Efficient trihalomethane quantification in drinking water for minimally-equipped water treatment plants labs

Chlorine is a common disinfectant used in water treatment. However, its reaction with organic matter can lead to the formation of harmful byproducts, such as trihalomethanes (THMs), which are potentially carcinogenic. To address this issue, the aim of this work was to enhance a colorimetric method capable of quantifying THMs in drinking water through UV/Vis Spectrophotometry, using cost-effective equipment, and validate this methodology for the first time according to established validation protocols. The method's innovation involved replacing the solvent pentane with the more common hexane, along with adjusting the heating ramp, elucidating the mechanisms involved in the process. This method involves the reaction between THMs, pyridine, and NaOH to produce a colored compound, which is then monitored through molecular absorption spectroscopy in the visible region. The method was thoroughly validated, achieving a limit of detection of 13.41 μg L^-1 and a limit of quantification of 40.65 μg L^-1. Recovery assays ranged from 86.1 % to 90.7 %, demonstrating high accuracy. The quality of the linear fit for the analytical curve exceeded R² > 0.98. The method was applied to real samples, revealing concentrations ranging from 13.58 to 55.46 μg L^-1, all way below the legal limit in Brazil (Maximum Contaminant Levels (MCL) = 100 μg L^-1). This cost-effective and straightforward method is suitable for integration into water treatment plant laboratories.