Analytical and Bioanalytical Chemistry Research
Volume:7 Issue: 4, Autumn 2020

AgNPs-Tragacanth conjugate gel as an eco friendly and low cost membrane was applied for the effective electromembrane extraction (EME) of Tenofovir disproxil fumarate, an important acidic and high polar (log p=1.25) antiviral drug, followed by HPLC-UV determination. The effect of various parameters on the extraction efficiency including the presence of AgNPs, tragacanth gum concentration, gel thickness, pH values of the donor and acceptor phases, applied voltage, extraction time and agitation rate were investigated and optimized. The best extraction efficiency was obtained with: 2.5% w/v of tragacanth gum, 4.0 mm gel thickness, donor phase pH = 7.0, acceptor phase pH = 8.0, applied voltage: 30 V, extraction time: 15 min and agitation rate: 500 rpm. During method validation under the optimized conditions good linearity dynamic range (LDR) between 10-750 ngmL-1 with coefficient of determination (R2) =0.999 was obtained. Limit of detection (LOD) and Limit of quantitation (LOQ) were estimated to be 5.55 ng mL-1 and 10 ng mL-1, respectively. According to the validation results, the RSD values for intra and inter-day precisions were in the range of 0.53 to 10.04% and the relative error (RE %) ranged between -2.31 to 8.20% Finally the applicability of this method in real samples was confirmed by an acceptable performance in extraction and determination of TDF in human plasma samples.

In this study, a dispersive liquid–liquid microextraction method using an extraction solvent lighter than water has been developed for the extraction and preconcentration of cholecalciferol and calcifediol from plasma samples followed by high performance liquid chromatography determination. Initially, acetonitrile and sodium chloride (NaCl) are added into the plasma as an extraction solvent and a salting–out agent, respectively. After manual shaking, the mixture is centrifuged. In the presence of sodium chloride, a two–phase system is formed. Then a portion of the upper phase is removed and mixed with n–hexane at µL–level and rapidly injected into distilled water by a syringe. In this process, the analytes are extracted into the fine droplets of n–hexane (as an extraction solvent). Under optimal conditions, enrichment factor was obtained 92 and 94 for calcifediol and cholecalciferol, respectively. The intra– (n=6) and inter–day (n=4) precisions were less than or equal to 8.1% at a concentration of 10 ng mL–1 of each analyte. Finally, this method was applied to the analysis of the analytes in human plasma samples.

One new azo Schiff-base derivative: 4-bromo-1,2-bis[2-hydroxy-5-(phenylazo) benzylideneamino]benzene (H2L) was synthesized and characterized by common spectroscopic techniques and elemental analysis. The ability of the new chemosensor for detection of some main and transition metal ions was studied by UV-Vis spectroscopy in the mixture of DMSO: water (9:1). Upon addition of Ca2+ and Cd2+ ions, dramatic changes were observed in the UV-Vis spectrum of ligand (one new absorbance band appeared in the range of 430- 450 nm, while the absorbance band at 351 nm disappeared). The stoichiometry of the complexes was determined using the Job method. The binding constants of Ca2+ and Cd2+ with receptor by Benesi-Hildebrand plots were found to be 2.874×104 M-1 and 6.445×104 M-1, respectively. The results indicated the receptor can recognize Ca2+ and Cd2+ ions from other cations in aqueous solution. Finally, the structure and electronic properties of the ligand and its complexes with Ca2+ and Cd2+ ions were analyzed by DFT and TD-DFT calculations.

Poly (threonine) modified carbon paste electrode (PTMCPE) can be used as a responsive and selective electrocatalytic sensor for the estimation of riboflavin (RF) by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The proposed electrode creates a catalytic enhancement in redox behavior of RF when equated with bare carbon paste electrode (BCPE). Under optimized conditions, RF quantification at modified electrode has shown a detection limit of 1.78×10-7 M in the linear range of 0.2-1 µM and 1-5 µM. Simultaneous analysis of RF with folic acid (FA) and ascorbic acid (AA) shows well-separated peaks leading to a quick and selective analysis of RF. The fabricated sensor can be successfully applied to RF analysis in human blood serum and B- complex tablet with acceptable results. Simultaneous analysis of RF with folic acid (FA) and ascorbic acid (AA) shows well-separated peaks leading to a quick and selective analysis of RF. The fabricated sensor can be successfully applied to RF analysis in human blood serum and B- complex tablet with acceptable results.

Lead is known as a toxic metal for human health and used in many industries. For instance, it is frequently used as a material for plumbing systems in drinking water cooler. Another typical materials containing lead is glaze which is a thin layer of liquid put on a piece of bowl or some ceremicware. Determination of lead amount leached from these samples is necessary and this could raise awareness of lead toxicity to consumers. Simple on-line spectrophotometric system for the determination of lead at trace level with on-line preconcentration step using Amberlite IR-120 as a sorbent packed in a minicolumn was developed. It is based on lead-4-(2-Pyridylazo)-resorcinol (PAR) complex formation to be detected spectrophotometrically at 519 nm. Under the optimal conditions, the linear range of 70-1000 µg l-1 with a correlation coefficient (R2) of 0.9998 was obtained. The limit of detection, LOD (based on 3Sx/y/m) of 55 µg l-1 and the relative standard deviation (RSD) within 5% (at 70 and 500 µg l-1, n=10) were achieved. The enrichment factor of 47 was provided (at 4 min loading time). The column can be reused up to 84 cycles. The proposed method was successfully applied for detecting lead contamination in drinking water samples discharged from water coolers and leachates from glazed bowls with satisfactory recoveries within the range of 90-107%.

The intensive use of thiram and thiophanate methyl fungicides in agriculture leaves residues on crops and contaminates groundwater and surface water bodies through leaching. For the purpose of monitoring pollution arising out their use a spectrofluorimetric method has been validated for screening these fungicides in environmental samples viz. water, soil and foodstuffs. The measurement of fluorescence intensity of cerium(III) species at 365 nm resulting from ceric ammonium nitrate oxidation of dimethyl dithiocarbamate and o-phenylene bis-thiourea (products of the reaction of thiram and thiophanate methyl respectively with potassium tert.-butoxide) formed the basis of the method. As little as 0.18 and 0.22 µg mL-1 of thiram and thiophanate methyl can be determined. A simple and rapid solid-phase extraction and purification procedure prior to the spectrofluorimetric determination shows high recoveries of these fungicides from spiked water and grain samples in the range 86.00-98.00% and 88.50-97.50% with a maximum RSD of 2.60 % indicates good accuracy and precision of the method. Their risk of contamination of water bodies as groundwater ubiquity score (GUS) has also been evaluated based on their adsorption study on four soils and values in the range -0.48 to 0.98 classify them as non-leacher fungicides.

As a promising alternative for the mercury film electrode (MFE), the bismuth film electrode (BiFE) has been widely used in the field of electrochemical analysis. BiFE shows attractive properties and excellent performance such as environmentally friendliness, high sensitivity, easy preparation, well-defined signals and negligible effect to dissolved oxygen. According to recent experimental reports many electrochemical analysis have been studied with the use of BiFEs. Toxic heavy metal ions, pharmaceutical substances, pesticides and other biological molecules and products are determined with the BiFE. The voltammetric behavior of tannic acid (TA) at bismuth film modified glassy carbon electrode (Bi-GCE) has been studied by linear sweep voltammetry (LSV). Bismuth film was deposited on glassy carbon electrode (GCE) by single potential step chronoamperometric deposition at -450 mV for 120 s. TA shows a well-defined cathodic peak on the modified electrode at around -0.6 V vs. Ag/AgCl in Briton Robinson (BR) buffer solution of pH 3.6 at Bi-GCE. The effect of deposition time, deposition potential, bath concentration and pH of supporting electrolyte on the reduction current of TA were optimized. Under optimum conditions TA shows a linear range between 0.05 μM to 200 μM and the limit of detection (LoD) was found to be 0.035 μΜ. The developed method was used for determination of TA in tea samples.

Polythiophene (PT) coated magnetic multi-walled carbon nanotubes (MMWCNTs) as a magnetic sorbent was synthesized and characterized by FT-IR, SEM, XRD, and VSM. The sorbent was applied for simultaneous solid-phase microextraction of trace amounts of lead and cadmium ions from various matrices. The retained analytes were eluted using nitric acid solution (0.5 mol L-1) and quantified by flame atomic absorption spectrometry. The main factors affecting the extraction of lead and cadmium such as pH, type and concentration of eluent, amount of the sorbent, ionic strength and sample volume were investigated and optimized. Under the optimized conditions, the detection limits (based on 3Sb/m) of 0.54 and 0.03 µg L-1 and the enhancement factors of 197.6 and 195.5 were obtained for lead and cadmium, respectively. The relative standard deviations of 1.5% (n = 6) at 50.0 µg L-1 of lead and 2.1% at 5.0 µg L-1 of cadmium were achieved. The method was found to be effective, selective, rapid, and simple for the determination of trace amounts of lead and cadmium and was successfully applied to the determination of lead and cadmium in water, black tea, rice, and milk samples without evident interference from the complex matrix. Furthermore, the sorbent showed high capacity, and the precision and accuracy of the method were satisfactory. The validity of the method was examined through the recovery experiments and independent analysis by electrothermal atomic absorption spectrometry.

A simple solid phase extraction (SPE) based on sodium dodecyl sulfate grafted chitosan nanocomposite was applied for simultaneous spectrophotometric determination of crystal violet (CV) and malachite green (MG) content of water samples. For the data analysis of the overlapped spectra of the two dyes, the partial least square regression (PLSR) has been utilized. The synthesized sorbent was characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results showed the SDS was successfully cross-linked with the chitosan. Various parameters affecting the simultaneous extraction of the analytes, such as pH of sample solution, sample flow rate and the volume and flow rate of eluent were optimized by central composite design and response surface methodology (RSM). Figures of merits consisting of sensitivity, analytical sensitivity, limits of detection (LOD) and limit of quantitation (LOQ) were calculated to 0.89 ng ml -1 , 762.07, 0.06 ng ml -1 and 0.20 ng ml -1 for CV, and 0.15 ng ml -1 , 128.24, 0.17 ng ml -1 and 0.53 ng ml -1 for MG. The calibration curve showed high correlation coefficients of 0.9995 and 0.9993 for CV and MG, respectively. Moreovere, preconcentration factor and extraction recovery of the analytes were computed based on the regression coeffients of PLSR acting as a multivariate net analyte signal filter.

In this work, the electrochemistry of the ethanolic leaf extract of Melissa officinalis L., as an herbal medicine, was studied. The antioxidant activity of the plant was evaluated using the cyclic voltammetry technique. The results showed that this extract is oxidized at low potentials compared to quercetin, salicylic acid and gallic acid as standard synthetic antioxidants. It was also concluded that the increase in the antioxidant activity causes a decrease in Ep A and an increase in the number of hydroxyl groups on the aromatic ring. The DPPH assay (free radical scavenging activity) was applied in order to estimate the antioxidant activity. The antioxidant activity of rosmarinic acid (as the main natural compound in this herb) against Cytochrome P450 3A4 (4D75), Myeloperoxidase (1DNW), and Thyosine (PBD ID: 3nm8) (reactive oxygen species (ROS) generating enzymes) was investigated through molecular docking studies. The interaction of rosmarinic acid with Thyosine exhibited the most inhibitory effect with -10.5 kJ mol-1 binding affinity value. The results indicated that the rosmarinic acid is bound exclusively to the binding sites of the ROS generating enzymes and has a significant role in counteracting the destructive effects of oxidative stress in the biological system. Finally, the electrochemical oxidation of the ethanolic leaf extract of Melissa officinalis L., has been studied in the presence of captopril by cyclic voltammetry method in the biological pH range. The results showed that the electrochemically generated compounds from this herb can participate in the chemical reaction with captopril and reduce the concentration of the active form of this drug.