Surface functionalization of natural hydroxyapatite by polymerization of ß-cyclodextrin: application as electrode material for the electrochemical detection of Pb(II).

A composite material prepared by polymerization of ß-cyclodextrin (ß-CD) on the surface of natural hydroxyapatite using citric acid as cross linker, was employed as electrode material for the detection of Pb(II). Hydroxyapatite was obtained from bovine bones, following a three-step procedure including pre-calcination, chemical treatment with (NH4)2HPO4, and calcination. The structure and morphology of the pristine hydroxyapatite (NHAPP0.5) and its functionalized counterpart (NHAPp0.5-CA-ß-CD) were examined using XRD, FTIR, and SEM. Upon deposition as thin film on a glassy carbon electrode (GCE), the ion exchange ability of NHAPp0.5-CA-ß-CD was exploited to elaborate a sensitive sensor for the detection of lead. The electroanalytical procedure was based on the chemical accumulation of Pb(II) ions under open-circuit conditions, followed by the detection of the preconcentrated species using differential pulse anodic stripping voltammetry. The reproducibility of the proposed method, based on a series of 8 measurements in a solution containing 2 µM Pb(II) gave a coefficient of variation of 1.27%. Significant parameters that can affect the stripping response of Pb(II) were optimized, leading to a linear calibration curve for lead in the concentration range of 2 × 10-8 mol L-1 - 20 × 10-8 mol L-1 (R2 = 0.998). The detection limit (3S/m) and the sensitivity of the proposed sensor were 5.06 × 10-10 mol L-1 and 100.80 µA.µM-1, respectively. The interfering effect of several ions expected to affect the determination of lead was evaluated, and the proposed sensor was successfully applied in the determination of Pb(II) ions in spring water, well water, river water and tap water samples.

A new sensor based on an amino-montmorillonite-modified inkjet-printed graphene electrode for the voltammetric determination of gentisic acid.

An amperometric sensor based on an inkjet-printed graphene electrode (IPGE) modified with amine-functionalized montmorillonite (Mt-NH2) for the electroanalysis and quantification of gentisic acid (GA) has been developed. The organoclay used as IPGE modifier was prepared and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, CHN elemental analysis, and thermogravimetry. The electrochemical features of the Mt-NH2/IPGE sensor were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibited charge selectivity ability which was exploited for the electrochemical oxidation of GA. The GA amperometric response was high in acidic medium (Brinton-Robinson buffer, pH 2) due to favorable interactions between the protonated amine groups and the negatively charged GA. Kinetic studies were also performed by cyclic voltammetry, and the obtained electron transfer rate constant of 11.3 s-1 indicated a fast direct electron transfer rate of GA to the electrode. An approach using differential pulse voltammetry was then developed for the determination of GA (at + 0.233 V vs. a pseudo Ag/Ag+ reference electrode), and under optimized conditions, the sensor showed high sensitivity, a wide working linear range from 1 to 21 µM (R2 = 0.999), and a low detection limit of 0.33 µM (0.051 ± 0.01 mg L-1). The proposed sensor was applied to quantify GA in a commercial red wine sample. The simple and rapid method developed using a cheap clay material could be employed for the determination of various phenolic acids.