Bifunctional sensor of nitric oxide and oxygen based on hematite nanotubes embedded in chitosan matrix

A novel hybrid bifunctional sensing platform for simultaneous determination of NO and O₂ has been developed, whereby hematite nanotubes are immobilized into the chitosan matrix onto a gold electrode (labeled as HeNTs-Chi/Au). The HeNTs distributed in porous-structured chitosan matrix not only offer abundant active sites for bifunctional sensing of NO and O₂, but also facilitate oxidation of NO and reduction of O₂ dramatically. Straight calibration curves are achieved in analyte concentration ranges of 5.0 × 10⁻⁸ to 1.25 × 10⁻⁶ mol L⁻¹ for NO and 2.5 × 10⁻⁷ to 6.0 × 10⁻⁶ mol L⁻¹ for O₂. Also, the detection limits are low of 8.0 × 10⁻⁹ mol L⁻¹ for NO and 5.0 × 10⁻⁸ mol L⁻¹ for O₂. Such an efficient bifunctional sensor for NO and O₂ offers great potential in quantitation of NO levels in biological and medical systems, since NO level is highly regulated by various reactive oxygen species.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

Ionic studies of sodium alginate isolated from Sargassum terrarium (brown algea) karachi coast with 2,1-electrolyte

Physical and chemical analysis of the polysaccharide isolated from Sargassum Terarrium (brown algae) of Karachi coast showed characteristics of the sodium alginate. Optical rotations and sulphated ash content were found and FTIR spectra showed a sharp and strong absorption band at 1600 cm^?1 representing carboxylate ion which conforms high uronic acid content of the product. The viscosities of aqueous 0.1% sodium alginate solution were measured in the presence of copper II chloride (CuCl₂). The viscosities were found to be increased with the increase in the concentration of electrolyte. Viscosities were also found affected with temperature. ‘A’ and ‘B’ coefficients of Jones–Dole equation were evaluated. The increase in positive values of ‘B’ coefficient with the rise of temperature led to conclusion that given electrolyte in 0.1% aqueous sodium alginate solution behaves as structure maker. Thermodynamic parameters regarding to activated state like energy of activation E_η, change in free energy of activation ΔG_η and change of entropy of activation ΔS_η were also evaluated. Straight-line plots of log η versus 1/T observed with positive slopes show the effect of temperature on the viscosities of solutions. Energy of activation (E_η) was found to be decreased with the rise of temperature. Change in free energy of activation (ΔG_η) was also found to be increased with increase in concentrations of electrolyte and also with rise of temperature. The values of change in entropy of activation (ΔS_η) were also calculated. Negative values of ΔS_η were found to be increased with increase in concentration of electrolyte and also with rise of temperature.     

Viscometric studies on saccharides in aqueous magnesium chloride solutions at T = (288.15 to 318.15) K

The viscosity B-coefficients of mono-, di-, tri-saccharides and the derivatives (methyl glycosides) in m_B = (0.5, 1.0, 2.0, and 3.0) mol · kg⁻¹ aqueous solutions of magnesium chloride have been determined from viscosity data using the Jones–Dole equation at T = (288.15, 298.15, 308.15, and 318.15) K. The viscosity B-coefficients of transfer (Δ_tB), the temperature derivatives of B-coefficients (dB/dT), pair and triplet viscometric interaction coefficients (η_AB, η_ABB) have been determined. The viscosity B-coefficients data of systems studied in water have been reported earlier. The results have been interpreted in light of the solute–solute and solute–solvent interactions occurring in these systems. The comparison of results has been made with those reported in the presence of potassium chloride, ammonium sulphate, and sodium sulphate.     

Rheological properties of wheat gliadins in aqueous propanol

Rheological properties of wheat gliadins in 50%(V/V) aqueous propanol were carried out as a function of gliadin concentration c and temperature.The solutions at 20 g L 1 to 200 g L 1 behave as Newtonian fluids with an flow activation energy of 23.5 27.3 kJ mol 1.Intrinsic viscosity [η] and Huggins constant k H are determined according to Huggins plot at c ≤ 120 g L 1.The results reveal that gliadins are not spherical shaped and the molecular size tends to increase with temperature due to improved solvation.     

The effect of sodium benzoate and sodium 4-(phenylamino)benzenesulfonate on the corrosion behavior of low carbon steel

Abstract  

The effect of sodium benzoate (SB) and sodium 4-(phenylamino)benzenesulfonate (SPABS) on the corrosion behavior of low carbon steel has been investigated using gravimetric method in the temperature range of 30–80 °C, velocity range of 1.44–2.02 m s⁻¹ and concentration range of 6.94 × 10⁻⁴ to 4.16 × 10⁻³ mol dm⁻³ SB and 3.69 × 10⁻⁴ to 2.06 × 10⁻³ mol dm⁻³ SPABS. Optimization of temperature, fluid velocity, and inhibitors concentration has been made. The obtained results indicate that the inhibition efficiency (w _IE %) at 1.56 m s⁻¹ is not in excess of 81.5% at 4.16 × 10⁻³ mol dm⁻³ SB and 84.4% at 2.06 × 10⁻³ mol dm⁻³ SPABS. The inhibitive performance of these compounds showed an improvement with increasing concentration up to critical values of SB and SPABS; beyond these concentrations no further effectiveness is observed. These inhibitors retard the anodic dissolution of low carbon steel by protective layer bonding on the metal surface. The adsorption of SB and SPABS on the low carbon steel surface was found to obey the Freundlich isotherm model. The FT-IR spectroscopy was used to analyze the surface adsorbed film.     

Microviscosity dependence of the Raman band shape of methyl-isobutyl ketone

The Raman band shape analysis of the CO stretching mode of vibration of methyl-isobutyl ketone in solution phase reveals that macroscopic consideration of hydrodynamic force is not sufficient to correlate the vibrational relaxation rate (τ_v⁻¹) with parameter ƒ(ϱ, η, n), involving dynamic viscosity (η). The band shape analysis was therefore attempted taking the microscopic parameter, microviscosity (η_m) into account through a modified parameter ƒ_m. The correlation of τ_v⁻¹ with ƒ_m is reported.     

The effect of sodium benzoate and sodium 4-(phenylamino)benzenesulfonate on the corrosion behavior of low carbon steel

Abstract  The effect of sodium benzoate (SB) and sodium 4-(phenylamino)benzenesulfonate (SPABS) on the corrosion behavior of low carbon steel has been investigated using gravimetric method in the temperature range of 30–80 °C, velocity range of 1.44–2.02 m s⁻¹ and concentration range of 6.94 × 10⁻⁴ to 4.16 × 10⁻³ mol dm⁻³ SB and 3.69 × 10⁻⁴ to 2.06 × 10⁻³ mol dm⁻³ SPABS. Optimization of temperature, fluid velocity, and inhibitors concentration has been made. The obtained results indicate that the inhibition efficiency (w _IE %) at 1.56 m s⁻¹ is not in excess of 81.5% at 4.16 × 10⁻³ mol dm⁻³ SB and 84.4% at 2.06 × 10⁻³ mol dm⁻³ SPABS. The inhibitive performance of these compounds showed an improvement with increasing concentration up to critical values of SB and SPABS; beyond these concentrations no further effectiveness is observed. These inhibitors retard the anodic dissolution of low carbon steel by protective layer bonding on the metal surface. The adsorption of SB and SPABS on the low carbon steel surface was found to obey the Freundlich isotherm model. The FT-IR spectroscopy was used to analyze the surface adsorbed film. Graphical abstract  Low carbon steel corrosion in presence of sodium benzoate and sodium 4-(phenylamino)benzenesulfonate has been investigated. The adsorption mechanism obeyed Freundlich isotherm model. FT-IR was used to analyze the adsorbed film      

One-step fabrication of chitosan–hematite nanotubes composite film and its biosensing for hydrogen peroxide

This work reports on a novel chitosan–hematite nanotubes composite film on a gold foil by a simple one-step electrodeposition method. The hybrid chitosan–hematite nanotubes (Chi–HeNTs) film exhibits strong electrocatalytic reduction activity for H₂O₂. Interestingly, two electrocatalytic reduction peaks are observed at −0.24 and −0.56 V (vs SCE), respectively, one controlled by surface wave and the other controlled by diffusion process. The Chi–HeNTs/Au electrode shows a linear response to H₂O₂ concentration ranging from 1 × 10⁻⁶ to 1.6 × 10⁻⁵ mol L⁻¹ with a detection limit of 5 × 10⁻⁸ mol L⁻¹ and a sensitivity as high as 1859 μA μM⁻¹ cm⁻².     

Application of molecularly imprinted polymer solid-phase extraction for salivary cotinine

A method constituted by molecularly imprinted solid-phase extraction (MISPE) with high-performance liquid chromatography coupled to diode array detector (HPLC-DAD) was developed for cotinine analysis in saliva samples. For this purpose, the separation was carried out with a C18 reversed-phase column at 20 °C. The mobile phase which was composed of a mixture of 09:91 (v/v) acetonitrile/phosphate buffer, pH 6.3, was delivered with isocratic flow rate at 1.4 mL min⁻¹. Employing MISPE, the best conditions were achieved with 1.5 mL of saliva plus 1.5 mL of 0.1 mol L⁻¹ of acetate buffer, pH 5.5, which were then passed through a cartridge previously conditioned with 2 mL acetonitrile, 2 mL methanol, and 2 mL of 0.1 mol L⁻¹ sodium acetate buffer, pH 5.5. The washing was carried out with 1 mL deionized water, 1 mL of 0.1 mol L⁻¹ sodium hydroxide, and 1 mL hexane; finally; the cotinine elution was carried out with 3 mL methanol/water (97.5: 2.5, v/v). Linearity ranged from 30 to 500 ng mL⁻¹ with r > 0.99. Intra-assay, interassay precision, and accuracy ranged from 3.1% to 10.1%, 5.2% to 15.9%, and 99.22% to 111.17%, respectively. The detection and quantification limits were 10 and 30 ng mL⁻¹, respectively. This investigation has provided a reliable method for routine cotinine determination in saliva, and it is an important tool for monitoring cigarette smoke exposure in smokers. The method was applied in five smokers’ samples who consumed around five to 20 cigarettes per day and the values of cotinine in saliva were from 66.7 to 316.16 ng mL⁻¹.     

New thioether–dithiolate complexes of Cp1Ir and some reactivity features

The reaction of [Cp1IrCl₂]₂ (Cp* = η⁵ − C₅Me₅) with the tridentate 3-thiapentane-1,5-dithiolate ligand, S(CH₂CH₂S⁻)₂ (tpdt), led to the formation of [Cp1Ir(η³ − tpdt)] (1) in 81% isolated yield. Subsequent reactions of 1 with [Cp1IrCl₂]₂ in 2:1 and 1:1 molar equiv ratios resulted in the formation of [Cp1Ir(μ − η²:η³ − tpdt)Cp1IrCl][PF₆] (2) and [Cp1Irμ − η²:η³ − tpdt)Cp1IrCl][Cp1IrCl₃] (3) in 86 and 79% yields, respectively, based on 1, whereas the reactions of 1 with [(COD)IrCl]₂ (COD = 1,5-cyclooctadiene) in 2:1 and 1:1 molar equiv ratios resulted in the formation of the homo-bimetallic derivatives Cp1Ir(μ − η¹:η³ − tpdt)(COD)IrCl (4) (92% yield) and [Cp1Ir(μ − η²:η³ − tpdt)(COD)Ir] [(COD)IrCl₂] (5) (82% yield). Reactions between 1 and [(COD)RhCl]₂, yielded the hetero-bimetallic derivatives Cp1Ir(μ − η¹:η³ − tpdt)(COD)RhCl (6) and [Cp1Ir(μ − η²:η³ − tpdt)(COD)Rh][(COD)RhCl₂] (7), in 92 and 93% yields, respectively. The reaction of 1 with methyl iodide gave mono-methylated derivative [Cp1Ir(η³-C₄H₈S₃Me)]I (8) (93% yield). All these compounds have been comprehensively characterized.     

Adduct formation of [(η7-C7H7)Hf(η5-C5H5)] with isocyanides,phosphines and N-heterocyclic carbenes: An experimental and theoretical study

The reactions of [(η⁷-C₇H₇)Hf(η⁵-C₅H₅)] (1b) with the two-electron donor ligands tert-butyl isocyanide (tBuNC), 2,6-dimethylphenyl isocyanide (XyNC), 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe) and trimethylphosphine (PMe₃) are reported. The 1:1 complexes [(η⁷-C₇H₇)Hf(η⁵-C₅H₅)L] (2b, L = tBuNC; 3b, L = XyNC; 4b, L = IMe, 5b, L = PMe₃) have been isolated in crystalline form, and their molecular structures have been determined by X-ray diffraction analyses. The stabilities of these hafnium complexes were probed via spectroscopic and theoretical methods, and the results were compared to those previously reported for the corresponding zirconium complexes derived from [(η⁷-C₇H₇)Zr(η⁵-C₅H₅)] (1a). The X-ray crystal structure of the PMe₃ adduct [(η⁷-C₇H₇)Zr(η⁵-C₅H₅)(PMe₃)] (5a) was also established.     

A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin in palladium nanoparticles/graphene-chitosan nanocomposite film

Thermally two-dimensional lattice graphene (GR) and biocompatibility chitosan (CS) act as a suitable support for the deposition of palladium nanoparticles (PdNPs). A novel hydrogen peroxide (H₂O₂) biosensor based on immobilization of hemoglobin (Hb) in thin film of CS containing GR and PdNPs was developed. The surface morphologies of a set of representative membranes were characterized by means of scanning electron microscopy and showed that the PdNPs are of a sphere shape and an average diameter of 50 nm. Under the optimal conditions, the immobilized Hb showed fast and excellent electrocatalytic activity to H₂O₂ with a small Michaelis–Menten constant of 16 μmol L⁻¹, a linear range from 2.0 × 10⁻⁶ to 1.1 × 10⁻³ mol L⁻¹, and a detection limit of 6.6 × 10⁻⁷ mol L⁻¹. The biosensor also exhibited other advantages, good reproducibility, and long-term stability, and PdNPs/GR–CS nanocomposites film would be a promising material in the preparation of third generation biosensor.     

Electro-catalytic effect of Al2O3 supported onto activated carbon in oxidizing phenol at graphite electrode

In this work, the electro-catalytic oxidation of phenol was studied using the aluminum oxide supported onto activated carbon (Al₂O₃/AC). The later was successfully prepared by impregnating aluminum particles in the activated carbon (AC) using heat treatment. Al₂O₃/AC was characterized by X-ray diffraction (XRD) and infrared spectroscopy (IR). The electro-catalytic performance of the Al₂O₃/AC for phenol oxidation was studied using cyclic voltammetry (CV), chronoamperometry, linear sweep voltammetry polarization, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV) in 0.1 mol L^?1 Na₂SO₄. It has been shown that the proposed catalyst exhibits remarkably an electro-catalytic performance toward phenol oxidation. Moreover, the oxidation peak currents are linearly dependent on the concentration of phenol in the wide ranges from 1.0 × 10^?3 mol L^?1 to 1.0 × 10^?4 mol L^?1 and 8.0 × 10^?5 mol L^?1 to 1.0 × 10^?6 mol L^?1 with a detection limit of 1.51 × 10^?7 mol L^?1 (signal (S) to noise (N) ratio, S/N = 3) and response time of 3 min. The possible interferences were evaluated in 1.0 × 10^?5 mol L^?1 of phenol. The proposed catalyst also indicated suitable repeatability and stability. Moreover, the proposed Al₂O₃/AC–CPE has been successfully applied for the phenol analysis in natural waters and olive oil samples with good recoveries.     

Hybrid graphene oxide/DAB-Am-16 dendrimer: Preparation,characterization chemical reactivity and their electrocatalytic detection of l-Dopamine

Graphene oxide (GO) was chemically modified with a poly(propylene)imine Generation 3.0 dendrimer (DAB-Am-16). The characterization, structure and properties of hybrid graphene oxide/DAB-Am-16 dendrimer was studied by Raman spectroscopy, Fourier-Transforming Infrared Spectroscopy (FT-IR), X-Ray Photoelectron Spectroscopic (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Thermogravimetric analysis. After functionalized the hybrid material (GOD) can interact with copper and subsequently with hexacyanoferrate (III) ions (GODHCu). The GODHCu incorporated into a graphite paste electrode (20% w/w) was applied to an electrocatalytic detection of neurotransmitter l-dopamine using differential pulse voltammetry. The analytical curve showed a linear response in the concentration range from 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹ with a corresponding equation Y(A) = 1.706 × 10⁻⁵ + 0.862 [l-dopamine] and a correlation coefficient r² = 0.998. The detection limit was 6.36 × 10⁻⁷ mol L⁻¹ with a relative standard deviation of ±4% (n = 3) and an amperometric sensitivity of 0.862 A/mol L⁻¹.     

O-atom transfer biomimetic oxidation of benzoin in the presence of monooxomolybdenum(IV) thiolate complexes

Novel catalytically active monooxomolybdenum(IV) species containing four thiolate ligands obtainable in solution by NaBH₄ reduction of [Mo^vO(SC₆H₅)₄]⁻, [Mo^vO(Z-cys-Val-OMe)₄]⁻, (Z=benzyloxycarbonyl), or [Mo^vO(S₂C₆H₄)₂]⁻ perform the pyridine-N-oxide oxidation of benzoin in N,N-dimethylformamide at 30 °C. The order of catalytic activity is [Mo^vO(Z-cys-Val-OMe)₄]⁻ > [Mo^vO(S₂C₆H₄)₂]⁻ > [Mo^vO(SC₆H₅)₄]⁻ ([benzoin]/[oxidant]/[catalyst]= 20/20/1), while the oxidation by air under the same catalytic conditions gives a different order, [Mo^vO(Z-cys-Val-OMe)₄]⁻> [Mo^vO(SC₆H₅)₄]⁻ >[Mo^vO(S₂C₆H₄)₂]⁻. During the catalytic cycle in the amine-N-oxide oxidation, two intermediate species, [Mo^IVOL₄]²⁻ and [Mo^VIO₂L₄]²⁻, were detected by ¹H NMR, while in the air oxidation an unidentified Mo(VT) species is involved.     

In situ emulsification microextraction using a dicationic ionic liquid followed by magnetic assisted physisorption for determination of lead prior to micro-sampling flame atomic absorption spectrometry

For the first time, a simple and efficient in situ emulsification microextraction method using a dicationic ionic liquid followed by magnetic assisted physisorption was presented to determine trace amounts of lead. In this method, 400 μL of 1.0 mol L⁻¹ lithium bis (trifluoromethylsulfonyl) imide aqueous solution, Li[NTf₂], was added into the sample solution containing 100 μL of 1.0 mol L⁻¹ 1,3-(propyl-1,3-diyl) bis (3-methylimidazolium) chloride, [pbmim]Cl₂, to form a water immiscible ionic liquid, [pbmim][NTf₂]₂. This new in situ formed dicationic ionic liquid was applied as the acceptor phase to extract the lead-ammonium pyrrolidinedithiocarbamate (Pb-APDC) complexes from the sample solution. Subsequently, 30 mg of Fe₃O₄ magnetic nanoparticles (MNPs) were added into the sample solution to collect the fine droplets of [pbmim][NTf₂]₂, physisorptively. Finally, MNPs were eluted by acetonitrile, separated by an external magnetic field and the obtained eluent was subjected to micro-sampling flame atomic absorption spectrometry (FAAS) for further analysis. Comparing with other microextraction methods, no special devices and centrifugation step are required. Parameters influencing the extraction efficiency such as extraction time, pH, concentration of chelating agent, amount of MNPs and coexisting interferences were studied. Under the optimized conditions, this method showed high extraction recovery of 93% with low LOD of 0.7 μg L⁻¹. Good linearity was obtained in the range of 2.5–150 μg L⁻¹ with determination coefficient (r²) of 0.9921. Relative standard deviation (RSD%) for seven repeated measurements at the concentration of 10 μg L⁻¹ was 4.1%. Finally, this method was successfully applied for determination of lead in some water and plant samples.     

Interactions of some amino acids and glycine peptides with aqueous sodium dodecyl sulfate and cetyltrimethylammonium bromide at T=298.15 K: a volumetric approach

The apparent molar volumes V_φ of glycine, alanine, valine, leucine, and lysine have been determined in aqueous solutions of 0.05, 0.5, 1.0 mol · kg⁻¹ sodium dodecyl sulfate (SDS) and 1.0 mol · kg⁻¹ cetyltrimethylammonium bromide (CTAB) by density measurements at T=298.15 K. The apparent molar volumes have also been determined for diglycine and triglycine in 1 mol · kg⁻¹ SDS and CTAB solutions. These data have been used to calculate the infinite dilution apparent molar volumes V₂⁰ for the amino acids and peptides in aqueous SDS and CTAB and the standard partial molar volumes of transfer (Δ_trV_2,m⁰) of the amino acids and peptides to these aqueous surfactant solutions. The linear correlation of V₂⁰ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH₃⁺, COO⁻), CH₂ group and other alkyl chains of the amino acids to V₂⁰. The results on the partial molar volumes of transfer from water to aqueous SDS and CTAB have been interpreted in terms of ion–ion, ion–polar and hydrophobic–hydrophobic group interactions. The volume of transfer data suggests that ion–ion or ion–hydrophilic group interactions of the amino acids and peptides are stronger with SDS compared to those with CTAB. Comparison of the hydration numbers of amino acids calculated in the present studies with those in other solvents from literature shows that these numbers are almost the same at 1 mol · kg⁻¹ level of the cosolvent/cosolute. Increasing molality of the cosolvent/cosolute beyond 1 mol · kg⁻¹ lowers the hydration number of the amino acids due to increased interactions with the solvent and reduced electrostriction.     

Viability of Using Glycerin as a Co-substrate in Anaerobic Digestion of Sugarcane Stillage (Vinasse): Effect of Diversified Operational Strategies

Vinasse, from sugar and ethanol production, stands out as one of the most problematic agroindustry wastes due to its high chemical oxygen demand, large production volume, and recalcitrant compounds. Therefore, the viability of using glycerin as a co-substrate in vinasse anaerobic digestion was tested, to increase process efficiency and biogas productivity. The effect of feeding strategy, influent concentration, cycle length, and temperature were assessed to optimize methane production. Glycerin (1.53% v/v) proved to be a good co-substrate since it increased the overall methane production in co-digestion assays. CH₄ productivity enhanced exponentially as influent concentration increased, but when temperature was increased to 35 °C, biogas production was impaired. The highest methane productivity and yield were achieved using fed-batch mode, at 30 °C and at an organic loading rate of 10.1 kg COD m⁻³ day⁻¹: 139.32 mol CH₄ m⁻³ day⁻¹, 13.86 mol CH₄ kg COD_applied, and 15.30 mol CH₄ kg COD_removed. Methane was predominantly produced through the hydrogenotrophic route. In order to treat all the vinasse produced by a mid-size sugar and ethanol plant, nine reactors with 7263.4 m³ each would be needed. The energy generated by burning the biogas in boilers would reach approximately 92,000 MW h per season and could save up to US$ 240,000.00 per month in diesel oil demand.

     

Carrier-mediated hollow fiber liquid-phase microextraction for preconcentration followed by spectrophotometric determination of amoxicillin

Preconcentration followed by ultraviolet spectrophotometric determination of amoxicillin (Amox) in pharmaceuticals and water samples by using a three-phase hollow fiber microextraction technique based on carrier-mediated transport has been presented. Amox was extracted from an aqueous solution (source phase) at pH 9.0 into 1-octanol containing 5% (w/v) Aliquat-336 impregnated in the pores of a hollow fiber. It was then back-extracted into NaCl solution (pH = 4.0) which was already positioned as the receiving phase inside the lumen of the hollow fiber. The extraction took place due to the concentration gradient of the counterion between the source and the receiving phases. Under the optimized conditions, an enrichment factor of 240 and a limit of detection of 0.2 μmol L⁻¹ were obtained. The calibration curve was linear (R² = 0.9967) in the concentration range of 0.5–10.0 µmol L⁻¹ Amox. The interday relative standard deviation (n = 9) and the intraday relative standard deviation (n = 3) for 1.0 × 10⁻⁶ mol L⁻¹ Amox solution were 7.3 and 6.4%, respectively.