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CHAPTER V
Chemistry and
National Well-Being
V-A. Better Environment
Every society tries to provide itself with adequate food and shelter and a
healthful environment. When these elemental needs are assured, attention
turns to comfort and convenience. The extent to which all these wishes can be
satisfied determines a society's "quality of life." However, choices are usually
required because one or another of these needs or wishes is more easily satisfied
at the expense of others. Today we find our desires for more abundant consumer
goods, energy, and mobility in conflict with maintenance of a healthful envi-
ronment. A major concern of our times is the protection of our environment in
the face of increasing world population, increasing concentration of population
(urbanization), and increasing standards of living.
Environmental degradation with its accompanying threats to health and
disruption of ecosystems is not a new phenomenon. Human disturbance of the
environment has been noted from the earliest recorded history. The problem of
sewage disposal began with the birth of cities. Long before the 20th century,
London was plagued with air pollution from fires used for heating and cooking.
An early example of an industrial hygiene problem was the reduced longevity
of chimney sweeps attributed retrospectively to cancer arising from prolonged
exposure to soot with its trace carcinogen content (polynuclear aromatic
hydrocarbons).
There is small consolation, though, in the fact that environmental pollution is
not a new invention. The global population burgeons upward, while cities grow
even faster. Per capita consumption and energy use continue to increase.
Pollution problems are becoming increasingly obvious, and we are recognizing
subtle interactions and secondary reverberations that went unnoticed before. A
number of environmental disturbances have begun to manifest themselves on a
global scale. Occasional industrial accidents, like those at Bhopal and Seveso,
remind us that large-scale production of needed consumer products may require
handling of large amounts of potentially dangerous precursor substances.
193
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194
CHEMISTRY AND NATIONAL WELL-BEING
On the positive side, the public awareness has been raised about the
importance of maintaining environmental quality. In the United States, a large
majority of citizens from across the political spectrum have indicated that they
are prepared to pay more for "cleaner" products (e.g., lead-free gasoline) and to
pay more taxes to improve their environment. These attitudes are spreading
abroad, an essential aspect of containment of the problems more global in scope.
Elective strategies for safeguarding our surroundings require adequate
knowledge and understanding. We must be able to answer the following
questions:
What potentially undesirable substances are present in our air, water,
soil, and food?
Where did these substances come from?
What options are there- alternative products and processes to alleviate
known problems?
What is the quantitative degree of hazard as a function of the extent of
exposure to a given constituent?
How shall we choose among and implement available options that over
corrective action?
Plainly, chemists play a central role in answering the first three crucial
questions. To find out what is around us, we need analytical chemists to apply
and develop ever more sensitive and selective analytical techniques. To track
pollutants back to their origins, again we look to analytical chemists acting as
sleuths, now usually in collaboration with meteorologists, oceanographers,
voicanologists, climate dynamicists, biologists, and hydrologists. But finding
origins can require detailed chemical understandings of reaction sequences and
transformations that intervene between the source and the final noxious or
toxic product. Then, developing options calls on the full range of the chemist's
arsenal. If the worId's mortality rate from malaria is not to be reduced with DDT
because of its environmental persistence, what substances can be synthesized
that are as elective as DDT in saving lives and spontaneously degradable as
well? If we must use lower grade energy sources to satisfy our society's energy
needs, what catalysts and new processes can be developed to avoid exacerbating
aIready-existing problems of acid rain and carcinogen release from coal-fired
power plants?
Thus our society must assure the health of its chemistry enterprise if it wants
earlier warning of emerging environmental degradation, better understandings
of the origins of that degradation, and access to a full array of economically
feasible options from which to choose solutions. Other disciplines make their
own particular contributions, but none plays a more central and essential role
than chemistry.
The fourth question, the quantitative degree of the hazard/exposure equation,
is the province of the medical profession, toxicologists, and epidemiologists.
These scientific disciplines face serious challenges now that society has recog-
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V-A. BETTER ENVIRONMENT
nized the inverse relationship between what is taken to be a tolerable risk and
the cost to society in attaining it. The medical profession must refine its
knowledge of risks associated with such substances as lead in the atmosphere,
chloroform in drinking water, radiostrontium in milk, benzene in the work-
place, and formaldehyde in the home. A qualitative statement that a certain
class of substances might be carcinogenic will no longer suffice. We must be able
to weigh risks and costs against benefits that would be lost if use of that class
of substances were restricted. We must be able to compare these risks to those
already present because of natural background levels. More importantly,
society cannot afford to pay the exorbitant cost of eliminating all risk, because,
as the requested degree of risk approaches zero, the cost escalates toward
infinity.
Finally, the choice among options and their implementation moves properly
into the public arena. Chemists and scientists in the other relevant disciplines
have a secondary, but important, informational responsibility here. Every
political decision deserves the best and most objective scientific input available.
There is nothing more frustrating to our citizens and our government than to
befaced with decisions without the benefit of facts and a usefully predictive
scientific knowledge base. Scientists, including chemists, must meet their
responsibility to provide the public, the media, and the government with
an objective picture expressed in language free of technical jargon to help
establish the scientific setting for a given decision and the options that lie before
us.
Turning Detection into Protection
All our environmental protection strategies should be founded on realistic
hazard thresholds and on our ability to detect a particular offending substance
well before its presence reaches that threshold. Chemists must continue to
sharpen their analytical skills so that, even at minute concentrations well
below the hazard threshold, a given substance can be monitored long before
crisis-corrective action is dictated. When this is possible, we see that detection
can be equated to protection.
Unfortunately, the media, the public, and government agencies have too often
equated detection with hazard as a result of the prevalent assumption that a
substance that is demonstrably toxic at some particular concentration will be
toxic at any concentration. There are innumerable examples to prove that this
is not a generally applicable premise. Consider carbon monoxide (CO). This
ubiquitous atmospheric constituent becomes dangerously toxic at concentra-
tions exceeding 1000 parts per million and is considered to have adverse health
effects for prolonged exposure to concentrations exceeding 10 parts per million.
We do not, however, leap to the conclusion that CO must be completely removed
from the atmosphere. This would be foolish (and impossible) because we live and
thrive in a natural atmosphere that always contains easily detectable CO at
about 1 part per million. Clearly, our task is to decide where we should place
195
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196
CHEMISTRY AND NATIONAL WELL-BEING
controls between the known toxicity threshold and the known safe range- as
EPA has in fact attempted to do.
In recent trends, the naive "zero-risk" approach is gradually being supplanted
by a more sophisticated risk assessment/risk management rationale. In both the
assessment and management phases, a major theme is the crucial importance of
being able to analyze complex air, water, soil, and biological systems that may
contain hundreds of natural chemical compounds. The roles that chemical
analysis and monitoring play in protecting and managing our air and water
resources are analogous to the role that intelligence-gathering plays in protect-
ing and promoting the nation's public interest in the military, geopolitical, and
economic realms. Conclusions regarding causes and erect, sources, movement,
and fates of pollutants in crucial issues such as acid deposition, global climatic
change, ozone layer destruction, and toxic waste disposal depend upon environ-
mental measurements that must be made with sufficient selectivity and
sensitivity. Enormously costly decisions about how to protect and enhance the
quality of our air, water, and land resources are sometimes based on environ-
mental "intelligence" that can be grossly inadequate and inaccurate. Crash
projects to remedy crises caused by past indiscretions or ineffective strategies
that were based on insufficient knowledge have been expensive. A small
fraction of the money spent on such a corrective program, if invested in
long-term fundamental environmental science and monitoring techniques, can
significantly reduce the need for future expensive remedial programs.
THERE ARE 22 DIFFERENT TETRACHLORODIOXINS Increased effectiveness of
environmental measure-
ments requires improved sur-
veilIance tools. The challenge
is to measure trace levels of a
particular compound present
in a complex mixture contain-
ing many innocuous com-
pounds. The principal objec-
tives of research in envir-
ct~o~ct
Cl
C1~0~ 2,3,6,9
C'
Ct
CO~O~Ct
HOW MUCH IS IN THE TOXIC 2,3,7,8 FORM?
AN ANALYTICAL CHALLENGE
onmental analysis and moni-
toring are improved sensitiv-
ity, selectivity, separation,
sampling, accuracy, speed,
and data interpretation. For
example, an active research
area is connected with sepa-
ration techniques to allow
rapid and unequivocal analy-
sis of complex mixtures of pollutants and pesticides found in toxic wastes,
polluted streams and lakes, and biological samples. A success story in analytical
selectivity is the development of analytical methods to allow separation and
OCR for page 197
V-A. BETTER ENVIRONMENT
quantitative measurement of each of the 22 individual isomers of tetrachIo-
rodioxin at the parts-per-trillion level.
Research is needed on multi-stage separation and detection methods, such as
tandem mass spectrometry. Additional research on developing techniques that
exploit the separation powers of selective sorbents, liquid chromatography,
supercritical fluid chromatography, field flow fractionation, and parametric
pumping will be fruitful. Attention must be given to basic research that will
produce selective detectors (based, e.g., on laser-induced fluorescence or on
chemiluminescence) that can be used to simplify analysis and minimize inter-
ferences that can accompany environmental sampling.
Highly reactive species in the atmosphere cannot be sampled and transported
to the laboratory for analysis. Such substances pose special challenges in
measurement and will require research aimed at remote sensing techniques
capable of measuring them in situ. Past successes include the measurement of
formaldehyde and nitric acid in the atmosphere of Los Angeles, during severe
smog attacks, by Fourier transform infrared spectroscopy in which absorbance
due to these pollutants was measured in situ over a 1-kilometer path. With
these experiments it was possible to perform a detailed characterization of the
simultaneous concentrations of formaldehyde, formic acid, nitric acid,
peroxyacetyl nitrate, and ozone in the ambient air at the part-per-billion level
at which these substances are contributors to photochemical smog. Notice that
1 part per billion (1 part of a pollutant in 109 parts of air) is a minute
concentration, but it is still sufficient to be significant in atmospheric reactions.
Differential scanning laser devices based on radar-like technology ("lidar") have
been used successfully to measure sulfur dioxide plume profiles downwind of
coal-fired power plants at the part-per-million level. Tunable diode lasers are
also capable of providing real-time in situ detection of pollutants from internal
combustion engines and industrial processes.
Several laser techniques, including linear methods (e.g., absorption, fluores-
cence), nonlinear methods (e.g., coherent antistokes Raman spectroscopy, opti-
cal heterodynes), and double resonance methods (e.g., laser magnetic reso-
nance), need to be examined more extensively. Other spectroscopic methods,
such as Fourier transform infrared and photoacoustic spectroscopy, are prom-
ising and warrant further study. One goal of such research should be better
measurements in the stratosphere and troposphere. Rapid, reliable, accurate,
and less-expensive methods are needed for measuring concentrations of trace
species, such as OH radicals, that play key roles in atmospheric chemistry.
At the same time that research aimed at more sophisticated measurement
technology is conducted, parallel efforts need to be devoted to simpler, less costly
routine monitoring techniques.
Research directed at fixing the chemical state of environmental constituents
(speciation research) is gaining importance because we now recognize that
transport mechanisms and toxicities vary markedly with chemical form. Chro-
mium in the hexavalent oxidation state is toxic, while in the trivalent form it is
197
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198
CHEMISTRY AND NATIONAL WELL-BEING
much less so, and, for some living systems, it may be an essential trace element.
Arsenic in some forms can move rapidly through aquifers, while other forms are
rapidly adsorbed on rock or soil surfaces. Of the 22 distinct structural arrange-
ments of tetrachIorodioxin, the most toxic is three orders of magnitude more
toxic (to test animals) than the second most toxic. These examples illustrate the
importance of analytical methods that allow identification of chemical form as
well as quantity of potential pollutants. Electrochemistry, chromatography, and
mass spectrometry are among the powerful tools for speciation studies.
The complexity of environmental problems requires analysis of massive
amounts of data. Research is needed to assist in the interpretation and wise use
of the accumulated information. Developments in the field of artificial intelli-
gence that use pattern recognition should provide valuable interpretive aid.
Recent advances in microprocessors and small computers should be exploited to
develop intelligent measuring devices and attention should be given to better
handling, archiving, and dissemination of environmental data.
Ozone in the Stratosphere
The possibility of polluting the stratosphere to the point of partially depleting
the protective ozone layer was first raised only about a dozen years ago. This
seemingly improbable notion found much scientific support, and it is now one of
the best examples of a potentially serious environmental problem of global
extent. It is a problem, furthermore, that exemplifies chemistry's central role in
its understanding, analysis, and solution.
Why do we need to worry about stratospheric chemistry? Ozone in the
stratosphere is the natural filter that absorbs and blocks the Sun's short
wavelength ultraviolet radiation that is harmful to life. The air in the
stratosphere a cloudless dry, cold region at altitudes between about 10 to 50
km mixes slowly in the vertical direction, but rapidly in the horizontal.
Consequently, harmful pollutants, once introduced into the stratosphere, might
remain there for periods as long as years, and, if so, they will rapidly be
distributed around the earth across borders and oceans, making the problem
truly global. A large reduction of our ozone shield would result in an increase of
potentially dangerous ultraviolet radiation at the earth's surface.
To understand how easily the ozone layer might be perturbed, it is useful to
recognize that ozone is actually only a trace constituent of the stratosphere; at
its maximum concentration ozone makes up only a few parts per million of the
air molecules. If the diffuse ozone layer were concentrated into a thin shell of
pure ozone gas surrounding the earth at atmospheric pressure, it would
measure only about 3 millimeters (his inch) in thickness. Furthermore, ozone
destruction mechanisms are based on chain reactions in which one pollutant
molecule may destroy many thousands of ozone molecules before being trans-
ported to the lower atmosphere, chemically transformed, and removed by rain.
Chemistry's crucial role in understanding this problem has emerged through
the identification and measurement of several ozone-destroying chain processes.
OCR for page 199
V-A. BETTER ENVIRONMENT
Fifty years ago, the formation of an ozone layer in the midstratosphere was
qualitatively described in terms of four chemical and photochemical reactions
involving pure oxygen species (O. 02, and ON Today, we know that the rates of
at least 150 chemical reactions must be considered in order to approach a
quantitative model for simulating the present stratosphere and predicting
changes resulting from the introduction of various pollutants. The chemistry
begins with absorption of solar ultraviolet radiation by O2 molecules in the
stratosphere. Chemical bond rupture occurs, and ozone, O3 and oxygen atoms,
O. are produced. Then, if nitric oxide, NO, is somehow introduced into the
stratosphere, an important chemical chain reaction takes place.
UV down
.
\'
STRATO SPHERED
D to 18
OZONE
ABSORBS
UV
LIGHT
f~ -)N~O+hv~N + NO
(33+ NO~N(~2 ~ O2
O ~ NO2 ~ NO ~ O2 NO2+ OH
net °+O3 iO2+O2
50 km
280°E
0 7 tort
HNO3
UV down ~ N2O
~ JO to 300 nm~ ~
TROPOSPHERE ~- ~ ~ ~~ KA1N 210 1E
f I: : . : : 2 : : :! : : : _ ~
an _ _.-: .-:: __:: :-. - :~-:: =_—My_ - ~ ~ 7^ HA__
A. -c_ - ., _-. - .. : . e— -I -.~. -` ~ ~ V W ~ 1
~ . : :~7~1 : :::::::: .:::::::: -'} I....:::: ' :-~_`
_- ..~ .- .-. -' -.- ' ' c.' '-- - ' - ' ' - . ~ ..~ - ~
I ,.,.,., ,., ,. , , ., , , , c .. , ,, ,, . . _ .... 115~ _
,d~ R;,~~1'~:'~''·'· ~~'"~"--—
˘~ 1O-15km
., 11~ ~ ~.,
The NO and NO2 reactions together furnish a true catalytic cycle in which
NO and NO2 are the catalysts. Neither species is consumed, because each is
regenerated in a complete cycle. Each cycle has the net effect of destroying one
oxygen atom and one ozone molecule (collectively called "odd oxygen". This
catalytic cycle is now believed to be the major mechanism of ozone destruction
in the stratosphere. In the natural atmosphere, the oxides of nitrogen are
provided by biogenic emissions at the Earth's surface by soil and sea bacteria of
nitrous oxide, N2O. This relatively inert molecule slowly mixes into the
stratosphere where it can absorb ultraviolet light and then react to form NO and
NO2.
Of course, oxides of nitrogen directly introduced to the stratosphere are
expected to destroy ozone as well, and this was the basis of the first perceived
threat to the ozone layer large fleets of supersonic aircraft flying in the
_
stratosphere and depositing oxides of nitrogen via their engine exhausts.
Nuclear explosions also produce copious quantities of oxides of nitrogen, which
are carried into the stratosphere by the buoyancy of the hot fireballs. A
significant depletion of the ozone layer in the event of a major nuclear war was
199
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200
CHEMISTRY AND NATIONAL WELL-BEING
forecast in a 1975 study by the National Academy of Sciences, although this
environmental erect of nuclear war may pale in comparison with the recently
suggested potential of a "nuclear winter." Both effects underscore the delicacy of
the atmosphere and its sensitivity to chemical transformations.
Then, in 1974, just as the possible impact of stratospheric planes was reaching
the analysis stage, concern was raised about other man-made atmospheric
pollutants. Halocarbons, such as CFCI3 and CF2CI2 (chIorofluoromethanes, or
CFMs), had become popular as spray-can propellants and refrigerant fluids,
mainly because of their chemical inertness. The absence of reactivity meant
absence of toxicity or other harmful effects on terrestrial life. Ironically, this
meant that there was no place for the CFMs to go but up up into the
stratosphere where ultraviolet photolysis could occur. Chemists then recognized
that if this occurred, the resultant chlorine species, CT and ClO, could enter into
their own catalytic cycle, destroying ozone in a manner exactly analogous to the
destruction caused by the oxides of nitrogen.
, .
STR A TO split Fit
UV down
to 180nm
rCF2CD2 + he ) C9 + CF2CD
OZONE |F O3 ~ c/ ~ L9U · oz
ABSORBS ~ 0 ~ coo ~ c, ~ O2
LIGHT l net ° ~ O3 ~ O2+ O2
~ UV down ~ CF2C02 relet HC0
TROPO SPHERE I_
~ - - - Ad. - - ~ . - -. _
50 Em
280° ~
\0.7 tort
CD ~ CHID
10-15km
RAIN 210°Z
~ . . . . . . . ~ . . ^ : . . . . arc ~ ~~ ~
~~ ~~. ~ 70torr
A is. ~ . ..... . ~ ~
~ , ^,~ ~-------·-----~-·~-~~-;- - --.--. - ·-~
Once this possibility had been recognized, analysis of the whole stratospheric
ozone chemistry began in earnest. An international committee of scientific
experts assembled by the National Academy of Sciences examined in detail the
state of our knowledge of every aspect of the problem. It became clear that the
additional chemistry introduced to the stratosphere added not just these 2
catalytic chemical reactions to the roster, but a total of about 40 new reactions
involving such species as CI, ClO, HCI, HOCI, ClONO2, the halocarbons, and
several others. Most of these reactions had never before been studied in the
laboratory.
I,aboratory kineticists and photochemists responded to the challenge by
.
OCR for page 201
V-A. BETTER ENVIRONMENT
providing reliable rate con-
stants and absorbances for
the proposed processes using
the growing arsenal of mod-
ern experimental methods.
Recent progress in the exper-
imental accomplishments of
this field has been remark-
able. It has become possible,
a/
CH4 ~ O3 \
HOCl
/\
To
HCl _ Cl
OH ``
ClO
O1 NO /
for example, to generate he \ / NO2
nearly any desired reactive REACTIONS KEY TO \
molecular species in the labo- STRATOSPHERIC \ ~
ratory in a variety of ways, to PROTECTION ClONO2
bring them together with
other reactive species, and to
measure their rates of reaction under known, controlled conditions. Such direct
measurements of these extremely rapid reactions were only a distant goal a
decade ago, but they are now a reality.
Finally, field measurements of minor atmospheric species have been revolu-
tionized by some of the recent advances in analytical chemistry. Methods
originally developed for ultra-sensitive detection of extremely reactive species
in laboratory studies have been modified and adapted to measure such constit-
uents as O. OH, Cl, ClO and others at parts-per-trillion concentrations in the
natural stratosphere. This has been accomplished recently in experiments in
which a helium-filled balloon carries an elaborate instrument package to the
top of the stratosphere where the package is dropped while suspended by a
parachute. As the instrument traverses the stratosphere, it measures concen-
trations of several important trace chemical species and telemeters the infor-
mation to a ground station. Very recently, the first successful reel-down
experiment was performed in which the instrument package was lowered 10 to
15 km from a stationary balloon platform and reeled back up again like a giant
yo-yo. This method results in a huge increase in the amount of data that can be
obtained in a single balloon flight. It will also allow for the first time a study of
the time evolution and variability of the stratosphere.
Much has been accomplished in the past 10 years. Many of the needed 100 to
150 photochemical and rate processes have been measured in the laboratory,
and many of the trace species measured in the atmosphere. Yet, research
remains to be done. For example, two of the important chemical species
containing chlorine, HOCl and ClONO2, have yet to be measured anywhere in
the stratosphere. Refinements in the reaction rates for many of the important
processes are still required, and exact product distributions for many of the
reactions are still lacking. Nevertheless, the original NAS study, the research
20}
OCR for page 202
202
Natural Sources
Marsh— I ndustry—Transportation
Ocean
Man-made Sources
CHEMISTRY AND NATIONAL WELL-BEING
programs it spawned, and the subsequent follow-up studies provided a firm and
timely basis for legislative decisions about regulation of CFM use. Industrial
chemists produced alternative, more readily degradable substances to replace
the CFMs in some applications. Monitoring programs are in place so that trends
in the stratospheric composition can be watched. The stratospheric ozone issue
provides a showcase example of how science can examine, clarify, and point to
solutions for a potential environmental disturbance. Premature initiation of
regulation was avoided because the problem was recognized early enough to
permit deliberate, objective analysis and focused research to narrow the
uncertainty ranges. From first recognition on, chemists played a lead role.
Reducing Acid Rain
Acid rain is one of the more obvious and pressing results of degradation of air
quality. Acidic substances and their precursors are formed when fossil fuels are
burned to generate power and provide transportation. These substances are
principally acids derived from oxides of sulfur and nitrogen. There are some
natural sources of these compounds such as lightning, voIcanos, burning
biomass, and microbial activity, but, except for rare volcanic eruptions, these
are relatively small compared with emissions from power plants, smelters, and
vehicles in industrial regions.
The effects of acidic rainfall are most evident and highly publicized in Europe
and the northeastern United States, but areas at risk include Canada and
Prevailing Winds
~ ,.. i' Airy': .' . it, '\ W >'W\ W"
, ~ ~ ,' ',, Photochemistry
_,~T: ~c~ ~3~ ~ Aquatic Ecosystem
ACID RAIN—SOURCES HERE, IMPACT THERE
OCR for page 203
V-A. BETTER ENVIRONMENT
perhaps the California Sierras, the Rocky Mountains, and China. In some places
precipitation as acidic as vinegar has occasionally been observed. The extent of
the erects of acid rain is the subject of continuing controversy. Damage to
aquatic life in lakes and streams was the original focus of attention. More
recently, damage to buildings, bridges, and equipment has been recognized as
another costly consequence of acid rain. The effect of polluted air on human
health is the most difficult to quantify.
Greatest damage is done to lakes that are poorly buffered. When naturally
alkaline buffers are present, the acidic compounds in acid rain, largely sulfuric
acid, nitric acid, and smaller amounts of organic acids, are neutralized, at least
until this alkalinity is consumed. However, lakes lying on granitic (acidic)
strata are susceptible to immediate damage because acids in precipitation can
dissolve metal ions, such as aluminum and manganese, causing reduction in
biological productivity and, in some lakes, the decline or elimination of fish
populations. Damage to plants from pollution ranges from adverse effects on
foliage to destruction of fine root systems.
In a region such as the northeastern United States the principal candidates
for pollutant reduction are the power plants burning coal with high- sulfur
content. Chemical scrubbers that prevent the emission of the pollutants offer
one of the possible remedies. Catalysts that reduce oxides of nitrogen emissions
from both stationary and mobile sources offer yet another example of the role
that chemistry can play in improving air quality.
The various strategies for reducing acid rain involve possible investments of
billions of dollars annually. With the stakes so high, it is imperative that the
atmospheric processes determining the transport, chemical transformation, and
fate of pollutants be well understood.
Acid deposition consists of both "wet" precipitation (as in rain and snow) and
dry deposition (in which aero-
sols or gaseous acidic com-
pounds are deposited on sur-
faces such as soil particles,
plant leaves, etc.~. What is
finally deposited has usually
been injected into the atmo-
sphere in a quite different
chemical form. For example,
sulfur in coal is oxidized to
sulfur dioxide, the gaseous
form in which it is emitted
from smokestacks. As it
moves through the atmo- lARGE UNCERTAINTIES REMAIN IN THE GLOBAL NOx BUDGET
sphere, it is slowly oxidized and reacts with water to form sulfuric acid the
form in which it may be deposited hundreds of miles downwind.
The pathways by which oxides of nitrogen are formed, undergo chemical
203
TROPOPAUSE
-o 5
Z
o
, _
V)
0 1
~14 28
En
as
~ ~ :,
~ 4-24 ,~
- 1 °
NH3 + OK] ~ NOx
1
1- 10
L I GHTN I NG
(PRECIPITATION: ~
—W~
MICROBIAL I
ACTIVITY DRY DEPOSITION 12-42
IN SOILS I j
~ 1
4 - 1 6
12-22
TERRE STR 1 A L
< 1
OCR for page 268
268
TABLE V-5
~ ~ ~ .
CHEMISTRY AND NATIONAL WELL-BEING
laser Raman spectroscopy, second harmonic generation surface spectroscopy,
and laser ellipsometry all provide information about the surface chemical bonds
of adsorbed atoms and molecules. Solid state nuclear magnetic resonance is
specially well suited for determination of the structure of high surface area
solids like the molecular sieve materials.
Instrument Developments Needed
There are many, well-perfected techniques for the study of surfaces under
well-controlled conditions. Developments of the next few years will focus more
attention on techniques that clarify the molecular structure and behavior of the
adsorbate. EELS is such a technique. While great effort and design skill has
been invested in achieving the EELS resolution now available, about 40 cm-i,
it is only marginally able to provide the structural information desired. A
10-fold improvement is needed, to a spectral resolution of 5 cm-i or better; such
a gain would enormously increase the value of this technique.
Research systems have been built with capacity to move a sample from an
ultrahigh vacuum environment into contact with a gas and then to return to the
vacuum situation. This is an important capability and should be made available
commercially. Surface samples should be readily held at cryogenic tempera-
tures down to 4 K. Laser techniques, too, offer special promise for chemistry-
oriented surface studies. Then, to open the door to kinetics of reactions as they
take place on surfaces, techniques must be developed for pulsed excitation and
subsequent temporal analysis on a short time scale.
Costs
Table V-5 lists some of the most important instruments from Table V-4 and
approximate current costs. It
is important to realize that
rarely can an investigator ef-
fectively address a problem of
surface chemistry with only
one of these techniques. In-
stead, an effective laboratory
will need the synergism and
flexibility provided by having
access to three or four comple-
mentary techniques. For ex-
ample, the first five entries in
Table V-5 are mutually sup-
portive. Thus, the research
group of a single investigator
will require a capital investment exceeding $500K and, of course, a substantial
on-going support to ensure cost-e~ective maintenance and operation of these
systems.
The instruments listed in Table V-4 permit us now to inaugurate a new era
Approximate Current (1985) Costs ($) for
Surface Science Instruments
Electron energy loss spectrometer
Low energy electron diffraction
Auger electron spectrometer
Tunable laser sources and detectors
Thermal Resorption mass spectrometry
X-ray photoelectron spectrometer
TDS
XPS
_ A A
Ion-scattering spectrometer ISS
Secondary ion mass spectrometer (static mode) SIMS
Secondary ion mass spectrometer (dynamic mode) SIMS
Rutherford back-scattering system
Laser microprobe mass spectrometer
Raman microprobe
X-ray absorption fine structure attachment
to synchrotron
EELS 200-225K
LEED 150-175K
AES 150-250K
100-150K
150-200K
150-200K
150-175K
170-200K
650-700K
500-600K
300-325K
150-170K
400-500K
EXAFS
OCR for page 269
V-E. INSTRUMENTATION
of investigation of chemistry in the surface domain. Sections IlI-A, IlI-B, and
V-D show that both the economic and intellectual stakes are high. We must
increase chemistry funding levels to place these powerful tools in the hands of
those chemists working on catalysis. Only then can we expect to maintain a
worId-leadership position in this crucial field. The United States cannot afford
merely to watch with admiration as the field of catalysis is developed in properly
equipped laboratories abroad.
Surface Analysis
As is always the case, sensitive measurement techniques can be regarded as
analytical tools. This is the case in the surface sciences. Every one of the
capabilities listed in the last column of Table V-1 can be put to analytical use in
the pursuit of questions that may be only remotely connected to the surface
sciences. As an example, a state-of-the-art laser microprobe device designed to
desorb molecules from a solid surface can be used to detect the presence of a
pesticide on the leaf of a plant. Such a capability was quite impossible only 10
years ago; today it permits us to contemplate tracking the amount, stability,
weathering, and chemistry of a pesticide in field use.
Of course, the analytical technique may, as well, be concerned with monitor-
ing or clarifying chemical changes that take place on a surface or with a surface.
Many of these analytical studies relate to catalysis. In Section V-D, examples
were given of the use of EELS to determine the molecular structures that exist
on a catalyst surface as it functions. Similarly, X-ray photoelectron spectroscopy
(ESCA) studies of the cobalt molyb~ate catalyst show another facet of the
chemical role of a catalyst.
This catalyst (with 3 percent
cobalt) is used commercially
to remove sulfur from petro-
leum (to reduce acid rain).
In actual use, the catalyst
surface is first prepared by
chemical exposure to hydro-
gen gas at a high temperature
to reduce surface oxides.
Then, the catalyst is "acti-
vated" by exposing it to a hy-
drogen sulfide/hydrogen mix-
ture. Understanding how the
catalyst has been chemically
changed in each of these
treatments is a crucial part of
understanding how the cata-
Tyst works. Present-day
ESCA measurements clearly reveal the changes in the cobalt atoms as the oxide
coating is removed by hydrogen and then as they are converted to the sulfide.
269
14. cat 1970 cat 1980
~T - ~ --
1 1 1 1 1 1 1 1
790 786 782 778 774
BINDING ENERGY (eV)
/\
J
Before _'
A ter reduction
in H2
After activation
.}
'it
~ P
with H2S In
1 1 1 1 1 1 1 1—1
790 786 782 778 774
BINDING ENERGY (eV)
ESCA SHOWS HOW A COBALT CATALYST
CHANGES ON ACTIVATION
OCR for page 270
270
C"
a:
:)
cn
CHEMISTRY AND NATIONAL WELL-BEING
Fifteen years ago, the best ESCA equipment in existence was unable to
distinguish these changes.
The myriad of applications that lie somewhere between the two examples
mentioned above has been made possible by the array of surface science
instruments shown in Table V-4. These applications have given rise to surface
analysis, a new subdivision of analytical chemistry.
Applicability
Surface analysis is quite different from bulk analysis; frequently, factors
important for surface analysis are not important to bulk analysis. The most
common distinguishing feature is the effective sampling depth of the analytical
technique used. For each technique, the sampling depth of that technique
defines the exact surface sampled. Sampling depth is important because the
measuring technique should be appropriate to the phenomenon under study.
For example, bonding to the surface, Nettability, and catalysis involve only a
few atomic layers, whereas passivation and surface hardening treatments
involve 10 to 1000 atomic layers. Typical sampling depths for the primary
surface analytical techniques are one or two atomic layers for low energy in ion
scattering, ~ A for static SIMS, 20 ~ for the ESCA and Auger techniques, and
100 ~ for dynamic SIMS. Laser mass spectrometry, the Raman microprobe, and
scanning electron microscopy reach into the surface from 1000 to 10,000 ~ (i.e.,
to 1 micron).
Another important matter is the microscopic heterogeneity or microcrystal-
linity of the sample. The dis-
O ~ OO ~ OOO LATERS tribution of the species across
MEL - / a surface and its depth rlistri
button inward from the sur-
face can determine the behav-
ior of the surface and must be
known. The shallower the
sampling depth of the tech-
nique, the more finely it is
able to define the depth pro-
file of a sample.
8
~3_~
~~//////~/~/////////~//////~
WORE FUNCTION ///////
__////
OPTICAL ABSORPTION ~
I,
.
CORROSION I
_///////
_ ~
_
ISS SIMS ESCA SIMS LASER SEM
(STATIC ) AUGER (DYNAMIC ) MS RAMAN
HOW DEEP IS THE SURFACE?
Developments Needed
A major challenge in the
development of surface ana-
lytical instrumentation is the
reinforcement of its quantita-
tive dimension. Most of the
examples given have been
concerned with what is there.
We must also be able to deter-
OCR for page 271
V-E. INSTRUMENTATION
mine how much. Relative quantitative surface analysis measures a species of
interest against a component already present. To quantify surface species
without resorting to such internal standards is a difficult problem whose
solution will expand surface analysis to many applications, particularly those
. . . . .
nvo. ~vlng organic species.
Another important problem is the development of microprobes that can
provide both chemical and spatial information about surface species. Currently,
Auger and ion microprobes are useful in this respect for probing elemental
composition, such as the presence and location of the trace contaminants
phosphorus and lead in silicon chips. However, they are not able to probe for
large organic molecules such as carcinogens or therapeutic drugs. Thus,
development of new organic microprobes is an urgent need. Characterization of
small particles is another important challenge for surface analysis: this is
~ · ~ ~ · ~ ~ -
~ ~ ~ ,
particularly important in environmental monitoring where the analysis of
carcinogenic hydrocarbons on particulates is a current problem. Finally. devel-
~ ~ ~ · · 1 1 ~ ~ 1 _ _ 1 _ ~
~ -—.~ 7 -- - -—
opment of new hardware IS Important. An example has been mentioned earlier:
it is important to interface high-vacuum surface spectroscopic techniques with
samples at atmospheric pressure. Development of cells to permit real time
examination of surfaces in contact with a reactive gas is a challenging
instrumental problem.
Costs
The cost listed in Table V-5 are applicable in analytical uses as well. Just as
for research applications, surface analytical problems are seldom solved by a
single, stand-alone technique. Instead, the more interesting problems require a
combination of instrumental approaches. Therefore, an effective surface ana-
lytical laboratory will have to be equipped with several instruments. A
considerable capital investment is implied, again approaching or exceeding
$500K.
Chromatography
Chromatography separates molecules or ions by partitioning species between
a moving and stationary phase. The technique exploits small differences in
properties such as solubility, adsorbability, volatility, stereochemistry, and ion
exchange, so that understanding the fundamental chemistry of these interac-
tions is basic to progress in the field. Liquid chromatography has shown an
impressive growth since 1970. The current $400M annual sales are mainly by
U.S. manufacturers. The growth has come through innovations, such as high
pressure and gradient moving phases to give greater speed and resolution,
bonded-molecule stationary phases to give greater selectivity and column life,
and electrochemical, fluorometric, and mass spectrometric detectors sensitive to
as little as 1o-~2 g. Although gas chromatography is a more mature field by
perhaps a decade, important advances continue to appear. High-speed separa-
tions can now be accomplished in a few tenths of a second; portable instruments
271
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272
CHEMISTRY AND NATIONAL WELL-BEING
the size of a matchbox are in use. A complex mixture can be separated into
literally thousands of components using fused silica capillary columns that are
a direct spin-off from optical fiber technology for communications. It is even
possible to separate compounds that differ only in isotopic composition.
Despite this well established record of success, chromatography is still
expanding its horizons. High-performance liquid chromatography and capillary
column chromatography provide convincing examples of new concepts advanc-
ing the field.
High-Performance Liquid Chromatography (HPI~CJ
During the 1970s, theoretical understandings of the complex flow and mass
transfer phenomena involved in chromatographic band dispersion helped opti-
mization of column design. During this same period, small diameter (3 to 10
micron) silica particles with controlled porosity were introduced and synthetic
advances in silica chemistry led to tailoring of particle diameter, pore diameter,
and pore size distribution. Today, 15-cm columns with efficiencies exceeding
10,000 theoretical plates are routine.
The instrumentation ancillary to these high-performance columns required
development of specialized pumps to drive liquid flows with high precision and
low pulsation through the small particle columns. Detector advances occurred
as well. First UV and refractive index, then more selective detectors based on
fluorescence and amperometry/coulometry, were developed for HPEC.
Still another major advance of the 1970s was the introduction of chemically
bonded phases in which surfaces of porous silica are functionalized with
organosilanes. Especially important is the use of hydrocarbonaceous phases
(such as n-octy] and n-octadecyI) in which the mobile liquid phase is typically an
organic-aqueous mixture. This is called reversed phase chromatography
(RPEC), and it currently provides well over 50 percent of all HPEC separations.
It is especially well suited to substances at least partially soluble in water (e
drugs, biochemically ::3nd nolvn,~rl~r ~rom~t.ir.~)
_' ~ or-- ^
Am. ____ ~ . .. . ~ .. ... .
~ _ ·= 7
1nus no IS a vlorant new wltn new crevelopments continually affecting
many disciplines. New small particle supports based on silica and organic
polymeric materials have recently been introduced for the ion exchange and
reversed phase HPEC separation of biopolymers. Whereas separations previ-
ously required days for completion, today it is becoming possible to accomplish
1 1 1 ~ · - · . ~ - ~ · . ~ ~
even netter resolutions within a tew minutes. (column design is improving as
well. Instead of the conventional 4- to 5-mm diameters, narrower bore columns
from .6-2-mm i.d. are providing routes to sensitive analyses even when the
amount of sample is limited. Also, the lower flow rates at the same linear
velocity permit coupling of LC to powerful vapor phase detectors, such as mass
spectrometry and flame ionization. Open tubular capillary IN columns of 1- to
10-micron inner diameter are being investigated for the potential of generating
high resolving power in the separation of extremely complex mixtures (e.g.,
OCR for page 273
V-E. INSTRUMENTATION
fossil energy fuels). In all these examples, specially designed instruments are
needed to accommodate the small sample sizes.
Finally, the microprocessor/computer is playing an increasing role. "Smart"
HPEC instruments are under development that use statistical optimization
schemes. Semi-empirical solvent and stationary phase characterization
schemes have been developed to enhance the power of these approaches. New
detectors of greater sensitivity and selectivity are on the horizon. In particular,
laser spectroscopy promises to yield highly sensitive devices for subpicogram
detection.
Because of these performance improvements, HPEC is having a major impact
on diverse fields of biochemistry, biomedicine, pharmaceutical development,
environmental monitoring, and forensic science. Today, peptide analysis and
isolation requires HPEC because of its separating power and speed. Analysis of
PTH-amino acids in protein/peptide sequencing is conventionally accomplished
by RPEC. In clinical analysis, therapeutic drug monitoring can be accomplished
by HPEC. The analysis of catecholamines is typically accomplished by RPEC
with electrochemical detection. Isoenzyme analysis, important, for example, in
assessment of damage after heart attack, can be rapidly accomplished by HPEC.
Analysis of parent drugs and their metabolites in a pharmoco-kinetic study is
typically accomplished by HPI,C. The isolation of synthesized drugs in purified
form is typically achieved by HPEC. The analysis of polar and high-molecular-
weight organic species in waste streams can be performed by EPIC, while the
separation and analysis of phenols by RPEC is recommended. Analysis of
narcotics, inks, paints, and blood represent only a few of the samples of forensic
relevance.
Capillary Chromatography
This version of chromatography dispenses with the granular materials
normally packed into the column. Instead, it uses an open capillary tube with a
thin retentive layer on its inner wall. It began with capillary gas chromatog-
raphy and now is being transferred to use with liquids.
Although many satisfactory GC columns are available today, surface inves-
tigations are continuing to improve the general understanding of thin liquid
films and related superficial interactions. Glass as an inert material for the
preparation of GC capillary columns carried with it a fragility that discouraged
many potential users. Now we have flexible, fused-silica capillaries with a
polymer overcoat; these columns are a spin-off of fiber-pntics technolo~v. The
. . ... . . . . . .
,& ~"
advances In capillary column recnno~ogy lea to intensive commercialization
during the 1970s. Today's capillary columns exhibit efficiencies between 105 to
106 theoretical plates and are capable of separating literally hundreds of
components within a narrow boiling-point range. As the corresponding chro-
matographic peaks are separated by seconds or less, the sample input and
output measurements must be comparably rapid. Direct introduction of samples
at the nanogram levels has been developed, and much effort has been spent on
273
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CHEMISTRY AND NATIONAL WELL-BEING
optimization of gas-phase ionization detectors. Among these detectors are some
of the most sensitive measurement devices known. Combined advances in the
column and detector areas now make feasible trace analytical determinations
below 10-~2-gram levels by capillary gas chromatography. The highly sensitive
electron capture detector and element-specific detectors, in conjunction with
capillary GC, currently find numerous applications in environmental and
biomedical research.
Of particular note is the combination of capillary GC with powerful identifi-
cation methods, such as mass spectrometry and Fourier transform infrared
spectroscopy, as mentioned in Section V-D. The combined techniques are now
routinely capable of identifying numerous compounds of interest that are
present in complex mixtures in only nanogram quantities. They have been used
to identify new biologically important molecules, as well as in drug metabolism
studies, forensic applications, and identifications of trace environmental pollu-
tants.
During the last decade, microcolumn high-performance liquid chromatogra-
phy (HPEC) has been under intensive development. Two advantages are the
reduced consumption of the expensive and often environmentally undesirable
mobile phase and the possibility of exploring new detection methods. Open
tubular columns and partially packed columns of"capilIary dimensions" have
been tried. The open tubular columns for GC typically have 200- to 300-micron
inner diameters to obtain optimal solute mass-transfer processes between the
two chromatographic phases. Because of radial diffusion rates, liquid chroma-
tography in open tubular columns necessitates considerably smaller column
dimensions, as small as ~ to 10 microns, and nanoliter volumes are needed for
both sample introduction and detection volumes. Packed capillary columns of
dimensions ranging from 40 to 300 microns have now been developed that
perform satisfactorily: several hundred thousand theoretical plate performance
can now be achieved in several hours' time, and resolution of quite complex
mixtures has been demonstrated.
Microcolumn technology has recently found yet another application in capil-
lary high-voltage zone electrophoresis. The small diameters (typically 60
microns) of open tubular columns permit application of voltages in excess of
30,000 volts without overheating. Very efficient separations of certain charged
species were already demonstrated, but improvements are still needed.
Capillary supercritical fluid chromatography has recently emerged as a
promising approach to the analysis of complex nonvolatile mixtures. As the
solute diffusion coefficients and viscosities of supercritical fluids are more
favorable than those observed in the normal condensed phase, chromatographic
performance is substantially enhanced. Furthermore, the relative optical trans-
parency of supercritical fluids makes them attractive for certain optical detec-
tion techniques. Besides its analytical potential, supercritical fluid chromatog-
raphy appears to be an ideal method for measuring physicochemical parameters
in the vicinity of the critical point.
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V-E. INSTRUMENTATION
Field-Flow Fractionation (FFF)
Chromatography becomes more difficult to apply as molecular size grows and
becomes ineffectual in separating macromolecules and colloidal particles in the
size range .01 to 1 micron in diameter. A recent innovation, field flow
fractionation, may fill this need.
In FFF, a liquid sample is injected into a thin (.1-.3 mm), ribbon-like flow
channel. A thermal, sedimentation, or electric field gradient is applied through
the ribbon. Each constituent in the sample distributes itself in a steady-state
concentration gradient that is determined by its response to the gradient and its
diffusional properties. Since flow through the channel is fastest near the middle
of the ribbon, constituents that are pulled close to the wall move more slowly
through the ribbon than constituents that reside near the middle of the flow
channel. Separations are thus achieved. A useful aspect of this technique is that
the strength of the applied field can be varied in a deliberate and programmed
way during the course of the separation.
Thermal gradients are effective in separating most synthetic polymers.
Sedimentation gradients separate large colloids, and electrical fields are appro-
priate for charged species. Because of the range of operating parameters, FFT
has proven capable of separating both charged and uncharged species in either
chain or globular configuration. The method works both in aqueous and
nonaqueous media. The mass range of molecules and particles to which FFF has
been applied extends from molecular weights of 1000 up to 10~8, that is, up to
particle sizes of about 100-micron diameters FFF appears to be applicable to
nearly any complex molecular or particulate material within that vast range.
Because the channel geometry and flow are well characterized, the rate of
displacement of a given constituent can be related rigorously to such properties
as mass, size, diffusivity, density, charge, and thermal diffusion rates. Hence,
the above properties can be determined by measuring displacement rates, and
FFT becomes an accurate tool for particle characterization.
Applications of FFF have so far included macromolecules and particles of
biological and biomedical relevance (proteins, viruses, subcellular particles,
liposomes, artificial blood, and whole celIs), of industrial importance (both
nonpolar and water soluble polymers, lattices, coal liquid residues, emulsions,
and colloidal silica), and of environmental significance (waterborne colloids and
fly ash).
Costs
Chromatography is an essential too] to every synthetic chemist and to
analytical chemists in a variety of fields. An advanced analytical gas chromato-
graph might cost $20K, an HPEC about the same, and a preparative (large
volume) chromatograph somewhat more, perhaps $30K. While each item has
only a modest cost, three or four such instruments will be needed as dedicated
275
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276
an
a:
o
CHEMISTRY AND NATIONAL WELL-BEING
.
instruments by each research group. Thus the total may approach $100K, a
capital investment that must be available for effective research.
Infrared Spectroscopy
The infrared spectral region reveals molecular vibrational motions. Because
these motions are sensitive to bond strengths and molecular architecture,
infrared spectroscopy has become one of the routine diagnostic tools of chemis-
try. A large, research-oriented chemistry department might operate five to ten
such instruments with capabilities ranging from rugged, low-resolution instru-
ments for instruction in an advanced first-year chemistry course to high-
resolution Fourier transform instruments (FTIR) suited to molecular structure
determination and specialized research use.
Computer-Aided Spectrometers
Modern research infrared spectrometers incorporate dedicated computer
capability for programmed operation, data collection, and data manipulation.
The major impact of computers, however, has been their influence on the
accessibility and reliability of Fourier transform interferometers. As mentioned
earlier in Section TTT-E, the perfection of the Fourier transform algorithm plus
the reduction in accompanying computer costs brought the interferometer from
a trouble-plagued, research-only instrument to a
routine, high-performance workhorse. Spectral
resolutions of .25 cm-i are readily obtained over a
long scan range (e.g., 4000 to 400 cm- in 20 or
30 minutes. A notable capability is the ease and
accuracy with which difference spectra can be
displayed. One important application relates to
infrared spectra of biological samples in which
evidence of a chemical change associated with a
localized biological function can be completely
masked by the heavy infrared spectrum of the
inactive substrate. The digitized data permit pre-
cise spectral subtraction so that the background
spectrum can be virtually eliminated to reveal
the spectral changes of interest. Another vivid
display of the value of the difference capability is
provided by photolysis of molecules suspended in
a cryogenic solid ("matrix isolations. If the digi-
tized spectrum before photolysis is subtracted
from the spectrum after photolysis, only the fea-
tures that change are seen. Any molecule that is
DIFLUOROPROPENE IN
SO L I D KRYPTON, 12
4~
cis
gauche
hL`11 ~ 1 41
I gaucbet |
~rA4,
cis1
1 400 1200 1000
V(cm l)
s~
BEFORE PBOTOLTSIS (hi)
Ha_
~ DETER (hi)— BEEORE (hi) ~
__0
FTIR DIFFERENCE SPECTROSCOPY
SHOWS ROTAMER INTERCONVERSION
OCR for page 277
V-E. INSTRUMENTATION
being consumed presents its spectral features downward, while the product
spectral features extend upwards. This has been used, for example, to distin-
guish the two rotameric forms (cis- and gauche-) of 2,3,-difluoropropene in the
cluttered spectrum of a complex mixture. Interconversion is caused by laser
irradiation of one of the adsorptions of one rotamer.
Applications
The coupling of FTIR with gas chromatographic separations in a variety of
analytical uses has been discussed in Section V-D. This coupling is facilitated by
computerized data collection, and it is made possible by the reduced scan time
that accompanies the high-performance characteristics of FTIR instruments.
Also as noted in Sections V-A and V-D, infrared spectroscopy is a specially
effective method for monitoring and studying atmospheric chemistry. This is
because gaseous molecules of Tow molecular weight are important, including
formaldehyde, nitric acid, sulfur dioxide, acetaldehyde, ozone, oxides of chlorine
and nitrogen, nitrous oxide, carbon dioxide, and the freons. These substances
are influential participants in photochemical smog production, acid rain
stratospheric disturbance of the ozone layer, and the greenhouse effect.
TABLE V-6 Additional Instrumental Techniques in Modern Chemistry
Instrument
Information Obtained
Approximate
Cost ($)
Ion cyclotron resonance spectrometer
Laser magnetic resonance spectrometer
Laser-Raman spectrometer
Fluorimeter
Circular dichroism spectrometer
Flow cytometer
Protein sequencer
Oligonucleotide synthesizer
Electron diffraction
Scintillation counter
Reaction rates of gaseous molecular ions
Precise molecular structures of gaseous
free radicals
Vibrational structure of molecules or of
chromophores in complex
Energies and lifetimes of electronically
excited molecules
Stereoconformations of complex molecules
Laser-activated cell sorter
Automated analysis of protein sequence
Automated synthesis of design oligonucle-
otides
Molecular structures of gaseous molecules
Tracking radio-tracers through chemical
reactions
125K
75K
60K
40K
50K
150K
120K
40K
150K
50K
Costs
Fourier transform infrared spectrometers are now sufficiently easy to use-
with the high performance described above that they are becoming ubiqui-
tous. In 1983, perhaps 200 such instruments were sold by U.S. companies, and
foreign instruments are appearing (from West Germany and Canada). Costs
277
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CHEMISTRY AND NATIONAL WELL-BEING
currently range from $140K to $200K, depending upon the resolution and scan
range. Accessories permit long-wavelength spectroscopy to 10 cm-i and near-
infrared spectroscopy reaching into the visible.
Other Instrumentation
In Sections IlI-E, IV-E, and V-E, there has been explicit discussion of more
than a dozen different classes of instrumentation that are important in defining
and advancing the current frontiers of chemistry. By no means, however, is the
list all-inclusive. Table V-6 lists additional types of equipment, what kinds of
chemical information each one provides, and approximate current costs.
Plainly, these, too, contribute to the capital investment needed to sustain
frontier research in chemistry.
Representative terms from entire chapter:
intellectual frontiers
