Analysis of Ion and Dissolved Organic Carbon Interference on Soil Solution Nitrate Concentration Measurements Using Ultraviolet Absorption Spectroscopy

Abstract

Nitrate is often present in surface water, soil solution, and groundwater at undesirable or toxic levels. This study follows development of an in situ nitrate monitoring probe and examines its performance in the presence of potentially interfering ionic species and dissolved organic carbon (DOC). Ultraviolet (UV) absorption spectroscopy measurements of aqueous NO3− were obtained under conditions where prevalent ionic species (i.e., Na+, K+, Ca2+, Mg2+, NH4+, Zn2+, Cu2+, Mn2+, Fe2+, Fe3+, Al3+, Cl−, H2PO4−, HPO42−, SO42−, and HCO3−) and DOC were present at maximum characteristic concentrations for a range of pH levels, allowing UV interference on NO3− concentrations from individual ions to be investigated. While most solutions did not show interference, Fe2+ ions and DOC absorbed ultraviolet light strongly in regions of the spectrum where NO3− also exhibited significant absorption. Natural water samples showed very low concentrations of Fe2+, which do not cause interference with nitrate measurements. A two‐wavelength measurement scheme was adopted to correct for the potential interference of DOC in measurements of aqueous NO3−. A multivariate calibration is presented to account for possible interference from both DOC and other ions in solution. The application of the UV spectroscopy probe is especially useful for deep vadose zone measurements of nitrate, as typically DOC concentrations will exponentially decrease with depth, and ion interference will be low.

Effects of different‐intensity laser acupuncture at two adjacent same‐meridian acupoints on nitric oxide and soluble guanylate cyclase releases in human

“…LA at PC4 for 20 minutes generated typical three peaks of absorbance spectra in PTIO solution injected to special silicon tube which was placed on PC4 just after acupuncture treatment (Figure ). According to previous findings, the first (235 nm) and second (351 nm) peaks were considered to come from , and the third peak (565 nm) came from sGC . To confirm this speculation, standard molecules were analyzed by the same conditions.…”

Continuous in-situ monitoring of nitrate concentration in soils – a key for groundwater protection from nitrate pollution

“…All water samples were first analyzed for nitrate and DOC concentration by standard laboratory protocols. The porewater samples were then examined for absorption at a few specific wavelengths that have been 185 previously suggested for direct nitrate measurement in untreated soil water: (i) 302 nm (Moo et al, 2016), (ii) 235nm (Shaw et al, 2014;Tuli et al, 2009)), and (iii) where the absorbance used for calibration equals the absorbance at 220 nm after subtraction of twice the absorbance at 275 nm (hereafter 220/275 nm) (Armstrong, 1963). An additional measurement at 220 nm, as suggested by (Michael et al, 2017), was also carried out, but there was no significant difference in absorption characteristics compared to the 220/275 nm method.…”

“…Although UV absorbance spectroscopy for nitrate analysis is very common, it has some limitations when applied to natural water samples, which contain a variable concentration of dissolved organic carbon (DOC). Shaw et al (2014) studied the possible interference in UV absorbance spectroscopy for nitrate analyses by the 80 different ions that are commonly found in water samples originated from natural sources. They showed that the main interference is caused by DOC, with the nitrate absorbance signal being completely quenched above 50 ppm DOC (Shaw et al, 2014).…”

“…Shaw et al (2014) studied the possible interference in UV absorbance spectroscopy for nitrate analyses by the 80 different ions that are commonly found in water samples originated from natural sources. They showed that the main interference is caused by DOC, with the nitrate absorbance signal being completely quenched above 50 ppm DOC (Shaw et al, 2014). As a result, absorption-signal masking by DOC, which is commonly found in agricultural soils, can prevent the use of UV absorbance-based methods for nitrate evaluation in water samples (Fig.…”

Real-time monitoring of nitrate in soils as a key for optimization of agricultural productivity and prevention of groundwater pollution

“…These rapid changes are dictated by irrigation-precipitation pattern, fertilization and cultivation methods, plant uptake, and natural soil biochemical processes (Oren et al, 2004;Thompson et al, 2007;Vázquez et al, 2006). Šimůnek and Hopmans (2009) suggested a passive nitrate uptake model with threshold root-zone nitrate concentration (C max ), which, E. Yeshno et al: Real-time monitoring of nitrate in soils as a key in combination with the root water uptake, sets the maximum nitrate uptake from the root zone. The model imposed a jump in nitrate deep leaching when concentration exceeded the threshold values (C > C max ).…”