In this research, it is aimed to develop an alternative, facile, functional, non-toxic, low-cost, and eco-friendly new spectrophotometric and smartphone-based green analytical methods for the quantitative sensing of nitrite. One of the important features of this research is enabling the use of two portable instruments for field analysis, especially the option of using a smartphone that is in-expensive and accessible to everyone compared to bulky instruments. The proposed method is based on a diazo-coupling reaction of catechin-rich phenolic compounds found in green tea ex-tract with p-Aminobenzoic acid (PABA) in the presence of an acidic medium and NO2-. Under op-timal conditions, calibration equations were obtained by utilizing the color intensity increase of the yellow water-soluble azo dye in direct proportion to the increasing NO2- concentration. The analytical response of the developed spectrophotometric method exhibited linearity in the con-centration range of 0.2-1.1 mg L-1 at the wavelength of 440 nm with the LOD and LOQ values of 0.05 mg L-1 and 0.15 mg L-1, respectively. For the smartphone-based method, between ab-sorbance obtained from B values and increasing NO2- concentration gave a linearity in the con-centration range of 0.05-0.8 mg L-1 with the LOD and LOQ values of 0.017 mg L-1 and 0.050 mg L-1, respectively. The potential interfering effect of common water ions was investi-gated and also interference of Fe2+ was easily eliminated using Na2EDTA. Validation was per-formed at a 95% confidence level against the current reference and the Griess reference methods by applying both developed methods to real water samples.