design and application of ion selective...
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Design and application of ion selectiveelectrodes in atmospheric pollution analysis
Item Type text; Thesis-Reproduction (electronic)
Authors Kneebone, Barbara Maria Nowicki, 1948-
Publisher The University of Arizona.
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DESIGN AND APPLICATION OF ION SELECTIVE ELECTRODES
IN ATMOSPHERIC POLLUTION ANALYSIS
by
Barbara Maria Nowicki Kneebone
A Thesis.Submitted to the Faculty of the
DEPARTMENT OF CHEMISTRY.
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCTENSE'
In .the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 7 2
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillmentof requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED:
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
HenryProfessor of Chemistry
ACKNOWLEDGEMENTS
The author wishes to express her sincere thanks to
Dr. Henry Freiser for his invaluable advice and guidance through
out the course of the research and in the preparation of this
thesis.
The author is also grateful to Dr. Jarvis Moyers for
all his assistance.
This work was supported by a grant from the Arizona
Mining Association.
TABLE OF CONTENTS
Page
LIST OF TABLES..................................................... vi
LIST OF ILLUSTRATIONS.............................................. vii
ABSTRACT............................................................. viii
INTRODUCTION........................................................ 1
STATEMENT OF THE PROBLEM........................................... 6
EXPERIMENTAL........................................................ 7
Apparatus and Measurements................................... 7Materials..................................................... 7Construction of Coated-Wire Aliquat-Nitrate
Electrode.................................................. 8Primene and Tribenzylamine Nitrate
Electrodes........................................... 9Copper (I)-neocuproin Nitrate Electrode............... 9Iron(II)-bathophenanthroline Nitrate
Electrode............................................ 9Testing of the Electrodes.................................... 10Interference Studies.......................................... 10Conditioning and Storage of the Electrodes.................. 11pH Profile.................................................... 11Spectrophotometric Determinations of Nitrate................ 11
Phenoldisulfonic Acid Method.............................. 12Xylenol Method..................................... 12Jacobs and Hochheiser Method for
Nitrite......... 7 ...................................... 13Testing of the Electrode in H_0„ Absorbing
Solutions.................................................. 14Determination of Optimum Quantity of MnO^................... 14Testing of the Electrode in a Dynamic System................. 14Effect of Bubbling Rate...................................... 15
RESULTS AND DISCUSSION............................................. 17Coated-Wire Aliquat-Nitrate Electrode....................... 17Testing of the Electrodes.................................... 17Interference Studies.......................................... 18
iv
V
TABLE OF CONTENTS-Continued
Page
Conditioning and Storage of the Electrodes................. 22pH Profile................................................... 24Spec tropho tome trie Determinations of Nitrate............... 24Testing of the Electrode in H^O^ Absorbing Solutions...... 32Determination of Optimum Quantity of MnO^.................. 32Testing of the Electrode in a Dynamic System............... 32Effect of Bubbling Rate..................................... 37Effect of Concentration of Absorbing Solution.............. 37Testing of the Electrode on Air Samples.................... 40Effect of Absorption of SO^................................. 42
SUMMARY............................................................ 44
REFERENCES......................................................... 46
i
LIST OF TABLES
Table Page
1. Typical Response of an Aliquat-NO^ Electrode........... 19
2. Typical Responses of Other Nitrate Electrodes........... 21
3. Effect of Interfering Anions on Aliquat-NO^, Electrode Response.................................... 23
4. Effect of Conditioning in 0.1 M KNO^.............. 25
5. Effect of Conditioning in Aliquat-NO^ Solution......... 26
6. Effect of Storage in Air.................................. 27
7. Results of Phenoldisulfonic Acid Method Average ofThree Determinations.................................. 29
8. Results of Xylenol Method Average of TenDeterminations......................................... 30
9. Results of Jacobs-Hochheiser Procedure Average ofFive Determinations................................... 31
10. Effect of Peroxide Solutions on Electrode Response...... 33
11. Effect of Treating 2% Peroxide-Nitrate Solutionswith Various Reagents................................. 34
12. Effect of Adding Varying Amounts of MnO^ to 3%Peroxide-Nitrate Solutions............................ 35
13. Comparison of Spectrophotometrie (Xylenol) andElectrode Methods..................... '............... 36
14. Comparison of Bubbling Rates............................. 38
15. Comparison of Absorbing Solutions................... 39
16. Results of Tests on Air Samples.......................... 41
17. Effect of S0^ on Nitrate Electrode Response............ 43
vi
LIST OF ILLUSTRATIONS
Figure Page
1. Schematic of Gas Dilution System......................... 16
2. Typical Electrode Response Curve......................... 20
3. pH Profile of Aliquat-NO^ Electrode..................... 28
vii
I
ABSTRACT
The currently used spectrophotometrie methods for the
determination of NO^ in the atmosphere are time-consuming. An
alternative procedure was developed utilizing a coated-wire
nitrate-selective electrode to measure the concentration of
nitrate ion.
The optimum conditions for preparation and use of
the electrodes were determined. The effect of interfering
anions on electrode performance was studied.
The results obtained with the method developed in
this study were found to compare well (1-4% relative error)
with the accepted spectrophotometric methods.
Finally, the procedure was tested on air samples
collected on a roof of Biological Sciences East on March 29,
and April 5, 1972, for 24-hour periods begun at 3:00 p.m.3Concentrations of NO^ of 119 pg/m (March 29, 1972) and
3216 pg/m (April 5, 19 72) were found. These abnormally high
values might be attribted to heavy truck traffic in the area
during the time of the tests.
INTRODUCTION
The determination and analysis of air pollutants is a major
concern in every large metropolitan or industrial area. The nitrogen
oxides, NO and NO^ together referred to as NO^, are particularly
important because they participate in many photochemical reactions
and are largely responsible for the formation of the brown haze of
smog. Prolonged inhalation of nitrogen oxides results in a failure
to set up respiratory defense reflexes, thus causing pulmonary edema
(Jacobs, 1949). The generally accepted maximum allowable concen
tration for daily 8-hour exposure is 25 parts of NO^, other than
nitrous oxide, per million parts of air. Concentrations of 20-50 ppm
are irritable to the eyes.
Nitrogen oxides are produced by the reactions in combustion
engines and almost all combustions involving fossil fuels. NO is
present in automobile exhaust in concentrations ranging from a few ppm
to several thousand ppm (McFarland and Benton, 1972) . In automotive
exhaust gases at complete combustion and top speed, the concentration
of NO may be as high as 4000 ppm. NO and NO^ occur in parts per
hundred million concentration in polluted air where oxidation of NO
takes place very slowly at ambient conditions without sunlight. The
equilibrium concentrations of NO and NO^ depend on the amount of
oxygen available and the presence of oxidizing and reducing agents.
The oxidation of NO is the rate-controlling step in the absorption of
low concentrations of NO^. This step can be improved by adding a
strong oxidant, such as KMnO^, so that NO can be oxidized in the
liquid absorber (First and Viles, 1971).
Currently the method of choice for the determination of
nitrogen oxides in automobile and truck exhuasts and in stack gases
is the phenoldisulfonic acid method (Jacobs, 1960). In this method
not only all of the nitrogen oxides, except nitrous oxide, but also
nitrates and nitites and organic nitrogen-bearing compounds readily
decomposed and oxidized to nitrate are also included in the determin
ation.
The gas sample is taken in an evacuated sample collector
containing an oxidizing absorbent consisting of hydrogen peroxide in
dilute sulfuric acid. The nitric acid formed reacts to nitrate the
phenoldisulfonic acid added to the solution, forming a yellow-colored
compound. The absorbance is measured spectrophotometrically and the
nitrate concentration is determined from a set of standard curves,
(ASTM Designation: D1608-58T). In the ASTM method, two curves are
prepared. One covers the range 2 to 100 ppm and the other 100-500 ppm
NOg based on 1-liter samples of dry gas at 60°F and 760 mm.
Reducing agents such as sulfur dioxide interfere with this
method by reacting with the hydrogen peroxide and reducing its con
centration to a level such that it cannot oxidize all of the NO toxnitrate. The main drawback of this method is that it is very tedious
and time-consuming.
3
A well-known method for the determination of NO^ or by-
formation of an azo dye was devised by Griess in 1879 and modified by
Saltzman (1954). NO^ is first absorbed as nitrite which is then used
to diazotize sulfanilamide in phosphoric acid. The coupling agent
used is N-(1-naphthyl)-ethylenediamine dihydrochloride. The absorb
ance is measured at 550 nm. NO^ in the range of parts per hundred
million can be determined by this method.
The xylenol method (Jacobs, 1960) is another spectrophoto-
metric method for the determination of NO^. Air is sampled by the use
of an evacuated flask containing sulfuric acid. The nitric acid pro
duced nitrates the xylenol reagent (1.0 ml of 2,4-xylenol added to
99 ml of glacial acetic acid) to produce 4-hydroxy-l,3-dimethyl-5-
4 ^ nitrobenzene. The product is extracted with toluene and the absorb
ance is measured at 435 nm.
Because the available spectrophotometric methods are tedious
and time-consuming, it is very desirable to have a method which requires
a minimum of sample preparation and handling, and which is relatively
fast, accurate and reproducible. Measurement with ion-selective elec
trodes fits these specifications. The Orion nitrate ion-selective
electrode has already found application in the determination of NO^ in
the ppm range (DiMartini, 1970). The analytical technique employed
involves gas phase oxidation of NO or NO^ by ozone, followed by absorp
tion and hydrolysis of N^O^.
Use of potential measurements to obtain concentrations of
components of interest is a well established analytical technique.
Electrodes used for this purpose can be classified in the following
ways: (1) Electrodes of the first type are fine metal wires, such
as copper or silver, which respond to changes in the activities of
their respective ions. These are available for only a few metals.
Competing equilibria also restrict the use of this type of electrode.
(2) Electrodes of the second type are metal wires which are coated
with a poorly soluble salt of the metal. An example is the Cl
sensitive Ag/AgCl electrode. These M/MX type electrodes are good for
various X, but again their use is restricted by the availability of
suitable compounds. Wider applicability of this approach involves
membranes. The family of glass electrodes, including the classical
pH electrode, was the first example of the membrane electrodes and
has been most widely studied (Eisenman, 1967). More recently, several
types of solid state and liquid membrane electrodes have been devel
oped (Durst, 1969). Among the former are the fluoride electrode
(Frant and Ross, 1966) whose sensitive area is a lanthanum fluoride
crystal membrane, the silicone rubber based membranes of Pungor (1967)
containing, for example, silver halides, sulfides and barium sulfate,
and the Cu responsive electrode of Hirata and Date (1970) consisting
of Cu^S impregnated silicone rubber or epoxy resin film.
Among the so-called liquid membrane electrodes are the Ca"*""*"
sensitive electrode whose liquid phase is the calcium salt of a
phosphate ester (Ross, 1967) and the series of anion sensitive elec
trodes developed by Coetzee and Freiser (1969) which are based on
ion association extraction systems utilizing a quaternary ammonium
ion. Coetzee and Freiser showed that the range of applicability of
the nitrate sensitive electrode extends at least to 10 Si. It should
therefore be possible to apply this approach to the determination of
nitrogen oxides.
STATEMENT OF THE PROBLEM
The measurement of nitrogen oxides in the atmosphere is of
considerable analytical importance because of the hazardous nature
of even low levels of this class of compounds. Present spectrophoto-
metric methods are time-consuming and tedious. The applicability of
ion-selective electrodes to this problem will be explored and a suit
able analytical procedure will be developed.
EXPERIMENTAL
Apparatus and Measurements
All potentiometric measurements were made with an Orion
research model 701/digital pH meter using a Beckman Fiber Junction
Reference Electrode. The gas dilution system used was Calibration
System Model 309 comprising a constant temperature control oven and
a diluent and chamber flow controller (Analytical Instrument Develop
ment Co., Inc.). AID Permeation Tubes 3209 and 3393 containing NO^
were used in the system. A Gilford 2400 spectrophotometer was used
for all absorbance measurements.
Materials
ACS Reagent grade chemicals were used except as noted.
Aliquat^ 336S (methyl tricaprylyl ammonium chloride), Lot No. 8A371,£
was obtained from the Chemical Division of General Mills. Primene
81R was obtained from Rohm and Haas. Polyvinyl chloride, medium
molecular weight, and polymethyl methacrylate were from Monsanto Co.
Decyl alcohol, melting point 5.5-6.5°C, was from Eastman Kodak. Cyclo
hexanone, boiling point 154-156°C, was from Matheson, Coleman and Bell
Methyl acetate was Baker grade. Hydrogen peroxide (30%) was obtained
from Mallinckrodt. 2 ,4-Xylen-l-ol and o-phenol-m-disulfonic acid were
from K & K Laboratories. Toluene was spectrophotometric grade from
Matheson, Coleman and Bell. Dry nitrogen was from Dye Oxygen Co.
Construction of Coated-Wire Aliquat-Nitrate
All electrodes were prepared in the manner recently developed
in this laboratory. (Cattrall and Freiser, 1971; James, Carmack and
Freiser, 1972). A 15 ml sample of Aliquat 336S was dissolved in approx
imately 2 ml of decanol and this solution was shaken with six 10 ml
aliquots of 1.0 M KNO^ to effect the exchange of NO^ for Cl . Shaking
time on a wrist-action shaker was approximately 10 minutes for each
aliquot. After each shaking the aqueous phase was separated and dis
carded. The final aqueous phase was tested for the presence of Cl
with AgNO^. The absence of Cl indicated complete exchange. The
organic phase was centrifuged to remove traces of water.
A solution of polymethylmethacrylate was prepared by dissolv
ing about 0.5 g of plexiglass shavings in a minimum amount of methyl
acetate. A 4 ml volume of this plastic solution was mixed with 1 ml
of the Aliquat-NO^ solution. A platinum wire approximately 1 mm in
diameter whose tip had been melted in an oxygen-gas flame to form a
spherical button was soldered to a length of RG-58 coaxial cable. The
wire was then dipped in the Aliquat-plastic mixture several times to
coat it uniformly and allowed to dry for approximately 30 minutes. The
sensitive electrode tip was immersed in Aliquat-NO^ solution and
allowed to stand in it overnight. Prior to use, the exposed portion
of the wire was wrapped tightly with Parafilm.
Primene and Tribenzylamine Nitrate Electrodes
In the same manner, a nitrate electrode was prepared by
substituting Primene SIR in decanol for the Aliquat. Yet another
electrode was constructed with 0.02 M tribenzylamine in amyl alco
hol in place of the Aliquat.
Copper(I)-neocuproin Nitrate Electrode
A solution of Cu(I)-neocuproin-NO^ was prepared by mixing
2 ml of 0.01 M CuSO^, 2 ml of 0.3 M hydroxylamine sulfate, 5 ml of-4pH 6 phosphate buffer and 10 ml of 2x10 M KNO^ and shaking for 1 min-
-3ute with 5 ml of 2x10 M neocuproin in methyl isobutyl ketone. Anhy
drous Na^SO^ was added to the extract to remove traces of water. The
solvent was then evaporated under vacuum and the residue was dissolved
in a few drops of isoamyl alcohol. This was then mixed with 5 ml of a
saturated solution of polyvinyl chloride in cyclohexanone. A platinum
wire was coated with the mixture in the manner described and allowed
to dry for 1 hour. The electrode tip was then soaked in 0.1 M KNO^
until used.
Iron(II)-bathophenanthroline Nitrate Electrode
A solution of Fe(II)-bathophenanthroline-NO^ was prepared by
adding 5 ml of a 1% solution of hydroquinone to 5 ml of 0.14 M FeSO^•
( N H ^ ) • 6^0, adjusting the pH to 4 with sodium citrate, then adding
5 ml of 0.015 M bathophenanthroline and 5 ml of 0.2 M NaNO^. The
solution was shaken 3 times with 5 ml portions of isoamyl alcohol. The
extract was then shaken with a small amount of anhydrous Na^SO^ to get
10
rid of traces of water. A 2 ml volume of the organic phase was then
mixed with 5 ml of a saturated plexiglass solution and a platinum
was coated with the mixture and allowed to dry. The electrode tip
was then immersed in the organic solution and allowed to remain in it
overnight. Prior to use, the electrode tip was soaked in 0.1 M KNO^
for 2 hours.
Testing of the Electrodes-1 -5A series of solutions of KNO^ in the range 10 to 10 M
was prepared. The electrode tip was rinsed off with deionized water
then immersed in one of the standard solutions. The potential vs. the
reference electrode was measured once equilibrium was established,
which was evidenced by a stable reading. A stable reading was one
which did not fluctuate by more than + 0 . 2 mv.
Interference Studies
The effect of foreign ions on the response of the electrodes
was studied by making potentiometric measurements on solutions contain
ing 9, 18 and 24 times as much of the interfering anion as nitrate- 3present. The reference solution was 5x10 M KN0„. The test solutions— 3
were thus 5x10 ^ M in N0o plus 0.04, 0.09 and 0.12 M in the ion of— 3 —interest. The electrode was first immersed in the reference solution
then rinsed and immersed in the test solution, then rinsed and again
tested in the reference solution. The electrode was allowed to reach
the same potential in the reference solution after each test. This
procedure was followed for all ions tested.
11
Conditioning and Storage of the Electrodes
An Aliquat-NO electrode was prepared in the usual manner, jthen tested without pre-conditioning. The electrode tip was then
soaked in 0.1 M KN0_ for 1% hours and re-tested. Next the electrode — 3was soaked for 24 hours and tested again. The electrode was then
soaked for 7 days in 0.1 M KNO^ and tested.
Conditioning in an Aliquat-NO^ solution was also invest
igated. After the tip was allowed to harden slightly, it was immersed
in the solution of Aliquat-NO^ in decanol which had been used in the
coating. Soaking times from a few minutes to as long as three weeks
were used. Prior to testing, the tip was rinsed off with deionized
water and dried.
Storing the electrode in air between trials, with no soaking,
was investigated as was storing in air with a short period of soaking
in 0.1 M KNOg prior to testing.
pH Profile
The response of the electrode as a function of pH was studied. - 2The pH of a 10 M KNO^ solution was adjusted with concentrated H^SO^
and dilute NH^OH added dropwise. After each addition the solution was
stirred, the pH was measured and the potential recorded.
Spectrophotometric Determinations of Nitrate
The three most widely used spectrophotometric methods in the
determination of nitrogen oxides were tested in order to compare the
results with those obtained using the nitrate selective electrodes.
Phenoldisulfonic Acid Method
The procedure was followed exactly as outlined in Jacobs
(1960).
Reagents: o-phenol-m-disulfonic acid, 3% freshly
prepared, KNO^ stock solution (0.4266 g/1) , 0.05 M H^SO^, 1.0 M NaOH,
KNO^ standard solution (1:10 dilution of the stock).
Procedure: Transfer 0.0, 2.0, 4.0, 6.0 and 10.0 ml of the
standard solution to evaporating dishes. Add 25.0 ml of the oxidiz
ing absorbing solution (3 ml added to 100 ml H^SO^) to each dish.
Add NaOH to each sample until just basic to litmus. Evaporate each
to dryness and allow to cool. Add 2 ml of phenoldisulfonic acid very
carefully to each dish and triturate thoroughly. Add 1 ml H^O and
4 drops concentrated H^SO^ to each and heat for 3 minutes with occa
sional stirring. Allow to cool, add 10 ml H^O and mix thoroughly.
Add 15 ml cool, concentrated NH^OH dropwise to each with constant mix
ing. Test with litmus to make sure an excess is present. Filter the
solutions through 7 cm, rapid, medium textured filter paper into 50 ml
volumetric flasks. Wash the evaporating dishes three times with 4-5 ml
H^O. Dilute to the mark. Measure the absorbances at 400 nm in a
1.0 cm cell.
Xylenol Method
Reagents: Xylenol reagent (1.0 ml of 2,4-xylen-l-ol added
to 99 ml of glacial acetic acid), 85% I^SO^ (480 ml of concentrated
acid added to 117 ml of Ho0), 0.4 M NaOH, KN0o stock solutionz — 3
13
(0.1630 g/1), working standard (1:5 dilution of the stock), dilute
working standard (1:10 dilution of the working standard).
Procedure: Transfer 0.0, 1.0, 2.0 and 5.0 ml of the dilute
working standard and 1.0 and 2.0 ml of the working standard to 40 ml
extraction vials. Add H^O to make the volume 5 ml. Add 15 ml 85%
H^SO^, mix, and allow to cool. Add 1 ml xylenol reagent and mix.
Heat at 60°C for 30 minutes, then cool to room temperature. Transfer
the samples to separatory funnels, adjust the volume to 60 ml and add
10 ml of toluene. Shake for 2 minutes, allow the phases to separate,
then discard the aqueous layer. Add 25 ml H^O, shake for 2 minutes,
then discard the aqueous layer. Add 10 ml of 0.4 M NaOH and shake for
5 minutes. Filter the NaOH phase through Whatman #1 filter paper.
Measure the absorbance at 435 nm.
Jacobs and Hochheiser Method for NO^
Reagents: Absorbing solution (2 ml butyl alcohol per liter
of 0.1 M NaOH), N-(l-naphthyl)-ethylenediamine dihydrochloride
(Img/ml), diazotizing reagent (20 g of sulfanilamide in 1 1 of H 2 O
containing 50 ml of phosphoric acid), stock NaNO^ (0.150 g/1), standard
solution (1:10 dilution of the stock), 1% H^O^.
Procedure: Add 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 ml of the
standard to 35 ml of absorbing reagent contained in 50 ml volumetric
flasks. Add 1 drop of H^O^, 10 ml of diazotizing reagent and 1 ml of
coupling reagent to each. Dilute to the mark. Measure the absorbance
at 550 nm.
Testing of the Electrode in HgOg Absorbing Solutions
Test solutions of KNO^ were made up in 3%, 2% and 1% .
Electrode response was measured in these solutions. The solutions
were then boiled for varying lengths of time with a trace of ferrous
ion in order to destroy the peroxide, and measurements were made
again. Three 50 ml samples of nitrate solutions in peroxide were
also treated with (1) 1 ml of 0.01 M hydrazine sulfate plus 1 drop
of 0.001 M NiS04 , (2) with 1 ml of 0.01 M NagSO , (3) with 1 ml of
0.01 M hydroquinone, all solutions being heated for 1 hour at 70°C.
After cooling, the solutions were tested for nitrate with the elec
trode. To another set of solutions 0.001 g of MnO^ was added and
they were allowed to stand for 30 minutes until no more oxygen was
evolved. The solutions were then filtered and measurements were
then made.
Determination of Optimum Quantity of MnO^-4A series of solutions of 5x10 M KN0o was made up in 3%— 3
^2^2' Varying amounts of MnO^ were added to 10 ml aliquots of each.
They were allowed to stand for 30 minutes, then were filtered through
Whatman #1 filter paper. Measurements were made against a 5x10 ^ M
pure reference solution.
Testing of the Electrode in a Dynamic SystemThe AID constant temperature control oven was assembled with
the sealed glass chamber containing an NO^ permeation tube which
leaked at the rate of 1010 ng/rain. The temperature was set at 30°C
and the system was allowed to equilibrate undisturbed for 2 days. Dry
nitrogen was used as the diluent and carrier gas. (See Figure 1). The
system was connected in series with three 250 ml gas washing bottles
(Corning No. 1760), each containing 3% H 2 O2 absorbing solution. The
pressure regulator on the tank was set at 40 p.s.i. and the pressure
regulator on the oven was set at 30 p.s.i. Collection time was 50 min
utes for each run. Chamber flow was 1 1/min. and dilutent flow was
5 1/min. The solutions were allowed to stand undisturbed for 2 hours
after the gas was bubbled through them. Three 20 ml aliquots were
then taken from the first bottle and approximately 0.01 g of was
added to each. After 30 minutes the solutions were filtered and the
nitrate concentration of each was measured by the xylenol method. A
set of standards was run simultaneously.
Electrode measurements were made on solutions consisting-4of 10 ml of the test solution and 4 ml of 10 M KNO^ which had been
made up in 3% ^^02 and treated with Mn02 in the manner described.
Effect of Bubbling Rate
The oven and collecting solutions were set up in series as
previously described. The mixture of NC^ and Ng was bubbled through
the absorbing solutions at rates of 0.575, 0.1 and 3.0 1/min. for
50 minute periods. The solutions were allowed to stand for 2 hours.
Aliquots from the first and from the second bottles were then treated
with Mn0 2 and measured by both the xylenol and electrode methods as described in the previous section.
BulkheadJumper TubesFittings
FrontPanelNupro
Valve
BulkheadFitting Gas Mixing
Oven
Flow /Controller
Glass Chamber and Sealing DevicePressure „
Regulator
tjPressureGauge
CaseAssembly
DualRotameterAssembly Figure 1. Schematic of Gas Dilution System
HO'
RESULTS AND DISCUSSION
Coated-Wire Aliquat-NLtrate Electrode
The coated-wire ion selective electrode was developed by
Carmack, Cattrall, Freiser, James and Kneebone (1972) in this labora
tory and discussed in communications by Cattrall and Freiser (1971)
and James 3 Carmack and Freiser (1972). - The nitrate electrode used
in this work was a coated-wire adaptation of the Aliquat-NO^ . liquid
membrane system investigated by Coetzee and Freiser (1969) and Matsui
and Freiser (1970). It was found that it made no difference whether
the active species was mixed with the plastic or whether the electrode
tip was first dipped in the plastic, then in the solution of the ion-
association complex. The thickness of the coating did not affect the
performance of the electrode. The important factor was that the elec
trode tip was completely coated and the remaining exposed wire was
tightly wrapped with Parafilm
Testing of the Electrodes
Electrodes were tested by measuring response as a function
of log (nitrate ion activity) and comparing it with ideal9 i.e.,
Nernstian behavior„ In most cases with the Aliquat electrode there
was a 50-55 mv change for every decade change in activity, which is
reasonably close to the 59.2 mv change expected for ideal behavior.
The relationship was linear to 10 ̂M NO^ , although the useful
range* could be extended to 10 M. The correlation coefficient of the
17
line obtained in each case was usually between 0.995 and 0.999. A
typical set of responses is given in Table 1, A Nernstian plot is
shown in Figure 2.
. The response time of the electrodes was rapid. Between
30 and 60 seconds was required for the system to come to equilibrium.;
The readings could be reproduced during a test run to dr 1 mv or better
but the absolute potential readings varied from day to day anywhere
from 5 to 15 mv. In order to use the electrodes as reliable instru
ments , it is necessary to re-standardize them for each test run and
to bracket the sample solution with a standard reference sample.
Working coated-wfre electrodes were prepared with tribenzyl-
amine, Primene and neocuproin. The response was close to ideal, how
ever, only in the case of the neocuproin electrode. Within a few days
though, its response became erratic, so it was abandoned.
Attempts to construct an electrode using the Fe(II) batho-
phenanthroline system were not successful. A potential could not be
established when the electrode was tested. It was surmised that the
equilibrium was too slow, making the response time,unreasonably long.
Typical responses for these electrodes are given in Table 2.
Interference Studies
Selectivity coefficients were calculated from the Eisenman
equation; T n/z -iAE = (slope) log 1 4- K. ai .
Table 1
Typical Response of an Aliquat-NO^ Electrode
[no3 ] / ■ -log aN0 - 3
Potential
10 5 M 5.0 . 241 mv .10-4 ^ 4.0 221
5xio"4 3.31 183io"3 3.02 165-35x10 2.34 128.
10 2.05 1135xl0“2 1.39 81io™1 1.12 71
Slope = 52.6 i 1.2 mv*
Intercept = 208*0 i 3.1 mvCorrelation = 0,998Coefficient
*Range given corresponds to 1.0 standard deviation
PO
TE
NT
IAL
(MV)
2 0
220
/
/
LOG NITRATE ACTIVITY
Figure 2. Typical Electrode Response Curve
21
Table 2 .
.Typical Responses of Other Nitrate Electrodes
[NO^ ] Neocuproin Bathophen Tribenzylamine Primene
10 5 M 546 mv -80 mv 393 mv 7 6 mv
io"4 545 -127 . 391 70
5x10“4 514 -132 . 349 45
io“3 500 . -110 303 36-35x10 465 -112 . 256 . 21
io“2 445 -Ill 234 15
5xl0~2 418 -90 200 4
H 405 -79 169 -2 .
Slope 49 .5 ± 1.0 ft 23.8 ± 1.7 76.2 ± 5.2
Intercept 348,4 i 2.8 ft -31.7 ± 4.5 84.1 ± 14.5
CorrelationCoefficient
0.998 0.992 0.986
22
where and a ~ are the activities of the interfering anion and 3
nitrate ion in the test solution, respectively. When the.addition of
the foreign ion changed the activity of the nitrate ions the following
corrections were applied:
AE = AEmeasured + slope(Alog. 3 • . -
where Alog a is the difference in the logarithm-of the activity of the
nitrate ion in the two solutions, Selectivity coefficients are given
in Table 3.
A log K value smaller than -2.5 indicates that there is
virtually no interference from the foreign ion,. It was found that
sulfate did not interfere even at a concentration 24 times that of
nitrate. This is important in aJLr pollution analysis since SO^ inter
feres with conventional analyses. The differences in response between
the reference and the test solutions were due to a change in activity.
The study also revealed that Cl and NO^ were moderate
interferents? having log K values of -1.4 and -0.8, respectively,
C10^ was a strong interferent whose log K value was 0.26.
Conditioning and Storage of the Electrodes
The effects of conditioning and storage were evaluated by-1 -4noting the differences in slopes (measured between 10 and 10 M)
and in response time. (See Tables 4, 5, and 6.) Storing the elec
trodes in an aqueous 0.1 M KNO^ solution for more than 3 days rendered
the electrode useless.
23
Table 3
Effect of Interfering Anions on Aliquat-NO Electrode Response3 .
Anion Conc.Ionic
,. Strength . .
PotentialsTest
...Reference ..Soln. . . . log K
Cl™. 0.04 M 0.045 144 rav ' 142 mv -1.5
0.09 0.095 144 136 -1.4
0.12 0.125 141 128. -1.3
NO ~ 0.04 0.045 139 122. -0.82.0.09 0.095 130 101 -0.7
0.12 . 0.125. 126 92 -0.8
cl°3~ 0.04 0.045 122 56 . 0.27
0.09 0.095 124. 49 0.26
0.12 0.125 124 44 0.26
so".4 0.04 0.125 131 136 undefined
0.09 0.275 134. 140 -3.1
0.12 0.365 134 141 -3.1 .
Reference Solution 5x10 ̂M KNO— 3Electrode response in series of pure test solutions
54 mv/10~-fold change in conc.
24It appeared that the NO^ in the coating was leached out with pro
longed soaking. The electrode.functioned best if stored in Aliquat-- - 3NO^ solution, then rinsed and soaked for 15-30 minutes in 10 M KNO^-
Storage in the air was also quite satisfactory if the electrode was
conditioned in Aliquat-NO^ solution prior to use. Results are
collected in Tables 4, 5, and 6.
• pH Profile
The electrodes can be used in the pH range 3-8.5. Below-f —pH 3, there is strong interference from H and above 8.5, OH inter- .
feres. (See Figure 3.)
Spectrophotometric Determinations of Nitrate '
Of the spectrophotometric methods that were investigated,
the phenoldisulfonic acid method was the most time consuming, although
quite reliable. (Correlation coefficient of 0.999). The Jacobs-
Hochheiser procedure for nitrite was the most simple to perform and
also very reliable (0.997), but was not suited to our needs since we
were working with nitrate. The xylenol method was comparatively
simple, involving only extractions, and very reliable (1,000). This
method was therefore subsequently used in testing the electrodes for
their usefulness in air pollution analysis of NO^« Results for the
three methods are given in Tables 7, 8 and 9.
Table 4
Effect of Conditioning in 0.1.M KN0„ d
Conditioning Time0 . . IJg.hr s .. . 24..hrs. . ...3 d ay s
Response Time 15 min. 3 min. 15 sec. 10 min.
Slope 29.0 ± 6.2 mv 40.1 ± 3.6 mv 47.3 t 3,6 mv 95.2 ± 22.1 mv
Intercept 221.0 ±17.2 mv 199.3 + 9.8 mv 160.8 i 8.2 mv 400.1 ± 61,0 mv
Correlation Coefficient .
0.957 0.992 0.994 0.950
Table 5
Effect of Conditioning in Aliquat-NO^ Solution
Conditioning Tiine0 15 min. • 8 hrs. .... .. . . 2..wits.
Response Time 6 min. 30 sec. 10 sec. 20 sec.
Slope 47.8 ± 2.7 my 4 8,3 t 1.4 mv 54.7 i 1,0 mv 54.1 ± 1.2 mv
Intercept 82.2 ± 7.7 mv 62.1 i 3.4 mv -27.3 Z 2.6 mv -37.4 + 3.1 mv
CorrelationCoefficient
0.992 0.997 0.998 0,997
27,
Table 6
Effect of Storage in Air
Storage Time3 days 3 days
No soaking prior Soaked 15 min. into use, .......... Aliquat^NO^*
Response Time• 4 min. 1 min.
Slope 55.2 + 3.1 mv 61.0 ± 0.9 mv
Intercept 18.0 - 5.7 mv 88.4 dr 2.4 mv
Correlation 0.996 0.999Coefficient
PO
TEN
TIA
L (M
V)
AA-
pHFigure 3. pH Profile of Aliquat-NO^ Electrode
K>00
29Table 7
Results of Phenoldisulfonic Acid MethodAverage of Three Determinations
[N03 ] X 106 Absorbance
0.0 0.000
3.8 0.095
7.6 0.210 •
11.4 0.303
18.0 0.531 . .
Slope 0.053 * 0.0001
Intercept -0.006 ± 0.0002
Correlation 0.999Coefficient
30
Table 8
Results of Xylenol MethodAverage of Ten Determinations
[NOp x 106 Absorbance
0.0 , 0.036
3.2 0.044
6.4 0.056
16.0 0.088
32.0. 0.142 .
64.0 . 0.250
Slope 0.011 ± 0.000
Intercept 0.034.± 0.000
Correlation 1.000Coefficient
Table 9
Results of Jacobs~Hochheiser ProcedureAverage of Five Determinations
[N02 ] x 106 Absorbance
0.0 0.000
CO 00 0.027
17.6 0.052
26.4 0.098
35.2 . 0.122
44.0 0.152 .
Slope 0.156 ±0.005
Intercept -0.003 ± 0.003
Correlation 0,997Coefficient
Testing of the. Electrode in Absorbing Solutions
Because the' pH limitations precluded the use of strongly
basic absorbing solutions 9 it was decided to use hydrogen peroxide
as the absorber for NO . Tests with solutions of various percentages
of H2̂ 2 indicated that peroxide was a strong interferent both as a foreign, extractable ion and as a readily decomposed substance which
produced oxygen bubbles which adhered to the coated surface of the
electrode. (See Table 10,) Various reagents were tested for their
efficacy in destroying the peroxide. Finely divided MnO^ was found
to be the most effective* (See Table 11,)■
Determination of Optimum Quantity of MnO^
•It was determined that 0.01 g was the optimum amount to be
used for a 50 ml solution of 3% « This is a slight excess, but .
the reaction is speeded considerably. It was necessary to wait about
15-30 minutes for the complete decomposition of the H^O^.
(See Table 12.)
Testing of the Electrode in a Dynamic System
The significance of the results of these tests is that the
electrode method compared favorably with the xylenol method. The
results for the two agreed within 1-4% of each, which is within the
limits of experimental error. (See Table 13♦)
The importance of this to air pollution work is.that a
method has been found which is much simpler and faster than the
spectrophotometric methods currently in use, and just as reliable.
Table 10
33
Effect of Peroxide Solutions on Electrode Response
Electrode Potentials[N0,_] St’d KN0„ KN0„ in 3% H„0o . in 2% in 1% *■ * * . . . .
10"4 252 230 276 298
5xl0“4 224 216 264 263
10"3 209 207 244 245
5xl0"3 176 192 • 209 219
io~2 164 176 198 204
5xl0™2 127 158 . 159 177
'H '
• s 115 145 154 168
Slope 48.3 ±J 1.0 30.4 ±3.6 46.1 ± 2.8 44.9 ± 2.
Intercept 62.1 ± 2.6 115.6 ± 9.6 101.3 ± 7.4 114.4 ± 6.'
Correlation 0.999 0.997 0.991 0.997Coefficient
34
Table 11
Effect of Treating 2%. Peroxide-Nitrate Solutions with Various Reagents
PotentialsSt ?d KNO^ FeSO^ Hydrazine Na^SO^ Hydroquinone MnO^
• ■ • Sulfate •• ..... . •
-410 M 435 401 424 438 401 436
io“3 379 359 367 386 346 379-210 321 313 301 330 287 320-110 265 244 238 280 241 263
35
. Table 12 .
Effect of Adding Varying Amounts ofMnCL to 3% Peroxide-Nitrate Solutions
Amt. MnO^ Potential Reaction Time
4.54 mg 113.8 mv 45 min.
6.55 113.3 40.
18.63 112.8 20,
27.76 112.6 20.
89.25 . 113.3 15 min.
-AReference Solution; 5x10 M KN0o— 3Reference Potential; 113.1 mv
36
Table 13
Comparison of Spectrophotometfic (Xylenol) andElectrode Methods
[N03"] FoundSolution Spec. Method • ■Electrode % Rel . Error
A 3.30xl0"5 3.38xl0~5 2.3
B 2.82 . 2.87 1.9
C 2.20. 2.24 2.0
D 1.40 1.42 . • 1.5
E 2.80 2.85 1.9
F 1.00 1.03 2.6
' - ..; - - 37Additional advantages include.the facts that the electrodes are
small* portable? inexpensive*.sturdy and easily constructed, con
ditioned and stored.
Two problems were encountered in the experiment concerning
the permeation tube. The "first such device used in the gas dilution
system was in some.way defective, so that the entire contents leaked
out within a few days and the system had to be flushed out. The
usual life-time of NO^ permeation tubes is approximately three.months.
This can be lengthened somewhat if they are kept under refrigeration
when not in use.
Another difficulty was that occasionally the system was not ■
completely flushed out between runs so that there was a build-up of
NOg, which resulted in higher nitrate concentrations in the absorbing
solutions than calculated.
Effect of Bubbling Rate
No significant difference was found between! the slow and
the fast bubbling rates. (See Table 14.) The slower rate is prefer
able, however, since there is less splashing of the solution onto the
walls of the bottles.
Effect of Concentration of Absorbing Solution
It was found that either a 2 or 3% solution could be
used for absorbing the NO^, (See Table 15.) A 1% solution would also
Table 14
Comparison of Bubbling Rates
[NO^] FoundSolution Gas-Flow-. • Spec,: M e t h o d -• Electrode ,
A 0,575 1/min 4.21xl0“5 4.30x10""5
B IT 1.30 1.34
C u 1.31 1.34 '
D 0.100 2.71 2.79
E IT 4.00 4.11
F U 1.23 1.25.
. G 3,000 1.67 1.71
H .it 1.74 1.80
I IT 2.72 2.79
39
Table 15
Comparison of Absorbing Solutions
Solution z h 2o2[No3-)
Spec'. MethodFound
Electrode % RaL. Error
A 3 3.30xl0~5 3.38xl0"5 2.3
B IT 2.82 2.87 1-9
C II 2.20 2.24 2.0
D 2 4.22 4.31 3.3
E II 1.31 1.34 • 2.8
F II 1.30 1.34 3.1
G 1 1.43 1.47 3.0
H II 1.14 1.18 3.7
I II 4.10 - 4.20 2.6
: ; : .40be adequate except in the presence of large, amounts of S0o whichz .
might.reduce the concentration to a level such that all of the NOzwould not be oxidized.
-Testing of the Electrode on Air Samples
The air samples were taken and tested to see whether there
were any strong interferences present that had not been anticipated. •
Because the results of the two methods in each case.agreed within 3%
of each other, it was inferred that no such interferences were present.
The difference in the two concentrations of NO foundx3(119 and 216 pg/m ) was attributed to a change in collection efficien
cy since the fritted bubbler was in the third bottle during the
first run and in-the first bottle during the second.run. It was
difficult to interpret these results otherwise because the samples
were taken on two days and factors such as amount of traffic in the
area and ambient atmospheric conditions were different». (See Table 16.)
The Arizona State Dept, of Health in its Air Pollution
Control Implementation Plan (1972) used the federal primary standard 3
of 100 ]ig/m (annual average) as its ambient air quality standard
for NO-. The values obtained for NO in this study, expressed in
terms of NO^, are somewhat high reflecting the presence of abnormally
heavy truck traffic in the area during the test periods.3The occupational standards for ambient air are 9 mg/m
3for NO^, and 30 mg/m for NO averaged over 8-hour period (Federal
Register, August 13, 1971). Thus, using the method developed, it
would be sufficient to sample the air for 20 minutes or 4 minutes
Table 1641
Results of Tests on Air • Samples
Sample 1 (March 29, 1972)
NO Found x
Xylenol Method 119.3 yg/m^3Electrode Method 119 yg/m
Sample 2 (April 5, 1972)
NO Found x
3Xylenol Method 216 yg/m
3Electrode Method 216 yg/m
4 2
to determine whether the pollution levels of or NO 9 respectively 5
were below these values.
Effect of Absorption of SO ̂'
It was found that a SO^ concentration approximately
30 times that of the nitrate in an absorbing solution could be
tolerated. This would result in a 5% error in the calculated
concentration. (See Table 17.)
Table 1743
Effect of SO^ on Nitrate;. Electrode Response
Reference Potentials
(IxlO"4 M KNO„) 114.6 mv
[SO^ ] . Potential % Error
3x1 (f3 118.5 5.0
5xl0"3 119.1 5.8
7xl0"3 119.4 6.7
10~2 . 119.8 8.3
SUMMARY -
A procedure was developed for the determination of NO^ in
the atmosphere based on the use of a coated-wire ion-^selective elec
trode to measure the concentration of nitrate ion.
The optimum conditions for preparation and use of the
electrodes were determined. .
1. Electrodes can be constructed either by mixing the
Aliquat-NCL complex with the plastic solution and coating
the wire or by first coating the wire with plastic then
dipping it in the solution of the ion-association complex.
2.. The electrodes may be stored in Aliquat-NO^ solution,
then rinsed with de-ionized water and used9 or they may be
stored in air and conditioned in Aliquat-NO^ solution prior
to use. ■
The electrode was tested in absorbing solutions and it
was found that peroxide was an interference. It was discovered that
MnO^ was an excellent agent for destroying the excess-peroxide. A
procedure was then established for measuring NO^ inair samples.
1. Connect three 250 ml gas washing bottles in series, each
containing 100 ml of 2% .
2. Pump air through the solutions at a rate of approximately
2 1/min.
■ : ? 45
3. Let the solutions stand for a few hours. Add about 0.01 g
of to 50 ml from each of the solutions. Wait about
15-30 minutes for the decomposition of the . Filter
the solutions.
4. Mix 10 ml of the test solution with 4 ml of 10 ̂M KN0— 5which has been made up in 2% and treated with MnO^ •
in the manner described.
5. Measure the potential of the solution with an Aliquat-NO^
electrode along with.a set of standards.
This method was tested against the xylenol method. Results
from the two agreed within 1-4%. Sulfate concentrations approximately
30 times that of nitrate can be tolerated.
REFERENCES
Arizona State Dept. of Health, State of Arizona Air Pollution Control Implementation Plan, 1-16 (January, 1972).
Carmack, G.s R. Cattrall, H. Freiser, H. James, and B , Kneebone, Patent applied for, January 19, 1972.
Cattrall, R. and H» Freiser, Anal. Chem., A3, 1905 (1971).
Coetzee, C„ and H. Freiser, Anal. Chem. , 41, 1128 (1969).
DiMartini, R., Anal. Chem., 42, 9 (1970).
Durst, R., Ed., Ion-Selective Electrodes, Nat. Bur. Stand. (U.S.) Spec. Publ. 314, Washington, D.C., November, 1969).
Eisenman, G., Ed., Glass Electrodes for Hydrogen and Other Cations. New York: Marcel Dekker, Inc., 1967.
Federal Register, 36(157), 15102 (August 13, 1971).
First, M. and F. Viles, Jr., J. Air Pollut. Contr. Assoc., 21, 122 (1971).
Frant, M. and J. Ross, Science, 154, 3756 (1966).
Hirata, H. and K, Date, Talanta, 17, 883 (1970).
Jacobs, M. , The Analytical Chemistry of Industrial Poisons, Hazards and Solvents, 2nd ed., New York: Interscience Pub., Inc., 1949.
Jacobs, M. , The Chemical Analysis of Air Pollutants. New York:Interscience Pub., Inc., 1960.
James, H. , G. Carmack and H. Freiser, Anal. Chem. , 44_, 856 (1972).
Matsui, M. and H. Freiser, Anal. Lett. , _3, 161 (1970).
McFarland, J., and C. Benton, J. Chem. Ed., 49, 21 (1972).
Pung'or, E, , Anal, Chem. , 39, 28A (1967).
Ross, J., Science, 156, 3780 (1967).
Saltzman, B . , Anal. Chem. , 26, 1949 (1954).
4 6