Exploration of Time-Resolved Raman analysis for on-the-go nitrate sensing
Abstract
This thesis explores technological alternatives that could enable on-the-go sensing of macronutrients (nitrate, phosphate, and potassium) in agricultural contexts as a means to optimize the use of agricultural inputs and limit chemical run-off. An objective review is provided of chemical, electrical, biological, and optical techniques that could enable insitu sensing with minimal sample preparation, limited sampling time, little maintenance, and infrequent calibration. This review suggests that optical methods such as Raman spectroscopy have potentially significant advantages over other sensing approaches. To assess this hypothesis, a low-cost, compact, fiber-coupled prototype Time-Resolved Raman Spectroscopy (TRRS) system was used to investigate nitrate/water solutions (since soil N is most often the major limiting soil macronutrient) over a field relevant range of concentrations (0 to 120 ppm nitrate-N) and define ideal system sensitivity for nitrate in aqueous solution. Work carried out to optimize system performance through automation, signal processing, and selection of equipment parameters (e.g., counting thresholds, monochromator slit widths, counting windows, and sampling time) is presented, resulting in a strong correlation (r2 = 0.95) between photon counts and nitrate concentration in aqueous solutions and a detection limit of approximately 20 ppm nitrate-N. Finally, the performance achieved with the TRRS system is compared with previously reviewed technologies using a framework that incorporates quantitative measures of performance with qualitative indicators of technology fieldability and economics to assess future potential for the system.
Degree
M.S.C.E.
Advisors
Sinfield, Purdue University.
Subject Area
Agronomy|Agriculture|Environmental engineering
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