Analytical Sciences

Microliter Operation for Determination of Nitrate-Nitrogen via Simple Zinc Reduction and Color Formation in a Well Plate with a Smartphone

Pheeraya JAIKANG,*,** Sununta WANGKARN,*,** Pathinan PAENGNAKORN,*,*** and Kate GRUDPAN*,**

*Center of Excellence for Innovation in Analytical Science and Technology, Chiang Mai University, Chiang Mai 50200, Thailand
**Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
***Biomedical Engineering Institute, Chiang Mai University, Chiang Mai 50200, Thailand

We propose a simple greener colorimetric method for the determination of nitrate-nitrogen by operating on a 96-well microplate and using a smartphone camera as a simple detector. A slurry containing 0.3 mg zinc was used for reduction of nitrate to nitrite, the reduction solution was transferred to a 96-well microplate to react with Griess reagent to form a pink azo dye product. The color product image was captured and processed by a smartphone camera and ImageJ software, respectively. The limit of detection and limit of quantitation were 0.04 and 0.10 mg/L nitrate-nitrogen, respectively, for the smartphone camera. Application to real samples was demonstrated. The proposed method results showed no significant difference (at 95% confidence) with the hydrazine reduction method. The proposed method could be used as an alternative method for on-site analysis due to the advantages of portability and rapidity; duplicate run of 20 samples could be carried out simultaneously in 12 min.

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