Organic carbon causes interference to nitrate and nitrite measurements by UV/Vis spectrometers: The importance of local calibration

Sari Anneli Uusheimo, Tiina Valpuri Tulonen, Lauri Matti Juhani Arvola, Hanna Arola, Jarmo Linjama, Timo Huttula

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Compared with sporadic conventional watersampling, continuous water-quality monitoring with opti-cal sensors has improved our understanding of freshwaterdynamics. The basic principle in photometric measure-ments is the incident light at a given wavelength that iseither reflected, scattered, or transmitted in the body ofwater. Here, we discuss the transmittance measurements.The amount of transmittance is inversely proportional tothe concentration of the substance measured. However, thetransmittance is subject to interference, because it can beaffected by factors other than the substance targeted in thewater. In this study, interference with the UV/Vis sensornitrate plus nitrite measurements caused by organic carbonwas evaluated. Total or dissolved organic carbon as well asnitrate plus nitrite concentrations were measured in variousboreal waters with two UV/Vis sensors (5-mm and 35-mmpathlengths), using conventional laboratory analysis re-sults as references. Organic carbon increased the sensornitrate plus nitrite results, not only in waters with highorganic carbon concentrations, but also at the lower con-centrations (< 10 mg C L−1) typical of boreal stream, river,and lake waters. Our results demonstrated that local cali-bration with multiple linear regression, including bothnitrate plus nitrite and dissolved organic carbon, can cor-rect the error caused by organic carbon. However, high-frequency optical sensors continue to be excellent tools forenvironmental monitoring when they are properly calibrat-ed for the local water matrix.
Original languageEnglish
JournalEnvironmental Monitoring and Assessment
Volume189
Issue number357
Pages (from-to)357
Number of pages10
ISSN0167-6369
DOIs
Publication statusPublished - 27 Jul 2017
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 1181 Ecology, evolutionary biology
  • Boreal water monitoring
  • Calibration
  • Nitrate
  • High-frequency sensor
  • Optical measurement
  • Organic carbon

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