EPA-670/4-75-005
ApriM975
Environmental Monitoring Series
-------
-------
EPA-670/4-75-005
April 1975
INVESTIGATION OF THE ORION RESEARCH CYANIDE MONITOR
By
Robert J. O'Herron
Methods Development and Quality Assurance Research Laboratory
Program Element No. 1HA327
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
REVIEW NOTICE
The National Environmental Research Center—Cincinnati
has reviewed this report and approved its publication.
Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
11
-------
FOREWORD
Man and his environment must be protected from the adverse effects
of pesticides, radiation, noise and other forms of pollution, and
the unwise management of solid waste. Efforts to protect the
environment require a focus that recognizes the interplay between
the components of our physical environment—air, water, and land.
The National Environmental Research Centers provide this multi-
disciplinary focus through programs engaged in
• studies on the effects of environmental
contaminants on man and the biosphere, and
• a search for ways to prevent contamination
and to recycle valuable resources.
This report is part of a continued effort by the Instrumentation
Development Branch, Methods Development and Quality Assurance
Research Laboratory (MDQARL), NERC-Cincinnati, to investigate
instruments and provide information to both users and suppliers.
The intention is also to upgrade instrumentation, and to make it
possible to choose the most suitable instrument for a particular
application.
A. W. Breidenbach, Ph.D.
Director
National Environmental
Research Center, Cincinnati
111
-------
ABSTRACT
The model 1206 Orion Research cyanide monitor was investigated
using the Orion specifications and environmental considerations as
a guide. This is one of the Series 1000 monitors manufactured by
Orion which duplicate laboratory analyses made with ion-selective
electrodes. The Series 1000 monitors perform single parameter
measurements of concentration, it is reported, and continuously
display the results on a panel meter and a strip chart recorder.
Sample pretreatment techniques are applied against an array of
interferences encountered in the use of ion-selective electrodes.
The cyanide monitor employs a silver/sulfide--sodium reference
electrode set in the indicator method to detect, continuously, the
level of cyanide in a sampled stream. Cadmium, copper, nickel,
and zinc complexes of cyanide are broken by two reagents added in
the fluids-chemical section. The breakdown of tightly bound
cyanide complexes of iron, cobalt, and platinum are not effected
by the addition of these reagents. Hydrogen cyanide (HCN) is
converted to the free cyanide ion for detection by the electrodes.
Laboratory tests under controlled environmental conditions showed
the electronic stability (drift) to be within 0.1% over the temper-
ature range of 5C to 35C. Sensor stability, over the temperature
range 5C to 35C was tested by applying free cyanide ion (standard
solutions of 1 mg/1 and 10 mg/1) as direct input to the monitors.
The results of these tests showed that Orion's specified tolerance
of ±10% of reading was met. Two out of three electrode sets tested
for linearity were within Orion's tolerance of ±0.02 ppm below 0.25
ppm and ±10% of readings above 0.25 ppm cyanide concentration.
Dynamic on-stream measurements were made from a metal plating pro-
cess rinse stream in a field installation of the monitor, and these
measurements were periodically compared with those of the standard
method for total cyanide. This field installation revealed the
comparisons were widely variable. Steady-state comparisons were
made of field-collected samples with the standard method for
determining total cyanide. These tests revealed that a 15% to 20%
loss in cyanide concentration resulted from the required straining
and filtering of the sample input to the monitor.
IV
-------
CONTENTS
Abstract iv
List of Figures and Tables v
Acknowledgments vi
Sections
I Conclusions 1
II Recommendations 4
III Introduction 5
IV The Orion Cyanide Monitor 8
V Laboratory Evaluation 11
VI Field Evaluation 17
VII Laboratory Tests with Field Sample 22
VIII References 24
FIGURES AND TABLES
Figure
Number
1 Series 1000 Monitors 8
2 Block Diagram of the Chemical Sensing Section 10
3 Preamplifier Output Voltage--CTA Temperature
Transistion from 45C to 30C 14
4 Fluid Connections to Monitor 17
5 Regression Line with 95% Confidence Limits for
the Mean Response 21
Table
Number
1 Ten Day Operation 11
2 Environmental Tests with Continuous Measurement
of Sample 13
3 Linearity and Lower Limit Detection of Cyanide
Standards 15
4 Comparison of Cyanide Monitor Field Installation
Data with Laboratory Analysis of Total Cyanide 20
5 Relative System Response with Varying Pressure
Input 22
6 Laboratory Test with Cyanide Waste Samples Col-
lected in the Field 23
-------
ACKNOWLEDGMENTS
We gratefully acknowledge the support and help of L. B. Lobring
(Physical and Chemical Methods Branch, MDQARL) in preparing stan-
dards and analyzing samples; P. P. Kovatis (of the Metal Finishers
Foundation) in securing industry cooperation to permit the monitor
to be installed on a cyanide waste stream; R. P. Lauch (instrumen-
tation Development Branch, MDQARL) for contributing suggestions
that helped in selecting hydraulic test apparatus; and T. J.
Stasiak and W. T. O'Connell (Orion representatives) for their
installation assistance and helpful suggestions throughout this
investigation.
VI
-------
SECTION I
CONCLUSIONS
1. Modification in components and procedures made by Orion during
the interval of this evaluation of the cyanide monitor indi-
cated the model tested was still in the prototype stage of
development.
2. Being in an early stage of production, some improvements in
quality control of components appear to be necessary.
3. Electronic drift at constant temperature (20C) was less than
0.1% for a 1-week interval.
4. Electronic drift over the temperature range 5C to 35C was
0.12%.
5. Sensor drift over the temperature range 5C to 35C was within
Orion's specified tolerance of ±10% of reading for cyanide
standards of 1 mg/1 and 10 mg/1. This occurs if the operation
is within Orion's framework: the constant temperature assem-
bly is maintained 5C above ambient temperatures of 25C and the
automatic restandardization has taken place after the tempera-
ture change.
6. Two of three electrode sets tested were within Orion's toler-
ance of ±0.02 ppm on concentrations below 0.25 ppm cyanide and
±10% of reading on concentrations above 0.25 ppm cyanide. The
other electrode set ranged slightly higher--to within 0.04 ppm
on concentrations below 0.25 ppm cyanide.
7. As a result of this investigation, Orion has had the instruc-
tion manual, which lacked clarity and depth, rewritten and
broadened in scope.
8. Data from the cyanide monitor installed in a field location
varied widely from the standard method determinations of total
cyanide. This variability was caused by:
a. an inability to maintain input pressure to the filter
at the recommended 15 to 20 psi: the strainer and
a throttling value clogged when the monitor was unat-
tended,
-------
b. a drop in cyanide concentration across the strainer
and filter,
c. an inability of the monitor to measure total cyanide,
and
d. the long delay (8 to 10 minutes with adequate pressure
input) of fluids in transit and of electrode response
dampened the abrupt and cyclic variations in cyanide
concentrations of the wastewater sampled. (Note:
Discussions with Orion personnel about problems en-
countered in maintaining suitable pressure input to
the filter has resulted in a new prefilter design.)
9. Steady-state tests with field samples showed that a 15% to 20%
loss in cyanide concentration occurred across the strainer and
filter.
10. Essentially all of the cyanide passing the filter was measured
by the monitor for these particular samples. (Note: This is
sample dependent.)
11. Response time to a change in cyanide concentration was a func-
tion of the sample input pressure.
12. As a result of the number of tests and the length of time
necessary to complete these tests, there were no long-term
tests made of the effectiveness of either the electrodes (4
month replacement) or the filter (1 month replacement).
13. The monitor does not measure iron, cobalt, platinum, gold, and
silver complexes of cyanide. Chlorine is a negative interfer-
ence. High levels of sulfide (10 mg/1 and above) cause a
positive interference and must be avoided. Orion continues
its research effort to counteract these interferences.
14. In summary, the cyanide monitor includes stable electronics
that performed very well over changing environmental condi-
tions. Ambient temperature should be controlled, not to
exceed 30C because high temperature reduces the life of the
electrodes. Fluids flow requires that the temperature be
controlled above OC. The reference voltage feedback techni-
que employed in the automatic restandardization approach is
clever; it is effective in compensating for the long-term
drift that's encountered in the use of ion-selective elec-
trodes. Application of the monitor should not be considered
-------
routine. Care and maintenance will be a continuing require-
ment. Qualified personnel, aware of sample characteristics
and monitor limitations, are required to interpret the data;
i.e., qualified chemists should perform periodic comparison
tests with the standard method for total cyanide. The monitor
measures some of the loosely bound metal cyanide complexes,
but not those which are tightly bound. The presence and the
effect of other interferences, e.g., chlorine and sulfide, on
the electrode signal output should be known.
-------
SECTION II
RECOMMENDATIONS
The Orion cyanide monitor does not measure total cyanide, and
problems were encountered with its use. However, the standard
method for measuring total cyanide cannot be performed rapidly,
unattended, inexpensively, continuously, or with few problems.
Each method performs capably in some category. Therefore, it is
recommended that the desirable qualities of each be utilized to
their fullest extent. The cyanide monitor cannot measure total
cyanide, but with care and proper maintenance, it can measure
some forms of the cyanide present in certain wastes. And Orion
is planning future improvements. At present, the cyanide monitor
can be used where continuous surveillance is required on wastes
suspected of having excessive cyanide. Dual set-point, high-
and low-alarm limits, included in the monitor, can be employed
to actuate a sampling device when a predetermined limit has been
exceeded. Thus, samples can be screened in the field so that the
time-consuming analysis of the standard method for total cyanide
can be expedited. If it can be shown that positive interfer-
ences are not present, gross violations of effluent standards as
indicated by a calibrated and functional monitor, should be use-
ful.
The Orion Series 1000 monitors are designed and developed to meet
needs of Industry. As a result of these developments, as in the
case of the cyanide monitor, these instruments could also be of
use to EPA procurements provided the application and performance
requirements are well defined.
-------
SECTION III
INTRODUCTION
Ion-selective electrodes developed within the past two decades
have been employed with instrument systems under favorable process
conditions for control purposes. Generally, these instruments were
utilized as indicators of gross process upsets. The mere presence
of a measured parameter could be indicative of a breakdown at some
point within a process. In these earlier process control applica-
tions of ion-selective electrodes, pretreatment of the sample has
primarily involved obtaining favorable pH and controlling the
temperature. These instrument systems measured sample parameters
under favorable process conditions and performed useful control
functions in industrial processes. That is, the uncomplexed, free
ion was measured in samples where interferences were known to be
minimal.
In recent years, several manufacturers have made a concerted effort
to use continuous monitors for concentration values of parameters.
Interferences encountered with the use of ion-selective electrodes
make it necessary to pretreat the sample in monitoring systems.
The interferences can be due to the sample itself or to the
measuring electrode and the reference electrode. Ion-selective
electrodes respond to the free, unbound ion, not the total concen-
tration of a chemical species. Increased use of ion-selective
electrodes in laboratory analyses over the years has resulted in
methods being developed to free bound ions so that concentrations
can be determined. Ions resulting in electrode interferences
must be either removed or avoided through chemical pretreatment
techniques. The amount and type of other ions in solution (ionic
strength)* affect the signal output of ion-selective electrodes.
The activity, a, of an ion is related to the concentration, C, by
the equation
a = YC (1)
where y is the activity coefficient, which is dependent upon the
total ionic strength of the solution. Ionic strength adjusters
(ISA) are available that when added to standardizing solutions and
samples, "swamp out" differences so that the activity coefficient
of the ion being sensed is about the same in all solutions.
The pH of the sample may also result in interferences: bound ions
-------
may be decomplexed at a favorable pH or interfering ions may be
preferentially complexed within a certain pH range. In addition,
either the hydrogen (H+) or hydroxyl (OH~) ions may be an elec-
trode interference. Therefore, sample pH adjustment is a usual
requirement.
The voltage output of ion-selective electrodes is characterized by
the Nernst equation at constant temperature.
E = E° + (0.19841T/n) log a. (2)
The variation as a result of temperature change is described by
T. S. Light.2
dE/dT = dE°/dT + (0.19841/n) log a. +
(0.19841T/n)(d log a^dT) (3)
Sample temperature affects not only the Nernstian slope term
[(0.19841/n) log ajj , but also the "solution temperature coeffi-
cient" term [0.19841T/n)(d log ai/dT)]. Light has discussed the
solution temperature coefficient term:
"The activity of an ion may be affected by its
activity coefficient and for weak or complex
forming electrolytes by its equilibrium rela-
tionships. Since activity coefficients and
equilibrium constants may each have tempera-
ture coefficients of their own, the 'solution
temperature coefficient' term may become quite
complex."
Because temperature compensation techniques normally correct for
the Nernst slope term only, temperature control of the sample is
generally selected by Orion. Sample color and turbidity do not
interfere with the voltage relationships in the use of ion-
selective electrodes. Filtering is necessary, however, to combat
clogging of tubing or fouling of electrodes.
In regard to reference electrodes, Orion has stated, "Our experi-
ence over the past several years has shown that most of the
problems that users of specific ion electrodes have reported to
us are directly traceable to the liquid junction in the external
reference electrode."3 Requirements for 0.1 to 0.2 mv accuracy
-------
for 1% to 2% ion activity, as opposed to approximately 6 mv to
obtain 0.1 pH unit accuracy, were indicated. These tougher re-
quirements for specific ions have led Orion to advise using a
second specific ion electrode,4 as a reference electrode--one
whose level can be kept constant.
-------
------- |