Analytical Sciences

Determination of Nitrite and Nitrate in Water Samples by an Automated Hydrodynamic Sequential Injection Method

Sarawut SOMNAM,* Jaroon JAKMUNEE,*,** Kate GRUDPAN,*,** Narong LENGHOR,*** and Shoji MOTOMIZU***

*Department of Chemistry and Research Laboratory for Excellence in Development of Miniaturization in Flow-based Analysis, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
**Science and Technology Research Institute, Chiang Mai University, Chiang Mai 50200, Thailand
***Department of Chemistry, Faculty of Science, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530, Japan

An automated hydrodynamic sequential injection (HSI) system with spectrophotometric detection was developed. Thanks to the hydrodynamic injection principle, simple devices can be used for introducing reproducible microliter volumes of both sample and reagent into the flow channel to form stacked zones in a similar fashion to those in a sequential injection system. The zones were then pushed to the detector and a peak profile was recorded. The determination of nitrite and nitrate in water samples by employing the Griess reaction was chosen as a model. Calibration graphs with linearity in the range of 0.7 - 40 μM were obtained for both nitrite and nitrate. Detection limits were found to be 0.3 μM NO₂^- and 0.4 μM NO₃^-, respectively, with a sample throughput of 20 h^-1 for consecutive determination of both the species. The developed system was successfully applied to the analysis of water samples, employing simple and cost-effective instrumentation and offering higher degrees of automation and low chemical consumption.

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