Comparative validation of amperometric and optical analyzers of dissolved oxygen: a case study Irja Helm & Gerli Karina & Lauri Jalukse & Todd Pagano & Ivo Leito Received: 20 December 2017 /Accepted: 16 April 2018 # Springer International Publishing AG, part of Springer Nature 2018 Abstract A comprehensive comparative validation for two different types of dissolved oxygen (DO) analyzers, amperometric and optical, is presented on two represen- tative commercial DO analyzers. A number of perfor- mance characteristics were evaluated including drift, intermediate precision, accuracy of temperature com- pensation, accuracy of reading (under different measure- ment conditions), linearity, flow dependence of the read- ing, repeatability (reading stability), and matrix effects of dissolved salts. The matrix effects on readings in real samples were evaluated by analyzing the dependence of the reading on salt concentration (at saturation concen- tration of DO). The analyzers were also assessed in DO measurements of a number of natural waters. The un- certainty contributions of the main influencing parame- ters were estimated under different experimental conditions. It was found that the uncertainties of results for both analyzers are quite similar but the contributions of the uncertainty sources are different. Our results imply that the optical analyzer might not be as robust as is commonly assumed; however, it has better reading stability, lower stirring speed dependence, and typically requires less maintenance. On the other hand, the am- perometric analyzer has a faster response and wider linear range. Both analyzers seem to have issues with the accuracy of temperature compensation. The ap- proach described in this work will be useful to practi- tioners carrying out DO measurements for ensuring reliability of their measurements. Keywords Electrochemical sensors/mass sensitive sen- sors . Optical sensors/luminescent sensors . Validation . Dissolved oxygen Introduction Dissolved oxygen (DO) concentration is a key parame- ter for characterizations of aqueous environments. It is increasingly evident that the DO concentration in the world’ s oceans is not constant, but is decreasing in many parts of the ocean (Schmidtko et al. 2017; Diaz and Rosenberg 2008). This strongly influences marine life (Jessen et al. 2017); ocean circulation is related to the uptake of CO 2 (incl anthropogenic) by the ocean, and is ultimately related to our planet’ s climate (Stramma et al. 2011). Accurate measurements of DO concentration are very important for studying these processes, understan- Environ Monit Assess (2018) 190:313 https://doi.org/10.1007/s10661-018-6692-5 Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10661-018-6692-5) contains supplementary material, which is available to authorized users. I. Helm : G. Karina : L. Jalukse : I. Leito (*) Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia e-mail: ivo.leito@ut.ee T. Pagano Department of Science & Mathematics, Rochester Institute of Technology, Rochester, NY 14623, USA Present Address: G. Karina : L. Jalukse Estonian Veterinary and Food Laboratory, Kreutzwaldi 30, 51006 Tartu, Estonia