Development of low-cost methodologies for the determination of total phosphorus, total nitrogen and COD, as an alternative of commercially available kit tests

Abstract Water quality assessment is essential for understanding and managing water resources and identifying potential health and environmental risks. A method for a parameter valuation should be characterized by high accuracy and precision. This study presents a comprehensive comparative analysis of three crucial water quality parameters (especially in wastewater) - total phosphorus (TP), chemical oxygen demand (COD), and total nitrogen (TNb) - by employing two distinct analytical methodologies for each parameter. Widely adopted commercial kits and low-cost in-house developed photometric procedures were rigorously developed, validated, and compared across various analytical performance metrics. Notably, the TNb method represents an approach where nitrogenous compounds are oxidized and measured photometrically as nitrate without the conventional reduction step. The two methods for each parameter were statistically compared and the results demonstrate that the in-house methods consistently achieved lower detection limits, with precision and accuracy comparable to those of the commercial kits.