RESUMO
In this paper, an alternative voltammetric method for the determination of elemental sulphur in cosmetic products is presented. It is based on the decrease of triphenylphosphine oxidation current in the presence of elemental sulphur by using a glassy carbon electrode. A solution of 2% (m/v) acetic acid and 0.6 mol L-1 sodium acetate in methanol was used as a supporting electrolyte. The experimental conditions for indirect determination of elemental sulphur were established. Using square-wave voltammetry, the analytical curve was linear in the elemental sulphur concentration range of 9.94-271 µmol L-1, with a detection limit of 2.59 µmol L-1. The method was successfully applied to determine elemental sulphur in soap bars and anti-acne cream, without any preliminary sample treatment, therefore, it is shortened and simplified. The results obtained with the indirect voltammetric method were not statistically different in comparison with a titrimetric one, at a 95% confidence level. Additionally, excellent recovery percentages were obtained, proving no matrix interferences.
RESUMO
A glassy carbon electrode was modified with a TiO2-gold nanoparticle hybrid integrated with multi-walled carbon nanotubes in a dihexadecylphosphate film (TiO2-Au NP-MWCNT-DHP/GCE) and applied to amperometric determination of ascorbic acid (AA). The modified sensor displays fast charge transfer and shows an irreversible anodic behavior for AA by cyclic voltammetry. Under optimal experimental conditions and using amperometry at 0.4 V, the analytical curve presented a statistical linear concentration range for AA from 5.0 to 51 µmol L-1, with a limit of detection of 1.2 µmol L-1. The electrode was successfully applied to the determination of AA in pharmaceutical and fruit juice without the need for major pretreatment of samples. Graphical abstract Schematic of a new sensing platform for ascorbic acid (AA). It is based on a glassy carbon electrode (GCE) modified with TiO2-Au nanoparticles integrated into carbon nanotubes in a dihexadecylphosphate film. The sensor was applied to amperometric determination of AA in juice and pharmaceutical samples.