Analytical and Bioanalytical Chemistry Research
Volume:7 Issue: 1, Winter 2020

The electrochemical response of S- and R-naproxen enantiomers was investigated on L-cysteine/reduced graphene oxide modified glassy carbon electrode (L-Cys/RGO/GCE). The production of the reduced graphene oxide and L-cysteine on the surface of the glassy carbon electrode was done by using electrochemical processes. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the enantioselective interaction between the chiral surface of the electrode and naproxen (NAP) enantiomers. The L-Cys/RGO/GCE was found to be successfully enantioselective toward sensing S-NAP in the presence of R-NAP. The linear dynamic range was found to be 5.0×10−6–1.3×10−4 mol L−1 for both naproxen enantiomers with detection limits of 3.5×10−7 and 2.5×10−6 mol L−1 for S- and R-NAP, respectively. This study shows development of an excellent enantioselective sensor constructed based on L-Cys/RGO/GCE for recognition naproxen enantiomers. The modified electrode could be used successfully for the determination of one naproxen enantiomer in the presence of the other.

Ammonium sulfate is one of the subsidiary components in the stealth liposome structure. The ratio of ammonium ion bound to liposome sphere to ammonium ions outside the liposome plays an important role in drug delivery formulation; accordingly, in order to quantify the ammonium ion in the liposome structure, a rapid and sensitive method was validated using a conductivity detector. Through this method, the amount of ammonium enclosed in the liposomal spheres is determined by subtracting the amount of extra-liposomal ammonium content from the total amount of ammonium present in the liposome structure. Destruction of the liposome structure with the aid of 1% w/w Triton-X-100 solution allows for the analysis of the total ammonium ion present in the liposome structure. In the present research, ultrafiltration made it possible to isolate and analyze the extra-liposomal ammonium ions. This measurement was performed using an ion exchange chromatography column, isocratic elution flow and a linearity of 0.9998. Based on this signal-to-noise method, LOD was determined as 0.0003 mmol/L ammonium ion, with a signal-to-noise ratio of 3:1 and RSD was 1.4%. With a signal-to-noise ratio of 10:1, LOQ was determined as 0.001 mmol/L ammonium ion with RSD 1.2%. In the determination of the total ammonium ion, the individual percentage recovery ranged from 100.00 to 100.93% and for the external ammonium ion analysis, the individual percentage recovery varied from 95.87 to 98.12% for all three levels and RSDs are 0.27, 0.71, and 0.71% for these concentrations.

A simple and solvent-minimized sample preparation technique based on hollow fibre-protected liquid-phase micro-extraction has been developed for extraction of fifteen organic sulphur compounds from aqueous samples. The analysis of the extracted them was performed by gas chromatography equipped with mass spectrometry and/or flame photometric detectors. 3.3 µL of organic solvent located in the lumen of hollow fibre was used to extract OSCs from an 8 mL of aqueous sample. Several parameters influencing extraction efficiency such as salt concentration, stirring speed, temperature, sample volume, organic phase volume and extraction time were studied and optimized using super-modified simplex method. Under optimized conditions, including extraction solvent (toluene) extraction time (15 min ), salt addition (4 % w/v), stirring rate (1200 rpm), sample volume (8 ml SV), organic solvent volume (3.3 µl) and extraction temperature (35oC), the limits of detection varied from 0.1 to 8.7 µg/L and 0.7 to 99.4 µg/L for GC-FPD and GC-MS, respectively. The calibration graphs were linear over three orders of magnitude for most of the studied OSCs. The relative standard deviations for inter- and intra-day analysis were in the range of 5 to 10%, and the relative recoveries of the analytes from the three different real water samples were more than 83%. The results were compared with those obtained using direct single drop micro-extraction and headspace single drop micro- methods. The proposed method is reliable and can be considered useful for routine monitoring of the organic sulphur compounds in surface water samples.

A new, cost-effective, and environmental-friendly cloud point extraction methodology was described for enrichment of copper, manganese and nickel in several water samples. The method involves the complexation of copper, manganese or nickel with 2-amino-6-(1,3-thiazol-2-diazeyl)-phenol at pH 7.0, then extraction into Triton X-114. After dilution of the surfactant-rich phase with acidified methanol, the enriched analytes concentration was estimated by flame atomic absorption spectrometry. Parameters that influenced cloud point extraction, such as pH, reagent, surfactant and nitric acid concentrations, centrifuge rate and time, temperature, incubation time, as well as interferences were evaluated and optimized. The preconcentration factor was 100, enrichment factors were 14, 11.10 and 11.30 and the detection limits were 0.37, 1.20, and 1.30 µg L-1 for copper, manganese, and nickel, respectively. The method presented relative standard deviation as precision were 2.20%, 2.50 and 3.20% for copper, manganese, and nickel, respectively. The accuracy of the new preconcentration procedure was checked by the analysis of the standard reference materials (SRM 1570a Spinach Leaves and SRM 1515 Apple Leaves), and successfully applied to determine Cu2+, Mn2+ and Ni2+ in real water samples with relative recovery values in the range of 95.0%–99.0% for the spiked samples.

Alginate-metal complexes were prepared with divalent (Ca, Ba, Zn) and trivalent metals (Fe, Al) via congealing method in form of beads. Alginate mixed metals (Ca & Fe) complexes were also prepared by simultaneous and consecutive congealing. The studied beads were blank beads and racemic ketoprofen (KTP) loaded beads. Metal content was determined by atomic absorption spectroscopy and was 1.8% to 30.4%. IR spectra were registered and showed interaction between ketoprofen carboxylic OH and alginate hydroxyl OH, thus chiral interaction is suggested. Chiral HPLC was used to monitor enantioselective release (ESR) of racemic ketoprofen enantiomers in a phosphate buffer solution (PBS) at pH=7.4.ESR is expressed as the relative chromatographic area of R-enantiomer to S-enantiomer (R/S ratio). For divalent metal complexes, over the first 50 min of release, R/S was < 1; with starting value (0.53) in case of calcium, indicating important ESR, but less important in case of barium. However, in case of zinc R/S was >1 with starting value of 1.1, indicating weak ESR. No significant results of ESR were obtained for trivalent metal complexes, where R/S is almost 1 in case of iron and aluminum. For alginate beads which simultaneously congealed with (Ca & Fe), R/S was >1. Nevertheless, consecutively congealed alginate gave opposite ESR behavior; R/S was 1 for Fe then Ca congealed alginate.

Univariate calibration method is a simple, cheap and easy to use procedure in analytical chemistry. A univariate analysis will be successful if a selective signal can be found for the analyte(s). In this work, two simple ways were used to find the selective signals, spectral ratio plot (SRP) and loading plot (LP). Both of them were able to discover the selective regions in the recorded data sets. For SRP, the spectral profiles of unknown mixture and standard sample of analyte were necessary. However, in LP, multivariate data of standard addition procedure was necessary to discover the selective zones. After discovering the selective wavelengths, the standard addition method can be used to determine the concentration of given analyte. The standard addition curve was interpolated to reduce any bias error. To demonstrate the ability of LP and SRP, several synthetic and real datasets were analyzed and the results were reported. The SRP and LP were used to determine some additives in food and hygienic real samples using spectrophotometric data.

In this work, a TiO2 nanoparticle modified carbon ionic liquid electrode (CILE) was employed as a sensitive sensor for the investigation of the electrochemical behavior of indomethacin (IND). This nanocomposite sensor has been fabricated by incorporation of TiO2 nanoparticles and the ionic liquid 1-hexylpyridinium hexafluorophosphate (HPFP). The surface of the electrode was studied by scanning electron microscopy (SEM). Differential pulse voltammetry (DPV) was used for quantification of sub-micromolar amounts of IND. Electrochemical parameters of the electrode reaction of IND, including the electron transfer coefficient (α) and the electron-transfer number (n), were calculated by cyclic voltammetry (CV) methods. Under selected conditions, the anodic peak current was linear for the concentration of IND in the broad range of 1.0 × 10-7 to 1.0 × 10-4 M with the detection limit of 2.1× 10-8 M. Moreover, the analytical performance of the proposed method for the determination of IND content in plasma samples was evaluated with good sensitivity and acceptable recoveries.

An anodic stripping differential pulse voltammetric method was proposed for rapid and sensitive determination of hypochlorite ion. A modified electrode was prepared by modification of carbon paste using alumina nanopowder . The method that is rapid, simple and accurate is based on the electrooxidation hypochlorite ion accumulated at the elexctrode urface. Nanoalumina modification increased the oxidation peak current for hypochlorite ion. The effects of different parameters on the electrode response were studied and the optimum condition was established. The response of the sensor was linear in the range 0.1-800 μg mL-1 of hypochlorite ion, with a correlation coefficient of 0.9992 at the optimum condition. The limit of detection was obtained as 0.025 μg mL-1. The effects of some cations, anions and organic species, which may coexist with hypochlorite ion in real samples, on the current response of hypochlorite, were investigated. The investigated chemical species do not interfere. Hypochorite ion in water and dairy product samples was successfully determined using the proposed electrode.

Herein, a simple, sensitive, and rapid chemosensor was reported for the colorimetric detection and determination of oxalate ions. This system produces a visible color change from purple to yellow based on indicator displacement assay (IDA) approach. The reaction of Eriochrome Cyanine R (ECR) as an indicator and Vanadyl ions (VO2+) at pH 6.00 acts as a chemosensor for oxalate ions (Ox). Adding oxalate ions to the designed chemosensor, causes the displacement of the Vanadyl ions with the oxalate ions to binding the indicator. Due to this displacement, the solution color returns to yellow with about 80 nm blue shifts (530 to 450 nm). Also, the formation constants of ECR-VO2+ and VO2+-Ox complexes were determined to be 6.13 and 13.94, respectively using spectrophotometric titration. Under the optimized experimental conditions, the chemosensor exhibited a dynamic linear range for oxalate ions from 8.30 ×10-7 M to 1.13 ×10-4 M, with a detection limit (S/N=3) of 5.40 ×10-7 M. The relative standard deviation (RSD) value was evaluated to be 0.52% for five determinations of oxalate (6.02 µM). The designed sensor was applied successfully for the determination of oxalate ions in human urine samples with the recoveries of 96.36 to 105.73% showing satisfactory results.

MG has been extensively used as fungicide and parasiticide in fish farms. At present, the use of MG in aquaculture is forbidden because MG and its metabolite were reported to cause human carcinomatosis and mutagenesis. Owing to its low cost and availability, MG may still be used. Herein, extraction and preconcentration methods were developed for spectrophotometric determination of trace amounts of malachite green (MG) in different samples. The methods are based on the extraction of dye by SiO2 coated magnetic nanoparticles (Fe3O4@SiO2) and chloropropyltriethoxysilane (CPTS) core–shell magnetic nanocomposite (Fe3O4@SiO2-CPTS). The influence of pH, dosage of the adsorbent and contact time on the extraction of the dye was explored by response surface methodology. The calibration curve was linear in the range of 0.01-15.00 mg L-1 with detection limit of 2.0×10-4 mg L-1 by Fe3O4@SiO2-CPTS. Extraction and preconcentration based on the two magnetic nanoparticles were successfully applied for determination of MG in various water and fish samples.