We report on a novel optofluidic system consisting of a silica-based 1D photonic crystal, integrated planar waveguides, and electrically insulated fluidic channels. An array of pillars in a microfluidic channel designed for electrochromatography is used as a resonator for on-column label-free refractive index detection. The resonator was fabricated in a silicon oxynitride platform, to support electro-osmotic flow, and operated at $\lambda =1.55\mu \mathrm{m}$ . Different aqueous solutions of ethanol with refractive indices ranging from n=1.3330 to 1.3616 were pumped into the column/resonator, and the transmission spectra were recorded. Linear shifts of the resonant wavelengths yielded a maximum sensitivity of $\Delta \lambda ∕\Delta \mathit{n}=480\mathrm{nm}$ /RIU (refractive index unit), and a minimum difference of $\Delta \mathit{n}=0.007$ RIU was measured.