CO2 Microbubble Preconcentration Coupled with Portable Mass Spectrometry for Rapid On-Site Perfluorocarboxylic Acid Quantification in Dynamic Waters

Abstract In-situ detection is essential for pollutant source tracking and timely environmental management, particularly in dynamic water systems. However, implementing such detection remains challenging for trace organic contaminants such as per- and polyfluoroalkyl substances (PFASs) because their pg mL−1 level concentrations and complex matrix interferences often necessitate time-consuming LC−QqQ MS workflows. Herein, we developed a field-deployable analytical platform integrating CO2 microbubble preconcentration and portable MS to enable the rapid quantification of perfluorocarboxylic acids (PFCAs), a major class of PFASs. This platform leverages PFCA surface activity to drive sequential transfer from bulk water to the CO2 bubble−water interface and subsequently into bursting microdroplets, achieving >1100-fold enrichment of two common PFCAs, PFOA and PFNA, within 5 min. This enrichment may be associated with fine, slow-rising CO2 microbubbles that prolong interfacial contact and CO2-induced acidification that may favor anionic PFCA accumulation at the bubble−water interface. Based on this platform, method validation with PFOA and PFNA in drinking water revealed 80−112% recovery, high inter- and intraday precision of 3−16% RSD, and method quantification limits of 0.55−1.0 pg mL−1. Field deployment in lake and river waters successfully quantified PFOA and PFNA at concentrations of 2.4−4.1 and 0.8−1.1 pg mL−1, respectively. To our knowledge, this is one of the first portable MS/MS-based workflows capable of pg mL−1 level PFCA quantification in environmental waters. Crucially, these on-site results were consistent with conventional laboratory-based analysis, supporting this platform as a rapid (<10 min) and practical tool for dynamic environmental monitoring.