For an accurate determination of the gas-particle partition of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like biphenyls (DLPCBs) in dust-rich flue gas, a parallel monitoring procedure with an isokinetic and a non-isokinetic train was used. For four flue gas samples, the two trains gave a significantly different weight of the collected fly ash particles despite the equal gas volume sampled. On the basis of the quantitative values of PCDD/F and DLPCB homologues and the weight of the collected particles, ratios of each homologue in the real flue gas samples in gaseous form were predicted using simultaneous equations. For the four flue gas samples examined, the predicted gaseous ratios were considerably higher that those calculated using a previously reported equation, suggesting that there are some properties which affect partitions of PCDD/Fs in flue gas besides their saturation vapor pressures and fly ash concentration. The partitions for higher temperature flue gases obtained by fractional determinations of each collection device were additionally different from those predicted by the parallel collection, indicating that conventional determination by fractional measurements is subjected to large errors in dust-rich flue gas due to severe adsorption of gaseous PCDD/Fs and DLPCBs onto particles collected on a low-temperature collection device. (c) 2007 Elsevier B.V. All rights reserved.