Phosphate Solution pH Research Articles

Determination of Free Chemical Potential for Finasteride Diffusion through SDS Micelle Suggested as Alternative Living Membrane System

Abstract: As an alternative living cell membrane, sodium dodecyl sulfide (SDS) has been investigated at this study, spectroscopic assessment of Finasteride diffusion through the alternate model of the cell membrane in two distinct polar solutions, buffer phosphate solution pH 7.4 and Cyclohexane(Non-polar solution), has been studied. Finasteride in buffer phosphate solution showed a definite ?max at 253 nm, which was consistent with the default values. The results also reveal that the non-polar medium has a lower attenuation coefficient and a shorter maximum wavelength than the polar medium. The pH 7.4 finasteride solution demonstrated remarkable stability over time.
 Diffusion rate of Finasteride was investigated using Sodium Dodecyl Sulfate (SDS) as an alternative cell membrane model. The chemical potential was determined to be - 6294.76 J mol-1, showing the spontaneity of the compound's diffusion process.
 The results indicated that Finasteride may diffuse (at a rate constant of 51.11 min-1) from the aqueous media and other identified components to the inner micelle; the equilibrium constant for diffusion was calculated to be 11.5.
 Keywords: Finasteride, Diffusion, Chemical potential, SDS, Alternative model, Cell membrane.

Screen-Printed Sensor Based on Potentiometric Transduction for Free Bilirubin Detection as a Biomarker for Hyperbilirubinemia Diagnosis

Novel reliable and cost-effective potentiometric screen-printed sensors for free bilirubin (BR) detection were presented. The sensors were fabricated using ordered mesoporous carbon (OMC) as an ion-to-electron transducer. The ion-association complex [Ni(bphen)3]2+[BR]2− was utilized as a sensory recognition material in the plasticized Polyvinyl Chloride (PVC) membrane. The membrane was drop-casted on the OMC layer, which is attached on a carbon conductor (2-mm diameter). In a 50 mM phosphate solution of pH 8.5, the electrodes offered a Nernstian slope of −26.8 ± 1.1 (r2 = 0.9997) mV/decade with a range of linearity 1.0 × 10−6–1 × 10−2 M towards free bilirubin with a detection limit 8.8 × 10−7 M (0.52 µg/mL). The presented sensors offered good features in terms of reliability, ease of design, high potential stability, high specificity and good accuracy and precision. Chronopotentiometric and electrochemical impedance spectrometric measurements were used for short-term potential stability and interfacial capacitance calculations. The sensors were used for the determination of free bilirubin in biological fluids. The data obtained are fairly well consistent with those obtained by the reference spectophotometric method. Based on the interaction of free BR with albumin (1:1), the sensors were also utilized for the assessment of albumin in human serum.

Revisiting the Mechanism of Hydrolysis of Betanin.

Betanin (betanidin 5-O-β-D-glucoside) is a water-soluble plant pigment used as a color additive in food, drugs and cosmetic products. Despite its sensitivity to light and heat, betanin maintains appreciable tinctorial strength in low acidic and neutral conditions, where the color of other plant pigments, such as anthocyanins, quickly fades. However, betanin is an iminium natural product that experiences acid- and base-catalyzed hydrolysis to form the fairly stable betalamic acid and cyclo-DOPA-5-O-β-D-glucoside. Here, we show that the decomposition of betanin in aqueous phosphate solution pH 2-11 is subject to general base catalysis by hydrogen phosphate ion and intramolecular general acid and base catalysis, providing new insights on the mechanism of betanin hydrolysis. UV/Vis absorption spectrophotometry, 1 H NMR spectroscopy and mass spectrometry were used to investigate product formation. Furthermore, theoretical calculations support the hypothesis that the nitrogen atom of the tetrahydropyridine ring of betanin is doubly protonated, as observed for structurally simpler amino dicarboxylic acids. Our results contribute to the study of betanin and other pigments belonging to the class of betalains and to deepen the knowledge on the chemical properties of imino acids as well as on iminium-catalyzed modifications of carbonyl compounds in water.

Voltammetric growth of tin oxides in borate solution of pH 8.7

<p class="PaperAbstract"><span lang="EN-US">Voltammetry has been employed to study the growth of tin oxides in buffer solution of 0.3 mol L<sup>-1</sup> H<sub>3</sub>BO<sub>3</sub> + 0.15 mol L<sup>-1</sup> Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>·10H<sub>2</sub>O (pH 8.7). Voltammetric data were compared with the results of tin in a phosphate solution of pH 8.7, presented in the previous work, in order to study the influence of these anions on the growth of tin oxides. The thicknesses of grown oxides were determined using ex-situ ellipsometric technique and the volume per charge unity of the film, V<sub>f</sub>, was calculated for different charge densities of the film. The results showed that less dense films were obtained at higher sweep rates. Tin oxide films grown in phosphate solution at 2 mV s<sup>-1</sup> were denser than those grown in borate solution at the same sweep rate. The kinetic parameters, determined applying the ohmic model, showed that there are no significant differences between the kinetics at the metal/film interface of tin in borate and tin in phosphate solutions. Despite these facts, the ionic specific resistivity for oxide film growth in borate solution were significantly higher than in phosphate solution. This result indicates that incorporation of anions occurs during the growth of the films.</span></p>

Ellipsometric measurement of thickness of tin oxides grown by voltammetry in phosphate solution of pH 8.7

<p class="PaperAbstract"><span lang="EN-US">The voltammetry induced growth of tin oxides on tin in the buffer solution of 0.18 mol L<sup>-1</sup> Na<sub>2</sub>H<sub>2</sub>PO<sub>4</sub> and 0.18 mol L<sup>-1</sup> KH<sub>2</sub>PO<sub>4</sub> (pH 8.7) has been studied. Ex-situ ellipsometric mea­surements were made in an order to determine thicknesses of the grown oxides. From these results the film volume per charge unit, </span><span lang="EN-US">V</span><sub><span lang="EN-US">f</span></sub><span lang="EN-US">, was calculated for different charge den­sities of the film. This parameter was used to calculate the variable ionic resistivity of the film, </span><span lang="EN-US">ρ</span><sub><span lang="EN-US">f</span></sub><span lang="EN-US">, considered by the Ohmic model for the case of voltammetric growth of oxides on metals having a previously existing continuous film. Tin oxide films grown at 2 mV s<sup>-1</sup> showed to be less dense for values of charge density below 50 C m<sup>-2</sup>, having </span><span lang="EN-US">V</span><sub><span lang="EN-US">f</span></sub><span lang="EN-US"> near <br /> 5.7x10<sup>-10</sup> m<sup>3</sup> C<sup>-1</sup>. For higher values of charge density, tin oxide films become denser, having </span><span lang="EN-US">V</span><sub><span lang="EN-US">f</span></sub><span lang="EN-US"> near 0.5x10<sup>-10</sup> m<sup>3</sup> C<sup>-1</sup>. The calculated values of the variable ionic resistivity of the film during voltammetric growth showed that </span><span lang="EN-US">ρ</span><sub><span lang="EN-US">f</span></sub><span lang="EN-US"> passes through a minimum (justifying the maximum in current densities). This behavior was also found by other authors in the cases of Zn, Nb, Ni and galvanized steel sheets.</span></p>

Preparation of layered double hydroxides using boron mud and red mud industrial wastes and adsorption mechanism to phosphate

AbstractPhosphate removal was important for wastewater treatment, and adsorption was an efficient treatment process. In this study, the layered double hydroxide adsorbent (BR‐LDH), which was prepared under alkali conditions using industrial residues boron mud and red mud, was used to adsorb the phosphate. The prepared BR‐LDH was characterised by X‐ray diffraction, Scanning electron microscopy, Energy‐dispersive X‐ray spectroscopy, and Thermo‐gravimetric‐differential thermal analysis. Adsorption experiments were carried out as a function of dosage, contact time, temperature and initial pH of phosphate solution. The removal ratio of phosphate onto OBR‐LDH reached 93%. The adsorption data showed a good compliance with the pseudo‐second‐order kinetic model. In addition, the mineral composition, the functional groups, the valence of elements and zeta potentials of OBR‐LDH before and after adsorption were used to analyse the adsorption mechanism. The result of real wastewater suggested that OBR‐LDH was excellent adsorbent for phosphorus removal from actual wastewater.

A three phase hollow fiber liquid-phase microextraction for quantification of lamotrigine in plasma of epileptic patients by capillary electrophoresis.

A three phase hollow fiber liquid-phase microextraction technique combined with capillary electrophoresis was developed to quantify lamotrigine (LTG) in plasma samples. The analyte was extracted from 4.0 mL of a basic donor phase (composed of 0.5 mL of plasma and 3.5 mL of sodium phosphate solution pH 9.0) through a supported liquid membrane composed of 1-octanol immobilized in the pores of the hollow fiber, and to an acidic acceptor phase (hydrochloric acid solution pH 4.0) placed in the lumen of the fiber. The extraction was carried out for 30 min at 500 rpm. The eletrophoretic analysis was carried out in 130 mmol/L MES buffer, pH 5.0 with a constant voltage of +15 kV and 20°C. Sample injections were performed for 10 s, at a pressure of 0.5 psi. The detection was performed at 214 nm for both LTG and the internal standard lidocaine. Under the optimized conditions, the method showed a limit of quantification of 1.0 μg/mL and was linear over the plasmatic concentration range of 1.0-20.0 μg/mL. Finally, the validated method was applied for the quantification of LTG in plasma samples of epileptic patients.

Calcium phosphate with high specific surface area synthesized by a reverse micro-emulsion method

ABSTRACTA reverse micro-emulsion method has been investigated to control crystal morphology in a nanometer region and to increase specific surface area for calcium phosphate. The nanocrystals with the control of its morphology is a candidate of drug delivery carriers. This study investigated the effects of mixing volume ratios of two surfactants, tween80 (T) and aliquate 336 (A) in kerosene as an oil phase, and pH values in the nano-region on crystalline phases and specific surface area of calcium phosphate synthesized by the reverse micro-emulsion method. A di-ammonium hydrogen phosphate solution including phosphoric acid at pH of 6.3 and a calcium nitrate solution at pH of 5.7 were adjusted, and both the solutions were separately added into the kerosene with the surfactants. Both the emulsions were then mixed at the same volume and the Ca/P ratio of 1.0, and stirred at room temperature for 24 hours. The crystalline phases were dependent on the T amounts; pure DCPD with the specific surface area of 6.7 to 12 m2/g was obtained at the T/A ratio of 4, the mixture of DCPD and DCPA with that of 48 to 162 m2/g was at the ratios of 5 to 8, and a low crystalline HAp with 163 m2/g was at the ratio of 9. These specific surface areas of DCPD (T/A=4) and HAp (T/A=9) were apparently higher than those prepared with a wet method, 7.8 times and 1.8 times respectively. DCPA with 43 m2/g was successfully produced to decrease the pH of phosphate solution at T/A of 9. The change of crystalline phases would be explained as follows; the increase of T amount decreased the micro-emulsion sizes to reduce bulk water to be DCPA, and increased the pH to precipitate HAp nanocrystals.

A Sensitive Voltammetric Determination of Anti-Parkinson Drug Pramipexole Using Titanium Dioxide Nanoparticles Modified Carbon Paste Electrode

In this study, a facile sensor based on TiO2 nanoparticles modified carbon paste electrode was developed for voltammetric determination of pramipexole in pharmaceutical formulations and biological samples. Surface of the fabricated electrode have been characterized using field emission scanning electron microscopy. Under the optimized experimental conditions, the modified electrode was exhibited excellent electrocatalytic activities and a sensitive oxidation peak at 0.9 V in the phosphate solution of pH 5.0 for electrooxidation of pramipexole. The plot of pH vs. Ep generated a slope of 62.5 mV per pH in the pH range of 3.0-13.0 indicating the contribution of an equal number of electrons and protons in the electrode process. A differential pulse voltammetry method was developed in the concentration range of 0.46-100 μmol L-1 with a limit of detection of 0.14 μmol L-1. The proposed method is simple, rapid, and inexpensive and also showed good selectivity and sensitivity toward pramipexole.

Adsorptive removal of phosphate by Mg–Al and Zn–Al layered double hydroxides: Kinetics, isotherms and mechanisms

Phosphate removal is important for the natural water or wastewater treatment, and adsorption is an efficient treatment process. In this study, Mg–Al and Zn–Al layered double hydroxides (LDHs) were synthesized by co-precipitation method at a constant pH of 9–10. The prepared LDHs were characterized by X-ray diffraction (XRD) and BET surface area determination. The XRD patterns showed the characteristic basal reflections of hydrotalcite-like LDH materials. BET surface area of Zn–Al LDH was larger than that of Mg–Al LDH. Adsorption experiments were carried out as a function of LDHs dosage, contact time and initial pH of phosphate solution. The adsorption of phosphate reached equilibrium quickly at about 40min. The experimental data showed a good compliance with the pseudo-second-order kinetic model. The Freundlich and Langmuir models both described the adsorption isotherm data well (R2>0.98). Zeta potential and fourier transform infrared spectroscopy (FTIR) analyses were used to elucidate adsorption mechanisms. The results indicated that phosphate species were adsorbed via electrostatic attraction, ligand exchange and ion exchange. The removal ratio of phosphate onto Zn–Al LDH was higher than Mg–Al LDH and reached 95% respectively, suggesting that Mg–Al and Zn–Al LDHs were excellent adsorbents for phosphorus removal from aqueous solution.

Intercalation of Gastropod Shell Derived Calcium Oxide in Clay and Application in Phosphate Removal from Aqua Medium

The phosphate sorption potential of the layered framework of naturally occurring clay, which acts as a host in the sorption process, was boosted via intercalation of CaO derived from a Gastropod shell (GS). GS was used as precursor for the synthesis of the CaO in the perspective of waste recycling and cost minimization in environmental remediation. The phosphate sorption potential, PZC, and the surface area of raw clay sample were substantially enhanced by the intercalation process. The value of the Langmuir monolayer sorption capacity (qm mg/g) increased from 49.02 to 71.43, PZC values increased from 4.70 to 7.20, and the surface area (m2/g) value increased from 23 to 103 after the intercalation process. The modification caused no change in the clay surficial microstructure but increased the lattice spacing of the clay framework. Increase in phosphate solution pH triggered monotonical reduction in the magnitude of phosphate sorbed while increase in phosphate solution ionic strength and concentration of anionic interferences caused an increase in the amount of phosphate sorbed per gram of sorbent. Phosphate sorption caused no change in the surficial microstructure of either sorbents but the crystallinity of the sorbent was considerably impacted, especially in the raw sample

Determination of phase diagrams and thermoseparation behaviour of aqueous two-phase systems composed of ethylene oxide–propylene oxide random copolymer and potassium phosphate

Abstract The application of aqueous two-phase systems (ATPS) is a cost-effective and simple method of protein separation (including enzymes) from complex systems. The first stage of designing the protein purification process in an ATPS involves the identification of the conditions for the formation of a given extraction system. For this purpose, the conditions for the formation of ATPSs in a thermoseparating EO50PO50 polymer/potassium phosphates system have been studied. Factors determining the ATPS formation comprised: separation temperature (4ºC or 20ºC), phosphate solution pH (6, 7.5 or 9) as well as the concentration of NaCl introduced into the systems (0.085 M, 0.475 M and 0.85 M). ATPS without NaCl were prepared as well. The conditions for the formation of the primary EO50PO50/potassium phosphate ATPS were determined with their phase diagrams. It was observed that with an increase of phosphate pH and NaCl concentration in the system, there was a decrease of the EO50PO50 and phosphate concentrations necessary to form a primary ATPS. After the primary two-phase separation, the top phase (rich in the EO50PO50 polymer) was partitioned from the bottom phase (rich in phosphates). Next, by means of polymer phase thermoseparation, a secondary two-phase system was formed. In the secondary EO50PO50/phosphate ATPS, the bottom phase was formed by the concentrated EO50PO50 polymer (30-80% concentration), while the top phase by a solution composed mainly of water, containing phosphate ions and remains of EO50PO50 polymer (3-7%).

Phosphate adsorption on lanthanum hydroxide-doped activated carbon fiber

A novel adsorbent, lanthanum hydroxide-doped activated carbon fiber (ACF-LaOH), has been prepared by the ultrasound-assisted chemical precipitation method for phosphate removal from waste water. Based on the single-factor method, response surface methodology (RSM) by using a Box–Behnken design (BBD) was applied to assess the mutual interactions and effects between the three factors and the optimized preparation conditions (concentration of La3+ of 0.11mol/L, ultrasonic power at 206W and ultrasonic time of 7.3min). Adsorption kinetics and isothermal adsorption studies showed that the pseudo second-order model and the Langmuir isotherm fitted the experimental data quite well, indicating that the adsorption process was mainly through chemical interactions. At last whereas most importantly, the phosphate adsorption mechanism was investigated by analyzing the scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy and the relationship between the adsorption amount and the pH of phosphate solution. The results demonstrated that ligands exchange, electrostatic interactions and Lewis acid–base interaction were the three main mechanisms for phosphate adsorption. The ligands exchange and electrostatic interactions became weaker, but the Lewis acid–base interaction was strengthened with the increase of pH values giving rise to the decrease of adsorption amount.

RAPID AND SENSITIVE DETERMINATION OF KETOPROFEN IN MICRO-WHOLE BLOOD SAMPLES BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY AND ITS APPLICATION IN A PHARMACOKINETIC STUDY IN RATS

A new simple and sensitive method for determination of ketoprofen in micro-whole blood samples was developed, and its usefulness was demonstrated by the characterization of the oral pharmacokinetics of this drug in rats. Whole blood samples were added with perchloric acid to precipitate proteins, and supernatant was injected into the chromatographic system. Separation of compounds was achieved with a Symmetry C18 column eluted with a mixture of acetonitrile and 0.1 M potassium dihydrogen phosphate solution pH 3.5 (48:52 v/v) as the mobile phase at flow rate of 1.0 mL/min. Detection was carried out by absorbance at 260 nm. Under these conditions the method was linear in the range 0.1–15 µg/mL. In order to demonstrate the usefulness of this method, oral pharmacokinetics of ketoprofen after administration of 1, 3.2, and 10 mg/kg was evaluated in rats. Blood samples were obtained at selected times during 24 hr and successfully analyzed by the method described. It is concluded that the method is suitable for pharmacokinetic studies of ketoprofen using small volume of sample.

Liquid chromatographic analysis of oxytocin and its related substances

A selective gradient liquid chromatographic (LC) method for the determination of oxytocin (OT) and its related substances in bulk drugs has been developed. The method uses a reversed-phase C18 column (25 cm × 4.0 mm i.d.), 5 μm kept at 40 °C. The mobile phases consist of acetonitrile, dihydrogen phosphate solution pH 4.4 and water. The flow rate is 1.0 ml/min. UV detection is performed at 220 nm. A system suitability test (SST) was developed to govern the quality of the separation. The separation towards OT components was investigated on different C18 columns. The developed method was further validated with respect to robustness, precision, sensitivity and linearity. A central composite design was applied to examine the robustness of the method. The method shows good precision, sensitivity, linearity and robustness. Two commercial OT samples were examined using this method. Furthermore, the method proved to be successful when applied to analyze a marketed OT formulation for injection.

Hydroxyapatite synthesis from biogenic calcite single crystals into phosphate solutions at ambient conditions

Hydroxyapatite is one of the most important bone substitute biomaterials. Here, it has been successfully overgrown on biogenic seed crystals at ambient conditions. Single crystals of calcite from Atrina rigida, Paracentrotus lividus and Heterocentrotus mammillatus have been soaked in phosphate solution with different concentrations and pHs for 2 months. X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy have been used to characterize soaking precipitates. The results show that the conversion of calcite to hydroxyapatite occurs to an extent which depends on composition and morphology of seed crystals, and starting concentration and pH of phosphate solutions. In the same experimental conditions, synthetic calcite single crystals did not convert to hydroxyapatite. The morphological observations suggest for hydroxyapatite formation, a mechanism that involves a superficial dissolution of calcite and a subsequently overgrowth of hydroxyapatite. Moreover, the final architectural assembly of the hydroxyapatite crystals resembles the shape of the starting biogenic seed crystals.

Evaluation of a carbon paste electrode modified with organofunctionalised SBA-15 nanostructured silica in the simultaneous determination of divalent lead, copper and mercury ions

The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructured silica organofunctionalised with 2-benzothiazolethiol in the simultaneous determination of Pb(II), Cu(II) and Hg(II) ions in natural water and sugar cane spirit ( cachaça) is described. Pb(II), Cu(II) and Hg(II) were pre-concentrated on the surface of the modified electrode by complexing with 2-benzothiazolethiol and reduced at a negative potential (−0.80 V). Then the reduced products were oxidised by DPASV procedure. The fact that three stripping peaks appeared on the voltammograms at the potentials of −0.48 V (Pb 2+), −0.03 V (Cu 2+) and +0.36 V (Hg 2+) in relation to the SCE, demonstrates the possibility of simultaneous determination of Pb 2+, Cu 2+ and Hg 2+. The best results were obtained under the following optimised conditions: 100 mV pulse amplitude, 3 min accumulation time, 25 mV s −1 scan rate in phosphate solution pH 3.0. Using such parameters, calibration graphs were linear in the concentration ranges of 3.00–70.0 × 10 −7 mol L −1 (Pb 2+), 8.00–100.0 × 10 −7 mol L −1 (Cu 2+) and 2.00–10.0 × 10 −6 mol L −1 (Hg 2+). Detection limits of 4.0 × 10 −8 mol L −1 (Pb 2+), 2.0 × 10 −7 mol L −1 (Cu 2+) and 4.0 × 10 −7 mol L −1(Hg 2+) were obtained at the signal noise ratio (SNR) of 3. The results indicate that this electrode is sensitive and effective for simultaneous determination of Pb 2+, Cu 2+ and Hg 2+ in the analysed samples.

Evaluation of a carbon paste electrode modified with organofunctionalised SBA-15 silica in the determination of copper

The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructuredsilica organofunctionalised with 2-benzothiazolethiol for determination of Cu(II) ions in sugar cane spirit(cachaça) is described, based on differential pulse anodic stripping voltammetry (DPASV) procedure.The Cu(II) oxidation peak was observed at – 0.03 V (vs. SCE) in phosphate solution (pH 3.0). The resultswere obtained using optimised conditions such as 100 mV pulse amplitude, 3 min accumulation time, 25mV s -1 scan rate in phosphate solution pH 3.0, resulting in a linear dynamic range from 8.0 x 10 -7 to 1.0 x10 -5 mol L -1 Cu(II) and a limit of detection 2.0 x10 -7 mol L -1 . Cu(II) spiked in a cachaça sample wasdetermined with 102.5 % mean recovery at mmol L -1 level. Interference from other metallic cations presentin the sample was avoided by the standard addition procedure.

Evaluation of a carbon paste electrode modified with organofunctionalised SBA-15 silica in the determination of copper

The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructured silica organofunctionalised with 2-benzothiazolethiol for determination of Cu(II) ions in sugar cane spirit (cachaca) is described, based on differential pulse anodic stripping voltammetry (DPASV) procedure. The Cu(II) oxidation peak was observed at 0.03 V (vs. SCE) in phosphate solution (pH 3.0). The results were obtained using optimised conditions such as 100 mV pulse amplitude, 3 min accumulation time, 25 mV s-1 scan rate in phosphate solution pH 3.0, resulting in a linear dynamic range from 8.0 x 10-7 to 1.0 x 10-5 mol L-1 Cu(II) and a limit of detection 2.0 x10-7 mol L-1. Cu(II) spiked in a cachaca sample was determined with 102.5 % mean recovery at mmol L-1 level. Interference from other metallic cations present in the sample was avoided by the standard addition procedure.

Electrochemical and ellipsometric study of polypyrrol films in solutions containing ascorbic acid

The growth of polypyrrol layers on gold electrodes in phosphate solutions of pH = 6.7 was analyzed using “in situ” voltammetric and ellipsometric techniques. Significant variations in optical indices and thickness were detected as a function of the applied potential and the aging time of storage in phosphate solutions with or without ascorbic acid. More compact layers were grown at 1.4 V vs. RHE than by applying a lower potential. The more compact layers show a slow but progressive increase in thickness or swelling after several hours of storage in the electrolyte. This effect increases when the interface is cathodically polarized. Optical indices and thickness of the layers formed under the different applied potential/time programmes were estimated.