Sampling and measurement of volatile particles is a challenging task. It has been hampered by lack of a reliable technique capable of accurately capturing the phase-partition process of the pollutants without generating bias and artifacts in the data. The objective of this research is to design a new vapor-particle separation technique for performing the phase separation on-line (the sampling aspect), which, simultaneously, enables characterization of the vapors and particles. The new vapor-particle separator (VPS) consists of a thin metallic microporous membrane for (1) extraction of vapor molecules that are thermally desorbed from the condensed particulate phases and (2) collection of the vapors for subsequent chemical analysis. We evaluated this new separator using synthetic particles made of nonvolatile and or semi-volatile chemicals, and reported the laboratory test results in this paper. The laboratory particle test results showed reasonably high particle transmission efficiency across all particle sizes. The thermal dynamics of nanoparticles was succinctly observed on-line. The results successfully demonstrated the ability of VPS to separate particles and vapors thus enabling a faithful observation of the thermal behavior. We believe the new technology will make a great contribution to the measurement of volatile particles.