Analytical and Bioanalytical Chemistry Research
Volume:5 Issue: 1, Winter - Spring 2018

A procedure for separation/preconcentration of para-aminophenol (PAP) in pharmaceutical formulation, based on cloud point extraction (CPE) as a prior step to determination by UV-Vis spectrophotometry has been developed. The analyte reacted with 4-dimethylamino benzaldehyde (DAB) in acidic media to form a shift base, which were separated and preconcentrated in a mixed micelle of the anionic surfactant sodium dodecylsulfate (SDS) and the nonionic surfactant Triton X-114. The parameters affecting the extraction efficiency of the proposed method, such acid concentration, reagent concentration, amount of surfactants, and incubation time were optimized. Under the optimum conditions, the linear range was 50-1000 ng ml-1 of PAP with a correlation coefficient (r) of 0.998. The limit of detection was 30 ng ml-1. Relative standard deviation (RSD) for five replicate determinations of 200 ng ml-1 PAP was 1.4 %. In this work, the concentration factor of 10 was reached. Also the improvement factor of the proposed method was 3.3. The proposed method was successfully applied for determination of p-aminophenol in pharmaceutical formulations. The advantages of this method are simplicity of operation, rapidity and low cost.

Ion pair dispersive liquid- liquid microextraction (IP-DLLME) method combined with flame atomic absorption spectrometry was proposed for the determination of trace amounts of copper(II). By using pyrocatechol violet as chelating agent and cetyltrimethyl ammonium bromide as an ion pairing agent, the trace amount of copper(II) was extracted in chloroform. The factors influencing the formation copper-ligand complex and the extraction efficiency such as, sample pH, extraction time, type and volume of extraction solvent and dispersive solvent, ion pair and ligand concentration were optimized. Under optimum experimental conditions, the enhancement factor of 10.0 was obtained from only 5.0 ml of aqueous phase. The linear dynamic range and the detection limit were 6.0 - 100 μg l-1 and 3.7 mg l-1, respectively. The relative standard deviation for ten replicate determinations of 40.0 µg l-1 of Cu2 was 1.9 %. Developed method was successfully applied for determination of copper in soil, multivitamin tablet, tea and water samples with good spike recoveries.

A magnetic nano-composite based on modified styren-maleic anhydride copolymer and Fe3O4 nano-particles was introduced as a new sorbent for solid-phase extraction and preconcentration of trace levels of silver ion from aqueous solutions. The size and morphology of the nano-sorbent were characterized via X-ray diffraction analysis, scanning electron microscopy and Fourier transform infrared spectroscopy. Following its desorption with hydrochloric acid, silver was detected by flame atomic absorption spectrometry. Different variables affecting the separation/pre-concentration of the silver ion were optimized. Under the optimized conditions, the calibration graph was linear in the 1–200 µg L–1 concentration range, with a correlation coefficient of 0.9991. The limit of detection and relative standard deviation for six replicate determinations at a silver ion level of 100 µg L–1 were 0.3 µg L–1 and 1.1 %, respectively. The preconcentration factor and adsorption capacity of the sorbent for silver ion were 100 and 78.2 mg g–1, respectively. The accuracy of the method was confirmed by analyzing the certified reference material NIST SRM 1566b. The method was successfully applied to determine silver ion in water samples and in radiology films, and satisfactory recoveries were obtained in the range of 96.8–99.6 % for the spiked samples.

In this work a new chemically modified carbon paste electrode was constructed for accurate, simple, sensitive and selective determination of molybdenum (VI) ions. The results of modified electrode by an ion imprinted polymer were compared with those obtained with carbon paste electrode. The results showed the stripping peak currents had a dramatic increase at the modified electrode. Under the optimal conditions, the linear dynamic range and limit of detection were 0.2-500.0 and 0.04 ng mL-1, respectively. The relative standard deviation for five successive measurements of 5.0 and 20.0 ng mL-1 of Mo(VI) ions were 1.8 and 1.4 %, respectively. The reproducibility and stability of the designed modified electrode response were also investigated. By examining the effect of different cations and anions on the determination of the target ion, it was found that the electrode is highly selective for the determination of Mo(VI) ions. Furthermore, the present method was applied to the determination of Mo in real samples with satisfactory results.

A novel carbon paste electrode modified with ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) and magnetic core-shell manganese ferrite nanoparticles (MCSILCPE) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electro-oxidation of tryptophan, is described. Cyclic voltammetry (CV), choronoamperometry (CHA) and square wave voltammetry (SWV) were used to investigate oxidation of tryptophan in aqueous solution. The diffusion coefficient (D=3.53 ×10-6 cm2/s), was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.0), the oxidation of tryptophan at the surface of such an electrode occurs at a potential about 150 mV less positive than that of an unmodified carbon paste electrode. SWV exhibits a linear dynamic range from 5.0×10-6 to 4.0×10−4 M tryptophan. The morphology of the modified electrode was studied using SEM. The limit of detection was equal to 1.1×10-6 M. The electrode was also employed to determination of tryptophan in urine samples.

Recently solution scanometry, as a new, simple, fast, portable, and economic method was introduced for determination of acidity constants of indicator and dyes. In this study, a method was applied for the determination of the acidity constant of p-Rosolic acid (RA) and Bromoxylenol blue (BXB) indicators. The method is based on scanning of Plexiglas® sheet containing colored solutions with a flatbed scanner. The obtained images were analyzed to red, green, and blue (RGB) values using software written in visual basic 6. For comparison, the acidity constants of the indicators were determined by spectrophotometric method using the Hypspec program. The corresponding distribution diagrams were also drawn through the Hyss2009 program. The comparison between the presented and traditional UV-Vis spectrophotometric method was performed, and similar trends in results of both methods were observed. The obtained values of pKa by solution scanometric and spectrophotometric method showed good agreement with corresponding values which were reported in the literature.

The interaction of the perimidone drug in solution state with the σ-acceptor iodine, the aliphatic π-acceptor tetracyanoethylene (TCNE) and the aromatic π-acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) have been studied through the initial formation of ionic intermediate to charge transfer (CT) complex in methanol at room temperature. The spectral studies of the complexes were determined by UV-Visible, Fourier transform infrared (FT-IR). The stoichiometries of the complexes were found to be 1:2 and 1:1 ratio by the photometric molar ratio between primidone with π-acceptors and σ-acceptor, respectively. The equilibrium constants (KCT), molar extinction coefficient (εCT) and spectroscopic-physical parameters (standard free energy (ΔGo), and ionization potential (Ip)) of the complexes were determined upon the modified Benesi–Hildebrand equation. The most stable mono-protonated form of perimidone is characterized by the formation of +N H (pyrimidine ring) intramolecular hydrogen bonded. In the high-wavenumber spectral region ∼3400 cm−1, the bands of the +N H stretching vibrations could be potentially useful to discriminate the investigated forms of perimidone.

In the present work, the simultaneous determination of Brilliant green (BG) and Crystal violet (CV) dyes with overlapped absorption spectra in binary mixture solution, was carreid out using the partial least squares (PLS) and direct ortogonal signal correction-partial least squares (DOSC-PLS) methods. The results obtained indicate that by applying DOSC on the calibration and prediction data for each dye, the prediction errors are significantly minimized. Walnut shell, as an abundant lignocellulosic agricultural waste, was modified using NaOH, and subsequently characterized by the Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and BET techniques. The potential application of the prepared adsorbent for the removal of the cited dyes was investigated. The effects of the experimental parameters such as the initial pH, adsorbent dosage, initial dye concentration, and contact time on the adsorption efficiency in the single solutions and their binary mixture are studied. The optimum experimental conditions were found to be 0.8 g/L of the adsorbent at room temperature, pH 7.0, and a contact time of 13 minutes. These advantages make it appropriate for dye removal. The analysis data shows that the Langmuire isotherm can satisfactorily explain the equilibrium data. The maximum adsorption capacity (qm) for BG and CV in their single solutions was found to be 146.40 and 123.2 mg/g, respectively, whereas these values for their binary mixture were 79.07 and 96.01 mg/g, respectively. The exhausted NMWNS was regenerated using a dish-washing liquid and reused for removal of the cited dye species from aqueous solutions.

A glassy carbon electrode was modified with graphene oxide nanosheets and a hybrid of copper-cobalt hexacyanoferrate. The nanocomposite was characterized by cyclic voltammetry, FT-IR and scanning electron microscopy. Cyclic voltammetry showed a stable and reversible redox pair with surface confined characteristics in phosphate buffer solution (0.1 M, pH 3). Hydrodynamic amperometry was used for determination of glutathione at pH 3. The catalytic oxidation peak current varied linearly with the concentration of glutathione in the range of 3.3 × 10-7 to 5.5 × 10-5 M with a limit of detection of 2.5 × 10-7 M. The repeatability was evaluated for 5 successive measurements of a GSH solution (0.48 mM) by the proposed method as relative standard deviation (RSD%), which was 3.02%. When 3 different electrodes were used, the RSD% for GSH determination was 3.34%. The modified electrode was used in the determination of glutathione in hemolysed erythrocyte samples with satisfactory results.

The present study describes a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of S-RRR and R-SSS nebivolol (nebivolol enantiomers) in human plasma using solid phase extraction technique. Method of both S-RRR and R-SSS nebivolol (nebivolol enantiomers) has been developed and validated using racemic nebivolol D4 as an internal standard. Analytes from human plasma were extracted by ion exchange cartridges and subsequently separated on chiral column using acetonitrile: ammonium carbonate in water, 158 mg/L 80:20% v/v as a mobile phase, at a flow rate of 0.9 mL/min. Quantification of S-RRR and R-SSS nebivolol and R-nebivolol D4 was performed using multi-reaction monitoring mode (MRM) in positive mode. The calibration curve was linear (r2 > 0.99) over the concentration range of 20.0 to 6000 pg/mL for S-RRR and R-SSS nebivolol. The intra-day and inter-day assay precision revealed within ±15% (at LLOQ level ±20%) with accuracy within 85%-115% (at LLOQ level 80% -120%). The LC-MS/MS method was fully validated for all the validation parameters as per current regulatory requirement (US FDA, EU) such as selectivity, matrix effect, recovery and stability (in solution and in matrix stability).

Most of previous papers in the field of dye removal used one dye or dyes with nearly separate spectra that simplifies dyes concentration determination by Beer's law at different λmax. In many real situations, dyes with highly overlapped spectra exist and their concentrations can be determined by multivariate analysis methods. In this study, principal component-wavelet neural network (PC-WNN) was used for concentration determination of rhodamine B (RB), methylene blue (MB) and malachite green (MG) in ternary solutions. Biosorption of dyes by pistachio hull was selected as model. The effects of operating parameters were studied by Doehlert experimental design. The maximum uptake capacity of pistachio hull for cationic dyes was 0.682 mmol/g. It was found that the overall biosorption data was described by the pseudo second-order kinetic model. Nine isotherm models were nonlinearly fitted to experimental data and Redlich-Peterson and Radke-Prausnitz isotherm models had the best fit for biosorption equilibrium data.

The characterization of and construction of a new optical sensor based on the immobilization of Pyrocatechol Violet on a triacetylcellulose membrane was described to for the determination of bismuth (III) in real samples. The interaction between sensing membrane and bismuth (III) was caused at pH 3.80 in acetate buffer solution and the color changed from yellow to blue along with the appearance of a strong peak appears at 613 nm. The effect of parameters on the preparation of the sensor and determination of V (IV) ions was investigated. At the optimal condition, this optical sensor has a linear range of 4.98-47.60 µM with a limit of detection of 0.11 µM. Bismuth (III) can be detected within 10 min. The working range was improved by using PC-ANN algorithm. The sensor could be regenerated with 0.1 M hydrochloric acid solution. Bismuth (III) detection method was applied to determine Bismuth (III) ions in biological and environmental samples.

Four novel receptors were designed and synthesized for colorimetric detection of F− ions. The introduction of four electron withdrawing groups into the backbone of the receptors makes the two phenolic groups efficient hydrogen bonding sites. The binding properties of receptors with anions were examined for the first time by UV–Vis, 1H NMR and fluorescence spectroscopies. The addition of F− resulted in a marked red shift of the charge-transfer absorbance band accompanied by a color change. The addition of other anions such as Cl−, Br−, I−, NO3−, ClO4−, CN− and HSO4− did not result in observable spectral change and solution color change. The 1H NMR titration revealed that the colorimetric response was considered to be the direct consequence of hydrogen-bond formation between the phenolic groups of the receptors and fluoride ions followed by deprotonation. The current sensory systems could as well be served as practical tool for immediate and qualitative detection of inorganic 'anions in real-life applications'.