Showing papers on "Titration published in 2018"

Aquatic Chemistry Concepts

Abstract: PART 1: INTRODUCTION. Overview. Thermodynamic Principles. PART 2: ACID/BASE CHEMISTRY. [H+] as an Important and Meaningful Thermodynamic Variable in Aquatic Chemistry. The Proton Balance, Electroneutrality, and Mass Balance Equations. Introduction to Quantitative Equilibrium Calculations. pH as a Master Variable. Titrations of Acids and Bases. Buffer Intensity b, and the Effects of Changes in b With pH on Titration Curves. Chemistry of Dissolved CO2. Gran Titrations. PART 3: MINERAL/SOLUTION CHEMISTRY. Solubility Behaviors of Simple Mineral Salts, and Metal Oxides, Hydroxides, and Oxyhydroxides. Solubility Behavior of Metal Carbonates in Closed Systems. Solubility of Metal Carbonates in Open Systems With a Gas Phase of Constant pCO2. Solubility Control, Solubility Limitation, the Coexistence of Multiple Solid Phases, and Multiple-Solid Predominance Diagrams. Solubility as a Function of Particle Size. Solid/Solid and Liquid/Liquid Solution Mixtures. The Gibbs Phase Rule. PART 4: METAL/LIGAND CHEMISTRY. Complexation of Metal Ions by Ligands. PART 5: REDOX CHEMISTRY. Redox Reactions pe, and EH. Introduction to pe-pH Diagrams: The Cases of Aqueous Chlorine, Hydrogen, and Oxygen. pe-pH Diagrams for Aqueous Lead in the Absence of CO2. pe-pH Diagram for Aqueous Lead in the Presence of CO2 With Fixed CT. pe and Natural Systems. The pe Changes in a Stratified Lake During a Period of Summer Stagnation: An Example of a Redox Titration. PART 6: EFFECTS OF ELECTRICAL CHARGES ON SOLUTION CHEMISTRY. The Debye-Huckel Law and Related Equations for the Activity Coefficients of Aqueous Ions. Electrical Double Layers in the Aqueous System. Stability and Coagulation of Colloidal Suspensions. INDEX.

Boehm Titration Revisited (Part I): Practical Aspects for Achieving a High Precision in Quantifying Oxygen-Containing Surface Groups on Carbon Materials

Abstract: Practical aspects of the Boehm titration method are evaluated for obtaining reliable results in the quantification of oxygen-containing surface groups in a short time. Analytical criteria such as accuracy, repeatability, precision, and robustness are applied. Oxidized multi-walled carbon nanotubes (MWCNTs) are used as the model substance. Different reaction bases (NaHCO3(aq), Na2CO3(aq), NaOH(aq)) are applied and treatment times are studied. We also show that smaller amounts of carbon material can be reliably analyzed by using an autotitrator combined with a pH electrode. We find that indirect titration with Na2CO3 results in the highest titration precision and accuracy despite the lower base strength compared with NaOH. Therefore, CO2 impurities do not have to be removed and only 7 min is necessary for one titration. The titration error with respect to the proposed method is 0.15% of the aliquot volume. The mixing method during the carbon treatment with bases (stirring, shaking, ultrasound treatment) has no influence on the result as long as one allows a few hours for the reaction to complete. Finally, we provide a standard operating procedure for obtaining results with high precision during Boehm titration.

Complex Coacervation of Milk Proteins with Sodium Alginate.

Abstract: Beta-lactoglobulin (BLG) and bovine serum albumin (BSA) coacervate formation with sodium alginate (ALG) was investigated by turbidimetric analysis, zeta potential, particle size, viscosity, transmission electron microscopy (TEM) and isothermal titration calorimetric (ITC) measurements as a function of pH (1.0–7.0) and protein/alginate mixing ratio (1:1, 1.5:1, 2:1, 1:0, and 0:1 wt.). Critical pH values of phase transitions for BSA–ALG complexes (pHC, pHφ1, and pHφφ2) representing the formation of soluble and insoluble complexes of a protein–ALG mixture (2:1) at pH 4.8, 4.2, and 1.8, respectively. In the case of BLG–ALG, critical pH values (pHC, pHφ1, and pHφ2) were found to be 4.8, 4.2, and 1.6, respectively. The pHopt values, expressed by the highest optical density, were pH 2.8 for BSA–ALG and 2.4 for BLG–ALG. TEM and zeta-potential results showed that maximum coacervate formation occurred at pH 4.2 for both protein–polysaccharide solutions. The interaction between BLG–ALG and BSA–ALG was spontaneously ...

A bifunctional chemosensor for detection of volatile ketone or hexavalent chromate anions in aqueous solution based on a Cd(II) metal–organic framework

Abstract: A new porous metal–organic framework with chemical formula of [Cd3(cpota)2(phen)3]n·5nH2O (MOF-1) (H3cpota = 2-(4-carboxyphenoxy)terephthalic acid & phen = 1,10-phenanthroline) has been synthesized and characterized by infrared spectroscopy, elemental analysis, thermogravimetry and X-ray single crystal and powder diffracting methods. MOF-1, as a potential material of the sensing applications, has an uncommon 3D microporous structure in which the trinuclear [Cd3(phen)3(μ2-COO)4]2+ SBUs are interconnected by the V-shaped cpota3− ligands. MOF-1 has good stabilities not only in aqueous solution in the range of pH = 1.0 ∼ 14.0 but also in solid from room temperature (RT) to 330 °C. Fluorescence titration, cyclic and anti-interference experiments demonstrate that MOF-1 is an excellent probe for volatile organic ketones (acetone/2-butanone) and hexavalent chromate (CrO42−/Cr2O72−) in aqueous solution. The luminescence investigations in the aqueous solution of pH = 9 reveal that the MOF-1 can efficiently and selectively detect Cr(VI) ions without the interference of other metal cations. Quenching mechanisms are also studied in detail.

A novel pyrene-based dual multifunctional fluorescent probe for differential sensing of pH and HSO3− and their bioimaging in live cells

Abstract: We designed and synthesized a new fluorescent probe for detecting pH and HSO3− using pyrene as an electron donor (D) and pyridine as an electron acceptor (A). The fluorescent probe for sensing pH and HSO3− could distinguish these by their spectral properties in different media. pH titrations indicated that the probe displayed a ratiometric emission (pH 7.10–1.36) with a pKa of 4.26, responded linearly to minor pH fluctuations within the acidic pH range of 3.00–5.50 in CH3CN/H2O (1/3, v/v), and exhibited a remarkable emission enhancement (pH 7.10–13.09) with a pKa of 10.91 and a linear response in the extremely alkaline pH range of 9.75–11.35 in CH3CN/H2O (1/19, v/v). Interestingly, the probe also responded to HSO3− with an obvious turn-off fluorescence signal in PBS buffer (pH = 5.00, 1.5% DMSO). This could be attributed to the Michael addition of HSO3− to the α,β-unsaturated ketone, which resulted in breaking of the conjugation. The detection limit (LOD) of the probe for HSO3− based on the definition by IUPAC was calculated to be 1.9 nM. Furthermore, the probe was employed successfully for the imaging of pH and HSO3− in live cells, which indicated that the probe was a suitable indicator for imaging the distribution of pH or HSO3− and tracking their changes.

A novel microporous Tb-MOF fluorescent sensor for highly selective and sensitive detection of picric acid

Abstract: A new three-dimensional metal–organic framework (MOF) sensor with molecular formula (C2H6NH2)2[Tb2(ptptc)2(DMF)(H2O)]·DMF·6H2O (complex 1) has been constructed from terphenyl-3,3′,5,5′-tetracarboxylic acid (H4ptptc) and terbium nitrate under solvothermal conditions. The structure of complex 1 was characterized by single-crystal X-ray diffraction analysis (XRD), elemental analysis, IR spectroscopy and thermogravimetric (TG) analysis, and the purity was further confirmed by powder X-ray diffraction (PXRD) analysis. XRD analysis reveals that complex 1 crystallizes in a triclinic system P space group and consists of a three-dimensional anionic network which has one-dimensional channels. Fluorescence titration experiments showed that complex 1 displayed real-time, highly selective and sensitive fluorescence quenching behavior towards picric acid with a nanomolar scale experimental detection limit (100 nM). Recycling titration experiments suggested that the as-synthesized probe has good reversibility and can be used for at least five cycles in fluorescence titration experiments without obvious fluorescence intensity reduction or framework structure destruction. Furthermore, the high selectivity and sensitivity as well as good recyclability of complex 1 make it a potential fluorescent sensor for picric acid.

Effect of pH and Salt on Surface pKa of Phosphatidic Acid Monolayers

Abstract: The pH-induced surface speciation of organic surfactants such as fatty acids and phospholipids in monolayers and coatings is considered to be an important factor controlling their interfacial organization and properties. Yet, correctly predicting the surface speciation requires the determination of the surface dissociation constants (surface pKa) of the protic functional group(s) present. Here, we use three independent methods—compression isotherms, surface tension pH titration, and infrared reflection–absorption spectroscopy (IRRAS)—to study the protonation state of dipalmitoylphosphatidic acid (DPPA) monolayers on water and NaCl solutions. By examining the molecular area expansion at basic pH, the pKa to remove the second proton of DPPA (surface pKa2) at the aqueous interface is estimated. In addition, utilizing IRRAS combined with density functional theory calculations, the vibrational modes of the phosphate headgroup were directly probed and assigned to understand DPPA charge speciation with increasin...

Adsorption of anionic and cationic dyes on biochars, produced by hydrothermal carbonization of waste biomass: effect of surface functionalization and ionic strength

Abstract: In this work, surface-functionalization agents and various salts as auxiliaries were used to improve the adsorption capacity of biochars produced via hydrothermal carbonization of glucose, cellulose, and hazelnut shell. The effect of surface functionalization with different acids and bases as well as neutral salts on the adsorption of methylene blue and methyl orange was investigated using Boehm titration, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy techniques. Surface functionalization of biochars leads to an increase in the number of oxygen-containing functional groups on the surface, thus increasing the adsorption capacity. To probe the influence of ionic strength on the adsorption process, three auxiliaries, namely potassium chloride, cetyltrimethylammonium bromide, and sodium bicarbonate, were examined. The increase in total electrolyte concentration signicantly affected the pH of the solution and as a result electrostatic interactions between dyes and biochars. Dye adsorption capacities reached 234.57 mg/g for methylene blue and 306.13 mg/g for methyl orange in the presence of cellulose-based and NaOH-functionalized biochar and glucose-based H2SO4-functionalized biochar, respectively.

Identification of functional groups of Opuntia ficus-indica involved in coagulation process after its active part extraction

Abstract: Opuntia ficus-indica that belongs to the Cactaceae family and is a member of Opuntia kind has received increasing research interest for wastewater treatment by flocculation The objectives of this study were (i) to provide more information regarding the active constituents of Opuntia spp and (ii) to improve the extracting and using conditions of the flocculant molecules for water treatment A classic approach by jar test experiments was used with raw and extracted material by solubilization and precipitation The surface properties of solid material were characterized by FTIR, SEM, zeta potential measurement, and surface titration The splitting based on the solubility of the material with pH and the titration of functional groups completed the method The optimal pH value for a coagulation–flocculation process using cactus solid material (CSM) was 100 and a processing rate of 35 mg L−1 The alkaline pH of flocculation suggests an adsorption mechanism with bridging effect between particles by water-soluble extracted molecules To validate this mechanism, an extraction water was carried out at pH = 10 (optimum of flocculation) and the solution was acidified (pH = 7) to allow precipitation of so considered active flocculant molecules The strong flocculant property of this extract was verified, and titration of this solution showed at least one specific pKa of 90 ± 06 This pKa corresponds to phenol groups, which could be assigned to lignin and tannin

Characterization of a highly Al3+ -selective fluorescence probe based on naphthalimide-Schiff base and its application to practical water samples.

Abstract: A new fluorescent Al3+ -probe, N-allyl-4-[3,3'-((2-aminoethyl)azanediyl)-bis(N´-(2-hydroxybenzylidene)propanehy-drazide)]-1,8-naphthalimide (L), was designed and synthesized based on 1,8-naphthalimide. The probe L contains 1,8-naphthalimide moiety as the fluorophore and a Schiff base as the recognition group. The structure of L was determined by single crystal X-ray. L emission at 526 nm increased on addition of Al3+ under excitation wavelength at 350 nm. L exhibited high selectivity and sensitivity fluorescence emission towards to Al3+ in ethanol/Tris-HCl buffer solution (1:1, v/v, pH = 7.2) as compared with other tested metal ions. A good linearity with a correlation coefficient (R2 ) of 0.99 was observed in the concentration range 2-10 μM. The binding constant and the detection limit of L for Al3+ were calculated to 2.6 × 104 M-1 and 0.34 μM, respectively. The results of experiments that including Job plot, ultraviolet-visible (UV-Vis) light titration, fluorescence titration, ESI-MS and 1 H NMR titration, indicated a 1:1 stoichiometric complex between L and Al3+ . L was highly effective in monitoring Al3+ in real-life Yellow River and tap water samples.

Preparation, characterization, and application of low-cost açaí seed-based activated carbon for phenol adsorption

Abstract: Activated carbon (ACAcai) was obtained from the activation of acai seeds at 800 °C under CO2 flow. The surface groups of the material were determined by Boehm titration and information about surface charge was obtained using the methodology of the point of zero charge (PZC). Boehm titration and PZC tests showed that the ACAcai sample has a basic character. The optimum pH range for the adsorption process is 3.5–8 and the optimum dosage is 0.1 g/50 mL of phenol solution. ACAcai has a surface area of 496 m2 g−1 and pore volume of 0.217 cm3 g−1. The adsorption kinetics follows the pseudo-second-order model. The Langmuir isotherm model satisfactorily described the experimental data. The maximum adsorption capacity obtained was of 133 mg g−1 at 25 °C. Deionized water, NaOH solution (0.1 M), and ethanol were used as desorption agents, but none of them showed promising results for the regeneration of ACAcai. The thermodynamic studies show that the adsorption process is exothermic, spontaneous, and favorable.

Characterization and application of microalgae hydrochar as a low-cost adsorbent for Cu(II) ion removal from aqueous solutions

Abstract: Hydrochar prepared from the hydrothermal liquefaction of microalgae is characterized and investigated for copper removal from aqueous solution. Two hydrochars were prepared at 210 °C (HD210) and 250 °C (HD250). The effect of the initial solution pH, the initial Cu(II) concentration, the contact time, and the temperature will be investigated. According to the elemental analysis, the volatile matter in the hydrochars was lower and ash content was higher than those of microalgae. Also, pore characteristic analysis revealed that the surface area of the HD250 was higher than that of the HD210 suggesting a higher potential for the adsorption process. FTIR analysis and Boehm titration showed that both hydrochars contained oxygen-containing functional groups (OFG) on the surface which were effective for the copper removal. The adsorption experiments indicated that the amount of copper adsorbed reached a maximum value at the pH of 5 which was considered as the optimum solution pH. In addition, HD250 had a higher amount of copper adsorption than that of HD210 at all values of the solution pH. The adsorption data at the optimum solution pH was well fitted by the Langmuir’s isotherm model and the adsorption process could be well described by the pseudo-2nd order kinetic model. Moreover, thermodynamic analysis revealed that copper adsorption onto the hydrochar was a physical endothermic process.

Hybrid Macrocycles for Selective Binding and Sensing of Fluoride in Aqueous Solution.

Abstract: Synthesis and anion binding properties of hybrid macrocycles containing ammonium and hydrogen bond donor groups are reported Receptor properties were studied in a 10 mM MES buffer solution at pH 62, at which the receptors carry two positive charges at the secondary amine groups Receptor 1 was found to bind fluoride with the highest affinity (105 M–1) and selectivity among the synthesized receptors It was the only receptor that demonstrated fluorescence increase upon addition of fluoride Other titration experiments with halides and oxyanions led to an anion-induced aggregation and fluorescence quenching The mechanism of the particular turn-on fluorescence for fluoride was explained by the ability of receptor 1 to encapsulate several fluoride anions Multiple anion coordination resulted in the protonation of the tertiary amine group and subsequent hindering of the PET process 1H and 19F NMR titrations, single-crystal X-ray structure of chloride complex, and DFT calculation suggest that 1 can perfectl

Colorimetric determination of acidity constant using a paper-based microfluidic analytical device

Abstract: Acid dissociation constant is an important chemical characteristic of organic and inorganic compounds and it affects both chemical properties and biological activities of the molecules. Herein, a very simple, fast and cost-effective method based on microfluidic technology has been reported for colorimetric determination of acidity constants. The designed device works based on pH-metric titration of colorful indicators followed by colorimetric measurements by a smart phone mobile device or a flatbed scanner. So, it does not need sophisticated instrumentation and is accomplished in a very short time (about 1 min). All titration steps are transferred on a star-like designed µPAD device: (1) spotting 0.3 µL buffers of different pHs at the end of the channels (reaction zones), (2) spotting a 30 µL portion of the indicator on the center of µPAD followed by movement of indicator solution toward the reaction zone by capillary action of the paper. The measured color change of the indicators at the reaction zone is fitted to the Henderson–Hasselbalch equation, through which acidity constants are calculated. The performance of the device was evaluated by measuring acidity constant of 4 indicators including bromothymol blue, bromocresol green, bromocresol purple and phenolphthalein. A very close agreement was achieved between those measured by the suggested device here and the previously reported values. The reproducibility of this method was lower than 5% for relative standard deviation of three replicate measurements.

Sensitive fluorescent assay for copper(II) determination in aqueous solution using quercetin–cyclodextrin inclusion

Abstract: Environmentally friendly probe materials for detecting copper ions were studied in this research. Fluorescent emission of quercetin (Q) was observed in the buffer solution (pH = 7.40), and (2-hydroxypropyl)-β-cyclodextrin (CD) could enhance the fluorescence intensity of Q. The UV/Vis spectrum showed that the Q-CD system was formed. After adding copper ions into the Q-CD system, the fluorescent emission intensity of Q-CD system generated quenching, and other metal ions could not bring change, which meant the Q-CD system showed good selectivity to copper ions. The fluorescence titration spectra showed that the concentration of copper ions was inversely proportional to fluorescence intensity, and gave a good linear change in fluorescence emission intensity in response to the concentration of copper ions ranging from 5.0 × 10−8 to 8.3 × 10−6 mol L−1. The calibration curve of the relationship between the intensity and copper ions concentration was y = −9.24x + 844.51 (R2 = 0.997). The detection limit of copper ions was measured to be 2.3 × 10−8 mol L−1. The probable mechanism was studied by UV/Vis spectrum and Job's plot method. The results indicated that Q-CD-Cu(II) complex was formed and intramolecular charge transfer (ICT) took place. At last, the probe was successfully applied for determination of copper ions in water bodies, vegetables and fruits with good recovery. The study showed that Q-CD system could detect copper ions as a fluorescent probe with high selectivity, sensitivity and larger linearity range.

Titrations without the Additions: The Efficient Determination of pKa Values Using NMR Imaging Techniques

Abstract: It can be very informative to acquire NMR spectra of a sample as a function of the solution pH. Examples can be found in the design of host–guest complexes or in the determination of the pKa values of organic molecules. In the conventional procedure, a series of spectra must be recorded and the pH of the sample adjusted manually between successive NMR measurements. As an alternative to this laborious procedure, we demonstrate how controlled pH gradients may be established in 5 mm NMR tubes and analyzed using standard NMR equipment in a “single shot” experiment. Using 1H NMR imaging techniques and a set of NMR pH indicator compounds, we are able to measure the pH of a sample as a function of position along a pH gradient. We are thus able to obtain the necessary set of 1H NMR spectra as a function of pH from a single sample in a single NMR experiment. As proof of concept, we demonstrate how the technique may be employed for the determination of the pKa values of small organic molecules. We are able to measure pKa values from 1 to 11 to within 0.1 units of their literature values. The method is robust to variations in the setting of the pH gradients and can be readily implemented through an automated sample changer.

A versatile quinoxaline derivative serves as a colorimetric sensor for strongly acidic pH

Abstract: A facile and reliable method to monitor strongly acidic pH was developed. The sensing mechanism was found to involve the protonation–deprotonation equilibrium of the synthesized probe HQphy (1) (N-phenyl-N′-quinoxalin-2-ylmethylene-hydrazine) within a working range of pH 0.7–2.7. The eventual sensing of Fe3+ was the outcome of acidity imparted by [Fe(H2O)6]3+ ions in solution during the formation of [Fe(H2O)5(OH)]2+. The protonation–deprotonation phenomenon of HQphy was investigated using 1H NMR and single crystal X-ray diffraction experiments. The protonated probe, H2Qphy+, was crystallized with FeCl4−/ClO4− counter anions as [H2Qphy][FeCl4]·H2O (2)/[H2Qphy][ClO4]·H2O (3). A further complex containing the [H2Qphy] cation (4) was also formed. The complexes were characterized by SC-XRD experiments. Moreover, single crystal to single crystal transformation is observed between 1 and 3. In order to understand the sensing mechanism, various analytical studies, such as UV-Vis titration, ESI-MS spectrometry analysis and 1H NMR, were carried out in detail. A theoretical study correlates well with the experimental data, where the π(L) → π*(L) transition of the ligand is red shifted by 100 nm due to protonation of the quinoxaline moiety. The probe enables discrimination of trihalo acetic acid from its mono- and di-analogues.