Laser-Based Sensor for Nitrate Isotope Analysis in Water Pollution Monitoring

In this Small Business Innovative Research (SBIR) effort, Los Gatos Research (LGR) proposes to utilize its patented Off-Axis ICOS technology to develop an analyzer for the accurate determination of 15N/14N, 18O/16O, and 17O/16O isotope ratios in nitrates (d15N, d18O, and d17O). The system will employ the bacterial denitrification method to convert nitrates (NO3-) into N2O, and then utilize a mid-infrared Off-Axis ICOS analyzer to rapidly ( & lt; 5 minutes) determine nitrate concentration, d15N, d18O, and d17O to better than & plusmn; 1%, & plusmn; 0.2 & permil;, & plusmn; 0.5 & permil;, and & plusmn; 0.5 & permil; respectively. Nitrate contamination in water is an ubiquitous, world-wide problem, and the resulting instrument will help provide nitrate source apportionment, identify multiple nitrate sources, study spatial mixing of nitrate pollution, and identify areas in which natural nitrate attenuation processes are taking place. Additionally, the SBIR analyzer can be used to help quantify the nitrate pollution and N2O emission impacts of emerging biofuels. In Phase I, LGR demonstrated technical feasibility by fabricating a prototype system for quantification of N2O, 15N14NO, 14N15NO, and 14N14N18O in digested nitrate samples. The prototype was tested on a variety of gas cylinders and found to quantify [N2O], d15N, d15Na, d15Nb, and d18O with a precision of & plusmn;0.01 ppb, & plusmn;0.42 & permil;, & plusmn;0.40 & permil;, & plusmn;0.50 & permil;, and & plusmn;0.75 & permil; respectively (1s, 1000s for [N2O] = 320 ppb). Repeated measurements of discrete reference gas injections demonstrated that the Phase I sensor was precise to better than & plusmn;0.25 & permil; and & plusmn;0.53 & permil; for d15N and d18O respectively with minimal dependence of the isotope ratio on nitrous oxide concentration over a wide dynamic range of [N2O] = 0.25 - 2 ppm. Potential cross-interferences with ambient water vapor and higher hydrocarbons were mitigated by using front-end cold trap. The instrument was then used to characterize nitrate-polluted water samples obtained from the Abbotsford aquifer (British Columbia, Canada). The Phase I system was directly compared to isotope ratio mass spectrometry (IRMS) measurements and found to be accurate to within & plusmn;2.4 & permil; and & plusmn;3.2 & permil; for d15N and d18O. This data clearly showed that the high levels of nitrate pollution were due to animal waste and fertilizer ammonium runoff and not to atmospheric deposition or fertilizer nitrate runoff. Due to the novelty of the Phase I measurements, they will be presented at the European Geophysical Union Spring Meeting (Vienna, Austria) and the American Geophysical Union Fall Meeting (San Francisco, California). Finally, the results were also used to help identify Phase II improvements. In Phase II, Los Gatos Research will refine the Nitrate Isotope Analyzer hardware, electronics, and software to improve the instrument accuracy, precision, and stability. Then, the technology will be extended to include measurements of d17O. The instrument will be automated by including provisions for autonomous sample conversion and handing. Subsequent to extensive laboratory testing at LGR, the analyzer will be deployed at the International Atomic Energy Agency (Vienna, Austria) and tested by the Isotope Hydrology Laboratory at no charge to this SBIR effort. A second Nitrate Isotope Analyzer will be fabricated and deployed at Purdue University, where Professor Greg Michalski in the Department of Chemistry will verify its accuracy against an isotope ratio mass spectrometer (IRMS) and use it to quantify water pollution sources including atmospheric deposition, nitrate fertilizers, and soil runoff. During Phase III, LGR will sell the N2O isotope analyzers to isotope measurement laboratories, environmental research groups, global monitoring stations, and water quality management agencies. A preliminary market analysis suggests a 5-year commercial revenue exceeding $40M for these