초록 ▼

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 allow

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 O 3. In the disclosed 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.

대표청구항 ▼

We claim: 1. A method to determine a NO concentration in a test sample in a reaction chamber, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: treating said test sample with a gas sample having a known concentration of ozone a pr

We claim: 1. A method to determine a NO concentration in a test sample in a reaction chamber, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: treating said test sample with a gas sample having a known concentration of ozone a priori exceeding a concentration of NO in the test sample, whereby the ozone and NO react to form a product mixture comprising O2 and NO2; allowing the reaction of ozone and NO to go to completion; measuring a concentration of ozone in said product mixture; and quantifying the concentration of NO in said test sample by calculating an ozone difference between said gas sample and said product mixture. 2. The method of claim 1, wherein the gas sample is air and wherein ozone is added to the air prior to measuring the ozone concentration of said gas sample. 3. The method of claim 1, wherein the test sample comprises a human breath. 4. The method of claim 3, wherein the reaction mixture is formed in a reaction chamber comprising a flexible wall. 5. The method of claim 4 further comprising the step of evacuating the reaction chamber prior to repeating said method by adding one or more subsequent test samples comprising NO to said evacuated reaction chamber. 6. The method of claim 1, wherein the steps of measuring the concentration of ozone in said gas sample and the concentration of ozone in said reaction mixture further comprise using an ultraviolet absorbance spectrometer. 7. A method to determine a NO concentration in a test sample in a reaction chamber, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: treating said test sample with a gas sample having a known concentration of ozone a priori exceeding a concentration of NO in the test sample, whereby the ozone and NO react to form a product mixture comprising O2 and NO2; measuring a concentration of ozone in said product mixture; quantifying the concentration of NO in said test sample by calculating an ozone difference between said gas sample and said product mixture; and applying a correction factor to calculate a concentration of NO when the reaction of ozone and NO does not achieve completion. 8. The method of claim 7, wherein the correction factor when [O3]>>[NO] has the formula kcorrection=1/{1-exp(-k[O3]t)}, wherein [NO]sample=kcorrection[NO] measured, [NO]measured comprises a measured concentration of NO, [NO]sample comprises a concentration of actual NO in said gas sample, [O3] comprises the concentration of O3, t is the contact time between NO and O3, and k is the second order rate constant for the gas-phase reaction of NO with ozone. 9. The method of claim 7, wherein the test sample comprises a human breath. 10. The method of claim 9, wherein the steps of measuring the concentration of ozone in said gas sample and the concentration of ozone in said reaction mixture further comprise using an ultraviolet absorbance spectrometer. 11. The method of claim 7, wherein the reaction mixture is formed in a reaction chamber comprising a flexible wall. 12. The method of claim 11 further comprising the step of evacuating the reaction chamber prior to repeating the steps of said method by adding one or more subsequent test samples comprising NO to said evacuated reaction chamber. 13. A method to determine a concentration of a reactive nitrogen oxide capable of producing NO in a concentration of parts per million or less by volume, in a sample of gas, the method comprising: reacting the sample of gas comprising the reactive nitrogen oxide to produce a mixture comprising NO; providing a gas comprising a baseline concentration of ozone a priori exceeding a concentration of produced NO to a reaction chamber; introducing the mixture comprising NO into said reaction chamber, whereby the ozone and NO form a product mixture comprising O 2 and NO2; measuring a concentration of ozone in said product mixture comprising O2 and NO2; and quantifying the concentration of the reactive nitrogen oxide in said gas sample by calculating an ozone difference between said baseline ozone value and the ozone measured in said product mixture. 14. The method of claim 13, wherein the reactive nitrogen oxide is selected from the group consisting of NO2, NO3, NOx, NOy, N2O5, HNO2, HNO3, HNO4, peroxyacetyl nitrate (PAN), and ClNO 3; wherein NOx is a mixture of NO and NO2 and NOy is a combination of reactive nitrogen oxides. 15. A method to determine a NO concentration in a continuously flowing gas sample, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: mixing said continuously flowing gas sample with a continuous flow of ozone, wherein a concentration of ozone in a continuously flowing gas mixture a priori exceeds a concentration of NO; introducing said continuously flowing gas mixture into an apparatus having a first chamber and a conduit in connection with each other via a connection means; wherein said first chamber has a sufficiently large volume to enable a substantially large fraction of the NO to react with ozone while passing through the first chamber but a sufficiently small volume to minimize a reaction with slower reacting potential interfering compounds; engaging the connection means to cause the continuously flowing gas mixture to pass through the conduit and to bypass the first chamber, wherein said conduit has a sufficiently small volume whereby only a small fraction of NO reacts with ozone while passing through the conduit; measuring the concentration of ozone in or downstream of said conduit, thereby establishing a first ozone value; engaging the connection means to cause the continuously flowing sample gas comprising NO to pass through the first chamber and to bypass the conduit; measuring the concentration of ozone in or downstream of said first chamber, thereby establishing a second ozone value; and quantifying the concentration of NO in said continuously flowing gas sample by calculating an ozone difference between said first and second ozone values. 16. The method of claim 15, wherein the conduit further comprises a second chamber having a sufficiently small volume to enable potential interfering compounds having fast reactions with ozone to react nearly completely with ozone while passing therethrough, whereby NO reacts only to a small extent with ozone while passing therethrough. 17. The method of claim 15, wherein the steps of measuring the first and second ozone values further comprise using an ultraviolet absorbance spectrometer. 18. The method of claim 15, wherein the ozone added to said first chamber is produced in situ. 19. A method to determine a NO concentration in a continuously flowing gas sample, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: mixing said continuously flowing gas sample with a continuous flow of ozone, wherein a concentration of ozone in a continuously flowing gas mixture a priori exceeds a concentration of NO; introducing said continuously flowing gas mixture into a reference detection cell; measuring the concentration of ozone in said reference detection cell, thereby establishing a reference ozone value; passing the continuously flowing gas mixture into a reaction chamber, wherein said reaction chamber has a sufficient volume to enable a substantially large fraction of the NO to react with ozone to form a product mixture comprising O2 and NO2 while passing through the reaction chamber but small enough that slower reacting potential interfering compounds do not substantially react; introducing the product mixture into a detection cell; measuring a concentration of ozone in said detection cell; and comparing the reference ozone value and ozone concentration measured in said detection cell to determine a concentration of NO in the continuously flowing sample gas. 20. The method of claim 19 further comprising the step of continuously flowing the gas sample comprising NO into a small volume reaction chamber prior to introducing said mixture into the reference detection cell, said small volume reaction chamber having a sufficiently small volume to enable potential interfering compounds having fast reactions with ozone to react nearly completely with ozone while passing therethrough and where NO reacts only to a small extent with ozone while passing therethrough. 21. The method of claim 19, wherein the steps of measuring the concentration of ozone in each of the reference and detection cells further comprise using an ultraviolet absorbance spectrometer. 22. The method of claim 19, wherein said ozone is produced in situ. 23. A method to determine a NO concentration in a continuously flowing sample of gas, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: chamber; mixing said continuously flowing sample of gas with a continuous flow of ozone, wherein a concentration of ozone in a continuously flowing gas mixture a priori exceeds a concentration of NO; passing said continuously flowing sample gas through a variable volume reaction chamber variably positioned to have a sufficiently small volume to enable potential interfering compounds having fast reactions with ozone to react nearly completely with ozone while passing therethrough and where NO reacts only to a small extent with ozone while passing therethrough; measuring the concentration of ozone in or downstream of said reaction chamber, thereby establishing a first ozone value; passing a continuously flowing sample gas comprising NO through said variable volume reaction chamber variably positioned to have a sufficiently large volume to enable a substantially large fraction of the NO to react with ozone while passing through the chamber but small enough that slower reacting potential interfering compounds do not substantially react; measuring the concentration of ozone in or downstream of said reaction chamber, thereby establishing a second ozone value; and quantifying the concentration of NO in said continuously flowing gas sample by calculating an ozone difference between said first and second ozone values. 24. The method of claim 23, wherein the variable volume reaction chamber further comprises a bellows. 25. A method of determining a NO concentration in a continuously flowing sample of gas, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: mixing said continuously flowing sample of gas with a continuous flow of ozone, wherein a concentration of ozone in a continuously flowing gas mixture a priori exceeds a concentration of NO; providing a reaction chamber in serial connection with a scrubber and an upstream connection means; passing said continuously flowing gas mixture into said scrubber, wherein said scrubber removes NO from said gas mixture before the gas mixture enters said reaction chamber; measuring the concentration of ozone in or downstream of said reaction chamber, thereby establishing at least one ozone value for the scrubbed sample gas; engaging the connection means to cause the continuously flowing sample gas mixture comprising NO to bypass said scrubber and enter the reaction chamber; wherein said reaction chamber has a sufficiently large volume to enable a substantially large fraction of the NO to react with ozone while passing through the chamber but small enough that slower reacting potential interfering compounds do not substantially react; measuring the concentration of ozone in or downstream of said reaction chamber, thereby establishing at least one ozone value for a non-scrubbed gas mixture; and quantifying the concentration of NO in said continuously flowing gas sample by calculating an ozone difference between said scrubbed gas and said non-scrubbed gas. 26. The method of claim 25, wherein the steps of measuring the concentration of ozone in the scrubbed gas and the non-scrubbed gas further comprise using an ultraviolet absorbance spectrometer. 27. The method of claim 25, wherein the ozone added to said scrubbed sample gas or said sample gas is produced in situ. 28. A method to determine a NO concentration in a continuously flowing sample of gas, wherein said concentration is in the range of parts per million or less by volume, the method comprising the steps of: providing a first reaction chamber in parallel with a second reaction chamber; connecting a scrubber in series with said first reaction chamber; mixing said continuously flowing sample of gas with a continuous flow of ozone, wherein a concentration of ozone in a continuously flowing gas mixture a priori exceeds a concentration of NO; passing a split stream of said continuously flowing sample gas to each of said reaction chambers, wherein said scrubber removes NO from said gas sample stream entering said first reaction chamber; measuring the concentration of ozone in or downstream of said first reaction chamber, thereby establishing a first reactor ozone value; measuring the concentration of ozone in or downstream of said second reaction chamber, thereby establishing a second reactor ozone value; and comparing the first and second ozone values to determine a concentration of NO in the continuously flowing sample gas. 29. A method to determine a NO concentration in a human breath sample, wherein said concentration is in the range of parts per million or less by volume the method comprising the steps of: providing a gas sample comprising a known concentration of ozone a priori exceeding said concentration of NO; adding a human breath sample comprising NO to said gas sample, whereby the ozone and NO react to form a reaction mixture in a reaction chamber; allowing a sufficient time to lapse, thereby enabling a destruction or conversion of ozone in the reaction mixture; measuring a concentration of ozone in said reaction mixture; and quantifying the concentration of NO in said breath sample by calculating an ozone difference between said gas sample and said reaction mixture.