Effects of Inorganic Orthophosphate and Pyrophosphate on Dissolution of Calcium Fluoride in Water

1988 ◽  
Vol 67 (2) ◽  
pp. 447-449 ◽  
Author(s):  
F. Lagerlöf ◽  
E. Saxegaard ◽  
P. Barkvoll ◽  
G. Rølla
Keyword(s):  
Aqueous Solutions ◽  
Calcium Fluoride ◽  
Clinical Studies ◽  
Slow Release ◽  
Dental Enamel ◽  
Fluoride Release ◽  
Ph Values ◽  
Rate Of Dissolution ◽  
Low Concentrations ◽  
Ph Dependent

Calcium and fluoride release from excess solid calcium fluoride was monitored for 15-30 min in aqueous solutions containing various concentrations of inorganic orthophosphate and pyrophosphate. Low concentrations of these ions (1-10 μmol/L) considerably inhibited the rate of dissolution of calcium fluoride. This inhibition was pH-dependent, being reduced at pH values below 5. It is suggested that a reduced calcium fluoride dissolution rate, in the presence of phosphate, can account for the relatively slow loss of calcium fluoride from dental enamel observed in recent clinical studies. It also appears that calcium fluoride coated with phosphate may provide a pH-controlled slow release of fluoride that may be of clinical significance and a major component of the cariostatic mechanism of topically applied fluoride.

Kinetics analysis of the decay of phenylhydrazonopropanedinitrile addition products with thiols in aqueous solutions

1989 ◽  
Vol 54 (12) ◽  
pp. 3387-3396 ◽  
Author(s):  
Marián Antalík ◽  
Ernest Šturdík ◽  
Dušan Podhradský ◽  
Ingrid Poleková ◽  
Ľudovít Drobnica
Keyword(s):  
Experimental Data ◽  
Carbon Atom ◽  
Aqueous Solutions ◽  
Decisive Role ◽  
Kinetic Description ◽  
Kinetics Analysis ◽  
Imino Group ◽  
Ph Values ◽  
Ph Dependent ◽  
Good Agreement

The reactions of phenylhydrazonopropanedinitriles with thiols are reversible and with increasing pH-values of aqueous solutions the equilibrium is shifted them to the side of the reactants. A mechanism of the decay of corresponding addition products was proposed and the kinetic description based on this mechanism is in good agreement with the obtained experimental data. From the viewpoint of the decay, the pH-dependent dissociation of the proton of the imino group formed by addition of thiol to the nitrile carbon atom plays a decisive role. The obtained knowledge is useful with respect to the use of phenylhydrazonopropanedinitriles as affinants for selective and reversible sorption of low-molecular thiols and thiol-proteins in affinity chromatography as well as for the study of the mechanism of the effect of these substances in oxidative and photosynthetic phosphorylation and biological systems in general.

scholarly journals Cadmium Removal from Aqueous Systems UsingOpuntia albicarpaL. Scheinvar as Biosorbent

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Rosa Icela Beltrán-Hernández ◽  
Gabriela Alejandra Vázquez-Rodríguez ◽  
Luis Felipe Juárez-Santillán ◽  
Ivan Martínez-Ugalde ◽  
Claudia Coronel-Olivares ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Functional Groups ◽  
Raman Spectra ◽  
Infrared And Raman Spectra ◽  
Aqueous Systems ◽  
Cadmium Removal ◽  
Ph Values ◽  
Natural Adsorbent ◽  
Low Concentrations ◽  
Heating Up

The aim of this research was to investigate the use of a natural adsorbent like nopal (Opuntia albicarpaL. Scheinvar) for removing cadmium from aqueous solutions with low concentrations of this metal. Two treatments were applied to the cladodes: a dehydration to get dehydrated nopal (DHN) and heating up to 90°C to obtain a thermally treated nopal (TN). After examining the effect of various pH values (2–7), the capacity of each biosorbent was examined in batch sorption tests at different dosages (0, 500, 1000, 1500, 2000, and 3000 mg L−1). The results indicated that adsorption of cadmium to biomass of DHN and TN was highly dependent on pH and biosorbent dosage. The best removal of cadmium (53.3%, corresponding toqeof 0.155 mg g−1) was obtained at pH 4.0 by using the TN sorbent. Infrared and Raman spectra confirmed that cadmium removal occurred via adsorption to –OH functional groups.

Adsorption Behaviors of Hydroquinone onto Porous Adsorbents

2012 ◽  
Vol 610-613 ◽  
pp. 1971-1974
Author(s):  
Zeng Yin Zhu ◽  
Bing Li ◽  
Hai Suo Wu ◽  
Wei Liu ◽  
Jin Wei
Keyword(s):  
Activated Carbon ◽  
Phenolic Compounds ◽  
Aqueous Solutions ◽  
Adsorption Capacity ◽  
Molecular Species ◽  
Adsorption Kinetic ◽  
Adsorption Behaviors ◽  
Low Concentrations ◽  
Porous Adsorbents ◽  
Ph Dependent

As the toxicity even at low concentrations, pollution of phenolic compounds has become an issue of international concern. Adsorption has been proven to be the effective and widely used method for phenolic compounds removal. In this study, porous resins as adsorbents for the removal of hydroquinone from aqueous solutions were evaluated. Activated carbon F400D was employed for comparison. The faster adsorption kinetic was observed on the mesoporous XAD-4, while the higher adsorption capacity was obtained on the microporous NDA150, which had larger surface area. Despite the different surface properties and pore structures of the studied adsorbents, similar trends of pH-dependent adsorption were observed, implying the importance of the hydroquinone molecular species to the adsorption onto the porous adsorbents. This work provided an understanding of adsorption behavior of hydroquinone on porous adsorbents.

Detection of low concentrations of volatile amines in aqueous solutions using pH-dependent fluorophores

2015 ◽  
Vol 10 (5-6) ◽  
pp. 337-344 ◽  
Author(s):  
B. B. Meshkov ◽  
I. V. Ionova ◽  
V. P. Tsybyshev ◽  
M. V. Alfimov ◽  
V. A. Livshits
Keyword(s):  
Aqueous Solutions ◽  
Low Concentrations ◽  
Ph Dependent ◽  
Volatile Amines

HPLC Analysis of Oxytetracycline Residues in Honey

1986 ◽  
Vol 49 (5) ◽  
pp. 383-388 ◽  
Author(s):  
PETER SPORNS ◽  
SUET KWAN ◽  
LAWRENCE A. ROTH
Keyword(s):  
High Performance Liquid Chromatography ◽  
Liquid Chromatography ◽  
Aqueous Solutions ◽  
High Performance ◽  
Hplc Analysis ◽  
Extraction Procedure ◽  
Hplc Method ◽  
Limits Of Detection ◽  
Ph Values ◽  
Double Extraction

Oxytetracycline (OTC), also known commercially as Terramycin, was determined to be more stable in honey than in buffered aqueous solutions at similar pH values and temperatures. A rapid high performance liquid chromatography (HPLC) method was developed to detect and quantitate OTC using a 1:1 dilution (wt/wt) of honey samples in water. Using 355 nm as the wavelength of detection, amounts as low as 0.5 μg/ml could be detected in the above solution. The limits of detection were lowered considerably by a double extraction procedure.

Flow Behaviors of High Acyl Gellan Aqueous Solutions as Affected by Temperature, and Calcium and Gellan Concentrations

2008 ◽  
Vol 4 (5) ◽  
Author(s):  
Yiqun Huang ◽  
Pawan Singh Takhar ◽  
Juming Tang ◽  
Barry G Swanson
Keyword(s):  
Shear Rate ◽  
Aqueous Solutions ◽  
Apparent Viscosity ◽  
Flow Resistance ◽  
Effect Of Temperature ◽  
Temperature Changes ◽  
Influence Of Temperature ◽  
Rheological Behaviors ◽  
Low Concentrations ◽  
Influence Of Temperature On

Rheological behaviors of high acyl (HA) gellan are not well understood partially because of its relatively late commercialization compared to low acyl gellan. The objective of this study was to investigate the effect of temperature (5-30 °C), calcium (0, 1 and 10 mM) and gellan concentrations (0.0044-0.1000% w/v) on the flow behaviors of high acyl gellan aqueous solutions using rheological tests. Gellan solutions with 0 or 1 mM added Ca++ exhibited shear thinning behavior at gellan concentrations above 0.0125%. The influence of temperature on apparent viscosity (shear rate, 100 s-1) of gellan solutions can be described with an Arrhenius relationship. The apparent viscosity of gellan solution at low concentrations was more sensitive to temperature changes. The addition of Ca++ led to a decrease in flow resistance for a dilute gellan solution (<0.0125%), but an increased resistance for a relatively concentrated gellan solution (>0.0125%).

Vanadium(IV)−Citrate Complex Interconversions in Aqueous Solutions. A pH-Dependent Synthetic, Structural, Spectroscopic, and Magnetic Study

2001 ◽  
Vol 40 (23) ◽  
pp. 5772-5779 ◽  
Author(s):  
M. Tsaramyrsi ◽  
M. Kaliva ◽  
A. Salifoglou ◽  
C. P. Raptopoulou ◽  
A. Terzis ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Magnetic Study ◽  
Citrate Complex ◽  
Ph Dependent

scholarly journals Kinetics of thiamin cleavage by sulphite

1969 ◽  
Vol 113 (4) ◽  
pp. 611-615 ◽  
Author(s):  
J. Leichter ◽  
M. A. Joslyn
Keyword(s):  
Aqueous Solutions ◽  
Rate Constant ◽  
Sulphur Dioxide ◽  
First Order ◽  
Ph Values ◽  
Rate Of Reaction ◽  
Kinetics Of

Results are presented on the rate of thiamin cleavage by sulphite in aqueous solutions as affected by temperature (20–70°), pH(2·5–7·0), and variation of the concentration of either thiamin (1–20μm) or sulphite (10–5000μm as sulphur dioxide). Plots of the logarithm of percentage of residual thiamin against time were found to be linear and cleavage thus was first-order with respect to thiamin. At pH5 the rate was also found to be proportional to the sulphite concentration. In the pH region 2·5–7·0 at 25° the rate constant was 50m−1hr.−1 at pH5·5–6·0, and decreased at higher or lower pH values. The rate of reaction increased between 20° and 70°, indicating a heat of activation of 13·6kcal./mole.

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