Release Of Hydroxyl Ions Research Articles

Toxic Metal Sensing through Novel Use of Hybrid Inorganic and Polymeric Ion-Exchangers

A new sorption-based technique for sensing trace toxic metals (e.g., lead, copper, zinc) in water is described in the article. The methodology uses a novel, environmentally benign, inorganic hybrid sorbent material (HSM) and the pH is the sole surrogate parameter for the detection of toxic metals. HSM is a granular composite of calcium magnesium silicate (Ca2MgSi2O7), sparingly soluble, and maintains a near-constant alkaline pH in contact with water due to steady release of hydroxyl ions (OH−) caused by slow hydrolysis of HSM. When water containing common electrolytes (Na+, Ca2+, Cl−, SO4 2−) is passed through the HSM bed in a mini-column, the exiting pH consistently remains around 9.0. In contrast, in the presence of trace concentration of toxic metals (say lead or zinc) in water, there is a significant drop in pH (>2 units) under otherwise identical conditions. The drop in pH and breakthrough of toxic metal at the column exit occur concurrently. Since the pH is the sole indicating parameter, the presence of commonly occurring buffering species is likely to interfere with the sensing process. While interference of bicarbonate is avoided through adjustment of the inlet pH, the effect of phosphate and natural organic matter (NOM) is overcome using a hybrid anion exchanger (HAIX) prior to HSM. In HAIX, hydrated ferric oxide nanoparticles, dispersed within the polymeric phase, selectively remove phosphate or other weak acid anionic ligands (e.g., fulvate in NOM). This technique validates the detection of lead and zinc in synthetic water, tap water, and river water. The use of HAIX in conjunction with HSM allows the selective removal of phosphate/NOM, while HSM offers selective binding of toxic metal at slightly alkaline pH (∼9.0) resulting from its unique dissolution behavior. Also, different toxic metals, such as Pb, Cu, and Zn, are apt to form labile metal-hydroxy complexes at this pH condition causing dissipation of OH− in the aqueous phase. In essence, all these phenomena synergistically work for interference-free sensing of toxic metals through pH change. Except the pH meter or the indicator solution, no other instrument or chemical is required. This technique has immense potential for field applications in both the developed and the developing world.

PH and calcium ion release evaluation of pure and calcium hydroxide-containing Epiphany for use in retrograde filling

ObjectiveHydroxyl (OH-) and calcium (Ca++) ion release was evaluated in six materials: G1) Sealer 26, G2) White mineral trioxide aggregate (MTA), G3) epiphany, G4) epiphany + 10% calcium hydroxide (CH), G5) epiphany + 20% CH, and G6) zinc oxide and eugenol.Material and MethodsSpecimens were placed in polyethylene tubes and immersed in distilled water. After 3, 6, 12, 24, and 48 h, 7, 14, and 28 days, the water was assessed for pH with a pH meter and for Ca++ release by atomic absorption spectrophotometry.ResultsG1, G2, G4, and G5 had the highest pH until 14 days (p<0.05). G1 presented the highest Ca++ release until 6 h, and G4 and G5, from 12 h through 14 days. Ca++ release was greater for G1 and G2 at 28 days. G6 released the least Ca++.ConclusionMTA, Sealer 26, epiphany, and epiphany + CH release OH - and Ca++ ions. Epiphany + CH may be an alternative as retrofilling material.

Evaluation of calcium ion, hydroxyl ion release and pH levels in various calcium hydroxide based intracanal medicaments: An in vitro study

Aims:Evaluation of calcium ion and hydroxyl ion release and pH levels in various calcium hydroxide based intracanal medicaments.Objective:The purpose of this study was to evaluate calcium and hydroxyl ion release and pH levels of calcium hydroxide based products, namely, RC Cal, Metapex, calcium hydroxide with distilled water, along with the new gutta-percha points with calcium hydroxide.Materials and Methods:The materials were inserted in polyethylene tubes and immersed in deionized water. The pH variation, Ca++ and OH- release were monitored periodically for 1 week. Statistical Analysis Used: Statistical analysis was carried out using one-way analysis of variance and Tukey's post hoc tests with PASW Statistics version 18 software to compare the statistical difference.Results:After 1 week, calcium hydroxide with distilled water and RC Cal raised the pH to 12.7 and 11.8, respectively, while a small change was observed for Metapex, calcium hydroxide gutta-percha points. The calcium released after 1 week was 15.36 mg/dL from RC Cal, followed by 13.04, 1.296, 3.064 mg/dL from calcium hydroxide with sterile water, Metapex and calcium hydroxide gutta-percha points, respectively.Conclusions:Calcium hydroxide with sterile water and RC Cal pastes liberate significantly more calcium and hydroxyl ions and raise the pH higher than Metapex and calcium hydroxidegutta-percha points.

Evaluation of pH and Calcium Ion Release of Root-end Filling Materials Containing Calcium Hydroxide or Mineral Trioxide Aggregate

IntroductionTo evaluate calcium ion release and pH of Sealer 26 (S26) (Dentsply, Rio de Janeiro, RJ, Brazil), white mineral trioxide aggregate (MTA), Endo CPM Sealer (CPM1) (EGEO SRL Bajo licencia MTM Argentina SA, Buenos Aires, Argentina), Endo CPM Sealer in a thicker consistency (CPM 2), and zinc oxide and eugenol cement (ZOE). MethodsMaterial samples (n = 10) were placed in polyethylene tubes and immersed in 10 mL of distilled water. After 3, 6, 12, 24, and 48 hours and 7, 14, and 28 days, the water pH was determined with a pH meter, and calcium release was assessed by atomic absorption spectrophotometry. An empty tube was used as the control group. ResultsThe control group presented a pH value of 6.9 at all studied periods and did not show the presence of calcium ion. S26 presented greater hydroxyl ion release up to 12 hours (p < 0.05). From 24 hours until 28 days, S26, MTA, CPM1, and CPM2 had similar results. In all periods, ZOE presented the lowest hydroxyl ion release. CPM1, followed by CPM2, released the most calcium ions until 24 hours (p < 0.05). Between 48 hours and 7 days, CPM1 and CPM2 had the highest release. A greater calcium ion release was observed for CPM2, followed by CPM1 at 14 days and for S26, CPM1, and CPM2 at 28 days. ZOE released the least calcium ions in all periods. ConclusionSealer 26, MTA, and Endo CPM sealer at normal or thicker consistency release hydroxyl and calcium ions. Endo CPM sealer may be an alternative as root-end filling material.

Sensing of toxic metals through pH changes using a hybrid sorbent material: Concept and experimental validation

AbstractThis article reports a new hybrid sorbent material that is capable of detecting trace concentration of toxic metals, such as zinc, lead, copper, nickel, etc., through pH changes only. The material is essentially a composite granular material synthesized through rapid fusion of a mixture of amorphous hydrated ferric oxide (HFO) and akermanite or calcium magnesium silicate (Ca2MgSi2O7). When a water sample is rapidly passed through a mini‐column containing this hybrid material, effluent pH at the exit always remains alkaline (≈9.0) because of slow hydrolysis of akermanite and steady release of hydroxyl (OH−) ions. This exit solution turns pink through the addition of a phenolphthalein indicator. Commonly encountered electrolytes containing sodium, calcium, chloride, and sulfate have no impact on the exit pH from the mini‐column. However, when trace concentration of a heavy metal (say lead) is present in the sample water, a considerable drop in pH (&gt;2 units) is observed for the exiting solution. At this point, the solution turns colorless through the addition of a phenolphthalein indicator. Moreover, the change in the slope of pH, i.e., −dpH/dBV, provides a sharp, noticeable peak for each toxic metal where BV is the bed volumes of solution fed. The technique allowed detection of zinc and lead through pH swings in synthesized samples, spiked Bethlehem City water, and also in Lehigh River water in the presence of phosphate and natural organic matter (NOM). Using a simple preconcentration technique, lower than 10 μg/l of lead was detected with a significant peak. From a mechanistic viewpoint, high sorption affinity of HFO surface sites toward toxic metal cations, ability of akermanite to maintain near‐constant alkaline pH for a prolonged period through slow hydrolysis and labile metal‐hydroxy complex formation causing dissipation of OH− ions from the aqueous phase provide a synergy that allows detection of toxic metals at concentrations well below 100 μg/l through pH changes. Nearly all previous investigations pertaining to toxic metals sensing use metal‐selective enzymes or organic chromophores. This simple‐to‐operate technique using an inexpensive hybrid material may find widespread applications in the developing world for rapid detection of toxic metals through pH changes. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Phosphorus deficiency does not enhance proton release by roots of soybean [ Glycine max (L.) Murr.

Little work has been done on root exudation in soybean under P deficiency. This study examined the effect of P supply on release of protons and carboxylates by roots of soybean ( Glycine max Heinong 35), and to correlate the release with excess uptake of cations over anions. Plants were either reliant on N 2 fixation or supplied with nitrate and were grown in nutrient solution with 1–50 μM P for 7 weeks. Release of protons and carboxylates from roots, and concentrations of Ca, Mg, K, Na, P, S, Cl and N in plants were measured weekly from week 4. Unlike in many other species, P deficiency decreased proton release per unit root biomass in N 2-fixing plants and increased release of hydroxyl ions in nitrate-fed soybean. While P deficiency generally decreased uptake of K, Ca, Mg, S, Cl and P, it increased nitrate uptake per unit root biomass. Irrespective of P supply, amounts of protons released correlated well with excess uptake of cations over anions by the roots. Phosphorus deficiency increased release of carboxylates but the amounts released were small. The results suggest that soybean displays strategies of P acquisition through decreasing proton release which favors P mobilization in acid soils, and increasing root-to-shoot ratio and specific root length.

Preparation of large-sized hydroxyapatite single crystals using homogeneous releasing controls

Hydroxyapatite (HAP) single crystals with size of tens of micrometer have been synthesized by a controlled homogeneous precipitation method. A complex of calcium bis(2-ethylhexyl) sulfosuccinate (Ca(AOT) 2) and Na 2HPO 4 used to supply the calcium and phosphate ions during the reactions. Hexamethylenetetramine (HMT) is applied as a pH regulator to control the homogeneous release of hydroxyl ions in the bulk solution. Since HAP formation is sensitive to pH, the controlled release of hydroxyl ions by the hydrolysis of HMT can trigger the crystallization of HAP, which is regulated by the solution temperature. The formed HAP crystals have large and smooth crystal facets and their lattice structure can be easily determined by using atomic force microscopy. The control experiments show that HMT plays an important role in the formation of the large HAP since it can provide the homogeneous supersaturation fields in the bulk solution. The application of Ca(AOT) 2 is another helpful factor which reduces the supersaturation level during the crystallization process. This synthesis strategy provides a facile pathway to obtain HAP single crystals at least one order in magnitude larger than the conventional ones.

Carbon and nitrogen mineralization in acidic, limed and calcareous agricultural soils: Apparent and actual effects

Soil pH and calcium carbonate contents are often hypothesized to be important factors controlling organic matter turnover in agricultural soils. The aim of this study was to differentiate the effects of soil pH from those related to carbonate equilibrium on C and N dynamics. The relative contributions of organic and inorganic carbon in the CO 2 produced during laboratory incubations were assessed. Five agricultural soils were compared: calcareous (74% CaCO 3), loess (0.2% CaCO 3) and an acidic soil which had received different rates of lime 20 years ago (0, 18 or 50 t ha −1). Soil aggregates were incubated with or without rape residues under aerobic conditions for 91 days at 15 °C. The C and N mineralized, soil pH, O 2 consumption and respiratory quotient (RQ=ΔCO 2/ΔO 2) were monitored, as well as the δ 13C composition of the evolved CO 2 to determine its origin (mineral or organic). Results showed that in non-amended soils, the cumulative CO 2 produced was significantly greater in the limed soil with a pH>7 than in the same soil with less or no lime added, whereas there was no difference in N mineralization or in O 2 consumption kinetics. We found an exponential relationship between RQ values and soil pH, suggesting an excess production of CO 2 in alkaline soils. This CO 2 excess was not related to changes in substrate utilization by the microbial biomass but rather to carbonates equilibrium. The δ 13C signatures confirmed that the CO 2 produced in soils with pH>7 originated from both organic and mineral sources. The contribution of soil carbonates to CO 2 production led to an overestimation of organic C mineralization (up to 35%), the extent of which depended on the nature of soil carbonates but not on the amount. The actual C mineralization (derived from organic C) was similar in limed and unlimed soil. The amount of C mineralized in the residue-amended soils was ten times greater than in the basal soil, thus masking the soil carbonate contribution. Residue decomposition resulted in a significant increase in soil pH in all soils. This increase is attributed to the alkalinity and/or decarboxylation of organic anions in the plant residue and/or to the immobilization of nitrate by the microbial biomass and the corresponding release of hydroxyl ions. A theoretical composition (C, O, H, N) of residue and soil organic matter is proposed to explain the RQ measured. It emphasizes the need to take microbial biomass metabolism, O 2 consumption due to nitrification and carbon assimilation yield into account when interpreting RQ data.

Assessment of calcium and hydroxyl ions release from mineral trioxide aggregate mixed with four different vehicles (In Vitro Study)

This study was carried out ot determine whether the dissociation of mineral trioxide aggregate (MTA) depends on the vehicle used with ti yb evaluating the release of calcium ions (Cat) and hydroxyl ions (OH) from mixing of MTA whti four types of vehicles: distilled water, camphorated monochlorophenol (CMCP), plain local anesthetic solution, and chlorhexidine gluconate, using Atomic Absorption Spectrophotometer (AAS) and digital pH meter respectively. The results demonstrated that hte distilled water and plain local anesthetic solution are hte most suitable vehicles to eb mixed with MTA and can be routinely used ni preference ot al the other vehicles

Nanocrystalline tetracalcium phosphate cement.

Calcium hydroxide cements can lack long-term stability and achieve sustained release by matrix-controlled diffusion of hydroxyl ions. Tetracalcium phosphate (TTCP) hydrolyzes slowly to form calcium hydroxide and a thin insoluble apatite layer that prevents further reaction. In this study, mechanical amorphization was used to create a setting calcium-hydroxide-releasing cement from TTCP. The effect of high-energy ball milling of TTCP on the mechanical properties of the cement was investigated. X-ray diffraction data were used to determine the phase composition of the set cements. An accelerated in vitro test compared pH of water after prolonged boiling of nanocrystalline TTCP cements and a calcium salicylate material. As milling time increased, cement compressive strength and degree of conversion increased. Hydroxyl ion release from the cement was comparable with that from a calcium salicylate material. This new cement system offers the antimicrobial potential of calcium salicylate materials combined with the long-term stability of insoluble apatite cements.

A laboratory study evaluating the release of hydroxyl ions from various calcium hydroxide products in narrow root canal-like tubes.

The aim of the present study was to describe pH changes in a variety of buffering solutions within a narrow test tube containing either a gutta-percha point with incorporate calcium hydroxide, a commercial calcium hydroxide paste (Calcicur) or a freshly mixed paste of calcium hydroxide in distilled water. The test material was placed centrally in a test tube of 2 mm inner diameter. Saline (1%) was placed at one end, whilst the buffering solutions were introduced at the other. The pH of the buffering solutions was monitored using electrodes placed at each end of the test tube. It was found that the pH 4.01 buffer strongly resisted pH changes at levels below 6.0, whilst saliva and bovine serum was buffered less and more evenly in the whole range up to pH 11.5. The calcium hydroxide containing gutta-percha points caused the pH to increase quickly in the sodium chloride solution to levels above 11.5. However, in bovine serum, in saliva and in the pH 4.01 buffer the pH remained below 8.5, 8.0 and 6.0, respectively, 1 mm from the point. In contrast, the release of hydroxyl ions from the two calcium hydroxide pastes brought pH above pH 11.5 irrespective of the buffering of the solutions 5 mm from the paste. It is concluded that Calcicur and the calcium hydroxide-water mixture contained substantially more available calcium hydroxide than did the calcium hydroxide containing gutta-percha points, with the result that the release of hydroxyl ions from the points was limited in comparison to that from the pastes.

In vitro release of hydroxyl ions from calcium hydroxide gutta-percha points

In endodontic practice, calcium hydroxide is widely used for a number of reasons associated with its high pH. The purpose of the present study was to determine in vitro the alkalizing potential of newly introduced calcium hydroxide gutta-percha points that are proposed for temporary filling of root canals. The materials tested were: calcium hydroxide gutta-percha points; chemical pure calcium hydroxide powder mixed with distilled water; and Reogan rapid, a nonsetting calcium hydroxide preparation. The materials were placed into dialysis tubing and transferred into plastic vials containing bidistilled water. Measurements were taken by a digital pH meter after 10, 20, and 30 s; 1, 15, and 30 min; and 1, 2, 3, 24, 48, 72, 96, and 120 h. The calcium hydroxide containing gutta-percha points showed a significantly lower alkalizing potential than Reogan rapid and calcium hydroxide mixed with distilled water (p < 0.05).

Release of hydroxyl ions during specific adsorption of chloride by variable‐charge soils

AbstractThe release of hydroxyl ions during specific adsorption of chloride by variable‐charge soils of China was studied by comparing the difference in pH of the suspension between a HCl‐treated system and a HNO3−treated system. A difference occurred only for the variablecharge soils, but not for the permanent‐charge soil. The release of OH− ions decreased upon removal of free iron oxides. The quantity of released OH was larger for electrodialyzed soils than that for untreated soils. It was less than 10% of the amount of Cl added. The OH/CI ratioincreased with increasing addition of HCl, suggesting that more OH relative to H2O was replaced by CI.

In vitro release of hydroxyl ions from six types of calcium hydroxide nonsetting pastes

The role of intracanal medication in root canal treatment is very important. Calcium hydroxide (Ca(OH)2) is considered to fulfill many of the properties of an ideal root canal dressing mainly due to its alkalizing pH. It is bacteriocidal and neutralizing to the remaining tissue debris in the root canal(s) and through the continuous release of OH- ions it promotes an alkalizing osteogenic environment for the surrounding tissues. The purpose of this study was to examine the pH values of various Ca(OH)2 based on compounds used as intracanal medicaments over a period of 5 days. The following materials were tested: Calasept, Calcicur, Calxyl blue, Calxyl red, Reogan rapid, and Tempcanal. After a fast OH- release period (2 h) each compound reached an asymptotic pH state. The results showed that all materials exhibited alkalizing pH with Reogan rapid, Calxyl Red, and Calcicur being the most potent (p = 0.05). The final pH of each compound correlated positively with the Ca(OH)2 mass fraction contained in it.

Simultaneous Production and Recovery of Fumaric Acid from Immobilized Rhizopus oryzae with a Rotary Biofilm Contactor and an Adsorption Column

An integrated system of simultaneous fermentation-adsorption for the production and recovery of fumaric acid from glucose by Rhizopus oryzae was investigated. The system was constructed such that growing Rhizopus mycelia were self-immobilized on the plastic discs of a rotary biofilm contactor during the nitrogen-rich growth phase. During the nongrowth, production phase, the biofilm was alternately exposed to liquid medium and air upon rotation of the discs in the horizontal fermentation vessel. The product of fermentation, fumaric acid, was removed simultaneously and continuously by a coupled adsorption column, thereby moderating inhibition, enhancing the fermentation rate, and sustaining cell viability. Another beneficial effect of the removal of fumaric acid is release of hydroxyl ions from a polyvinyl pyridine adsorbent into the circulating fermentation broth. This moderates the decrease in pH that would otherwise occur. Polyvinyl pyridine and IRA-900 gave the highest loading for this type of fermentation. This fermentation system is capable of producing fumaric acid with an average yield of 85 g/liter from 100 g of glucose per liter within 20 h under repetitive fed-batch cycles. On a weight yield basis, 91% of the theoretical maximum was obtained with a productivity of 4.25 g/liter/h. This is in contrast to stirred-tank fermentation supplemented with calcium carbonate, whose average weight yield was 65% after 72 h with a productivity of 0.9 g/liter/h. The immobilized reactor was operated repetitively for 2 weeks without loss of biological activity.

Effect of root canal filling materials containing calcium hydroxide on the alkalinity of root dentin.

The effect of root canal filling pastes containing calcium oxide resp. calcium hydroxide on the alkalinity of extracted human teeth was investigated using a colour indicator (cresol red). An aqueous suspension of calcium hydroxide (Pulpdent), which is normally used for temporary root canal filling, most consistently produced alkalinity. Removal of the smear layer following instrumentation of the root canal led to increased proportion of alkaline-positive spots in dentinal locations distant from the canal. A clearly smaller effect was found with a calcium salicylate cement (Sealapex) and an oil-paste (Gangraena Merz), both of which are available for definite root canal fillings. Following removal of the smear layer, these hard-setting preparations caused moderate alkalinity in dentin adjacent to the canal but no effect was observed in locations more distant from the canal. Neither at locations adjacent to nor distant from the root canal was alkalinity found when another calcium salicylate cement (Apexit) was used. Apparently the release of hydroxyl ions into root dentin from calcium hydroxide containing root canal filling materials is not solely influenced by the absolute amount of calcium hydroxide, but also depends on other ingredients which variably inhibit the release of these ions.

In vitro release of calcium and hydroxyl ions from two types of calcium hydroxide preparation

Non-setting and setting pastes are the most common forms of calcium hydroxide, used in endodontics. The aim of this study was to investigate the differences in the availability of calcium and hydroxyl ions from some commercial preparations of both types. In vitro released calcium and hydroxyl ions were determined by a potentiometric method, after diffusion through sintered glass. The non-setting pastes evaluated were Calcipulpe, Calxyl Red, Calxyl Blue and Cinacal; while setting base materials were represented by Dycal, Nu-Cap and Reolit. The data obtained showed significantly higher availability of calcium and hydroxyl ions from non-setting pastes, compared with 'alkaline cements' (P < 0.05). Great variations in the amount of released ions were also found among samples of the same material.

Release of calcium and hydroxyl ions from set endodontic sealers containing calcium hydroxide

Endodontic sealers that contain calcium hydroxide are claimed to possess calcification-promoting properties. Similar liners and hard-setting bases exhibit great variations in their alkalinizing potential and this property has been correlated with their biological effect. The purpose of this study was to investigate the release of calcium and hydroxyl ions from three root canal sealers by extraction with water. Calcium was assessed by EGTA titration and hydroxyl ions by measuring pH. The pattern of release of ions differed in all three sealers. In Sealapex it was similar to that of the control bases, Dycal and Life. Another sealer, Hermetic, rapidly dumped the extractable calcium hydroxide, while release of calcium from CRCS was negligible. The alkalinizing potential was more durable in all three. Disintegration of the pellets of Sealapex indicated that solubility may be the price for increased activity.

Adsorption of short-chained organic acids on stannic oxide

The uptake of styryl phosphoric acid (SPA) by stannic oxide was studied using three independent measures of the adsorption process: (i) adsorption isotherms, (ii) zeta potentials of stannic oxide particles before and after adsorption and (iii) the release of hydroxyl ions from the stannic oxide during SPA uptake. The uptake of structurally similar styryl sulfonic acid, benzene arsonic acid and benzene sulfonic acid was also measured. The results are consistent with exchange chemisorption between phosphonate anions and surface hydroxyl groups being the main adsorption mechanism for SPA between pH 3 and 5.

Synthetic macromolecular catalysts exhibiting proteolytic activity. Importance of polyelectrolyte complexes catalyst-protein in proteolysis

The interaction between casein and a synthetic macromolecular catalyst represented by a polyelectrolyte with hydrophobic groups was studied. Casein behaves like a polyampholyte as it forms a macromolecular complex with the catalyst: the interaction is accompanied by a release of hydrogen ions at pH < p K i and by a release of hydroxyl ions at pH > p K i . The synthetic macromolecular catalyst exhibits a proteolytic activity over a broad pH range from 2 to 10. The activity at a given pH is given by a cooperative interaction between the protein and the catalyst, and is connected with the macromolecular nature of the casein substrate; the interaction of the catalyst with low-molar-mass substrates is of different character.