SEPA
United States
Environmental Protection
Agency
Environmental Monitoring and Supports
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S4-82-017 June 1982
Project Summary
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i'
t.
The Standard Calibration
Instrument Automation
System for the Atomic
Absorption Spectrophotometer
Dennis P. Ryan
The Environmental Monitoring and
Support Laboratory-Cincinnati (EMSL-
Cincinnati) has, as part of its mission,
the development of enhanced data ac-
quisition and reduction systems which
provide high quality analytical data
from environmental samples. The
standard calibration instrument auto-
mation system for the flameless
atomic absorption instrument sup-
ports this mission in the area of metals
analysis. This paper summarizes the
capabilities of the system and directs
the reader to other documents which
fully explain the related hardware.
software, and user environments.
This Project Summary was deve-
loped by EPA's Environmental Moni-
toring and Support Laboratory, Cin-
cinnati, OH, to announce key findings
of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The standard calibration instrument
automation system for the flameless
atomic absorption instrument is part of
the EPA laboratory automation system.'
This system utilizes a Data General
NOVA 840 minicomputer with an
extended BASIC Language which is
modified to allow for real time data
acquisition in a multiuser, time sharing
environment.2 The instruments in-
volved are commercially available and
may vary considerably in relation to
their output.
The instrument standard calibration
(ISC) system can be adapted to collect
and process data from a variety of
instruments including single or double
beam systems, with or without back-
ground correction, and sequenced
through manual injections or in concert
with an automatic sample device.2
Interfacing with microprocessor based
"intelligent" instruments has also been
implemented with this system.3 The
system provides for the following
functions:
• calibration using regression or inter-
polation,
• plotting of calibration curves,
• determination of concentrations,
• quality control assessments in real
time for spiked samples, duplicate
samples, laboratory control stand-
ards, laboratory reagent blanks,
and instrument check standards,
• compensation for dilution,
• reagent blank subtraction,
• editing of suspect results,
• remeasurement of questionable
samples,
• printing of progress reports and
final reports,
• bidirectional communication with
the EPA national Sample File Con-
trol data base,
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• checking the instrument and inter-
face hardware, and
• plotting of raw data when applic-
able.
The system can also operate in an
unattended mode when an automatic
sampling device is available.
The system has been successfully
implemented on a number of direct
asperation instruments, and may be
adapted to TOC and UWIS applications.
The following paragraphs describe
the major features of the system and
reference the three volumes of a
complete report which can be obtained
from the EPA.4'5'6
Nature of the System
The ISC system is a command struc-
tured single analyte standard calibra-
tion system, in concert with an appro-
priately interfaced FlamelessAA instru-
ment, the ISC system may be used for
measuring metal concentrations in
environmental samples. It has discrete
measure/edit capabilities or it can be
used to analyze a set of samples auto-
matically. It has applications in both
research and production environments
and can be used in conjunction with the
EPA Sample File Control System7 or as a
stand-alone automation system.
The ISC system may be adapted to
other instrument systems which pro-
duce a response which varies linearly
with the presence of an analyte (as in
total organic carbon analyses).
Data Acquisition
The ISC system may easily be adapted
to acquire instrument response data of
the following types: 1) fast (60 Hz)
analog signals from single or double
beam instruments, 2) serial ASCII char-
acter data transmitted through EIA-
RS232C compatible interfaces, or 3)
manually entered data via a terminal
keyboard.
When the analog-interfaced instru-
ments are used, the system utilizes
analog to digital (A/D) converters and
related system software2 to translate
the incoming signal into a series of dig-
itized numbers. This data array is then
processed through a software module
which quantifies the peak absorbance
value of the measurement. Figure 1
shows an example plot of the peak
absorbance data array.
Many newer instruments are capable
of accurately producing a fully reduced
absorbance value and outputting this
result via a string of ASCII characters.
F-U R H ft C-E P-6-ft-K D-*-T-A P-L-O-T
PLOTTED* 5/20S1980 - 13'53-28 RAN> I/ & 0 - 9-33
PEAK HO- 19 TYPE' SPIKED UNKNOWN HHL PCS' 1?
.64SB
.6600
.6750
.6980
.7050
.7200
.7350
.7500
.7650
.7800
.7950
.8100
50
100
150
200
290
Figure 1. Example peak plot.
These instruments require interface
hardware which can receive and store
the ASCII characters. Ths ISC system
utilizes an ASCII Character Buffer inter-
face3 for this purpose. Instrument data
may be buffered in this device for subse-
quent use by the data acquisition
module. The software "reads in" a
string of data and extracts the absor-
bance value contained within.
In situations where the interface
hardware and software are not easily
available, the ISC system maybe used in
the manual data entry mode. After key-
board data entry, the analyst is still able
to use the computational, quality as-
surance, and reporting capabilities of
the system.
Calibration and Plotting
The system is capable of accumulat-
ing absorbance measurements on in-
strument calibration standards and
generating regression equations relat-
ing absorbance to known concentration.
Any number of standards maybe identi-
fied in the sample wheel pattern and their
order is unrestricted. As many as six
replicate measurements may be made
on a given calibration standard and all
replicates will be used in the subse-
quent regression. The system will auto-
matically perform the regression on the
standards in an automatic sequence
and it will produce one or more equa-
tions during the process. Forced-zero
linear, regular linear, quadratic, and
cubic equations and their correspond-
ing fitting errors will be formed for a
given set of standards unless the
number of standards prohibits higher
order equations.
After a successful calibration is
formed, all subsequent absorbance
measurements will result in the display
of sample concentration using the cur-
rent computational mode.
The user may change the computa-
tional mode at any time without neces-
sitating a recalibration. The user will
also have the opportunity to edit poor
standard measurements and recali-
brate the remaining standards during
post-run processing.
The ISC system is configured in such
a way as to allow the user to view the
calibrations curves after regression has
been performed. Figure 2 illustrates an
example calibration curve. These curves
are generated to an appropriate gra-
phics terminal at the request of the ana-
lyst. An automatic run will continue
during the curve generation process. At
the completion of the run, the analyst
may use the data gained from the plots
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to selectively edit the standard data and
recalibrate, or he may select another
computational mode to calculate con-
centrations and generate an updated
run status report.
Quality Control
Quality control assessments are pro-
vided seconds after the related samples
are measured. Spiked samples, dupli-
cate samples, laboratory control stand-
ards, and reagent blanks are all auto-
matically evaluated against limits
provided by the Sample File Control Sys-
tem (as described below) or by the ana-
lyst. Instrument check standards are
automatically assessed against limits
provided by the analyst.
In addition, all non-standard samples
receiving multiple replicate measure-
ments will cause the ISC system to
supply a mean and standard deviation of
the computed concentrations. This will
assist greatly in those cases where pre-
cision is a problem.
Compensation for Dilution
Dilution information is taken into
account so that the system reports true
concentrations. Samples which exhibit
instrument responses above the high-
est calibration standard are flagged as
off scale and the analyst is given the
opportunity to dilute the sample and
remeasure it. Sample information may
be easily modified to purge old absor-
bance data and install new dilution
volumes prior to the remeasurement of
the sample.
Spike volumes and concentrations
are considered along with dilution
volumes in order to compute concentra-
tions and recoveries with a high degree
of integrity. A special feature is avail-
able for spiked samples so that negative
spikes may be made. (This is sometimes
called spiking by successive dilution and
should not be confused with the
Method of Standard Additions.8)
Reports
The ISC system produces a variety of
reports at various stages of the run.
Before the run begins, a wheel pattern
report may be generated. During the
run, an on line report is generated to the
user terminal after each sample is mea-
sured. After regression is performed, a
calibration report is generated to the
selected output device(s). After a run
has been completed a status report is
generated to the selected output devices.
A "final report" is also available to the
analyst after all post processing is com-
pleted as shown in Figure 3.
C-JH.-I-B-R A T-I-O-N CHJ-R-U-E
OPERATOR' DPR INSTRUMENT' GF|g_RH 33
ANALYTE' XX RAN' 9S2B/199B PLOTTED- 9x20/1960
DEGREE- 1 FITTING ERROR- 3.71 X
CONCENTRATION - -1.63E-01 +3.49E+02 »
A
B
S
0
R
B
A
N
E
40 38 CO 78
CONCENTRATION IN UG/t.
80
100 110
Figure 2. Example calibration curve.
FLAMELESS AA
INSTRUMENT: PE5000
ANALYST: TLK
UNITS: MG/L
STANDARD CALIbRATION FINAL REPORT
NM464
PARMETH CODE: 2134UU1
WHEEL SAMPLE
POS
9
10
11
IS
13
11
Ib
\b
17
IB
19
20
21
IDENTIFIER
LR6
81-06542 LU1
(Jl-0t>b43
81-06b44
•U-UfebUb
rtl-ufa5«b
91-06b47
dl-0t>548
4i-ue549
61-0bb50
81-06551 LSO
bl-06b51 LSe
81-ob542 L02
SAMPLE
CONCENTRATION
+3.&12E-03
+.B3281
+. 124872
+.101642
+1.1716-03
+3.U12E-03
t'l.biae-03
+3.612E-03
+1.171E-02
+4.422E-02
+8.S17E-02
+ .b3
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unique combination of parameter,
method, preparation procedure, and
environmental source.
The system can also send back to the
Sample File Control computer a "run
results file" containing the measured
concentration of the samples and
related data.
Documentation
The ISC system is currently operating
reliably in a number of EPA Laboratories
but the conceptual framework of the
system is available to any laboratory
through the system specifications docu-
ment.4 This document contains project
definition, functional requirements, and
system design information. A second
document is available as a guide to sys-
tem usage.5 This manual is packed with
figures and examples to aid the user in
learning about or operating the system.
Finally, a detailed program description
document is available.6 This document
contains a flowchart, a variable descrip-
tion table, a program listing, and a sum-
mary description for each of the twelve
major BASIC programs in the system.
These documents do not fully describe
the instrument interface aspects of the
system.2'3
Conclusion
The ISC system is a flexible approach
to environmental analysis. It facilitates
increased production while performing
on-line quality assurance tests. It is user
oriented in that is minimizes superflu-
ous or redundant keyboard entry. And it
is laboratory conscious in that it devel-
ops "clean" final reports and supports
the interface with the SFC data base
management system. This system,
along with others developed at the
EMSL-Cincinnati, could extend labora-
tory budgets through increased produc-
tion, and improve laboratory evalua-
tions through increased production and
increased data quality.
References
1. The Status of the EPA Laboratory
Automation Project, W. L. Budde, et.
al., April 1977, EPA-600/4/-77-
025. Physical and Chemical Methods
Branch, Environmental Monitoring
and Support Laboratory, Environ-
mental Protection Agency, Cincin-
nati, Ohio.
2. Instrument Calls and Real Time Code
for Laboratory Automation, L. Taber,
et. al., June 7, 1978, Lawrence Liv-
ermore Laboratory Report No. UCRL-
52392.
3. A Computer Interface for a Perkin-
Elmer 5000 Atomic Absorption
Instrument, John M. Teuschler, et.
al., January 1980, Physical and
Chemical Methods Branch, Environ-
mental Monitoring and Support
Laboratory, Environmental Protec-
tion Agency, Cincinnati, Ohio.
4. The Standard Calibration Instrument
Automation System for the Atomic
Absorption Spectrophotometer Part
I - Functional Specifications, Dennis
P. Ryan, July 1981, Physical and
Chemical Methods Branch, Environ-
mental Monitoring and Support
Laboratory, Environmental Protec-
tion Agency, Cincinnati, Ohio.
5. The Standard Calibration Instrument
Automation System for the Atom-
ic Absorption Spectrophotometer
Part II - User's Guide, Dennis P.
Ryan, July 1981, Physical and
Chemical Methods Branch, Environ-
mental Monitoring and Support
Laboratory, Environmental Protec-
tion Agency, Cincinnati, Ohio.
6. The Standard Calibration Instrument
Automation System for the Atomic
Absorption Spectrophotometer Part
III - Program Documentation, Dennis
P. Ryan, July 1981, Physical and
Chemical Methods Branch, Environ-
mental Monitoring and Support
Laboratory, Environmental Protec-
tion Agency, Cincinnati, Ohio.
7. Design Specifications for the EPA
Sample File Control System, Frances
Fallen, November 10, 1980, Unpub-
lished Document, Computer Ser-
vices and Systems Division, Office
of Administration, Environmental
Protection Agency, Cincinnati, Ohio.
8. The Automation of Flameless Atomic
Absorption Spectrophotometers Us-
ing the Method of Additions - Func-
tional Specifications, Gregory S.
Roth, Physical and Chemical Methods
Branch, Environmental Monitoring
and Support Laboratory, Environ-
mental Protection Agency, Cincinnati,
Ohio.
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Dennis P. Ryan is with the University of Cincinnati Computing Center,
Cincinnati, OH 45220.
John M. Teuschler is the EPA Project Officer (see below).
The complete reports entitled:
"The Standard Calibration Instrument Automation System for the Atomic
Absorption Spectrophotometer,"
Part I - Functional Specifications (Order No. PB 82-187 832; Cost: $9.00)
Part II - User's Guide (Order No. PB 82-187 840; Cost: $10.50)
Part III - Program Documentation (Order No. PB 82-187 857; Cost:
$19.50)
The above reports will be available only from: (prices are subject to change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
6USGPO: 1982—559-092/3425
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Fees Paid
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Protection
Agency
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