Chemiluminescence selectivity enhancement in the on-chip Ru(bpy)₃ ²⁺ system: The potential role of buffer type and pH in the determination of hydrochlorothiazide in combined formulations and human plasma

A simple and highly selective on-chip Ru(bpy)₃ ²⁺–oxidant chemiluminescence (CL) approach for estimation of a diuretic drug, hydrochlorothiazide (HCZ), in biological fluids was realized in the presence of other fixed-dose combination drugs by manipulating simultaneously the method of active species (Ru(bpy)₃ ³⁺) production and type of carrier buffer with pH used for the CL reaction. Chemical oxidation processes involved in the Ru(bpy)₃ ²⁺–Ce(IV) CL system have been successfully miniaturised in this study using a microfabricated device to generate Ru(bpy)₃ ³⁺ instantaneously. The proposed system was then screened using HCZ and other drugs in the presence of various buffers and pH to explore the difference in CL emission. Ammonium formate buffer (0.15 M) at pH 4.5 exhibited excellent selectivity towards HCZ when Ru(bpy)₃ ³⁺ was produced by chemical oxidation using Ce(IV). The newly developed conditions do not involve any kind of prior separation or isolation procedure to remove other combination therapy drugs in formulation and biological samples. The method under fully optimised conditions exhibited wide linearity over the concentration range 0.5–1000 ng ml⁻¹ and low detection and quantification limits of 0.13 and 0.47 ng ml⁻¹ respectively for HCZ. Acceptable levels of recoveries were obtained for HCZ from human plasma using the proposed method (98.9–100.8%) in the presence of other antihypertensive combination therapy drugs. This study postulates that such miniaturised devices may find applications especially for on-site analysis, such as doping control examinations.