Microfluidic photoinduced chemical oxidation for Ru(bpy)₃ ^3 + chemiluminescence — A comprehensive experimental comparison with on-chip direct chemical oxidation

For the first time, the analytical figures of merit in detection capabilities of the very less explored photoinduced chemical oxidation method for Ru(bpy)₃ ^2 + CL has been investigated in detail using 32 structurally different analytes. It was carried out on-chip using peroxydisulphate and visible light and compared with well-known direct chemical oxidation approaches using Ce(IV). The analytes belong to various chemical classes such as tertiary amine, secondary amine, sulphonamide, betalactam, thiol and benzothiadiazine. Influence of detection environment on CL emission with respect to method of oxidation was evaluated by changing the buffers and pH. The photoinduced chemical oxidation exhibited more universal nature for Ru(bpy)₃ ^2 + CL in detection towards selected analytes. No additional enhancers, reagents, or modification in instrumental configuration were required. Wide detectability and enhanced emission has been observed for analytes from all the chemical classes when photoinduced chemical oxidation was employed. Some of these analytes are reported for the first time under photoinduced chemical oxidation like compounds from sulphonamide, betalactam, thiol and benzothiadiazine class. On the other hand, many of the selected analytes including tertiary and secondary amines such as cetirizine, azithromycin fexofenadine and proline did not produced any analytically useful CL signal (S/N = 3 or above for 1 μgmL^− 1 analyte) under chemical oxidation. The most fascinating observations was in the detection limits; for example ofloxacin was 15 times more intense with a detection limit of 5.81 × 10^− 10 M compared to most lowest ever reported 6 × 10^− 9 M. Earlier, penicillamine was detected at 0.1 μg mL^− 1 after derivatization using photoinduced chemical oxidation, but in this study, we improved it to 5.82 ng mL^− 1 without any prior derivatization. The detection limits of many other analytes were also found to be improved by several orders of magnitude under photoinduced chemical oxidation.