The chemical composition of polydisperse SiO2/TiO2 multicomponent particles was investigated at different heights from the burner surface using an in situ measurement system. Multicomponent particles were generated in a H-2/O-2 coflow diffusion flame using two sets of precursors - titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS). In order to maintain a 1:1 mole ratio of TTIP to TEOS in the vapor, the flow rate of the carrier gas N-2 was fixed at 0.6 SLM for TTIP and 0.1 SLM for TEOS. An in situ sampling probe was used to supply the particles to the differential mobility analyzer, which was calibrated using a commercial model 3071A manufactured by TSI. The monodisperse multicomponent particles were classified based on their mobility diameter. An clectrophoretic collector was used to collect the classified particles and the composition of the particles was measured by energy dispersive spectrometry. The chemical composition of the multicomponent particles was obtained at different heights (z = 40, 60 and 80 mm) from the surface of the burner. The results show that the chemical composition of silica (Si) decreases with increasing height from the burner surface and increasing mobility diameter of the aggregates. The ratio of Si:Ti approacheed 1:1 far downstream.