Analysis of 20 Free Amino Acids in a Shanghai Drinking Water Treatment Plant Using Solid-Phase Extraction Coupled with Liquid Chromatography-Tandem Mass Spectrometry

Numerous studies have demonstrated that amino acids serve as important precursors of odor-causing disinfection byproducts (O-DBPs), which may lead to taste and odor issues in drinking water after disinfection. Monitoring these O-DBP precursors is critical for safeguarding public health and mitigating odor-related risks. Therefore, this study conducted long-term monitoring of free amino acids (FAAs) levels in a drinking water treatment plant (DWTP) in Shanghai. A highly sensitive analytical method based on solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry (SPE-LC-MS/MS) was developed, demonstrating excellent linearity and precision. The method achieved quantification limits (LOQs) ranging from 0.02 to 0.55 nM, enabling the detection of trace-level amino acids. In the raw water, the total concentration of free amino acids ranged from 7 to 70 μg/L, with the highest level observed in March (69.66 μg/L) and the lowest in August (7 μg/L). Arginine (Arg), valine (Val), aspartic acid (Asp), serine (Ser), glutamic acid (Glu), glycine (Gly), and alanine (Ala) were identified as the dominant FAAs in the raw water of the DWTP, with concentrations significantly higher than those of other FAAs.