How the Infrared Spectrometer Reached the Bench ... - Spectroscopy

GUEST
E D I T O R I A L
How the Infrared Spectrometer
Reached the Bench Chemist
P AUL
A. WILKS
The infrared spectrometer
as we know it today got its
start during the late
1930s. Although Coblentz
had discovered the infrared
(IR) spectrum toward
the end of the 19th century, 30
years went by before the real
value that existed in the IR
spectrum began to be appreciated.
Work began in earnest in
several universities, notably at
the University of Michigan
(Ann Arbor), the University of
Minnesota at Minneapolis–St.
Paul, and at the Massachusetts
Institute of Technology (Cambridge),
usually in the department
of physics.
The IR laboratories were almost
always tucked away in
the basement of the physics
building for several reasons.
Dispersion of IR radiation into
discrete wavelengths was usually
accomplished with a rock salt prism
that had to be kept in a dry atmosphere.
Energy levels were measured with a thermocouple
having a signal that was fed to
a galvanometer with a movement that
was amplified by a lamp-and-scale device.
This mechanism required a solid base
that was free from vibration. Furthermore,
the output of the thermocouple
would drift substantially with ambient
temperature changes. The net result was
that the early spectroscopists found basement
locations best suited for the construction
of the vibration-free, humidityand
temperature-controlled rooms
needed for successful operation of the
spectrometers.
Also, needless to say, the spectroscopists
were loath to admit outsiders
that might upset the equilibrium of their
habitat — especially during the scanning
A whole new world for
IR analysis opened up
when Dow Chemical
spectroscopists created
the double-beam
spectrophotometer.
of a spectrum, which frequently took several
hours. As a result, the early spectroscopists
were looked on — rightly or
wrongly — as recluses who spoke only to
other spectroscopists. And IR spectroscopy
became something
of a black art that could be
practiced successfully only
by aficionados. IR spectroscopists
continued to consider
themselves members of
an elite group even after commercial
IR spectrometers began
to appear in the marketplace.
The early IR instruments
were single beam and were
used primarily for quantitative
analyses (1). The spectra
that they recorded followed
the black body emission
curve and had the atmospheric
absorption bands superimposed
on them. Spectroscopists
had to replot
spectra either manually or
automatically to obtain useful
quantitative data from them.
A whole new world for IR
analysis opened up when
Dow Chemical spectroscopists, under the
direction of Norman Wright, created the
double-beam spectrophotometer. Its
spectra had a flat baseline and atmospheric
bands were largely cancelled out.
The result was an excellent spectrum
with absorption bands uniformly presented
from one end of the wavelength
region to the other. These spectra could
be used to directly identify materials as
well as to provide structural information
on unknown molecules and the new ones
constantly being created by organic
chemists.
In 1951, PerkinElmer (Norwalk, CT)
introduced the model 21 double-beam IR
spectrometer — one of the most successful
scientific instruments ever developed,
and one that started PerkinElmer on its
way to becoming a leading manufacturer
of analytical instruments.
14 SPECTROSCOPY 16(12) DECEMBER 2001 www.spectroscopyonline.com

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GUEST EDITORIAL .............................
The founding fathers
of IR spectroscopy, rather
than being proved wrong
that having IR fall
into the hands of
nonspectroscopists
would prove to be a
disaster, would be proud
that the technology they
so carefully nurtured had
become so widely useful
in solving real-world
analytical problems.
In spite of its excellence in producing
high-quality IR spectra, the model 21 did
have some faults. One of the most serious
was that if the operating controls were
not properly set, the instrument could
produce what came to be known as “spurious
absorption bands” often caused by
overshoot in the recording system. This
occasionally led to wrong conclusions being
drawn about the structure of a new
molecule.
Van Zandt Williams, then Perkin-
Elmer’s vice president of sales and research,
became concerned that use of IR
instruments such as the model 21 by inexperienced
operators who mistakenly interpreted
spectra, properly recorded or otherwise,
would eventually give IR
spectroscopy a bad name and restrict its
use. Furthermore, some of the spectra
published by commercial organizations
were recorded on materials of dubious purity,
which could also lead to false
conclusions.
In an effort to rectify these shortcomings,
Williams, Wright, and a group of
other dedicated spectroscopists banded
together to form the Coblentz Society,
which describes itself as “a nonprofit
organization in support of standards of
excellence in vibrational spectroscopy.”
Having recently celebrated its 47th anniversary,
the Coblentz Society has indeed
been IR spectroscopy’s watchdog. It
has made available hundreds of topquality
IR spectra from materials of
proven purity; it has sponsored seminars
and given awards for contributions to the
field; and it has acted as an ambassador
of IR to other societies and organizations.
However, like the early spectroscopists, it
has remained somewhat aloof from the
real world of IR in quality control, process
monitoring, forensics, and environmental
monitoring. As a result, its members are
largely from research centers and academia,
and the society still looks on IR
analysis as a science rather than a practical,
widely applicable analytical tool.
In the mid-1950s, as director of marketing
at PerkinElmer, I was invited to the
Dupont Experimental Station. I was
shown plans for a major expansion of the
station. Each section would have several
analytical alcoves rather than a single analytical
services center. As I recall, one of
the Dupont people managing the expansion
of the Experimental Station said,
“The idea is to provide tools so that the
bench chemist could use them to make
his own analyses when he needed them
rather than wait his turn for results from
a central facility. We believe IR is one of
the most useful analytical methods a
bench chemist can have to assist him in
his work. However, currently available
spectrometers like the model 21 are too
complex and expensive. We need an instrument
that the average chemist can
use that is sufficiently low priced that we
can place one in every analytical alcove.”
When I brought back this message to
my associates at PerkinElmer, it sparked
an intense internal debate. Technically it
was feasible to design a simple, fixedparameter
instrument that could produce
medium-resolution spectra and that could
be marketed at a fraction of the cost of
the model 21. However, the Coblentz approach
argued that putting such an instrument
in the hands of the bench
chemist could only lead to disaster
through misinterpretation of the spectra
produced by it. More significantly,
PerkinElmer management was totally opposed,
fearing that the availability of a
low-cost IR spectrometer would kill the
golden goose — the model 21.
The debate ended abruptly when industrial
espionage yielded the information
that arch-rival Beckman was working
on such an instrument.
A crash program ensued and Perkin-
Elmer’s model 137 Bench Chemists instrument
was unveiled at the 1955 Pittsburgh
Conference (as was the similar
Beckman model IR5). The sales curve of
the model 21 was watched carefully during
the following months; it showed
scarcely a blip in its steady growth curve.
Meanwhile, acceptance of the model 137
was immediate. Its first-year sales of 600
units showed that it was reaching an entirely
new unfilled market for IR analysis,
the one envisioned by the Dupont
planners.
The model 137 and its descendants
formed the basis for PerkinElmer’s IR
program for the next 20 years, until the
advent of Fourier transform–infrared
(FT-IR) spectrometers. Even the FT-IR
program has followed the same pattern
with the original, costly, research-only instruments
being succeeded by eversimpler,
lower-cost models aimed at
bench chemists. Even special-purpose
FT-IR spectrometers are beginning to appear,
such as the Midac (Irvine, CA)
open-air monitor and SensIR Technologies’
(Danbury, CT) portable microscope
FT-IR instrument. FT-IR is also moving
into process monitoring — a far cry from
the research laboratory.
The founding fathers of IR spectroscopy,
rather than being proved wrong
that having IR fall into the hands of nonspectroscopists
would prove to be a disaster,
would be proud that the technology
they so carefully nurtured had become so
widely useful in solving real-world analytical
problems.
REFERENCES
(1) P. A. Wilks, Spectroscopy 16(3), 12 (2001).
Paul A. Wilks is president of Wilks Enterprise
(140 Water St., South Norwalk, CT
06854) and a member of Spectroscopy’s
editorial advisory board. He can be contacted
by phone at (203) 855-9136 and by
e-mail at pwilks@wilksir.com.◆
DECEMBER 2001 16(12) SPECTROSCOPY 15