| Abstract [eng] |
Near-Infrared Study Of Biuret And Urea In Urea Amonium Nitrate Fertilizer The aim of this work is to investigate the possibility to determine the composition of urea ammonium nitrate fertilizer (UAN) using near–infrared (NIR) spectroscopy. The major goal is to create a calibration model which would be able to determine the concentrations of different compounds in the fertilizer with high degree of precision. Urea ammonium nitrate fertilizer consists of four major compounds: urea, ammonium nitrate, biuret and water. It is worth noting that biuret is a side–product from the production of urea and is unwished component in UAN. The major challenge of this work is to be able to determine biuret concentration, which is only up to 1%. Biuret molecule vibrations possess high similarity to urea vibrations (35%) which makes it very hard to distinguish. The range of forty samples with different concentrations were made and their absorptions spectra were investigated using a spectrophotometer in 0,88–1,90 μm wavelength region using a 2 mm width cuvette. Upon finishing the experiment the modeling using multivariate curve resolution (MCR) method was carried. Samples were divided into two groups. Thirty samples were used for calibration and ten for model validation. During the creation of the calibration model it was noticed that there is a need to add a fifth component to model parameters to account for non–linear effects such as hydrogen bond, temperature differences or different gas in the compound. After carrying optimization, model is capable of predicting all four components with 99,8–99,9% degree of precision. Absorption profiles of biuret and urea in UAN were compared with the profiles of biuret and urea absorption in other compounds like melted urea, solid urea or biuret–NaOH solution. This shows that same material is capable of having different absorption spectra depending on the state of matter and surrounding medium. |
