Biomass pyrolysis produces hundreds of compounds through an intermediate fluid phase. It is not yet understood how the network of biomass polymers (cellulose, hemicelluloses, lignin) gives rise to this intermediate "soft" network and how volatiles are ejected from this "metaplast" and then transported within the pores. To understand such mechanisms, it is needed to develop analytical methods for analyzing heavy species (eg. cellulose or hemicelluloses oligomers) which are ejected and condensed in bio-oils or extractables by water after a quench of biomass particles. Several HPLC methods were developed the past years and the most common ones are based on Ion Chromatography such as HPAEC-PAD (High Pressure Anion Exchange Chromatography coupled to a Pulsed Amperometric Detector). The lack of specificity in detection for this method was recently overcome by Yu et al. (Curtin Univ.). HPAED-PAD-MS coupling was developed to quantify liquid products from cellulose decomposition. However, due to a high salt content, an in-line desalter has to be used for mass spectrometry leading to a loss of information. Another way to overcome this problem is to use Size Exclusion Chromatography (SEC) especially because of its non-chemical selectivity, thus all type water-soluble content can be analyzed in addition to a high molecular mass limit (up to 4000 Da). Levoglucosan and DPs=2 to 5 polysaccharides were analyzed by both SEC-Evaporative Light Selective Detector (ELSD) combined by Electro Spray Ionisation (ESI)-Mass Spectrometry (MS), in order to compare accuracy in quantification between mass spectrometry ion signals and ELSD's signals. Ultimately, SEC has allowed a good separation of major cellulose oligomers and highly reproducible signals were observed with both detection techniques. Furthermore, this method is then applied to quantify carbohydrates pyrolysis products extracted by water from biomass particles after a quench at different temperatures. New major heavy intermediate species are revealed.