A MWCNTs-COOH/PSS nanocomposite-modified screen-printed electrode for the determination of synthetic phenolic antioxidants by HPLC with amperometric detection

Abstract

New sensing platforms based on screen-printed carbon electrodes modified with composites based on polystyrene sulfonate and oxidized multi-walled carbon nanotubes (PSS/MWCNTs-COOH/SPCE) have been used to develop a novel HPLC method with electrochemical detection (ECD) for the determination of the most used synthetic phenolic antioxidants in cosmetics: butylhydroxytoluene (BHT), butylhydroxyanisole (BHA), tert-butylhydroquinone (TBHQ) and propyl gallate (PG). Optimal separation conditions were achieved using methanol: 0.10 mol L^-1 acetate solution at pH 6 as mobile phase with a gradient elution program from 60 to 90% of methanol percentage in 15 min. The electrochemical detection was carried out in amperometric mode using the PSS/MWCNTs-COOH/SPCE at + 0.80 V vs. Ag. Under these optimal separation and detection conditions, the limits of detection (LOD) were between 0.11 and 0.25 mg L^-1. These LOD values were better, especially for BHT, than those previously published in other HPLC methods. Linear ranges from 0.37 mg L^-1, 0.83 mg L^-1, 0.69 mg L^-1 and 0.56 mg L^-1 to 10 mg L^-1 were obtained for PG, TBHQ, BHA and BHT, respectively. RSD values equal or lower than 5% and 8% were achieved for repeatability and reproducibility, respectively. The HPLC-ECD method was successfully applied to analyze different cosmetic samples. Recovery values within 83-109% were obtained in the validation studies.

Keywords: Carbon nanotubes; Electrochemical detection; HPLC; Nanocomposites; Polystyrene sulfonate; Synthetic phenolic antioxidants.

Fig. 1

Chemical structures of BHT, BHA, PG and TBHQ

Fig. 2

SEM images of the working electrode surface of A SPCE, B PSS/SPCE and C PSS/MWCNTs-COOH/SPCE and D PSS/MWCNTs/SPCE

Fig. 3

Complex plane impedance spectra obtained for SPCE (■), PSS/SPCE (●) and PSS/MWCNTs-COOH/SPCE (▲) in a 1.00 mmol L⁻¹ [Fe(CN)₆]^4−/3− and 0.10 mol L⁻¹ KCl solution. Experimental conditions: open circuit potential, 10 mV of amplitude and frequency range from 10 kHz to 0.10 Hz

Fig. 4

Linear sweep voltammograms of 200 mg L⁻¹ of A TBHQ, B BHA, C BHT and D PG in 0.10 mol L⁻¹ BR buffer solution at pH 6 in the presence of 50% of methanol on different SPCE: SPCE (—), PSS/SPCE (—) and PSS/MWCNTs-COOH/SPCE (—). Scan rate: 0.100 V s⁻¹

Fig. 5

A Hydrodynamic voltammograms of PG (■), TBHQ (●), BHA (▲) and BHT (▼) at 10 mg L⁻¹ concentration (n = 3) using 0.10 mol L⁻¹ pH 6 acetate solution containing 85% methanol at 1.0 mL min⁻¹ flow rate as carrier. B Chromatogram obtained for 5.0 mg L⁻¹ multi-analyte solution of SPA using the PSS/MWCNTs-COOH/SPCE electrode in the ECD at + 0.80 V vs. Ag

Fig. 6

Chromatogram of A micellar water and B moisturizing cream obtained before (—) and after (—) fortification with PG, TBHQ, BHA and BHT, using the proposed HPLC-ECD method with the PSS/MWCNTs-COOH/SPCE electrode