Comparison between Modified and Unmodified Carbon Paste Electrodes for Hexavalent Chromium Determination

Immobilization of diphenylcarbazide on paper-based analytical devices for the pre-concentration and detection of chromium VI in water samples

A novel approach using a smartphone for the detection of Cr (VI) has been developed. In this context, two different platforms were designed for the detection of Cr (VI). The first one was synthesized via a crosslinking reaction of chitosan with 1,5-Diphenylcarbazide (DPC-CS). The obtained material was integrated into a paper to develop a new paper-based analytical device (DPC-CS-PAD). The DPC-CS-PAD exhibited high specificity toward Cr (VI). The second platform (DPC-Nylon PAD) was prepared by covalent immobilization of DPC onto a Nylon paper and then its analytical performances regarding Cr (VI) extraction and detection were evaluated. DPC-CS-PAD presented a linear range of 0.1-5 ppm with detection and quantification limits of about 0.04 and 0.12 ppm, respectively. The DPC-Nylon-PAD exhibited a linear response of 0.1-2.5 ppm with detection and quantification limits of 0.06 and 0.2 ppm, respectively. Furthermore, the developed platforms were effectively applied for testing the effect of the loading solution volume for trace Cr (IV) detection. For the DPC-CS material, a volume of 20 mL allowed the detection of 4 ppb of Cr (VI). In the case of DPC-Nylon-PAD, the loading volume of 1 mL permitted the detection of the critical concentration of Cr (VI) in water.

Raspberry-Like Gold Nanoparticles Based On Nanoclusters Anchored on Cyclodextrin-Functionalized Nanoparticles: Synthesis and Ultrasensitive Electrochemical Detection of Chromium(VI) Ions

A facile synthetic strategy is devised to construct raspberry like gold nanoparticles (RbNPs) formed by gold nanoclusters wrapped around β-cyclodextrin functionalized gold nanoparticles (CD-AuNPs@AuNCs). An efficient and sensitive electrochemical sensor for the detection of Cr(VI) has been developed based on RbNPs. The sensing platform exhibits an excellent wide linear range (100 pg mL^-1 to 10 μg mL^-1 ), extremely low detection limit (40.91 fg mL^-1 i. e. 0.79 pM), which may pave a new way to fabricate other ultrasensitive electrochemical sensors based on the designed RbNPs.

A New Electrochemical Method to Determine Tryptophan in Fruit Juices: Development and Validation

Tryptophan (Trp) is an essential amino acid usually found in fruit juices. Its determination is necessary for food companies because of its relation to human health. In this work, a new electrochemical method based on sonogel–carbon electrodes (SNGCEs) was developed and validated using an ultra performance liquid chromatography (UPLC) method as a reference method for the determination of Trp in fruit juices. Cyclic voltammetry (CV), chronoamperometry, and differential pulse voltammetry (DPV) techniques were applied to investigate the oxidation of Trp on a previously polarized SNGCE surface in a Britton–Robinson (BR) buffer solution at pH 3.6. The operating conditions for electroanalysis were optimized using a Box–Behnken design (BBD), obtaining an oxidation peak for Trp at 0.749 V. The linear range for this method was from 0.1 to 5 mg/L. The intraday and interday precision, expressed as a relative standard deviation (RSD), were 3.1% and 2.7%, respectively. The average recovery was 99.01%, and the limit of detection and quantitation were 0.33 and 1.09 mg/L, respectively. Therefore, from the quality analytical parameters obtained, it can be concluded that the new electrochemical method can be successfully used for the routine analysis of Trp in fruit juices. As far as we are concerned, this is the first time that a methodology for Trp determination was performed in this kind of real food matrices.

Electrochemical reduction of Cr(VI) in water: lessons learned from fundamental studies and applications

Converting toxic Cr(vi) to benign Cr(iii) would offer a solution to decontaminate drinking water. Electrochemical methods are ideally suited to carry out this reduction without added external reductants. Achieving this transformation at low overpotentials requires mediating the transfer of protons and electrons to Cr(vi). In this review thermodynamic parameters will be discussed to understand Cr(vi) speciation in water and identify reduction pathways. The electrochemical reduction of Cr(vi) at bare electrodes is reviewed and mechanistic considerations are discussed. Works on modified electrodes are compared to identify key parameters influencing the reduction. An overview of current applications to Cr(vi) reduction is briefly discussed to link fundamental studies to applications.

Recent Advances in Electrochemical Monitoring of Chromium

The extensive use of chromium by several industries conducts to the discharge of an immense quantity of its various forms in the environment which affects drastically the ecological and biological lives especially in the case of hexavalent chromium. Electrochemical sensors and biosensors are useful devices for chromium determination. In the last five years, several sensors based on the modification of electrode surface by different nanomaterials (fluorine tin oxide, titanium dioxide, carbon nanomaterials, metallic nanoparticles and nanocomposite) and biosensors with different biorecognition elements (microbial fuel cell, bacteria, enzyme, DNA) were employed for chromium monitoring. Herein, recent advances related to the use of electrochemical approaches for measurement of trivalent and hexavalent chromium from 2015 to 2020 are reported. A discussion of both chromium species detections and speciation studies is provided.