EPA-R2-73-254
JUNE 1973 Environmental Protection Technology Series
Polarographic
Determination of NTA
National Environmental Research Center
Office of Research and Monitoring
US. Environmental Protection Agency
Corvallis, Oregon 97330
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
-------
EPA-R2-73-254
June 1973
POLAROGRAPHIC DETERMINATION OF NTA
by
Thomas B. Hoover
Southeast Environmental Research Laboratory
College Station Road
Athens, Georgia 30601
Project 16020 - EWE
Program Element 1B1027
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price 75 cents domestic postpaid or 50 cents QPO Bookstore
-------
ABSTRACT
Pulse differential polarography was found to be a more
sensitive and precise method "than linear sweep voltam-
metry for the determination of UTA as the bismuth-
complex in natural and waste waters. % Itidium was a less
satisfactory complexant. Relative standard deviations
of less than 5% were obtained by the dual cell, pulse
differential technique at 1 ppm NTA and calibrations
were linear from 0.01 to 4 ppm. Copper, added at con-
centrations greater than 10-5 M, caused low analytical
results for NTA. No other significant interference by
metals or complexants was found. An acetate electro-
lyte was much better than chloride for the determination
of bismuth-NTA complex in sewage-type samples. Recom-
mended procedures are given in the Appendix.
ii
-------
CONTENTS
Page
Abstract ~~iT~
List of Figures iv
List of Tables v
Acknowledgments vi
Sections
I Conclusions and Recommendations 1
II Introduction 2
III Experimental 4
Instrumentation
Indicator Choice
Indium Complexation
Bismuth Complexation
IV Results and Discussion 14
Instrument Evaluation
Indium
Bismuth, Chloride Medium
Bismuth, Acetate Medium
V References 39
VI Appendix 43
111
-------
FIGURES
No. Page
1 Excitation Waveform for Pulse Differential
Technique 5
2 Determination of the Indium-NTA Complex in
Sewage Effluent by Pulse Differential 6
Polarography
3 Determination of the Bismuth-NTA Complex in
Seawater by Pulse Differential Polarography 24
4 Copper and Bismuth-NTA Waves by Linear Sweep
Voltammetry 25
5 Effect of Sewage Effluent on the Bismuth-NTA
Polarographic Wave in Chloride Electrolyte ^7
6 Calibration Curves for the Determination of
the Bismuth-NTA Complex — Chloride
Electrolyte 28
7 Determination of the Bismuth-NTA Complex in
Distilled Water by Dual Cell Pulse Differen-
tial Polarography 34
8 Determination of the Bismuth-NTA Complex in
Distilled Water by Dual Cell Pulse Differen-
tial Polarography 35
9 Differential Pulse Polarographic Estimation
of NTA in Raw and Treated Municipal Sewage 36
IV
-------
TABLES
No. Page
1 Effect of pH on the Polarography of In-NTA
in 0.2 M Sodium Chloride
10
2 Calibration Runs for the Determination of
NTA as the Indium Complex ^ 17
3 Recovery of NTA in the Presence of 5 x 10~5
M of Fe, Mn, Cu, or Bi 19
4 Recovery of In-NTA in the Presence of Metals
and Complexants 20
5 Calibration Runs for the Determination of
NTA as the Bismuth Complex in Chloride
Electrolyte 23
6 Calibration Runs for Bi-NTA in Chloride
Electrolyte—Sewage Effluent and River Water 29
7 Calibration Runs for the Determination of
NTA as the Bismuth Complex in Acetate
Electrolyte 31
8 Recovery of Bismuth-NTA in the Presence of
Metals and Complexants in Acetate
Electrolyte 38
v
-------
ACKNOWLEDGMENTS
Most of the experimental work was performed by George
D. Yager, whose initiative led to the development of the
acetate procedure.
Sydney H. Young assisted with the studies on indium.
VI
-------
SECTION I
CONCLUSIONS and RECOMMENDATIONS
Nitrilotriacetic acid (NTA) was determined with a
standard deviation of 3 ]ag/& in natural and waste waters
as the bismuth complex using dual-cell pulse differen-
tial polarography.
*
Indium was a less satisfactory complexant than bismuth
for the determination of NTA.
An acetate electrolyte gave better results in sewage
type samples than a chloride electrolyte. The acetate
electrolyte is therefore recommended for the polaro-
graphic determination of NTA in natural waters and
waste waters containing less than 0.1 percent chloride.
A chloride electrolyte is recommended for saline samples.
Analytical procedures for both are given in the Appendix.
Linear sweep (LS) voltammetry was a more rapid analyti-
cal technique than pulse differential (PD) polarography/
but was less sensitive. Dual cell PD is therefore
recommended for analyses in which the greatest sensi-
tivity and precision are required. Dual cell LS is
recommended for routine and repetitive analyses when the
highest precision is not needed.
The effects of possible interference by metal ions and
complexants were evaluated. Copper at concentrations
greater than about 1 mg/& may lead to low results for
NTA.
Linear calibration curves for the determination of NTA
were obtained for the concentration range of 0.01 to
4.0 mg NTA/I, according to the recommended procedures
in the Appendix.
-------
SECTION II
INTRODUCTION
Nitrilotriacetic acid (NTA) was used briefly as a
builder in laundry detergents, partially replacing
polyphosphate. The high degree of biodegradability of
NTA makes its use attractive, especially in regions
where detergent phosphates contribute materially to
eutrophication. On the other hand, the potential health
hazards of NTA in the environment that have led to a
moratorium on its use (1) dictate that reliable analy-
tical methods should be available for monitoring the
build-up of NTA in the environment should commercial
use be resumed.
Many analytical methods for NTA have been developed,
most of which utilize complexation with metals for the
separation or determination. Colorimetric methods have
been based on the measurement of Fe(III) (2), Cu(II)
(3), or Zn(II) (4,5) with appropriate color reagents.
Swisher (2) separated NTA as the Fe complex, together
with any other soluble Fe complexes, decomposed the
complexes, and determined the resulting Fe. The other
authors above measured the excess metal ion after
reaction with complexants in the sample. Consequently,
these methods are not specific for NTA unless elaborate
separation procedures are used. The zinc-zincon colori-
metric procedure (5) has been automated to provide
rapid analyses with relative standard deviations of
2-10% in the concentration range 0.1 to 10 mg NTA/&.
However, several metal ions cause negative interference,
sewage-type samples give high results, and the method
is not applicable to saline waters.
The Cu-NTA complex has been employed analytically, with
a copper-ion selective electrode as the detector (6,7).
Like the colorimetric procedures, this technique lacks
specificity but it is especially suitable for continuous
monitoring (6) or for complexometric titrations (7).
Methods employing gas chromatography (gc) (6,8,9,10)
determine NTA directly as a suitably volatile ester, and
thus have an important advantage of specificity. On the
other hand, the determination of total NTA requires its
separation from complexing metals, generally by ion-
exchange pretreatment, with the possible loss of NTA
-------
(11). Furthermore/ to esterify the NTA, substantially
all the water must be removed by evaporation. This
step is lengthy and may lead to losses (6). The better
of the gc methods require injections of at least 0.2
yg as NTA and give relative standard deviations of 7
to 13% (9,10).
Polarographic methods are based on the reduction of a
suitable metal ion complexed with NTA. Since the half-
wave potentials for the reduction of several complexes
of the same ion usually vary appreciably according to
the ligand, this procedure is nearly as specific for
NTA as are the gc methods. In fact,some of the earliest
polarographic studies were made for the purpose of
resolving a series of similar chelating agents (12) or
for determining NTA as an impurity in EDTA (13,14).
The objectives of this project were
• to develop and evaluate an analytical method
for NTA that would determine 10 yg/£ or more
with 15% accuracy in seawater and in waste
water, and
• to evaluate and compare some of the newer
polarographic techniques of high analytical
precision, specifically, pulse differential
polarography (PD) and linear sweep voltarametry
(LS).
-------
SECTION III
EXPERIMENTAL
INSTRUMENTATION
The experimental plan was significantly influenced by
the type of instrumentation that could be obtained and
by the equipment purchase schedule. The first analyti-
cal instrument obtained, and work horse for the entire
project, was a Princeton Applied Research (P.A.R.) Model
170 Electrochemistry System. It is one of a few
general-purpose electroanalytical instruments (15) that
offer great versatility in types of experiments that
can be conducted and range of parameters that can be
controlled. It was selected primarily for its pulse
polarography capability, a relatively new technique
having great sensitivity.
In the pulse differential (PD) mode, the current is
sampled and its value stored twice during the life of
each drop from the mercury electrode. These measure-
ments are taken before and after a square potential
pulse of 50 mV is applied to the electrode on top of a
continuous ramp potential that may be increasing a few
mV during the life of the drop. The pulse excitation
wave form is shown schematically in Figure 1. The
second current measurement is taken after sufficient
time has passed (about 40 msec) to allow the charging
current associated with the pulse to decay to an insig-
nificant level. The difference between two current
measurements on the same drop gives a derivative-type
of polarogram (Figure 2) that is nearly independent of
random fluctuations in drop size. The 48 msec measure-
ment cycle is completed near the end of the drop life,
when the drop size is changing slowly. The technique is
especially useful for trace determinations because the
effect of the residual current is removed automatically
in the subtraction step.
The P.A.R. Model 172 Mercury Drop Timer is an essential
component of the PD system because it provides accurate
drop times of 0.5, 1, 2, or 5 seconds precisely syn-
chronized with the current measurement. The timer dis-
lodges the mercury drop from the capillary using opposing
solenoids that give a nearly vibrationless acceleration
to the capillary.
-------
151 ^ 55 msec
msec
TIME
Figure 1. Excitation waveform for pulse differential
technique
-------
INDIUM - NTA IN SEWAGE EFFLUENT
TECHNIQUE: SINGLE P D
0.4 ppm NTA
-0.7 -0.9 V
-0.7 -0.9 V
Figure 2. Determination of the indium-NTA complex in
sewage effluent by pulse differential
polarography
6
-------
A Chemtrix Model SSP-5A Polarographic System was
obtained to provide*a more direct comparison with the
dual-cell linear-sweep (LS) voltammetric technique used
by Afghan and Goulden (16,17). Although the Model 170
provided LS programming, it was not designed for dual
cell work, the voltage sweep was not synchronized with
the DME, and sweep rates were limited to less than 0.5
V/sec by the X-Y recorder.
On the other hand, the Model SSP-5A was designed for
dual dropping mercury electrodes and provided sweep
rates from 0.05 to 20 V/sec. The current-potential
response of the cell was displayed on a Tektronix Type
564B storage oscilloscope and a Tektronix camera system
provided a permanent record of the traces (Figure 4).
The polarographic programming and amplification circuitry
were supplied as two special plug-in modules for the
oscilloscope and drop timing was controlled by a solenoid
on the electrode stand. Drop times were continuously
variable from about 0.5 to 10 sec by an R-C timing cir-
cuit. When the solenoid closed it tapped the capillaries
to dislodge a drop from each and simultaneously sent a
pulse to the programming module to initiate the polaro-
graphic sequence.
Near the end of the project the P.A.R. Model 174/51
Linear Sweep Module Accessory became available, together
with an adapter kit to allow its use with the Model 170.
This modification made possible dual cell operation in
either PD or LS modes. The output of the LS mode was
displayed on the Tektronix oscilloscope, using general-
purpose plug-in modules 3A75 and 3B3 Time Base.
After some experimentation the cells for use with either
instrument were made from 18 x 75 mm test tubes of
borosilicate glass or polycarbonate. Platinum leads
were sealed in the bottoms to make contact with the
mercury anode and plastic caps were made with holes for
the capillary, for the nitrogen inlet (2-mm polyethylene
tubing), and for the sample introduction. In most
experiments the cathode potential was controlled with
respect to the mercury pool. When reference electrodes
were used they were made of silver wire anodized in a
chloride solution. The salt bridge consisted of a 3-mm
glass tube, drawn to a tip, plugged with filter paper,
and filled with saturated KC1. The reference electrodes
were periodically compared with a Beckman SCE or with the
reference electrode of a combination glass pH electrode.
-------
INDICATOR CHOICE
The choice of metal ion to be used as a polarographic
indicator for NTA depends somewhat on the objective of
the analysis. To determine total NTA in natural or
waste waters one should use an ion that forms a suf-
ficiently strong complex to displace all other ions
that are likely to be present in significant concentra-
tions. On the other hand, to determine free NTA in the
presence of natural complexes one should select an
indicator ion that does not appreciably displace the
equilibria among ions naturally present in the sample
but forms a sufficiently strong complex with NTA to
give an identifiable polarographic wave. The stability
constants of complexes of NTA with many metals have
been determined in fundamental studies of chelation
(14,18,19).
A second consideration in the choice of an indicator
ion is the resolution that can be obtained in a complex
mixture. Since the width of a polarographic wave is
inversely proportional to the number of electrons
involved in the electrode reaction, a three-electron
reduction will give a sharper, more easily identified
wave than two-or one-electron reductions. Bi(III)
(6,17) and In(III) (20) have been preferred for the
determination of total NTA, although methods have also
been based on Cd(II) (21,22,23), and Pb(II) (17).
INDIUM COMPLEXATION
Studies of the indium-NTA complex were made to determine
whether NTA could be measured reliably in the presence
of a considerable excess of indium. Afghan (24) and
Taylor (6) raised an objection to the use of indium
because the In-NTA complex has a half-wave potential
within 200 mV of that for free indium. A large excess
of the reagent therefore tends to obscure the In-NTA
wave. Haberman (20) solved this problem by titrating
the sample with indium reagent until a free In(III)
wave just appeared. He then used this wave as a baseline
for the following In-NTA reduction. He showed, however,
that up to 2-fold excess In did not change the indicated
concentration of the NTA more than 10%.
A second problem with excess indium arises from the
recognized tendency of indium in many media to show
dc polarographic minima (25,26,27) rather than a
8
-------
constant diffusion current. This behavior would cause
a downward-sloping baseline for the In-NTA peak in the
PD mode of measurement.
A stock solution of indium (1 x 10~3 M) was made from
In(NOs)3(Alfa inorganics) in 0.5 M NaCl buffered to
pH 4.7 with 0.1 M acetate (20). Preliminary trials
indicated that flatter baselines for the In-NTA peak
were obtained if additional acetate (or tris(hydroxy-
methyl)aminomethane) buffer was not added to the sample
solutions. Consequently, calibration curves were run
in 0.2 M NaCl supporting electrolyte, or in 60% sea-
water, with indium stock solution added to give the
desired total In concentration (usually about 1 x 10~5
M).
The effect of pH was studied in a series of solutions
containing 1 ppm NTA (as the acid form, CgHgOeN) and
100% excess In in 0.2 M NaCl. The pH was adjusted with
dilute HC1 in 0.5-unit steps from pH 2.5 to pH 4.5.
The results, summarized in Table 1, indicate that the
widest peak separation and greatest response to In-NTA
were obtained at pH 4.0-4.5, where the flattest base-
lines were also observed. In another, more limited
trial, however, better baselines were found at pH 3.0.
In subsequent work, 0.2 M NaCl adjusted to pH 4.0 was
adopted as the standard supporting electrolyte.
Since the literature contains no data on the polaro-
graphic parameters for the reduction of the In-NTA
complex, solutions containing 100% excess indium were
studied by dc polarography, LS voltammetry, and
chronoamperometry. It was assumed, without independent
verification, that a 1:1 complex was formed (28).
Under the above conditions, approximately equal limiting
currents were observed for the free In and for the
complex. These studies confirmed that the indium wave
in a chloride medium is reversible and diffusion-
limited, and involves a 3-electron transfer.
The diffusion current constant, I, in the usual units
of mA-fc secl/2 mole~lmg~2/3, was 5.9 + 0.5 for artificial
drop times of 0.5 to 2 sec and 5.5 +_ 0.5 for natural
drop times of 3-8 sec; m values were in the range 0.7-
2.3 mg/sec. DeSesa et al. (29) found a diffusion
current constant of 3.7 in an acetate medium.
-------
Table 1
Effect of pH on the Polarography of
In-NTA in 0.2 M NaCl
PH Ei/2(vs Ag,AgCl) AE (rn3+-In-NTA) In-NTA,ip
2.5 -0.72 V 90 mV 0.158 yA
3.0 - .75 120 .254
3.5 - .76 130 .294
4.0 - .79 160 .335
4.5 - .82 190 .312
El/2(In3+) = -0.63 V (Ag^gCl)
10
-------
The In-NTA wave was also diffusion limited and showed
a polarographic minimum, as reported by Haberman (20).
The reduction apparently was pseudo-reversible, as
reported by Staroscik (28) for an acetate electrolyte,
since the combination of LS and chronoamperometric
data (30) led to anomalously low values for n (less
than 0.5 electron). I was markedly dependent on drop
time, with values of 3.1 + 0.4 for artificial times of
0.5 to 2 sec and 9.8 + 0.8 for natural times of 2-8
sec.
BISMUTH COMPLEXATION
The Bi-NTA complex is the basis for an automated
analytical method for NTA, using LS (16) and was proven
applicable to seawater samples (31). The present work
was undertaken primarily to evaluate the PD technique
as a means of increasing analytical sensitivity. The
Chemtrix instrument was obtained to provide a nearly
direct comparison with the Afghan (17) procedure. In
the course of the investigation considerable inter-
ference was encountered in sewage-type samples and an
acetate electrolyte was developed to overcome these
problems.
The chloride media were based on those used by Afghan
(16). The final analysis solution was about 0.1 M in
total chloride (from NaCl or HC1), and contained
bismuth, diluted in the sample to give 100% excess
(using bismuth stock solution — 1 x 10-3 M Bids in 1
M HC1). The final pH was adjusted to about pH2. When
interference from iron was suspected 0.02%, NH2OH-HC1
was added. In seawater the added chloride was omitted
and the sample was diluted to 60%.
The optimum acetate medium contained 0.1 M acetic acid,
1 x 10-5 M Bi(NO3)3 and 0.02% NH2OH.R2S04, at pH 4.0.
It was convenient to use a stock solution of 1 x 10~3
M Bi(NC>3)3 in 9'5 M acetic acid plus 0.5 M sodium
acetate. The 1:100 dilution of the stock solution in
the sample gave the correct pH in unbuffered samples.
The polarography of Bi(III) has been studied
extensively and was recently reviewed by Bond (32).
His major conclusions were that the reversibility of
the reduction of the chloride complexes correlated with
the degree of complexation in the bulk solution. At
sufficiently high chloride concentrations the reduction
11
-------
was completely reversible. Other halide ions provided
sufficient complexation in the double-layer for pseudo-
reversible reduction but the aquo complex of bismuth
was reduced irreversibly because of the slow removal of
water from the ion.
In the chloride electrolyte used in the present work the
reduction of the Bi-Cl complex cannot be observed
because it overlaps the mercury oxidation process. NTA,
of course, forms a stronger complex with bismuth, dis-
placing chloride and giving a separate polarographic
wave at a more cathodic potential.
No published data are available for the polarographic
reduction of bismuth in an acetate medium, or for the
formation of bismuth-acetate complexes. When we dis-
covered empirically that an acetate electrolyte was
advantageous for determining NTA, we undertook some
studies to better understand the electrochemical process
involved.
As a first step we attempted to define the presumed
Bi-NTA complex in acetate electrolyte by the method of
continuous variations. No stoichiometric relation could
be determined. For all bismuth concentrations, includ-
ing zero, a polarographic current proportional to the
total NTA concentration was observed, but the propor-
tionality constant increased with Bi concentration up to
a slight excess of the 1:1 molar ratio of BiiNTA. This
may parallel the observation of Staroscik and Webs (28)
that the polarographic current for In-NTA in an acetate
medium decreased with increasing excess NTA, eventually
yielding an adsorption wave.
We found, in the dc polarography of solutions containing
no bismuth or less than 2:5 mole ratio of Bi:NTA, that
El/2 = -0.21 to -0.24 v(SCE). The diffusion current
"constant", J, was more nearly independent of mercury
flow rate when calculated for the total NTA concentra-
tion than for bismuth or excess NTA concentrations.
The wave shape corresponded to a pseudo-reversible
process, with an of 1.5 to 1.9. No ac polarographic
wave could be observed in these solutions.
NTA appears to facilitate the reduction of bismuth by
displacing water from the aquo complex and forming a
1:1 Bi-NTA complex in the double layer. However, the
12
-------
mechanism of the diffusion-limited process in the
absence of bismuth is unclear.
The effect of pH (between pH 1.5 and 4.5) was studied
in solutions containing 1 x 10~5 M Bi and 5 x 10~6
NTA. The chloride medium contained 0.1 M total
chloride and the acetate medium was made 0.02 M in
acetic acid and 0.08 M in NaClC>4 for an equal ionic
strength. The pH was adjusted with NaOH solution. In
the chloride electrolyte, in contrast to the report of
Afghan and Goulding (17), the peak current recorded in
the PD mode increased sharply from pH 1.5 to pH 2.0 and
changed little at further increases to pH 4.0, having
a slight maximum at pH 2.5. In the acetate medium the
peak current did not vary more than 10% over the pH
range of 2.0 to 4.5, but showed a broad maximum at pH
3.0. In both systems the peak potential (£"1/2) shifted
to more cathodic values with increasing pH. The shift
over 2.5 pH units was about 50 mV in the acetate.
Another study of four solutions at an ionic strength of
0.1 and pH 3.0 showed that increasing the total acetate
concentration from 0.02 to 0.1 M had negligible effect
on either the peak current or potential.
13
-------
SECTION IV
RESULTS AND DISCUSSION
INSTRUMENT EVALUATION
The precisions attainable by the various instrumental
techniques studied are best compared by reference to
Table 7. In this table are presented the calibration
results obtained with the optimum chemical and instru-
mental conditions.
The practical choice for an analytical application
involves a balance between speed and convenience on one
hand and precision on the other. Dual-cell PD has a
distinct advantage in terms of precision and detection
limits. However, it is slower than LS and there is
relatively less to be gained from automation of the
sample preparation. The P.A.R. instrumentation used in
this project cost three times as much as the Chemtrix
instrument; but the price differential might be sub-
stantially reduced by substitution of the P.A.R. Model
174 specialized analytical version for the Model 170.
The Model 174 provides single- and dual-cell PD and LS
capabilities at a price competitive with other LS
instruments.
The Chemtrix Model SSP-5A is a compact, special-purpose
instrument that provides as wide a range of programming
variables as one is likely to need for the LS technique.
The major problem in obtaining reproducible results
appeared to be in setting the initial potential for the
voltage scan. The small meter and manual potentiometer
on the instrument made it difficult to set this value
much closer than 0.1 V. The setting seemed to be
reasonably stable when left untouched for repetitive
measurements and it should be a simple matter to
provide a fine-tuning adjustment to simplify arbitrary
changes.
The Chemtrix drop timer and cell stand, in comparison
with the P.A.R. model, was crude. The relay-actuated
drop knocker was noisy and imparted considerably
turbulence to the solution in the cell. Drop times
were continuously adjustable by means of a potentio-
meter control and were not re-settable without a stop
watch. The mercury stand did not provide for varying
the height of the mercury column, except for a very
14
-------
small differential adjustment between the cells.
Our Chemtrix instrument had a poor repair record. In
the first twelve months transistors in the drop timer
circuit were replaced three times. The plug-in
amplifier module was replaced by the manufacturer four
times and components of the amplifier were replaced in
the field twice. Eventually, the entire instrument,
including oscilloscope, was recalled by the factory for
repair and calibration.
The great versatility of the Model 170 Electrochemistry
System is provided at the cost of a rather bewildering
set of controls. For routine measurements of the same
type, however, only a few need to be adjusted indivi-
dually. The effects of changing the available instru-
mental parameters were not investigated fully or
systematically, although some such studies have been
reported (33). Resolution can be improved at the cost
of lengthening the analysis time by decreasing the
potential scan rate. The analytical signal can be
increased by increasing the pulse amplitude or the time
of current sampling, both of which cause distortion and
poorer resolution, and by increasing the drop time,
which lengthens the analysis time.
The major operating problems involved sensitivity of
detection. The nanoampere range of the Model 170 was
nearly unusable because of a high noise level. In
dual cell operation, there was an optimum pre-amplifier
gain setting in the 174/51 module and an optimum current
range setting on the Model 170. Also, the current
offset and electrode balance controls, in dual-cell
operation, required painstaking adjustment to avoid
amplifier saturation.
The Model 170 was very reliable electronically, and no
troubles developed in two years. After about three
months of operation with the 174/51 dual-cell attachment,
problems arose that seemed to involve both components.
The routine trouble-shooting checks were inadequate to
identify the source of malfunction and the entire
instrument was returned to the manufacturer.
15
-------
INDIUM
Calibrations
A number of calibration runs made under different con-
ditions are summarized in Table 2. These include com-
parisons of seawater and sodium chloride as supporting
electrolytes. Most were made by the PD technique, with
a single cell. Each calibration run is internally
consistent with respect to operating conditions but
different runs are not necessarily comparable in sensi-
tivity .
The parameters of mercury flow rate and potential scan
rate, in particular, were not always the same. The
effect of scan rate on the observed current (33) was
not fully recognized at the time, but rates of 2 or 5
mV/sec were usually employed. The current is directly
proportional to the area of the mercury drops, and a
compromise can be made between sensitivity and analysis
time most directly by varying the drop time. In these
experiments the mercury flow rate was usually in the
range 0.5 to 1.0 mg/sec and the drop time was one
second.
Because of the above variations in experimental condi-
tions the calibrations are best compared in terms of
the linearity and scatter of the points. Table 2 gives
the parameters for least-squares fits to the experimental
points by the equation
J(nA) = a + b X(ppm NTA) (1)
or, in the case of calibration by standard addition,
J(ppm found) = a + b X(ppm taken) (2)
When the intercept a is enclosed in parentheses its
value is smaller than its standard deviation. The
table shows the effects of improved technique, since the
relative standard deviations were about 10% for the
first two runs and decreased to 1% in Run 9. Runs 3
and 4 were a direct comparison of sodium chloride and
seawater electrolytes run at the same time; the slope
of the calibration curve was anomalously low in sodium
chloride.
16
-------
Table 2
Calibration Runs for the Determination of NTA as the Indium Complex
n, No. Concentration Std. Dev.
Run of Points Range (ppm NTA) a(nA) b (nA/ppm of Fit(nA) Remarks
1
2
3
4
5
6
7
8
9
10
14
9
4
4
6
6
6
5
5
7
0
0
0
0
0
0
0
0
0
0
.2 -
.2 -
.2 -
.2 -
.2 -
.2 -
.2 -
.1 -
.1 -
.1 -
2.
2.
2.
2.
1.
1.
1.
1.
1.
3.
0
0
0
0
2
2
2
0
0
2
(-5)
-28
0.09
0.07
(7)
(0.02)
(0.03
(0.4)
(-1.0)
(8)
181
354
0.77
0.98
293
0.99
1.00
94
272
152
14
44
0.07
0.08
19
0.05
0.05
1.8
2.8
21
NaCl and seawater,
combined , PD
Seawater ,
NaCl
, std.
Seawater ,
PD
NaCl
Na5P
NaCl
NaCl
NaCl
NaCl
60%
+ 1.6
3°10'
, std.
, std.
, LS
, PD
Sewage
PD
addn . , PD
std. addn. ,
x 10~5 M
PD
addn. , PD
addn. , PD
effluent,
LS
11 7 0.1 - 3.2 26 817 40 60% Sewage effluent,
PD
-------
The same solutions were used in Runs 5, 6, and 7. The
method of standard additions was compared for two
different operators in Runs 6 and 7, while a calibration
curve was computed for the original solutions in Run 5.
In this case, the relative standard deviation is lower
for the addition technique (5%) than for the calibra-
tion curve (6.3%) .
Runs 8 and 9 are a direct comparison of the single-cell
PD (P.A.R.) and LS (Chemtrix), both in sodium chloride
electrolyte. The relative standard deviation/ at 1
mg NTA/&, is 1% for the former and 2% for the latter.
In 60% sewage effluent both techniques were much poorer
(runs 10 and 11), with relative standard deviations of
5% for PD and 14% for LS. Two chart recordings from
Run 11 are shown in Figure 2.
Interferences
The response to NTA in the range of 0.4 mg/& was not
significantly affected by EDTA, citric acid, or
NaH2PO4 in varying proportions up to four times the
concentration of NTA. The total indium concentration
was 2 x 10~5 M in all cases. Table 3 shows recoveries
(the fraction, in percent, of the concentration of the
added species that was indicated by the analysis) of
randomized concentrations of NTA from 0 to 2.0 mg/Jl
in the presence of 5 x 10~5 M Fe(III), Mn(II), Cu(II),
or Bi(III). Under these conditions bismuth appeared to
complex a significant portion of the NTA, leading to
low results.
The effect of interferences might be mitigated by using
the standard addition method of calibration. This
approach assumes that a linear response to NTA would be
observed, although the interferences might change the
slope of the calibration curve. A test is summarized
in Table 4, where 5 lag of NTA was added to 10 ml of the
original solution. The initial concentrations of NTA
were selected in a randomized order in the range 0.2 to
2.0 mg/Jl. The trials of Fe(III) plus hydroxylamine
were made at a constant level of NTA. A least-squares
fit of the data gave the equation.
Y(ppm NTA found) = 0.11 + 0.95 X(ppm NTA taken) (3)
with a standard deviation of fit of 0.14 ppm.
18
-------
Table 3
Recovery of NTA in the Presence of 5 x 10
Fe, Mn, Cu, or Bi
Fe(III) MnJ11) Cu(II) Bi(III)
TA Taken
0 . 8 ppm
1.2
1.4
1.6
Found
0.86
1.18
1.36
1.50
Taken
0.4
1.8
2.0
Found
0.35
1.59
1.96
Taken
0.8
1.0
1.0
1.6
Found
0.69
0.94
0.81
1.61
Taken
0.2
1.4
1.4
1.8
Found
0.02
1.04
0.84
1.62
-------
Table 4
Recovery of In-NTA in the Presence
of Metals and Coroplexants
L Taken
mg/fc)
1.6
1.6
1.6
1.8
0.2
1.8
1.4
0.6
1.2
0.6
1.2
1.0
1.0
1.0
1.0
0.4
1.0
0.8
1.4
NTA Found
(rog/A)
1.58
1.55
1.53
2.03
0.49
L98
1.67
0.72
1.16
0.59
.58
1.05
0.81
0.99
1.13
0.43
1.61
0.88
1.14
Interference
Cu
Cu
Zn
Zn
Mn(II)
Mn(II)
Bi
Fe(II)
Fe(II)
Fe(III)
Fe(III)
N2H4-HC1
N2H4+Fe(III)
N2H4+Fe(III)
N2H4+Fe(III)
EDTA
EDTA
Na5P3Oi0
NasPqOin
Concentr,
x!06,
8
16
4
8
4
8
2
8
16
8
16*
40
12*
16
32
8
16*
8
16
* More than twice the standard deviation from the
least-squares fit.
20
-------
Three solutions, indicated in Table 4, deviated by more
than twice the standard deviation and were not included
in the calculation. The least-squares equation shows
that the standard addition method tended to give high
results, especially at lower concentrations, and that
the precision was rather poor (14% relative standard
deviation). Both results may be a consequence of a
non-linear response to NTA in the presence of some or
all of the additives.
Fe(III) interfered at 1.6 x 10~5 M but hydrazine effec-
tively removed the interference. The high result for
1.6 x 10~5 M EDTA is a consequence of the standard-
addition technique. After the addition of 0.5 ppm NTA
the sum of NTA and EDTA concentrations was in molar
excess of the total indium (2 x 10~5 M), causing a
lower response for the standard addition.
Since Haberman (20) observed that a large excess of
indium had to be added to some sewage samples to obtain
a polarographic wave for free In, a few titrations were
made. Indium solutions of 2 to 8 x 10~^ Af concentra-
tion were prepared in three distilled water and three
sewage effluent samples (15 ml of sewage effluent in
a final volume of 25 ml) and the excess In was titrated
with NTA by following the decrease in height of the
In(III) wave in dual-cell LS. Although two of the
effluent samples had very little excess In (2 x 10~5 M
total concentration) the results indicated 1.7 to
1.9 x 10~5 M oomplexed indium, corresponding to an
indium-complexing power of the original effluent of
3 x 10-5 M.
As noted by Haberman (20) NTA did not release In from
this complex in a polarographically determinable form.
The mean slopes of the three titrations in distilled
water corresponded to 1.7 moles of In removed per mole
of NTA. The corresponding value in the effluent
samples was 1.4 moles of In per mole of NTA. These
numbers probably do not represent a stoichiometric
complex, but reflect an accumulation of NTA in the
double layer surrounding the mercury drop. Staroscik
and Webs (28) observed that, for an increasing excess
of NTA, the In-NTA wave decreased in height and
eventually was transformed to an ill-defined adsorption
wave.
21
-------
BISMUTH, CHLORIDE MEDIUM
Calibrations
Since an analytical procedure had already been
developed (17) and applied to seawater samples (31),
relatively little was done in the way of evaluating
specific interferences or in modifying the procedure.
Calibration runs were made primarily to evaluate the
instrumentation, particularly for PD. Five such
calibrations, made early in the project, are summarized
in Table 5, in which the parameters for least-squares
fits of equation 1 are shown in the same format as in
Table 4. The most noteworthy point is the great varia-
tion in precision. The relative standard deviations
range from about 1% (Run 1) to 13% (Run 4). The poor
precision is believed to result more from unfamiliarity
with the instrument than from the chemical procedure.
Typical chart recordings, taken from Run 3, are shown
in Figure 3.
Interferences
Although Afghan et al. (17) found that copper did not
interfere in the determination of the Bi-NTA complex
and that Bi quantitatively displaced Cu from its NTA
complex at 2 x 10"^ M concentration, other workers have
not confirmed these results. Gahler (31) found that in
the presence of 2 mg Cu/fc, the concentration of NTA
indicated by a dc polarographic measurement was high,
and Taylor et al. (6) , using the same type of instru-
mentation and procedure as Afghan (17) observed an
interference in tap water that they believed to result
from copper. Figure 4 shows traces obtained by LS of
solutions containing NTA and Cu. Curves 1, 2, and 3
correspond to solutions of 2 mg NTA/& and curve 4 to a
1 mg NTA/£ solution. Curves 3 and 4 were obtained with
1 x 10-5 M Cu, Curve 2, with 0.5 x 10~5 M Cu, and
Curve 1, with no copper. The test and reference
solutions all were 0.1 M in NaCl, and 1 x 10~5 M in Bi
at pH 2.0.
A better test of the analytical procedure would have
been obtained with NTA and Cu, but no Bi, in the appro-
priate reference solutions. These results, however,
show that the copper peak precedes and interferes with
the Bi-NTA wave. There is no indication that copper
22
-------
Table 5
Calibration Runs for the Determination of NTA
as the Bismuth Complex in Chloride Electrolyte
to
U)
Run
1
2
3
4
5
n, No.
of Points
5
9
8
9
9
Concentration
Range (ppm NTA)
0.2 - 1.6
0.2 -
0.2 -
0.2 -
0.2 -
1.8
2.0
2.0
1.0
a(nA)
-68
(-18)
(-6)
(-1)
(9)
b (nA/ppm)
648
375
374
395
209
Std. Dev.
of Fit(nA) Remarks
8
24
17
52
7
NaCl (PD)
NaCl (PD)
Seawater (PD)
NaCl
Seawater (LS)
-------
BISMUTH - NTA IN SEAWATER
TECHNIQUE: SINGLE P D
MEDIUM: CHLORIDE
00 nA
I.36 ppm NTA
0.7 ppm NTA
-0.3 -0.5 V
0 -0.2 -0.4 V
Figure 3. Determination of the bismuth-NTA complex in
seawater by pulse differential polarography
24
-------
Figure 4.
Copper and bismuth-NTA waves by linear sweep
voltammetry
25
-------
complexes any NTA at pH 2.0.
When the method was tried in waste waters difficulties
appeared, particularly in trying to match the sample
and reference scans in the LS technique. Figure 5
shows some typical results obtained with the Afghan (17)
procedure in an effluent from a small activated-sludge
plant serving a residential development in Clarke
County, Georgia. The fresh sample was filtered through
0.45 y Millipore but no preservative was added. Figure
5(a) shows the sample (A) and reference (B) scans, as
well as the difference, for no added NTA; thus, the
only difference between the cells is 1 x 10~5 M Bi
added to cell A. Figures 5(b) and 5(c) were taken at
a later time but for the same effluent and procedure.
Curves 4, 1, and 2, respectively, of Figure 5(b) are
the difference traces for 0.5, 1.0, and 2.0 mg NTA/£.
In Figure 5 (c) , curves A and B are for sample and
reference, respectively, and 1 is the difference, for
0.2 mg NTA/& in A, while Curve 2 is the difference
trace for 1.0 mg NTA/£. For more than about one ppm of
NTA fairly satisfactory traces and calibration curves
were obtained, but at lower concentrations of NTA the
problem of matching the cells was more severe.
This difficulty in determining low levels of NTA in
natural or waste waters is further illustrated in
Figure 6, which shows calibration curves obtained in
the above sewage effluent and in Oconee River water,
by both LS and PD techniques. The slopes of the curves
are strikingly different for the two sources, showing
that a calibration based on distilled water standards
would be highly inaccurate for at least one of the
samples. Because of the non-zero intercepts of the
curves in Figure 6, the method of standard additions
would not be a great improvement and could not be used
for low levels of NTA. The parameters of the least-
squares equations for these calibrations are given in
Table 6.
Interference from sulfur compounds in some sewage
samples has been reported (17) , and treatment with
hydrogen peroxide was recommended. We were not able
to achieve any improvement through hydrogen peroxide
treatment and found it difficult to remove the excess
26
-------
M^HB^^^^Bl^^^W. f^f
mmm
Figure 5.
Effect of sewage effluent on the bismuth-NTA
polarographic wave in chloride electrolyte
27
-------
LS
nA
100
50
0.5
1.0
I
PD
nA
400
200
1.5 ppm NTA
Figure 6.
Calibration curves for the determination of
the bismuth-NTA complex — chloride
electrolyte
28
-------
Table 6
Calibration Runs for Bi-NTA in Chloride Electrolyte-
Sewage Effluent and River Water
rel. std. dev.
at 1 ppm NTA
Oconee River, PD Technique
Y(nA) = (-18±4) + (286±5) X (mg NTA/£), 1.7%
Oconee River, LS Technique
Y(nA) = (-16±2) + (95±2) X (mg NTA/fc) , 2.4%
Sewage Effluent, PD
Y(nA) = (-32±7) + (175±8) X (mg NTA/£), 5.3%
Sewage Effluent, LS
Y(nA) = (-13±3) + C69.0±3.6) X
(mg NTA/&), 6.1%
29
-------
peroxide sufficiently. About this time we discovered
that an acetate electrolyte gave greatly superior
results in waste waters and we discontinued investigation
of the chloride medium.
BISMUTH, ACETATE MEDIUM
Calibrations
Calibrations in the acetate medium are summarized in
Table 7. The experiment of Run 1 was a balanced,
incomplete block design for testing four levels of NTA
in four sources of water, in duplicate. The standard
deviation of the duplicates was 13 nA, including one
pair that differed by 43 nA (the outlier was not
discarded). No significant effects were found for the
water sources, which included distilled, tap, river
water and sewage effluent. Accordingly, the results
were pooled for the calibration shown in Run 1.
Another similar balanced, complete block design was
used to compare the LS and PD techniques using six
sources of water: distilled, tap, woodland stream,
Oconee River, and effluent from a small activated
sludge treatment facility and from a municipal sewage
treatment plant. No significant differences due to
source were observed in the LS mode, and the pooled
results are summarized in Run 2. For the PD results
source effects were significant at the 95% level of
significance and the data have been subdivided. The
potable and natural waters are combined in Ran 3 and
results for the two effluents are summarized in Run 4.
The effluents gave a somewhat lower response to NTA
than the "clean" waters but gave somewhat better
precision.
A direct comparison of calibration in distilled water
and in sewage effluent, both by PD, is shown in Runs 7
and 8. These were made at higher concentrations of NTA
and the bismuth concentration was increased to 5 x 10~5
M. Both lines show negative intercepts (a) greater than
their standard deviations, corresponding to about 0.2
mg NTA/Jl, but the slopes of the calibration curves are
essentially identical and the precision is somewhat
better in the effluent. The much lower response factor
(2>) in comparison with Runs 1, 3, or 4 results from a
change of capillaries, differing by a factor of nearly
three in mercury flow rate.
30
-------
u>
Table 7
Calibration Runs for the Determination of NTA
as the Bismuth Complex in Acetate Electrolyte
n, No. Concentration Std. Dev.
Run of Points Range (ppm NTA) g(nA) b (nA/ppm) of Fit (nA) Remarks
1
2
3
4
5
6
7
8
24
24
16
8
8
5
4
4
0.05 -
0.2 -
0.2 -
0.2 -
0.05 -
0.2 -
1
1
0.50
1.5
1.5
1.5
0.2
0.8
4
4
(1.5)
(0.1)
(3)
(3)
2.9
-22
-35
-30
313
77.8
339
308
40.6
347
164
162
11
4.5
20
7
0.9
3
19
4
PD; four types
of water source
LS (Chemtrix) ;
six types of
water source
PD; four types
of "clean" water
PD; two sewage
effluents
LS (Chemtrix) ;
distilled water
PD; distilled
water plus
NaClO4
PD; distilled
water
PD; sewage
effluent
-------
w
N)
Table 7 (cont'd)
Calibration Runs for the Determination of NTA
as the Bismuth Complex in Acetate Electrolyte
n, No. Concentration Std. Dev.
Run of Points Range (ppm NTA) a(nA) b(nA/ppm) of Fit (nA) Remarks
9
10
11
12
13
5
7
10
9
12
0.01 -
0.01 -
0.01 -
0.02 -
0.02 -
0.12
0.1
0.1
2.0
2.0
(-.1)
-1.0
0.6
-26
(5)
354
99.0
242.4
669
857
0.6
0.5
0.8
39
23
Dual PD;
distilled water
LS (PAR) ;
distilled water
Dual PD; stream
water
PD; sewage
effluent
Dual PD; sewage
effluent
-------
When the dual-cell modification of the P. A. R. Model
170 was obtained a comparison of LS and PD modes on the
same instrument was made in Runs 10 and 11. Single-cell
and dual-cell PD operation were compared in Runs 12 and
13. The high precision attainable with dual-cell PD
is indicated in Runs 9, 11, and 13. Chart records for
the complete calibration Run 9 are shown in Figure 7,
and for the two lowest concentrations of Run 11 in
Figure 8.
A demonstration of the presence of NTA in raw and
treated municipal sewage is shown in Figure 9. Samples
from the Athens Oconee treatment plant were preserved
with 1% formaldehyde and filtered through 0.45 u
Millipore. The samples were analyzed by the dual-cell
PD technique in acetate electrolyte. The raw sewage
gave a peak of about 3.0 nAf which increased to 21.5
nA when the cell was spiked with 0.1 mg NTA/£. The
effluent sample gave a peak of 2.0 nA, increasing to
19.5 nA when spiked with 0.1 mg NTA/fc. These results
indicate 16 and 11 yg/&, respectively, in the cells, or
about 30 and 20 yg NTA/£ in the original raw and treated
samples. Since the standard deviation of the corre-
sponding calibration was equivalent to 4 yg NTA/&, the
difference between the samples may not be real, although
some degradation of the NTA in the treatment process
would be expected. Instrumental problems prevented
confirmation or further study of NTA in natural samples.
Interferences
In preliminary studies of the effects of metal ions on
the determination of NTA, Fe(III) and Cu(II) seemed to
interfere most significantly. Heating the sample with
at least 0.02% of either hydrazine sulfate or hydro-
xylamine hydrochloride, as in the chloride procedure
(17), effectively removed all interference from iron
at concentrations up to 1 x 10~5 M (0.5 ppm).
In the presence of 1 x 10"^ M Cu, NTA recoveries were
about 80-90% and were quite variable. Although the
problem seemed to be associated with low concentrations
of chloride ion, it was not completely explained or
solved. In the acetate medium, free of chloride,
separate waves were observed for Cu(II), Bi(III), and
Bi-NTA at half-wave potentials of +0.07, -0.005, and
-0.16V (vs. SCE), respectively- In the presence of
33
-------
ppm NTA
0. 12
BISMUTH - NTA
CALIBRATION IN DISTILLED WATER
TECHNIQUE: DUAL P D
MEDIUM: ACETATE
10 nA
0.01
-0.3 -0.5 V (Hg pool)
Figure 7. Determination of the bismuth-NTA complex in
distilled water by dual cell pulse differen-
tial polarography
34
-------
BISMUTH - NTA IN STREAM WATER
TECHNIQUE^ DUAL P D
MEDIUM: ACETATE
I nA
0.02 ppm NTA
0.01 ppm NTA
-0.3 .-0.4 V
-0.4 -0.5 V
Figure 8. Determination of the bismuth-NTA complex
in distilled water by dual cell pulse
differential polarography
35
-------
Raw Sewage
Treated Effluent
21.5 nA
19.5 nA
Raw plus 0.1 ppm NTA Effluent plus 0.1 ppm NTA
Figure 9. Differential pulse polarographic estimation
of NTA in raw and treated municipal sewage
36
-------
0.02% hydroxylamine hydrochloride (3 x 10 3 M) or 0.1 M
sodium chloride, the Cu(II) wave at +0.07V disappeared
and was replaced by a very large wave at +0.21V, which
may be due to mercury oxidation. These potentials were
measured with a mercury-mercurous sulfate reference
electrode having a potential of +0.360V vs. SCE. EDTA
was tried as a masking agent for copper but had no
effect, probably because bismuth was able to displace
copper from the EDTA complex.
Both copper and chloride might be expected in natural
and waste waters at the concentrations used in these
studies and the analyst should be aware of the possi-
bility of low results for NTA due to copper. The cali-
bration results reported in the preceding section,
however, did not reveal any problems in applying the
method to a variety of water sources.
A number of possible interferences were investigated by
single-cell PD at NTA concentrations of 0.2, 0.5, and
1.0 mg/&. The average recovery was calculated from the
slope of the best calibration curve through the origin
for each set of NTA concentrations, relative to
standards prepared in the same Oconee River water but
without added metals or complexants. The results are
summarized in Table 8. Lead, at 1 x 10~4 M concentra-
tion, caused a low recovery of NTA but did not inter-
fere significantly at 1 x 10~5 M. High concentrations
of calcium and magnesium (400 mg/£) also led to low
recoveries of NTA but no other interferences were
found. Citric acid, at 1 x 10~5 M concentration, was
included in several of the preliminary tests with no
perceptible effect on the response to NTA.
37
-------
Table 8
Recovery of Bi~NTA in the Presence
of Metals and Complexants in Acetate Electrolyte
Average Recovery,
Interference Percent
Fe(III), lxlQ-5 M 101
Fe(IIl) + Mn(II), each lxlQ-5 M 100
Fe(III) + NasPaOio, each lxlO~5 M 97
Mn(II) , 1x10-4 M 303
Pb(II), IxlO-4 M 78
Pb(II), IxlO-5 M 96
Cd(II), 1x10-4 M 98
Zn(II), 1x10-4 M 99
Ca(II), 400 mg/1 (1.0xlO~2 M) 49
Mg(II), 400 mg/1 (1.7xlO~2 M) 72
P043-, 1x10-5 M 103
Na5p3°10f 1x10-4 M 97
38
-------
SECTION V
REFERENCES
1. Longbottom/ J. E.. Determination of Nitrilotriacetic
Acid by High-Speed Ion Exchange Chromatography.
Anal. Chem. 44: 418-420, February 1972.
2. Swisher, R. D., M. M. Crutchfield, and D. W.
Caldwell. Biodegradation of Nitrilotriacetate in
Activated Sludge. Environ. Sci. Technol. !_: 820-
827, October 1967.
3. Pfeil, B. H. and G. F. Lee. Biodegradation of
Nitrilotriacetic Acid in Aerobic Systems. Environ.
Sci. Technol. 2: 543-546, July 1968.
4. Thompson, J. E. and J. R. Duthie. The
Biodegradability and Treatability of NTA. J. Water
Pollution Control Fed. 40; 306-319, February 1968.
5. Methods for Chemical Analysis of Water and Wastes,
1971. Analytical Quality Control Laboratory,
Cincinnati, Ohio. Report No. 16020-07/71.
Environmental Protection Agency. 1971. 205-215.
6. Taylor, J. K., W. L. Zielinski, Jr., E. J. Maienthal,
R. A. Durst, and R. W. Burke. Development of Method
for NTA Analysis in Raw Water. National Bureau of
Standards. Report EPA-R2-72-057. Environmental
Protection Agency. 1972. 19-21.
7. Rechnitz, G. A. and N. C. Kenny. Determination of
Nitrilotriacetic Acid (NTA) with Ion-Selective
Membrane Electrodes. Anal. Lett. 3_: 509-514,
October 1970.
8. Rudling, L. Determination of Nitrilotriacetic Acid.
Water Research. 5_: 831-838, October 1971.
9. Chau, Y. K. and M. E. Fox. Nitrilotriacetic Acid
in Lake Water. J. Chromatogr. Sci. 9: 271-275, May
1971.
10. Warren, C. B. and E. J. Malec. Quantitative Deter-
mination of Nitrilotriacetic Acid and Related Amino-
polycarboxylic Acids in Inland Waters. J. Chromatogr.
6±: 219-237, February 1972.
39
-------
11. Longman, G. F-, M. J. Stiff, and D. K. Gardiner.
The Determination of Nitrilotriacetic Acid (NTA)
in Sewage and Sewage Effluent. Water Res. 5:
1171-1175, December 1971. ~
12. Hoyle, W., I. P- Sanderson, and T. S. West.
Polarographic Resolution of Mixtures of Complexans.
J. Electroanal. Chera. _2: 166-173, 1961.
13. Farrow, R. N. P. and A. G. Hill. A Modified Method
for Determining Traces of Nitrilotriacetic Acid in
Ethylenediaminetetraacetic Acid. Analyst 90: 241-
242, 1965.
14. Daniel, R. L. and R. B. LeBlanc. Polarographic
Determination of Nitrilotriacetic Acid in
(Ethylenedinitrilo)tetraacetic Acid. Anal. Chem.
31: 1221-1223, 1959.
15. Ewing, G. W. General-Purpose Electroanalytical
Instruments. J. Chem. Ed. 46; A717 et seq., 1969.
16. Afghan, B. K., P. D. Goulden, and J. F. Ryan.
Automated Method for Determination of Nitrilotri-
acetic Acid in Natural Water, Detergents, and Sewage
Samples. Anal. Chem. 44; 354-359, February 1972.
17. Afghan, B. K. and P. D. Goulden. Determination of
Trace Quantities of Nitrilotriacetic Acid by
Differential Cathode-Ray Polarography. Environ.
Sci. Technol. 5_: 601-606, July 1971.
18. Koryta, J. and I. Koessler. The Polarographic
Determination of the Stability Constants of the
Complexes Formed by Some Heavy Metals with
Schwarzenbach's Complexones. Collect. Czech. Chem.
Commun. 15; 241-259, 1950.
19. Sillen, L. G. and A. E. Martell. Stability Constants
of Metal-Ion Complexes. Special Publ. No. 17.
London, The Chemical Society, 1964.
20. Haberman, J. P. Polarographic Determination of
Traces of Nitrilotriacetate in Water Samples. Anal.
Chem. 43: 63-67, January 1971.
40
-------
21. Wernet, J. and K. Wahl. Spezifische Bestimmung von
Nitrilotriessigsaeure (NTE) in ppm-Konzentrationen
in Oberflaechenwasser und Abwasser. (Specific
Determination of Nitrilotriacetic Acid (NTA) in
the ppm-Range in Surface Water and Sewage).
Fresenius1 Z. Anal. Chem. (Berlin). 251; 373-374,
1970.
22. Asplund, J. and E. Wanninen. Polarographic
Determination of Low Concentrations of Nitrilotri-
acetate in Lake Water. Anal. Lett. 4: 267-275,
May 1971.
23. Al-Sulimany, F. and A. Townshend. Polarographic
Determination of Tripolyphosphate Ions and of
Tripolyphosphate and Nitrilotriacetic Acid in
Admixture. Analyst (London). 98; 34-39, 1973.
24. Afghan, B. K. Differential Cathode Ray
Polarography for Trace Analysis with Special Refer-
ence to NTA and its Complexes with Heavy Metals.
Department of Fisheries and Forestry, Canada.
(Presented at International Symposium on Identifi-
cation and Measurement of Environmental Pollutants.
Ottawa. June 15, 1971), 19 p.
25. Bulovova, M. Polarography of Indium. Collect.
Czech. Chem. Commun. 19: 1123-1132, 1954.
26. deLevie, R. and A. A. Husovsky. On the Negative
Faradaic Admittance in the Region of the Polaro-
graphic Minimum of Indium(III) in Aqueous NaSCN
Solution. J. Electroanal. Chem. 22; 29-48, 1969.
27. Pospisil, L. and R. deLevie. Thiocyanate Electro-
catalysis of the Reduction of Indium(III). J.
Electroanal. Chem. 25; 245-255, 1970.
28. Staroscik, R. and K. Webs. Polarographic Behavior
of Indium(III) in Nitrilotriactic Acid Solutions.
Chem. Anal. (Warsaw). 12; 1275-1281, June 1967;
Chem. Abstr. 68; 65177 m, 1968.
29. DeSesa, M. A., D. N. Hume, A. C. Glamm, Jr., and
D. D. DeFord. Polarographic Characteristics of
Metallic Cations in Acetate Media. Anal. Chem. 25;
983-984, June 1953.
41
-------
30. Malachesky, P- A. Correlation of Linear Sweep
Voltammetric and Chronoamperometric Data for
n-Value Determinations. Anal. Chem. 41; 1493-1494,
September 1969.
31. Gahler, A. R., Pacific Northwest Water Laboratory,
EPAr personal coiraminication. 1971.
32. Bond, A. M. The AC and DC Polarographic Reduction
of Bismuth (III) in Acidic Halide and Other Media.
Electrochim. Acta. 17; 769-785, April 1972.
33. Christie, J. H., J. Osteryoung, and R. A.
Osteryoung. Instrumental Artifacts in Differential
Pulse Polarography. Anal. Chem. 45: 210-215,
January 1973.
42
-------
SECTION VI
APPENDIX
RECOMMENDED NTA ANALYSIS PROCEDURES
SALINE WATERS - MORE THAN 0.1% CHLORIDE
Reagents
1 N Hydrochloric Acid
1 M Sodium or Potass ium Chloride
1 x 10~3 M Bi: Dissolve 50 ± 2 mg
Bi(NO3)3-5H2O in 100 ml 1 N HC1.
1% Hydroxylamine Hydrochloride
NTA stock solution, 2 g/1. Dissolve 1.434 g
H0 in 500 ml distilled water.
Procedure
Place 5.0 ml of sample in each of two 10-ml volumetric
flasks and add 0.2 ml of 1% hydroxylamine hydrochloride
to each. Add 0.1 ml of 1 N HC1 to the reference and
0.1 ml of 1 x 10~3 M Bi to. the sample flask. If the
original sample contained less than about 0.5% chloride,
add 1.0 ml of 1 M chloride solution to each flask and
dilute to the mark with distilled water. If the
original water sample contained more than about 0.5%
chloride do not add additional salt solution, but dilute
to the mark with distilled water. Place 3.0 ml of
sample and reference solutions in the respective cells,
de- aerate for 10 minutes , and run a polarographic scan
from about -0.2 to -0.4 V vs. the mercury pool anode.
Compare the peak currents with those for standard
solutions similarly prepared with freshly diluted NTA
stock solution. The procedure is applicable to NTA
concentrations from 0.05 to 5.0 mg/1.
43
-------
NATURAL AND WASTEWATERS - LESS THAN 0.1% CHLORIDE
Reagents
Acetate electrolyte, 9.5 M in acetic acid plus
0.5 M in sodium acetate.
1 x 10-3 M Bi: Dissolve 50 + 2 mg Bi(N03)3-H2O
in 100 ml of the acetate eTectrolyte.
1% Hydroxylamine sulfate solution
NTA stock solution, same as above.
Procedure
Place 5.0 ml of sample in each of two 10-ml volumetric
flasks, add 0.2 ml of 1% hydroxylamine sulfate solution
to each and heat nearly to boiling. Cool to room
temperature and add 0.1 ml of acetate electrolyte to the
reference and 0.1 ml of 1 x 10~3 M bismuth solution to
the sample. Dilute each to the mark with distilled
water, mix, and place 3.0 ml in the respective cells.
De-aerate for 10 minutes and run a polarographic scan
from -0.1 to -0.3 V (vs. SCE). The mercury pool anode
can be used as a reference but its potential is apt to
vary with different sample sources. It is preferable
to use an external reference electrode with a sodium
perchlorate salt bridge to both cells. Compare the peak
currents with those for standard solutions similarly
prepared from freshly diluted NTA stock solution. The
procedure is applicable to NTA concentrations from 0.01
to 5.0 mg/1.
4 U. S. GOVERNMENT PRINTING OFFICE : 1973—514-156/365
44
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
l.jReportffo.
3. Accession No.
w
4. Title
POLAROGRAPHIC DETERMINATION OF NTA
7. AuthoT(s)
Hoover, Thomas B.
5. Report Date
6.
8. Performing Organization
Report No.
9. Organization
Southeast Environmental Research Laboratory
Athens, Georgia 30601
Project No.
EPA, 16020-EWE
11. Contract/Grant No.
13 Type ••{ Repoi t and
Period Covered
15. Supplementary Notes
Report EPA-R2-73-254, June 1973. 9 fig, 8 tab, 33 ref.
16. Abstract
Pulse differential polarography was found to be a more sensitive and
precise method than linear sweep voltammetry for the determination of
NTA as the bismuth complex in natural and waste waters. Indium was a
less satisfactory complexant. Relative standard deviations of less than
5% were obtained by the dual cell pulse differential technique at 1 ppm
NTA and calibrations were linear from 0.01 to 4 ppm. Copper, added at
concentrations greater than 10-5 M, caused low analytical results for
NTA. No other significant interference by metals or complexants was
found. An acetate electrolyte was much better than chloride for the
determination of bismuth-NTA complex in sewage-type samples. Recommended
procedures are given in the Appendix.
17a. Descriptors
*Analytical Techniques, *Polarographic Analysis, *Nitrilotriacetic Acid,
Sea Water, Sewage, Chemical Analysis, Water Analysis
17b. Identifiers
*Bismuth-NTA, *Indium-NTA, Linear Sweep Voltammetry, Differential
Pulse Polarography
lie. COWRR Field & Group
05A
18. Availability
19. Security
~ (Repots)
*0. Security C/.ss.
(Page) .-..-
Abstractor T. B. Hoover
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
institution EPA, Southeast Env. Res. Laboratory
WRSIC 1O2 iKEV.JUN? 1971)
------- |