Internal standard in flow injection analysis with amperometric detection

Batch-injection analysis with amperometric detection of the DPPH radical for evaluation of antioxidant capacity

This work proposes the application of batch-injection analysis with amperometric detection to determine the antioxidant capacity of real samples based on the measurement of DPPH radical consumption. The efficient concentration or EC50 value corresponds to the concentration of sample or standard required to scavenge 50% DPPH radicals. For the accurate determination of EC50, samples were incubated with DPPH radical for 1h because many polyphenolic compounds typically found in plants and responsible for the antioxidant activity exhibit slow kinetics. The BIA system with amperometric detection using a glassy-carbon electrode presented high precision (RSD = 0.7%, n = 12), low detection limit (1 μmol L(-1)) and selective detection of DPPH (free of interferences from antioxidants). These contributed to low detection limits for the antioxidant (0.015 and 0.19 μmol L(-1) for gallic acid and butylated hydroxytoluene, respectively). Moreover, BIA methods show great promise for portable analysis because battery-powered instrumentation (electronic micropipette and potentiostats) is commercially available.

Flow analysis in Brazil: contributions over the last four decades

Timeline with the main contributions of Brazilian researchers to flow analysis.

Two new electrochemical methods for fast and simultaneous determination of codeine and diclofenac

In this paper, we present two new electrochemical methods for fast and simultaneous determination of codeine (CO) and diclofenac (DCF). The first one is based on batch injection analysis with amperometric detection (BIA-MPA) and the second one is based on capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D). The proposed BIA-MPA method is highly-precise (RSD of 1.1% and 0.9% for DCF and CO, respectively; n=10), fast (300 injections h(-1)) and has low detection limits (1.1 and 1.0 µmol L(-1) for DCF and CO, respectively). The proposed CE-C(4)D method allows the determination of CO and DFC in less than 1 min with high precision (RSD of 0.3% and 0.7% for DCF and CO, respectively; n=10) and low detection limits (11 and 21 µmol L(-1) for DCF and CO, respectively). Both proposed methods were applied to the determination of CO and DCF in pharmaceutical samples with similar results to those achieved by high-performance liquid chromatography (HPLC) at a 95% confidence level.

Direct amperometric determination of tert-butylhydroquinone in biodiesel

The direct amperometric determination of tert-butylhydroquinone (TBHQ) in biodiesel at an unmodified glassy carbon electrode is reported. A biodiesel aliquot was added into an electrochemical cell containing a 75% (v/v) ethanol-water solution under stirring (with final concentration of 50 mmol L(-1) HClO(4)). The amperometric method involved the continuous application of three sequential potential pulses to the working electrode (700 mV for 300 ms, 0 mV for 100 ms and -50 mV for 1s). TBHQ was continuously monitored at the first (direct oxidation) and optionally at the second (reduction) potential pulse while the third potential pulse was applied for cleaning of the electrode surface. For comparison, the samples were also analyzed by high-performance liquid-chromatography and a good agreement between the results was verified. Recovery values for spiked samples were between 90% and 95% and the reproducibility of the proposed method was around 5% (n=5). The proposed method can be easily adapted for on-site analysis.