Per- and polyfluoroalkyl substances (PFAS) are thermally persistent and may survive or transform during waste incineration. Standardised methods for sampling PFAS in flue gas have only recently become available, and full-scale experience remains limited. This report focuses on the polar PFAS fraction captured by US EPA method OTM-45, with particular emphasis on ultra-short-chain PFAS. To our knowledge, this is among the first attempts to determine ultra-short-chain PFAS in flue gas under full-scale sampling conditions, although such claims should be interpreted cautiously. Measurements were performed at the Linköping waste-to-energy plant during two sampling days in October 2025 using modified OTM-45 trains. In both configurations, the sampling flow was halved and the sampling time doubled to reduce bubbling in the impingers, and a condensation flask was placed upstream of the XAD-2 resin to provide drier gas. On the first day, a WAX sorbent was also included to test whether PFAS could be captured in the wet gas. The modifications clearly changed the behaviour of the sampling train. Mobile, water-soluble compounds were mainly captured in the condensation flask. The clearest findings were the replacement chemical C6O4 (11.4 ng; 3.5 ng/Nm³) and the ultra-short-chain PFAS perfluoropropanoic acid (PFPrA; 2.0 ng; 0.67 ng/Nm³), both detected in the condensate and unaffected by blanks. TFA could not be evaluated due to high background, PFMeS coincided with field blanks, and PFEtS and PFPrS were not detected. Longer-chain PFAS were detected only at low levels, comparable to blank levels. Overall, the modified train improved capture of mobile polar species, but robust quantification still requires strict blank control and repeated sampling.