•Two aromatic isomers between 2- and 3-hydroxy benzoic acid were identified.•Chemical oscillator was first used as a matrix in identifying aromatic isomers.•Chemical oscillation was used in qualitative analysis.•Such a Briggs-Rauscher oscillator involving an enzyme-like macrocyclic complexA new technique for identification of two aromatic isomers between 2-hydroxy benzoic acid (2-HBA) and 3-hydroxy benzoic acid (3-HBA) was finalized by using their perturbation effects on a Briggs-Rauscher (BR) oscillator, in which a tetraazamacrocyclic Ni complex, [NiL](ClO4)2 was used as catalyst. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. By putting two isomers into this BR oscillator, the 2-HBA caused a decrease in potential (amplitudes), an increase in the period of oscillation (∆ T) and a decrease in number of the oscillation cycle (n) while no influences of 3-HBA on the BR oscillation were observed. Hence, these two aromatic isomers of hydroxy benzoic acid (HBA) were identified in the range from 1 × 10− 5 to 2.2 × 10− 4 mol L− 1. Reaction mechanism of BR has been proposed with reference to the NF and FCA models. An explanation of perturbation mechanism for the BR is that, only 2-HBA reacted with IO2• to form 1,2-quinone while the 3-HBA didn't.A novel technique for identification of two aromatic isomers between 2- and 3-mono hydroxy benzoic acid was reported by using their different perturbation effects on Briggs-Rauscher oscillator.Download high-res image (155KB)Download full-size image

•A novel Briggs–Rauscher (BR) oscillating system could be used for distinguishing two isomers.•This Briggs–Rauscher oscillating system involves a macrocyclic complex as catalyst.•Cyclohexane-1,3-dione (1,3-CHD) and 1,4-cyclohexanedione (1,4-CHD) were distinguished.•Two isomers were distinguished by their different perturbation effects on BR system.•1,3-CHD involves radical oxidization while 1,4-CHD involves idiodation and elimination.In the analytical field, previous applications of chemical oscillation focused on quantitative analysis. We report in this paper a novel qualitative method electrochemically distinguishing two positional isomers by utilizing their perturbation effects on a catalyzed Briggs–Rauscher (BR) oscillation. The catalyst in the system is a macrocyclic nickel (II) complex NiL(ClO4)2, where the ligand L in the complex is 5,7,7,12,14,14-hexemethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The experimental results indicated that addition of cyclohexane-1,3-dione (1,3-CHD) or 1,4-cyclohexanedione (1,4-CHD) could affect the profiles of potentiometric oscillations, but their changes in the profiles are greatly different. When 1,3-CHD was injected into the oscillating system, there was an initial spiking of the oscillations, accompanying by quenching of oscillations before the regeneration of oscillations. While 1,4-CHD was injected into the dynamic mixture, the oscillatory system responded to the perturbation with only slight decrease followed by a sharp increase in the potential, before it resumed to its normal oscillation state. The perturbation of 1,3-CHD involves inhibition time, whereas the perturbation of 1,4-CHD does not. Hence these two positional isomers could be distinguished by using their different perturbation effects on a BR dynamic system in the range of 9.0 × 10−4 to 8.0 × 10−3 M. Our assumption is that, perturbation of 1,3-CHD on the oscillating system involves a radical oxidization process to produce carboxylic acid, whereas perturbation of 1,4-CHD assumes idiodation and elimination steps to form 1,4-benzoquinone. Such different perturbation mechanisms are responsible for the difference in potentiometric oscillation profiles change. This hypothesis was confirmed by products analysis by FTIR and UV spectra.

This paper reports a novel method for identification of two aliphatic position isomers between α-ketoglutaric acid (α-KA) and β-ketoglutaric acid (β-KA) by their different perturbation effects on a Briggs–Rauscher oscillating system, in which tetraaza-macrocyclic complex [NiL](ClO4)2 is used as the catalyst. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The experimental results have shown that addition of α-KA into the system does not affect the oscillating patterns, while the presence of β-KA in a dynamic system influences the oscillatory amplitude. A more interesting feature is that, in the presence of a higher concentration of β-KA, there are damped oscillations after the initial spike, followed by quenching (more exactly: very small oscillations) of the oscillations before the subsequent regeneration of oscillations. A qualitative approach was thus established by employing a Briggs–Rauscher system for identification of these two isomers. The concentrations of these two isomers that can be distinguished lie over the range between 5.0 × 10–6 and 2.5 × 10–3 mol/L. A reaction mechanism based on the FCA model has been proposed. An explanation is that β-KA reacts with HOO• radicals to form acetone, whereas the α-KA does not.

A new and convenient method for the determination of Alizarin Red S by the perturbations caused by different amounts of Alizarin Red S on a novel B-Z oscillating system is proposed. This new type Belousov-Zhabotinskii involves a macrocyclic copper(II) complex [CuL](ClO4)2 as catalyst and malic acid as the substrate. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. It is found that the relationship between the change in the oscillation amplitude and the logarithm of the Alizarin Red S concentration in the range of 1.5 × 10−7 to 1 × 10−3 M fits a polynomial model: ΔA = 659 + 184.2 log [Alizarin Red S]+ 12.9 log2 [Alizarin Red S]. The RSD obtained with ten samples is 4.4%. The probable mechanism involving the perturbation of Alizarin Red S on the oscillating chemical system is also discussed.

A new analytical method for the determination of pyrogallol, by the perturbation caused by different amount of pyrogallol on a novel oscillation system is reported. This novel oscillation system, which is of Belousov–Zhabotinskii-type, involves a macrocyclic complex [CuL](ClO4)2 as catalyst and malic acid as the substrate. The ligand L in the complex is 5,7,7,12,14,14-hexemethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The experimental results show that the change in the amplitude of the potentiometric oscillation is linearly proportional to the logarithm of the concentration of pyrogallol in the range 1.5 × 10−6 to 1 × 10−4 M, with a correlation coefficient of 0.9959. The obtained relative standard deviation (R.S.D.) with eight samples is 1.6%. Some aspects of the potential mechanism of action of pyrogallol on the oscillating chemical system are also discussed.