Rapid Determination of Nitrate Nitrogen Isotope in Water Using Fourier Transform Infrared Attenuated Total Reflectance Spectroscopy (FTIR-ATR) Coupled with Deconvolution Algorithm

Abstract

Nitrate is a prominent pollutant in water bodies around the world. The isotopes in nitrate provide an effective approach to trace the sources and transformations of nitrate in water bodies. However, determination of isotopic composition by conventional analytical techniques is time-consuming, laborious, and expensive, and alternative methods are urgently needed. In this study, the rapid determination of 15NO3− in water bodies using Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) coupled with a deconvolution algorithm and a partial least squares regression (PLSR) model was explored. The results indicated that the characteristic peaks of 14NO3−/15NO3− mixtures with varied 14N/15N ratios were observed, and the proportion of 15NO3− was negatively correlated with the wavenumber of absorption peaks. The PLSR models for nitrate prediction of 14NO3−/15NO3− mixtures with different proportions were established based on deconvoluted spectra, which exhibited good performance with the ratio of prediction to deviation (RPD) values of more than 2.0 and the correlation coefficients (R2) of more than 0.84. Overall, the spectra pretreatment by the deconvolution algorithm dramatically improved the prediction models. Therefore, FTIR-ATR combined with deconvolution and PLSR provided a rapid, simple, and affordable method for determination of 15NO3− content in water bodies, which would facilitate and enhance the study of nitrate sources and water environment quality management.

Solid-State 13C Nuclear Magnetic Resonance Study of Soluble and Insoluble β-Glucans Extracted from Candida lusitaniae

“…Although severe overlapping does not allow detailed analysis, the simulation of C1-C6 carbon peaks of interest, attributed to β-glucans, were achieved with good precision based on R 2 and RMSE values. The R 2 values of 0.9851, 0.9300, 0.9676 and RMSE values of 0.0169, 0.0438 and 0.0249 were achieved for AWS, AN and HWN, respectively, indicating a good fit [29]. Chemical shift assignments for individual C1-C6 β-glucan and chitin carbons were based on an analysis of the literature and the deconvolution of obtained spectra, which are summarized in Table 1.…”

“…The fitting was iterated until convergence, and a Chi-Square tolerance value of 10 −9 was obtained. The R 2 and RMSE (root-mean-square error) values from the summary of curve-fitting were used as indicators for goodness of fit, with higher R 2 and lower RMSE values indicating a good fit [29].…”