A comprehensive evaluation of methods for assigning molecular formulas to dissolved organic matter (DOM) reveals promising avenues for improving the accuracy of such analyses, which are pivotal for studying the carbon cycles impacting aquatic ecosystems. Researchers analyzed six distinct methodologies and developed a metrics evaluation framework to assess their efficacy based on similarity, accuracy, and correctness. Results indicate Formularity and TRFU stand out as the leading methods for molecular formula (MF) assignment, boasting similarity ratios ranging from 93% to 99% and low Bray-Curtis distances of 0.13 to 0.14.
Dissolved organic matter plays a significant role as both energy source and carbon reservoir within aquatic ecosystems. Accurate assessment of its composition is increasingly important due to human activities like wastewater discharge and agricultural changes, which can disrupt the carbon balance of these systems. Assigning accurate molecular formulas through high-resolution mass spectrometry allows for improved analysis of DOM components, yet methods have varied historically, leading to potential misclassifications.
The study employed literature reviews from multiple databases including the Web of Science, Scopus, and others, identifying 25 relevant publications focused on MF assignment methods. Each method was assessed based on various criterial measures—filter rules, elemental limits, and ambiguous compound selection rules—which have been found to significantly influence assignment results. Formularity uses classic chemical rules alongside the Woods Hole Oceanographic Institution database for its calculations, whereas TRFU, developed as MATLAB-based code, enhances the handling of complex DOM samples.
The evaluation framework established considers multiple dimensions of assessment, utilizing metrics like similarity ratios to analyze correctly assigned molecular formulas against known chemical databases. Overall, Formularity and TRFU achieved correctness rates of 86% and 87% respectively, along with low chemical diversity errors, making them highly effective for accurate DOM characterization. Other methods, such as TEnvR, ICBM, and MFAssignR, displayed higher error rates when unassigned formulas reached up to 47% ± 18%.
Another key finding demonstrated TRFU's superior performance at moderate levels of dissolved organic carbon (DOC), whilst Formularity excelled at both high and low DOC concentrations. Understanding these differences can guide researchers on method selection, leading to more effective evaluations of DOM's properties.
This study stands as both timely and significant, emphasizing the need for clear methodologies and standardized procedures for molecular formula assignments, which can greatly impact our capacities for environmental analysis and management. Support for the research came from the National Key Research and Development Program along with the National Natural Science Foundation of China, underscoring the importance of financial investment toward enhancing environmental science's analytical frameworks.
The outcome of such methodologies not only refines scientific inquiry but also aids broader ecological insights, enhancing our comprehension of aquatic ecosystems' roles within global biogeochemical cycles. Continued exploration within this field will be invaluable for advancing our overall environmental scientific toolkit.