IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 26 Analysis and Characterization Monday, 24 August 2026 / Hall B+C Collectively, the 34 IHSS samples contain 92126 gold-standard formulae. Some gold-standard formulae were found in multiple samples, so the entire data set can be reduced to 23168 unique gold-standard formulae. The presentation will examine the distribution of the unique gold-standard formulae among the IHSS samples, including the comparability of FA samples isolated from the same source at different times, the comparability between standard and reference samples from the same source, and between FA and HA samples isolated simultaneously. It also addresses how frequently unique CHO and CHONS formulae occur across multiple IHSS samples (e.g., 2, 5, or 10 samples) and whether CHO and CHONS formulae show similar probabilities of appearing across multiple samples. These and other comparative questions will be addressed in the presentation. In addition, general chemical differences among IHSS samples from aquatic and terrestrial sources will be discussed for four general subsets of molecular formulae: ReducedUnsaturated (O/C<=0.5, H/C<=1.0), Oxidized-Unsaturated (O/C>0.5, H/ C<=1.0), Oxidized-Saturated (O/C>0.5, H/C>1.0), and Reduced-Saturated (O/ C<=0.5, H/C>1.0). References 1. X. Zhang, M. Harir, J. Schick, M. Lucio, E. M. Perdue, P. Schmitt-Kopplin, Environmental Science & Technology 60 (2026) 7859. 2. E. M. Perdue, N. W. Green, Analytical Chemistry 87 (2015) 5079. 3. N. W. Green, E. M. Perdue, Analytical Chemistry 87 (2015) 5086. Acknowledgement All samples were provided by Prof. Paul Bloom, chair of the IHSS Standard and Reference Collection Committee.
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