Method and apparatus to detect a gas by measuring ozone depletion

Abstract

The present invention relates to an apparatus and method for determining the concentration of nitric oxide (NO) in a gas mixture such as air. The gas sample containing NO is mixed with a gas containing ozone (O3), and the change in the ozone concentration is measured after a sufficient time is allowed for the reaction between NO and O3 to take place and destroy a measurable quantity of O3. In the preferred embodiment, the concentration of ozone is measured using the technique of UV absorption. In this case, the invention has the advantage over other instruments for measuring NO of having absolute calibration based on the known extinction coefficient for ozone at ultraviolet wavelengths. The invention discloses both static and dynamic flow systems, and the NO concentration measurements may be made over a wide pressure range.

Description

FIELD OF INVENTION

[0001] The present invention relates to gas analysis, and more particularly to the detection and measurement of nitric oxide (NO) in gases such as air and human breath by measuring ozone depletion. A suitable application of the invention is the measurement of the concentration of NO in the inhaled or exhaled air of a human being or other living organism. Another suitable application is the measurement of NO in ambient air for air pollution monitoring and for scientific studies of atmospheric chemistry. The invention also applies to measurements of nitrogen dioxide (NO2) in a gas mixture such as air when NO2 is first reduced to NO via a photolytic or chemical reaction. In ambient air, the invention may be used to measure the sum of NO and NO2 concentrations, commonly referred to as NOx The invention also applies to the measurement of reactive oxides of nitrogen such as NO2, nitrate radical (NO3), dinitrogen pentoxide (N2O5), nitrous acid (HNO2), nitric acid (HNO3), peroxynitric acid (HNO4), peroxyacetyl nitrate (PAN), chlorine nitrate (ClNO3) and particulate nitrate, collectively referred to as NOy, either separately or in combination. These nitrogen oxide species may be caused to produce NO in a chemical reaction, as in the reaction at a heated molybdenum oxide surface or in the reaction at a heated gold surface in the presence of a suitable reducing agent such as hydrogen or carbon monoxide (CO). The present invention measures the concentration of NO produced in such reactions.

[0002] The invention may be applied to the detection and quantification of any substance that may be treated so as to release gaseous NO. For example, it is known in the art of chromatography that many compounds containing nitrogen can be heated or reacted with other chemicals to produce NO gas. The NO produced by heating or by reaction with other chemicals may be detected and quantified using the invention described here. Similarly, various substances containing nitrogen such as fertilizers and chemicals used as explosives will slowly decompose to release NO gas, and that NO gas can be detected and quantified using this invention. The detection of fertilizers and explosives may be enhanced by heating the sample to increase the rate of release of NO gas.

[0003] The invention also applies to the detection and quantification of chemical compounds that do not contain nitrogen themselves but that will react with a nitrogen-containing compound to produce NO gas. An example is the detection and quantification of carbon monoxide (CO) where air containing CO is mixed with a nitrogen-containing compound such as NO2 and heated in the presence of a catalytic surface such as a gold surface to produce NO. The NO thus produced can be detected and quantified using this invention as a means of detecting and quantifying the CO in the air sample.

[0004] More generally, this invention applies to the measurement of the concentration of any chemical species in a gas such as air if that gas reacts with ozone at a sufficient rate to cause a measurable change in the ozone concentration. Examples of other chemical species that may be quantified include but are not limited to alkynes and alkenes such as acetylene, ethylene and propylene, compounds commonly found in petrochemical feedstocks.

BACKGROUND OF THE INVENTION

[0005] Scientific work over the past decade has demonstrated that the concentration of NO in human breath can be a good indicator of inflammation in the lungs caused by asthma and other respiratory diseases. As a result, there is presently a need for a simple, lightweight, low cost instrument for the measurement of NO in human breath. This invention addresses that need in particular, but is also applicable to the measurement of NO, NO2 NOx, NOy and various gases that react with ozone that are present in air and other gas mixtures such as cylinders containing compressed gases and petrochemical feedstocks for chemical synthesis.

[0006] At present, the concentration of NO in a gas sample such as air is most commonly measured by mixing the gas sample with air or oxygen containing ozone gas at low pressures. In a reaction chamber, nitric oxide molecules react with ozone (O3) molecules, to form nitrogen dioxide (NO2) and oxygen (O2) molecules. A small fraction of those reactions also results in the emission of photons having a red or near-infrared wavelength. The concentration of NO in the gas sample is determined by measuring the intensity of that photon emission. This technique, referred to as the “NO+O3 Chemiluminescence” technique is highly sensitive and widely used in the measurement of NO concentrations in ambient air and in inhaled and exhaled human breath. The principal disadvantages of this technique are: 1) a vacuum pump is required, making the instrument large, heavy and highly consumptive of electrical power; 2) a cooled, red-sensitive photomultiplier tube is required, adding to the bulk and weight of the instrument and making it relatively expensive; and 3) the mixing ratio of ozone required for sensitive detection is high, typically a few percent, and requires a high-voltage (several hundred volts) electrical discharge to produce the ozone, thereby increasing the risk of human exposure to this toxic gas and to the danger of electrical shock.

[0007] Another technique for measuring concentrations of NO in air samples involves contacting a gas sample with an alkaline luminol solution. As with the ozone-based method described above, this technique produces chemiluminescence. This approach has the advantage of not requiring a vacuum pump and of detecting photons in the visible region where the photomultiplier tube need not be cooled. However, sensitive detection using this technique requires the use of chromium (VI) oxide CrO3 to oxidize NO to NO2 prior to contact with the luminol solution, and measures must be taken to eliminate large interferences in the measurement from CO2and water vapor, both of which are present in exhaled breath at high concentrations.

[0008] This invention makes use of the same chemical reaction used in the conventional NO+O3 chemiluminescence instrument commonly used in air pollution monitoring and breath analysis. However, the invention differs significantly from that instrument in that the basis of detection is not chemiluminescence (detection of photons emitted by the reaction). Instead, the invention measures the decrease in the concentration of ozone that occurs in the chemical reaction. Advantages of this invention over the conventional NO+O3 chemiluminescence technique are: 1) the concentration of ozone required is much lower, in the low part-per-million range rather than the percent range; 2) the instrument can be operated at any pressure, such as ambient atmospheric pressure, and therefore does not require a vacuum pump; 3) a photomultiplier tube is not required; and 4) the instrument can be based on the extinction of UV light and, therefore, is potentially self-calibrating, which might eliminate the need for compressed cylinders containing standard concentrations of NO.

SUMMARY OF THE INVENTION

[0009] The main aspect of the present invention is to provide a simple ozone depletion measurement method and apparatus to detect NO concentration in a test sample.

[0010] Another aspect of the present invention is to use known UV instruments to detect levels of O3.

[0011] Another aspect of the present invention is to provide a flexible test chamber for use as a portable home test kit for lung disease patients.

[0012] Another aspect of the present invention is to provide batch and continuous flow methods and apparatus to measure O3 depletion.

[0013] Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic layout of a theoretical test chamber to mix NO and ozone (O3) in a static system.

[0015] FIG. 2 is a flow chart of the basic steps of the preferred embodiment method in the static system.

[0016] FIG. 3 is a schematic layout of an alternate embodiment chamber having an expandable wall to provide a test chamber that does not require a vacuum or a pressurized environment.

[0017] FIG. 4 is a schematic layout of a alternate embodiment chamber using a UV absorption system to detect concentrations of O3.

[0018] FIG. 5 is a schematic layout of an alternate embodiment chamber using a combination of the flexible wall and the UV absorption system.

[0019] FIG. 6 is a schematic layout of an alternate embodiment test apparatus using a continuously flowing gas stream measurement technique which provides batch data analysis.

[0020] FIG. 7 is a flow chart of the basic steps to practice the invention using the FIG. 6 apparatus.

[0021] FIG. 8 is a schematic layout of the FIG. 6 apparatus using a UV absorption O3 measurement technique, the initial prototype.

[0022] FIG. 9 is a schematic layout of an enhanced continuous flow apparatus which constantly measures O3 concentration in the test gas in a pre- and post-reaction chamber.

[0023] FIG. 10 is a flow chart of the steps to practice the invention with the FIG. 9 apparatus.

[0024] FIG. 11 is a sample chart of a theoretical test result using the FIG. 8 apparatus.

[0025] FIG. 12 is a sample chart of a theoretical test result using the FIG. 9 apparatus.

[0026] FIG. 13 is a schematic layout of an alternate embodiment test apparatus using a continuous flowing gas stream measurement technique with a variable reaction volume.

[0027] FIG. 14 is a schematic layout of an alternate embodiment test apparatus using a continuously flowing gas stream measurement technique with a NO scrubber which provides batch data analysis.

[0028] FIG. 15 is a flow chart of the steps to practice the invention with the FIG. 14 apparatus.

[0029] FIG. 16 is a schematic layout of an alternate embodiment test apparatus using a continuous flowing gas stream measurement technique with a NO scrubber that provides continuous data analysis.

[0030] FIG. 17 is a flow chart of the steps to practice the invention with the FIG. 16 apparatus.

[0031] FIG. 18 is an actual chart of data obtained using apparatus 80 of FIG. 8.

[0032] Before explaining the disclosed embodiment of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown, since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.

DETAILED DESCRIPTION OF THE DRAWINGS

[0033] Referring first to FIG. 1 it is understood that the reaction O3+NO→NO2+O2+light energy occurs inside reaction chamber 1. However, the present invention does not measure the light energy as does the prior art. Rather, the present invention measures a decrease in O3 concentration which equates to a concentration of NO in the test sample. This O3+NO reaction occurs within batch system 10 in reaction chamber 1. First ozone (O3) is added to the test chamber 1 via ozone inlet 3. The generic ozone meter 5 measures the O3 concentration. Then the patient 109 exhales his breath sample via sample inlet 2 into the test chamber 1. The test sample contains an unknown amount of NO. The meter 5 measures the concentration of O3 after the O3+NO reaction is sufficiently complete to determine the concentration of NO in the breath sample. The tube 6 feeds the ozone meter 5 the gases from the test chamber 1. The exhaust port 4 is opened after the measurements are done. Known in the art are several valving methods to accomplish the above measurements. For example, the test chamber 1 could be run at a vacuum pressure with the appropriate valves at tubes 2, 3 and 4. The above system is an example of a static rather than a continuous flow system.

[0034] Practice of the present invention requires knowledge of the reaction rate of NO+O3 and the extinction coefficient for O3; both of which are well known in the art. Alternatively, calibration standards could be used to establish the concentration of NO in the sample.

[0035] If the reaction takes place but is not complete, a correction may be applied according to the formula [NO]sample=[NO]measured/{1−exp(−k[O3]t)} where NOmeasured is the concentration of NO measured, [NO]sample is the actual NO concentration in the gas sample, [O3] is the concentration of O3 and t is the contact time between NO and O3. k is the second order rate constant for the gas-phase reaction of NO with ozone. This calculation assumes pseudo-first order kinetics with [O3]>>[NO]. If this condition does not hold, then one skilled in the art can apply the well-known results of second-order kinetics to correct for the concentration of NO that remains unreacted. Referring next to FIG. 2 the static or batch process using the FIG. 1 equipment is described. The first step is numbered 20. Step 20 calls for adding O3 to test chamber 1. Step 21 calls for using ozone meter 5 to measure the O3 concentration in the test chamber 1. Step 22 calls for adding an air sample with an unknown concentration of NO in it. FIG. 1 shows the measurement of a human breath sample. Step 23 calls for allowing a period of time to pass to allow the O3 to react with the NO. This reaction decreases the concentration of O3 in test chamber 1. Step 24 calls for the measurement of the O3 concentration after the O3+NO reaction is sufficiently complete. Step 25 calls for a comparative calculation of the O3 concentration before and after the test sample was added into the test chamber 1. The calculation yields actual NO concentration as the below noted example indicates. Step 26 calls for the evacuation of the test chamber 1 to prepare for another measurement. Known in the art are several ways to clear the test chamber 1.

[0036] Referring next to FIG. 3 another batch system 30 functions the same as the FIG. 1 system and the FIG. 2 process. The new feature in FIG. 3 is the flexible membrane 7 on at least one side of the test chamber 1. This flexible membrane 7 could also be built as an entirely flexible polymer bag. The benefit of the flexible membrane 7 is to allow a user 109 to blow his breath into inlet tube 2 and expand the flexible membrane 7, assuming all other tubes 3, 4 are short. This expansion eliminates the need for lab equipment to evacuate the test chamber 1 before the test. Thus, the batch test apparatus 30 is suited for an inexpensive home use kit for patients who require daily monitoring of their lung condition.

[0037] Referring next to FIG. 4 the batch systems of FIGS. 1, 2, 3 may be configured to use an ultra-violet (UV) light sensing meter to detect ozone concentration. The batch apparatus 40 represents this UV system. A UV light source 8 emits UV light through an optional lens 9 which transmits the focused light rays through left window 32 in the test chamber 1. The light travels through the test chamber 1 and is absorbed by the O3 to decrease the light intensity according to the Beer-Lambert law. The light then travels out right window 32 through an optional filter 11 and into a photodetector 12. The photodetector 12 may be a photodiode or a photomultiplier tube known in the art.

[0038] Referring next to FIG. 5 a preferred home use batch apparatus 50 comprises a flexible membrane 7 in a test chamber 1 plus a UV measurement system as described in FIG. 4.

[0039] Referring next to FIGS. 6, 7 a continuously flowing gas system 60 is shown. The designation “conduit 14” represents the common pathway volume of the O3+air sample without the large volume reaction chamber 15. The theory of operation is that when a test sample or a continuously flowing sample is sent through conduit 14, little or no O3 reacts with NO, and a baseline O3 measurement is established. When a second test sample or a continuously flowing sample is sent through the large volume reaction chamber 15, practically all of the NO is reacted with O3, thus yielding an accurate NO concentration by a comparison of the two measurements. Optimally, the volume of conduit 14 would be zero, so that 0% reaction of O3+NO would occur while the gases transit this pathway, and the volume of reaction volume 15 would be infinite, so that this reaction would proceed to 100% completion. In this simple model, the concentration of NO would then be the simple difference of the O3 concentrations measured by ozone meter 5.

[0040] An alternative embodiment to conduit 14 is the small volume reaction chamber 61. The actual volume of chamber 61 is chosen such that there is sufficient time for potentially interfering compounds to react to a large extent with O3 but not enough reaction time for a significant amount of NO to react with O3. Examples of potential interferences whose effects can be eliminated in this way include some alkenes such as ethylene.

[0041] In practice, the conduit 14 may actually be a small volume reaction chamber 61 which serves to cancel out the effects of interfering compounds by allowing those compounds to react with an approximately equal amount of ozone in the conduit (or small reaction volume) and the large volume reaction volume.

[0042] A sample inlet 2 contains an unknown NO concentration perhaps from a long human breath exhalation. Ozone is supplied either by an inlet 3 or an in-line O3 generator 16 which could be a photochemical reactor. Valve 13 diverts the combined flow from inlets 2 and 3 to either the conduit 14 (or small volume reaction chamber 61) or the large volume reaction chamber 15 via connecting tube 6. The ozone meter 5 is connected to the exhaust port 4.

[0043] Step 70 of FIG. 7 shows a test sample of gas initiated into sample inlet 2. Decision step 71 provides for either a continuous O3 flow through inlet 3 in step 72, or for in situ production of O3 with the O3 generator 16. In step 73 O3 and the test sample are sharing the tube at tube segment 62, and the valve 13 is first set to flow the mixture through the conduit 14 (or small volume reaction chamber 61). Step 74 measures the output from the conduit 14 (or small volume reaction chamber 14) with ozone meter 5.

[0044] Step 75 sets valve 13 to the large volume reaction chamber 15 so that a second O3 measurement can be made in step 76. Step 77 compares the two measurements to determine the NO concentration in the continuous sample of gas. Repeat measurements can be made by returning to step 73.

[0045] Referring next to FIG. 8 the same procedure described by FIG. 7 can be used. The generic ozone meter 5 of FIG. 6 has been replaced with a detection cell 17 connected at tube segment 63. The known means to measure O3 in the detection cell 17 consists of shining a UV light 8 through an (optional) lens 9, through the left UV transparent window 32, through the test sample in detection cell 17, out the right UV transparent window 32, through the (optional) optical filter 11, and into photodetector 12 (a photodiode, photomultiplier tube or the equivalent). An optional gas pump 18 can be used to draw the gas through the apparatus.

[0046] Referring next to FIGS. 9, 10 a continuous flow system 90 uses the small volume reaction chamber/large volume reaction chamber concept, but sends the same gas sample through a first measurement in reference detection cell 19 and a second measurement in detection cell 17. Arrows F1, F2 indicate the gas flow directions.

[0047] Step 100 initiates a continuous gas sample into inlet 2. Decision step 101 provides for either a continuous O3 flow into inlet 3, or in situ O3 production in O3 generator 16. The test sample and O3 mixture at conduit 14 (or small volume reaction chamber 61) are fed into the reference detection cell 19 and the O3 concentration is measured in step 103. The same gas sample travels into the large volume reaction chamber 15, and the O3 and NO react. Step 104 measures the reacted gas mixture in detection cell 17.

[0048] Step 105 does the comparison of the two measurements to determine the NO concentration in the test sample. Repeat measurements are done by returning to step 103.

[0049] Referring next to FIG. 11, the theoretical response to two samples of human breath is shown using the NO detection system 60 of FIG. 6. The baseline signal is obtained when the solenoid valve 13 is positioned such that the ozone mixed with sample air passes through conduit 14 (or the small volume reaction chamber 61). The positive excursions in signal (points 111-120) are obtained when the solenoid valve 13 is positioned such that ozone mixed with sample air passes through the large volume reaction chamber. For this NO detection system, the NO measurement in breath is intermittent, where the measurements return to “BASELINE” after each breath sampling period 111-120. However, if the baseline is sufficiently stable, the breath sampling period could cover the entire time of expiration of an entire human breath.

[0050] Referring next to FIG. 12, the theoretical response to two samples of human breath is shown using the NO detection system 90 of FIG. 9. For this NO detection system, the NO measurement is continuous because the “BASELINE” is continuously measured in detection cell 17 and its value subtracted from the continuously measured sample value in reference cell 19.

[0051] Referring next to FIG. 13, the NO detection system 130 is an alternative to the NO detection system 60 of FIG. 6. In this NO detection system the solenoid valve, conduit and large volume reaction volume are replaced by a single variable volume reaction chamber 20 (such as bellows or combination of piston and cylinder) that can be compressed to form a conduit (or small volume reaction chamber) and expanded to form a large volume reaction chamber. Shrinking and expanding the variable volume reaction chamber 20 of FIG. 13 is equivalent to switching the solenoid valve 13 of FIG. 6. When a bellows is used, this NO detection system has the advantage that the surfaces exposed to the ozone mixed with gas sample are the same for the conduit (or small volume reaction chamber) and large volume reaction chamber. This could be important because it is known in the art that ozone can be decomposed on surfaces, and a difference in ozone destruction at the conduit (or small volume reaction chamber) and large reaction volumes could result in a false NO signal.

[0052] Referring next to FIGS. 14, 15 the NO detection system 140 is another alternative to the NO detection system 60 of FIG. 6. In this NO detection system a solenoid valve 13 is alternately switched such that a gas sample entering inlet 2 (Step 81) passes through either bypass tube 600 (Step 87) or NO scrubber 28 (Step 82). The NO scrubber 28 contains materials known in the art to remove NO from the gas sample. Following the connecting tubing or scrubber, ozone is added to the gas sample through inlet 3 (Step 84, 89) or alternatively is produced directly in the flowing stream using photochemical reactor 16 (Steps 83, 88). Next, the mixture of gas sample and ozone flows through the large volume reaction chamber 15 to allow NO to react with O3 (Steps 85, 91) and is then detected using the generic ozone meter 5 (Steps 86, 92). The NO concentration is calculated as the ozone concentration measured when the gas sample passes through the NO scrubber 28 minus the ozone concentration measured when the gas sample passes through bypass tube 600 (Step 93). A correction can be applied if the reaction time is insufficient for NO and O3 to react completely in the large volume reaction chamber.

[0053] Referring next to FIGS. 16, 17 the NO detection system 148 is another alternative to the NO detection system 60 of FIG. 6. In this NO detection system, a continuously flowing gas sample entering the system through sample inlet 2 (Step 141) is split into two continuously flowing gas streams (Step 142). One of the parts of the continuously flowing gas stream flows through a NO scrubber 28 (Step 143). Gas containing ozone is continuously added to this partial continuously flowing gas sample through inlet 3 (Step 145). The partial continuously flowing gas sample+ozone then flows through the left large volume reaction chamber 15, which allows ozone to react with any interfering species which may be present in the continuously flowing gas sample (Step 147), and also compensates for the time required for the remainder of the continuously flowing gas sample+ozone to flow through the apparatus. It is well known in the art that this latter timing issue can also be addressed through electronic manipulation of the measurement data. After passing through the large volume reaction chamber 15, the ozone in the continuously flowing gas sample+ozone is detected using left generic ozone meter 5 (Step 149), and the partial continuously flowing gas sample+ozone exit the instrument via left outlet 4. Simultaneously to the aforementioned steps involving the partial continuously flowing gas sample, the remainder continuously flowing gas sample passes through bypass tube 6000 (Step 144). Gas containing ozone, split from the source supplying the aforementioned partial continuously flowing gas sample is continuously added to the remainder continuously flowing gas sample through inlet 3 (Step 146). The remainder continuously flowing gas sample+ozone then flows through the right large volume reaction chamber, where the ozone reacts with the NO present in the remainder partial continuously flowing gas sample (Step 148). The ozone is then detected using right generic ozone meter 5 (Step 150), and the remainder continuously flowing gas sample+ozone exit the instrument via right outlet 4. The NO concentration in the continuously flowing gas sample is calculated as the difference between this measurement and that obtained by left generic ozone meter 5 (Step 151). A correction can be applied if the reaction time is insufficient for NO and O3 to react completely in the right large volume reaction chamber.

EXAMPLE

[0054] Referring next to FIG. 18, experimental results for measurements of NO are shown for the NO detection system 80 of FIG. 8. In this experiment only the large volume reaction chamber 15 was used, and the baseline ozone was measured by removing the sample NO from inlet 2 rather than by passing the ozone and sample air mixture through the small reaction volume. Ozone was generated by use of a photochemical reactor (not shown but located directly on inlet 3) and admitted to the system via inlet 3. Measurements of ozone were made every 10 seconds by absorbance of light having a wavelength of 254 nm. With no sample air added, the ozone concentration was in the range 3550 to 3650 parts-per-billion by volume (ppbv); see “BASELINE O3 CONCENTRATION.” The total flow rate of sample air and O3 was 0.95 L/min, the volume of the large volume reaction chamber was 100 cm3, and the total pressure was 0.71 atm, resulting in a reaction time of 4.5 seconds. Using the well-known rate constant for the NO+O3 reaction of 1.8×10−14 cm3 molec−1 s−1, it is calculated that 99.4% of the NO in the sample reacts with O3. Air was sampled three times each for five different NO concentrations labeled groups I, II, III, IV, V. Ozone concentrations declined each time sample air was admitted to the system, corresponding to measured NO concentration group I=1317, group II=651; group III=309, group IV=97; group V=31 ppbv for the five different air samples tested.

[0055] The formula to obtain the NO concentration of 1317 in group 1 is to subtract the average of readings 94, 95, 96 from the average of the baseline at points 97, 98, 99. The measurement is then corrected by multiplying by 1.006 to correct for the 0.6% of NO that does not react within the large volume reaction chamber.

[0056] Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. Each apparatus embodiment described herein has numerous equivalents.

Claims

1. A method to determine a NO concentration in a test sample, the method comprising the steps of: measuring a concentration of O3 in a gas sample; adding a test sample to the gas sample; and measuring a decrease of O3 in a reacted mixture of the gas sample and the test sample to determine the NO concentration in the test sample.

2. The method of claim 1, wherein the gas sample is air and the O3 is added to the air before the measuring step.

3. The method of claim 2, wherein the test sample is a human breath.

4. The method of claim 3 further comprising the step of using a reaction chamber for the adding of the test sample to the gas sample.

5. The method of claim 4 further comprising the step of using a reaction chamber having a flexible wall.

6. A method to measure a concentration of a chosen gas in a sample of gas, the method comprising: adding O3 to a reaction chamber; measuring an O3 concentration in the reaction chamber; selecting a chosen gas that reacts with ozone; adding a gas sample containing the chosen gas to the reaction chamber; waiting a period of time for the O3 to react with the chosen gas; measuring the O3 concentration in the reaction chamber; and comparing the O3 concentration before the addition of the gas sample to the O3 concentration after the addition of the gas sample to determine the concentration of the chosen gas in the gas sample.

7. The method of claim 1 further comprising the step of using a reaction chamber.

8. The method of claim 7 further comprising the step of using a UV ozone detector for measuring the concentrations of O3.

9. The method of claim 5 further comprising the step of using a UV ozone detector for measuring the concentrations of O3.

10. (FIG. 6) A method to determine a NO concentration in a continuously flowing sample of gas, the method comprising the steps of: introducing the continuously flowing sample of gas containing NO into a test apparatus having a conduit and a large volume reaction chamber; adding O3 to the continuously flowing sample of gas; sending the O3+the continuously flowing sample of gas mixture to the conduit; measuring an O3 concentration in or downstream of the conduit; sending the O3+continuously flowing sample of gas mixture to the large volume reaction chamber; measuring an O3 concentration in or downstream of the large volume reaction chamber; and comparing the O3 measurements of the conduit and large volume reaction chamber to determine the NO concentration in the gas sample.

11. The method of claim 10, wherein the conduit further comprises a small volume reaction chamber.

12. The method of claim 10 further comprising the step of using a UV ozone detector for the O3 measuring steps.

13. A method to determine a NO concentration in a continuously flowing sample of gas, the method comprising the steps of: introducing the continuously flowing sample of gas+O3 mixture into a reference detection cell; measuring an O3 concentration in the reference detection cell; sending the continuously flowing sample of gas+the O3 mixture into the large volume reaction chamber; sending the continuously flowing sample of gas+O3 mixture from the large volume reaction chamber into a detection cell; measuring an O3 concentration in the detection cell; and comparing the O3 measurements in the reference and detection cells to determine the NO concentration in the continuously flowing sample of gas.

14. The method of claim 13 further comprising the step of continuously flowing the gas sample into a small volume reaction chamber prior to sending the gas sample+O3 mixture into a reference detection cell.

15. The method of claim 13 further comprising the step of using a UV ozone detector for the O3 measurements.

16. A method to measure a concentration of a chosen substance in an original sample, the method comprising the steps of: treating the original sample to form NO in a gaseous state thereby forming a gas sample; measuring a concentration of O3 in a reaction chamber; adding the gas sample to the reaction chamber; and measuring a decrease of O3 in the reaction chamber, thereby determining the NO concentration in the gas sample and further determining the concentration of the chosen substance in the original sample.

17. A method to detect a nitrogen based explosive in an original sample, the method comprising the steps of: treating the original sample to form NO in a gaseous state thereby forming a gas sample; measuring a concentration of O3 in a reaction chamber; adding the gas sample to the reaction chamber; and measuring a decrease of O3 in the reaction chamber, thereby determining the NO concentration in the gas sample and further determining whether a nitrogen based explosive exists in the original sample.

18. A method to measure a concentration of a chosen nitrogen containing substance in an original sample, the method comprising the steps of: treating the original sample to form NO in a gaseous state thereby forming a gas sample; measuring a concentration of O3 in a reaction chamber; adding the gas sample to the reaction chamber; and measuring a decrease of O3 in the reaction chamber, thereby determining an NO concentration in the gas sample and further determining the concentration of the nitrogen containing chosen substance in the original sample.

19. A method to determine a concentration of a chosen chemical compound in an original sample, said chemical compound does not contain nitrogen, said chemical compound will chemically react with another compound which does contain nitrogen, the method comprising the steps of: treating the original sample with a nitrogen containing compound to induce a chemical reaction, thereby producing a gas sample containing NO; measuring a concentration of O3 in the reaction chamber; and measuring a decrease of O3 in the reaction chamber, thereby determining the NO concentration in the gas sample, and further determining the concentration of the chosen chemical compound in the original sample.

20. (FIG. 13) A method to determine a NO concentration in a continuously flowing sample of gas, the method comprising the steps of: introducing a continuously flowing sample of gas containing NO into a test apparatus having a variable volume reaction chamber (VVRC) with the VVRC set at a small volume; adding O3 to the continuously flowing sample of gas; sending the O3+continuously flowing sample of gas mixture to the VVRC with the VVRC set at the small volume; measuring an O3 concentration in or downstream of the VVRC with the VVRC set at the small volume; setting the VVRC to a large volume; sending the O3+continuously flowing sample of gas mixture to the VVRC while it is set to the large volume; measuring an O3 concentration in or downstream of the VVRC set at the large volume; and comparing the O3 measurements of the VVRC set at the small volume to the measurements of the VVRC set at the large volume to the determine NO concentration in the gas sample.

21. The method of claim 20, wherein the VVRC further comprises a bellows.

22. (FIG. 14) A method to determine a NO concentration in a continuously flowing sample of gas, the method comprising the steps of: assembling a test apparatus having a NO scrubber connected to a large volume reaction chamber and having a bypass connected to the large volume reaction chamber; sending the continuously flowing sample of gas to the NO scrubber; adding O3 to the continuously flowing sample of gas; sending the O3+continuously flowing sample of gas mixture to the large volume reaction chamber; measuring the O3 concentration in or downstream of the large volume reaction chamber; sending the continuously flowing sample of gas to the bypass tube; adding O3 to the continuously flowing sample of gas; sending the O3+continuously flowing sample of gas mixture to the large volume reaction chamber; measuring the O3 concentration in or downstream of the large volume reaction chamber; and comparing the O3 measurements of the NO scrubber measurement and the bypass measurement to determine the NO concentration in the continuously flowing gas sample.

23. The method of claim 22, wherein the step of adding the O3 to the gas sample is done after the step of sending the continuously flowing gas sample to either the bypass tube or NO scrubber.

24. The method of claim 23 further comprising the step of using a UV ozone detector for the O3 measuring steps.

25. An apparatus to determine a NO concentration in a test sample, the apparatus comprising: means for measuring a concentration of O3 in a gas sample functioning to determine an O3 baseline; means for adding a test sample to the gas sample functioning to create a chemical reaction between the O3 and NO; and means for measuring a decrease of O3 in a reacted mixture of the gas sample and the test sample functioning to determine the NO concentration in the test sample.

26. An apparatus to measure a concentration of a chosen gas in a sample of gas, the apparatus comprising: means for measuring an O3 concentration in a reaction chamber functioning to determine an O3 baseline; means for adding a gas sample containing a chosen gas that reacts with ozone, to the reaction chamber functioning to create a chemical reaction between O3 and the chosen gas; and means for measuring a decreased O3 concentration in the reaction chamber after the chemical reaction takes place functioning to determine the concentration of the chosen gas in the gas sample.

27. An apparatus to determine a NO concentration in a continuous test sample, the apparatus comprising: means for continuously flowing a gas sample containing NO into a test apparatus having a conduit and a large volume reaction chamber functioning to fill the conduit and the large volume reaction chamber with the gas sample; means for sending O3+gas sample mixture to the conduit functioning to create an O3 baseline; means for sending the O3+gas sample mixture to the large volume reaction chamber functioning to create a chemical reaction between the O3 and the NO; means for measuring a decreased O3 concentration in or downstream of the large volume reaction chamber functioning to determine the NO concentration in the gas sample.

28. An apparatus to determine a NO concentration in a continuously flowing sample of gas, the apparatus comprising: means for continuously flowing a gas sample containing NO and O3 into a conduit functioning to fill the conduit with the gas sampled and O3; means for sending the continuously flowing gas sample+O3 mixture into a reference detection cell functioning to fill the reference detection cell with the gas sample and O3 mixture; means for measuring an O3 concentration in the reference detection cell functioning to create an O3 baseline; means for continuously flowing the gas sample containing NO and O3 into a large volume reaction chamber functioning to create a chemical reaction of the gas sample+O3; means for sending the continuously flowing gas sample+O3 reaction mixture into the detection cell functioning to prepare for an O3 measurement; means for measuring a decreased O3 concentration in the detection cell functioning to determine the NO concentration in the gas sample.

29. (FIG. 16) A method to determine a NO concentration in a continuously flowing sample of gas, the method comprising the steps of: assembling a test apparatus having a NO scrubber connected to a first large volume reaction chamber and having a bypass connected to a second large volume reaction chamber; simultaneously sending the continuously flowing sample of gas to the NO scrubber and first large volume reaction chamber and to the bypass and the second large volume reaction chamber; simultaneously adding O3 to the first and to the second large volume reaction chamber; measuring an O3 concentration in the first large volume reaction chamber; measuring an O3 concentration in the second large volume reaction chamber; and comparing the O3 measurements from the first and second large volume reaction chambers to determine the NO concentration of the continuously flowing sample of gas.