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Computer Systems for Chemical Research.

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all the demands to be made of the computer in “off-line”
and “on-line” operation and finally contacted numerous
computer manufacturers. It was soon apparent that one of
the manufacturers was able to satisfy the special needs of
“on-line” operation at a reasonable price. The decision for
this system was made by the members of the committee
and the purchase was financed by the Max-Planck-Gesellschaft and, supplementarily, out of the resources of the
Experience gained with the system since 1968 is described
in the following reports from the standpoints of the
different groups. The preparative chemist, even though he
himself is least direcrly involved, usually benefits from the
advantages of the system. Accordingly, the secondary field
defined above was developed further. There are good
prospects that the new system will benefit the primary field
not only indirectly but directly if it is possible to link the
computer with an analytical system (i. e., a gas chromatograph) and reactor to control the reaction process. Such
a mode of operation would extend the available laboratory
techniques. In the Miilheim Institute the first attempts of
this kind have already been successful.
A few remarks on the following progress reports appear
to be in order:
The reports are by no means written only for the specialist.
The chemist not familiar with data processing should also
take an interest in these problems; even without a detailed
knowledge he will quickly appreciate what possibilities
exist. A certain amount of repetition was unavoidable. Also,
one must become accustomed to computer terminology ;
a few technical terms are explained in a glossary.
Finally, a word of warning: The methods of experimental
analysis available today entice us to work on and to solve
problems at great expense which, with regard to the real
worth of the knowledge obtained, can in no way be justified.
The analytical apparatus can soon become overburdened
without really achieving anything new. A critical evaluation
and selection of the problems to be treated with these
tremendous resources is more important than ever before.
In the enthusiasm over our present facilities, we should
never forget the outstanding achievements of those who
worked without these resources, i. e. before 1952.
For the theoretician, on the other hand, direct access to a
computer installation is absolutely essential for fruitful
Received: November 18,1971 [A 865 IE]
German version: Angew. Chem. 84,370 (1972)
Computer Systems for Chemical Research
By Engelbert Ziegler, Dieter Henneberg, and Gerhard Schomburg[*]
1. Introduction
2. Applications in Chemical Research
As in almost all areas of our daily lives, digital computers
have also invaded the field of chemical research. If one
thinks of the first successes of Corey and Wipke“’, who
used a computer system for the determination and optimization of synthesis paths in preparative chemistry, or of
the development of documentation systems for chemical
literature or for molecular spectra, one can imagine the
new possibilities which will become available to the chemist in the future through the increased use of computers
and how the chemist’s way of working could be affected.
The customary applications of computers can be divided
into two areas :
The purpose of this paper is not so much to give a picture
of future developments in the field but rather to serve as a
brief survey of the current uses of digital computers in
chemical research and of the corresponding computer systems. The system developed at the Max-PIanck-Institut
fur Kohlenforschung in Miilheim/Ruhr, Germany, is
Dr. E. Ziegler, Dr. D. Henneberg, and Dr. G. Schornburg
Max-Planck-Institut fur Kohlenforschung
433 Miilheimmuhr, Kaiser-Wilhelm-Platz 1 (Germany)
1. Computational tasks (“off-line” operation) and
2. connection of analytical measuring instruments to a
computer system (“on-line” operation).
2.1. Off-line Applications
Calculation problems from theoretical chemistry, such as
those arising in the various computational approaches to
M O theory or in reaction kinetics, are usually solved in
off-line operation. Also falling into this category are the
various kinds of computations in the field of spectroscopy
and for literature and spectra documentation.
Many of these computer programs place considerable
demands on the efficiency and capacity of the computer.
A core memory of 32 K 36-bit (or at least 32-bit) words is a
typical requirement. Aside from this, extensive computing
time requirements are characteristic for such off-line proAngew. Chem. internal. Edit. / Vol. 11 (1972) No. S
grams. Even on large computers, computing times of
an hour or more are by no means a rarity. (For example,
evaluation programs for X-ray structure analysis run
particularly long.) A further characteristic of most of these
programs (exception : documentation systems) is the relatively low number of input and output operations.
As long as the programs have been tested out and average
turn-around times of several hours or even days are considered tolerable, then conventional batch operation, in
which the programs are processed one after another, is
For small caIculations of all types, however, like those which
can occur in the daily laboratory routine, a faster access to
the computer and fast reporting of the results are desirable.
An input-output teleprinter terminal located in the laboratory and connected to a computer considerably facilitates
the use of the computer for such tasks.
2.2. On-line Applications
A completely different type of use for a computer is the
real-time acquisition of data from analytical instruments
coupled to the computer. The data occur either in digital
form or-more frequently-as analog values, normally a
voltage. For computer processing these voltages must first
be digitized with an analog-to-digital (A/D) converter. An
interface between the A/D converter and the computer
allows proper mutual communication.
One could consider it irrelevant whether a card reader, a
magnetic tape, or an A/D converter is connected to the
computer. Viewed from this angle the interface to an analytical instrument would merely be an additional peripheral
unit in a normal computer system such as is used for the
previously mentioned off-line computations.
However, whereas conventional peripheral devices like
magnetic tapes or card readers transmit data to the computer according to the needs of the program, the data from
an analytical instrument must be taken by the computer at
the points in time which are determined by the on-line
experiment (real-time data acquisition).
The typical demands on an on-line system cannot be specified without going deeper into the individual problems. The
structure of an on-line system is essentially determined by :
Frequency of changes in problem specifications
Degree of operational reliability required
Existing laboratory structure and the possible extent of
reorganization necessary
Available financial means for purchase and maintenance
Available personnel.
Besides the computer, an A/D converter, a real-time clock
as an external timer, as well as relay inputs and outputs for
registration and control of start/stop events normally make
up the hardware of an on-line system. In almost all cases a
peripheral data storage medium (preferably disk or tape)
is indispensable. Closed-loop systems often also need a
D/A converter.
3. On-line Systems for Analysis
Spectroscopic and analytical instruments have been continually improved ; they have usually also become correspondingly more complicated and more expensive. The
direct connection of these instruments to a digital computer is a further step in this direction. However, for the
analyst and the spectroscopist this step is in no way unproblematic. On the one hand they are offered tempting
new possibilities; on the other hand they see themselves
confronted with, for them, a new and multifariously complicated subject. Moreover, since the purchase costs for an
on-line system are at least as high as for a large analytical
instrument, one should consider the installation of such a
computer system especially thoroughly. For that reason
several arguments for the computerization of analytical
instruments are enumerated here. Their weights depend
on the specific requirements of a laboratory and must be
discussed for the individuaI case :
Increase in the accuracy and precision of analysis
Speeding up of the evaluation
Increase in analysis through-put
Gain of more information
Performing new types of experiments
Control of an experiment
Processing of spectra for documentation purposes
Data rate (data points per second)
Saving of personnel
Data volume (number of data points)
Supervision of personnel.
Precision of measured values
Number of analytical devices of the same type to be served
The multiplicity of measuring instruments on the market,
the tasks which vary considerably from laboratory to
laboratory, the differing forms of organization of the analytical work, and finally the large number of computer types
which come into question have brought about the development of many very different on-line systems. Most of the
present systems can be placed in one of the following
categories :
Storage and temporary storage of data
1. dedicated (single-purpose) systems
Reduction of data in real-time
Extent of closed-loop operation
Number of analytical methods to be served simultaneously
Complexity of data evaluation
Type and speed of parameter input and result output
Requisite flexibility of hardware and software
Angew. Chem. internat.. Edit.
Vol. 11 (1972) 1 N o . 5
2. multi-method systems
3. mixed systems (both on-line and off-line processing),
with satellite computers or without.
Table 1. Areas of application for the various types of on-line systems.
Typical computer requirements
Dedicated systems
1. one instrument per computer
2. variable-purpose dedicated system
small computer, 4-8
small computer, 4-8
3. several instruments of the same type
per computer
small to medium-sized computer
slow data acquisition, simple evaluation,
8-16 K
limited instrument control
usually medium-sized computer,
8-16 K
Multi-method systems
(small OJ medium-sized computer)
Especially suited for
Typical environment
instrument control, fast data acquisition,
long running experiments
alternative connection to one of several
largely independent of
laboratory type
research lab
routine industrial lab
(e.g. quality control)
routine lab with
essentially unchanging
d em a n d s
Mixed system
(with conversational time-sharing
large computer, 32 K ;
extensive periphery
real-time data acquisition, processing of
large volumes of data. complicated
el aluation procedures, limited instrument
control functions
research and industrial
labs with many analytical methods
Satellite systems
(with dedicated satellites)
large computer, 48 K ; several
small computers; extensive
periphery ; possibly complicated
data transmission
instrument control, many devices with high
data rates, complicated evaluation
procedures, off-line calculations
large institutions with
a wide range of analytical methods, large
computer centers with
some real-time applications
The areas of application of these three categories of on-line
systems are summarized in Table 1. Their essential characteristics will be briefly described below.
3.1. Dedicated Systems
To this group belong the computer systems that serve either
one single instrument or several instruments of the same
type (such as a group of gas chromatographs). It is essential
that the computer work with a uniform programming
system (“software”).
3.1.1. Computer Systems for a Single Instrument
Measuring devices for fast-running physical events (for
instance a Fourier-transform NMR spectrometer or a fastscan mass spectrometer)produce very many digitized values
in a short time (data rates in the kHz region) that have to
a small dedicated computer may be necessary for devices
with such demands.
Single-instrument computer systems (Fig. 1)can be adapted
to the requirements of the respective instruments and are
particularly suited for experiments that require many feedback control operations from the computer, for example
the computer-controlled single-crystal diffractometer. With
this latter application a measurement usually extends over
several days ; therefore, a particularly high system reliability, usually not achieved by complicated computer systems,
is required.
From an economical standpoint such on-line systems are
still very unfavorable ; normally the computer together
with peripherals and interface is more expensive than the
measuring instrument itself. However, the development of
“integrated” measuring instruments is foreseeable. Here
the computer hardware is distributed as an integral constituent over the components of the instrument. This, of
course, entails a completely new construction of conventional analytical instruments. As a consequence of continuing further development and reduction in cost of components such instruments with a “built-in” computer need
not necessarily be more expensive than the currently existing instrument without computer.
Control signals
Teletype lines
be accepted by the computer and further processed or
stored away. In addition to the high data rates, complicated
evaluation programs are frequently necessary. Therefore,
Fig. 2. The outputs of several identical instruments are connected to
the computer through a multiplexer.
Angew. Chem. internal. Edit.1 Vol. 11 (1972) 1 No. 5
3.1.2. Multiple Instruments of the Same Type on one
For economic reasons one would today still try to serve as
many instruments as possible simultaneously with one
computer (Fig. 2). If it is a question of devices all of one
type, like a number of gas chromatographs, then it is relatively simple for all ofthe instruments to work with the same
programming system ;this means that only one copy of the
data acquisition routines and evaluation programs need
be in the computer.
3.2. Multi-method Systems
different types of instruments (for instance gas chromatographs and IR, NMR, or mass spectrometers)are connected
to the same computer systems for simultaneous service,
then different evaluation programs and often also different
data acquisition programs are required, depending on the
application. In such a system a monitor program is necessary; it is reponsible €or distributing the central processor
time among the programs.
In order to be able also to gather the data from active instruments during data processing, the computer must operate
with an “interrupt system” with several priority levels. With
this system an external real-time clock can interrupt the
currently running program by an electronic impulse. On
such an interrupt, the monitor program decides which
instrument takes its turn for the acquisition of data next,
switches the multiplexer to the corresponding channel, and
starts the A/D conversion. Until the completion of this
activity (signaled by another interrupt), the computer can
return to the previously interrupted program or switch to
another one.
The programming effort for such a multi-method system
is quite considerable. The paralie1 measurements must be
tuned to each other in relation to memory requirements,
external storage demands, data rates, and computing times.
Program maintenance (removal of programming errors,
technical programming improvements, installation of new
evaluation algorithms) can become quite a serious problem
in such a system. During alteration of a program only relatively large “nice” computers prevent any influence (for
instance through faulty programming) on parallel running
programs. Therefore all program changes must be tested
out on the total system, which is frequently quite troublesome. However, the more instruments of different types are
connected to the computer system simultaneously, the
more frequent such changes wi11 be, which then disturbs
the total operation considerably.
For this reason, multi-method systems are not suited for
use with small or medium-sized computers, in particular
for research laboratories with frequently changing problems. However, such systems could be useful for some
rndustrial laboratories working with a set of tested programs for an extended period.
The advantage of a multi-method system over several
dedicated systems iies in a saving of hardware. Only one
central processor is required and duplication of some periAngew. Chem. internat. Edir
1 Vol. 11 11972) 1 N o . 5
pheral units (which therefore can be of better quality)
3.3. Mixed Systems (Simultaneous On-line and Off-line
If a computer system serves not only several directly connected analytical instruments, but also concurrently runs
one or more off-line programs (“background processing”),
then it may be called a “mixed system”.
If such a system is to work effectively, then an efficient central computer is required, the hardware of which guarantees that individual programs are completely protected
from one another. Since many off-line programs are not
completely tested and are therefore potentially faulty, such
program protection is indispensable.
A mixed system offers the advantage that the many
peripherals usually associated with a large computer, like
line printers, card readers, disks and magnetic tapes, offer
on-line users possibilities which d o not exist with small
computer systems.
Besides the large centrai computer some mixed systems
employ several subordinate small computers (“satellites”)
for the acquisition of data from the connected analytical
instruments and for pre-processing of these data. Through
the satellite computers the central computer can be relieved
of the pure “bookkeeping” tasks and need only occupy
itself with the extensive calculations of the data evaluation
A variant of the satellite system is the “multi-mini” system
in which a small computer (if possible of the same type as
the satellites) is used as the central computer, or in which
there is no central computer. In the latter case the small
dedicated computers are connected with each other in a
network fashion. The lack of an efficient central computer
means, however, that heavily computational programs
cannot be accommodated. In addition, the operating system of the small central computer, which must organize
the data commnnication to the satellites, clearly cannot be
so flexible and efficient as is possible with a large computer
Section 4 presents a general discussion of the advantages
and disadvantages of a mixed system taking the Miilheim
Computer System as a typical example.
3.4. Failsafe Systems
The computerization of analytical instruments makes analytical laboratories largely dependent on the computer ;
therefore the greater the number of instruments connected
to the system, the more serious a system breakdown can be.
The most certain measure against such “disasters” would
be an identical second system that processes the same data
in parallel with the first system. However, such an expenditure is normally justified only for some process-control
computer installations supervising manufacturing processes. Obviously in this case one would try to keep the duplicate system as small as possible.
Core storage
In addition to these there are smaller labor-saving programs of all types.
The extensive spectroscopic, analytic, and physical chemistry laboratories of the Institute have at their disposal a
large number of analytical instruments, some of which
should be connected directly to a computer (for the current
state see Section 4.6):
1. “Slow” instruments (data rate ca. 20 Hz)
Card reader
On- linesystem
User time-sharing system
Fig. 3. The Du Pont company’s failsafe system. On failure of the central
processor responsible for the real-time processing, the other processor
automatically takes over the duties of the first one.
gas chromatographs
Imass spectrometer
NMR instruments
R spectrometer
1 ESR instrument
1 spectral polarimeter
2. “Fast” instruments (data rate 1 to 20 kHz)
2 low-resolution fast-scan mass spectrometers
For the computerized experiments in the field of chemical
research no such high operationa1 reliability is required ;
partial security against the worst failures is sufficient.
Interesting in this respect is a failsafe-system being built at
the Du Pont company’s Experimental Station in Wilmington, Delaware, USA[’]. This system consists of two coupled
(PDP-10) central processors, one of which normally serves
exclusively for the real-time acquisition of data from the
analytical instruments, while the other is used for the evaluation of the real-time data and the execution of off-line
programs (Fig. 3). Part of the memory and some of the
peripheral units are commonly accessible to both central
processors. Should the central processor responsible for
the real-time data acquisition fail, then the other one takes
over this task automatically.
1 pulse NMR instrument
While the purchase of one or more computer systems for
all of these areas of application was under discussion in
1967, two alternatives were open to the Institute :
1. The purchase of a medium to large computer that would
be used in batch mode for all off-line computing problems,
supplemented by a number of small computers for several
dedicated on-line systems for the analytical instruments.
2. The purchase ofa single,more capable computer possessing both the hardware and software for a multiprogramming time-sharing system and simultaneous off-line and
on-line operation.
4.2. Hardware Cofliguration of the PDP 10
4. The Miilheim Computer System
4.1. Computer Applications at the Max-Planck-Institut
in Miiiheim/Ruhr
At the Max-Planck-Institut fur Kohlenforschung, including the radiation chemistry division, in Mulheim/Ruhr,
almost all possible applications for computers in chemical
research are represented. Among the off-line tasks programs exist for :
X-ray structure analysis
MO theory
Reaction kinetics
Simulation and iteration of spectra
Evaluation of spectra
Spectra documentation
For financial and organizational reasons the second alternative was chosen.
In December 1968, the first part of a PDPIO insta1lation‘’l
was put into operation; in April and September 1969, the
additional hardware required for the on-line applications
was installed; in July 1970, the system was expanded by the
addition of 32 K of core memory and a disk pack unit. The
present system configuration is represented in Figure 4.
The hardware of the PDPIO central processor includes
366 machine instructions (including floating-point and
byte instructions), an interrupt system with seven priority
levels, as well as memory protection registers. The present
memory capacity is 64 K 36-bit words. Two channels for
fast data transmission connect the memory with a fixedhead disk (average access time 17 ms, transmission rate
77K wordsjs, capacity 5GQK words) and a disk pack
(average access time 60 ms, transmission rate 62 K wordsjs,
capacity 5000 K words).
Support of the Institute’s administration.
A part of the fixed-head disk is used for temporary copies
of the core image of running programs (“swapping” operation) if the memory is not sufficient to hold all parallel
p] Dr. E. A . Abrahamson, Dr. J . f o k , and Dr. .I.
Read, Wilmington,
Delaware, private communication.
p] Producer: Digital Equipment Corporation, Maynard, Mass.(USA).
Literature documentation
Angew. Chem. iniemat. Edit. / Vol. 11 (1972) 1 No. 5
relays to be opened and dosed by the computer. With this
equipment the computer recognizes start and stop commands for the real-time data acquisition and can control
external events. Non time-linear registering instruments
like IR spectrometers notify the operating system of the
time for every A/D conversion by closing an external contact.
running programs. However, the major portion of disk
space serves for storage
of programs and data.
Additional peripheral units include a line printer, a card
reader, magnetic tape units, a plotter, paper tape reader
and punch, as well as 22 input/output teleprinters which
serve as user terminals for time-sharing operation.
4.3. Time-sharing Operation
8 DEC tapes
In the current version of the operating system up to 23 jobs
can be handled simultaneously. The jobs are initialized by
the users at any time from the teletype stations distributed
throughout the Institute. The jobs each control the running
of one prcgram that the user has started by typing a
command at the teletype. Data can be entered and the
results printed out via the teletype. (Any other peripheral
units can naturally also be used for data input/output.)
,Magnetic tapes
1000 iines/min
Card reader
Contact scanner
72 contacts
2L lerminals
22 Ieletypes
1 CRT display
1 pnp-8
I72 contacts1
Reai-time clock 20 kHz
Fig. 4. Hardware configuration of the PDPlO installation at the MaxPlanck-Institut fur Kohlenforschung in Miilheimmuhr, Germany.
Several special units serve as interfaces between the computer system and the directly connected analytical instruments : Up to 32 “slow” instruments can be connected to
a high quality A/D converter by means ofa multiplexer unit.
This A/D converter works with a 13-bit resolution in 11
amplification ranges, and therefore has a dynamic range
of nearly 10’. The total data rate amounts to 3.3 kHz with
automatic range selection.
For the “fast” instruments another A/D converter is used
that can work with data rates between 1.25 and 20 kHz.
The resolution is 10 bits; the dynamic range 2.5 x lo5,and
is subdivided into three ranges of amplification. Up to eight
instruments can be connected to this A/D converter by
means of a multiplexer. However, in order not to disturb
the normal time-sharing operation and the simultaneous
data acquisition from the “slow” instruments only one of
the eight possible ‘-fast”instruments is allowed to be active
at any one time. Due to the short recording times of about
2-3 seconds for such instruments, this restriction is no
serious hindrance.
The clocking of the data for each of the twoA/D converters
is done by a real-time clock (quartz oscillator, 20 kHz) and
two digital counters.
72 contact inputs allow the recognition of the closing and
opening ofexternal circuits ;72 reIay drivers permit external
Angew. Chem. internat. Edit.
Vol. 11 (1972) / N o . 5
TTY 1 7
TTY 1 1
TTY 1 5
2’30=2:’12 T T Y 6
St 1 4
2 9 , 4:)
TiY 1.3
1 *(
4 D S T A T 44
YFYl 1
Li I I’
T T S; ;1
0 0 : 3 1 :1 7
3i3: ‘32
Fig. 5. “Snapshot” of the state of the simultaneously processed jobs m
the Miilheim System: SELDAT (Job 1 ) is the data acquisition program
on-line instruments, MSDAT (Job 2) the data acquisition
for the “SLOW”
and pre-reduction program for the mass spectrometer; ORGAN1 (Job
3) is a control program that initializes several programs; REFREP
(Job 8) produces outputs of gas chromatograms; PARAM (Job 12) is
used to input parameters for on-line runs of “slow” instruments:
NMRCAT (Job 18) is a time-averaging program for NMR spectra.
The commands typed in on the teletype are interpreted by
the operating system. The operating system also determines the distribution of central processor computing
time, the allocation of memory, and the assignment of
peripheral units to the individual jobs. Whenever a job
begins an input or output operation via one of the seven
priority levels of the interrupt system, or after the apportioned amount of computing time (“time slice”-from 0.5 to 2
seconds) has run out, the operating system searches for
another job to occupy the central computing unit. Figure 5
shows a representative “snapshot” of computer operation.
The time-sharing mode of operation allows a regular
dialog between a program and a user. Figure 6 is an example
of such a dialog; here the input of parameters for a plotting
program is presented. Explanations and warnings for the
inexperienced user have been provided in the program.
The scientist who has immediate access to the computer
and the banks of data stored there by way of a teletype
located at his place of work can use the computer as a
constantly available thinking aid just as on a less sophisticated level he uses a slide rule or mathematical tables.
to check the status of all instruments in question at regular
time intervals; on completion of a data acquisition experiment the evaluation is carried out automatically. (For
a detailed description of the software organization see [2, 31.)
4.5. Flexibility of the System
.H D A T P L T
K E I N DA r E N S A TZ F U E t i A N S C H L U S S 15 V O e H A N D E N !
The time-sharing system allows a very flexible, stepwise
evaluation of the measured data. An evaluation program
can be organized in dialog form so that the user can receive
intermediate results over the teletype and can be questioned
E I N cCH>.
D I E Z E I C H N U N G MIHD 1 0 . 1 6
Fig. 6. Example of a programmed dialog: By typing the command “R DATPLT” the user
starts a program for plotter representation of a spectrum which was measured on-line; he
specifies necessary parameters in a dialog with the program. (For clarity, all user responses
appear underlined.)
4.4. Organization of Real-time Data Acquisition
The dynamic time-sharing operation enables on-line and
off-line jobs to be run simultaneously. For the real-time
data acquisition a common data-job is needed for all
“slow” instruments and one data-job for each active “fast”
instrument. These are programs which essentially contain
data buffers for the individual instruments. The individual
data are read in by the computer on one of the interrupt
levels, so that the running programs are only interrupted
for several microseconds. As long as instruments are
actively transmitting data, the corresponding data-jobs
must remain in the core, i. e., they may not be moved out
to the disk during monitor swapping operations. This
feature and a preferential allocation of computing time
distinguish the data-jobs from the other user programs.
For the “slow” instruments the data are transmitted bufferwise to the disk without any pre-processing ; separate data
sets are used for each device. For the “fast” mass spectrometers a pre-reduction of the data is carried out by the
data-jobs; only reduced data reach the disk.
After the stop command the data belonging to each
instrument are further processed by analysis programs
(which run as separate jobs). If several instruments (for
example a group of gas chromatographs) use the same
analysis program, then this program can be initialized
as to further steps in the evaluation. The individual steps
of the evaluation can also be carried out with several
sequentially callable programs. According to the intermediate results the user can decide freely which programs
to use for further processing. For example, for a molecular
spectrum, procedures for smoothing and for improving the
resolution, peak searching algorithms, and so on, could
be used in any sequence depending on the results of the
experiment. The freedom of the user is not affected in any
way by other users who are working with the computer at
the same time-apart from the competition for common
peripheral units such as line printers and plotters.
This high degree of flexibility is not only advantageous but
necessary for analytical laboratories in a research institute
with frequently changing analytical problem^[^*^]. However,
a standard program can still be used for certain routine
analyses with fixed evaluation procedures. This program
needs no parameter input and supplies the final result in the
form of a report on the teletype.
The time-sharing mode of operation proves especially
advantageous in the development and check-out of new
programs. As an example, new evaluation programs can
be tested out without the danger of disturbing other users.
With text editors it is possible to modify programs over the
teletype and to immediately try out the corrected programs
-without the long turn-around times associated with batch
Angew. Chem. mlernat. Edit. 1 Vol. I I (1972) No. 5
systems. This direct contact between the programmer and
the computer has considerably accelerated the development
of programs for on-line applicatjon.
major portion of the software for on-line applications.
Members of most of the analytical groups of the Institute
arealso involved to some extent with program development.
4.6. Current State and Reliability of the
Miilheim System
Good teamwork between the computer personnel and the
analysts proved to be an essential prerequisite for the
successful construction of the system. Cooperation is also
necessary with the electronics enginers to ensure troublefree connection of analyticai instruments.
So far, 23 gas chromatographs, an NMR spectrometer, an
IR spectrometer, a spectral polarimeter (“Cary 6 0 3 an
ESR instrument, and a slow mass spectrometer are connected uia the “slow” A/D converter; a fast-scan mass spectrometer and a pulsed NMR instrument are connected through
the “fast” A/D converter.
Of the currently used computing capacity (in 24 hour operation 20 to 25%) almost 90% are off-line calculations and
only about 10% are for the acquisition and processing of
on-line data.
Off-line programs requiring more than 28 K of core must
run at night, i. e. between 5 p. m. and 8 a.m. One reason for
this is that they would cause an unreasonable amount of
swapping activity during daytime operation ; a second
reason is that for very large programs the amount of core
left free by the resident monitor (presently 41 K) is not
sufficient, so a special operating system must be loaded.
The reliability ofthe operating system has increased through
continual improvements in the course of time, so that
practically no software crashes occur any more.
However, there are still occasional hardware failures that
usually result in down-times of an hour to one or two days
(maximum to date).
4.7. Disadvantages of the Miilheim System
A large computer system such as the Miilheim system is
always unflexible if changes are necessary in the very complex operating system. Besides the interrupt routines for
the real-time data acquisition, all the controlling routines
necessary in real-time for a connected instrument must be
present as subroutines in the operating system. For this
reason it is impossible to provide for real-time control of
cases in which the operating system would have to be
changed too frequently because of changing experimental
requirements. AdditionaIIy, the “book-keeping’’ cost of
real-time routines in a time-sharing system is substantial.
In particular, however, no real-time experiments that run
over very long periods, for example several days, should be
connected to a large system; the normal operation can be
interrupted not only by regular maintenance work, but
also by unforeseeable system failures. For this reason no
attempt was made to have the Institute’s automatic X-ray
diffractometer controlled by the PDP10i6].
4.8. Personnel Requirements
The Miilheim computer installation is run by a physicist,
a mathematician, two programmers, an operator, and a
maintenance engineer. This group also developed the
Angew. Chem. internal. Edit. 1 Vol. 11 11972) 1 NO. 5
5. Comparison of Computer Systems
for Chemical Research
Since most research laboratories have access to a large
computing center where off-line programs can be run, the
main interest is usually focused on the purchase of an
on-line system (seehowever Sections 5.6 and 5.7). The scopes
of the various types of on-line systems have already been
discussed in Section 3. It is, however, fitting to consider
once more the advantages and disadvantages of small
dedicated systems and Iarge mixed systems.
5.1. Programming
The parts of programs for real-time data acquisition and
possibly real-time control are easier to develop and in most
cases also easier to modify in dedicated systems than in
large ones with complicated operating systems.
On the other hand, the analysis programs are simpler to
produce in large systems because they can usually be written
in a high-level programming language such as FORTRAN.
Programs for debugging and text editing are available for
fast program modification as well as labor-saving peripheral
devices (listings, copying programs). (See also Table 2.)
5.2. Computing Capacity
For some evaluation procedures (for example in mass
spectroscopy) the greater computing power and larger
storage capacity of a large system are desirable and sometimes also essential. In such cases the use of small systems
is often limited to pure data acquisition or limited preprocessing, so that the stored data must be evaluated later
off-line in a computing center.
5.3. Flexibility
As already emphasized elsewhere, a large mixed system
which makes possible a conversational time-sharing mode
is in many respects more flexible for the user than a dedicated system.
This holds for the programming as well as for the handling
of data. The possibility of modifying programs without
great difficulty and adapting them to new demands is
especially important for laboratories with frequentIy
changing tasks.
Table 2. Programming of on-line systems
Dedicated systems
1. one instrument
per computer
2. variable-purpose
dedicated system
Real-time data acqulsition
and processing
very simple (no overlapping
of different analytical
Testing and editing of
evaluation programs
troublesome (normally
done in assembly
Flexible use of different
evaluation programs
possible with extensive periphery
difficult (small memory,
few testing aids, program
3. several instruments of
the same type per computer
simple (but possibly complicated scanning algorithms)
very troublesome
(assembly language,
several instruments)
Multi-method systems
difficult (timing correlation)
very difficult (assembly
language, different analytical methods)
very tedious (a change for
one method influences all
the others)
Mixed systems
very difficult (implementation within a complete
operating system); timesharing operating system
from the manufacturer is a
very simple (no influencing
of other users, fast work
with text editors, effcient
testing aids, ease of use
because of extensive periphery)
Satellite systems
simple for dedicated satellites, but conflicts with
operating system possible
very simple (FORTRAN, no overlapping
of evaluation programs
of different instruments
or of data acquisition
parts, complicated evaluation procedures can
be employed, access to
extensive banks of data)
In contrast, dedicated systems are more flexible in their
hardware composition. They are therefore better suited
for laboratories tending to experiment with hardware.
5.4. Maintenance and Operation
No maintenance personnel is normally required for a dedicated system and the user need not make allowances for
other users. Small systems are also usually more reliable
than complicated large systems.
Although failures are more frequent with large systems,
they usually do not last so long since a maintenance engineer
is invariably close at hand.
5.5. Laboratory Organization
Only dedicated systems come into question for small, individual laboratories. Also laboratories with several analytical instruments but only infrequent analyses can work
extremely simple (because of
possibility of time-sharing
dialogs!), stepwise evaluation
possible depending on intermediate results
with a dedicated system connected to one instrument at a
time depending on requirements (standard interface essential !). Such a “multi-purpose’’ small-computer system,
which might be transportable between laboratories, is
loaded with a different programming system according to
the particular analytical instrument connected to it. “Interpreter” languages (BASIC, FOCAL, etc.) or languages
especially developed for analytical methods can be used
for a relatively simple data evaluation.
However, for larger laboratories or for a number of neighboring small laboratories the advantages of a large computer system cannot be ignored.
5.6. The Decision to Buy
The decision to buy a small system is easier to make because
of the lower costs and the corresponding lower risks. The
purchase of a large system may require the collaboration
of many interested parties. Any agreement must be based
not only on financing, type, and size of the system to be
Table 3. Management considerations concerning on-line systems.
Dedicated systems
I. one instrument per computer
2. variable-purpose dedicated
3. several instruments of the same
type per computer
Typical price (DM)
Decision to buy
Operational costs
(low costs, low risk, no organizational difficulties,
fast operational capability)
Multi-method systems
400000-1 500000
not so easy
(the mutual interests of several parties must be met,
limited system efficiency)
Mixed system
2 000 000
Satellite systems
3 000000
(high costs, many parties concerned, possible remaintenance engineer and
organization or merging of labs, time-consuming
planning and development, consideration of existing computer centers, company politics, or national necessary
motives concerning computer manufacturers)
Angew. Chem. internat. Edit. 1 Vol. I 1 (1972) 1 No. 5
purchased, but also on the later organization and manner
of operation (see Table 3).
In many cases existing computing centers hinder the purchase of a large mixed system. However, it is often overlooked that many of the existing computer installations,
even without scientific or chemical applications, are running
near capacity or will be within a few years. Moreover, at
least in the industrial area, the computing centers are
normally oriented toward commercial applications. Scientific and technical applications, for which other types of
computers and other forms of organization of computing
operation are more suited, often appear as intruders.
5.7. Future Developments
Large mixed systems are desirable not only because of the
requirements of data acquisition and processing for the
directly connected analytical instruments : As previously
mentioned, the early developments of computer programs
for the support of the preparative chemist, the implementation of documentation systems, as well as continuously
improved methods of interpretation in spectroscopy stimulate the purchase of large computers for the field of chemical
research. Moreover, since many documentation systems
and complicated evaluation procedures utilize the data
sets from on-line systems, the most intimate possible
the mixed system optimally offers-of
on-line and off-line systems is desirable.
Because of the relatively low level of exploitation of a large
system by on-line tasks alone, such a system becomes
economical only with the inclusion of several intensive
off-line computations. A simiiar degree of computer usage
could be attained by using the computer for training
Received: November 18,1971 [A 868 IE]
German version: Angew. Chem. 84, 371 (1972)
Translated by Allan B. Wilson, Miilheimpuhr
[I] E . J . Corey and W T: Wipke, Science 166, 178 (1969).
[2] E. Ziegler, Pittsburgh Conference on Analytical Chemistry and
Applied Spectroscopy, Cleveland 1969 ; E . Ziegler, D. Henneberg, and
G . Schomburg: Pittsburgh Conference on Analytical Chemistry and
Applied Spectroscopy, Cleveland 1970.
[3] E . Ziegler, D.Henneberg, and G . Schomburg, Anal. Chem. 42, 51A
Aug. (1970).
[4] G. Schomburg, F . Weeke, B. Weimann, and E. Ziegler: 8th Internat.
Symposium on Gas Chromatography, Preprints, Paper 15; G. Schoniburg, F. Weeke, B. Weimann,and E . Ziegler,Angew. Chem. 84,390 (1972):
Angew. Chem. internat. Edit. 11, 366 (1972).
[ 5 ] D . Henneberg, K . Casper, B. Weimann, and E. Ziegler, Angew.
Chem. 84, 381 (1972); Angew. Chem. internat. Edit. 11, 357 (1972).
[6] C . Kruger, Angew. Chem. 84,412 (1972); Angew. Chem. internat.
Edit. 11, 387 (1972).
Computer-Aided Analysi's of Organic Mass Spectra
By D. Henneberg, K. Casper, E. Ziegler, and B. Weimann"]
1. Introduction
After introduction of the sample into the spectrometer,
mass spectrometric analysis may be divided into three
phases : Measurement of one or more spectra; evaluation
or work-up of the data; and finally interpretation with a
view to answering the particular question of the analysis.
Evaluation means determination of the masses present
und their relative intensities as well as determination of
metastable ions with the assignment of their possible
origins. Data work-up refers to correction of spectra by
averaging and/or background subtraction and also the
choice of the most suitable representation for the information, i. e. bar-graph spectrum, table, mass chromatogram,
or element map. The last step, that of interpretation, involves identifying molecular fragments, hetero-atoms, and
structural elements responsible for the observed peaks, as
well as the recognition of mixtures. It requires further
quantitative determinations on mixtures or isotopically
labeled compounds and identification or classification by
comparison with calibration spectra.
[*] Dr. D. Henneberg, K. Casper, Dr. E. Ziegler, and B. Weimann
Max-Planck-Institut fur Kohlenforschung
433 Miilheimpuhr, Kaiser-Wilhelm-Platz 1 (Germany)
Angew. Chem. internat. Edit.
Vol. I 1 (1972) 1 No. 5
We wish to demonstrate with a few examples how the use
of a computer system can effectively support all three
phases of mass spectrometric analysis. In order to be able
to show the impressive advantages of computer use, especially in the measurement of spectra, we would first like to
give a few illustrations of the possibilities of mass spectrometric analysis with special emphasis on the more recent
instrumentation and methods.
Three techniques have made the application of mass spectrometry particularly interesting, and in some cases indispensable, in the analysis of organic compounds.
1. The combination of a gas chromatograph (GC) and a
mass spectrometer (MS) is of particular value in the analysis
of mixtures of easily vaporizable compounds. In this technique the eluate from a GC is continuously analyzed by
mass spectrometry. In the course of a chromatographic
analysis it is possible to obtain the mass spectra of all
resolved components (see Fig. 4). It is assumed that the
spectra are recorded rapidly so that distortion due to
changes in the partial pressures is minimized.
2. The direct vaporization of samples having low vapor
pressures results in a considerable increase in the types of
analyzable compounds. Modern mass spectrometers allow
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