Final Solution pH Research Articles

Effect of Cellophane and Chitosan Coatings on Qualitative and Biochemical Characteristics of Sweet Pepper, Cultivar “California wonder” during Storage

Introduction Bell pepper (Capsicum annuum L.) from Solanaceae family is one of the most important vegetables which are fruit pods on the capsicum plant grown for their sweet fruits and delicate peppery flavor they extend to the recipes. Sweet pepper contains an impressive list of plant nutrients that found to have disease preventing and health promoting properties. Unlike in other fellow chili peppers, it has very less calories and fats. 100 g provides just 31 calories. Because of their versatility, low calories, intense flavor and high concentration of vitamins, sweet peppers are a great snack raw and an easy addition to many different recipes. In recent years extending shelf-life of this perishable vegetable has been accomplished (Banaras et al., 2005). The losses in vegetable quality and quantity between harvest and consumption affect the crop productivity. It is estimated that the magnitude of the postharvest losses of fresh horticultural crops is from 5 to 25% in developed countries and of 20 to 50% in developing countries. Fresh peppers are often eaten raw and supplied pre-cut to manufacturers as ready-to-use ingredients. However, the main problems limiting their shelf life occur by shriveling, decay development on the cut surface, as well as degreening of the vegetable among different degraded quality characteristics (Sakaldas and Kaynas, 2010). Those problems are correlated to an undesirable loss of water during metabolism or diffusion through the skin and respiration. Temperature management is the most effective tool for extending the shelf life of fresh horticultural commodities. Nowadays, to reduce high losses and keeping product’s quality, in addition to lowering temperature, coating and packing must be noticed. Therefore, in this study, dipping in chitosan solution and coatings by edible Chitosan was assayed to improve quality of sweet peppers storability during cold storage. Material and Methods Plant material and sample preparation: Green peppers obtained from a Research farm, College of Agriculture, Ilam University, Ilam, Iran were used in the present study. The fruits were sanitized with hyperchlorinated water (1 mL/L) and rinsed with tap water. Peppers were divided in random into different group for chitosan treatments. Treatments and storage condition: The green peppers were dipped for 2 min into a solution either 0% (control) or 1% (w/v) chitosan (Chitosan, 80-95% deacetylation degree, medium molecular weight). The coating solution was prepared by dispersing 0 and 10 g of chitosan powder into 1L of distilled water containing 1% (v/v) glacial acetic acid (Kyu Kyu Win et al., 2007) and final pH of the solution adjusted to pH 5.0. After being air dried for 2 hrs. at room Temperature, ten similar sizes fruits were placed in each plastic crate, tightly closed by cellophane films and stored at 10°C, 85-90% relative humidity to be later assessed for further analyses intended for 14 and 28 days. The control samples of ten untreated fruits per crate were kept unsealed under similar environmental conditions of temperature and relative humidity separately. The current study carried out as a factorial assay on the basis of a RCBD with three replications during 2013-2014 at Ilam University. The main factor was included of four treatments (control, Chitosan coating, Cellophane sealing and Chitosan coating + Cellophane sealing) and the sub factor was included of storage period duration (14 and 28 days). Data were subjected to ANOVA using SAS software version 9.2. Verification of significant differences was done using Duncan's Test at 5% probability level. Results and discussions Results showed that fruits quality declines with long storage, but treatments with Cellophane and Chitosan decreased weight loss and kept firmness, TSS, titratable acidity, sugar/acid ratio, ascorbic acid, antioxidant activity, total phenol, and catalase and peroxidase enzymes better than control. Furthermore, for most of the traits no significant difference was observed between treatments, although cellophane coating recorded more fungal infection and lower marketability. Shelf life enhancement by Chitosan has been already reported on carrot, orange and Japanese Medlar (Rashidi et al., 2009, Ahmad et al., 1989 & Ding et al., 2002) through its antimicrobial activity (Xing et al., 2011) and suppressing respiration by blocking stomata. It has been reported that both edible and nonedible coverage (such as chitosan and cellophane) of fruits can provide a modified atmosphere surround them which results in decreasing the rate of their maturity and senesces. Taking overall quality into consideration, the best treatment was joint application of cellophane and chitosan. That treatment appears to be an effective method for improving the postharvest quality of peppers which could more effectively preserved quality and biochemical characteristics. These fruits remained hydrated, green and had good visual appearance after storage. The low rate of respiration of these fruits may also account for the retention of pepper quality.

Adsorption of methylene blue onto citric acid treated carbonized bamboo leaves powder: Equilibrium, kinetics, thermodynamics analyses

In this article, the adsorption of methylene blue (MB) from its aqueous solution onto citric acid treated carbonized bamboo leaves powder as an adsorbent is reported. The adsorbent was characterized by determining the density, pHpzc (6.6), particle size (32.53μm), and was analyzed by SEM, BET (surface area 393.3m2/g) and FTIR. Batch experiments were performed as a function of various operating parameters - initial concentration (100 to 400mg/L), contact time (10 to 100min), adsorbent dose (0.2 to 1.4g/L), shaker speed (50 to 350rpm) and temperature (290 to 305K) at natural pH of 7.5. The batch data followed Temkin isotherm amongst seven isotherms and pseudo-second order kinetic model. Further, analysis of batch data upon various diffusion models indicated that film diffusion was controlling the rate though intra-particle diffusion was taking place. Thermodynamic parameters (ΔG0: −33.70 to −25.43kJ/mol; ΔH0: 134.97kJ/mol; ΔS0: 554.51J/mol·K) revealed spontaneity of adsorption and the nature was chemisorption which also followed the activation energy (84.07 to 98.90kJ/mol) estimated from pseudo-second order rate constant as a function of temperature. Novelties achieved were - higher removal of MB (99.97%), higher adsorption capacity (725mg/g), final solution pH well within the safe discharge limit. Besides, the seasonal variation was used to investigate the temperature effect in a novel manner.

Review of Models and Variables Affecting Phosphorus Removal during Processing of Iron Ores Designated for Production of Orthopedics Devices

A review has been carried out to show models and variables affecting phosphorus removal during processing of iron ores in acid solution designated for production of orthopedics devices Review of literatures show that the level of phosphorus removal during iron ore processing in acid solutions is largely dependent on the initial and or final pH of the leaching solution A decrease in the final solution pH is indicative of increased phosphorus removal and dissolution in the leaching solution hence increased acidity of the leaching solution Scanning Electron Microscopy SEM of the dephosphorized iron ore depicted small caked particle clusters

Equilibria model for pH variations and ion adsorption in capacitive deionization electrodes

Ion adsorption and equilibrium between electrolyte and microstructure of porous electrodes are at the heart of capacitive deionization (CDI) research. Surface functional groups are among the factors which fundamentally affect adsorption characteristics of the material and hence CDI system performance in general. Current CDI-based models for surface charge are mainly based on a fixed (constant) charge density, and do not treat acid-base equilibria of electrode microstructure including so-called micropores. We here expand current models by coupling the modified Donnan (mD) model with weak electrolyte acid-base equilibria theory. In our model, surface charge density can vary based on equilibrium constants (pK's) of individual surface groups as well as micropore and electrolyte pH environments. In this initial paper, we consider this equilibrium in the absence of Faradaic reactions. The model shows the preferential adsorption of cations versus anions to surfaces with respectively acidic or basic surface functional groups. We introduce a new parameter we term “chemical charge efficiency” to quantify efficiency of salt removal due to surface functional groups. We validate our model using well controlled titration experiments for an activated carbon cloth (ACC), and quantify initial and final pH of solution after adding the ACC sample. We also leverage inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC) to quantify the final background concentrations of individual ionic species. Our results show a very good agreement between experiments and model. The model is extendable to a wide variety of porous electrode systems and CDI systems with applied potential.

Characteristics and metal leachability of incinerated sewage sludge ash and air pollution control residues from Hong Kong evaluated by different methods

The improper disposal of incinerated sewage sludge ash (ISSA) and air pollution control residues (APCR) from sewage sludge incinerators has become an environmental concern. The physicochemical, morphological and mineralogical characteristics of ISSA and APCR from Hong Kong, and the leachability and risk of heavy metals, are presented in this paper. The results showed that a low hydraulic and pozzolanic potential was associated with the ISSA and APCR due to the presence of low contents of SiO2, Al2O3 and CaO and high contents of P, S and Cl (especially for APCR). Although high concentrations of Zn and Cu (especially for ISSA) followed by Ni, Pb and As, Se were detected, a low leaching rate of these metals (especially at neutral and alkaline pH) rendered them classifiable as non-hazardous according to the U.S. EPA and Chinese national regulatory limits. The leached metals concentrations from ISSA and APCR were mainly pH dependent, and metals solubilization occurred mainly at low pH. Different leaching tests should be adopted based on the simulated different environmental conditions and exposure scenarios for assessing the leachability as contrasting results could be obtained due to the differences in complexing abilities and final pH of the leaching solutions.

Evaluating electrocoagulation and chemical coagulation for removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions

High efficiency reverse osmosis (HERO) produces high pH concentrate streams that often contain high levels of dissolved silica. Removal of silica from these concentrate streams is desirable before brine concentration and crystallization. This research investigated removal of dissolved silica from simulated HERO concentrate solutions using electrocoagulation (EC) with mild steel anodes and chemical coagulation with FeCl3. At pH values of above 10, the mild steel anodes immediately passivated and were not able to deliver Fe2+ ions into the solution. This necessitated lowering the solution pH value via HCl or FeCl3 addition prior to EC. At pH values ≤10, iron dosing by EC was in agreement with that given by Faraday's law. The optimal initial pH value for operating the EC process was 8, which required addition of 17.8mM HCl or 5.8mM FeCl3. An EC iron dose of 4.0mM resulted in 76–89% silica removal for solutions with initial pH values between 4 and 8. Higher dosing up to 9.3mM increased silica removal by only 5%. Chemical coagulation was not as effective as EC, and was able to achieve a maximum removal of 64% with a 4.0mM FeCl3 dose. Solution ionic strength had no measurable impact on silica removal by EC, but did affect final solution pH values and silica removal by chemical coagulation. For both EC and chemical coagulation, the initial pH value of solution had greater impact on silica removal than the iron dose.

Characterization, Dissolution, and Solubility of Zn-Substituted Hydroxylapatites [(ZnxCa1−x)5(PO4)3OH] at 25°C

A series of Zn-substituted hydroxylapatites [(ZnxCa1−x)5(PO4)3OH, Zn-Ca-HA] with the Zn/(Zn + Ca) molar ratio (XZn) of 0~0.16 was prepared and characterized, and then the dissolution of the synthesized solids in aqueous solution was investigated by batch experiment. The results indicated that the aqueous zinc, calcium, and phosphate concentrations greatly depended on the Zn/(Zn + Ca) molar ratio of the Zn-Ca-HA solids (XZn). For the Zn-Ca-HA dissolution at 25°C with an initial pH of 2.00, the final solution pH increased, while the final solution calcium and phosphate concentrations decreased with the increasing XZn. The final solution zinc concentrations increased with the increasing XZn when XZn≤0.08 and decreased with the increasing XZn when XZn = 0.08~0.16. The mean Ksp values for (ZnxCa1−x)5(PO4)3OH at 25°C decreased from 10−57.75 to 10−58.59 with the increasing XZn from 0.00 to 0.08 and then increased from 10–58.59 to 10–56.63 with the increasing XZn from 0.08 to 0.16. This tendency was consistent with the dependency of the lattice parameter a on XZn. The corresponding free energies of formation (ΔGfo) increased lineally from −6310.45 kJ/mol to −5979.39 kJ/mol with the increasing XZn from 0.00 to 0.16.

Preparation of ultrafine silica from potash feldspar using sodium carbonate roasting technology

A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na2CO3 and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows: an Na2CO3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO2 was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a temperature of 40°C, a CO2 flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipitation rate and granularity of the SiO2 particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.

Erosive potential of several fruit-flavored liquors in Korea

Purpose: The aim of this study was to evaluate the erosive potential of several fruit-flavored liquors marketed in Korea by measuring pH, titratable acidity, and variations in pH utilizing an ISO method. Materials and Methods: Six fruit-flavored liquors were investigated. An orange juice and three kinds of soju were selected as the control beverage. The pH and titratable acidity of the beverages were determined by 1 M NaOH until the pH 5.5 and 7.0 (recorded as TA_5.5 and TA_7.0, respectively). All measurements were performed in triplicate. The process of ISO 28888 was used for measurement of the pH variation (DeltapH) using an under-saturated hydroxyapatite solution (screening solution) and determining the difference between the initial and final pH of the screening solution. The average DeltapH was determined based on 4 measurements. Results: All the fruit-flavored liquors tested in this study showed a pH lower than the critical pH for dental erosion (4.5). The average pH of the fruit-flavored liquors was 2.77 and was also lower than the pH of the soju and an orange juice (control drinks). TA_5.5 and TA_7.0 values of the fruit-flavored liquors were 4.92ml and 7.13ml, respectively. The fruit-flavored liquors showed an erosive potential capable of damaging the enamel surfaces, whereas the orange juice had the highest titratable acidity. The changes in pH determined using the screening solution confirmed that the fruit-flavored liquors had erosive potential, with DeltapH value of 1.53. Conclusions: The fruit-flavored liquors tested in this study might have a strong potential to erode dental hard tissues.

Treatment of POME using Fenton oxidation process: removal efficiency, optimization, and acidity condition

In this study, the performance of a Fenton oxidation process was evaluated for the treatment of high-concentrated palm oil mill effluent (POME). Experiments were designed using the central composite design model of the response surface methodology (RSM). Four independent variables (reaction time, H2O2 concentration, Fe2+ ions concentration, and initial solution pH) and two dependent responses (COD and final solution pH) were investigated. The results show that at a low Fe2+ concentration and pH of about 3, an acceptable COD removal efficiency was achieved. At optimum conditions of pH 3.5 and 90 min reaction time, COD removal exceeded 85% and was successfully optimized by RSM. A significant model (p < 0.0001) was obtained for final pH condition and statistically reached a satisfactory level with a correlation coefficient (R2) of about 0.71. This study, therefore, demonstrates the capacity of Fenton process to successfully remove COD from high-concentrated POME under the right combination of process variables.

Mechanism of Hg(II) immobilization in sediments by sulfate-cement amendment

Reactive amendments such as Portland and super-sulfate cements offer a promising technology for immobilizing metalloid contaminants such as mercury (Hg) in soils and sediments through sequestration in less bioavailable solid forms. Tidal marsh sediments were reacted with dissolved Hg(II) in synthetic seawater and fresh water solutions, treated with Portland cement and FeSO4 amendment, and aged for up to 90 days. Reacted solids were analyzed with bulk sequential extraction methods and characterized by powder X-ray diffraction (XRD), electron microscopy, and synchrotron X-ray absorption spectroscopy at the Hg LIII- and S K-edge. In amended sediments, XRD, SEM and sulfur K-edge XANES indicated formation of gypsum in seawater experiments or ettringite-type (Ca6Al2(SO4)3(OH)12.26H2O) phases in fresh water experiments, depending on the final solution pH (seawater ∼8.5; freshwater ∼10.5). Analysis of Hg EXAFS spectra showed Cl and Hg ligands in the first- and second-coordination shells at distances characteristic of a polynuclear chloromercury(II) salt, perhaps as a nanoparticulate phase, in both seawater and fresh water experiments. In addition to the chloromercury species, a smaller fraction (∼20–25%) of Hg was bonded to O atoms in fresh water sample spectra, suggesting the presence of a minor sorbed Hg fraction. In the absence of amendment treatment, Hg sorption and resistance to extraction can be accounted for by relatively strong binding by reduced S species present in the marsh sediment detected by S XANES. Thermodynamic calculations predict stable aqueous Hg–Cl species at seawater final pH, but higher final pH in fresh water favors aqueous Hg-hydroxide species. The difference in Hg coordination between aqueous and solid phases suggests that the initial Hg–Cl coordination was stabilized in the cement hydration products and did not re-equilibrate with the bulk solution with aging. Collectively, results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt as the primary immobilization mechanism.

Unprotected and interconnected Ru0 nano-chain networks: advantages of unprotected surfaces in catalysis and electrocatalysis.

Seedless, surfactantless and support-free unprotected, metallic, interconnected nano-chain networks of ruthenium nanoparticles (NPs) were successfully synthesized via the reduction of ruthenium(iii) chloride (RuCl3) with sodium borohydride (NaBH4) at three different temperatures, viz. 30 °C, 45 °C and 60 °C. The molar ratio of RuCl3 solution and borohydride was optimized to be 1 : 1.5 to produce stable colloids with the optimum final solution pH of 9.7 ± 0.2. Average diameters of the interconnected nano-chain networks prepared at 30 °C (Ru-30), 45 °C (Ru-45) and 60 °C (Ru-60) were 3.5 ± 0.5 nm, 3.0 ± 0.2 nm and 2.6 ± 0.2 nm respectively. The morphology and composition dependent catalytic and electrocatalytic activities of these unprotected Ru nano-chain networks (Ru-30, Ru-45 and Ru-60) were studied in detail. The catalysis study was performed by investigating the transfer hydrogenation of several substituted aromatic nitro compounds. It was observed that Ru-60 was relatively more active compared to Ru-30 and Ru-45, which was reflected in their rate constant values. The electrocatalytic activities of Ru-30, Ru-45 and Ru-60 were screened for anodic water splitting in alkaline medium (0.1 M NaOH) and it was found that all of them showed almost the same activity which required an over-voltage of 308 ± 2 mV to obtain an anodic current density of 10 mA cm-2. The catalytic and electrocatalytic performances of these unprotected Ru0 networks were compared with Ru0 nanomaterials prepared under similar conditions with three different surfactants, viz. CTAB, SDS and TX-100, which revealed that unprotected Ru0 networks are better catalysts than those stabilized with surfactants. The superior catalytic and electrocatalytic performance is due to the availability of unprotected Ru0 surfaces. The present route may provide a new possibility of synthesizing other surfactant-free, unprotected metal colloids for enhanced catalytic and electrocatalytic applications.

Copper and nickel ion removal from synthesized process water using BSA-coated bubbles

Biosorption of a ternary system containing copper, nickel and calcium ions was conducted to examine the ability of air-filled emulsions (AFE) to remove heavy metal ions from a synthetic process water. AFE is a novel colloidal material containing fine air bubbles encapsulated by a thin film of cysteine-rich protein. AFE introduces a high interfacial surface area between metal ions and extractant. Impact of different experimental conditions such as calcium ion concentration, AFE dosage and final solution pH on metal ion uptake was explored. Calcium ions exhibited an adverse effect on copper removal, which reduced by 70% due to both higher affinities of active binding sites for calcium ion compared to that of copper and nickel ions and bridging flocculation of microbubbles occurred in the solution. The results acquired from potentiometric titration showed the presence of three functional groups on the surface of bubbles (carboxylic, thiol and amine groups), the carboxylic group being the most abundant.

Sorption of radionuclides and metals to graphene oxide and magnetic graphene oxide

Graphene oxide (GO) and two magnetic graphene oxide (MGO) composites with a different amount of magnetite were synthesized, characterized and used in sorption experiments. The effect of pH on sorption of Am(III) and Pu(IV) isotopes as well as Co(II), Ni(II), Cu(II) and Pb(II) to GO and MGO was studied in equilibrium and kinetic experiments. The adsorption capacities varied from 30 to 574 mg g−1 while rate constants ranged from 0.29 to 0.46 min−1 and increased in the following order Co, Cu, Pb and Ni. Large variations in the uptake of studied elements by adsorbents depending on initial and final pH of solutions were observed.

The enhancement of porosity of carbon xerogels by using additives

Resorcinol-formaldehyde carbon xerogels were synthesized by means of microwave heating by using precursor solutions with pH values ranging from 3 to 7 and adding various amounts of sodium sulfate, hexadecyltrimethylammonium bromide and Span80. It was found that the amount of additive that can be introduced depends to a large extent on the final pH of the precursor solution. Characterization of the porous structure of the carbon xerogels thus synthesized demonstrated that their porosity was modified by interactions between the additives and the polymeric structure of the xerogels. It is worth noting that carbonaceous materials with a pore size that could not be obtained by merely modifying the pH could be synthesized by adding different types of additive, with the result that a significant improvement of the porous properties of the carbon xerogels was achieved. The addition of sodium sulfate increased the size of the clusters and pores due to repulsive forces created between the additive and resorcinol anions. Hexadecyltrimethylammonium bromide gave rise to a dense branched structure with pores of a small size attributable to forces of attraction between the cations of the additive and resorcinol anions. In contrast, the presence of Span80 in the precursor solution produced a condensation reaction between the resorcinol and the additive, as a result of which the amount of resorcinol available for the sol–gel reaction was reduced.

The Characterization of Bismuth Vanadate Powder Synthesized by a Modified Microwave Method

Bismuth vanadate (BiVO4) powder was synthesized by a modified microwave method. Bismuth nitrate pentahydrate, ammonium metavanadate and 2-propanol were used as the starting precursors. The final pH of solution was adjusted to 7 and irradiation power at 600 Watt for 2 and 6 min. The yellow powder was filtered and dried at 100 °C for 24h. The phase of BiVO4 powder was characterized by X-ray diffractometer (XRD). Multi-phase of monoclinic and tetragonal phase was obtained without calcination step. The morphology of BiVO4 powder was investigated by scanning electron microscope (SEM). The BiVO4 powder was irregular in shape and agglomerated with the range particle of 0.1–0.3 μm. The functional group of BiVO4 powder was investigated by fourier transform infrared spectrometer (FTIR). The wavenumber at 498–502 cm-1 and 746–762 cm-1 was corresponding to the vibration of Bi-O bending and VO43- stretching, respectively.

Recovery of nickel and cobalt from leach solutions of nickel laterites using a synergistic system consisting of Versatic 10 and Acorga CLX 50

A direct solvent extraction (DSX) process to recover nickel and cobalt from laterite leach solutions is potentially more cost effective compared to the traditional precipitation and re-leaching method. A synergistic solvent extraction (SSX) system consisting of Versatic 10 and Acorga CLX 50 in ShellSol 2046 was studied for DSX nickel and cobalt recovery from a synthetic solution using semi-continuous tests. The effect of pH on the metal distribution profile and metal separation were investigated. It was found that the SSX system can effectively recover nickel and cobalt and separate them from manganese, calcium and magnesium. Over 99% of Ni and Co was extracted using four stages of semi-continuous extraction from the synthetic laterite solution at pH 6.3 and an A/O flowrate ratio of 1:1. More than 80% of the manganese was rejected to the raffinate. The co-extraction of calcium was less than 5% and the co-extraction of magnesium was negligible under these conditions. The co-extracted manganese and calcium were readily scrubbed in three stages semi-continuous scrubbing. The loaded strip liquor with a high concentration of nickel (71.3g/L Ni) was obtained after two-stage continuous stripping. The final strip solution pH of 3 would be suitable for nickel electrowinning. A conceptual DSX process flowsheet using the SSX system to recover nickel and cobalt from laterite leach solutions after iron removal has been proposed.

Designing and optimization of separation process of iron impurities from kaolin by oxalic acid in bench-scale stirred-tank reactor

Kaolin leaching by oxalic acid in a bench-scale stirred-tank reactor using response surface methodology and face centered central composite design based on three variables: oxalic acid concentration (X1: 0.1–0.3M), temperature (X2: 30–80°C) and duration of the leaching test (X3: 2–4days) was investigated. The experimental data obtained were fitted to a second-order polynomial equation using multiple regression analysis by Design-Expert 7 software and were analyzed by analysis of variance (ANOVA). According to ANOVA, all factors (X1, X2 and X3) influenced the response (dissolved iron concentration) and a positive regression coefficient of variables suggested an increase in dissolved iron concentration with an increase in oxalic acid concentration, temperature and time of leaching but there was not any interaction between them. The 3-D response surface plot and the contour plot derived from the mathematical model were applied to determine the optimal conditions. The optimum leaching conditions for maximum dissolved iron concentration were found to be oxalic acid concentration of 0.21M, temperature of 77°C and duration of the leaching test of 4days. After the washing stage of kaolin, in those experiments that pH was above 4, iron oxalate precipitate was formed and the percentage of residual iron in the sample after leaching was higher than expected. In general, the minimum amount of residual iron in the kaolin was 0.75% (w/w) that was obtained in tests where the oxalic acid concentration, temperature, time of the leaching and pH of final solution were 0.3M, 30°C, 2days and 3, respectively.

Changes in pH of irrigating solutions after contact with human root dentin.

The aim of this study was to analyze the in vitro behavior of the pH of different irrigating solutions, used alone or consecutively, after contact with extracted human teeth. Mandibular human premolars were selected. The middle thirds were divided into 6 parts. The specimens obtained were divided into 6 groups and treated with irrigating solutions: 1) distilled water; 2) 1% NaOCl; 3) 1% Citric Acid (CA); 4) 17% EDTA; 5) 1% CA + 1% NaOCl; 6) 17% EDTA + 1% NaOCl. Specimens were immersed in 1 mL of each solution at 37oC, those of groups 1, 2, 3 and 4, for 5 minutes, and the rest, consecutively for 2.5 minutes in each solution. Initial and final pH of the solutions were determined. Data were analyzed by the T Test, one-way analysis of variance (ANOVA) and Tukey multiple comparison Test. At 2.5 and 5 minutes there were significant differences between the initial and final pH for all solutions. The pH values decreased for distilled water and NaOCl, while they increased for CA and EDTA. In vitro, the pH of all solutions was modified after contact with root dentin at both test times (2.5 and 5 min).

Determining the Effect of Carrier Water pH and Bicarbonate Concentration on Final pH of Plant Growth Regulator Solutions

Chemical plant growth regulators (PGRs) are important tools in greenhouse ornamental crop production because growers must increasingly meet specifications for plant shipping and marketability. However, the role of water quality parameters such as pH or alkalinity (bicarbonate in this study) on final PGR solution pH is not well documented and could impact efficacy. We assessed the interaction of PGR type and concentration on the final spray solution pH when combined with carrier water of varying pH and bicarbonate concentration. Eleven PGRs commonly used in floriculture (ancymidol, benzyladenine, chlormequat chloride, daminozide, dikegulac-sodium, ethephon, flurprimidol, gibberellic acid, gibberellic acid/benzyladenine, paclobutrazol, and uniconazole) at three concentrations (low, medium, and high recommended rates for each product) were added to reverse osmosis (RO) carrier water adjusted to four pH (5.3, 6.2, 7.2, 8.2) levels or added to tap carrier water adjusted to four bicarbonate concentrations (40, 86, 142, 293 mg·L−1 of CaCO3). Resultant solution pH levels were measured. Plant growth regulators were categorized as acidic, neutral, or basic in reaction based on the change of the carrier water pH on their addition. Benzyladenine, chlormequat chloride, gibberellic acid, and gibberellic acid/benzyladenine acted as weak acids when added to RO water, whereas daminozide, ethephon, and uniconazole reduced final solution pH from 1.25 to 5.75 pH units. Flurprimidol and paclobutrazol were neutral in reaction with final solution pH being similar to that of the RO carrier water before their addition. Ancymidol and dikegulac-sodium were basic in reaction, increasing final solution pH in RO carrier water up to 2.3 units. There was an interaction between chlormequat chloride concentration and RO carrier water pH on change in pH. When added to tap carrier water, final solution pH increased for all except the stronger acids, daminozide, ethephon, and uniconazole, where it decreased up to 3.5 units, and benzyladenine, where it decreased 0.35 units at 40 mg·L−1 bicarbonate. There was an interaction between PGR concentration and bicarbonate concentration in tap carrier water for daminozide and ethephon. The magnitude of change in pH (final solution pH minus initial carrier water pH) with the addition of each PGR was greater for RO than for tap water containing 40 to 293 mg·L−1 bicarbonate for all 11 PGRs tested.