Practical considerations for the segmented-flow analysis of nitrate and ammonium in seawater and the avoidance of matrix effects |
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Authors: | Tae Keun Rho Stephen Coverly Eun-Soo Kim Dong-Jin Kang Sung-Hyun Kahng Tae-Hee Na Sung-Rok Cho Jung-Moo Lee Cho-Rong Moon |
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Affiliation: | 1. Ocean Observation and Information Section, KIOST, Ansan, 15627, Korea 2. BLTEC Korea Limited, Seoul, 07299, Korea 3. Marine Chemistry and Geochemistry Research Center, KIOST, Ansan, 15627, Korea 4. Department of Integrated Ocean Sciences, Korea University of Sciences and Technology, Ansan, 15627, Korea 5. Research Institute of Oceanography, Seoul National University, Seoul, 08826, Korea
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Abstract: | In this study we describe measures taken in our laboratory to improve the long-term precision of nitrate and ammonia analysis in seawater using a microflow segmented-flow analyzer. To improve the nitrate reduction efficiency using a flow-through open tube cadmium reactor (OTCR), we compared alternative buffer formulations and regeneration procedures for an OTCR. We improved long-term stability for nitrate with a modified flow scheme and color reagent formulation and for ammonia by isolating samples from the ambient air and purifying the air used for bubble segmentation. We demonstrate the importance of taking into consideration the residual nutrient content of the artificial seawater used for the preparation of calibration standards. We describe how an operating procedure to eliminate errors from that source as well as from the refractive index of the matrix itself can be modified to include the minimization of dynamic refractive index effects resulting from differences between the matrix of the samples, the calibrants, and the wash solution. We compare the data for long-term measurements of certified reference material under two different conditions, using ultrapure water (UPW) and artificial seawater (ASW) for the sampler wash. |
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