A Simple Method for Melatonin Determination in the Presence of High Levels of Tryptophan using an Unmodified Carbon Paste Electrode and Square Wave Anodic Stripping Voltammetry

Abstract

Electrochemical determination of melatonin in the presence of tryptophan is a challenge because of the coincidence of voltammetric signals of these compounds when executing a voltammetric technique. The new method for selective determination of melatonin based on the square wave anodic stripping voltammetry determination of an electroactive product of melatonin was suggested here. This product is produced by previously applied positive pre‐potential to a carbon paste electrode, immersed in the test solution. By this means, the electrochemical signal of melatonin was separated effectively from that of tryptophan, making it possible to determine melatonin in the presence of a high concentration of tryptophan. The effect of important parameters on electrode performance was studied and optimized. The optimum response was obtained at pH=2 and utilizing the pre‐potential magnitude of +0.8 V, applied for 10 s. A linear relationship was found between peak current intensity and melatonin concentrations over the range of 5.00×10−7 to 8.00×10−5 mol L−1. A detection limit of 8.30×10−8 mol L−1 was calculated for the method (S/N=3). The selectivity of the method was considerably high, because of the independence of melatonin signal to the presence of higher amounts of some potentially interfering agents such as ascorbic acid, tryptophane glucose, etc. As an analytical application, the proposed sensor was used for the determination of melatonin in pharmaceutical and food samples.

Unveiling the Collaborative Effect at the Cucurbit[8]uril‐MoS2 Hybrid Interface for Electrochemical Melatonin Determination

“…Accordingly, calculations (see Table SI_T1 and discussion in 1.2 of the Supporting Information) show that the complex formation originates a small shift towards higher values of the oxidation energies for MLT, in line with the experimental observation in the voltammograms in Figures 4 and S4. The electrochemical signal of the MLT oxidation involves the amino group of the structure [17] . In Figure 2A it is visible that the acetamide group is establishing a H‐bond with the oxygens of the CB[8].…”

“…The electrochemical oxidation mechanism of MLT on a GC electrode has been described in the scientific literature. [ 17 , 30 , 31 , 32 ] The oxidation process in a GC/MoS 2 /CB[8] is observed in the voltammogram at around 0.66 V, that is a higher voltage than that required for the oxidation of the “noncomplexed” MLT in a GC/MoS 2 electrode (Figure S4). These voltage values are related to the energy required to remove electrons from MLT.…”

“…[28,29] As depicted in our model, the synergetic effect produced by the MoS 2 /CB [8] combination leading to The electrochemical oxidation mechanism of MLT on a GC electrode has been described in the scientific literature. [17,[30][31][32] The oxidation process in a GC/MoS 2 /CB [8] is observed in the voltammogram at around 0.66 V, that is a higher voltage than that required for the oxidation of the "noncomplexed" MLT in a GC/MoS 2 electrode (Figure S4). These voltage values are related to the energy required to remove electrons from MLT.…”

“…MLT is of paramount significance in organisms since it regulates circadian rhythms and blood pressure, acts as antioxidant and anti‐inflammatory agent, and is a free radical scavenger playing therefore, an important role in cell protection. [ 12 , 13 , 14 ] Such a wide scope has made that recent applications are focused on MLT analysis in food,[ 15 , 16 , 17 ] pharmaceutical[ 16 , 17 , 18 ] or biological samples as urine, saliva and nails. [ 19 , 20 , 21 , 22 ] Therefore, various analytical methods have been developed for MLT quantification.…”

“…In contrast, the electrochemical ones offer a high sensitivity with cheaper and simpler instrumentation. In the literature, it is possible to find strategies using a bare glassy carbon electrode, [17] or using novel nanomaterials as modifiers of the electrode surface,[ 16 , 19 , 23 ] resulting an excellent alternative to increase the sensitivity and selectivity of the determination.…”