Phosphate Ions In Aqueous Solution Research Articles

Voltammetric determination of phosphates using ion-selective electrode based on organotin ionophore

This work describes the development of an amperometric phosphate-selective electrode with a plasticized membrane that includes bis(2-ethylhexyl)tin (IV) dichloride as an ionophore. The potentiometric response of the plasticized membrane was investigated, in addition to its selectivity for hydrophilic anions. The membrane provided a linear potential response with respect to HPO42- ions in the concentration range from 4·10-5 to 3·10-2 mol/L with a Nernst slope of 29 ± 2 mV·decade-1 activity. By using cyclic voltammetry, we characterized the ionophore-facilitated transfer of mono- and dihydro phosphate ions at the water/PVC-2-nitrophenyl octyl ether phase interface. An interphase distribution coefficient, a galvanic potential, a half-wave potential, the Gibbs energy of facilitated interphase transfer, as well as the Gibbs energy of facilitated interphase transfer were determined. Alternating current voltammetry was used to quantify phosphate ions in aqueous solutions. The linear response was observed in the range of phosphate concentrations from 2 to 10-6 to 1·10-4 mol/L and the detection limit was 8·10-7 mol/L under these conditions. This AISE has demonstrated high selectivity for phosphate ions in comparison to the most common anions in aqueous solutions. It has been used to determine the amount of phosphates in two fertilizers.

Potentiometric Phosphate Ion Sensor Based on Electrochemical Modified Tungsten Electrode.

Determination of phosphate ions in aqueous solutions attracts a great deal of interest in the areas of environment, medicine, and agriculture. As phosphoric acid is a poly basic acid, the different forms of existence at different pH result in direct determination facing a big challenge. Herein, we reported a potentiometric phosphate ion sensor based on a surface-modified tungsten electrode. Pure tungsten was electrodeposited at a constant potential of 0.2 V versus Ag|AgCl in Na2HPO4. WO3 and H3O40PW12·xH2O were electrodeposited on the surface of the tungsten electrode. The modified tungsten electrode was used as a working electrode in a two-electrode system to detect the concentration of phosphate ions in aqueous solutions. The detection limit of the modified tungsten electrode for phosphate ions is 10–6 M from pH 7 to pH 8 and 10–5 M from pH 9 to pH 10. It has good selectivity to other common anions. The long-term monitoring experiment showed that the potential fluctuation was less than ±3 mV in 24 h. Compared to conventional determination methods, the current phosphate ion sensor showed a close value in a real sample. The mechanism of phosphate ion response was investigated in detail. This sensor possesses advantages of simple manufacture, low cost, a wide pH range for detecting, and good selectivity.

A design for detecting phosphate ions in aqueous solution by luminescent Tb-coordination polymer

Phosphate usually plays an important role not only in biological processes but also in environmental pollution, and therefore there is an urgent need for a simple, quick and efficient method to detect phosphate ions. For this design, a new terbium coordination polymer (Tb-CP) has been prepared under hydro-solvothermal conditions using 3,3′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H3cpboda) in the existence of Tb(NO3)3‧6H2O. It was studied by infrared spectroscopy (IR), single crystal X-ray diffraction, thermogravimetric analysis (TGA), and fluorescence method. Structurally, the Tb-CP gives a 2D network based on binuclear Tb(III) units. Optically, the Tb-CP is prepared as a colloidal nanoparticle suspension for detecting phosphate in water solution. Namely, the suspensions show intense green emissions gradually disappear with the addition of PO43− ions, indicating that the Tb-CP can rapidly, sensitively and reversibly detect phosphate ions in aqueous solutions. This can be applied in pollutant monitoring with a limit of detection down to 4.53 × 10−8 M (0.0096 ppm). Furthermore, a convenient method is successfully set to observe PO43− ions in applications.

Removal of phosphate from wastewater using coal slag

ABSTRACT Adsorption is an efficient, cost-effective, and eco-friendly method for the treatment of phosphorus from wastewater. This work presents the adsorptive removal of phosphate ions in aqueous solution using coal slag (CS) from a thermal power plan. The surface morphological analysis showed that the CS particles were around 50 µm with a surface area of 9.20 m2 g−1 and adsorption average pore width of 6.42 nm, offering the high capability for phosphate ions adsorption. The optimising phosphate ions adsorption conditions were investigated based on various parameters, including contact time, pH, and amount of absorbent. The experimental results showed that the maximum loading adsorption capacity was 21.63 mg g−1 in the concentration range of 0–30 mg L−1 under optimising conditions (i.e. pH of 6, adsorbent dosage (0.1 g vol−1 used) and contact time of 45 min). Furthermore, the use of CS offers several benefits like reducing the sample pre-treatment steps for costly, less time-consuming and reliable methods.

A Turn-On Luminescence Method for Phosphate Determination Based on Fast Green-Functionalized ZrO2:Yb,Er@ZrO2 Core@Shell Upconversion Nanoparticles.

The development of practical and sensitive tools for detecting phosphate deficiency could facilitate engineering approaches to enhance crop yield and quality in phosphate-stressed environments, reducing the misuse of nonrenewable fertilizers and their consequent ecological impact. Herein, a 975 nm-activated method based on ZrO2:Yb,Er@ZrO2 core@shell upconversion nanoparticles is presented for rapid visualization and determination of the phosphate ions in aqueous solutions and extracts. At optimized thickness, the nondoped ZrO2 shell not only enhances the emission of the ZrO2:Yb,Er but also provides an active surface for the intense interaction with the phosphate group, allowing a "label-free" determination that avoids the use of additional phosphate-recognizing elements like ligands or antibodies. According to the experimental evidence, the optical output of the ZrO2:Yb,Er@ZrO2 nanoparticles specifically matches with the absorption spectrum of the fast green alimentary dye (FG) electrostatically attached to the nanoparticle surface, activating the Förster resonance energy transfer (FRET) and thereby the upconversion luminescence quenching. Upon addition of the phosphate ions and the covalent interaction with the ZrO2:Yb,Er@ZrO2-FG nanocomplex, the FG is gradually removed, displaying a fast and reproducible "turn-on" luminescence which allows measurements in a few minutes. This rapid response is due to the stronger coordination between the ZrO2 shell and the phosphate compared to the FG molecules (-31.97 and -5.99 eV, respectively). The detection method was then effectively modulated in a 20-1000 nM linear response range without interfering effects of commonly coexisting ions, achieving a detection limit up to 15 times lower than that obtained with the conventionally used colorimetric methods.

Simulation of Calcium Phosphate Prenucleation Clusters in Aqueous Solution: Association beyond Ion Pairing.

Classical molecular dynamics simulations and free energy methods have been used to obtain a better understanding of the molecular processes occurring prior to the first nucleation event for calcium phosphate biominerals. The association constants for the formation of negatively charged complexes containing calcium and phosphate ions in aqueous solution have been computed, and these results suggest that the previously proposed calcium phosphate building unit, [Ca(HPO4)3]4–, should only be present in small amounts under normal experimental conditions. However, the presence of an activation barrier for the removal of an HPO42– ion from this complex indicates that this species could be kinetically trapped. Aggregation pathways involving CaHPO4, [Ca(HPO4)2]2–, and [Ca(HPO4)3]4– complexes have been explored with the finding that dimerization is favorable up to a Ca/HPO4 ratio of 1:2.

Structure Determination of Phosphoric Acid and Phosphate Ions in Aqueous Solution Using EXAFS Spectroscopy and Large Angle X-ray Scattering.

The structures of hydrated phosphoric acid and phosphate ions (H2PO4-, HPO42-, and PO43-) in aqueous solution have been determined by P K-edge EXAFS and large angle X-ray scattering (LAXS). The P-O bond distance in all phosphate species studied is close to 1.53 Å. The P-(O)···Oaq distances have been refined to ca. 3.6 Å from the LAXS data giving a P-O···Oaq bond angle close to tetrahedral, suggesting that each oxygen or OH group of phosphoric acid and dihydrogen phosphate, on average, hydrogen bind three water molecules. The (P-)O(-H)···Oaq and (P-)O···(H-)Oaq hydrogen bonds in hydrated phosphoric acid and the H2PO4- ion are shorter than the hydrogen bonds in neat water. This supports previous infrared spectroscopic studies claiming that the hydrogen bonds in hydrated phosphoric acid and phosphate ions are stronger than the hydrogen bonds in neat water. Phosphoric acid and phosphate ions can therefore be regarded as structure making solutes. This is the first study applying transmission mode X-ray absorption spectroscopy (XAS) data collection on the P K-edge. It shows that XAS spectra collected in transmission mode have a much better S/N ratio than data collected in fluorescence mode, allowing accurate determination of P-O bond distances. Furthermore, P K-edge EXAFS data collected in fluorescence mode display a higher amplitude at high k than expected due to increasing radiated volume of the sample with increasing energy as the total absorption decreases sharply with increasing energy of the X-rays. As a result, the fluorescence signal becomes nonproportional to the intensity of the X-ray beam over the EXAFS spectrum. This results in an increasing amplitude of the EXAFS function with increasing energy of the X-ray beam resulting in too small Debye-Waller coefficients.

Alkaline phosphatase inhibition based conductometric biosensor for phosphate estimation in biological fluids

Determination of phosphate ions concentration is very important from both, environmental and clinical point of view. In this study, a simple and novel conductometric biosensor for indirect determination of the phosphate ions in aqueous solution has been developed. The developed biosensor is based on the inhibition of immobilized alkaline phosphatase activity, in the presence of the phosphate ions. This is the first time we developed a mono-enzymatic biosensor for indirect estimation of phosphate ions. The developed biosensor showed a broad linear response (as compared to other reported biosensors) for phosphate ions in the range of 0.5–5.0mM (correlation coefficient=0.995), with a detection limit of 50µM. Different optimized parameters were obtained as the buffer concentration of 30mM, substrate concentration of 1.0mM, and a pH of 9.0. All the optimized parameters were analyzed by analysis of variance, and were found to be statistically significant at a level of α=0.05. The developed biosensor is also suitable to determine the serum phosphate concentration, with a recovery of 86–104%, while a recovery of 102% was obtained from the water samples that were spiked with 500µM phosphate. A relative standard deviation in the conductance response for five successive measurements (n=5) did not exceed 7%, with a shelf life of 30 days. With a lower detection limit and a higher recovery, the biosensor provides a facile approach for phosphate estimation in biological fluids.

Vibrational Spectra of Phosphate Ions in Aqueous Solution Probed by First-Principles Molecular Dynamics

We have carried out "first-principles" Born-Oppenheimer molecular dynamics (BOMD) simulations of the phosphate ions H₂PO₄⁻ and HPO₄²⁻ in liquid water and have calculated their IR spectra by Fourier transform techniques from the trajectories. IR bands were assigned by a so-called "generalized normal coordinate analysis". The effects of including Hartree-Fock (HF) exchange into the density functional theory (DFT) computation of forces were studied by comparing results obtained with the well-known BP, BLYP, and B3LYP functionals. The neglect of dispersion in the functionals was empirically corrected. The inclusion of HF exchange turned out to yield dramatically improved and, thus, quite accurate descriptions of the IR spectra observed for H₂PO₄⁻ and HPO₄²⁻ in aqueous solution. An analysis of earlier computational results (Klähn, M. et al. J. Phys. Chem. A 2004, 108, 6186-6194) on these vibrational spectra, which had been obtained in a hybrid setting combining a BP description of the respective phosphate with a simple molecular mechanics (MM) model of its aqueous environment, revealed three different sources of error, (i) the BP force field of the phosphates is much too soft and would have required a substantial scaling of frequencies, (ii) the oversimplified water force field entailed incorrect solvation structures and, thus, qualitatively wrong patterns of solvatochromic band shifts, and (iii) quantitative frequency computations additionally required the inclusion of HF exchange. Thus, the results of the B3LYP BOMD simulations do not only characterize physical properties like the IR spectra or the solvation structures of the phosphate systems but also provide clues for the future design of simplified but nevertheless reasonably accurate DFT/MM methods applicable to phosphates.

Quantitative Luminescence Switching in CePO4:Tb by Redox Reactions

Luminescence-switching behaviors of CePO4:Tb3+ upon redox reactions were examined using KMnO4 and l(+)-ascorbic acid as an oxidant and a reductant, respectively. Powdery nanorod-like CePO4:Tb3+ particles were synthesized by liquid-phase reactions of rare-earth ions and phosphate ions in aqueous solutions at low temperatures. According to X-ray diffractometry, X-ray photoelectron spectroscopy, and transmission electron microscopy, the oxidizing treatment of CePO4:Tb3+ was found to bring about partial oxidation of Ce3+ to Ce4+ and a small degree of structural damage in the particle surface, which could be recovered by the subsequent reducing treatment. Photoluminescence (PL) intensity of CePO4:Tb3+ due to 5D4 → 7FJ (J = 3−6) electronic transitions of Tb3+ was decreased with increasing KMnO4 concentration in an exponential manner, resulting from excitation cutoff by an intervalence Ce3+ → Ce4+ charge transfer and emission cutoff by a Ce3+ absorption red-shifted to the visible region. Reversely, PL intensity was increased also in the exponential manner by increasing the l(+)-ascorbic acid concentration in reducing the previously oxidized CePO4:Tb3+, thereby achieving the quantitative, repetitive luminescence switching. Our results demonstrate that the luminescence switching is regarded as a surface phenomenon without a whole change of structure and valence in the CePO4:Tb3+ material.

A Metal–Macrocycle Complex as a Fluorescent Sensor for Biological Phosphate Ions in Aqueous Solution

AbstractWe synthesized tetraazamacrocycles 1 and 2 bearing two anthryl groups as sidearms, both of which exhibited high selectivity for the ZnII ion in switching‐on‐type responses in aqueous solution. For ligand 1, ZnII is coordinated by four nitrogen atoms of the macrocycle and two amino groups on the pendent arms, which results in proximity between the twofluorophores. So, 1‐ZnII shows obvious excimer emission in aqueous solution. When PPi or ATP was added (pH 7.4), the excimer emission of 1‐ZnII was quenched, whereas monomer emission was revived. To the best of our knowledge, no other known sensor has this characteristic under physiological pH conditions. At the same time, the obvious different fluorescence response of 1‐ZnII for PPi and ATP in water shows that receptor 1‐ZnII can be used as a selective fluorescent chemosensor for PPi and ATP anions.

Casein Phosphopeptides in Oral Health - Chemistry and Clinical Applications

The casein phosphopeptides (CPP) are derived from the milk protein casein by tryptic digestion. The CPP, containing the sequence -Pse-Pse-Pse-Glu-Glu- where Pse is a phosphoseryl residue, stabilize calcium and phosphate ions in aqueous solution and make these essential nutrients bioavailable. Under alkaline conditions the calcium phosphate is present as an alkaline amorphous phase complexed by the CPP, referred to as casein phosphopeptide-amorphous calcium phosphate (CPP-ACP). The CPP-ACP complexes readily incorporate fluoride ions forming casein phosphopeptide-amorphous calcium fluoride phosphate (CPP-ACFP). A mechanism is discussed which provides a rationale for the ability of the CPP-ACP to remineralize carious lesions in dental enamel. Clinical applications of the CPP-ACP as agents in the treatment of dental caries and other hypomineralized conditions are reviewed. It is concluded that the CPP are a safe and novel carrier for calcium, phosphate and hydroxide (fluoride) ions to promote enamel remineralization with application in oral care products, dental professional products and foodstuffs.

Blister-colorimetric determination of phosphate ions in water, agricultural samples, and biological samples

A procedure was proposed for the determination of phosphate ions in a blister cell (pellet cartridge) with a dry reagent mixture. The procedure is suitable for the quantitative determination of phosphate in different samples using a dry reagent mixture in an ampule or a blister without dissolving the reagents. After an ampule or a blister cell was opened and several drops of a test liquid were added, a color developed, whose intensity was proportional to the concentration of phosphate ions in the solution. The solution was then diluted to 2 mL with water and analyzed by photometry. The composition of the mixture was determined, and the procedure for the quantitative determination of phosphate ions was proposed; the procedure involves the formation and reduction of phosphomolybdic acid and the use of auxiliary reagents. The error of the colorimetric determination of phosphate ions in aqueous solutions, soil extracts, and urine was estimated with the participation of inexperienced operators.

Correction of a calibration scale for the rapid visual semiquantitative determination of phosphate ions in agricultural samples

A procedure was developed of fabricating a colored calibration scale for determining phosphate ions in aqueous solutions. The procedure is suitable for correcting hue steps depending on the analytical range of phosphate ions. A rapid procedure was proposed for visual testing in a blister cell with a bulk mixture of dry reagents. A test effect was observed immediately after the cell was opened and several drops of a test solution were added. Mixture compositions were developed for the visual determination of phosphate ions in a concentration range of 0.5–80 mg/L by the formation and reduction of phosphomolybdic acid using auxiliary reagents.

IR Spectra of Phosphate Ions in Aqueous Solution: Predictions of a DFT/MM Approach Compared with Observations

Due to the progress of density functional theory (DFT) accurate computations of vibrational spectra of isolated molecules have become a standard task in computational chemistry. This is not yet the...

Neutron scattering studies on the hydration of phosphate ions in aqueous solutions of K3PO4, K2HPO4 and KH2PO4

The difference methods of neutron diffraction and isotopic substitution (NDIS) were applied to the total scattering patterns of H/D substituted solutions containing three types of phosphate anion (H2PO4−, HPO42−, PO43−). The data were used to determine the pairwise structure associated with the hydrogen and oxygen atoms of the solution. The results are consistent with hydrogen bonds between the H2PO4−, HPO42− and PO43− anions and water molecules being respectively stronger than, comparable to and weaker than those between the hydrogen bonds of water molecules. It is also deduced that the coordination number for the PO43− ion is 15 ± 3, and a similar value is proposed for the other two anions.

Kinetic studies of proton-exchange reactions between imidazole groups of small molecules and hydrogen phosphate ions in aqueous solution using ultrasonic relaxation

Ultrasonic absorption in aqueous solutions of imidazole and three substituted derivatives, N-methyl-, 2-methyl-, and 4-methylimidazole, has been studied in the presence of potassium phosphate as a function of pH and salt concentration in the frequency range 0.46-5.7 MHz at 25°C. For all of these compounds, the ultrasonic absorption curves as a function of pH showed a sharp maximum in the vicinity of pH 7, due to a disturbance of the proton-exchange equilibrium between the imidazolium ion and hydrogen phosphate ion by the ultrasonic waves. An expression for the ultrasonic absorption due to this proton transfer has been derived from relaxation theory, using a reaction scheme of Eigen. A quantitative interpretation is given for both the pH and the phosphate concentration dependence of the ultrasonic absorption in the neutral pH range. The rate constant k R and the volume change ΔV for the reaction of dihydrogen phosphate ion with the unprotonated imidazole group have been determined by a curve-fitting procedure in which k R and ΔV were the only adjustable parameters

Progress of artificial carious lesions in enamel.

Progress of lesions with time is important from a practical point of view, but especially because it provides information on the mechanism of the caries process. Firstly, a theoretical description of lesion progress with time is derived. It is based on the assumption that (1) steady-state diffusion during the caries process takes place through very tiny holes in the enamel surface, (2) inhibitors make the enamel surface insoluble and diffuse during the process inwards (the inhibitors, e.g. diphosphonates or fluorides may be coming from an external solution or may orginate from the enamel itself), and (3) the inhibitor blocks enamel dissolution effectively if the inhibitor concentration XL exceeds the fraction of surface phosphate sites XL*. The theory shows that lesion depth (r1) is about proportional to the third root of demineralization time (t), and can be written as r13 = αt + q, α and q being constants. Second, a comparison is made with experimental lesion depth data from various authors in artifical lesion systems. The results show that lesion progress in human and bovine enamel at pH 4, 4.5 and 5 is very well described by the above formula. This result indicates strongly that inhibitor action and inhibitor penetration are important during the caries process. From the experimentally determined slope a the apparent diffusion coefficient Dapp of the process is determined as ≈ 10––5 cm2s––1. This value is comparable to D of Ca++ and phosphate ions in aqueous solutions and indicates that ion transport during the process takes place in water-filled channels.

Activity of phosphate ions measured with phosphate electrodes of the second kind

Phosphate electrodes of the second kind were employed to measure the activity of phosphate ions in aqueous solutions of orthophosphoric acid. The equation relating the emf with the activity of the various phosphate ions, which has been previously assumed to apply only under limited experimental conditions, is developed rigorously, and shown to be of general validity. The calculated results obtained by the use of the approximate equations developed agree well with the experimental values in the range of concentrations of phosphoric acid of 10 −2 to 10 −1 M. In the range of concentrations of phosphoric acid of 10 −4 to 10 M the activity of HPO 4 2− appears to be constant, and the change of emf between the phosphate electrodes and the H + electrodes is due only to the change in the activity of the hydrogen ions. The value of the phosphate electrodes of the second kind described in the literature appears to be limited, and considerable additional evaluation is necessary before they can be employed as reliable ion-specific reference electrodes.