EPA-R2-72-057
Environmental Protection Technology Series
September 1972
Development of Method for NTA
Analysis in Raw Water
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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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
i». 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..
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EPA-R2-72-057
September 1972
DEVELOPMENT OF METHOD FOR NTA ANALYSIS
IN RAW WATER
By
John K. Taylor
Walter L. Zielinski, Jr.
E. June Maienthal
Richard A. Durst
Robert W. Burke
National Bureau of Standards
Washington, D.C. 2023*4-
Project 16020 GVY
Project Officer
Dr. Thomas B. Hoover
Southeast Water Lab. - EPA
College Station Road
Athens, Georgia 30601
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. MVIRONMMTAL PROTECTION AGENCY
WASHINGTON, D.C. 20^60
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price 70 cents
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EPA Review Notice
>*.
This report has been reviewed'by the Environmenta'l'-Protec-
tion Agency and approved for publication. Approval does not
signify that the contents necessarily reflect the views and
policies of the Environmental Protection Agency nor does
mention of trade names or commercial .products constitute en-
dorsement or* recommendation for ,use. -A'-'
11
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ABSTRACT
The free acid form of nitrilotriacetic acid is readily
esterified by N,0-bis(trimethylsilyl)acetamide and gas chrom-
atographic analysis is directly applicable to this deriva-
tive. The response characteristic of NTA-trisilylester was
2,200 mm2 peak area per microgram of NTA at maximum sensi-
tivity of the hydrogen flame ionization detector. Accordingly,
gas chromatography has the potential for detecting NTA con-
centrations of practical interest providing that suitable
NTA isolation techniques can be developed.
The cupric ion-selective electrode provides the basis for a
sensitive electrochemical detector for NTA. Apparatus for
the on-stream determination of uncomplexed NTA has been
developed. This may be used for determination of total NTA,
after the latter is separated from bound metal ions and other
complexing agents by a suitable means, such as ion-exchange
chromatography.
Polarographic studies have shown that the bismuth-NTA complex
is a suitable method for the determination of NTA in most
waters. While some metal ions may interfere, a pre-electro-
lysis step and/or a standard addition technique seems feasible
to eliminate this problem.
Potentiometric titration with cupric ion should provide a
rapid and reliable referee method for the determination of NTA
in detergent formulations. Such a method would appear to be
superior to the spectrophotometric methods presently used,
since the latter are affected by turbidities which are en-
countered in many of the samples.
This report was submitted in fulfillment of Project 16020
GVY under the sponsorship of the Water Quality Office,
Environmental Protection Agency.
111
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CONTENTS
Section Page
I Conclusions 1
II . Re'commendations'. • 3
III Introduction 5
IV Gas Chromatographic Studies 7
V Ion-Selective Electrode Studies 15
VI Polarographic Studies 19
VII Potentiometric Titration Studies 23
VIII Acknowledgements 25
IX References . 27
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SECTION I
FIGURES
No. Page^
1 Gas Chromatographic Apparatus 8
2 Derivatization of Nitrilotriacetic Acid 9
3 Gas Chromatogram of Tri-Ester Derivative 10
4 Gas Chromatography-Mass Spectrometry System 11
5 Mass Spectrum of Silylated NTA 12
6 Gas Chromatographic Response for NTA 14
7 General View of Ion-selective Electrode 15
Apparatus
8 Close-up View of Ion-selective Electrode 16
Detector
9 Diagramatic View of Ion-selective Electrode 17
Detector
VI
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TABLES
No. Page
1 Retention Times Comparison of Silylated NTA 13
and Fatty Acids
2 Apparent NTA Content of Various Detergents 24
VI1
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SECTION I
CONCLUSIONS
The free acid form of nitrilotriacetic acid is readily
esterified by N,0-bis(trimethylsilyl)acetamide and gas chro-
matographic analysis is directly applicable to this deriva-
tive. The response characteristic of NTA-trisilyl ester was
2,200 mm2 peak area per microgram of NTA at maximum sensitivity
of the hydrogen flame ionization detector. Accordingly, gas
chromatography has the potential for detecting NTA concentra-
tions of practical interest, providing suitable NTA isolation
techniques can be developed.
The cupric ion-selective electrode provides the basis for a
sensitive electrochemical detector for NTA. Apparatus for the
on-stream determination of uncomplexed NTA has been developed.
This may be used for determination of total NTA, after the
latter is separated from bound metal ions and other complexing
agents by a suitable means, such as ion-exchange chromatography.
Polarographic studies have shown that the bismuth-NTA complex
is a suitable method for the determination of NTA in most
waters. While some metal ions may interfere, a pre-electro-
lysis step and/or a standard addition technique seems feasible
to eliminate this problem.
Potentiometric titration with cupric ion should provide
a rapid and reliable referee method for the determination
of NTA in detergent formulations. Such a method would appear
to be superior to the spectrophotometric methods presently
used, since the latter are affected by turbidities which are
encountered in many of the samples.
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SECTION II
RECOMMENDATIONS
The present study has identified three analytical techniques
that can provide the basis for the development of sensitive
methods for the determination of nitrilotriacettc acid at
trace levels of concentration. Gas chromatography has great
sensitivity, but its application depends upon the development
of techniques for separation of NTA from the water matrix.
The cupric ion-selective electrode may be used for chelometric
trace determinations, but an ion-exchange step to de-complex
the NTA and to separate it from other completing agents is a
prerequisite. Polarography has considerable utility but it
can also be improved by a suitable pre-treatment procedure.
Accordingly, the following recommendations are made for further
investigation:
1. Investigation of non-aqueous separation techniques that
would permit utilization of the gas chromatographic mea-
surement of NTA-trisilyl ester for trace analytical
purposes.
2. Investigation of simple ion-exchange processes for sepa-
ration of NTA as the free acid, as a preliminary step for
analysis by the cupric ion-selective electrode technique.
The object of the study would be to develop on-stream
methodology for which the technique is particularly ap-
plicable and for which the flow-cell designed in the
present work is directly utilizable.
3. Further investigation of pre-electrolysis as a technique
for removal of interfering ions, to extend the usefulness
of polarographic NTA determinations.
4. A study in-depth of the promising potentiometric titration
procedure to develop a referee method for the determination
of NTA in detergent formulations.
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SECTION III
INTRODUCTION
The constituents of household detergents are potentially
one of the largest sources of water pollution. Unless such
substances are readily biodegradable or easily removable
from water by conventional waste-treatment methods, they may
accumulate to undesirable levels. Accordingly, it is im-
perative that reliable analytical methodology is available to
monitor the concentrations of such substances in waste water,
before and after treatment, and to identify residual levels
that may'accumulate. Without the capability of adequate
analytical surveillance, deleterious if not dangerous con-
ditions could ensue.
The proposed use of nitrilotriacetic acid as a builder in
detergents is a case in point. While there are presently
several methods for the determination of this material, each
has its short comings for such reasons as complexity, cost,
or time requirements. Furthermore, most of these have not
been in use for a sufficient time that their reliability has
been fully evaluated under practical conditions.
It was the purpose of this work to investigate several
approaches to the problem of the determination of NTA in
waste water. Techniques selected for this study^Jjicluxle:
gas jcjrromatograpjiy; jjol.aro^gxaphyj j)otentiometric titrimetry;
ajMLTgliFse 1 ectllvfiZelegjb r o d ep qtentiometr y ~The studTes""17¥re
directed principally to the detection of residual levels in
waste water. Consideration was given to the potential for
development of monitoring techniques. A portion of this work
was directed toward the problem of determination of NTA in
detergent formulations by potentiometric titration.
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SECTION IV
GAS CHROMATOGRAPHIC STUDIES '
The investigation of gas chromatography as a technique for
the detection and analysis of NTA was undertaken from the
following points of view:
1. Optimization of the analytical conditions for the elution,
detection, and measurement of NTA.
2. Preparation of a suitable NTA derivative for analysis by
gas chromatography and verification of its structure.
3. Determination of detector response and its linearity for
NTA.
4. Preliminary investigation of recovery of NTA from aqueous
media.
The gas chromatograph analysis system is shown in Fig. 1. The
system was initially optimized in terms of helium carrier gas,
hydrogen, and air flow rates. Conditions for analysis were
then set as follows:
.Chromatographic column: 6 ft by 0.25 in o.d. stainless
steel tube packed with 10 percent w/w of UC-W98
silicone on 80-100 mesh acid washed, silane treated
Chromosorb W.
Detector: Hydrogen Flame ionization
Electrometer: Six input range and eight output attenuation
positions, provided an output signal of 1 x 10 12
amps at maximum sensitivity.
Column temperature: 180 °C ±1 °C
Column effluent flow rate: 65 cm3/min of helium
Hydrogen flow rate to jet: 45 cm3/min
Air flow rate to detector: 220 cm3/min
injection port temperature: 240 °C
Detector temperature: 240 °C
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Figure 1. Gas Chromatograph used in the analysis.
An earlier gas chromatography study [1] of the contamination
of EDTA by NTA demonstrated that the formation of NTA silyl
ester may be accomplished by the reaction of free NTA with
N,0-bis(trimethylsilyl)acetamide (BSA). The reaction is as
follows:
OSi(CH3)3
CH3C = NSi(CH3) 3 + N(CH2COOH)3 -"N (CH2 COOSi (CH 3) 3) 3
The reaction time was investigated and it was found that heat-
ing the reaction mixture of NTA in 0.1 cm3 BSA under mild
reflux for five minutes under a dry nitrogen atmosphere pro-
duced quantitative conversion of NTA to the ester form. Since
BSA will react with moisture, anhydrous conditions were main-
tained during derivative formation, as indicated in Fig. 2.
The BSA reagent was stored in a septum-sealed vial under re-
frigeration and withdrawn for use by penetrating the septum
with a needle attached to a dry syringe. Prior to the addi-
tion of BSA, the system was thoroughly purged with dry nit-
rogen, and a magnesium perchlorate drying tube was attached to
the top of the reflux condenser.
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Figure 2. Derivatization of nitrilotriacetic acid.
A gas chromatogram of the eluted NTA ester is shown in
Fig. 3. It was important to determine the structural authen-
ticity of the eluted peak. To accomplish this a gas chroma-
tograph-mass spectrometry (GC-MS) detection system (Fig. 4)
was used. Fig. 5 represents the mass spectrum of the eluted
peak with relative intensities greater than 1 percent of the
parent ion. The presence of an ion current at mass number 407
(shown in the insert in the figure) substantiates the identity
of the chromatographic peak as tris(trimethylsilyl)NTA ester.
This fact, together with the GC-MS observation that no lower
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NTA silyl ester appears at any point in the elution stream,
confirms that the derivatization reaction occurs stoichio-
metrically to form the totally es.terified derivative. The
ion currents at masses 392 and 364 represented the parent
ion minus one and three methyl groups, respectively. There
was no ion current at 334, confirming the absence of a
disilyl ester derivative. The highest current (base peak)
occurred at mass number 73, representing the trimethylsilyl
fragment.
A. Inject sample at high recorder attenuation
B. Solvent peak at high recorder attenuation
C. Switch to lower attenuation
D. NTA peak
Figure 3. Gas chromatogram of tri-ester derivative.
Nitrilotriacetic acid as present in water streams and beds
may be present in the chelated form. Chau [2] has stated
that some of |he metal jons which strongly complex with NTA
are Fe3 , Ni2 , and Cu2'. In addition to this problem, fatty
acids and hydrocarbons are included among candidate inter-
fering chemicals which occur in water streams. In regard to
the latter complication, the elution of hydrocarbon contam-
inants from a polar gas chromatographic column would occur
very rapidly, long before the elution of NTA tri-ester. The
retention comparison of long-chain fatty acids with that of
NTA tri-ester on the relatively non-polar silicone column is
shown in Table 1. Silylated myristic acid (Ci7H3602Si)
would present the most troublesome species, yet does not
10
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interfere with NTA measurement at concentrations below 10
times that of NTA. In severe cases of myristic acid con-
tamination, it is suggested that steps be taken to isolate
the NTA, or provide for selective NTA measurement. A mass
spectrometer represents a detector which can be used for
this purpose.
J
Figure 4. Gas chromatography-mass spectrometry system.
Considering the problem of NTA chelation with metal ions,
it has been determined that recoveries from aqueous solution
as assayed by the gas chromatographi£ procedure run below
40 percent, with the exception of Na _,_ It was obs_erved+that
wheiji aqu£ous + solutions containing Fe3^, Mg2- , Cu2 , Ca2 ,
Ni2 , Na , K and NTA were adjusted to pH 3 and were taken to
dryness, NTA was not recovered. A critical point in the evap-
oration step is reached as dryness is approached. When
11
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samples were taken past dryness, substantial losses of NTA
occurred. Even under ideal conditions, the concentration of
water samples without prior removal of metal ions effects low
recoveries of NTA. The recovery of NTA added to Potomac River
water was less than 3 percent.
Additional investigation of NTA isolation from chelated metal
ions is essential. Longman |3] has reported that a chelating
resin (Chelex 100) in the Na form has a high affinity for
metals chelated with NTA. The recovery of NTA from metal-free
aqueous media may be enhanced by taking the final concentration
to about 0.1 ml rather than to dryness, and introducing 1.5 ml
of BSA.
100
80
60
UJ
20
SILYLATED NTA (NITRILO TRIACETIC ACID)
BASE
MASS
NUMBER
407
392
364
RELATIVE
INTENSITY
0.25
0.42
0.38
ION
REPRESENTED
P
P-Me
P-3Me
WHERE P= PARENT
60 80 100 120
160 180 200
MASS NUMBER
220
240
260
280
300
Figure 5. Mass spectrum of silylated NTA.
Table 1
Retention Times Comparison of Silylated NTA and Fatty Acids
Silylated
Compound
Decanoic acid
Laurie acid
NTA
Myristic acid
Palmitic
Linoleic acid
Formula
Retention Time
(.minutes)
2.3
4.6
10.2
11.2
22.6
48.8
1 2
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The ch.romatograph.ic conditions of operation were detailed
above. For the determination of the level of detector response
and its linearity, standard solutions of NTA.we.re prepared
by reacting known amounts of NTA with BSA, followed by di-
lution with carbon disulfide. The standard solutions were
stored in septum-capped vials for gas chromatographic
analysis.
Measured aliquots were withdrawn through the septa with a
10 yl syringe containing a few yl of carbon disulfide next to
the plunger, followed by a few yl of air. The syringe con-
tents were injected into the inlet port of the gas chroma-
tograph using the carbon disulfide plug to flush the entire
NTA sample into the column. The carbon disulfide and excess
BSA reagent eluted within 1.5 minutes following injection.
The trisilyl NTA ester emerged at 10.2 ± 0.1 minutes. The
NTA standard solutions covered a sample injection weight
range of 0.22 to 23.5 yg, expressed as free NTA. The re-
sponse curve is given in Figure 6 in terms of mm2 peak area
for the NTA tri-ester peak as a function of sample weight of
free NTA. The nominal response was 2,200 mm2 peak area per
yg of NTA, corrected to maximum detector sensitivity. This
refers to a peak height above base of 30 percent of full
scale deflection on a 10 mV recorder at an unattenuated elec-
trometer input range of 10 for one microgram of NTA.
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Figure 6
GC RESPONSE (mm2 x 1(T3)
Gas chromatographic response for NTA.
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SECTION V
ION-SELECTIVE ELECTRODE STUDIES
An electrochemical detector based on the cupric ion-selective
electrode has been developed for the determination of com-
plexing agents, such as NTA, EDTA, eta., after separation by
ion-exchange chromatography. This detector was developed in-
dependently of the separation method, and the evaluation of
its response to NTA in the final system must await completion
of the chromatographic method.
The detector system, shown in Figures 7 and 8 and diagrammed
in Figure 9, is based on the response of a cupric ion-selective
electrode to electrochemically generated cupric ion in a
continuous, flow-through cell arrangement. In principle, the
detector system operates in this way: (1) cupric ion is gen-
erated coulometrically at a constant rate upstream from the
detector, i.e., between the outlet of the chromatographic
column and the detector; (2) the rate of generation is con-
tinuously variable to obtain optimum response at the detector
depending upon the concentration of the complexing agents ;
(3) the detector assembly, described in detail below, produces
a constant emf output until the cupric ion level is perturbed
by complexation with NTA or some other ligand; (4) since
the electrode only responds to the uncomplexed cupric ions,
the magnitude of the emf change can be related to the degree
of complexation and consequently to the amount of complexing
agent present.
Figure 7. General view of ion-selective electrode apparatus
15
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The detector assembly consists of a flow chamber machined
from Teflon into which is mounted the cupric ion-selective
electrode and a reference electrode designed for use in flow
assemblies. The indicator electrode is held securely in place
by the aluminum holder attached to the Teflon assembly as shown
in Figures 7, 8, and 9. This holder permits the electrode to be
seated tightly against the flow chamber lip, thus preventing
solution leakage around the electrode tip. The cupric ion in-
dicator electrode is mounted 60° from the vertical to avoid
bubble entrapment•in the flow chamber which could cause spurious
response.
Figure 8. Close-up view of ion-selective electrode detector.
In order to test the response characteristics of this system, an
electrolyte solution (0.01 M KN03) was flowed through the generator
and detector assemblies at constant rate (0.4 ml/min) using a syringe
pump (Figure 7). A constant current was applied to the coulometric
cupric ion generator. From a knowledge of the flow rate and current,
the concentration of cupric ion generated could be calculated and a
working curve established for the electrode system. This curve, is
linear from 5 ppm to about 0.2 ppm with a response slope of approx-
imately 21 mV/pCu (theoretical: 29.5 mV/pCu). The response time of
the electrode system to achieve a stable emf reading was measured
for step changes in the generator current, i.e., the cupric ion
activity. In general, at the very dilute cupric ion levels
generated (0.1 to 5 ppm), the time required to
16
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establish an equilibrium emf was about 3-4 minutes. Cal-
ibration of the electrode system in stirred standard solutions
showed similar behavior, i.e.; equilibration times of several
minutes and a sub-Nernstian response slope of approximately
23 mV/pCu. At higher cupric ion concentrations, the electrode
response is faster and more Nernstian.
The chromatographic procedure will require the removal of
divalent cations from the complexing ligands, perhaps using
a cation exchanger in the hydrogen ion form, followed by con-
version of the acid-form ligands to their sodium salts by
passage through another cation exchanger in the sodium form.
This procedure would result in a sample of the proper chara-
cteristics to be determined by the cupric ion electrode
detector.
Figure 9. Diagrammatic view of ion-selective electrode
detector.
17
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SECTION VI
POLAROGRAPHIC STUDIES
A number of polarographic methods for the determination of
NTA have been reported, most of them involving the addition
of an excess of metal ion and measurement of the reduction
peak of the metal-NTA complex. Daniel and LeBlanc utilized
addition of excess cadmium ion at a pH of 7-10 to determine
NTA in EDTA by conventional d.c. polarography [4,5]. Farrow
and Hill modified the method somewhat using standard additions
of the Cd-NTA complex and single cell cathode ray polarography
[6]. Haberman determined traces of NTA in river water and
sewage by the addition of excess indium and measurement of
the In-NTA reduction peak [7]. To increase the sensitivity
and reduce interferences, he used both cation and anion ex-
change column separations. Afghan and Goulden have developed
methods for the determination of traces of NTA in water by
measurement of either the Pb-NTA complex or the Bi-NTA complex
[8,9]. The method using the Bi-NTA complex has been adapted
by Gahler of the Water Quality Office, Pacific Northwest
Laboratory, Corvallis, Oregon, for the determination of NTA
in sea water [10], and by the Inland Waters Branch, Department
of Energy, Mines and Resources, Ottawa, Canada, for the
determination of NTA in water [11].
Preliminary studies were conducted involving the lead, the
cadmium and the bismuth complexes to determine which gave
the best defined polarographic peaks. Indium was not consid-
ered as Afghan [9] reports that very high concentrations of
indium are necessary for complete NTA recovery and at a mole
ratio of 5:1 of In:NTA, the polarographic peak of the indium-
NTA complex is extremely difficult to measure owing to its
proximity to the indium reduction peak. The Pb-NTA complex
was investigated in 3 different buffer systems: tris hydro-
chloride-ammonium hydroxide, glycine-ammonium hydroxide, and
ammonium chloride-ammonium hydroxide, around pH 7-8. The
Cd-NTA complex was also measured in an ammonium chloride-
ammonium hydroxide buffer system at pH about 9. The Bi-NTA
complex was then investigated in NaCl media at pH 2 and
appeared to give the best defined peaks and the highest peak
height for a given concentration of NTA. Plots of current -
vs-concentration were linear. A slope of about 0.1 yA/ppm
was found, with the instrumentation and electrodes used.
Aliquots of the supernatant liquid of several portions of
river-bottom mud which had been equilibrated with NTA solu-
tions for about a month to give final concentrations of 10
and 20 ppm of NTA were then analyzed. The river-bottom mud
solution contained about 5 percent solids. Values of 5.2
and 10.3 ppm of NTA were obtained, showing recoveries, of only
about 50 percent. The original NTA solutions used to prepare
the sludge mixtures were then analyzed to determine if the
19
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solution composition had changed. Values of 9.5 and 18.9 ppm
were obtained showing good agreement with the 10 and 20 ppm
starting compositions. It was postulated that part of the
NTA had equilibrated with the sludge, which then settled to
the bottom.
Several calibration curves in the region from 0.2 to 1.0 ppm
of NTA were then run on different days.
The recommended procedure for the preparation of the calibra-
tion curves was essentially that developed by Afghan and
Goulden [8,9] and recommended by Traversy [11]. This utiliz-
ed a differential cathode ray polarograph in the subtractive
mode of operation. Procedure: Aliquot 0.0, 1.0, 2.0, 3.0,
4.0, 5.0 ml of standard NTA solution (10 mg/1) into 50-ml
beakers. Add 5 ml of IN HC1 to the blank. Add 4.5 ml of IN
HC1 to each of the other solutions. Add 1 ml of 1 percent
hydroxylamine hydrochloride to each beaker to reduce any iron
present, then add 0.5 ml of bismuth solution (0.2 mg Bi/ml in
1M HC1). Add 25 ml of distilled water to each, adjust the
pH to 2.0 with ammonium hydroxide and dilute the solutions to
50 ml in a volumetric flask. Add about 1 ml of mercury to
each polarographic cell and transfer the solutions to the
cells. The blank solution is placed in the right hand cell
position, and a sample solution in the left hand cell
position. Deaerate with nitrogen for 10 minutes, then meas-
ure the Bi-NTA polarographic peak at about -0.25V vs a
mercury pool anode.
Some tap water solutions were also measured, but generally
erratic and incomplete NTA recovery was obtained. An inter-
fering peak, believed to be copper or ferric ion which had
not been successfully reduced, appeared close to the rising
portion of the Bi-NTA peak making reproducible measurement
of the Bi-NTA difficult. Although the solutions were meas-
ured subtractively with a tap water blank in the second
cell, it was not possible to balance out the base lines.
Gahler [10] found that as little as 2 ppm of copper in water
causes very high results. At first this seemed to be incon-
sistent with the above findings. Then it was realized that
he had used a low resolution conventional polarograph which
would present the Cu-Bi-NTA peak as a single peak. The
cathode ray polarograph separates the two peaks, but the
Bi-NTA peak follows the interfering peak so closely that a
diffusion level plateau from which to measure the base line
is not reached.
In view of the fact that the chromatographic separation of
NTA might not be feasible, it seemed possible that interfer-
ing metals ions could be separated by electrolysis of an
acidified solution of the tap water for several hours at
-0.9V. Preliminary efforts showed this to be feasible.
20
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Although NTA is reported to form complexes with few metal
ions commonly present in tap water at pH 2, except bismuth,
the possibility exists that incomplete NTA recovery from tap
water could result from its reacting with some other species
in the water. This effect could probably be overcome by a
standard addition technique. A set of tap water samples was
taken through the procedure as described above, except 4 ml
of additional NTA was added to each solution including the
blank. The recovery was quantitative, except for the 0.2
ppm level.
Sufficient instrumental sensitivity is available so that as
little as 0.05 ppm of NTA in the final solution could be
readily determined. This is the equivalent of 0.1 ppm in
the original water sample, however usually sufficient water
sample is available for preconcentration making possible the
determination of even lower levels of NTA.
In conclusion, it appears that the polarographic determina-
tion of NTA as the Bi-NTA complex is a suitable method. How-
ever, if the chromatographic separation of the NTA is not
performed, a pre-electrolysis step and/or the standard
addition technique may be necessary.
21
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SECTION VII
POTENTIOMETRIC TITRATION STUDIES
The potentiometric titration method described by Siggia, et al.
[12] was investigated for its applicability to the determina-
tion of NTA in detergents.
Titrations were performed in a 1:1 solvent mixture of water
and pyridine, using a platinum-calomel electrode system.
Microliter quantities of the 0.1M copper nitrate titrant were
added by means of a "Micrometric" syringe. Equilibrium was
readily established by magnetic stirring. Amounts of NTA in
the range of 0.5-5 mg in 10 ml of the mixed solvent gave sharp,
readily discernible end-points. Assuming a 1:1 Cu-NTA complex,
commercial samples of NTA and Na2NTA invaribly assayed 99-100
percent.
Several brands of commercial detergents were analyzed for NTA
by..the above procedure. Typical results are given in Table 2.
Table 2. Apparent NTA Content of Various Detergents
Detergent3 Wt. % NTA
Brand CH 8.1
Brand T <0.5
Brand CAb O8)
Brand DPC <0.5
Sample 18-135 11.4
Sample 26-184 5.7
a50-mg samples taken for analysis
gave a reverse titration curve relative to all other
samples and standards
clabel claimed phosphate- and NTA-free
The results given in Table 2 should be considered only as
preliminary values. Although known amounts of NTA were
recovered when added to the detergent samples, the varying
shapes of the titration curves from detergent to detergent
require further study and understanding. As an extreme
example the titration curve for one detergent, which is
2 -3
-------
undoubtedly high in phosphate, exhibited a negative rather
than positive break at what was considered to be the end-
point. The titration curves for all other samples, however,
were similar to those obtained for the standards.
With further+study, it is felt that a potentiometric titra-
tion with Cu 2 could afford a rapid and reliable reference
method for determining NTA in detergents. Spectrophotometric
procedures, although briefly examined in the early stages of
this investigation, do not appear as generally applicable
because of the turbidities which are encountered with many
of the samples.
2 4
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SECTION VIII
ACKNOWLEDGMENTS
The investigations described in this report were carried
out by the following members of the staff of the Analytical
Chemistry Division, Institute for Materials Research,
National Bureau of Standards:
Gas Chromatographic Studies - Walter L. Zielinski, Jr.
and William D. Dorko
Ion-Selective Electrode Studies - Richard A. Durst
Polarographic Studies - E. June Maienthal and
B. T. Duhart.
Potentiometric Titration Studies - Robert W. Burke
and Robert Deardorff.
Dr. David H. Freeman directed the gas chromatographic studies
Dr. John K. Taylor served as coordinator of activities and
prepared the final report.
The support of the project by the Water Quality Office,
Environmental Protection Agency and the help provided by
Dr. Thomas B. Hoover, Project Officer for EPA, are
acknowledged with sincere thanks.
2'5
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SECTION IX
REFERENCES
[1] National Bureau of Standards Technical Note 459,
D. H. Freeman, Editor, 23, (1968).
[2] Y. K. Chau and M. E. Fox, Canada Centre for Inland
Waters, Burlington, Ontario, Canada, preprint.
[3] G. F. Longman, Port Sunlight Laboratory, Unilever
Limited, Port Sunlight, Wirrall, Cheshire L624XN,
personal communication.
[4] R. L. Daniel and R. B. LeBlanc, Anal. Chem., 31,
1221 (1959). —
[5] R. B. LeBlanc, Anal. Chem., 3_1_ 1840 (1959).
[6] R. N. P. Farrow and A. G. Hill, The Analyst, 90, 241
(1965). —
[7] J. P. Haberman, Anal. Chem., 43_, 63 (1971).
[8] B. K. Afghan and P. D. Goulden, J. Environ. Soi.
& Teohnol., _5, 601 (1971).
[9] B. K. Afghan, "Differential Cathode Ray Polarography
for Trace Analysis with Special Reference to NTA and
Its Complexes with Heavy Metals", a talk presented at
the International Symposium on Identification and
Measurement of Environmental Pollutants, Ottawa,
Canada, June 15, 1971.
[10] A. R. Gahler, private communication.
[11] W. J. Traversy, "Methods for Chemical Analysis of
Waters and Waste Waters in Use in Water Quality
Division Laboratories", Inland Waters Branch,
Department of Energy, Mines and Resources, Ottawa,
Canada, 1971.
[12] S. Siggia, D. W. Eichlin, and R. C. Reinhart,
Anal. Chem., 21, 1745 (1955).
2 7
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Accession /Vumbor
Subject Field & Group
05A
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Analytical Chemistry Division, National Bureau of Standards
Title
DEVELOPMENT OF METHOD FOR NTA ANALYSIS IN RAW WATER
10
Authors)
Taylor, John K.
Zielinski, Walter L. , Jr
Maienthal, E. June
Durst, Richard A.
Burke, Robert W.
16
•21
Project Designation
EPA Project 16020 GVY
Note
22
Citation
Environmental Protection Agency report
number EPA-B2-72-057, September 1972.
23
Descriptors (Starred First)
Detergents*, Analytical Techniques*, Electrochemical Analysis,
Gas Chromatographic Analysis.
25
Identifiers (Starred First)
NitrilotTiacetic Acid*, Analytical Methods*
27
Abstract
A gas chromatographic method has been developed for the determination of
NTA, after esterification of the isolated free acid form with N,0-bis(tri-
methylsilyl)acetamide.
The cupric ion selective electrode provides the basis for a sensitive
electrochemical detector for NTA. Apparatus has been developed for the on-
stream determination of uncomplexed NTA. After the latter is separated
from bound metal ions and other complexing agents by a suitable means, such
as ion-exchange chromatography.
Polarographic measurement of the bismuth-NTA complex is suitable for the
determination of NTA in most waters. A pre-electrolysis step and/or a stan-
dard addition technique seems feasible to eliminate interference problems.
Potentiometric titration with cupric ion provides a rapid and reliable
referee method for the determination of NTA in detergent formulations and
when turbidities are encountered in samples.
This report was submitted in fulfillment of Project 16020 GVY under the
Sponsorship of the Water Quality Offices, Environmental Protection Agency.
Abstractor
John K. Taylor
Institution
National Bureau of Standards
WR:102 (REV. JULY 1969)
WRSIC
SEND TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 20240
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