A two-chip microdevice has been developed for the analysis of phenylephrine hydrochloride (PEH) in pharmaceutical formulations and biological fluids using (2,2′-bipyridyl)ruthenium(II) (Ru(bipy)₃²⁺)-peroxydisulphate chemiluminescence (CL) system. It was observed that a pre-derivatization step is required to obtain an analytically useful CL signal. Using 0.5 mol L⁻¹ formaldehyde solution as derivatization reagent, eighteen-time enhancement in the CL signal was observed. The derivatization reaction, photoreaction of (Ru(bipy)₃²⁺) with peroxydisulphate to produce (Ru(bipy)₃³⁺), reaction of (Ru(bipy)₃³⁺) with the derivatization product and detection of the produced CL signal were all carried out in this two-chip microdevice using minute quantity of reagents (27 μL per run). Various parameters that influence the derivatization reaction and the CL signal intensity were optimized. These include pH, flow rates and concentration of reagents used. A linear response was observed over the range 0.25 μg mL⁻¹ to 15.0 μg mL⁻¹ (R² = 0.9999) with RSD values of 0.03% (n = 15) for 1 μg mL⁻¹. The limit of detection (LOD) was found to be 0.027 μg mL⁻¹ (S/N = 3). The developed method was successfully applied for the analysis of PEH in biological fluids and pharmaceutical formulations.