In Situ Determination of Nitrate in Water Using Fourier Transform Mid-Infrared Attenuated Total Reflectance Spectroscopy Coupled with Deconvolution Algorithm

Abstract

Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy has been used to determine the nitrate content in aqueous solutions. However, the conventional water deduction algorithm indicated considerable limits in the analysis of samples with low nitrate concentration. In this study, FTIR-ATR spectra of nitrate solution samples with high and low concentrations were obtained, and the spectra were then pre-processed with deconvolution curve-fitting (without water deduction) combined with partial least squares regression (PLSR) to predict the nitrate content. The results show that the typical absorption of nitrate (1200−1500 cm−1) did not clearly align with the conventional algorithm of water deduction, while this absorption was obviously observed through the deconvolution algorithm. The first principal component of the spectra, which explained more than 95% variance, was linearly related to the nitrate content; the correlation coefficient (R2) of the PLSR model for the high-concentration group was 0.9578, and the ratio of the standard deviation of the prediction set to that of the calibration set (RPD) was 4.22, indicating excellent prediction performance. For the low-concentration group model, R2 and RPD were 0.9865 and 3.15, respectively, which also demonstrated significantly improved prediction capability. Therefore, FTIR-ATR spectroscopy combined with deconvolution curve-fitting can be conducted to determine the nitrate content in aqueous solutions, thus facilitating rapid determination of nitrate in water bodies with varied concentrations.

Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite

“…Nitrate complexation on Fh was also studied using in situ ATR-FTIR. At pH 5.5 ± 0.2, the presence of NO 3 – produced a broad peak at 1365 cm –1 (Figure S3b), consistent with a previous study . Due to similarities in symmetry, the spectra for hydrated outer-sphere surface complexes on Fh are similar to NO 3 – in solution .…”

“…At pH 5.5 ± 0.2, the presence of NO 3 − produced a broad peak at 1365 cm −1 (Figure S3b), consistent with a previous study. 74 Due to similarities in symmetry, the spectra for hydrated outer-sphere surface complexes on Fh are similar to NO 3 − in solution. 45 Thus, we interpret the peak at 1365 cm −1 as corresponding with NO 3 − outer-sphere complexes.…”

Equilibrium Studies of Iron (III) Complexes with Either Pyrazine, Quinoxaline, or Phenazine and Their Catecholase Activity in Methanol

“…In addition, all the complexes in this study presented bands of approximately 250 to 200 cm −1 , which were assignable to ν (Fe-O) of nitrate complexes [ 30 , 31 , 32 ]. The complexes with pyrazine, quinoxaline, and phenazine presented signals between 1600 and 1200 cm −1 that were associated to ring vibrations of the ligands [ 33 ], also nitrate ion signals appeared between 1200 to 1500 cm −1 [ 34 ]. In addition, signals in the vicinity of 3000 cm −1 were assigned to C-H stretching [ 35 , 36 ].…”

Optical and Crystal Structure Properties of ZnO Nanoparticle Synthesized through Biosynthesis Method for Photocatalysis Application

“…Narrow peaks at 1498 and 1386 cm −1 can be set to nitrate ions due to unreacted zinc nitrate residues [68]. It is known that the typical vibrational band of nitrate is usually in the range of 1200 to 1500 cm −1 [69].…”