Copper(II)–neocuproine reagent for spectrophotometric determination of captopril in pure form and pharmaceutical formulations

A simple, rapid, sensitive and accurate spectrophotometric method for the determination of captopril in pure form and pharmaceutical formulations is developed. The procedure is based on the reaction of copper(II) with captopril in the presence of neocuproine (NC) (2,9-dimethyl-1,10-phenanthroline) reagent in acetate buffer at pH 5.0. Copper(II) is reduced easily by captopril to Cu(I)–neocuproine complex, which shows an absorption maximum at 448 nm. Beer’s law was obeyed in the concentration range 0.3–3.0 μg mL^?1 with a minimum detection limit (LOD) of 0.039 μg mL^?1 and a quantification limit (LOQ) of 0.129 μg mL^?1. For more accurate results, Ringbom optimum concentration ranges was 0.5–2.7 μg mL^?1. The apparent molar absorbtivity and Sandell sensitivity were calculated. The validity of the proposed method was tested by analyzing the pure and pharmaceutical formulations and compared well with those obtained by the official method and demonstrated good accuracy and precision.     

Novel luminescent nanoparticles for DNA detection

Highly luminescent LaF₃:Ce³⁺/Tb³⁺ nanocrystals were successfully prepared and surface functionalized via Layer-by-Layer technology. These as-prepared nanocrystals are highly resistant to photobleaching and pretty dispersible in aqueous solution. Due to the efficient luminescence quenching of the nanocrystals by nucleic acids, a facile fluorescence quenching method was developed for the detection of trace amount of nucleic acids. Under optimal conditions, the fluorescence intensity was proportional to the DNA concentration over the range of 0.60–25.0 μg mL^?1 for calf thymus DNA (ct-DNA) and 0.60–30.0 μg mL^?1 for herring sperm DNA (hs-DNA), respectively. The corresponding detection limit is 0.21 μg mL^?1 for ct-DNA and 0.31 μg mL^?1 for hs-DNA, respectively. The results indicated that the reported method is simple and rapid with wide linear range. Also, the recovery and relative standard deviation of this method are reasonable and satisfactory.     

Application of modified multiwalled carbon nanotubes as solid sorbent for separation and preconcentration of trace amounts of manganese ions

In this work, the potential of modified multiwalled carbon nanotubes for separation and preconcentration of trace amounts of manganese ion is studied. Multiwalled carbon nanotubes were oxidized with concentrated HNO₃ and then modified with loading 1-(2-pyridylazo)-2-naphtol. Mn(II) ions could be quantitatively retained by modified multiwalled carbon nanotubes in the pH range of 8–9.5. Elution of the adsorbed manganese was carried out with 5.0 mL of 0.1 mol L^?1 HNO₃. Detection limit is 0.058 ng mL^?1 and analytical curve is linear in the range of 0.1 ng mL^?1–5.0 μg mL^?1 in the initial solution with a correlation coefficient 0.9977 and the preconcentration factor is 100. Relative standard deviation for eight replicate determination of 0.5 μg mL^?1 of manganese in the final solution is 0.41%. The effects of the experimental parameters, including the sample pH, flow rates of sample and eluent solution, eluent type, breakthrough volume and interference ions, were studied for preconcentration of Mn(II) ions in detail to optimize the conditions. The method was successfully applied for separation, preconcentration and determination of manganese in different samples.     

Determination of sulfonamides in food samples by membrane-protected micro-solid phase extraction coupled with high performance liquid chromatography

In the present study, a simple and sensitive extraction method based on polypropylene membrane-protected micro-solid phase extraction (MP-μ-SPE) has been developed for analysis of sulfonamides in food samples. Poly (methacrylic acid-ethylene glycol dimethacrylate) (p-MAA-EDMA) was synthesized using orthogonal array experimental design, optimized with three factors at four levels and evaluated on yield, hydrophobic and cation-exchange properties. The optimized p-MAA-EDMA was then employed as the sorbent in the MP-μ-SPE for extraction of sulfonamides from milk and chicken muscle samples, followed by high performance liquid chromatographic analysis with ultraviolet detection. Under optimized extraction conditions, good linearities (0.010–1.0 μg mL^?1 with r² > 0.9900), low limits of detection (0.38–0.62 ng mL^?1), and acceptable intra-day (2.7–13.7%) and inter-day (6.7–15.2%) relative standard deviations were obtained. It was demonstrated to be an effective approach to handle semi-solid/solid samples with good resistance to interference from “dirty” samples.     

Kinetic spectrophotometric determination of hyoscine butylbromide in pure form and in pharmaceutical formulations

A simple and sensitive kinetic method was described for the determination of hyoscine butylbromide in pharmaceutical preparations. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time of 15 min. The absorbance of the colored manganate ion was measured at 610 nm. The absorbance–concentration plot was rectilinear over the range of 1.0–10 μg mL^?1 (r = 0.9999) and detection limit of 0.092 μg mL^?1. The concentration of hyoscine butylbromide was calculated using the corresponding calibration equation for the fixed-time method. The determination of hyoscine butylbromide by the fixed-concentration and rate constant methods is also feasible with the calibration equations obtained but the fixed-time method has been found to be more applicable. The different experimental parameters affecting the development and stability of the colors were carefully studied and optimized. The proposed method was applied to the determination of hyoscine butylbromide in pharmaceutical formulations. The results obtained were in good agreement with those obtained using the official British Pharmacopeial method (2004).     

Validated voltammetric method for the determination of some antiprotozoa drugs based on the reduction at an activated glassy carbon electrode

A sensitive electrochemical procedure based on reduction of secnidazole (I), tinidazole (II) and ornidazole (III) at a glassy carbon electrode (GCE) was introduced. A study of the variation of the peak current with solution variables such as pH, ionic strength, concentration of drugs, possible interference, and instrumental variables such as scan rate, pulse amplitude, preconcentration time, accumulation potential, has resulted in the optimization of the reduction signal for analytical purposes. Linear calibration plots were obtained over the concentration ranges of 50–800, 50–750 μg mL^?1 for I, and both (II, III) respectively, in Britton–Robinson buffer of pH 7. The relative standard deviations of five replicate measurements of 1.0 and 10.0 μg mL^?1 of I, II and III concentrations were 4.7%, 4.9% and 5.3%, and 2.2%, 2.6% and 2.8%, respectively. The limits of detection (LOD) for I, II and III were found to be 2 × 10^?10, 3 × 10^?10 and 2.5 × 10^?10 mol L^?1 and limits of quantification (LOQ) for I, II and III were found to be 4.0 × 10^?8, 1.2 × 10^?8 and 4.4 × 10^?8 mol L^?1, respectively. The optimal conditions were: E_acc = ?0.9 V, t_acc = 30 s, scan rate = 20 mV s^?1, pulse-height = 90 mV and Britton–Robinson buffer of pH 7. The method was applied for the determination of the cited drugs both in raw materials and in pharmaceutical preparations with satisfactory results and compared with the official reference method. Complete validation of the proposed method was also done.     

Development of a solid phase extraction method for the multielement determination of trace metals in natural waters including sea-water by FI-ICP-MS

An automated solid phase extraction method by flow analysis on-line inductively coupled plasma mass spectrometry (FI-ICP-MS) for the determination of cobalt, chromium, nickel, cadmium, manganese, zinc, copper and lead in sea-water and other natural waters is described. The system is based on retention of the analytes onto a minicolumn packed with a chelating resin, 1,5-bis (2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide immobilized on aminopropyl-controlled pore glass, placed in the injection valve of a simple flow manifold. The effects of chemical and flow variables were investigated and selected as a compromise between sensitivity and sampling frequency. So, the sample solutions (adjusted to pH 8.0 ± 0.5) were passed through the column. After washing the column with water, the adsorbed metals were subsequently eluted into the plasma with 4% m/m nitric acid. Detection limits of the trace metals (180 s sample loading time at a sample flow rate of 0.7 mL min^? 1; sampling frequency 8.6 h^? 1) were 0.002 μg L^? 1 for Co, 0.057 μg L^? 1 for Cr, 0.117 μg L^? 1 for Ni, 0.004 μg L^? 1 for Cd, 0.210 μg L^? 1 for Mn, 0.260 μg L^? 1 for Zn, 0.030 μg L^? 1 for Cu and 0.020 μg L^? 1 for Pb, with enrichment factors between 2.2 and 6.8. The accuracy of the proposed method was checked with certified reference materials (CRMs) of sea-water SLEW 3, LGC6016 and CASS-5, river water SLRS-5 and fortified lake water TMDA-54.4. The results from the determination of these metals were in agreement with the certified values and recovery values ranged between 92.2 and 110.6%. The method was applied to the determination of these metal ions in sea-water samples collected in the Málaga Bay in order to realize a pilot study necessary to generate preliminary information on which to base a more detailed pollution study by heavy metals of the Bay.     

Flow-injection chemiluminescence determination of dihydralazine sulfate in serum using luminol and diperiodatocuprate (III) system

A novel flow-injection chemiluminescence (CL) method for the determination of dihydralazine sulfate (DHZS) is described. The method is based on the reaction of luminol and diperiodatocuprate (K₂[Cu(H₂IO₆)(OH)₂], DPC) in alkaline medium to emit CL, which is greatly enhanced by DHZS. The possible CL mechanism was first proposed based on the kinetic characteristic, CL spectrum and UV spectra. The optimum condition for the CL reaction was in detail studied using flow-injection system. The experiments indicated that under optimum condition, the CL intensity was linearly related to the concentration of DHZS in the range of 7.0 × 10^?9 to 8.6 × 10^?7 g mL^?1 with a detection limit (3σ) of 2.1 × 10^?9 g mL^?1. The proposed method had good reproducibility with the relative standard deviation 3.1% (n = 7) for 5.2 × 10^?8 g mL^?1 of DHZS. This method has the advantages of simple operation, fast response and high sensitivity. The special advantage of the system is that very low concentration of luminol can react with DPC catalyzed by DHZS to get excellent experiment results. And CL cannot be observed nearly when luminol with same concentration reacts with other oxidants, so luminol–DPC system has higher selectivity than other luminol CL systems. The method has been successfully applied to determine DHZS in serum.     

Kinetic spectrophotometric determination of pravastatin in drug formulations via derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl)

A simple and sensitive kinetic spectrophotometric method for the quantitative analysis of pravastatin sodium (PVS) in pure and pharmaceutical formulations has been described. The method is based on the formation of colored product between PVS and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in acetone medium at 55 ± 2 °C. The reaction is followed spectrophotometrically by measuring the increase in absorbance at 462 nm as a function of time. The initial rate and fixed time methods were adopted for constructing the calibration curves. The linearity ranges were found to be 15.0–50.0 and 10.0–70.0 μg mL^?1 for initial rate and fixed time methods, respectively. The limits of detection for initial rate and fixed time methods are 0.029 and 0.086 μg mL^?1, respectively. Both methods have been applied successfully for the estimation of PVS in commercial dosage forms with no interference from the excipients. The results are compared with the HPLC pharmacopoeial method.     

Mucin 4 detection with a label-free electrochemical immunosensor

Mucin 4 (MUC4) is a useful biomarker for endometriosis and cancers of the pancreas, esophagus and breast. The very first electrochemical immunosensor for the detection of MUC4 is reported, using carbon-based screen-printed electrodes modified by reaction with the diazonium salt of p-aminophenylacetic acid. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize and optimize the electrografting process. The in situ surface modification through diazotation with phenylacetic groups enables the chemical binding of the specific antibody, followed by its affinity reaction with MUC4. The immunosensor was optimized with respect to several parameters and is very promising for clinical applications, having a limit of detection of 0.33 μg mL^− 1 and a linear domain between 1 and 15 μg mL^− 1 obtained by electrochemical impedance spectroscopy measurements.     

The determination of trace lead in drinking water by flow injection spectrophotometry

Lead is the non-essential trace element in the human body, and it has been confirmed that drinking water is one of the sources of lead in human body. In the research, based on the sensitive colour reaction of lead with I^?–EV⁺–PVA, a simple, sensitive, accurate and portable method for the determination of trace lead in drinking waters was proposed. Chemicals and physicals had been optimized in detail. The apparent molar absorption coefficient was up to 7.4 × 10⁵ mol L^?1 cm^?1. The developed method provided a linearity range over 5–80 μg L^?1. The regression deviation was between 0.71% and 2.33%. The 3σ detection limit was 0.9 μg L^?1. Close to the quantitation limit for the analyte the relative standard deviation was 1.10% (n = 10) at 40 μg L^?1. The method developed here for analysis of lead yielded results that were comparable with those of the GFAAS.     

Assessment of a dynamic hollow-fibre liquid phase microextraction system for human blood plasma samples

A dynamic liquid phase microextraction (LPME) system, based on hollow-fibre supported liquid membrane (SLM) extraction, was developed for extracting ionisable xenobiotics from human plasma, and its performance was evaluated (in terms of extraction efficiency, reproducibility, durability and carry-over) using nitrophenolic compounds as model analytes at concentrations of 0.1–0.5 μg mL^?1 in aqueous standards. The efficiency and repeatability were tested also on spiked human plasma. The system is non-expensive, convenient, requires minimal manual handling and enables samples with volumes as small as 0.2 mL to be extracted. For plasma samples extraction efficiencies of between 30 and 58% were achieved within 20 min, including washing steps. The limit of detection (LOD) values were in the range 0.02–0.03 μg mL^?1. The developed system can provide enrichment factors up to eight, based on the injection-to-acceptor volume ratio (in this case 0.2–0.025 mL). The same hollow-fibre membrane was used up to 8 days with no loss of efficiency. Carry-over was lower than detection limit.     

Electrochemical immunosensors for interleukin-6. Comparison of carbon nanotube forest and gold nanoparticle platforms

Electrochemical immunosensors based on single wall nanotube (SWNT) forests and 5 nm glutathione-protected gold nanoparticles (GSH-AuNP) were developed and compared for the measurement of human cancer biomarker interleukin-6 (IL-6) in serum. Detection was based on sandwich immunoassays using multiple (14–16) horseradish peroxidase labels conjugated to a secondary antibody. Performance was optimized by effective blocking of non-specific binding (NSB) of the labels using bovine serum albumin. The GSH-AuNP immunosensor gave a detection limit (DL) of 10 pg mL^?1 IL-6 (500 amol mL^?1) in 10 μL calf serum, which was 3-fold better than 30 pg mL^?1 found for the SWNT forest immunosensor for the same assay protocol. The GSH-AuNPs platform also gave a much larger linear dynamic range (20–4000 pg mL^?1) than the SWNT system (40–150 pg mL^?1), but the SWNTs had 2-fold better sensitivity in the low pg mL^?1 range.     

A novel approach for determining total titanium from titanium dioxide nanoparticles suspended in water and biosolids by digestion with ammonium persulfate

Titanium dioxide (i.e. TiO₂) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO₂ nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO₂ as Ti⁴⁺ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO₂ nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti⁴⁺ from 6 μg mL^?1 aqueous suspensions prepared from 10 μg mL^?1 suspension of different forms of TiO_2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL^?1, and the limit of quantification (LOQ) was 0.20 ng mL^?1. Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO₂ of 1.8 and 1.6 ng mL^?1 for the wastewater samples, respectively, and 317.4 ng mg^?1 dry weights for the biosolids. The reactions between persulfate ions and TiO₂ were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.     

Determination of triclosan,triclocarban and methyl-triclosan in aqueous samples by dispersive liquid–liquid microextraction combined with rapid liquid chromatography

In this study, dispersive liquid–liquid microextraction (DLLME) combined with ultra-high-pressure liquid chromatography (UHPLC)–tunable ultraviolet detection (TUV), has been developed for pre-concentration and determination of triclosan (TCS), triclocarban (TCC) and methyl-triclosan (M-TCS) in aqueous samples. The key factors, including the kind and volume of extraction solvent and dispersive solvent, extraction time, salt effect and pH, which probably affect the extraction efficiencies were examined and optimized. Under the optimum conditions, linearity of the method was observed in the range of 0.0500–100 μg L^?1 for TCS, 0.0250–50.0 μg L^?1 for TCC, and 0.500–100 μg L^?1 for M-TCS, respectively, with correlation coefficients (r²) > 0.9945. The limits of detection (LODs) ranged from 45.1 to 236 ng L^?1. TCS in domestic waters was detected with the concentration of 2.08 μg L^?1. The spiked recoveries of three target compounds in river water, irrigating water, reclaimed water and domestic water samples were achieved in the range of 96.4–121%, 64.3–84.9%, 77.2–115% and 75.5–106%, respectively. As a result, this method can be successfully applied for the rapid and convenient determination of TCS, TCC and M-TCS in real water samples.     

Direct electrochemistry of single-stranded DNA on an ionic liquid modified carbon paste electrode

Electrochemical oxidation of thermally denatured single-stranded DNA (ssDNA) was studied on a room temperature ionic liquid N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (IL-CPE). A distinct oxidation peak appeared at +0.772 V (vs. SCE) on the IL-CPE after preconcentration of ssDNA at +0.35 V for 160 s in pH 7.0 phosphate buffer solution (PBS), which was attributed to the oxidation of guanine residue on the ssDNA molecular structure. The results showed an apparent negative shift of the oxidation peak potential and a great enhancement of the oxidation peak current on the IL-CPE compared with that of CPE. The electrochemical parameters of ssDNA on the IL-CPE were further calculated. Under the selected conditions, a linear calibration curve for ssDNA detection was obtained in the concentration range from 10.0 to 110.0 μg mL⁻¹ with the detection limit of 1.5 μg mL⁻¹(3σ).     

Macroporous Co3O4 platelets with excellent rate capability as anodes for lithium ion batteries

This paper reports the microwave-assisted synthesis of Co₃O₄ nanomaterials with different morphologies including nanoparticles, rod-like nanoclusters and macroporous platelets. The new macroporous platelet-like Co₃O₄ morphology was found to be the best suitable for reversible lithium storage properties. It displayed superior cycling performances than nanoparticles and rod-like nanoclusters. More interestingly, excellent high rate capabilities (811 mAh g^?1 at 1780 mA g^?1 and 746 mAh g^?1 at 4450 mA g^?1) were observed for macroporous Co₃O₄ platelet. The good electrochemical performance could be attributed to the unique macroporous platelet structure of Co₃O₄ materials.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

An efficient upconversion luminescence energy transfer system for determination of trace amounts of nitrite based on NaYF4:Yb3+, Er3+ as donor

Based on NaYF₄:Yb³⁺, Er³⁺ upconversion nanocrystals as donor and 4-((4-(2-aminoethylamino)naphthalen-1-yl)diazenyl) benzenesulfonic acid dihydrochloride (ANDBS) as acceptor, an efficient luminescence energy transfer (LET) system was developed for selective and sensitive determination of trace amounts of nitrite. Based on Griess Reaction, ANDBS was generated by the quantitative reaction of nitrite, sulfanilamide and N-(1-naphtyl)-ethylenediamine dihydrochloride (N1NED). The degree of the overlaps between the emission spectrum of NaYF₄:Yb³⁺, Er³⁺ and the absorption spectrum of ANDBS were effective for luminescence energy transfer. Under the optimal condition, the upconversion luminescence quenching of NaYF₄:Yb³⁺, Er³⁺ was in proportion to the trace amounts of nitrite. The detection limit for nitrite achieved is 0.0046 μg mL^?1 and the system shows high sensitivity towards nitrite at 0.008000–0.2500 μg mL^?1 range.     

Column solid phase extraction and determination of ultra-trace Au,Pd and Pt in environmental and geological samples

A new sorbent based on cysteine modified silica gel (SiG-cys) was prepared and studied for preconcentration and separation of noble metals Au(III), Pd(II), Pt(II), Pt(IV). Its extraction efficiency was examined by batch and column solid phase extraction procedures. Laboratory experiments performed showed that sorbent is characterized with high selectivity, permiting quantitative sorption (93–97%) of noble metals Au, Pd and Pt from acidic media 0.1–2 mol L^? 1 HCl and unsignificant sorption (less than 2%) for common base metals like Cu, Fe, Mn and Zn. The analytes retained on the sorbent are effectively eluted with 0.1 mol L^? 1 thiourea in 0.1 mol L^? 1 HCl and measured by ETAAS or ICP OES under optimal instrumental parameters. The sorbent showed high mechanical and chemical stability and extraction efficiency was not changed after 500 cycles of sorption/desorption. The sorbent was successfully applied in analyticals procedures for preconcentration and determination of Au, Pd and Pt in geological and soil samples. Detection limits (3σ criteria) achieved, depending on the instrumental methods used are: ETAAS (0.005 μg L^? 1 for Au in river and sea water, 0.002 μg g^? 1 for Au in copper ore and copper concentrate); ICP OES (0.03 μg L^? 1 for Pd and 0.06 μg L^? 1 for Pt in river and sea water, 0.006 μg g^? 1 for Pd in copper ore and copper concentrate and 0.002 μg g^? 1 for soluble Pt in soil). The accuracy of the procedures developed was confirmed by added/found method for sea and river water; by the analysis of national certified materials (copper ore and copper concentrate for Au and Pd) and by determination of the sum of soluble Pt(II) + Pt(IV) in spiked soil samples.