Investigation of a Simple and Cheap Source of a Natural Indicator for Acid-Base Titration: Effects of System Conditions on Natural Indicators

This study investigated a natural indicator for acid-base titration which is extracted from guinea corn leaves popularly called “waakye leaves” in Ghana. Four types of acid-base titration were studied: strong acid versus (v/s) strong base, strong acid versus weak base, weak acid versus strong base, and weak acid versus weak base. The indicator color change, pH range and the average titre values were determined for each type of acid-base titration. These values were comparable to those obtained from three standard indicators: methyl orange, methyl red and phenolphthalein. Total flavonoids (TF) and condensed tannin (CT) from the crude leaves extract were determined which might be the major reasons for the activity of the extract as an indicator for simple acid-base titration. The authors suggest that the natural indicator is cheap, available, simple to extract, user and environmentally friendly and could be an excellent replacement for standard indicators.

Spectroscopic study on variations in illite surface properties after acid-base titration

FT IR, Raman microscopy, XRD, 29 Si and 27 Al MAS NMR, were used to investigate changes in surface properties of a natural illite sample after acid base potentiometric titration. The characteristic XRD lines indicated the presence of surface Al Si complexes, preferable to Al(OH) 3 precipitates. In the microscopic Raman spectra, the vibration peaks of Si O and Al O bonds diminished as a result of treatment with acid, then increased after hydroxide back titration. The varied ratio of signal intensity between IV Al and VI Al species in 27 Al MAS NMR spectra, together with the stable BET surface area after acidimetric titration, suggested that edge faces and basal planes in the layer structure of illite participated in dissolution of structural components. The combined spectroscopic evidence demonstrated that the reactions between illite surfaces and acid leaching silicic acid and aluminum ions should be considered in the model description of surface acid base properties of the aqueous illite.

Determination of Carboxyl Group on Fabric by Acid-base Titration

Polycarboxylic acids have been widely researched as non-formaldehyde DP finishes since late 1980s. However, there has no satisfied wet chemical method for quantifi-cation the carboxylic groups or the esterlinkages on fab-ric, which is important in investigation some basic as-pects of the esterification between polycarboxylic acids and cellulose. In this paper, the wet chemical analysis method, Ca(AC)2 back - titration, had been established to determinate the COOH on fabric. The reliability of this method had also been proved.

Analysis of the electron transfer pathway in small laccase by EPR and UV-vis spectroscopy coupled with redox titration

Bacterial small laccases(SLAC) are promising industrial biocatalysts due to their ability to oxidize a broad range of substrates with exceptional thermostability and tolerance for alkaline p H. Electron transfer between substrate, copper centers, and O2is one of the key steps in the catalytic turnover of SLAC. However, limited research has been conducted on the electron transfer pathway of SLAC and SLAC-catalyzed reactions, hindering further engineering of SLAC to produce tunable biocatalysts for novel applications. Herein, the combinational use of electron paramagnetic resonance(EPR) and ultraviolet-visible(UV-vis) spectroscopic methods coupled with redox titration were employed to monitor the electron transfer processes and obtain further insights into the electron transfer pathway in SLAC. The reduction potentials for type 1 copper(T1Cu), type 2 copper(T2Cu) and type 3copper(T3Cu) were determined to be 367 ± 2 mV, 378 ± 5 m V and 403 ± 2 mV,respectively. Moreover, the reduction potential of a selected substrate of SLAC, hydroquinone(HQ), was determined to be 288 mV using cyclic voltammetry(CV). In this way, an electron transfer pathway was identified based on the reduction potentials. Specifically,electrons are transferred from HQ to T1Cu, then to T2Cu and T3Cu, and finally to O2.Furthermore, superhyperfine splitting observed via EPR during redox titration indicated a modification in the covalency of T2Cu upon electron uptake, suggesting a conformational alteration in the protein environment surrounding the copper sites, which could potentially influence the reduction potential of the copper sites during catalytic processes. The results presented here not only provide a comprehensive method for analyzing the electron transfer pathway in metalloenzymes through reduction potential measurements, but also offer valuable insights for further engineering and directed evolution studies of SLAC in the aim for biotechnological and industrial applications.

Determination of pKa values of alendronate sodium in aqueous solution by piecewise linear regression based on acid-base potentiometric titration

As a mono-sodium salt form of alendronic acid,alendronate sodium presents multi-level ionization for the dissociation of its four hydroxyl groups.The dissociation constants of alendronate sodium were determined in this work by studying the piecewise linear relationship between volume of titrant and p H value based on acidbase potentiometric titration reaction.The distribution curves of alendronate sodium were drawn according to the determined p Ka values.There were 4 dissociation constants(pKa_1=2.43,pKa_2=7.55,pKa_3=10.80,pKa_4=11.99,respectively) of alendronate sodium,and 12 existing forms,of which 4 could be ignored,existing in different p H environments.

Pitfalls and Uncertainties of Using Potentiometric Titration for Estimation of Plant Roots Surface Charge and Acid-Base Properties

Amount and properties of roots surface charge are important for nutrient uptake and balance in plants. Roots surface charge markedly varies at different rizosphere conditions (particularly pH and ionic strength), which can markedly alter during vegetation season. Among recently available measuring methods, surface charge-pH dependence of roots (as well as other biological objects) is most easily evaluated by potentiometric titration. Use of this method is also easy at different ionic strengths. Potentiometric titration also allows for estimation of the distribution of charge generating surface groups. However, many applications of this method seem to be based either on incorrect methodical or theoretical approaches. In this paper we discuss the methodical and theoretical backgrounds of the titration method. Basing on experimental titration curves of roots of barley grown in nutrient solution, we show inconsistency of surface charge results obtained at different measuring conditions. Limitations of theoretical interpretations of the results are outlined also.

Triphenylmethanol and Tris(2-(hydroxymethyl)phenol) Derivatives: Synthesis and Application as Indicators for Acid-Base Volumetric Titration

Polyphenols are naturally occurring compounds found largely in fruits, vegetables, cereals and beverages. Currently, there is much interest in the potential health benefits of dietary plant polyphenols as antioxidants. The effect of polyphenols on human cancer cells is most often protective and induces a reduction in the number of tumors or rate of growth. During our course of study on anticancer prodrugs, twelve triphenylmethanol and one tris(2-(hydroxymethyl) phenol derivatives were synthesized as a carrier of several drugs with optimized lipophilicity. Besides application of these compounds as a foundation for anticancer drug delivery systems, these compounds were evaluated as indicators for the acid-base volumetric titration of a standard solution of hydrochloric acid with a standard solution of sodium hydroxide. The experiments indicated a moderate-to-sharp color transition of the solutions near the neutralization point for most indicators. These indicators may have potential applications for acid-base titrations in a narrow range.

Stability of K-struvite in High Temperature and Acid-base Environment

K-struvite was prepared by precipitation method,and the stability of K-struvite in high temperature and acid-base environment were investigated by X-ray diffraction(XRD),thermogravimetric analysis(TG/DSC),and infrared spectroscopy(FT-IR).The results show that K-struvite decomposes from 50 to 110℃,and the mass loss begins at 50℃before being completely destroyed at 110℃,then further heating at temperature above 500℃leading to complete loss of the binding water in K-struvite.Moreover,K-struvite is more stable in alkaline environments than acidic environment.

Comparative Study on the Acid-Base Indicator Properties of Natural Dye, Turmeric Rhizome (Curcuma longa) and Synthetic Dyes

Acid-Base Indicator, Turmeric Rhizome (Curcuma longa) was extracted from the root of a turmeric plant. The turmeric was peeled, washed and dried in an oven at 60°C. It was ground into powder and soaked in hot and cold ethanol for the extraction. The extract was filtered and part of it was concentrated to yield a reasonable quantity of turmeric indicator. On standardization of acid with a base, 0.05 M base respectively of Sodium hydroxide (NaOH), sodium carbonate (Na2CO3) and Disodium borate (B4Na2O7) were used. Hot and cold extracts of turmeric were used as indicators and were compared with methyl orange and phenolphthalein. On the preliminary test carried out, hot and cold turmeric indicator showed yellow colour in acid medium and orange colour in the base. Methyl orange showed red colour in acid but yellow in the base, phenolphthalein was colourless in acid but pink in the base. During titration there were colour changes at the end points in the entire test carried out. The average volumes at ends points were calculated, the molar concentrations and mass concentrations of the acids used were also determined. The results showed that there was no difference between the natural indicators used and the existing synthetic indicators which are toxic to our environment.

Application of Amino Acid-Based Surfactant in Dishwasher Detergent

The application of amino acid-based surfactant in dishwasher detergent was studied in this paper. The foam and oil-removing performance of amino acid surfactants in alkaline condition were test to discuss feasibility of amino acid-based surfactant from natural origin as the alternative to traditional nonionic surfactants from petroleum origin in dishwasher detergent. Comparative study was conducted through using various amino acid-based surfactants and nonionic surfactants respectively, together with enzymes and peroxide to formulate dishwasher detergents, and their application properties such as foam performance and detergency were also evaluated when washing different tableware in automatic dishwasher. The results showed that among all tested amino acid surfactants, glutamate surfactants showed low foaming and high oil-removing ability in alkaline condition, and excellent decontamination ability in dishwashing tests.

Acid-base characterization of foursulfide minerals

The amphoteric properties of four sulfide minerals were characterized byacidimetric-alkalimetric titration. Chalcocite, galena, and sphalerite were found to bediprotic acids, while pyrite was determined to be a triprotic acid. Intrinsic acidity con-stants for the four minerals are as follows: chalcocite-pK_(a1)=5.25, pK_(a2)=9.68;galena- pK_(a1)=5.26, pK_(a2)=9.62; sphalente- pK_(a1)= 5.08, pK_(a2)= 9.13;and pyrite - pK_(a1) = 3.50,pK_(a2)=5.32, pK_(a3)=9.81.

Determination of aniline in environmental water samples by alternating-current oscillopolarographic titration

A new method for the determination of aniline in environmental water based on oscillopolarographic titration was presented in this paper. Several factors including the kind, concentration, and volume of acid, the dosage of potassium bromide, the temperature and concentration of concomitant substances were investigated in detail. The experimental results indicated that this method was simple, rapid, and sensitive. The linear range was 8.367 × 10(?4) to 2.789 × 10(?2) mol L(?1), the relative standard deviation (R.S.D.) was lower than 0.96%, and the spiked recoveries of aniline in environmental water samples were in the range of 99.4–106.9% under the optimal conditions. The results indicated that the present method could be used as an alternative method for aniline determination in realworld water samples.

Study of Complexes of Lanthanum with Amino Acids by Titration Calorimeter

The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1∶1 and 1∶2 in proportion have been determined by titration calorimeter at 298.15 K. The enthalpy change makes a predominant contribution to the stability of these complexes. The ring in amino acid associated with lanthanum ion helps to enhance the stability of complexes. Steric effects between rings in complexes leads to that the equilibrium constants of reaction of the complexes (1∶2) is much less than that of the complexes (1∶1).

POTENTIOMETRIC TITRATION OF CALCIUM IN SEAWATER

By using calcium ion selective elatrode (Ca ISE) as indicating electrode, saturated calomel electrode (SCE) as reference electrode and EGTA as titrant, calcium in seawater was determined by potentiometric titration in borate buffer solution. This method can reduce observation errors in the determination of the endpoint, and thus provide better analytical precision(<0.08%) than present complexometric titration.

Oxidative esterification of acetol with methanol to methyl pyruvate over hydroxyapatite supported gold catalyst: Essential roles of acid-base properties

Acetol is a major light oxygenate and readily produced from staged or fast pyrolysis of lignocellulose biomass. Herein we report that acetol can be selectively converted to methyl pyruvate, an important fine chemical, through oxidative esterification over Au-based catalysts. Detailed experimental studies showed that Au on amphoteric supports with appropriate strength and balanced ratio of acid and base sites can facilitate the desired oxidative-esterification pathway without accelerating undesired aldol-condensation or Cannizzaro reactions. In particular, hydroxyapatite (with a Ca/P ratio of 1.62) supported Au achieved 87% selectivity to methyl pyruvate at an acetol conversion of 62%.

Conductometric Titration for the Prediction of Conductivity in Solutions with Polymeric Membranes

The analytical technique of conductometric titration is used to characterize polymeric materials.This technique allows obtaining the polymer dry weight capacity(DWC) and the extent of reaction and establishing the optimal number of water molecules per sulfonic groups.In this particular case the polymer material under study was Nafion?117.Two different reactions were made: Neutralization and exchange.Both of them allow obtaining the same result.Conductometric titrations could be considered as a good method to study the neutralization and exchange reactions for polymeric materials used in fuel cells or electrolyzers.The implementation of this analytical technique allows reducing operation time of those types of materials.The waiting time between determinations permits to say that the amount of reactant consumed and products obtained were the same after each addition of titrant.

Extraction Mechanism of Rare Earths with Sec-Octylphenoxy Acetic Acid by Two-Phase Titration Technique

The compositions of the extracted complexes of La, Gd, Er and Y with sec octyl phenoxy acetic acid in heptane and the related apparent extraction equilibrium constants K M were determined using two phase titration technique. The stoichiometric compounds for La, Gd, Er and Y should be LaA 3·2.5HA, GdA 3·3HA, ErA 3·3.1HA and YA 3·4.3HA respectively. And their p K M are 3.43, 3.46, 3.08 and 2.58 respectively.

Rapid determination of phenolic compounds in water samples by alternating-current oscillopolarographic titration

A rapid, simple and sensitive method was demonstrated for the determination of phenolic compounds in water samples by alternating-current oscillopolarographic titration. With the presence of sulfuric acid, phenol could be transferred into a nitroso-compound by reacting with NaNO2. The titration end-point was obtained by the formation of a sharp cut in the oscillopolarographic with infinitesimal NaNO2 on double platinum electrodes. The results showed that phenol had an excellent linear relationship over the range of 4.82×10^-6 -9.65×10^-3 mol/L, the RSD of the proposed method was lower than 1.5%, and the spiked recoveries of three real water samples were in the range of 95.6%-106.9%.

Hepatic encephalopathy complicated with hyponatremia and acid-base disturbance and its prognosis

Objective:To improve the diagnosis and therapeutic effect of occurrence and development of hyponatremia and disorder of acid-base balance among patients with hepatic encephalopathy(HE) by elucidating the regularity and mechanism,as well as its influence on prognosis.Methods:327 HE patients admitted to our hospital from January 1990 to June 2010 were enrolled.Meanwhile 316 patients hospitalized in the medical department of the same hospital were chosen as the control group.Patients in both groups were given the same methods to measure arterial blood gas parameters(pH value,PaCO2,[HCO3-],TCO2,BE and SaO2),blood biochemistry([Na+],[K+],[Cl-]),liver function,kidney function and blood glucose,serum sodium,and thereupon tocalculate the anion gap(AG) and the potential [HCO3-],and acid-base balance disorder.Results:Among the 327 HE patients,hyponatremia was found in 188 cases(57.4%),of whom 132 patients died(70.2%).While among the 316 patients in control group,68 presented with hyponatremia(21.5%),and 19 died(27.9%).The incidence and mortality were significantly different between the two groups(P<0.001).All the 327 patients presented with different degrees of acid-base balance disorder and 178 died(54.4%),in whom 164(50.2%) belonged to simple acid-base balance disorder and 74(45.1%) died,136(41.6%) were dual acid-base balance disorder and 80(58.8%) died,27(8.2%) were triple acid-base disturbance and 24(88.9%) died.Whereas in the control group only 83 patients(26.2%) were recognized as simple and dual acid-base balance disorder,and 18(21.7%) died.There was higher incidence of acid-base balance disorder and mortality rate in HE group than control one(P<0.001).Conclusion:Hyponatremia is valuable to judge HE patients' prognosis.The key parameters in the judgment and evaluation on acid-base balance disorder among HE patients are the change of pH values and serum electrolyte values.When pH value ≤ 7.30 or > 7.55,it generally suggests a poor prognosis.