Sequential injection analysis with electrochemical detection as a tool for economic and rapid evaluation of total antioxidant capacity

This work presents a new flow-based coupled electrochemical technique for evaluation of “total antioxidant capacity (TAC)”. A sequential injection (SI) with amperometric detection was applied to the TAC analysis of commercial instant ginger infusion beverages using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. Besides having chromogenic properties, the ABTS reagent behaves as an electroactive species at the glassy carbon electrode in phosphate buffer pH 7.0, the decrease of the cathodic current signal of the ABTS⁺ radical after reaction with antioxidants can be monitored. The SI system, furnished with an in-house electrochemical detection cell (ECD), was optimized with respect to the applied potential, sample and reagent volume, and flow rate to the detector. Gallic acid was used as the standard antioxidant and the capacity was reported as gallic acid equivalent (GAE) unit. TAC measurements of ginger infusions at the optimum condition were performed using the proposed technique and also with the classical batch spectrophotometric ABTS assay. TAC values obtained from our method and the standard method are in good agreement (r² = 0.956). The SI-amperometric technique provided satisfactory precision (4.11% RSD) with rapid sample throughput (40 samples h⁻¹). Also using this method, the consumption of the expensive ABTS reagent was greatly reduced.     

Spectrophotometric determination of copper in alloys using naphthazarin

Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone; Naph) is proposed as a chromogenic reagent for the spectrophotometric determination of copper(II). The polynuclear complex has a mole ratio of Cu:Naph=4:6 in a 50% v/v ethanol/water medium containing 0.1 M ammonium acetate and 1.5% (w/v) sodium dodecyl sulfate. The copper-naphthazarin complex shows an absorption maximum at 330 nm with a molar absorptivity of 1.84x10(4) l mol(-1) cm(-1). Beer's law is obeyed up to 4.5 ppm of copper(II). The method was applied for copper determination in alloy samples with satisfactory results.