جستجوی مقالات مرتبط با کلیدواژه "conductometry" در نشریات گروه "شیمی"

One of the important molecules in homeostasis, especially for hormone metabolism, cellular membrane production, and vitamin D synthesis is cholesterol. However, studies showed that increased levels of this molecule would be associated with increased incidence of cardiovascular diseases including heart failure and myocardial infarction (MI). Thus, the measurement of the blood level of cholesterol is an important step for early detection and prevention of several diseases. Electrochemical sensors with high accuracy could be useful for the detection of cholesterol in body fluids. Due to the outstanding chemical and physical properties that nanoparticles possess, they are perfectly suited for the development of new and improved sensing devices. In particular, electrochemical sensors and biosensors are two types of sensing devices that could benefit from the use of nanoparticles. Many different kinds of nanoparticles, such as metal nanoparticles, oxide nanoparticles, semiconductor nanoparticles, and even composite nanoparticles, have found widespread application in electrochemical sensors and biosensors, respectively. This review has covered a variety of electrochemical biosensors for cholesterol detection, including conductometric, amperometric, and potentiometric-based biosensors, as well as their detection techniques and limitations.

It is known, that conductivity of liquid media as well as biological objects directly related to the mobility of ions, which in turn depends on electric field strength. This article describes general principles and applications of method and hand-made conductometry device for measurement conductivity of a single biological cells and liquid media in pulsed electric field with rising strength. The device allows to determine the conductivity in the range 0.1-105 μS/cm (with an error about 3%) in the field strengths 0-10 kV/cm, pulse duration 50 μs, repetition period 5-10 s. Conductometric measurements were carried out on mouse and cow oocytes in 0.3 M solution of sucrose and some 0.3M aqueous solutions: xylitol, sorbitol, mannitol, glucose, sucrose, conventional distillate and deionized apyrogenic water. It was found that with rising in the field strength, the conductivity of cells first increases gradually and almost linearly in the range 0.2-1.3 kV/cm, and then sharper and finally exponentially, with strength more 2.8 kV/cm and 3.3 kV/cm for mouse and cow oocytes respectively, i.e., electric breakdown of the cell membrane occurs. The conductivity of liquid media is almost independent of the field strength, but small variations in some media have shown the presence of conductive impurities in them, which are absent in the solvent. Thus, the cell conductivity changes in rising field strength can detect and investigate all stages of membrane electroporation (reversible and irreversible electric breakdown) and the method can serve for estimating the purity of the initial reagents as well as quality control of other liquid media.

The complexation reaction between hydroxyl ammonium (HONH3+) cation with 18-crown-6 (18C6) ligand was studied in dimethylsulfoxide – water (DMSO-H2O), methanol – water (MeOH-H2O) and dimethylformamid – methanol (DMF-MeOH), binary solutions at different temperatures using conductometric method. The obtained results show that the stoichiometry of the complex formed between HONH3+ cation with (18C6) in all of the binary mixed solvents is 1:1[ML], as well as, these results show that the nature and the composition of the solvent systems are important factors that are effective on the stability of the complex formed between the macrocyclic ligand and metal cation in solutions. A non-linear behavior was observed for changes of stability constants of the complex versus the composition of the binary mixed solvents. The values of thermodynamic parameters show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents and the complex is entropy stabilized, but enthalpy destabilized in most compositions of binary solutions.

Spectrophotometric and electrochemical studies were successfully used in quantitative analysis of Amitriptyline Hydrochloride (ATH) and Nortriptyline Hydrochloride (NTH). Conductometric titration were carried out in equeous solution using iodide and dopamine and serotonine as titrant. Two new methods using spectrophotometry are dascribed for the determination of (ATH) and (NTH) with potassium bromate as the oxidizing agent and acid dyes, Methyl orange and Indigo carmine. Both spectrophotometric methods are based on the oxidation of mentioned drugs by a known excess of bromate in acid medium and in the presence of excess of bromide followed by estimation of surplus oxidant by reacting with either Indigo carmine (method A) or Methyl orange (method B) and measuring the absorbance at 609 or 507 nm.

A new Schiff base ligand, 2,2'-{pyridine-2,6-diylbis[nitrilo(E)methylylidene]}bis(4 bromophenol),has been synthesized by reaction of the 2,6-diamino pyridine with 5-bromo salicylaldehyde at ethanolunder refluxing. The structure of the synthesized compound resulted from the IR, 1HNMR, MS andUV spectroscopy and elemental analysis data. Formation Constant (kf) value of it’s complexes withCu2+, Ni2+, Cd2+, Co2+ and Hg2+ has been determined Conductometrically. The formation constants ofthe resulting 1:1 complexes have been calculated from the computer fitting of the molar conductance- mole ratio data at different temperatures. The stability of the complexes to vary in acetonitrilesolvent was in the order of Cu2+ > Cd2+ > Co2+ > Hg2+ > Ni2+. The enthalpy and entropy changes ofthe complexation reactions have been evaluated from the temperature dependence of formationconstants.

The interactions between oxyphenonium bromide (OXBr) and two precipitating reagents, silver nitrate (AgNO3) and phosphomolybdic acid (PMA) have been studied by conductometric and spectroscopic techniques. The equilibrium constant, the solubility product constant and other functions related to the process of precipitating OXBr were calculated exploiting the conductometric procedure. Furthermore, new approaches towards equivalence point detection have been pursued. In this itinerary, differential conductivity methods and Boltzmann sigmoid fitting model were found to be more appropriate compared to the conventional routine. The described procedures allowed the determination of OXBr within the range of 1-20 mg using both reagents. The molar combining ratio reveals that (1:1) (drug: reagent) ion associates are formed for both reagents with OXBr. Moreover, the obtained precipitate has been spectroscopically characterized using IR and 1H-NMR. The proposed conductometric method was applied successively to pharmaceutical formulations containing OXBr and the results obtained were favorably compared with those obtained using the reference conductometric method.

In this study, spectroscopic and conductometric investigations of the interactions between oxyphenonium bromide (OXBr) and two dyes; chromotrope 2R (C2R) and ammonium reineckate (AMRT) are reported. The solubility product constant as well as other parameters related to the process of precipitating OXBr is premeditated operating the conductometric procedure. Moreover, contemporary approaches towards equivalence point localization have been pursued and compared. In this itinerary, the numerical differential conductivity methods were objective and systematic. However, Boltzmann sigmoid fitting model was more adequate for data analysis with less errors compared to the conventional and the differential methods. A molar ratio of (1:1) (OXBr:reagent) complexes in aqueous solutions have been determined conductometrically.The described procedures allowed the investigation of OXBr within the range of 3-15 mg using both reagents. Moreover, the obtained precipitate has been spectroscopically characterized using IR and 1H-NMR. The proposed conductometric method was applied successively to pharmaceutical formulations containing OXBr and the results obtained were favorably compared with those obtained using the reference method.

Two simple and sensitive conductometric procedures were investigated for the determination of torasemide (TOS) using potasium tetraphenyl borate (K TPB) and ammonium reineckate (Amm. RNC) were described. Optimized conditions including temperature, solvent and reagent concentration were studied. The suggested methods were used for conductometric determination of (TOS) in its pharmaceutical preparations. Precision, measured as relative standard deviation was less than 1% and accuracy was 99.76 %.The obtained results were comparable with data using the reported method. The proposed procedures were successfully adapted for the determination of (TOS) in plasma. For comparison, some interference was also determined by the condutometric titrations. At equimolar concentration levels, some molecules of similar structure interfere with the original drug. A reduction in interferent concentration by a factor of 10 negated the interference.

The complexation reaction between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix5) ligand with Zn2+, Ni2+, Co2+, Pb2+, Mn2+ and Cu2+ ions were studied conductometrically in different AcetoNitrile-NitroMethane (AN-NM) and AcetoNitrile-Methanol (AN-MeOH) mixtures. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance in various mole ratios. The enthalpy and entropy changes of the complexation reactions were derived from conductometric titrations in different AN-NM mixtures at various temperatures. The results revealed that Kryptofix5 forms very stable 1:1 complexes with mentioned cations in all AN-NM and AN-MeOH mixtures. It was found that the stability of the resulting complexes decreased with increasing nitromethane or methanol in the solvent mixture. The TΔS° vs. ΔH° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy-entropy compensation in the complexation reactions.

Ketotifen (KET)–selective electrode of both conventional polymer membrane and coated graphite types, based on incorporation of ketotifen–tetraphenyl borate (KETTPB) ion-pair have been constructed. The influences of membrane composition, temperature, pH of the test solution, ionic strength and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian concentration range 1.0×10-5 to 1.0×10-2 M and 5.0×10-6 to1.0×10-2 M with a slope of 57.5±1.07 and 59.0±0.9 mV per decade and lower limit of determination are 1.0×10-5 M and 5.0×10-6 M for conventional and coated graphite types, respectively. The electrodes display a good selectivity for ketotifen with respect to a number of common foreign inorganic and organic species. The response not affected by pH between 2.0 and 4.9. The electrode was successfully used for determination of ketotifen both in pure solution and in pharmaceutical preparation. The solubility product of the ion-pair and also the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductometrically.