NEW ACID-BASIC INDICATORS: RESEARCH USING A SMARTPHONE

Modern cameras, desktop scanners, smartphones allow not only registering an image, but also determining its color characteristics. That allows us to quickly, objectively and automatically determine the color characteristics of colored samples in acid-base titration, because there is a significant error at visually determining the pH range of the color transition. In analytical chemistry the characteristics of acid-base indicators are very important, in particular their pH transition interval. But the disadvantage of most indicators is the wide range of color transition: from 1 to 3 pH units. The aim of this work is to find new acid-base indicators that change color in an alkaline environment and have a narrow pH range of the color transition. We have developed the apparatus and technique of convenient and highprecision simultaneous determination of the pH of the medium and the color of the acidbase indicators. In acid-base titration the PH measurements were performed with a combined glass electrode AD1131 by рН-meter AD1000. The color transition was determined with help of a smartphone with the subsequent processing of the results by computer software. The color characteristics were measured for each channel of the RGB model in the range from 0 to 255. Our apparatus is small and mobile, and allows us simultaneously to measure the pH of the medium and accurately to determine the color characteristics. As a result, we can construct graphical dependencies of color on pH for each channel of the RGB model. We found the N-arylsulfonyl-2-aroylamido-1,4-benzo(naphto)quinone monoimines and 2,5-dibenzoylamido-1,4-benzoquinone are good acid-base indicators. They “work” in the pH range from 8.82 to 11.35 and have a very narrow color transition interval from 0.10 to 0.61. Solutions of these compounds in an alkaline medium have bright intense colors due to formation of mesomeric ions. That allows using of these indicators in the titration of weak acids with strong bases and vice versa by the method of neutralization.

The Thermodynamics of Copper (II) and Nickel (II)- Diamine Complex Formation in Aqueous Solution

<p>This work describes the accurate measurement of the thermodynamic functions Delta G degree and Delta H degree for the step-wise coordination equilibria between each of the ions H+, Ni2+, Cu2+, and, a series of C1-substituted 1,2-diaminoethanes in aqueous solution. The study Involved. (a) The construction of a sensitive constant temperature environment calorimeter for measuring the enthalpy changes in the complex-formation reactions, (b) The rigorous calibration of an electrode system, incorporating a glass electrode, for the direct potentiometric measurement of equilibrium hydrogen ion concentrations in the solutions containing complex ions. The thermodynamic functions Delta G degree and Delta H degree led to accurate Delta S degree values for the step-wise complex-formation reactions. The thesis considers the contribution of the entropy of ligation to the stability of complex ions. The molar entropies of the complex ions have been calculated and their values considered with respect to the coordination number and the possible structure, degree of hydration and steric properties of the ions.</p>

The Thermodynamics of Copper (II) and Nickel (II)- Diamine Complex Formation in Aqueous Solution

<p>This work describes the accurate measurement of the thermodynamic functions Delta G degree and Delta H degree for the step-wise coordination equilibria between each of the ions H+, Ni2+, Cu2+, and, a series of C1-substituted 1,2-diaminoethanes in aqueous solution. The study Involved. (a) The construction of a sensitive constant temperature environment calorimeter for measuring the enthalpy changes in the complex-formation reactions, (b) The rigorous calibration of an electrode system, incorporating a glass electrode, for the direct potentiometric measurement of equilibrium hydrogen ion concentrations in the solutions containing complex ions. The thermodynamic functions Delta G degree and Delta H degree led to accurate Delta S degree values for the step-wise complex-formation reactions. The thesis considers the contribution of the entropy of ligation to the stability of complex ions. The molar entropies of the complex ions have been calculated and their values considered with respect to the coordination number and the possible structure, degree of hydration and steric properties of the ions.</p>

Calibration of glass electrode half-cells v1

The purpose of this document is give glass-electrode half-cell calibration procedure with aqueous buffers.

Physicochemical Stability and Compatibility Testing of Voriconazole in All-in-One Parenteral Nutrition Admixtures

(1) Drug compatibility with all-in-one (AiO) parenteral nutrition (PN) admixtures is a very important pharmaceutical quality issue to be answered based on appropriate laboratory testing. We assessed voriconazole (V), a poorly water-soluble (logP ≈ 1) single-daily dosed antifungal drug monitored in patients and thus candidate for AiO PN admixing for convenient and safe patient care. We evaluated V compatibility and stability in AiO PN admixtures through adapted therapeutic drug monitoring method (drug stability) and visual microscopic emulsion stability by lipid droplets analysis improved by an automated microscopic digital assessment. (2) V was added in concentrations of 0.05/0.25/0.5 mg/mL (143.1/715.7/1431.5 µM), correlating to daily therapeutic dosing, to three commercially available industrial AiO PN admixtures. Three aliquots were stored in the refrigerator (4 °C), at room temperature (24 °C) and under stress conditions in a water bath (37 °C). Samples taken at 0/24/48/72/168 h after admixing were subjected to a stability-indicating one-week analysis. Assessment included visual examination, lipid droplet measurement according to an established and validated method (bright-field microscopy using oil immersion), pH measurement (glass electrode) and V identification/quantification (LC–MS/MS). (3) After one week, all samples at 37 °C showed slight yellow discoloration. The pH values remained stable. All samples met specifications for lipid droplets according to size (upper size ≤8µm, mean size <4.5 ± 2 µm) and number (n ≤ 9 lipid droplets >5 µm). V concentrations were within an acceptable range, calculated for every timepoint as percent of the theoretical concentration spiked into the AiO PN. The median recovery was 98.2% (min–max, 90–112%). (4) At therapeutic doses, commercial V formulations were compatible and stable within specifications over one week in commonly used volumes of commercial AiO PN admixtures at 4–37 °C.

A prototype device of microliter volume voltammetric pH sensor based on carbazole–quinone redox-probe tethered MWCNT modified three-in-one screen-printed electrode

As an alternate for the conventional glass-based pH sensor which is associated with problems like fragile nature, alkaline error, and potential drift, the development of a new redox-sensitive pH probe-modified electrode that could show potential, current-drift and surface-fouling free voltammetric pH sensing is a demanding research interest, recently. Herein, we report a substituted carbazole-quinone (Car-HQ) based new redox-active pH-sensitive probe that contains benzyl and bromo-substituents, immobilized multiwalled carbon nanotube modified glassy carbon (GCE/MWCNT@Car-HQ) and screen-printed three-in-one (SPE/MWCNT@Car-HQ) electrodes for selective, surface-fouling free pH sensor application. This new system showed a well-defined surface-confined redox peak at an apparent standard electrode potential, Eo′ = − 0.160 V versus Ag/AgCl with surface-excess value, Γ = 47 n mol cm−2 in pH 7 phosphate buffer solution. When tested with various electroactive chemicals and biochemicals such as cysteine, hydrazine, NADH, uric acid, and ascorbic acid, MWCNT@Car-HQ showed an unaltered redox-peak potential and current values without mediated oxidation/reduction behavior unlike the conventional hydroquinone, anthraquinone and other redox mediators based voltammetry sensors with serious electrocatalytic effects and in turn potential and current drifts. A strong π–π interaction, nitrogen-atom assisted surface orientation and C–C bond formation on the graphitic structure of MWCNT are the plausible reasons for stable and selective voltammetric pH sensing application of MWCNT@Car-HQ system. Using a programed/in-built three-in-one screen printed compatible potentiostat system, voltammetric pH sensing of 3 μL sample of urine, saliva, and orange juice samples with pH values comparable to that of milliliter volume-based pH-glass electrode measurements has been demonstrated.

The INVESTIGATION OF VARIOUS PHOSPHATE CORROSION INHIBITORS IN CARBON DIOXIDE

Corrosion leads to huge losses every year, and solving this problem is an important task. One of the effective methods of corrosion protection of equipment and pipelines in the oil industry is the use of corrosion inhibitors. Inhibitory protection is the most technological and effective way to control corrosion of oilfield equipment. The article deals with phosphate corrosion inhibitors of complex action in a carbon dioxide environment. The method of corrosion testing is generally accepted. Quantitative indicators of corrosion processes were calculated using formulas, and the measurement uncertainty was estimated using an algorithm using the Student's coefficient with a confidence probability of 0.95. In the course of the work, potentiometric determination of the pH of corrosive media using a combined glass electrode and an ionomer, conductometric and photocolorimetric determination of the content of iron (III) with potassium rhodanide, as well as methods of infrared spectroscopy and electron microscopy were carried out.

Analisis Perbandingan Kadar Keasaman (pH) Tanah Sawah Menggunakan Metode Kalorimeter dan Elektrometer di Desa Matang Setui

Telah dilaksanakan Kerja Praktek dengan judul Analisis Kadar Keasaman (pH) Tanah Sawah Menggunakan Metode Kalorimeter dan Elektrometer di Desa Matang Setui dengan tujuan mengetahui kadar keasaman (pH) tanah menggunakan metode Kalorimeter dan Elektrometer. Metode kalorimeter pada penelitian ini yaitu pengukuran menggunakan Perangkat Uji Tanah Sawah (PUTS), sedangkan elektrometer merupakan metode penetapan pH tanah dengan menggunakan pH meter (glass electrode). Berdasarkan hasil analisis dari kemasaman tanah yang telah diukur menggunakan metode kalorimeter dan elektrometer, tanah sawah yang terdapat di Desa Matang Setui termasuk ke dalam jenis tanah masam. Nilai pH yang terukur menggunakan metode Elektrometer pada titik percobaan yang pertama adalah derajat pH 5, titik kedua pH 5,3 dan titik ketiga dengan pH 5. Menggunakan metode kalorimeter pH yang terukur adalah 5-6. Berdasarkan percobaan yang telah dilakukan dapat dilihat bahwa nilai pH pada metode elektrometer tampak lebih tepat dibandingkan dengan menggunakan metode kalorimeter. Nilai pH yang ditunjukkan oleh metode elektrometer menunjukkan nilai yang lebih pasti, karena hanya menunjukkan satu nilai pH terukur.

Recent Advances in Optical, Electrochemical and Field Effect pH Sensors

Although its first definition dates back to more than a century ago, pH and its measurement are still studied for improving the performance of current sensors in everyday analysis. The gold standard is the glass electrode, but its intrinsic fragility and need of frequent calibration are pushing the research field towards alternative sensitive devices and materials. In this review, we describe the most recent optical, electrochemical, and transistor-based sensors to provide an overview on the status of the scientific efforts towards pH sensing.