Report No. SRIC 71-6
IMPROVED INSTRUMENTATION FOR
DETERMINATION OF EXHAUST GAS
OXYGENATE CONTENT
Contract No. CAPE 11-68 ( 1-69)
Annual Report April 1971
Alan G. Day, III, David P. Beggs,
Marvin L. Vestal and Wm. H. Johnston
With contributions from
Gordon J. Fergusson, F.W. Lampe, Austin
Wahrhaftig, Wm. F. Biller, Edward Kraftel,
Donald McCubbin, and Donald Kennedy
Scientific Research
Instruments Corporation
In Air and Wat*r PoUut»on Con«r»l Syctomt
6707 Whit.ifone Rd olHmor.. Md. 21207 Cabl. SRICOBP Tal (301) 944-4020
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Report No. SRIC 71-6
IMPROVED INSTRUMENTATION FOR
DETERMINATION OF EXHAUST GAS
OXYGENATE CONTENT
Contract No. CAPE 11-68 (1-69)
- Annual Report April 1971
Alan G. Day, III, David P. Beggs,
Marvin L. Vestal and Wm. H. Johnston
With contributions from
Gordon J. Fergus son, F.W. Lampe, Austin
Wahrhaftig, Wm. F. Biller, Edward Kraftel,
Donald McCubbin, and Donald Kennedy
Prepared for the National Air Pollution Control
Administration, Durham, North Carolina, 27701,
and the Coordinating Research Council, Inc., 30
Rockefeller Plaza, New York, New York.
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TABLE OF CONTENTS
Page
TABLE OF CONTENTS i
LIST OF FIGURES ii
LIST OF TABLES iv
ABSTRACT v
INTRODUCTION 1
PRELIMINARY LABORATORY EXPERIMENTS 4
Response Time Measurements 4
Investigation of Potential Interferences 8
Automobile Exhaust Monitoring 12
PRELIMINARY FIELD EVALUATION 17
Introduction 17
Results 19
Discussion 29
IMPROVEMENTS IN TECHNIQUE AND APPARATUS 33
Calibration System 33
Inlet System ( 42
Ammonia as a Reagent Gas 49
RESULTS AND DISCUSSIONS 54
APPENDIX 71
BIBLIOGRAPHY 73
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LIST OF FIGURES
Figure 1- Response of Chemical lonization Direct
Reading Mass Spectrometer to a Step Injec-
tion of Formaldehyde at the 10 ppm Level
Figure 2- Response of Chemical lonization Direct 6
Reading Mass Spectrometer to a Step Injec-
tion of Benzaldehyde at the 10 ppm Level
Figure 3- High Pressure Spectrum of Water 10
Figure 4- Response of the Direct Reading Chemical 13
lonization Mass Spectrometer at Masses
31 to 33 as a Function of Formaldehyde
Concentration in Nitrogen Using Methane as
the Reagent Gas at 1 part to 2 parts Nitrogen
Figure 5- Monitor of Acrolein Concentration During 14
Injection of 25 ppm Acrolein
Figure 6- Monitor of Formaldehyde Concentration 15
Figure 7- Graphical Depiction of the 7 Mode California 23
Standard Cycle
Figure 8- (Run l) Concentrations of Selected Components 24
of Exhaust Gas Measured During a 7 Mode
California Cycle Run on a Dynamometer.
Figure 9_ (Run 1) Concentrations of Selected Components 25
of Exhaust Gas Measured During a 7 Mode
California Cycle Run on a Dynamometer
Figure 10-(Run 2) Concentrations of Selected Components 26
of Exhaust Gas Measured During a 7 Mode
California Cycle Run on a Dynamometer
Figure 11- Response Time Measurements of the Total 28
Instrument and Inlet System
Figure 12- Vapor Pressure of Aldehyde as a Function 35
of Temperature
Figure 13- Diagram of Proposed Calibration System for 37
Aldehydes in the PPM Range
Figure 14- Schematic Diagram of New Inlet System 43
11
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Page
Figure 15- Overview of ReagentrSample Mixing Oven 44
Figure 16- View of AUTOSPECT with New Inlet System 45
Attached
Figure 17- Spectrum of Ammonia at 0.7 Torr, 50°C 50
Figure 18- Chemical lonization Spectrum of Acrolein 52
(Ammonia Reagent)
Figure 19- Spectra of Acrolein and Butene via C.I. by 60
Methane
Figure 20- Spectra of Acrolein and Butene via C.I. by 61
Ammonia
Figure 21- Spectra of Pentene and Crotonaldehyde via 62
C.I. by Methane
Figure 22- Spectra of Pentene and Crotonaldehyde via 63
C.I. by Ammonia
Figure 23- Spectra of Xylene and Benzaldehyde via C.I. 65
by Ammonia
Figure 24- Spectra of Xylene and Benzaldehyde via C.I. 66
by Methane
Figure 25- Spectra of Formaldehyde via C.I. by Methane 67
and Ammonia
Figure 26- Spectra of Acetaldehyde via C..I. by Methane 68
and Ammonia
Figure 27- Spectra of Propionaldehyde via C.I. by Methane 69
and Ammonia
111
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LIST OF TABLES
i i
Page
I. AUTOSPECT Measurements Vs. DuPont Analyses 20
Test Conducted at Scott, Laboratories, Inc.
H. AUTOSPECT Measurements Vs. S.R.L. 21
Chromotropic Acid Analyses
III. Comparison of Empirically Determined Diffusion 40
Coefficients of Aldehydes and Hydrocarbons
(Calculated for 273°K)
IV. Relative Sensitivities of Important Aldehydes and 55
Hydrocarbons Measured in a Series of Runs Under
Chemical lonization Conditions at 200*C Using
Methane and Ammonia as Reagent Gases
IV
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ABSTRACT
The application of chemical ionization mass spectrometry
to the instrumental analysis of oxygenates in automobile exhaust
gases is described. Initial monitoring experiments demonstrated
the capability of this technique to simultaneously measure the
instantaneous concentration of formaldehyde, acetaldehyde, acrolein,
propionaldehyde, crotohaldehyde, butyraldehyde, valeraldehyde,
and benzaldehyde, and the total aldehyde concentrations .
Preliminary field evaluation established the accuracy and
reliability of the instrument via suitable reference tests. The
unique ability of this instrument to simultaneously follow the
rapidly changing concentrations of nine oxygenates was also
verified.
However, it was concluded that the presence of significant
amounts of hydrocarbons in the exhaust gas interfered with the
r
measurement of acrolein, crotonaldehyde, benzaldehyde, and
tolualdehyde. Further, research resulted in the utilization of
ammonia as a reagent gas to overcome this problem and selectively
-------
ionize the unsaturated aldehydes in the presence of the hydrocarbons,
i .
An improved calibration procedure and inlet system were
developed. These advancements resulted in a reduction of
sample losses in the inlet system and an increase in the accuracy
of the instrument. The response time of the total system was
lowered to less than one second. The incorporation of these
improvements into the system along with the use of ammonia as
an alternate reagent gas has eliminated most of the major prob-
lems of the instrument.
VI
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INTRODUCTION
This is the final report for Phase II of the CAPE-11-68
(1-69) CPA-70-73 contract on the application of chemical ioniza-
tion to the measurement of oxygenates in automobile exhaust.
The high point of this year's work has been the successful field
test of AUTOSPECT at Scott Research Labs, Plumsteadville,
Pennsylvania. These tests demonstrated the ease with which this
instrument can continuously monitor eight different oxygenates
simultaneously from the exhaust of a motor vehicle being run
on a variable - load dynamometer. From the evaluations
of these tests, improvements in inlet design, calibration technique,
and the chemical ionization process have been initiated with
emphasis in improving the sensitivity to the parts per billion range
and eliminating exhaust hydrocarbon interferences and aldehyde
memory effects.
Previously, during Phase I of this contract, a prototype mass
spectrometer, -AUTOSPECT, was designed and built, which combined
the chemical ionization technique developed by Field and co-workers
-1-
-------
with a direct reading mass spectrograph developed at Scientific
1
Research Instruments. The ionization section of this proto-
type instrument included a specifically designed ion gun assembly
which enabled the production of ions under conditions for chemical
ionization i.e., pressure of from 1 to 10 Torr . The analyzer section
of the instrument employed the double focusing principle of Mattauch
and Herzog and included an array of fixed collectors at integral
masses from atomic mass unit 1 to 128.
AUTOSPECT was then used with methane as a reagent gas
to successfully produce protonated parent compounds (M + 1) of
all oxygenate compounds found in automobile exhaust as identified
2
by Oberdorfer. With the exception of acrolein, crotonaldehyde,
benzaldehyde, and tolualdehyde, no interferences were found to
be present with the aldehydes and ketones due to the presence of
hydrocarbons when measured with methane as the reagent gas.
After the preliminary field testing of AUTOSPECT during
Phase II it was found that with a vehicle with a 1969 style PVC
valve pollution device, enough hydrocarbons were emitted as to
significantly interfere with above mentioned aldehydes to merit
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an investigation of other compounds as reagent gases. Ammonia
was found to selectively ionize acrolein, crotonaldehyde, benzal-
dehyde, and tolualdehyde to produce the parent compound. This
is discussed in more detail in a later section of this report.
Phase II also included the successful development of a
calibration procedure whereby a liquid sample of an aldehyde or
ketone was injected into a flowing stream of nitrogen gas at a
fixed rate. The preliminary field tests pointed out a need for
improvement in this area. It was found that under field conditions
this system was too time consuming and too sensitive to temperature
fluctuations.
Also during preliminary investigations it was discovered that
great care must be taken in the design of the exhaust sample line,
particulate filter and sample-reagent mixing chamber so as to
prevent deposition of polymerized formaldehyde. This is discussed
in more detail in a later section.
-3-
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PRELIMINARY LABORATORY EXPERIMENTS
i
Response Time Measurements
Preliminary measurements of the response time of the total
system were made. The results of these experiments indicated
that the response time constant which was applicable to raw ex-
haust gas monitoring was three seconds. Since the response
time of the analysis system has been previously determined to be
less than one microsecond, the response time of the total sys-
tem is a reflection of the response time constant of the heated
sample inlet system itself.
Typical results of measurements of the response time of
the fixed collector direct reading mass spectrometer system
coupled to the heated inlet are shown in Figures 1 and 2. These
plots show the response of the instrument to the injections of
formaldehyde and benzaldehyde, respectively. These measure-
ments were performed by injecting a step pulse of the selected
aldehyde at approximately 0. 01 milliliters per minute into a
stream of nitrogen gas flowing at 10 liters per minute. These
-4-
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Mass 17
(Reagent)
H 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1-
Mass 31
( Formaldehyde)
> 1 1 1 1 1 1 ! 1 1 1 1 1 1 1 1 1 1 1 ' 1 1
Injection on
off
Figure 1 Response of Chemical lonization Direct Reading
Mass Spectrometer to a Step Injection of
Formaldehyde at the 10 ppm level
-5-
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Mass 17
( Reagent)
Mass 107
Benzaldehy^d
-\ r
i !
-J U
second
Injection
on
on
Figure 2 Response of Chemical lonization Direct Reading
Mass Spectrometer to a Step Injection of
Benzaldehyde at the 10 ppm level
-6-
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plots of the results show the effects of the step injections upon
the channels representing formaldehyde and benzaldehyde in
the mass spectrometer system. The effect of these step in-
jections upon the reagent ions (mass 17) is shown to be negligible.
This demonstrates that there are no spurious effects due to the
loss of an inordinate amount of reagent ions.
These results correspond to an experimental time con-
stant of approximately three seconds for both aldehydes. This
same time constant was observed for all other aldehydes measured.
The time constant of the inlet system was reduced to one second
by improving the total inlet system package. This improved
system is covered in a later section.
-7-
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Investigation of Potential Interferences
The use of methane as a reagent gas in chemical ioniza-
tion provides distinct and accurate measurement for all but a
few of the aldehydes and ketones present in automobile exhaust
gases. The saturated aldehydes and ketones are not impaired
by interferences from hydrocarbons. The oxygenated com-
pounds give ions principally at the parent mass plus one ion,
while the hydrocarbons of the same molecular weight produce
ions at the parent mass minus one.
However, hydrocarbons do interfere with unsaturated
aldehydes. Acrolein produces an ion at m/e 57 via chemical
ionization with methane. Butyl ions also at m/e 57 may be
produced by proton transfer to the butenes or by hydride ion
transfer, to the butanes. Thus the presence of butenes or
butanes in automobile exhaust will interfere with the mea-
surement of acrolein when methane is used as a reagent gas.
Pentenes and pentanes interfere in the measurement of croton-
aldehyde via a similar mechanism. The presence of pentenes,
pentanes and crotonaldehyde will all produce an ion at m/e 71
via chemical ionization with methane as the reagent gas. One
-8-
-------
of the advantages of chemical ionization is that one can vary the
reagent gas and thus vary the amount of energy which is trans-
ferred to the molecule upon ionization. Since the hydrocarbons
have a different proton affinity than the unsaturated aldehydes,
it should be possible to find a reagent gas which will ionize
hydrocarbons and not ionize the unsaturated aldehydes via the
chemical ionization process.
Because of its omnipresence, water was utilized as a
reagent gas in an attempt to modify or eliminate the interference
of hydrocarbons in the measurement of unsaturated aldehydes.
The typical spectra of water at 1 Torr is shown in Figure 3.
The various ions in the spectra are produced by a series of
equilibrium reactions. These equilibria along with the precursor
reactions are shown below.
H2O + e- »- H2O+ + 2e-
H2O+ -f H2O *- H3O+ + OH
H30+ + H20 =^r H(H20)2+
H(H20) + + H20 =^: H(H20)++ [
-9-
-------
IUU -
A 80-
W
(0
c
0)
S 60"
> *
V
**
1) 40 -a
20"
+
H30
H502+
+
H703
+
H904
+
HU0S
' '1
U 6 |
III II 1 1 1 II 1
ZO 40 60 80 80 100
m/e
iPigure 3. High Pressure Spectrum of Water
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The initial H3O ion is produced by a proton transfer reaction
from one water molecule to another. The other ions in the
equilibrium system are produced by the addition of one or more
water molecules to this H3O ion. In several experiments it was
found that water will indeed proton transfer to the various alde-
hydes in automobile exhaust. However, water will also react
with the hydrocarbons and thus produce the same interferences
at the m/e values of 57 and 71 as were experienced with methane
as the reagent gas. It was therefore concluded that water would
not be a suitable substitute as a reagent gas in an effort to elimi-
nate hydrocarbon interferences. It was later discovered that ammonia
may be used as a reagent gas to distinguish between the unsaturated
aldehydes and their interfering hydrocarbon compounds. This ap-
proach is discussed in detail in a later section.
Particular interference in the measurement of aldehydes by the
presence of H2, N2, O2, H2O, CO, CO2, NOx, H2S and SO2 was deter-
mined to be negligible. Experiments were undertaken to verify that
the quantitative measurement of each of the aldehydes involved in
this study were not in error due to the presence of the above constituents
of automobile exhaust.
-11-
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Automobile Exhaust Monitoring
The initial tests using the direct reading chemical ioniza-
tion mass spectrometer to monitor raw exhaust gases were con-
ducted at the SRIC laboratory in Baltimore, Maryland. These
measurements were accomplished using the heated inlet system
and continuous monitoring of the fixed collectors. The alde-
hydes monitored included formaldehyde, acetaldehyde, acrolein,
propionaldehyde, crotonaldehyde, butyraldehyde, valeralde-
hyde, benzaldehyde, and the total aldehyde concentrations.
Calibration of the system for each of these aldehydes was
accomplished by injecting the aldehydes at a known rate into a
stream of nitrogen gas simulating the automobile exhaust.
These calibrations were carried out in the concentration range
from 1-100 parts per million and the response was linear to
within 10 percent over this concentration range. An example of
a calibration response is shown in Figure 4.
Some of the results of the initial exhaust tests are shown
in Figures 5 and 6. During the calibration measurements the
system was operated using calibrated injections of pure individual
-12-
-------
~1
25-
lon
Current
(Amperes x 1010
1.5
1.0"
0.5-
100 200 300 400 500 600 700 800
Formaldehyde Concentration (parts per million)
900
1000
Figure 4 - Response of the direct reading chemical ionization mass spectrometer at masses 31
and 33 as a function of formaldehyde concentration in nitrogen using methane as the reagent
gas at 1 part to 2 parts nitrogen. The formaldehyde was injected as formalin solution contain-
ing 38% formaldehyde and 13% methanol in water. The response at mass 33 is due to the
protonated methanol.
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g
... H
£ 13
rt «
rf 2
1-1 0
4) O
P* O
Probe
n | Injection
I 25 ppm
(Probe
but
10
20 30
Time, sec,
40
50
60
Figure 5 Monitor of Acrolein Concentration
During Injection of 25 ppm Acrolein
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c
o
t*4
ri.
o> t>
-H C
'tJ o
£ G
V O
»! O
Idle Trans miss io
Load
c~ ^
I
10 ZO 30 40
n
Probe Out
>V
50 60 70 80
Time, sec.
Figure 6 Monitor of Formaldehyde Concentration
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aldehydes in nitrogen as well as using mixtures of the aldehydes.
No significant synergistic effects involving the mixtures of the
various aldehydes were observed.
The operation of the direct reading chemical ionization
mass spectrometer system was demonstrated to the APRAC Project
Group, Cape 11-68, on July 28, 1970. The response of the system
to individual aldehydes was demonstrated as well as continuous
measurements on raw engine exhaust. The system was operated
measuring the aldehydes emitted by a 1969 Cutlass as well as an
older car.
-16-
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PRELIMINARY FIELD EVALUATION
Introduction
Initial exhaust monitoring studies were undertaken at the
laboratories of Scientific Research Instruments Corporation in
Baltimore, Maryland. The results of these experiments demon-
strated the ease and speed of measurement using this method.
However, further studies were warranted to determine the ac-
curacy and overall reliability of the instrument under varying
conditions.
Observation of changes in the most useful parameters
could be obtained by accelerating, decelerating, and maintaining
the speed of an automobile under proper load conditions. These
tests could not be easily accomplished at the laboratories of
Scientific Research Instruments Corporation. At this point,
negotiations were completed jto provide the use of the automo-
bile dynamometer facilities at Scott Research Laboratories, Inc.
in Plumsteadville, Pennsylvania.
During the month of October 1970, a preliminary field
evaluation of the Scientific Research Instruments Corporation
-17-
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oxygenate analyzer program was conducted at Scott Research.
Laboratories, Inc., with the cooperation of Dr. William Biller.
This program included a series of steady state experiments
measuring selected oxygenate output of a 1969 Chevrolet pick-up
truck run on a dynamometer at constant speeds of zero, thirty,
and fifty miles per hour. Also oxygenate levels were measured
as the Chevrolet truck was run through a series of seven mode
California Standard Cycles.
In an effort to determine the accuracy and reproducibility
of the Scientific Research Instruments Corporation instrument,
duplicate reference samples were collected under the direction
of Dr. Emmett Jacobs of E.I. DuPont deNemours and Company.
These samples, collected during the steady state experiments,
were subsequently analyzed by the DNPH method and compared
with the results obtained by the Scientific Research Instruments
Corporation AUTOSPECT.
-18-
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Results
A series of steady state experiments measuring selected
oxygenate outputs of a 1969 Chevrolet truck on a dynamometer
were accomplished. Reference tests, using the DNPH method,
were conducted under the direction of Dr. Emmett Jacobs of
DuPont. A comparison of the results of these two methods
of analyses are shown in Table I. These results, in general,
show some agreement. The discrepancies are discussed
in the next section.
Another series of measurements for steady state runs
of zero, thirty, and fifty miles per hour were made in con-
junction with those of Scott Research Laboratories to be
analyzed using the chromatropic acid method. This latter
method can only be used to determine formaldehyde and total
aldehyde concentrations. The(formaldehyde results are given
in Table II. The total aldehyde concentration under this method
can only be reported as ppm of formaldehyde and are incom-
patible with the total aldehyde as measured by theAUTOSPECT.
The results are in agreement and show satisfactory reproducibility.
-19-
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TABLE I - AUTOSPECT MEASUREMENTS VS. DUPONT ANALYSES, TEST CONDUCTED
AT SCOTT LABORATORIES, Inc. (Preliminary Dynamometer Series - 1969 Chevrolet
Truck, All Concentrations in Parts Per Million)
OXYGENATE HOT-IDLE 19_MPH 50MPH
Formaldehyde
Acetaldehyde
Acrolein
Propionaldehyde
o
Crotonaldehyde
Butyr aldehyde
Benz aldehyde
Tolualdehyde
Total Aldehyde
tos pect
4.1
1.4
4.2
0.3
2.0
0.3
2.6
1.4
16
DuPont
7.9
1.0
0.2
0.2
1.3
0.2
0.8
0.2
12
Autos pect
42
8.4
8.8
2.1
5.4
1.2
3.8
2.1
74
DuPont
60
7.3
2.8
1.4
4.6
1.4
3.4
0.9
82
Autos pect
44
6.0
5.5
1.6
4.0
0.8
2.6
0.8
65
DuPont
59
7.3
1.9
1.4
4.3
1.8
3.4
0.8
80
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TABLE II - AUTOSPECT MEASUREMENTS VS. S.R.L.
CHROMOTROPIC ACID ANALYSES
MODE FORMALDEHYDE (p.p.m.)
Autospect Chromotropic Acid
Cold-Idle 6 9
30 m.p.h. 48 39
50 m.p.h. 50 53
Hot-Idle 5 8
30 m.p.h. 36 38
50 m.p.h. 46 40
-21-
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In order to establish the capability of AUTOSPECT
to accurately measure the concentrations of many oxygenates
which are rapidly changing, dynamic experiments were conducted.
A suitable test of these dynamic aspects as well as the response
time is the seven mode California Standard Cycle. A graphical
depiction of this cycle is shown in Figure 7. A series of dynamics
runs including the instantaneous measurement of the exhaust
of the 1969 Chevy truck run through standard California seven
mode cycles on a dynamometer were made and the results are
shown in Figures 8 - 10. The ability of the AUTOSPECT
to follow a continuous varying oxygenate concentration was
effectively proven. The response time of the instrument was
measured to be less than one second. The traces of acrolein,
crotonaldehyde, benzaldehyde, and tolualdehyde resemble the
traces of the total hydrocarbon concentration thus confirming
the effect of large hydrocarbon concentrations at their mass
numbers. Otherwise, the traces of formaldehyde, acetaldehyde,
and propionaldehyde appear to be representative of the true
concentrations of these oxygenates during this cycle.
-22-
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60
Automobile
Dynamometei
Speed 40
(M.P.H.)
20
Time
Figure 7 Graphical Depiction of the 7 Mode California Standard Cycle
-23-
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two
800
600 .
400
200
Total Hydrocarbons (NDIR)
20 «i Propionaldehyde
10
0
50
40
30
20
10
0
Acrolein -f Butene
0-30 30 30-15 15 15-50 50-0
Idle Accel. Cruise Decel. Cruise Accel. Decel.
Idle
Figure 8 - (Run 1)
Concentrations of Selected Components of Exhaust Gas Measured1
During a 7 Mode California Cycle Run on a Dynamometer.
-24-
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Total Hydrocarbons (NDIR)
20
10
Acetaldehyde ppm
50
40
30
20
10
Formaldehyde ppm
0-30 30 30-15 15
15-50
Idle Accel. Cruise Decel. Cruise Accel,
50-0
Decel.
Idle
Figure 9 - (Run 1)
Concentrations of Selected Components of Exhaust Gas Measured
During a 7 Mode California Cycle Run on a Dynamometer.
-25-
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1000-
Total Hydrocarbons (NDIR)
5004
100 -, Crotonaldehyde + Pentene
100- Benzaldehyde
100-1 Tolualdehyde
Idle 0-30 30 30-15 15 15-50
Accel.Cruise Decel.Cruise Accel.
50-0
Decel.
Idle
Figure 10 - (Run 2)
Concentrations of Selected Components of Exhaust Gas Measured
During a 7 Mode California Cycle Run on a Dynamometer.
-26-
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Since automobile exhaust contains about five percent water
vapor, which is in itself an excellent reagent gas, experiments
were performed to determine the feasibility of water as the
reagent gas. The us e of this technique would enable the elim-
ination of the addition of a reagent gas during measurements.
It was found that during the deceleration modes of the dynamic
cycle runs on a dynamometer, there was a sufficient drop in
water vapor concentration and concurrent rise in the hydro-
carbon concentration to cause incomplete ionization of the
oxygenates.
The response time of the total instrument and inlet system
was determined by rapidly accelerating the automobile and
measuring the lag time of the instrument response. The
results shown in Figure 11 show the response time to be less
than one second.
-27-
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D
D
D.
A
D
00
C
O
»i-t
4-J
ft
H
*->
d
4)
O
C
o
U
10
20
30 40
50
60
70
Time, sec.-
80
90
Figure 11 Response Time Measurements of the
Total Instrument and Inlet System
A = Acceleration
D - Deceleration
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Discussion
The comparison of the results of the steady state measurements
in Table I show some agreement and point out a need for further improve-
ments in the AUTOSPECT System. The discrepancies in total aldehydes
were due to disagreements in the formaldehyde and acrolein concen-
trations. It must be pointed out that the measurements obtained from
AUTOSPECT were corrected data. The aldehydes were measured
before and after scrubbing the exhaust gas stream with a NaHSO3
aqueous solution. This was needed because it was noted during the
experiment that residual amounts of aldehydes were remaining in the
inlet system. This would account for the discrepancies in the com-
parison of the results of formaldehyde.
In the Hot-Idle phase, it appears that the presence of hydro-
carbons interfere with the measurement of the unsaturated aldehydes.
The lack of correlation in the acrolein results at 30 MPH and 50 MPH
sesms inconsistent with the other data. This may be cause by experi-
mental error or the presence of butenes or butanes in the absence of other
hydrocarbons under these conditions.
The accuracy and precision of the chemical ionization mass
spectrometric technique has already been well established. Thus,
errors of measurement in the A U T OS P E C T probably lie
-29-
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in the inlet system. In collaboration with Scott Research Laboratories,
Inc. an improved inlet system has been designed and built. This
system includes a better calibration mechanism and an improved
sampling technique. This revised inlet system is incorporated
into the present instrument and will be used for all further testing.
A more detailed discussion of this inlet system is covered in a later
section.
The discrepancy in the acrolein measurements is due
primarily to the relatively large amounts of butyl ions formed
in the mass spectrometer from butene, butane, and higher mole-
cular weight hydrocarbon molecules. To a lesser extent croton-
aldehyde, benzaldehyde, and tolualdehyde have interferences due
to pentyl, xylyl, and substituted benzyl ions respectively. To
minimize these interferences, research has been done using
ammonia as a reagent gas. As discussed in another section, it
has been found that ammonia selectively ionizes aldehydes without
ionizing their hydrocarbon counterparts.
The results shown in Figures 8-10 effectively demonstrate^
the ability of AUTOSPECT to follow a continously varying oxygenate
concentration. The traces of masses 57, acrolein ;
-30-
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71, crotonaldehyde; 107 benzaldehyde; and 121, tolualdehyde,
closely resemble the traces of the total hydrocarbon concentration.
This confirms the effect of large hydrocarbon concentrations
at these mass numbers. The traces of formaldehyde, ace-
taldehyde, and propionaldehyde appear to be representative of
the true concentrations of these oxygenates during this cycle.
Presumably if the hydrocarbon interferences were removed
from the measurement of acrolein, crotonaldehyde, benzalde-
hyde and tolualdehyde, the form of their traces would be more
similar to the traces of the other aldehydes shown in Figures 8-9
Improved calibration and sampling technology will be
included in the construction of a modified inlet line which will
be used for further testing. Several new reagent gases will be
investigated further to determine their effectiveness in eliminat-
ing hydrocarbon interferences in the measurement of acrolein,
crotonaldehyde, benzaldehyde, and tolualdehyde. These im-
i
provements will result in a complete instrument of unique
accuracy, precision, and speed of measurement of oxygenates.
The use of water as a reagent gas provided the possibility
of the elimination of the reagent gas addition phase of the inlet
-31-
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system. However, the concentration of water in the exhaust
decreases sufficiently during deceleration to cause conditions
which would prevent complete ionization of the oxygenates
present. This condition is aggravated by the correspondingly
large increase of hydrocarbons which absorb much of the
ionizing process. This effect was especially prevalent in
measurements of an old or improperly tuned engine. It is
possible to overcome this problem by supplemental injection
of water vapor but it was decided that methane is superior in
overall performance as a reagent gas for measurement of
oxygenates in automobile exhaust.
-32-
-------
IMPROVEMENTS IN TECHNIQUE AND APPARATUS
Calibration System
A new calibration method has been devised as an
improvement over the previous constant rate injection
system. It was found from field evaluation runs that too much
time was wasted by having to carefully inject each aldehyde
individually and that instabilities resulted outside the clean
conditions of the laboratory. The new calibration procedure
involves generating a known gaseous mixture of the aldehydes
from diffusion tubes. The theory and practice for this method
3,4
are reasonably well defined.
The rate of diffusion of a liquid at constant temperature
out of a diffusion tube of known dimensions is given by the
following equation:
6
r= 2.Six 10 DMPA In P
TL P-p
I
where r = rate of diffusion of vapor out of diffusion
tube, micrograms/second
D = molecular diffusion coefficient of the vapor
into the diluent gas, square centimeters/second
-33-
-------
M = molecular weight of vapor
P = total pressure in diffusion cell, atmospheres
A cross sectional area of diffusional tube,
square centimeters
p = partial pressure at a temperature T of the
vapor, atmospheres
T = temperature °K
Li = length of diffusional path, centimeters
This rate of diffusion is sensitive to P, the total pressure,
and T, temperature, as shown by Altshuller3. He has shown
that for a total pressure change of 20 Torr there is a change of
1% to 3% as p, the partial pressure of the aldehyde, is increased
from 5 Torr to 600 Torr suggesting that the aldehyde diffusion
tubes should be operated at a temperature where the p is low.
Also he has determined that for a change in temperature of 1°C
there is a change of 4.9% in the diffusion rate for n-hexane
suggesting that the system be carefully thermostated. Figure
12 shows the vapor pressure plots versus temperature for most of
the aldehydes and hydrocarbons to be used. From this plot and
the above equation a change of 2.8 percent in diffusion rate for a 1%
change in temperature was calculated for crotonaldehyde at 30°C.
-34-
-------
I
iM
Ul
3
CO
0)
-------
The proposed calibration system will include a dif-
fusion tube for each aldehyde held at a constant temperature
of - 0.5°C in a constantly stirred water bath. A diffusion
tube for each aldehyde will be connected in tandem with a tube made
of Teflon of the a -polymer of formaldehyde via a monitored
nitrogen gas flow. A diagram of this system is shown in
Figure 13. The amount of time to approach steady state
conditions to within - 0.5% is given by the equation:
t = L2 where t = total time in seconds
2D
For benzaldehyde in a diffusion tube where L. = 5 cms.,
the time to approach equilibrium is calculated to be, t 3 minutes.
As of yet, no experimental values for D, the diffusion
coefficient, of aldehydes have been found, but two methods have
been found where the coefficient can be estimated ' to within
5% « One method according to Roberts, is based on
-36-
-------
Mass
Flowmeter
Constant Temperature
Ovens
1
OJ
CLpolyformaldehyde
1
_!
^
^
1 -
1
. i
Mt^.
Carrier
Gas
J.
f
To Sample
Figure 13 Diagram of Proposed Calibration System for Aldehydes in the PPM Range
-------
predetermined atomic and structual force constants and is
calculated from the equation:
0.5 -ic. / ri A \ - 1 ~i 0.75
where
K o.sn-^At Q - VTTT)
and
~TT = Normal boiling point, °K
D
^ , = Atomic and structual constants
\ I = Atomic and group constants centimeters /gram mole
/J^ = Dipole moment, 1018 ESU centimeters
£_, = Force constant
f\ = Boltzmann's Constant
-38-
-------
A simpler method, that of Fuller, Schettler and Gliddings, in-
volves knowing values of additive atomic volumes for C, H, and
O determined from a least squares fit program into \shich data
from previous diffusion coefficient experiments has been fed.
The diffusion coefficient is obtained from this equation:
.3 -^(J-, -L
10 I AM, M
where
T = temperature °K
Ma, Mb = molecular weight,grams/mole
P = pressure, atmospheres
y^; Vy = empirically determined diffusion volume,
atomic volume
The temperature dependency of D is given by the equation:
3 , i
D = Do T 760
273 P
An example calculation of the diffusion constant of benzaldehyde
by the method of Fuller, Schettler and Giddings is given in the
Appendix. Table III shows a comparison of the diffusion coef-
ficients determined for aldehydes from both the above methods.
-39-
-------
TABLE III: Comparison of Empirically Determined Diffusion
Coefficients of Aldehydes and Hydrocarbons
(Calculated for 273°K)
Compounds
Acetaldehyde
Acrolein
Propionaldehyde
Crotonaldehyde
Is o-B utyraldehyde
B enzaldehyde
p- Tolualdehyde
Pentene
TD ( 1 ) (cm /sec)
*
0.0975
0.1040
0.0894
0.0777
0.0599
*
*
Xylene 0.0541
*Adequate information not available
TTD( 2 ) (cm2/sec)
0. 115
0.0976
0.0946
0.0840
0.0820
0.0702
0.0658
0.0777
0.0670
TD(1) Method of Roberts
TT
D(2) Method of Fuller, Schettler and Giddings
-40-
-------
Later, these empirically determined coefficients will be cor-
related with concentration values experimentally determined by
the DNPH method.
The production of formaldehyde at known gaseous con-
centrations presents a special problem in that it so readily
polymerizes on the walls of the tubing. The injection of a for-
mula in solution at a known rate is still an attractive method in
this case if temperatures are carefully maintained. Another at-
tractive method, as suggested by John E. Sigsby, is to use a
solid alpha polymer form of formaldehyde sealed in a tube made
of Teflon . (In this case a stable formaldehyde gaseous
o o
mixture should be produced at temperatures of 150 - 200 C.)
It is expected that at a temperature between 150° and 200°C
the polymer will decompose to the monomer under steady state
conditions to form a constant gaseous mixture with N£.
-41-
-------
Inlet System
Preliminary evaluation of the AUTOSPECT instrumenta-
tion system has shown it to be an extremely valuable instrument
in measuring exhaust oxygenates, but has demonstrated the need
to improve the sample inlet system. It was found for instance
that special care must be taken to prevent formaldehyde polymer
condensation in the sample lines. With this in mind, a new
sample-reagent gas mixing system has been developed as shown
in Figures 14-16.
To minimize the length of auto exhaust sample line at atmos-
pheric pressure, the reagent gas mixing chamber and pressure
reduction point have been extended out from the main mass spec-
trometer unit, thereby decreasing the time the sample is present
in the inlet system at pressure above 1 mm Hg. This minimizes
the number of formaldehyde collisions with the tubing walls; and
as an extremely important feature, decreases the effective in-
strument response time.
The bulk of sampling lines and the fixed leaks has been
constructed of glass to enable visual detection and prevention of
-42-
-------
To
Mass Spec.
OJ
I
Asbestos
Pump
Exhaust
Gas
Pump
Reagent
Gas
Figure 14 Schematic Diagram of New Inlet System
-------
Figure 15. Overview of Reagent - Sample Mixing Oven.
-44-
-------
Figure 16. View of AUTOSPECT with New Inlet System Attached.
-45-
-------
any polymer deposition. Distortions in the flow pattern of exhaust
sample have been eliminated as much as possible by eliminating
obstructions. An example of this is the replacement of stem
valves with ball joint valves wherever possible. The Sample-
Reagent Mixing Oven was completely redesigned to provide opti-
mum conditions for efficient sample mixing without contamination
or sample loss.
The design of the inlet oven as shown in Figure 14 serves
a five-fold purpose:
(1) To dynamically mix the automobile exhaust flow
with the reagent gas in a fixed proportion. (This
proportion may be varied by altering the valve
s ettings.)
(2) To cause a rapid transit of exhaust sample to the
mass spectrometer.
(3) To maintain a constant pressure drop from 760 mm
Hg down to 1 mm Hg.
(4) To prevent any deposition of contaminant on the
walls and
(5) To prevent any electrical discharge from the high
voltage mass spectrometer source.
The gas flow system is constructed of glass and maintained at
a temperature of 150° - 200 G by two space heaters regulated
-46-
-------
by a constant voltage source inside an asbestos concrete oven.
These heaters are controlled by a thermistor. The oven is
divided into three different pressure ranges by two glass fixed
leaks. The first chamber is maintained at near atmosphere
pressure and contains a continuous flow of around 2 liters/minute
of auto exhaust sample. The second chamber is maintained at
a pressure between 200 and 600 mm Hg and contains a continuous
flow of a mixture of reagent gas and exhaust sample. Pressure
and reagent gas flow rate in this chamber can be independently
varied by metering the reagent gas into the chamber and by
adjusting a variable conductance valve between the chamber and
a mechanical valve. The third chamber is maintained at a pres-
sure of 1 mm Hg by the second fixed leak and is connected
directly to the source by a long length of heated glass tubing.
A 0-760 Torr pressure gauge is connected to each chamber.
The operation of the middle chamber of this inlet system
determines the effective machine response time, the effective
sensitivity, and prevents any electrical discharge from the high
voltage source. The pressure in this part of the system is con-
tinuously maintained at a pressure above 100 mm Hg to prevent
-47-
-------
a discharge through, the gas to ground. An optimum ratio of
reagent gas to sample has been determined experimentally to
be such that the available ionizing reagent gas is not saturated
during high outputs of sample hydrocarbons and water vapor.
There is six inches of tubing between the fixed leaks to
allow for the complete mixing of the reagent gas and exhaust
gas. The transit time between these two fixed leaks is the
major factor in determining the instrument response time. A
small aliquot of the gas mixture passes through the second fixed
leak to the mass spectrometer inlet line. This is a 1/4" O.D.
heated glass tube which carries the gas mixture at a pressure
of 1 Torr from the mixing oven to the mass spectrometer
source. This permits the transfer of the sample from the
point of sampling to the mass spectrometer itself at a low
pressure so that a minimum number of wall collisions occurs
and thus a minimum amount of sample is lost.
-48v
-------
Ammonia as a Reagent Gas
Ammonia appeared to be a good choice as a reagent gas
since it has a proton affinity of 202Kcal/mole5. This proton
affinity would enable it to distinguish between the unsaturated
aldehydes and their hydrocarbon interferences. The hydro-
carbons have proton affinities of 120-180 Kcal/mole6 while the
unsaturated aldehyde's are believed to have proton affinities
around 200 Kcal./mole. The spectra of pure ammonia at O.TTorr
is shown in Figure 17. The peaks at m/e 17, 18, 35 and 52 are
produced by the NH3 , NH4 , N2H7 and N3H10 ions respectively.
These ions participate in the following reaction scheme. Ammonia,
under electron bombardment, provides NH3 ions which then react
with neutral ammonia via ion-molecule reactions:
NH3+ + NH3 ^ NH4+ -1- NH2
NH4+ + NH3 ^± NZH7*
N2H7+ -I- NH3 ^± N3H10+
The resultant equilibria provide steady state concentra-
tions of NH4 , N2H7 and N3H10 ions which are available to
react with any sample molecules present. The reaction mech-
anism would be expected to proceed via a proton transfer from
one of the reagent ions (NH4 , N2H7 ) to the sample molecule.
NH4+ + A ->- AH+ + NH3
The products of these reactions would then be expected to
have an m/e value of one greater than the molecular weight of
the sample.
-49-
-------
100 .,
t
« 50
d
4*1
d
i i
V
>
H
4J
rt
-H
4)
«
*,
t
>. ,
w &
.i-
m
C
"c
l-l
_>
rt
*
»
NH,+
1
N2H7T
N3H10+
1
m/e 1
+
NH4*N2)
A
^
+
(N2H7*N2)
Jl
m/e
Figure 17 Spectrum of Ammonia at 0.7 Torr, 50°C,
-------
However, it was found that the chemical ionization of
aldehydes via an ammonia reagent gas produced ions at the same
m/e value as the molecular weight of the sample. This pheno-
mena is demonstrated in Figure 18. Here the chemical ioniza-
tion of acrolein by ammonia produces a strong peak at m/e 56
and no significant MW + 1 peak at m/e 57. There are two
p ossible mechanisms which may explain the observed results.
A direct charge transfer process may occur whereby the
sample molecule is ionized by a collisional transfer of an
electron from the sample molecule to the reagent ion:
NH4+ + A > A"1" + NH4
t
NH3 + H
An alternative process involves the addition of the ammonium
ion to the sample molecule with subsequent loss of a water
molecule to form the amine ion.
O O
NH4+ + R-C-H »- (R-CH-NH4) +
(M/e-18) (m/e = M) (m/e = M + 18}
H
° l
(R CH-NH4)+ ^ H20 + (R-C= NH2)
(m/e = M+ 18) (m/e =18) (m/e = M)
This results in a production of an ion with the same molecular
weight as the sample molecule ;however its structure is somewhat
different.
-51-
-------
1000.
t
(0
c
0)
5 500'
NH4
4)
rt
"3
«
1 A
N2H7+
t
SK
4J
i-t
m
c
fj
t-*
>
(NH4-N2) +
1
Figure 18 Chemical lonization Spectrum of Acrolein (Ammonia Reagent)
-------
The latter process appears to be the more probable
explanation at the present time. Future experiments should
definitely determine the mechanism of the ionization of alde-
hydes by ammonia under chemical ionization conditions.
These experiments will include an investigation of this
ionization process with a deuterated ammonia and an attempt
to observe the metastable peaks. These peaks should result
from the decomposition of the additive species to form the
amine ion. The metastable for the decomposition of
acrolein-ammonium ion to the corresponding amine would be
m = -5* = 43.32
m.
i
The observance of this metastable ion would demonstrate
the reaction pathway and provide proof of this reaction mechanism.
-53-
-------
RESULTS AND DISCUSSIONS
Chemical ionization measurements have been made on
several different aldehydes and known hydrocarbon interferences,
using both methane and ammonia as reagent gases. The mass
spectra obtained on one particular series of runs with both re-
agent gases is shown in Figures 19 thru 27. A summary of
relative sensitivities is shown in Table IV.
These series of measurements were carried out using
the new heated inlet system and calibrations were made using
constant diffusion rates of samples as discussed previously.
The diffusion tubes containing the samples were, in the case
of acetaldehyde, acrolein, propionaldehyde and pentene,
held at room temperature and in the case of crotonaldehyde,
benzaldehyde and xylene, held at 80°C in a constant tempera-
ture air bath. In the case of butene, a static mixture was made
up on a gas vacuum line with methane and ammonia. All the
runs were conducted at a source pressure of 0.7 Torr. A source
temperature of 200°C and an electron emission current of
200 microamperes were continuously maintained during each
experiment.
-54-
-------
Table IV: Relative Sensitivities of Important Aldehydes and Hydrocarbons Measured in a Series
of Runs Under Chemical lonization Conditions at 200°C Using Methane and Ammonia
as Reagent Gases.
Compound
Acetaldehyde
Acrolein
P r opionaldehy de
Crotonaldehyde
Benz aldehyde
Butene
Pentene
Xylene
Molecular
Weight
44
56
58
70
106
56
70
106
Concentration
(ppm)
348
12
120
47
1
74
83
7
Sensitivity with CH^
(10~10 amps /ppm)
P+l
0.45
0.85
2.00
3.80
4.00
1.50
1.20
3.20
Sensitivity with NHo
(10~10 amps /ppm)
P
0.003
0.050
0.600
0.350
1.000
0
0
0
-------
The results of these sensitivity measurements point
out the ability of ammonia to selectively ionize aldehydes
and not their hydrocarbon interferences. Note the lack of
sensitivity of the alkenes with ammonia. The sensitivities
of the homologous group of aldehydes and hydrocarbons show
a general increase in sensitivity with an increase in molecular
weight. This is to be expected because the increase in size of
the molecule increases the ionization cross section and thus the
probability of being ionized and detected. One of the reasons
for some deficiency of proportionality of molecular weight with
sensitivity is due to the fact that the constant temperature air bath
was not part of the final engineered version of the calibration
system and slight discrepancies in temperatures did exist.
The ability of ammonia to selectively ionize aldehydes
has one disadvantage in that it will not ionize formaldehyde to a
sufficient degree, and the sensitivity with acetaldehyde is low. How-
ever, since formaldehyde and acetaldehyde have no hydrocarbon
interferences, methane will still be an ideal reagent gas for
-56-
-------
these. Hence, it appears that a dual reagent system is most
suitable for the accurate measurement of each of the aldehydes
present in raw exhaust gases.
Following are a series of mass spectra which illustrate
the advantages and disadvantages of each of the two reagent
gases presently under consideration. These spectra were
taken by the AUTOSPECT while it was operating in the scan-
ning mode. Since this instrument was designed and built as
a direct reading mass spectrometer, its operation in the
scanning mode provides mass spectra of somewhat lower
quality than would be expected of an instrument designed as
a scanning mass spectrometer. Therefore, a chemical
ionization quadrupole mass filter was used to determine the
total spectra of aldehyde and hydrocarbon samples using
methane and ammonia as the reagent gases.
The liquid samples Were put in diffusion tubes which
were placed in a stream of nitrogen gas. The nitrogen stream
was then mixed with the reagent gas and passed over a probe
leading to the mass spectrometer source. Gaseous samples
were mixed directly with the nitrogen stream.
-57-
-------
Since the sensitivity of chemical ionization has already
been determined, these experiments were carried out mainly
to define the relative sensitivity of the instrument to each
sample with different reagent gases.
The concentration of each aldehyde and hydrocarbon is the
same for both reagent spectra. The concentration of each aldehyde
and its respective interfering hydrocarbon is approximately
similar. The lower molecular weight samples are less than
100 ppm while the higher molecular weight samples are around
1 ppm.
The presence of the reagent ions (GHg / ,
for methane and NH* , ^Hy for ammonia) does not interfere
with the measurement of any of the aldehydes. However,
methane does ionize water via proton transfer (to m/e 19) and
also causes some fragmentation of the alkenes (to m/e 43).
Ammonia does neither of the above and as a result produces less
extraneous ions in the spectra even though it does apparently react
with nitrogen to form an agglomerate ion (m/e 46).
-58-
-------
The utility of ammonia as a reagent gas is demonstrated
quite effectively by comparing Figure 19 with Figure 20. Both
acrolein and butene produce an M+ 1 peak when ionized by
methane. Thus the presence of butene in a sample would
extensively interfere with the measurement of the proper con-
centrations of acrolein.
However, a comparison of the two plots in Figure 20
shows that while ammonia will produce a substantial M"*"peak
for acrolein (tn/e ~ 56) it will produce virtually no M"*~ peak for
butene. Thus the measurement of the M peak of acrolein in
ammonia will not be affected by the presence of butene in the
sample.
The same phenomena is true for crotonaldehyde. The
chemical ionization of crotonaldehyde by methane (Figure 21)
produces ions at m/e 71 (M+l) but ions at this mass may also be
produced by the chemical ionization of pentene by methane. Ammonia,
however, serves as a good reagent gas for crotonaldehyde (Figure 22)
producing the M ions at m/e 70, while producing no significant ion-
ization of pentene in the interfering mass range.
-59-
-------
1^
tens it-)
S
.?
1«
* 4
4)
100-
90.
60-
40-
20-
CH5+
j-
H3O
Acrolein
C.I. by CH4
C2H5 +
(M+l) +
C TT + ,n
^3^5 xlO
1
III 1 1 1 I I 1 | 1 1 I i|i
10 20 30 40 50 60 81
m/e
to
v
tf
100-
90-
60
40
20
CH
1
,, +
°zHs
C3H5
II
Butene
C.I. by CH4
I I I I T I I I I - I I » » I I
10 20 30 40 50 60 70 80
m/e ».
Figure 19 Spectra of Acrolein and Butene via C.I. by Methane
-60-
-------
t
>«
03
£
V
K
NH4
Acrolein
C.I. by NH3
+
M+
xlOO
I I I I
10 20
I
30
40
I T
50
m/e
60 70
80
t
-------
C,H
4. V V*
90-
u
C
i i
I 4°"
4J
n)
I za
<
3H5 +
H30
C. 3
Crotonaldehyde
C.I. by CH4
/ _ _ . _ \
C3H5
i i i i i i i i i i i i i *
10 20 30 40 50 60 7C
^M+i;
xlO
.
i i
) 80
m/e
CD
C
93
lOO-i
90-
60_
-1 40-
^2 20^
v
K
C3H5
I.
Pentene
C.I. by CH4
I 1 1 J 1 I I I 1 I I
30 40 50 60 70 80
10 20
m/e --=>-
Figure 21 Spectra of Pentene and Crotonaldehyde via C.I. by Methane
-62-
-------
^
:ensi
c:
>
-u
0)
1 1 1 i | | i i i i i i
10 20 30 40 50 60 70 80
100-1
m/e
90-
CD
C 60 "!
-------
The effectiveness of ammonia is again demonstrated
(Figure 23) by its ability to specifically ionize benzaldehyde in
the presence of xylene. While methane will ionize both samples
to produce interference (Figure 24).
Several of the aldehydes studied with methane chemical
ionization did not show interferences from any alkenes. These
aldehydes were also studied using ammonia as the reagent gas.
As can be seen in Figures 25-27 the sensitivity of the ammonia
reagent gas increases as the molecular weight of the aldehyde
increases.
The sensitivity for formaldehyde is small, while it is
moderate for acetaldehyde and acceptable for propionaldehyde.
Methane is a suitable reagent for these oxygenates since it provides
good sensitivity with no interferences.
These results indicate that the best method , at present,
for the analysis of aldehydes in auto exhaust is the use of two
reagents in the chemical ionization process. Methane provides
the maximum sensitivity for formaldehyde, acetaldehyde, and
propionaldehyde, butyraldehyde, and valeraldehyde while ammonia
-64-
-------
100
£ 80-
H
to
a
1 60 -
14
u
r-l
rt 40-
l «
01
rt
20 '
Benzaldehyde
G.I. by NH3
' 10 ' 20 ' 3*0
N2H7+ M+
x4
ii l l l l i 1 1 1 1 1 1 1 i
40 50 60 70 80 90 100 11
m/e fe
1UU -
>. 80-
0)
e
V
c 60-
1 40 '
20-
NH/
Xylene
G.I. by NH3
I 1 1 i 1 i
10 20 30
N2H7+
M"". 10
F T I T T 1 1 I T I 1 I T r 1
40 50 60 70 80 90 100," 110
m/e^
Figure 23. Spectra of Xylene and Benzaldehyde via C.I. by Ammonia
-65-
-------
xuu -
.? 80-
"A
1 60 -
ft
3 40 .
20 '
CH '
-> Benzaldehyde
C.I. by CH4
G2H5" (M4-l)+
x50
1
1 I 1 I I 1 1 1 1 1 1 1 1 I I 1 1 1 1 I 1 I
10 20 30 40 50 60 70 80 90 100 110
m
/e
1VJU .
.? 80-
c
f 60-
^ 40-
20.
CH5
Xylene
C.I. by CH4
C2H5+
( M + 1 )+
x50
lllii.i
1 I I I 1 l 1 1 1 1 1 l 1 1 1 1 I I I 1 I I
10 20 30 40 50 60 70 80 90 100 110
tn/e ^
Figure 24. Spectra of Xylene and Benzaldehyde via C.I. by Methane
-66-
-------
100 _
t! 80 H
en
C
-------
100 -
z 8°-
10
c
o
c 60-
D
j« 40
i;
OS
20
NH4 +
Acetaldehyde
C.I. by NH3
4.
1 Xl°°
1 1 I 1 1 1 l 1 1 1 I 1 1 1 I
10 20 30 40 50 60 70 80
m/e ^
100 -
= 80 -
(C
c
-------
100
>s
+J
'» 80 -\
c
-------
provides good sensitivity for acrolein, crotonaldehyde, benz-
aldehyde and tolualdehyde with freedom from interference.
The improvements in the calibration and inlet systems
have increased the response time as well as the sensitivity.
These advancements have also increased the accuracy of the
total instrument. Further improvements and the completion
of detailed experiments will culminate in a successful establish-
ment of the ultimate sensitivity of this method.
-70-
-------
APPENDIX
Example Calculation of Diffusion Constant for Benzaldehyde
Method of Fuller Schettler and Giddings
10"3 T1'75 ( + V^"
1U i +
D=
A
A b
D= 10 * (273) i'75 (O.Q371 + 0.0094)*
IF (17.9)"^"+ (62.9)^1 2 ""
18.3 (0.0451)'
(7.45)z
D = 0.0702
cm"
sec
= 28 (N2)
M_ = 106 Benzaldehyde
B =
~L.v. = 112.66
A i
P= 1 aim
T= 273 dg. Kelvin
Method of Roberts
D= 4.44 f(-=-)
, E 0.75T,
where = b
K
d'1'5 (1. -O.Scr0'6) -
0 75
0.574 + ZAT
= 452°K
SAT = 0.094
Ve= 319.1 cm/gm. mole
j. = 2.00 ESU centimeters
-------
Method of Roberts
E_ _ (0.75) (452) j (7.01 x 10~2) 455
K = (0.574+0.094) = (1.265)
o- = ( 2.00):
2(7.01 x 10"2) (2.52)
E=7.01xlO~2 ^=2.52x10* cr=.113
D= 4.44^ (7.01 x 10"2)"0'5 (2.52x 102)"°'5[ ( l-( 0 . 5) ( 0 . 113)° "^ "»! °'75
D = 0.0599
-72-
-------
BIBLIOGRAPHY
1. This method is covered by patent rights of Esso Research
and Engineering Company with exclusive license to
Scientific Research Instruments Corporation, Baltimore,
Maryland.
2. P. E. Oberdorfer, "The Determination of Aldehydes in
Automobile Exhaust Gas, " Paper 670123 presented at
the SAE Automotive Engineering Congress, Detroit,
Michigan, January, 1967.
3. Altshuller, A. P. and Cohen, I. R. ."Applications of
Diffusion Cells to the Production of Knovn Concentrations
of Gaseous Hydrocarbons", Anal. Chem. J^Z, 802-810(1960).
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