U.S. patent number 3,647,387 [Application Number 05/020,919] was granted by the patent office on 1972-03-07 for detection device.
This patent grant is currently assigned to Stanford Research Institute. Invention is credited to Sidney W. Benson, Gilbert R. Haugen, Roland S. Jackson.
United States Patent |
3,647,387 |
Benson , et al. |
March 7, 1972 |
DETECTION DEVICE
Abstract
The presence of nitrogen containing compounds is detected by
sampling vapor in the vicinity of the suspected compounds, reacting
the vapor under conditions to convert the compound to nitric oxide.
The nitric oxide is reacted with atomic oxygen with the
chemiluminescent emission of light. This light is detected to
determine the presence of the suspected compound.
Inventors: |
Benson; Sidney W. (Palo Alto,
CA), Haugen; Gilbert R. (Palo Alto, CA), Jackson; Roland
S. (San Jose, CA) |
Assignee: |
Stanford Research Institute
(Menlo Park, CA)
|
Family
ID: |
21801286 |
Appl.
No.: |
05/020,919 |
Filed: |
March 19, 1970 |
Current U.S.
Class: |
436/107; 422/52;
436/172; 250/361C; 436/111 |
Current CPC
Class: |
G01N
31/00 (20130101); G01N 31/22 (20130101); G01N
21/766 (20130101); Y10T 436/170769 (20150115); Y10T
436/173845 (20150115) |
Current International
Class: |
G01N
31/00 (20060101); G01N 31/22 (20060101); G01N
21/76 (20060101); G01n 027/68 () |
Field of
Search: |
;23/232,232E,254,254E,23PC ;73/23 ;250/217 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Kiess et al., 7th Symposium (International) on Combustion, London
& Oxford, 28 Aug.- 3 Sept. 1958, pp. 207-209 relied
on..
|
Primary Examiner: Wolk; Morris O.
Assistant Examiner: Reese; R. M.
Claims
We claim:
1. A method of detecting the presence of nitrogen containing
compounds selected from the group consisting of nitroso, nitro,
nitric and amino compounds comprising the steps of:
sampling the atmosphere in the vicinity suspected of containing
said compounds to obtain a vapor sample;
heating said sample to thermally convert the compound into an oxide
of nitrogen;
adding a supply of atomic oxygen to the converted vapor to form a
mixture;
reacting said mixture in a chemiluminescent reaction yielding
nitric oxide with light emission characteristic thereof;
and measuring said emitted light.
2. A method according to claim 1 in which said compounds are heated
to a temperature of at least about 1,800.degree. F and said heating
is conducted in the presence of oxygen and in the presence of a
metal catalyst.
3. A process according to claim 1 in which said supply of atomic
oxygen is formed by subjecting a very pure stream of oxygen to a
radiofrequency discharge.
4. A process according to claim 1 in which the chemiluminescent
reaction is conducted at a reduced pressure.
5. A method according to claim 1 in which said mixture is removed
from a closed container containing a first member selected from
said vapor sample or said supply and said container is surrounded
by a higher pressure atmosphere of said other member.
6. A method according to claim 5 in which said first member is
oxygen, said atmosphere comprises nitrogen and the output from said
chamber is subjected to a radiofrequency discharge to form a
mixture of nitrogen oxide and atomic oxygen.
7. An apparatus for detecting the presence of nitrogen containing
compounds comprising in combination:
means for sampling the atmosphere in the vicinity suspected of
containing a nitrogen containing compound;
thermolytic reactor means receiving said sample for converting said
nitrogen compound into an oxide of nitrogen;
source means containing a supply of atomic oxygen;
reactor means receiving said converted sample and said supply for
chemiluminescent reaction thereof to form nitric oxide and
characteristic emission of light; and
photodetector means coupled to said reactor for detection of said
characteristic emission.
8. An apparatus according to claim 7 in which said thermolytic
reactor means includes a reactor chamber, means for heating the
chamber and a nitrogen oxide conversion catalyst disposed within
the chamber.
9. An apparatus according to claim 7 in which said source means
comprises a supply of diatomic oxygen, a chamber for receiving said
supply and a radiofrequency source coupled to said chamber for
subjecting said diatomic oxygen to a radiofrequency discharge for
conversion thereof to atomic oxygen.
10. An apparatus according to claim 7 further including closed
container means for receiving a first gas selected from said sample
or said source and means for applying said other gas to the
exterior of said container whereby said chemiluminescent reactable
mixture is formed only when said container contains a leak and
chemiluminescent emission in said reactor detects said leak.
11. An apparatus according to claim 7 in which said reactor is a
cylindrical tube having an internal light reflective surface, said
reactor containing axial inlet means for receiving said sample and
supply and an opposed axial light output aperture.
12. An apparatus according to claim 11 further including vacuum
pump means coupled to said tube.
13. An apparatus according to claim 12 further including light
baffle means disposed in said inlet means and in the line coupling
said vacuum pump to said tube.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the detection of nitrogen
containing compounds and, more particularly, to the detection of
these compounds by the chemiluminescent reaction of nitric oxide
and atomic oxygen.
2. Description of the Prior Art
The analysis and detection of nitrogen containing compounds has so
far relied on nonspecific physical methods such as mass
spectrometry, or the formation of particulate matter. The results
have not been completely satisfactory. Analytical techniques and
apparatus are needed which are specific to nitrogen containing
compounds.
SUMMARY OF THE INVENTION
The detection method in accordance with the invention relies on the
chemiluminescent reaction of nitric oxide and atomic oxygen. This
reaction yields light with a spectrum peaking in the violet. This
light can be detected with high efficiency by a photomultiplier.
The method of the invention may be utilized to determine the
presence of nitrogen oxides in air, and also is useful in the
detection of vapor of nitrogen containing compounds such as organic
amines, nitroso, nitro, or nitrate compounds by thermally and/or
catalytically converting the vapors to nitric oxide preliminary to
the desired chemiluminescent reaction.
When gas containing nitric oxide (NO) or nitrogen dioxide
(NO.sub.2) is mixed with gas containing atomic oxygen, the
following chain reaction takes place:
O+NO.sub.2 .fwdarw.NO+O.sub.2 (very fast) (1)
O+NO.fwdarw.NO.sub.2 +light (2)
It is noted that the NO.sub.2 which is a product of reaction 2 can
again serve as reactant in reaction 1. Thus, a chain reaction
occurs and more than one quantum of light can be produced per
molecule of NO or NO.sub.2.
The characteristics of available multipliers are such that
10.sup.5.7 photons/second can be detected easily. The forementioned
chemiluminescent chain is capable of emitting 10.sup. 20.1
photons/second for a liter of air containing one mole of nitric
oxide (NO). Thus, the chemiluminescent method of the invention is
capable of detecting 10.sup.- .sup.11 parts of vapor in the
atmosphere. This corresponds to a vapor pressure of approximately
10.sup.- .sup.8 mm. Hg., which is well below the vapor pressure of
many nitrogen containing organic compounds.
The detector is, thus, capable of detecting trace amounts of
nitrogen oxide vapors in an atmosphere or detecting the vapors
being emitted from liquid or solid nitrogen containing organic
compounds. The detection technique of the invention is also
applicable to determining the integrity of containers by evacuating
the container, filling the container with one of the reactants for
the above chemiluminescent reaction and placing the container in an
atmosphere of the other reactant. The contents of the container are
then reacted under chemiluminescent conditions and the light
emission detected by the invention to determine whether any gas has
leaked into the container.
The apparatus of the invention is readily fabricated from available
materials and can be compactly packaged into a portable instrument
for use in airborne or land based craft. The instrument is very
sensitive and reliable in the detection of compounds and the
analysis of atmospheres for nitrogen oxide air pollutants. The
apparatus may also be utilized as a security system to sense the
suspicious entry or presence of people or animals or to detect
leaks of organic nitrogen compounds from pipes or tanks.
These and other advantages of the invention will become readily
apparent as the invention becomes better understood by reference to
the following detailed description when considered in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view partly in section, of a detection system
according to the invention;
FIG. 2a and 2b are schematic illustrations of leak detection
systems in accordance with the invention;
FIG. 3 is a schematic view of an atmosphere sampling detector in
accordance with the invention.
FIG. 4 is a schematic view of a system for detecting the presence
of vapors of nitrogen containing compounds in accordance with the
invention; and
FIG. 5 is a more detailed view of a system for the detection of the
presence of nitrogen containing compounds.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1 the nitric oxide detection system in
accordance with the invention generally includes a reactor 10, a
light detection assembly 12, and a gas inlet assembly 14. The
reactor 10 may take many configurations. Preferably the reactor is
a cylindrical tube which confines the gas flow along the axis of
the photomultiplier tube 16. The interior surface 11 of the reactor
10 is preferably coated with a light-scattering substance such as
magnesium oxide and the interior of the tube functions as a gaseous
reaction chamber 13.
An aperture 15 is provided at one end of the reaction tube 10. The
light detection assembly 12 comprises a photomultiplier tube
housing 17 attached to the reactor opposite the aperture 15 for
viewing the light emission from the reaction. The housing contains
a photomultiplier tube 16 and a filter 22 disposed between the
aperture 15 and the light sensitive face 19 of the photomultiplier
tube 16. The high voltage lead 24 from the photomultiplier tube 16
is attached to a power supply 26. The signal lead 28 is attached to
a microammeter 30. The output signal from the microammeater 30 is
applied to a recording device such as a strip chart recorder
32.
The gas inlet assembly 14 includes an inlet branch 34. A first
conduit 36 containing a valve 38 and a light baffle 40 communicates
with inlet branch 34 and a source of atomic oxygen 35. A second
conduit 42 containing a metering valve 44 and a light baffle 46,
communicates with a source of gas 47 containing a suspected trace
of nitric oxide or nitrogen dioxide and with the inlet branch 34. A
vacuum pump 48 also communicates with the reactor 10 through a
light baffle 50 and a throttling valve 52. The internal surfaces of
the light baffles 40, 46 and 50 are blackened.
The apparatus is operated by reducing the pressure within reactor
10 to a level of about 1-10 mm. Hg., preferably 2-4 mm. Hg. Valves
38 and 44 are opened and the gas containing traces of nitrogen
oxide and the supply of atomic oxygen enter chamber 10 and react
with the emission of light. The vacuum pump 48 continually exhausts
the reactor 10 and allows new samples to enter.
The energy of the chemiluminescent photons is distributed over the
wavelength range of 4,000 to 8,000 A. There are two strong oxygen
transitions occurring during the reaction that emit light in the
near-infrared that are not coupled with the NO chemiluminescent
chain. These emissions can be eliminated by utilizing a broad band
pass filter having a broad band transmission in the range of
4,200-6,000 A, and a sharp cut off at each end of the range to
exclude radiation not coupled with the chemiluminescent chain.
The light emitted by the reaction of atomic oxygen with nitric
oxide is detected by a highly sensitive photomultiplier 16. These
devices are commercially available with gains as high as 10.sup. 8
having a photocathode with a radiant sensitivity at the wavelength
of maximum response of about 15 milliamps per watt.
The detection system in accordance with the invention provides
amplification both by the chemical amplification associated with
the chain reaction and the photoelectric amplification associated
with the photomultiplier. The chemical gain depends on the rate
constants of the chemical chain mechanism and the system parameters
such as concentration of atomic oxygen in the detection chamber,
volume of the detection chamber and light gathering efficiency of
the detection chamber. The photoelectric gain depends on the
quantum efficiency of the photoactive surface employed in the
photomultiplier, the number of dynodes and their geometry, and on
the system parameters such as overall voltage applied to the dynode
chains and the energy of the chemiluminescent photons.
The detection system in accordance with the invention can detect
trace amounts with commercially available photomultipliers. A
typical photomultiplier has an overall sensitivity of about
5.times. 10.sup. 4 amp/watt. High gain electrometers permit easy
detection of 10.sup.- .sup.8 amp which corresponds to a
detectability of 2.times. 10.sup.- .sup.13 watts. This is
equivalent to a flux of 5,000 A photons of 5.times. 10.sup. 5
photons per second. The chemiluminescence of the nitric oxide
reaction has a continuum between 4,000 and 8,000 A, peaking between
5,000 and 6,000 A. Since every molecule of nitric oxide can produce
many quanta of light during the time typically spent in the
reaction chamber, the chain reaction acts as a chemical amplifier.
This is a consequence of the very fast rate of reaction.
The steady state rate of flux for the NO+O system is given by:
I (photons/sec)=10.sup. 28.4 [NO] [0] V In a one liter chamber
having a light gathering efficiency, (.phi.) of 0.1 and an atomic
oxygen concentration of 5.times. 10.sup.- .sup.8 mole/liter at a
pressure of 5 torr, the chemical amplification factor is:
Thus, 10.sup.- .sup.14.4 moles of NO per liter of air at 5 mm. Hg
in the detection chamber will produce an output current of 10.sup.-
.sup.8 amp with the aforementioned photomultiplier. This
corresponds to 10.sup.- .sup.12.2 moles of NO per liter of air at
one atmosphere or one molecule of NO for every 10.sup. 11 of air
sampled, that is about 10.sup. 8 molecules NO/cc. air STP. This
represents a practical detectability. Higher sensitivity can be
realized by increasing light gathering efficiency and detecting
output currents of 10.sup.-.sup.-.sup.8 amp or lower which are all
quite possible.
Under these operating conditions, the 1 liter reaction chamber
should be swept out about every one quarter to one-fifth second.
This corresponds to pumping speed of 4 to 5 liters per second at 5
mm. Hg. At this flushing rate, the concentration of oxygen atoms
will have a steady state value only slightly over than the initial
value.
Experiments indicate that the continuum emitted by the
chemiluminescent chain increases proportionately with nitric oxide
concentration, irrespective of the wavelength as long as the bands
structure of the red region of the spectrum is filtered out. At a
pressure of 2 to 3 mm. Hg., there is only a moderate quenching of
the chemiluminescent emission between the exit and entrance to the
reaction chamber. A chamber pressure of 5 mm. Hg. increases the
recombination of atomic oxygen sufficiently to produce a noticeable
reduction in emission. Increasing the volume of the chamber will
increase the photomultiplier signal by increasing the photon flux
impinging on the photomultiplier. However, a larger volume requires
a corresponding larger pumping speed which increases the weight and
power consumption of the vacuum system.
The sensitivity of the system was determined by observing
photomultiplier signal as a function of the flows of 0.8 percent,
0.08 percent and 0.01 percent nitric oxide-nitrogen mixtures at
constant oxygen flow. The oxygen supply was commercial high purity
oxygen at 500 cc./min. Either resonance excitation, a far
ultraviolet source (less than 1,850 A), or direct microwave
excitation was used to dissociate the molecular oxygen. Detection
at parts per million of nitric oxide was demonstrated. Sensitivity
was dependent on the concentration of nitric oxide in the
calibration mixture. Sensitivity also increased with increasing
flow rate. Both of these effects are the consequence of the
increase in the recombination rate of atomic oxygen via the
chemiluminescent chain and of the increase in total pressure with
increasing flow. The effective concentration of atomic oxygen in
the reaction chamber is decreased by increasing nitric oxide
concentration and by increasing residence time in the chamber.
Maximum gain of the chemical amplifier is realized for low
concentrations of nitric oxide and fast flow rates, that is, very
little reduction of the effective concentration of atomic oxygen in
the reaction chamber.
The photomultiplier signal with zero added nitric oxide indicates
chemiluminescent flux produced from traces of nitrogen in the
oxygen supply. This signal decreases the overall gain of the system
by saturating the photomultiplier which prevents utilization of the
full gain of the photomultiplier. The catalytic recombination of
oxygen atoms by nitric oxide between the point of generation and
entrance into the reaction chamber reduces the effective
concentration within the chamber. High velocity flows can lessen
the effects of recombination as discussed above as does utilization
of chamber pressures of about 2 to 3 torr. Increase in the
photometric amplification and purification of the oxygen supply
will allow at least another factor of 1,000 in the amplification
and sensitivity of the system.
Very pure oxygen is commercially available in ultrahigh grade
purities of 99.999 percent. This oxygen is produced by electrolytic
dissociation of water and contains between 1- 6p.p.m. of nitrogen.
This is converted to nitric oxide by microwave discharge. The
nitric oxide can be removed by selectively adsorbing the nitric
oxide on silica gel, at low temperatures.
Another procedure for eliminating the traces of nitrogen is to
prepurify the oxygen by one of the following methods:
1. Selectively absorbing the oxygen with heated barium oxide to
form barium peroxide. The barium peroxide is cooled and evacuated
to remove the residual gas. Heating the barium peroxide reverses
the reaction producing chemically pure oxygen.
2. Pure oxygen can also be produced by the thermal decomposition of
pure potassium permanganate at 240.degree. C.
3. reduction of nitrogen impurities in the electrolytically
produced oxygen can be affected by degassing the water before
electrolysis in a high vacuum system and storing and transferring
the generated oxygen in the same system. Hydrogen impurities within
the electrolytically produced oxygen can be removed by passing
high-pressure oxygen through a heated bed of catalyst to convert
the hydrogen to water. Water and hydrocarbon impurities can be
removed through a series of liquid nitrogen traps containing
adsorbents. This technique is a most reliable source of
nitrogen-free oxygen.
Atomic oxygen is produced by the selective dissociation of oxygen.
The dissociation can be effected by absorption of ultraviolet
radiation in the 1,759-1,950 A region by a low-pressure oxygen flow
which produces predissociation into ground state oxygen atoms. This
radiation can be produced by microwave excitation of medium
pressure resonance lamps containing krypton, xenon, mercury or
bromine. The high temperatures of 1,900.degree. C. attainable with
a Nernst glow bar such as a zirconium oxide heater generate atomic
oxygen thermally.
However, direct microwave excitation produces higher oxygen
concentrations than either of the above techniques. Reduction of
the power in the microwave cavity should reduce the rate of
production of nitric oxide without reducing the oxygen atom
generation rate an equivalent amount. When the current in the
oscillator stage of the microwave generator was varied, the
background signal could be reduced without appreciably affecting
the sensitivity of the detection system to nitric oxide.
In FIGS. 2a and 2b the source of nitric oxide and monotomic oxygen
is utilized as a leak detector for a container 50. In FIG. 2a the
evacuated container 50 is fed a metered supply of chemically pure
oxygen from tank 52 through a line 54 containing a metering valve
56. The output from container 50 is fed to a microwave cavity 58
through a line 60 containing a valve 62. The microwave cavity 58 is
subjected to a radiofrequency discharge from discharge source 64.
If container 50 contains any leaks, nitrogen from the air will
enter the container 50 and contaminate the pure oxygen with
nitrogen. When this mixed gas is passed through the radio frequency
discharge, atomic oxygen and nitric oxide will be produced. This
chemiluminescent gas will pass through a line 36 containing a valve
38 the light baffle 40 into reactor 10 where the resulting light
will be detected by photomultiplier 16.
In the embodiment illustrated in FIG. 2b chemically pure oxygen
flows from source 52 into the microwave cavity 58 before entering
container 50. The container is disposed within a larger enclosure
66. Enclosure 66 is pressurized with nitric oxide from cylinder 67.
If there are any leaks present in container 50, the atomic oxygen
produced by the radiofrequency discharge from source 64 will be
contaminated with nitric oxide. When these gasses are fed to the
inlet assembly 14 to the reactor 10, the chemiluminescent emission
will be detected by photomultiplier tube 16.
The oxygen supply illustrated in FIG. 3 can be utilized for direct
determination of nitrogen dioxide vapors in air. The gas inlet
assembly 14 in this case includes, a sampling nozzle 70 containing
a pinhole aperture 71 for collecting the surrounding air. The air
is delivered to the inlet branch 34 through conduit 42 containing a
metering valve 44, a light baffle 46. Atomic oxygen enters the
branch 34 through the conduit 36. Suitably, atomic oxygen is
generated from an ultrapure supply container 72. The oxygen supply
passes through a microwave cavity 58 and is subjected to an RF
discharge from source 64. The two streams combine within the inlet
branch 34 and react axially within reactor chamber 13, to form
nitric oxide with chemiluminescent emission of characteristic
light. The light emission is detected by photomultiplier tube
16.
Carbon dioxide or carbon monoxide or sulfur dioxide or sulfur
monoxide impurities in the atmospheric air do not lead to chemical
amplification. The reactions of carbon dioxide and sulfur dioxide
are endothermic while that of nitrogen dioxide is exothermic. The
slower rate of their oxidative combination reactions will not
support chain reactions.
The gas inlet assembly illustrated in FIG. 4 is intended for use in
the collection of vapors of nitrogen containing compounds. The
vapor collection system of FIG. 4 includes a conversion unit 80
designed to convert organic nitrites, nitrates, or amines to nitric
oxide. The unit 80 can affect decomposition by thermal and/or
catalytic means. The unit 80 has an inlet port 82 communicating
with a sampling nozzle 84, and an output port 86 communicating with
conduit 42. The interior of unit 80 may be provided with a heating
wire 88 which is connected to a power supply 90. The interior
surfaces of the unit 80 or the surface of wire may be coated with a
catalyst such as a metal, suitably nickel, platinum, copper or
their alloys which participate in the conversion and decomposition
of the nitrogen containing vapor compounds.
An oven temperature of 1,250.degree. K. will decompose organic
nitrites and nitrates within microseconds. Under these same
conditions, an organic nitro compound will pyrolyze at a much
slower rate but it still will take no more than 3 milliseconds to
decompose 90 percent of the molecules. Therefore, pyrolysis of
these compounds can be regarded to take place instantaneously since
the residence time of a gas flowing with a convenient flow rate can
be several orders of magnitude larger than the lifetime of the
molecules. Traces of organic amine vapors in air when heated in a
conversion unit to about 1,800.degree. F. in the presence of a
noble metal catalyst such as platinum will be converted to nitric
oxide. The output from the unit 80 is combined with a source of
atomic oxygen within reactor 10. A chemiluminescent reaction
proceeds which is detected by photomultiplier tube 16. The
detection of animal vapors forms the basis of a detection unit for
people or animals. The output from the ammeter may be connected to
an alarm system or transmitted silently to remote stations to
indicate presence of people or animals in the vicinity of the
detector.
Nitrobenzene was introduced into pyrolysis unit 80 by passing
purified air over a liquid sample of nitrobenzene at room
temperature. A quartz tube having a 25 mm. I.D., 33 cm. long and
operated at a pressure of 1,020 mm. Hg produced 2 percent
conversion at 1,000.degree. K. When this unit was packed with
copper gauze having a surface coating of oxide, conversion
efficiency increased by a factor of 10. A third pyrolysis unit
constructed of copper tubing having an I.D. of 1.5 mm. and
fashioned into a tight coil had a conversion efficiency of 70
percent which became essentially independent of airflow above 15
ml./min. 100 percent conversion was obtained in a further pyrolysis
unit comprising a small quartz tube containing an internal nichrome
heater operated at red heat. The nichrome wire operated both as a
catalyst and a source of thermal energy. The metal catalyst not
only increases the combustion efficiency, but also reduces the
pyrolysis temperature.
A problem which must be accommodated is that of background which
might interfere with detection. There are two kinds of background:
(1) oxides of nitrogen and (2) naturally or normally occuring
organic nitroso, nitro, amine or nitrate compounds, which will
necessarily give a false positive signal. The first type of signal
may come from auto exhaust, though, there is no known wide spread
source of false signals of the second type.
Referring now to FIG. 5, more detailed detection system is
disclosed which includes provision for analysis of background and
calibration of the system. The system includes a reactor 100 which
includes a central cylindrical reaction chamber 102 joined at one
end by a photomultiplier housing 104 and at the other end by an
inlet chamber 106. A vacuum conduit 108 and pressure gauge 109 also
communicate with chamber 102. The conduit 108 contains a throttling
valve 110 and communicates with a mechanical vacuum pump 112
through a copper gauze reactor 114. The reactor 114 converts the
residual oxygen and oxides to harmless products before entering the
vacuum pump 112.
A high voltage lead 116 connects the photomultiplier tube to a
photomultiplier power supply unit 118 and a signal lead 120
connects the photomultiplier tube to a picoammeter 122. The output
from the ammeter 122 is applied to a strip chart recorder 124.
The inlet chamber 106 receives a supply of atomic oxygen through
conduit 126 and a supply of nitric oxide vapor through conduit 128.
The supply of atomic oxygen emanates from a regulated oxygen
storage cylinder 130. The oxygen flows from cylinder 130 through a
line 132 containing a toggle shutoff valve 134 and a
double-patterned, metering vernier valve 136, and an RF inductor or
microwave cavity 138. The microwave cavity is powered by an RF
oscillator 140 and RF power supply 142 through a lead 144.
The nitric oxide supply conduit 128 is fed from three alternate
sources through a 3-way rotary valve 146. One source comprises a
conduit 148 terminating in a nozzle 150 which contains a shutoff
valve 149 and a metering valve 147. The second source comprises a
conduit 152 containing in sequence a sampling nozzle 150, a
pyrolysis unit 154, a toggle shutoff valve 153 and a
double-patterned, vernier metering valve 155. The pyrolysis unit
154 contains a heating coil 156 powered by a power supply 158.
The third source of nitric oxide is a calibration source comprising
a conduit 160 containing in sequence a regulated gas cylinder 162
containing nitric oxide and carrier gas, a toggle shutoff valve 161
and a double-patterned vernier metering valve 163.
To conduct an analysis in accordance with the invention, the vacuum
pump 112 is turned on to reduce the pressure in the reactor 100 to
about 3 mm. of Hg. The system is first calibrated by turning rotary
valve 146 toward conduit 160 and opening valves 161 and setting
valve 163 while closing valves 153 and 149. Valve 134 is opened and
valve 136 regulated to a desired flow rate. RF oscillator 140 and
power supply 142 are turned on to create a supply of atomic oxygen.
The chemiluminescent reaction output is utilized to calibrate
ammeter 122 and recorder 124. Valve 161 is then closed, an the
rotary valve 146 turn toward conduit 148 regulated by means of the
metering valve 147. The photomultiplier output is again recorded to
determine the presence of nitrogen dioxide (NO.sub.2) to provide a
background signal. This signal may be utilized to reset the zero
level of the recorder 124 and ammeter 122.
Valve 149 is again closed and the rotary valve 146 turn toward
conduit 152. Shutoff valve 153 is opened and metering valve 155 set
to the desired level. The heater power supply 158 is adjusted to
provide a temperature within the pyrolysis unit 154 of, at least
about 1,250.degree. K. The pyrolysis unit 154 converts the mixture
of vapor of organic nitrogen compounds, and air to nitric oxide
which combines with the atomic oxygen within reactor 100 with the
chemiluminescent emission of light. The characteristic light output
is detected and measured by the photomultiplier tube and is
recorded by the recorder 124.
The type of nitrogen-containing compounds being pyrolyzed in the
furnace can be distinguished by varying the furnace temperature and
using various catalysts. If the temperature is lowered to
700.degree. K, the organic nitrites and nitrates should take about
10.sup.- .sup.2 sec to decompose, while the organic nitro compounds
will pass through the furnace unchanged. Thus, the signal of a
pyrolysis temperature of 1,250.degree. K represents the total
nitrogen-containing organic compounds, while the smaller signal at
an oven temperature of 700.degree. K gives an estimate of the
amount of organic nitro compounds present.
It is to be realized that only preferred embodiments of the
invention have been described and that numerous substitutions,
alterations and modifications are all permissible without departing
from the spirit and scope of the invention as defined in the
following claims.
* * * * *