Precision methane quantification in aquatic environments: Overcoming the challenge of dissolved oxygen interference...

Membrane inlet mass spectrometry (MIMS) is a well-established technique for measuring dissolved gases and volatile compounds due to its high sensitivity, rapid analysis, minimal sample preparation and low cost. While it has been applied to measure dissolved methane (dCH₄), the potential interference caused by dissolved oxygen (DO) in ionization has been overlooked. In this study, samples with different dCH₄ and DO concentrations were measured by MIMS, and the results revealed that dCH₄ could be overestimated when the effect of DO was not considered, especially for samples with high concentrations. We incorporated an orthogonal partial least squares (OPLS) model to identify and exclude DO interference for dCH₄ determination Quantification of standard samples showed that our innovative MIMS-OPLS method effectively reduced the deviation in dCH₄, achieving a 47.69 % reduction in root mean square error (RMSE) compared to the linear model without considering DO interference. Four applications, including batch samples, continuous processes and biochemical reaction mechanism studies, further demonstrated the reliability and accuracy of the MIMS-OPLS method for practical dCH₄ quantification. The MIMS-OPLS method is suitable for dCH₄ determination in waters with broad range of DO and provides precise insights into CH₄ formation and its mechanisms, further highlighting this new options for advancing aquatic environmental monitoring and biochemical research.