EGA-guided multi-shot pyrolysis GC/MS with spectral deconvolution for broad molecular profiling of Lake Biwa sediment...

Sediment organic matter is compositionally complex and difficult to profile by conventional extractive GC/MS. This study proposes an evolved gas analysis (EGA)-guided, deconvolution-assisted multi-shot pyrolysis GC/MS (msPy-GC/MS) workflow for broad-coverage molecular profiling of lake sediments, using Lake Biwa surface sediment as a validation case study. EGA-MS defined three temperature windows, and the 330-398 °C fraction was selected for compound-level interpretation because it provided the broadest class coverage. Chromatograms from 24 surface-sediment samples collected during 2018-2023 were processed by mass-spectral deconvolution and curated NIST library annotation. The workflow expanded the number of tentatively annotated pyrolysis products from 118 b y direct library annotation to 233 compounds grouped into nine chemical classes. Analytical repeatability was verified using four replicate aliquots of a validation sediment sample; 64 consistently detected compounds showed %RSD values of 1.7-9.6% (median 4.8%), and propagated index-level %RSD values were 2.9% for LOMI and 4.6% for ROMI. Compound-class sums were converted into operational molecular descriptors, including a Labile Organic Matter Index (LOMI) and a Recalcitrant Organic Matter Index (ROMI). LOMI was negatively associated with bottom-water dissolved oxygen (r = -0.62), and loading-normalized LOMI descriptors showed comparable or stronger associations (LOMI/total, r = -0.63), indicating information beyond bulk pyrolyzable organic-matter loading. The workflow provides a rapid, minimally pretreated, and repeatable approach for translating complex sediment pyrolysates into operational molecular descriptors relevant to oxygen-related changes in lake sediments.