Progress 07/01/21 to 02/28/22

Outputs
Target Audience:The target audience for this research is the agricultural and agronomic soil research community. This consists of academic, governmental, and industrial cusomers. While we do not expect this to relevant to individual farmers, the knowledge gained from this technology development may inform decisions at the farm level (e.g. nitrogen/fertilizer use and timing) Changes/Problems:Challenges In addition to the accomplishments, we did experience challenges, specifically in dealing with the inherent stickiness of hydroxylamine. Over the course of the project we developed a modified approach to sampling that bypasses the stickiness issue - rather than draw the interstitial gas to the instrument, we developed a method to bring soil water to the instrument via a dialysis technique, and vaporize it directly into the instrument. Therefore, rather than relying solely on the partial pressure of HA in the interstitial space, we bring the solution, which has much more HA in it than the interstitial space, to the instrument. This approach has enormous commercial potential, for both hydroxylamine measurements, as well as other solutes in soil water, such as NH4+, NO3-, and NO2-. What opportunities for training and professional development has the project provided?During this project we introduced a new postdoc to our group and much of these efforts were her first foray into operation of a TILDAS and trace gas sampling. In addition, this was an opportunity to test new liquid sampling approaches. How have the results been disseminated to communities of interest?We are plannign on disseminating this Phase I infomration via talks and poster at research conferences, and by reaching out to collaborators and potential customers. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Impact Statement During this Phase I SBIR effort we demonstrated the ability to measure hydroxylamine, a key intermediate in the nitrogen cycle that is critical to crop productivity. The eventual commercialization of this technology will allow researchers to better understand when and under what conditions nitrification is activated, in order to better optimize the nitrogen cycling for sustainable agricultural production. Overview The purpose of this SBIR project was to develop a measurement capability that enables real-time subsurface mapping of nitrification. This technology is based upon optical detection of hydroxylamine (HA), a nitrification intermediate. Major accomplishments included: High resolution spectroscopic analysis of hydroxylamine in the mid-infrared Modification and building of a TILDAS instrument for HA detection Quantitative measurements of HA down to micromolar concentrations Identification of the optimal sampling conditions and materials for gas phase HA measurements Demonstration of the instrumentation for sampling from soil gas probes Development of aliquidsampling scheme to allow for very high sensitivity HA detection We achieved the Phase I goals and developed a new sampling approach that addresses the difficulties of measuring gaseous hydroxylamine due to its tendency to stick to instrument and tubing walls. This new approach utilizes microdialysis probes to directly sample soil water (rather than interstitial space) and vaporizes the sample directly into the TILDAS instrument. The Phase I efforts consisted of multiple discrete tasks that provided proof of principle of the detection approach: 1) Spectroscopy study of hydroxylamine; 2) Instrument configuration; 3) Testing sampling artifacts and probe interface; 4) Laboratory testing of coupled system; 5) Phase II system design. As described below we made substantial progress on all tasks. Accomplishments Task 1: Spectroscopy During Phase I we explored the spectroscopy of hydroxylamine using a dual-laser TILDAS platform. We utilized a laser that emits near 1350 cm-1that was previously used for detection of SO2. We have confirmed detectivity near 1354 cm-1. For testing in Phase I we utilized this window for detection.we note that another spectral region, near 3,600 cm-1has been identified with at least a factor of two better sensitivity. Initial detection near 1354 cm-1has allowed us to determine approximate line strengths based upon the calculated Henry's law constants. Task 2. Instrument configuration A dual-laser TILDAS platform was used for testing during Phase I. We anticipate that the commercialization of the measurement will depend strongly on measuringothermolecules alongside hydroxylamine, so a dual-laser platform is necessary. We installed a 1354 cm-1quantum cascade laser (QCL) into the optical system, along with a mercury cadmium telluride (MCT) detector. The system uses a 76-m absorption cell with broadband mirrors. The software and electronics control were configured for QCL control. The TILDAS operates with an absorption cell pressure of <40 Torr, so it is pumped with a small 100 LPM pump. Initial testing of the system indicates 1-second absorbance noise of 9x10-6, averaging to ~5x10-6long term. Importantly this is not optimal for such a system, where the 1-second noise is typically <5x10-6in 1 second. More recently built lasers typically lase with powers >25 mW. During Phase II we will operate in a new spectral region with 5-6x line strengths, with a new, higher-power laser, which should result in a 1-second noise performance near 2x10-6. Task 3: Testing sampling artifacts and probe interface Most of the Phase I effort focused on understanding sampling artifacts. Because hydroxylamine is "sticky" we had concerns about whether there would be losses along tubing. Tube length We measured hydroxylamine detection when sampling from a 1-in tube vs 6-ft (72-in) perfluoroalkoxy (PFA) tube (1/4" OD, 1/8" ID). We found that there were no measurable differences between these tube lengths, indicating that there were not irreversible losses along these tubes at a ~1 SLPM flow rate. Tube material We did not observe differences when sampling from PFA vs SS. Thus, the standard approach we use for sampling (PFA and SS fittings) will be appropriate for measuring hydroxylamine. Flow Rate The hydroxylamine concentration was constant across flow rates from >2 SLPM to <0.4 SLPM (400 sccm). Specifically at 50 sccm the hydroxylamine was reduced by ~40%. Detection limit and linearity We observed very linear dependence from 0 to ~1.1 mM, which is well above the concentration we anticipate observing in real soil. Above 1.1 mM there is a clear deviation that we anticipate based upon Raoult's Law, and also as the spectroscopic absorption in the TILDAS analyzer is becoming optically black. We demonstrated detection of a reasonable concentration of hydroxylamine in interstitial space (according to Bruggeman et al), of 11 mM. Detection of this amount was straightforward, and the difference between this and bubbling through pure water is very clear. Based upon this, we calculate a limit of detection of <<1 uM hydroxylamine. Task 4. Laboratory testing of coupled system During this task we have installed a soil probe in an empty PVC soil column and flushed the column with a hydroxylamine vapor, measuring the resulting concentration recovered from the probe. The vapor from of a hydroxylamine solution was drawn through a bubbler, and into the column. The TILDAS was configured to sample alternately between the probe and the column space. We performed tests where we alternatedbetween sampling from the column vs the probe. We demonstratedthe ability to recover hydroxylamine through the probe sampling system. The measured hydroxylamine concentration is within 5% of the concentration expected based upon the column measurements (after accounting for 50:1 dilution. Microdialysis probes and the potential for extreme sensitivity A recurring issue with the trace gas probes for hydroxylamine detection is the inherent stickiness of NH2OH. During this project we also explored a different sampling approach - using microdialysis probes to extract microliter (mL) amounts of soil water in a manner similar to the diffusive gas probes.We demonstrated the ability of a microdialysis probe to quantitatively measure a HA solution. In this test an HA solution was made, and the microdialysis probe sampled from it. The dialysate was then drawn into a syringe and injected into the TILDAS absorption cell. The measured concentration is identical to that measured when sampling straight from the parent solution. As a final demonstration of the ability to measure hydroxylamine using this approach we injected 5 uL of solution extracted from soil that was treated with fertilizer (MG: Miracle Gro). The observed peak concentration is consistent with a HA concentration in solution of ~4 uM. Task 5. Phase II system design The goal of Task 5 was to develop a total system design for production in Phase II. This consists of i) the TILDAS design; ii) the sampling approach; and iii) automation for subsurface mapping. TILDAS Design In Phase I we focused on the 1354 cm-1region. However, there are two other regions of interest with much larger linestrengths.The nu4 region is where the Phase I studies focused due to laser availability. However, we anticipate that in Phase II we will use a new, more powerful laserto afford a >10x improvements in signal to noise, and a level of detection of <150 nM HA in 1 second. Sampling Approach During Phase I we demonstrated the ability to measure HA in solution, and we will pursue that further in Phase II, given the large commercial potential of such an approach. This relies on developing a means to inject microdialysis dialysate directly into the cell and automating sampling, which we anticipate doing readily by adapting our existing multisample selector technology.

Publications