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PubMed2002

A comparison of the antimicrobial efficacy of three calcium hydroxide formulations on human dentin infected with Enterococcus faecalis.

This study compared the antibacterial efficacy of three different formulations of calcium hydroxide by using human dentin specimens that were infected with Enterococcus faecalis. After exposure to three forms of calcium hydroxide (calcium hydroxide mixed with distilled water, calcium hydroxide mixed with 0.2% chlorhexidine, and calcium hydroxide mixed with camphorated paramonochlorophenol) for 7 days, dentin powder from the infected specimens was obtained and assessed for bacterial quantity by spectrophotometry. It was found that calcium hydroxide mixed with camphorated paramonochlorophenol killed all of the Enterococcus faecalis inside the dentinal tubules. This result was better than that obtained with calcium hydroxide mixed with distilled water or with 0.2% chlorhexidine (p < 0.05). Calcium hydroxide mixed with distilled water and calcium hydroxide mixed with 0.2% chlorhexidine were ineffective against these bacteria.

Anti-Infective Agents, Local↗
PubMed2004

FT-Raman spectroscopy of calcium hydroxide medicament in root canals.

AIM: To investigate chemical changes in calcium hydroxide introduced into human root canals as a medicament using Fourier transform-(FT) Raman spectroscopy. METHODOLOGY: Ten necrotic maxillary anterior teeth were selected in 10 patients. The teeth were divided into five treatment groups, according to the survey time. Root canal instrumentation was performed with hand instruments until the master apical file was size 40. Calcium hydroxide paste, in a 1 : 1.25 mixture by weight of powder and distilled water, was introduced directly into the root canal with a lentulo-spiral filler and then condensed with a finger plugger. The access cavity was sealed with a temporary dressing. After 2 and 4 days, then 2, 4 and 6 weeks, the calcium hydroxide paste was sampled with a K-file and then analysed using FT-Raman spectroscopy. The excitation source was an Nd : YAG laser with an excitation wavelength of 1064 nm. All spectra were taken with a laser power of 200 mW, 275-1185 scans, and 4 cm(-1) resolution. The conversion of calcium hydroxide to calcium carbonate was calculated on the basis of the spectral data obtained from the mixtures of both compounds. RESULTS: The calcium hydroxide paste in the apical region showed weak bands at 1088 and 284 cm(-1), in addition to bands associated with calcium hydroxide. The weak bands, assigned to calcium carbonate, became stronger with time. Calcium carbonate content increased rapidly in the first 2 days and then tended to increase slowly. Approximately 11% of the calcium hydroxide at the apical portion of the canal was converted to calcium carbonate after 6 weeks. However, little alteration of the paste was noticed in the samples from the middle portion of the canal. CONCLUSIONS: Calcium hydroxide medicament in root canals became transformed into calcium carbonate in the apical region within 2 days. Although the transformation continued with time, approximately 90% of the calcium hydroxide remained unchanged after 6 weeks.

Calcium Carbonate↗
PubMed1988

[Effects of the treatment of coffee pulp, fresh or ensilaged, with calcium hydroxide, on its nutritive value].

This study was carried out to determine the effects of the addition of calcium hydroxide on the chemical composition and nutritive value of fresh or ensilaged coffee pulp. Fresh or ensilaged pulp were mixed with 1, 2 and 3% of calcium hydroxide. The process was carried out during 0 and 16 hr, after which time the treated pulp was sun-dried for 36 hr until moisture content reached 12%. These samples were then analyzed for their proximate chemical composition and for some minerals (Ca, P, Na, K), as well as for caffeine, tannins and chlorogenic and caffeic acids content. Diets were then prepared from these materials, containing 15% protein and 15 or 30% fresh or ensilaged coffee pulp, and offered to weanling rats during six weeks. Information required on weight gain, food conversion, apparent digestibility and toxicity of the diets was recorded. Results of the chemical analysis revealed that the main changes found in both types of pulp as a result of the calcium hydroxide treatment were the following: a decrease in ether extract (from 4.0 to 2.5 g/100 g), crude fiber (from 18.3 to 11.9 g/100 g) and protein content (from 12.3 to 8.6 g/100 g) in an inverse relation to the amount of calcium hydroxide used. The amount of ash increased, fluctuated between 5.5 and 15.4%, depending on the amount of calcium hydroxide used. The latter affected the Ca:P ratio in the diets, where an average ratio of 7.2:1 was found in the control pulp (0% calcium hydroxide) and 59.0:1 in those treated with the highest amount of calcium hydroxide (3%). Regarding the caffeine, tannins and chlorogenic and caffeic acids contents, calcium hydroxide was effective in decreasing only tannins, more so in the fresh than in the ensilaged pulp; the decrease was in direct proportion to the amount of calcium hydroxide added and to the length of the Ca(OH)2 treatment. The results of the biological assays showed that the addition of Ca(OH)2 in either of the two time periods used and at either of the concentrations studied, did not improve the nutritive value of coffee pulp. There was always a better performance in the animals that consumed ensilaged pulp than in those fed fresh pulp. The animals fed 15% coffee pulp either fresh or ensilaged performed better than those consuming 30% coffee pulp.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Sorption of phosphate and Cr(VI) by Fe(III) and Cr(III) hydroxides.

Understanding the chemical behavior and interactions of Cr(VI) ( e.g., HCrO(4)(-)) and other anions, such as orthophosphate (P) with insoluble metal hydroxides ( i.e., Cr[III] and Fe[III]) in disposal landfills or in chromite ore processing residue (CORP)-enriched soil is very important in predicting the movement and the fate of Cr(VI). This study evaluates the sorption behavior of P and Cr(VI) by Fe(III) ( i.e., ferrihydrite), Cr(III) ( i.e., Cr[OH](3)), and coprecipitated Fe(III)/Cr(III) hydroxides. These metal hydroxide sorbents were synthesized, and sorption of P and Cr(VI) were conducted at different pH using a batch technology. Our results show that P and Cr(VI) sorption by metal hydroxides decreased with increasing suspension pH. Greater decrease in P sorption was observed when Cr(III) was present in the structures of hydroxides. Following the sorption of low concentration of P ( i.e., 0.5 mM), the sorption of subsequently added Cr(VI) by hydroxides was less influenced. However, Cr(VI) sorption was greatly inhibited when high concentration of P ( i.e., 10 mM) prereacted with hydroxides, particularly in Fe(III) hydroxide system. Results also indicated that high concentration of Cr(VI) (10 mM) could dissolve Cr(III) hydroxide at pH 3 and reprecipitate as an amorphous form of Cr(VI) and Cr(III) compound at pH about 6.5. Although coprecipitation of Cr(VI) with Cr(III) can inhibit Cr(VI) movement through soil profiles, the inhibition seems to be low due to the gradual release of Cr(VI) with increasing pH.

Adsorption↗
PubMed1988

The stability of uric acid in ammonium hydroxide.

We examined the stability of uric acid in dilute aqueous ammonium hydroxide solution by mass spectrometry. Uric acid decomposes in ammonium hydroxide even as dilute as 15 mmol/L when the mole ratio of ammonium hydroxide to uric acid is 50:1. There are at least four products of the decomposition, two of which have been identified as allantoin and urea. The slope of the decomposition curve indicates that uric acid is destroyed at an initial rate of 2-3% per hour. In ammonium hydroxide at a concentration of 1 mmol/L and a mole ratio of ammonium hydroxide to uric acid of less than or equal to 3.4, uric acid is not detectably decomposed. Evidently, any method for determination of uric acid that involves treating the analyte with ammonium hydroxide before analysis may destroy it. Therefore, a published method described as being "definitive" for uric acid (J Clin Chem Clin Biochem 1985; 23:129-35) could produce incorrect results because it involves storing the uric acid in 15 mmol/L ammonium hydroxide at a mole ratio of ammonium hydroxide to uric acid of greater than 120:1.

Ammonium Hydroxide↗
PubMed2006

Aluminum hydroxide adjuvant produced under constant reactant concentration.

Aluminum hydroxide adjuvant, AlO(OH), is used to potentiate the immune response to vaccines by adsorbing the antigen. The structure of aluminum hydroxide adjuvant is unusual as it is crystalline but has a high surface area due to its very small primary particles. The purpose of this study was to investigate the chemical and thermal conditions required to synthesize aluminum hydroxide adjuvant that is stable and exhibits a high protein adsorptive capacity. Aluminum hydroxide adjuvant was precipitated using a procedure in which the concentration of reactants was maintained constant throughout the precipitation. The precipitation variables were: 2.50, 2.75, and 3.00 OH/Al molar ratio; 0.5, 4.0, and 5.0 M NaCl; and 25, 60, and 65 degrees C. High sodium chloride concentration and high temperature facilitated the formation of AlO(OH) rather than crystalline forms of aluminum hydroxide, Al(OH)(3). The AlO(OH) produced was not stable because crystalline forms of aluminum hydroxide formed during aging at room temperature. Aluminum hydroxide adjuvant was stabilized for the study period of 12 weeks at room temperature by either the addition of 3.0 M NaCl after precipitation and washing or hydrothermal treatment at 110 degrees C for 4 h. Stabilization by the addition of sodium chloride required a hypertonic concentration of sodium chloride and was not practical as vaccines for parenteral administration are desired to be isotonic (equivalent to 0.15 M NaCl). Stabilization by hydrothermal treatment produced aluminum hydroxide adjuvant, which exhibited a high protein adsorptive capacity that did not change during the 12-week study period.

Adjuvants, Pharmaceutic↗
PubMed1992

Effect of magnesium hydroxide on the absorption and efficacy of tolbutamide and chlorpropamide.

The effect of magnesium hydroxide on the absorption and efficacy of tolbutamide and chlorpropamide was examined in a total of 32 healthy volunteers in two separate, randomized parallel-group studies, with 16 subjects in each study. After an overnight fast, the first group of 8 volunteers ingested 500 mg tolbutamide or 250 mg chlorpropamide with 150 ml water, and the second group the same doses of the active drugs with 150 ml water containing 850 mg magnesium hydroxide. Magnesium hydroxide increased the area under the plasma tolbutamide concentration-time curve (AUC) from 0 to 1 h and from 0 to 2 h by 5-fold and 2.5-fold, respectively. The peak plasma concentration, peak time and total AUC were not significantly altered. The incremental insulin area and the decremental glucose area from 0 to 1.5 h were significantly larger in the magnesium hydroxide group than in the controls. The maximum insulin response to tolbutamide was increased fourfold by coadministration of magnesium hydroxide, and it occurred about 1 h earlier than in the control group. In addition, the maximum fall in plasma glucose concentration was attained about 1 h earlier in the antacid group. A tendency to an increased rate of chlorpropamide absorption was observed after magnesium hydroxide, but it did not appear to affect the insulin and glucose responses to chlorpropamide. It is concluded that magnesium hydroxide increased the early bioavailability of tolbutamide, resulting in enhanced insulin and glucose responses. A tendency toward accelerated chlorpropamide absorption by magnesium hydroxide was also observed, but the efficacy of chlorpropamide was unaffected.

Adult↗
PubMed1988

Effect of magnesium hydroxide on the absorption of tolfenamic and mefenamic acids.

The effect of various antacids on the absorption of tolfenamic and mefenamic acids has been investigated in three separate crossover studies, each consisting of four phases. Single doses of magnesium hydroxide (85 mg, 425 mg and 1700 mg) or of water (150 ml) were given by mouth to 6 healthy volunteers immediately after tolfenamic acid 400 mg (Study 1), and, using an identical study design, after mefenamic acid 500 mg (Study 3). In Study 2 sodium bicarbonate 1 g, aluminium hydroxide 1 g, an antacid preparation containing both aluminium and magnesium hydroxides, or water alone were ingested with tolfenamic acid 400 mg. Plasma concentrations of tolfenamic and mefenamic acids and their cumulative excretion in urine were determined up to 24 h. Magnesium hydroxide greatly accelerated, in a dose-dependent manner the absorption of both tolfenamic and mefenamic acids. The peak times in plasma were shortened by about 1 h by 425 mg and 1700 mg magnesium hydroxide, and the peak plasma concentrations of both fenamates were elevated up to 3-fold. The area under the plasma concentration-time curve between 0 and 1 h of tolfenamic acid was increased up to 7-fold and that of mefenamic acid up to 3-fold. The total bioavailability of tolfenamic and mefenamic acids was only slightly increased. Aluminium hydroxide alone and in combination with magnesium hydroxide significantly retarded the absorption and lowered the peak plasma concentration of tolfenamic acid. Sodium bicarbonate had no significant effect on its absorption. The interaction with magnesium hydroxide leads to higher and earlier peak plasma concentrations of the fenamates.(ABSTRACT TRUNCATED AT 250 WORDS)

Antacids↗
PubMed1991

The solvent effects of calcium hydroxide irrigating solution on bovine pulp tissue.

The solvent effects of calcium hydroxide irrigating solution (used alone and in combination with sodium hypochlorite) on bovine pulp tissue were studied. Forty pieces of pulp tissue weighing 90 mg each were treated with calcium hydroxide solution alone, calcium hydroxide and sodium hypochlorite alternated, sodium hypochlorite alone, and saline alone. Each piece of tissue was treated for 32 min. Desiccated pretreatment and posttreatment weights were compared. There was no significant difference between the dissolution capability of calcium hydroxide solution used alone and of saline. No significant difference was noted between calcium hydroxide solution and sodium hypochlorite used alternately, and sodium hypochlorite used alone. However, both of these groups were significantly more effective at dissolving tissue than calcium hydroxide solution alone or saline. Calcium hydroxide solution was an ineffective solvent of pulpal tissue. If tissue dissolution is desired during root canal therapy, the use of calcium hydroxide solution as the sole irrigant is no more effective than saline.

Analysis of Variance↗
PubMed1997

Calcium hydroxide inhibits substrate adherence capacity of macrophages.

The purpose of this study was to investigate the effect of calcium hydroxide on substrate adherence capacity of rat inflammatory macrophages to determine if calcium hydroxide can alter macrophage function. Inflammatory macrophages were obtained from Wistar rats and resuspended in RPMI-1640 medium. Substrate adherence capacity assays were carried out in Eppendorf tubes for 15 min of incubation at 37 degrees C in a humidified atmosphere of 5% CO2. The adherence index (AI) was calculated. Results showed that calcium hydroxide decreased substrate adherence capacity of inflammatory macrophages in a time and dose-dependent manner. The lowest calcium hydroxide concentration that caused a significant inhibition of AI was 1 mM (p < 0.05), and the concentration of calcium hydroxide that caused half-maximal inhibition (IC50) was 1.54 mM (p < 0.01). We conclude that calcium hydroxide decreased substrate adherence capacity of macrophages. When adhesion as the first step in the phagocytic process and in antigen presentation is taken into account, calcium hydroxide could inhibit macrophage function and reduce inflammatory reactions in periapical tissues or in dental pulp when it is used in root-canals therapy or in direct pulp capping and pulpotomy, respectively. Moreover, this effect could explain, at least in part, the mineralized tissue-inducing property of calcium hydroxide.

Animals↗
PubMed1999

Humoral and cellular immunity induced by antigens adjuvanted with colloidal iron hydroxide.

The immunopotentiating activities of colloidal iron hydroxide, a novel, experimental mineral adjuvant, and of aluminium hydroxide. the licensed adjuvant for human vaccines, were compared. Our studies revealed that colloidal iron hydroxide and aluminium hydroxide behaved comparably with respect to supporting induction of an antibody response to tetanus toxoid. Furthermore, mice immunized with both, the experimental vaccine (tick-borne encephalitis virus (TBEV) antigen adsorbed to colloidal iron hydroxide) or with a commercially available TBEV vaccine (adjuvanted with aluminium hydroxide), developed long-lasting antibody responses which protected the animals from TBEV infection even one year after vaccination. The use of colloidal iron hydroxide as adjuvant had the additional advantage to reproducibly support induction of HIV-1 envelope-specific cytotoxic T lymphocytes (CTL), when used as adjuvant for a HIV-1 env-carrying recombinant fowlpox virus and being applied via the subcutaneous route. Aluminium hydroxide was much less active in this respect. Non-adjuvanted recombinant fowlpox elicited CTLs only when given intravenously or intraperitoneally, vaccination routes considered not to be suitable for routine use in humans. Further studies to evaluate the use of colloidal iron as possible alternative and/or supplement for routinely used mineral adjuvants may therefore be warranted.

Adjuvants, Immunologic↗
PubMed1991

Calcium citrate markedly enhances aluminum absorption from aluminum hydroxide.

The effect of calcium citrate on intestinal aluminum absorption, assessed by the increment in urinary aluminum excretion, was evaluated in eight normal men. Baseline urinary aluminum excretion was determined for 2 days; thereafter, subjects ingested aluminum hydroxide for 3 days. In a cross-over study, subjects were given either calcium citrate, 950 mg four times a day, or placebo during the 3 days of aluminum hydroxide ingestion (2.4 g/d). Plasma aluminum levels were measured on the second control day and the third day of aluminum hydroxide ingestion. Baseline urinary aluminum excretion was 0.02 +/- 0.004 (6.5 +/- 1.1 micrograms/g creatinine) and 0.03 +/- 0.005 mumol/mmol creatinine (7.4 +/- 1.3 micrograms/g creatinine). These values increased during aluminum hydroxide therapy, but values were much greater when calcium citrate was ingested with aluminum hydroxide. On 3 consecutive days, urinary aluminum excretion levels were 11.1 +/- 3.23, 8.8 +/- 2.9, and 5.3 +/- 0.7 times greater during the administration of calcium citrate with aluminum hydroxide than with aluminum hydroxide alone. Plasma aluminum levels did not differ in the two treatment groups. Thus, calcium citrate markedly enhances the absorption of aluminum from aluminum hydroxide and the two must not be prescribed together in patients with renal failure.

Adult↗
PubMed2000

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

AIM: 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. METHODOLOGY: 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. RESULTS: 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. CONCLUSION: 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.

Animals↗
PubMed1995

Diagnosis and management of cases of suspected dermatomycosis in The Netherlands: influence of general practice based potassium hydroxide testing.

BACKGROUND: Microscopy of a potassium hydroxide preparation of skin scrapings or nail clippings, although widely advocated as a test for dermatomycosis, is used in only a small proportion of cases. AIM: This study set out to investigate the effect of potassium hydroxide testing on the subjectively assessed probability that a dermatomycosis was present. METHOD: The study was undertaken in 1992 in Limburg, a province in the south of the Netherlands. Ten general practitioners and eight trainees completed a questionnaire and performed a potassium hydroxide preparation for each patient presenting with a skin condition that they thought might be caused by dermatomycosis. Skin or nail material was also sent to a microbiology laboratory where another potassium hydroxide preparation as well as a culture were performed, these two tests serving as a gold standard against which to judge the potassium hydroxide preparation by the general practitioners. Data from a total of 164 cases were analysed. RESULTS: The results of the potassium hydroxide test carried out in the practice had a considerable influence on the subjectively assessed probability that a dermatomycosis was present, especially if the outcome was positive. The indication for antifungal treatment was altered as a result of the test in a quarter of all cases, mostly from negative to positive. Use of the practice potassium hydroxide test could increase the proportion of correct therapeutic decisions from 54% to 69%, with 20% of cases being undertreated. Of cases that gave a positive test result in the practice 83% also had a positive laboratory test result, while of cases that gave a negative practice result 43% were positive in the laboratory. CONCLUSION: The potassium hydroxide test improves the diagnostic process in cases of possible dermatomycosis and may result in a change in management. The test can provide a confirmation of the diagnosis of dermatomycosis but is not useful in the exclusion of this diagnosis.

Clinical Laboratory Techniques↗
PubMed2003

Clinical application of calcium hydroxide in dental pathology and endodontics.

Calcium hydroxide has a hard tissue inducing effect. It is a powder, that can be mixed with a physiological saline to a paste. The paste is highly alkaline with a pH 12.5 and its application to the pulp results in necrosis of the part of coronal pulp tissue shows no or only a milled inflammatory reaction. Analyzing the pH and the concentration of calcium ions in the periapical area, it is obvious that at least 2 weeks are necessary for calcium hydroxide bactericide activity. Calcium hydroxide retains its anti-bacterial properties for about two months when placed under a restoration, after which it degrades to calcium oxide and other less effective calcium salts. All calcium hydroxide preparations have a limited shelf life as they eventually turn into calcium oxide. Calcium hydroxide can be used as linings, for indirect and direct pulp cupping, root dressing, root canal sealant, apical closure. The vehicles play a supportive role, giving pastes chemical characteristics such as dissociation and diffusion as well as favoring the correct filling of the root canal which are decisive factors for antimicrobial potential and tissue healing. The mechanism of action of calcium hydroxide on tissues, inducing the deposition of mineralized tissue, is an extremely important aspect for the indication of calcium hydroxide, because it demonstrates biological compatibility of calcium hydroxide.

Journal Article↗
PubMed2006

Interactions of bovine serum albumin with aluminum polyoxocations and aluminum hydroxide.

Interactions of aqueous solutions of aluminum polyoxocations (Al13-mers and Al30-mers) and aluminum hydroxide suspensions of varying particle sizes (26, 55, and 82 nm) with a model protein, bovine serum albumin (BSA), have been investigated using potentiometry, conductometry, viscometry, 27Al solution NMR, UV-vis spectroscopy, dynamic light scattering, zeta-potential measurements, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Increasing amounts of BSA partially convert Al13-mers and, to a larger extent, Al30-mers into amorphous Al hydroxide without gel formation. At the same time, BSA molecules can form unstable aggregates in the Al polyoxocation solutions which redisperse easily upon standing. In the case of Al hydroxide sols, BSA addition causes substantial gelation, the extent of which is proportional to the amount of BSA added and inversely related to the Al hydroxide particle size. Upon freeze-drying or centrifugation of Al species-BSA solutions, an interesting sheetlike morphology with 150-200 nm wide nanoribbons is observed for pure Al hydroxide nanoparticles and for solutions of Al polyoxocations with the highest amount of BSA studied. On the basis of the combined solution, colloidal and solid-state characterization of model Al species-BSA systems, a qualitative model of possible interactions in the Al polyoxocation-BSA and Al hydroxide-BSA systems is proposed wherein core-shell hybrid nanoparticles are formed from protein "core" and Al polyoxocation "shell" or Al hydroxide "core" and protein "shell".

Aluminum↗
PubMed2003

pH changes in root dentin after intracanal placement of improved calcium hydroxide containing gutta-percha points.

The in vitro pH changes in root dentin over a period of 2 weeks was investigated in 48 extracted bicuspids after intracanal placement of either Roeko Calcium Hydroxide Plus Points, aqueous calcium hydroxide paste, or gutta-percha points (control group) after root canal preparation. Microelectrodes were placed in outer and inner root dentin at cervical, middle, and apical thirds of the root to measure the pH at 1 h, 2 h, 3 h, 1 day, 3 days, 7 days, and 14 days. Roeko Calcium Hydroxide Plus Points reached a peak inner dentine pH of 11.67 and a peak outer dentine pH of 10.82 at 3 h. In addition, Roeko Calcium Hydroxide Plus Points maintained an outer dentine pH above 9.5 for approximately 2 days, whereas the aqueous calcium hydroxide paste did not reach this pH. However, the alkalinity in dentin with Roeko Calcium Hydroxide Plus Points was maintained for 7 days only, whereas aqueous calcium hydroxide paste maintained an alkaline environment throughout the 2-week period.

Analysis of Variance↗
PubMed1977

Relationship between zero point of charge and solubility product for hydroxides of polyvalent cations.

The zero point of charge (ZPC) of slightly soluble compounds is the pH at which their particles suspended in water have zero charge. The ZPC values of slightly soluble hydroxides were compared with their solubility product in the form of its negative logarithm, pKSP, and with th pH of their suspensions in pure water, pHSP, which is a function of pKSP. The ZPC-pKSP relation was nonlinear while the ZPC-pHSP relation was linear. Either equation can used to estimate the ZPC value of a hydroxide from its solubility product. The ZPC of a given hydroxide was higher than its pHSP because polyvalent cations are more extensively adsorbed and less extensively desorbed from the particle surface than the monovalent hydroxide ion. At the pHSP, there are equivalent amounts of the cation and of the hydroxide anion in solution, but the surface layer of the hydroxide particle contains an excess cation on an equivalent basis. This imbalance confers a positive charge to the particle. The solubility product of aluminum hydroxide, redetermined at 25 degrees by means of pH measurements, was 8 X 10(-33). Its ZPC, redetermined by microelectrophoresis, was 8.5 +/- 0.1.

Chemical Phenomena↗