Sensitive chemiluminescence determination of phentolamine mesylate and phenoxybenzamine hydrochloride based on K3Fe(CN)6–H2O2–fluorescein

A new, rapid and sensitive flow-injection chemiluminescence (FI-CL) method was developed and validated for the determination of two alpha (α)-adrenoreceptor blockers: phentolamine mesylate (PM) and phenoxybenzamine hydrochloride (PH). The method was based on the finding that K3Fe(CN)6 and H2O2 could oxidize fluorescein in an alkaline medium to produce a CL signal, and the joining of PM or PH could enhance the CL intensity significantly. A series of chemical and instrumental parameters affecting the CL response was investigated. Under the optimum conditions, the relative CL intensity was proportional to the concentration of sample solutions in the range 3×10−8 to 1×10−6 g/mL for PM and 5×10−8 to 5×10−6 g/mL for PH. The detection limits were 0.53 ng/mL for PM (r2=0.9947) and 2.60 ng/mL for PH (r2=0.9791). For 11 repeated measurements of 1.0×10−6 g/mL sample solutions, the relative standard deviations (RSDs) were <3.6%. The proposed method has been successfully applied to the analyses of PM and PH in injections and PH in tablets. A brief discussion on the possible CL reaction mechanism is presented.