Determination of adrenaline by using inhibited Ru(bpy)3 electrochemiluminescence

Adrenaline was found to inhibit strongly the electrochemiluminescence (ECL) from the Ru(bpy)₃²⁺/tripropylamine system when a working Pt electrode was maintained at 1.05 V (versus Ag/AgCl) in pH 8.0 phosphate buffer. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for determination of adrenaline. The method exhibited a good reproducibility, sensitivity, and stability with a detection limit (signal-to-noise ratio = 3) of 7.0×10⁻⁹ mol l⁻¹ and dynamic concentration range of 2×10⁻⁸ to 1×10⁻⁴ mol l⁻¹. The relative standard deviation was 2.2% for 1.0×10⁻⁶ mol l⁻¹ adrenaline (n=11). The method was successfully applied to the determination of adrenaline in pharmaceutical samples. Moreover, ECL emission spectra, UV-Vis absorption spectra and cyclic voltammograms of Ru(bpy)₃²⁺/tripropylamine/adrenaline were studied. The inhibition mechanism has been proposed as the interaction of electrogenerated Ru(bpy)₃^2+* and the o-benzoquinone derivatives, adrenochrome and adrenalinequinone, at the electrode surface.     

Reaction from isomeric parent ions in the dissociation of dimethylpyrroles

The major dissociation pathways of the [M-H]⁺ (loss of NH₃ or CH₄) and the [M+H]⁺ (loss of NH₃ or CH₃) ions from dimethylpyrroles have been determined to occur from isomeric parent ions. For the [M-H]⁺ ion (formed by loss of a methyl hydrogen), loss of NH₃ leads to the formation of the phenylium ion and is preceded by consecutive carbon ring expansions followed by a ring contraction to form protonated aniline. Loss of CH₄ occurs after the first carbon ring expansion, which forms protonated picoline. The relative partitioning between the two dissociation paths depends upon the internal energy content of the parent ion; the highest point on the potential energy surface is the second ring expansion step. The [M+H]⁺ ion reacts through a similar pathway via dihydro analogs of picoline and aniline. The proposed reaction pathways are supported by results of semiempirical molecular orbital calculations.