Quantitative detection of nitrate in water and wastewater by surface-enhanced Raman spectroscopy
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Quantitative detection of nitrate in water and wastewater by surface-enhanced Raman spectroscopy Shashikanth Gajaraj & Cui Fan & Mengshi Lin & Zhiqiang Hu
Received: 28 June 2012 / Accepted: 18 October 2012 / Published online: 30 October 2012 # Springer Science+Business Media Dordrecht 2012
Abstract The presence of inorganic nitrogen species in water can be unsuitable for drinking and detrimental to the environment. In this study, a surface-enhanced Raman spectroscopy (SERS) method coupled with a commercially available gold nanosubstrate (a goldcoated silicon material) was evaluated for the detection of nitrate and nitrite in water and wastewater. Applications of SERS coupled with gold nanosubstrates resulted in an enhancement of Raman signals by a factor of ∼104 compared to that from Raman spectroscopy. The new method was able to detect nitrate with linear ranges of 1–10,000 mg NO3−/L (R2 00.978) and 1–100 mg NO3−/L (R2 00.919) for water and wastewater samples, respectively. Among the common anions, phosphate appeared to be the
major interfering anion affecting nitrate measurement. Nevertheless, the percentage error of nitrate measurement in wastewater by the proposed SERS method was comparable to that by ion chromatography. The nitrate detection limits in water and wastewater samples were about 0.5 mg/L. The SERS method could simultaneously detect sulfate, which may serve as a reference standard in water. These results suggested that the SERS coupled with nanosubstrates is a promising method to determine nitrate concentrations in water and wastewater. Keywords Detection method . Gold nanosubstrate . Nitrate . SERS . Water and wastewater
Introduction Electronic supplementary material The online version of this article (doi:10.1007/s10661-012-2975-4) contains supplementary material, which is available to authorized users. Shashikanth Gajaraj and Cui Fan contributed equally to this work. S. Gajaraj : Z. Hu (*) Department of Civil and Environmental Engineering, University of Missouri, Columbia, MO 65211, USA e-mail: [email protected] C. Fan : M. Lin Food Science Program, Division of Food Systems and Bioengineering, University of Missouri, Columbia, MO 65211, USA
As inorganic nitrogen species such as ammonium (NH4+), nitrite (NO2−), and nitrate (NO3−) continue to enter aquatic systems from anthropogenic sources, it results in accelerated eutrophication in freshwater and marine ecosystems (Vitousek et al. 1997; Camargo et al. 2005). Elevated nitrate and nitrite concentrations cause methemoglobinemia in aquatic animals (Jensen 2003) and human infants (blue baby syndrome) (Greer and Shannon 2005). Hence, in National Primary Drinking Water Regulations, the United States Environmental Protection Agency (USEPA) enforces a maximum contaminant level of 10 mg/L for NO3−–N and 1 mg/L for
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NO2−–N in drinking water, and the concentration of nitrogen species in water requires close monitoring. Nitrates have been analyzed in the past by various methods including ultraviolet (UV)–vis spectroscopy, electrophoresis and electr
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