Highly sensitive determination of salicylic acid in skin care product by means of carbon nanotube/iron oxide nanoparticle voltammetric sensors

The present work reports the performance and the mechanism of detection of a voltammetric sensor for salicylic acid (SA) in a skin care product employing a carbon nanotube/iron oxide nanoparticle (SWCNT/ION) modified electrode. The coupling between Fe(III) → Fe(II) and SA → SA (radical) half-cell reactions at the surface of SWCNT/ION and the enlarged surface area are harnessed to enhance the sensor’s sensitivity. By means of differential pulse voltammetry under optimized conditions, the performance of the (SWCNT/ION) provided the following figure of merit: two linear working ranges 0.6–2.9 μmol/L (r2 = 0.996) and 2.9–46.3 μmol/L (r2 = 0.995), sensitivity 0.64 μA cm−2/μmol L−1, limit of detection (LOD) (3Sb/b) 0.02 μmol/L, and limit of quantification (10Sb/b) 0.07 μmol/L. The LOD is lower than most of the electroanalytical methodologies found in the literature. The determination of SA in a skin care product shows no difference, at 95% confidence level (Student’s t test), to that performed with HPLC/UV-Vis. Moreover, a single modified electrode can be used for at least 18 consecutive runs while losing less than 10% of its sensitivity. The sensitivity difference between electrodes made in different batches is only 5.4%.