'
...
(J
.J
Submitted
to
Journal
of
Chromatographic
Science
LBL-5411
Preprint
C',
J
REAL-TIME
ANALYSIS
OF
GAS
CHROMATOGRAMS
WITH
A
MICROCOMPUTER
SYSTEM
G.
M.
Bobba
and
L.
F.
Donaghey
July
1976
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LAnORATORY
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1 9
1976
LIBnf.'.RY
AND
DOCUMENTS
SECTION
Prepared
for
the
U.
S.
Energy
Research
and
Development
Administration
under
Contract
W
-7405-ENG-48
For
Reference
Not to
be
taken from this room
-
DISCLAIMER
This document was prepared
as
an account
of
work sponsored by the United States
Government. While this document is believed to contain correct information, neither the
United States Government nor any agency thereof, nor the Regents
of
the University
of
California, nor any
of
their employees, makes any warranty, express or implied, or
assumes any legal responsibility for the accuracy, completeness, or usefulness
of
any
information, apparatus, product, or process disclosed, or represents that its use would not
infringe privately owned rights. Reference herein to any specific commercial product,
process, or service by its trade name, trademark, manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation, or favoring by the
United States Government or any agency thereof, or the Regents
of
the University of
California. The views and opinions
of
authors expressed herein do not necessarily state or
reflect those
of
the United States Government or any agency thereof or the Regents
of
the
University
of
California.
'
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60
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9
7
Real-Time
Analysis
of
Gas
Chromatograms
with
a
Microcomputer
System
.G.
M.
Bobba
and
L.
F.
Donaghey
LBL-5411
Materials
and
Molecular
Research
Division,
Lawrence
Berkeley
Laboratory
and
Department
of
Chemical
Engineering,
University
of
California,
Berkeley,
California
94720
July,
1976
Abstract
The
real-time
performance
of
a
microcomputer
system
designed
for
dedicated
control
of
gas
chromatography
and
real-time
analysis
was
studied
to
determine
operating
characteristics
and
accuracy
of
the
peak-area
integration
algorithm.
The
software
program
developed
to
obtain
peak
areas
used
statistical
criteria
for
the
detection
of
the
start,
maximum
value,
and
end
of
a
chromatographic
peak.
The
accuracy
of
the
system
was
tested
with
propane-helium
mixtures
and
by
comparison
to
results
obtained
with
off-line
data
reduction.
The
study
showed
that
the
real-time
microcomputer
system
gave
peak
areas
which
were
lower
than
the
off-line
results
by
less
than
0.6
percent.
The
difference
was shown
to
arise
from
truncation
error
in
the
double-precision
octal
mathematical
subroutines,
and
to
error
in
the
assignment
of
a
baseline
at
the
peak-end.
•
0
~"J.
f,
6
u
8
-1-
Introduction
During
the
past
twenty
years
the
gas
chromatograph
has
evolved
extensively
as
an
analytical
device
~or
the
chemical
industry.
Since
the
development
of
the
computer,
many
types
of
computer-assisted
chromatographs
have
been
developed
to
analyze
and
reduce
gas
chromato-
graphic
data,
and
to
control
the
operation
of,the
instrument.
Quantitative
gas
chromatography
depends
ultimately
upon
the
accuracy
of
chromatographic
peak-area
measurements,
from
which
the
concentrations
of
components
present
in
the
sample
can
be
determined.
The
problem
is
compounded by
signal
noise
and
baseline
drift.
Inaccuracies
in
the
determination
of
the
start
and
end
of
each
chromatographic
peak
are
significantly
affected
by
these
problems.
Computer
systems
for
chromatography
which
are
on-line
offer
advantages
of
rapid
chromatogram
reporting
and
low
operator
assistance.
Electronic,
analog,
and
hybrid
integrators
have
been
developed
for
automatic
peak-area
integration
[1].
While
these
methods
are
low
in
cost,
they
are
often
limited
in
performance
and
are
inherently
inflexible
[2].
Computing
integrators
rely
on
noise
filtering
of
the
detector
signal
to
decrease
the
error
in
assigning
the
peak
baseline.
In
that
approach
the
filter
characteristics
must
be
fixed,
whereas
an
optimum
noise
filtering
involves
a
trade-off
between
the
peak
resolution
and
the
signal
slope
resolution,
so
that
baselines
are
frequently
assigned
improperly.
The
minicomputer
has
also
been
utilized
for
the
on-line
analysis
of
chromatograms,
with
the
variety
of
conceptual
approaches
and