, assemble a stable atom at
the front of the class with you circling
around the nuclear kids with your
electrons on a string. Ionization is simple enough — blatantly eat an electron! A simple exercise then shows the
students that there is an excess of protons now, and you can keep a tally on
the board to show that the net charge
on the atom is +1, corresponding to
the charge on that extra unbalanced
proton. If your compatriots want to eat
the jelly bean nucleus, you can explain
that such a reaction would fall into the
realm of nuclear chemistry, and that is
not what MS is all about.
Now we demonstrate the effect of an
external force. In this case, we are going
to recruit the teacher to represent an
electric force (the accelerating potential). Inform the students that the
teacher only exerts a force on ions —
the atoms with an unbalanced number
of protons and electrons in this case.
Describe the teacher as a repulsive force
(students smile and tend to agree with
that assessment). Thus, as the teacher
approaches an ion, the charged studentatom will be repelled. If that single electron had not been consumed, and the
atom remained neutral, the teacher
would have no effect. In this single part
of a simple overall exercise, the demonstration has shown atomic structure,
carried out a process of ionization, and
then shown the principle through
which an ion is physically transported
from the ion source into the mass analyzer of the mass spectrometer.
MS — Mass Analysis
Add some sophistication to the analogy. Now, instead of subatomic particles, the jelly beans will represent
atoms of elements, and different colored jelly beans are now different elements. Explain that each element has a
different mass and that the mass analyzer in the mass spectrometer is the
measuring tool so that we can tell the
difference. Gather three students at the
front of the classroom, because these
are your new partners for a demonstration of mass analysis via a time-offlight mass analyzer. Repeat that molecules are made of atoms, and because
each different combination of elements has a different mass, so each
jelly bean molecule that you assemble
in each student’s hand will have a different mass. The volunteer students
might be prompted to admit that the
mass of the jelly beans in their hands
does not feel that different, regardless
of whether they have five, eight, or 15
jelly beans grasped there. So ask the
students to count out the jelly beans;
then ask them to imagine that each
jelly bean weighs about 100 lb, some a
little bit less and some a little bit more.
Now a simple racetrack analogy
serves to cement the concept of time-of-
flight mass analysis for the students. Explain to each jelly bean–molecule student that they are about to run in a race
with those several hundred pounds
(some more, and some less) of jelly
beans in their hands. Remind them, and
get the remainder of the class to agree,
that students with more mass will traverse your makeshift racecourse more
slowly than the lighter-mass students.
You adopt a position at the finish line,
marking the finishing times of your jelly
bean–molecule students at various
times, and then explain the simple proportionality between mass and flight
time. Then, you explain that just as the
masses of real ions are orders of magnitude less than the jelly beans, or the students themselves, the flight times of the
ions are orders of magnitudes faster
than the race times you just measured in
the classroom. But, with the right tools,
we can measure these very short times
and therefore measure the masses of the
molecules as ions. When we know the
masses of the molecules and how they
fall apart (explain this by again examining the component parts of the jelly
bean molecule), then we know something about what the molecule is!
MS — Ion Detection
In this last part of the explanation, the
concept of scales must be explained.
The key concept here is the concept of
amplification accomplished with an
electron multiplier; the students will
recognize the term “multiplier,” and
preview the topic. And, using jelly beans
again, the analogy will remain with
them long after your visit to the classroom. Explain that jelly beans represented mass in the previous demonstrations, and now the jelly beans are going
to represent charge. “Mass and charge,”
you explain, “are what mass spectrometry is all about!” You will need student
volunteers again, this time, students assembled in three rows of four students
each. (Note that by this time, you will
have had the chance to involve almost
every student in the classroom in some
part of these demonstrations.) I bring
three paper bags to class, with one, two,
or three jelly beans inside. I explain that
the jelly bean charge is so small that if
one were to examine the bags, you
w w w. s p e c t r o s c o p y o n l i n e . c o m
would find it difficult to decide about
the number of jelly beans inside. What’s
needed is a multiplication so that the
jelly beans are forced to reveal themselves. So for each student in each of the
three lines, you explain that they are to
take whatever number of jelly beans
they find in the bag as it is handed to
them, add matching jelly beans one-forone, and then pass the bag on to the
next person behind them in line. Here
are the sequences:
1:2:4:8:16
2:4:8:16:32
3:6:12:24:48
That last student in the third line has
a lengthy counting task, and while that is
accomplished, you explain the principles
of multiplication in an electron multiplier, and how (holding up three bags
now with obviously different numbers
of jelly beans) multiplication makes it
easier to detect small differences.
Finally, at the end of the demonstrations, you ask if you should gather up
all your jelly beans and go home. Per-
April 2007
haps the jelly beans should stay in the
classroom if the students can remember the principles of separation based
upon different behaviors of Curly,
Larry, and Moe. Do they remember the
parts of the atom, and that a charge results when electrons and proton jelly
beans are unbalanced, and that the repulsive force finds you once you become unbalanced? Do they remember
that different jelly bean molecules also
can represent molecules of different
masses, that heavier masses move
slower in a race, and that we can use a
race to reveal differences in mass? Do
the students remember that multiplication can make small things and small
differences easier to detect? If they do,
leave the bags of jelly beans, thank the
teacher and the students, and remember that twenty years from now, these
students might be in attendance at the
ASMS annual meeting, searching for
jelly beans in the hospitality suites.
References
(1)http://www.nasaexplores.com/show_k
4_teacher_st.php?id=04040593431
Circle 21
22(4) Spectroscopy 27
(2)http://www.lessonplanspage.com/ScienceEdibleAtomLab-ForPeriodicTableAtomsGoodIdea46.htm
(3)http://ims.ode.state.oh.us/ODE/IMS/L
essons/Content/CSC_LP_S03_BB_L12
_I10_01.pdf
(4) J. Dalton, “Extraordinary Facts Relating
to the Vision of Colours, with Observation,” Mem. Literary Philos. Soc.
Manchester 5, 28–45 (1798).
Kenneth L. Busch
convinced students of a
third-grade class to loudly
chant “GC–MS” during an
explanation of MS, and
recalls that the teacher
was not amused. He is therefore reminded
that it is important to preview and gather the
insights of the teacher on the class presentation. He looks forward to the collection,
preparation, and publication of a collection of
elementary school demonstrations in the
field of MS. This column represents the views
of the author and not the National Science
Foundation. The author can be reached at
[email protected].