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

Abstract

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.

Cost-Effective Modern Chemical Sensor System for Soil Macronutrient Analysis Applied to Thai Sustainable and Precision Agriculture

“…Accordingly, 200 μL of the sample and 50 μL of reagent solution were fixed for all assays. In detail, the analytical procedure consisted of the following steps (as shown in Figure 7 ): (a) a microplate was placed on a pad for the guide taking the solution to a micro-well; (b) the standard solution was taken to the well; (c) the sample was placed in the well; (d) the reagent was prepared by dissolving it in ID water; (e) the reagent was mixed with the sample solution; (f) the mixture was incubated before measurement of color; (g) this microplate was placed in a lightbox; (h) the colors were detected by a smart device camera (Apple iPhone8, China) on a light-control box [ 18 ].…”

A New Paper-Based Microfluidic Device for Improved Detection of Nitrate in Water

“…The most commonly used reducing agents are cadmium, copperized cadmium, zinc, nitrate reductase, hydrazine sulfate, titanium (III) chloride, or vanadium (III) [28,31]. Cadmium reduction is the leading method used for nitrate detection; however, more researchers are using zinc since it is a less toxic reductant and not as harmful to humans or the environment as cadmium [43,44]. Moreover, it is worth mentioning that Jayawardane et al [33] obtained similar results for nitrate detection when using cadmium or zinc in a paper-based microfluidic device.…”

Inner Product of RGB Unit Vectors for Simple and Versatile Detection of Color Transition

“…Since the advent of commercial digital cameras in the 1990s, studies on analysis using digital images 1,2 have been reported. Recently, not a few studies using general photographing equipment, especially smartphones, [3][4][5] have been published for quantitation.…”