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

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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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