Effect Of Calcium Ion Concentration Research Articles

Co-encapsulation of curcumin and quercetin with zein/HP-β-CD conjugates to enhance environmental resistance and antioxidant activity

In this study, composite nanoparticles consisting of zein and hydroxypropyl beta-cyclodextrin were prepared using a combined antisolvent co-precipitation/electrostatic interaction method. The effects of calcium ion concentration on the stability of the composite nanoparticles containing both curcumin and quercetin were investigated. Moreover, the stability and bioactivity of the quercetin and curcumin were characterized before and after encapsulation. Fluorescence spectroscopy, Fourier Transform infrared spectroscopy, and X-ray diffraction analyses indicated that electrostatic interactions, hydrogen bonding, and hydrophobic interactions were the main driving forces for the formation of the composite nanoparticles. The addition of calcium ions promoted crosslinking of the proteins and affected the stability of the protein–cyclodextrin composite particles through electrostatic screening and binding effects. The addition of calcium ions to the composite particles improved the encapsulation efficiency, antioxidant activity, and stability of the curcumin and quercetin. However, there was an optimum calcium ion concentration (2.0 mM) that provided the best encapsulation and protective effects on the nutraceuticals. The calcium crosslinked composite particles were shown to maintain good stability under different pH and simulated gastrointestinal digestion conditions. These results suggest that zein–cyclodextrin composite nanoparticles may be useful plant-based colloidal delivery systems for hydrophobic bio-active agents.

Effect of calcium ion concentration on the ORR performance of Pd/C catalysts

Noble metal electrocatalysts prepared by microbial methods have attracted extensive attention because of their environmental protection and easy preparation.

Dispersion of bacterial cells during microbially induced calcium carbonate precipitation in fracture sealing

Fluid leakage through fracture networks is one of the primary environmental issues in water reservoir management, oil extraction, and geological carbon sequestration. Microbially induced calcium carbonate precipitation (MICP) offers a promising alternative to seal fractures and improve the performance of those relevant engineering over their service life. The dispersion of bacterial cells plays an important role in the growth and distribution of CaCO3 during the MICP process. The effect of calcium ion concentration, and flow rate on the diffusion behaviors of bacterial cells are studied by directly observing the mixing of two streams of solution, i.e., bacterial solution and cementation solution, in a microfluidic chip. Micromodel experiments show that the high concentration of calcium ion results in a significant retarding effect in the diffusion of bacterial cells given the chemotaxis. The transverse diffusion of motile bacteria might be suppressed by high-rate fluid flow or promoted by low-rate flow. Our work illustrates the significant impacts of solute concentrations and fluid flow rate on the dispersion of bacterial cells and deepens the understanding of the delivery of bacterial suspensions in fracture sealing with MICP.

Synergetic effect of cottonseed fatty acid salt and nonionic surfactant NP-4 in the froth flotation of siliceous-calcareous phosphate rock

Fatty acid is constricted when used in phosphate flotation alone as a collector due to its high reagent consumption and low separation efficiency. When fatty acids are mixed with other surfactants, the flotation performance can be greatly enhanced because of the synergetic effect, and therefore, widely adopted in industry. The cottonseed fatty acid salt (CSFA) and nonionic surfactant of NP-4 mixture was used in the upgrading of phosphate ores in this study. Batch flotation tests, droplet size distribution of CSFA, zeta potential measurements and X-ray photoelectron spectroscopy were conducted to elucidate the synergistic mechanism between the two surfactants. It was found that NP-4 improved the emulsification of CSFA and can reduce the adverse effect of calcium ion concentrations, which may otherwise be detrimental to CSFA. When mix CSFA with 10 wt% NP-4, an optimum separation between apatite and dolomite or quartz and lower reagent consumption were observed in flotation of siliceous-calcareous phosphate ore. With the aid of zeta potential measurement and XPS analysis, the adsorption behaviors of CSFA and NP-4 on the surfaces of apatite, dolomite and quartz was revealed. NP-4 enhanced the adsorption of CSFA on the surface of apatite and dolomite but decreased its adsorption on quartz, indicating that CSFA and NP-4 were co-adsorbed on surfaces of apatite and dolomite whereas in a competitive adsorption on the quartz surfaces.

Application of bio-based alkali to induce flocculation of microalgae biomass

One of the bottlenecks to commercialize microalgae-based biofuel production is harvesting of microalgae biomass from high dilute culture broth. Meanwhile, flocculation is identified as a low cost and promising technique to address this challenge. In this study, the flocculating potential of agricultural waste derived bio-based alkali from plantain peel ash was evaluated. The plantain peel ash and the produced bio-based alkali were characterized using inductively couple plasma mass spectrometry (ICP-MS) and scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDS). Results showed that more than 90% harvesting efficiency of microalgae biomass were obtained for both Nannochloropsis oculata and Dunaliella salina at 1, 2 and 3% v/v flocculant (bio-based alkali) dose, while the maximum biomass concentration factors were 20 and 14 at 1% v/v flocculant dose for N. oculata and D. salina respectively. The positive effect of calcium ion concentration on alkaline flocculation of freshwater microalgae species Neochloris conjuncta was demonstrated. Also, the characterization of the produced bio-based alkali indicates that the concentration of K+ (61,630 ppm) is highest, followed by Ca2+ (1,569 ppm) and Na+ (582 ppm), which clearly support the alkaline nature of the flocculant. The chromatogram obtained from SEM-EDS of the ash also corroborates the highest proportion of potassium in the ash sample. This study shows that the plantain peel-derived alkali can be used to effectively and efficiently harvest microalgae biomass from very dilute microalgae culture media.

TTX-resistant sodium currents in medial prefrontal cortex pyramidal neurons depend on extracellular Ca2+ concentration

Background: Previous reports reported the presence of TTX-resistant Nav1.8 and Nav1.9 sodium chan­nels in the cortex pyramidal neurons. A characteristic feature of Nav1.9 channels is activation at voltages close to — 70 mV. Therefore, they do not participate directly in the action potential but contribute to the regulation of the resting membrane potential. Their physiological role is modulation of cell excitability. The aim of the study was to investigate, with the use of patch clamp technique, the dependence of the activation thresholds of TTX–resistant sodium currents on the concentration of extracellular calcium in medial prefrontal cortex pyramidal neurons in rats. Results: The recorded values of the threshold of the voltage-dependent sodium currents were in the range of -65 mV to -75 mV. This suggests that the sodium currents may result from the presence of Nav1.9 channels in the rat pyramidal neurons. The threshold for the activation of sodium currents depended on the concentration of Ca2+. Increasing the concentration of calcium ions in the extracellular solution by 5 mM caused the depolarizing shift in the activation potential by about 10 mV. The effect of calcium ion concentration on the potential of TTX-resistant currents activation suggests that Nav1.9 channels are modulated by extracellular Ca2+ concentration. Conclusions: The study has experimentally confirmed that TTX-resistant channels are present in the cell membrane of the rat prefrontal cortex pyramidal neurons and may, therefore, take a physiological role in the conductivity of sodium currents in a manner dependent on the concentration of extracellular ions.

Effects of calcium ion concentration on calcification rates of six stony corals: A mesocosm study

A 1.5-ton indoor artificial coral reef mesocosm was established in order to evaluate the effects of changes in calcium ion (Ca2+) concentration on calcification of six stony corals, including two species of Acroporiidae (Acropora millepora and A. echinata), three species of Pocilloporidae (Pocillopora damicorins, Stylophora pistillata and Seriatopora caliendrum) and one species of Agariciidae (Pavona decussata). Periodic addition of CaCl2 was conducted to obtain a long-term series (23 weeks) of six reef coral calcification rates. Species-specific calcification rates were found among six stony corals, which shows linear increase in S. pistillata and A. millepora and exponential increase in S. caliendrum with elevated ambient seawater Ca2+ concentrations (ranging from 157.4 mg/L to 456.7 mg/L). Calcification rates tended to plateau with increased ambient seawater Ca2+ concentration (300–400 mg/L) for P. damicornis, while displaying a reverse parabolic pattern for A. echinata and P. decussata. We hypothesized that Ca2+ deposition by most stony corals would follow Michaelis-Menten kinetics, but the plateau would be reached at different Ca2+ concentrations for different coral species. Linear or exponential increases with Ca2+ concentrations observed in S. pistillata, A. millepora and S. caliendrum may be still at the initial stages of Michaelis-Menten curve, and they did not reach peak calcification rates at <460 mg/L of Ca2+ concentration. This work is valuable in providing instruction for the methodology and timing for periodical Ca2+ supplementation in closed recirculating aquacultural systems for stony corals.

Effect of Calcium Ion Concentration on Small Molecule Desorption from Alginate Beads

Spherical alginate beads were prepared by ionotropic gelation of sodium alginate through the use of calcium ions. Pyranine (Py) was added to the alginate solution as a small molecule probe for fluorescence studies. Desorption of Py in water from the alginate beads cross-linked with calcium ions was studied by using the steady state fluorescence technique. The fluorescence emission intensity (I) from Py was monitored during the desorption process at 512 nm using the time drive mode of the spectrofluorometer. The increase in I was attributed to Py release from the beads. The Fickian diffusion model was used to calculate the desorption coefficients, D, which were found to be increased up to 3% (w/v) CaCl2 concentration in the beads, and then decreased with a further increase of CaCl2 content. On the other hand, the encapsulation efficiency of Py in the calcium alginate beads presented the reverse behavior compared to D. It was observed that, when the content of CaCl2 was increased, the incubation time, t0, for the start of desorption increased.

Calcium Ion and Protocorm Differentiation for Cymbidium Hybrid Cymbidium Lucky Gloria × Cymbidium Lovely Moon 'Crescent'

The low protocorm rate of the hybrid Cymbidium Lucky Gloria × Cymbidium Lovely Moon Crescent (LLC) has long been a detriment to its propagation. In this paper, we describe the thorough research about the effects of calcium ion concentration on the protocorm differentiation for Cymbidium hybrid LLC in vitro through 4 levels of Ca2+ concentration in MS medium based on the trial test including medium experiment with different calcium concentrations and the use of calcium inhibitor La3+. Our studies revealed that Ca2+ played a key role in protocorm differentiation of LLC, which was against the generally accepted idea about the function of 6-benzyl aminopurine (6-BA) and indole-3-butyric acid (IBA) in hybrid cymbidium protorcorm differentiation in vitro. The Chain reaction constituted by cytokinin, calcium, and auxin is submitted to exloringly explain the function mechanism of Ca2+.

Formation of Tubes during Self-Assembly of Bacterial Surface Layers

Based on experimental studies on tube formation during self-assembly of bacterial surface (S)-layers, a mechanistic model for describing the underlying basic mechanisms is proposed and the effect of process parameters on growth velocity and tube radius is investigated. The S-layer is modeled as a curved sheet with discrete binding sites for the association of monomers distributed along the S-layer edges. Reported changes of the tube radius owing to genetic protein modifications are explained within the framework of continuum mechanics. S-layer growth velocity and shape development are analyzed by Monte Carlo simulation in their dependence on the attachment and detachment frequencies of monomers at the S-layer. For curved S-layer patches, a criterion for the formation of S-layer tubes is derived. Accordingly, tubes can form only within a certain range of the initial monomer concentration. Furthermore, the effect of calcium ion concentration on tube formation is discussed, including recent experimental findings on the calcium effect.

The effect of calcium ion concentration on the bone response to oxidized titanium implants

To investigate the effect of calcium concentration on the bone tissue response to Ca-incorporated titanium implants. Two titanium surfaces containing 4.2% and 6.6% calcium were prepared using the micro-arc oxidation process. The implants were inserted in the tibia of nine New Zealand White rabbits. After 6 weeks of healing, the bone response to the implants was quantitatively compared by biomechanical and histomorphometrical measurements. Ca 4.2% and Ca 6.6% containing implants revealed no distinctive differences in their qualitative surface chemistry; chemical bonding state of Ca in titanium oxide was mainly calcium titanates. No significant differences were observed between two implants in peak removal torque and shear strength comparisons (P>0.05). Histomorphometrical analyses presented no significant differences in bone-metal contact, bone area and newly formed bone measurements between two implants (P>0.05). From biomechanical and histomorphometrical measurements, the two calcium concentrations in this study did not differ significantly with respect to their influence on the bone tissue response. This similar bone response in rabbit tibiae may be explained by the similarity of the qualitative Ca chemistry in titanium surfaces.

Effect of Calcium Ion Concentrations on Osteogenic Differentiation and Hematopoietic Stem Cell Niche-Related Protein Expression in Osteoblasts

Apatite biomaterials have potential not only as cell vehicles for engineering bone tissue but also as regulators of calcium (Ca) concentration in situ for controlling osteoblast functions, for example, osteogenic differentiation and fate management of hematopoietic stem cells (HSCs). To design apatite materials having optimal chemical properties for the latter purpose, more detailed investigations into what effect Ca concentrations have on osteoblast functions is crucial. In this study, osteoblasts were cultured at different Ca concentrations, and the temporal alterations in osteogenic differentiation and HSC niche-related protein (angiopoietin-1, 2 [Ang1, 2]) expression were investigated. The different Ca concentrations (1.8-50 mmol/L) in the cell culture medium had no effect on the proliferation of osteoblasts, but did on the cell morphology. The higher Ca concentrations (<6 mmol/L) enhanced the mineralization as well as Ang1 expression. In addition, Ang1 expression in osteoblasts showed higher correlation with expression of connexin43, the major marker of cell-cell interactions, whereas Ang2 related to integrin beta1, the major marker of cell-matrix interactions. Thus, the local Ca concentration regulates cell morphology through the cell-cell or cell-matrix interactions, leading to the alteration of Ang1 expression in osteoblasts. Since these changes triggered by Ca are concerned with the osteogenic differentiation or reproduction of HSCs niche microenvironment, the results obtained in this study might be useful for designing apatite materials with optimal chemical properties.

A comparative study of the flocculation behaviour and final properties of synthetic and activated sludge in wastewater treatment

In this study, we have investigated in a comparative fashion the flocculation behaviour and final properties of both synthetic and activated sludge. Synthetic sludge was prepared according to established procedures; activated sludge was produced in a lab-scale, continuous-flow reactor which was fed with live activated sludge from a wastewater treatment plant. The novelty of our approach lies in the attempt to use the former as a key to characterising the physical and chemical properties of the latter. The effects of calcium ion concentration on flocculation dynamics for both sludges were measured on-line using the photometric dispersion analyser; the effects of calcium, polyelectrolyte conditioner and shear rate on final sludge properties were determined, including settleability, turbidity of supernatant, sludge volume index and dewatering, sludge conditioning, and floc strength and structure. It was thus possible to link the flocculation dynamics to the final sludge properties. The results indicate that calcium ions play an important role in the floc formation and the final floc size for both types of sludge by the construction of calcium bridges, and hence played a significant role in determining the final properties of the sludge. A qualitative link exists between the flocculation dynamics and the final properties for both types of sludge, and between the floc dynamics and properties of synthetic sludge on the one hand and those of activated sludge on the other. The two types of sludge have very similar settling and dewatering characteristics after cationic polymer conditioning. However, there are quantitative differences in the calcium concentration required for flocculation, the supernatant turbidity, the sludge-volume index and the floc strength. This difference is believed to be due to the absence of filamentous material in the synthetic sludge which is present in the activated sludge. The stable and well-defined nature of synthetic sludge makes it useful as a non-complex analogue for the physical and chemical properties of activated sludge, but filamentous cellulose should be added to improve quantitative agreement with activated sludge.

The Hemodynamic Effect of Calcium Ion Concentration in the Infusate During Predilution Hemofiltration in Chronic Renal Failure

It is the prevailing view that convective dialysis techniques stabilize blood pressure. Calcium concentration in the substitution fluid may be important in this respect. The aim of this study is to investigate the influence of calcium ion concentration in the substitution fluid on hemodynamic stability during predilution hemofiltration (HF). We conducted a randomized, crossover, blinded, controlled trial with 12 stable long-term hemodialysis patients without diabetes. Each patient was randomly assigned to substitution fluid with a calcium ion (iCa) concentration of 2.5 mEq/L (1.25 mmol/L; low-calcium session [L-HF]) or 3.5 mEq/L (1.75 mmol/L; high-calcium session [H-HF]) during 4.5 hours of predilution HF with a volume of 1.24 +/- 0.09 L/kg dry body weight and a temperature of 37 degrees C. Ultrafiltration was kept constant in each patient. Blood pressure (mean, systolic [SBP], and diastolic blood pressure [DBP]), pulse rate, arterial and venous temperature, energy transfer, and relative blood volume were measured at 15-minute intervals. Cardiac output, total peripheral resistance, stroke volume, and iCa were measured hourly. The 2 treatments were matched with the exception of iCa concentration. A significant intratreatment reduction in cardiac output and stroke volume was shown to the same extent for both groups. Intertreatment comparisons showed a significantly lower mean arterial pressure, SBP, DBP, and total peripheral resistance in the L-HF compared with the H-HF group. iCa concentration of 3.5 versus 2.5. mEq/L (1.75 versus 1.25 mmol/L) in the infusate during predilution HF stabilized blood pressure, possibly because of greater peripheral resistance rather than through changes in cardiac performance.

The effect of calcium ion concentration on osteoblast viability, proliferation and differentiation in monolayer and 3D culture

Our research group aims to develop an osteochondral composite using type II collagen gel with hydroxyapatite (HAp) deposited on one side. Soaking gels in Ca 2+ and phosphate solution is indispensable to HAp deposition, so relationships between cell behavior and Ca 2+ concentration were examined in two- and three-dimensional cultures. The present results indicate that 2–4 m M Ca 2+ is suitable for proliferation and survival of osteoblasts, whereas slightly higher concentrations (6–8 m M) favor osteoblast differentiation and matrix mineralization in both 2- and 3-dimensional cultures. Higher concentrations (> 10 m M) are cytotoxic. Purely from the perspective of calcium deposition, higher concentrations lead to increased accumulation of Ca 2+. Culturing cells in phosphate-containing gel in media with Ca 2+ also leads to time-dependent formation of HAp in the gel. Considering the viability of embedded cells, culturing scaffolds in media with Ca 2+ concentrations around 5 m M is useful for both HAp deposition and osteoblast behavior.

Use of surfactants to remove water-based inks from plastic film: effect of calcium ion concentration and length of surfactant hydrophobe

Effective plastic film deinking could permit the reuse of recycled polymer to produce clear film, reduce solid waste for landfills, reduce raw material demand for polymer production, and aid process economics. In this study, the deinking of a commercial polyethylene film printed with water-based ink was studied using surfactants in the presence of hardness ions (calcium ions) at various pH levels. The electrostatic properties of ink particles in a washing bath were also investigated. Synthetic anionic surfactant or fatty acid soap in the presence of calcium ions at alkaline pH levels was found to be nearly as effective at deinking as cationic, nonionic, or amphoteric surfactants alone. However, adding calcium ions decreases the deinking effectiveness of cationic, nonionic, and amphoteric surfactants. Increasing the length of the ionic surfactant hydrophobe enhances deinking. Zeta potential measurements showed that water-based ink particles in water reach the point of zero charge (PZC) at a pH of about 3.6, above which ink particles are negatively charged, so cationic surfactant tends to adsorb better on the ink than anionic surfactant above the PZC in the absence of calcium. As the cationic surfactant concentration is varied between 0.005 and 25 mM, the zeta potential of the ink particles reverses from negative to positive owing to adsorption of cationic surfactant. For anionic surfactants, added calcium probably forms a bridge between the negatively charged ink and the negatively charged surfactant head groups, which synergizes adsorption of the surfactant and aids deinking. In contrast, calcium competes for adsorption sites with cationic and nonionic surfactants, which inhibits deinking. All the surfactants studied here disperse ink particles effectively in the washing bath above pH 3 except for the ethoxylated amine surfactant.

Rheological properties of gellan solutions: effect of calcium ions and temperature on pre-gel formation

The critical overlap concentration ( C ∗) for dilute gellan dispersions was studied with respect to the effect of calcium ion concentration (0.25 and 0.5 mM Ca 2+) and temperature (5–25 °C), using steady shear rheometry. C ∗ was assumed to be associated with the formation of pre-gel structure at gellan concentrations close to the gelation threshold. As temperature decreased or Ca 2+ concentration increased, C ∗ declined. The temperature dependence of C ∗ in the presence and absence of added Ca 2+ could be described by the Eldridge–Ferry model, where heat of cross-link formation declined in a nearly linear manner with increasing levels of Ca 2+. This was interpreted as the result of a shift from a system dominated by hydrogen bonds to one mediated by ionic interactions. An alternative model, developed by Tang, Tung, and Zeng (1997a) for an ion-mediated polymer gelation mechanism, determined the energy of cross-linking at C ∗ to be only slightly less than reported for self-supporting gellan gels. This model also indicated that the number of Ca 2+ ions involved in cross-linking two adjacent double helical gellan strands was three, which suggested that the minimum size of a junction zone was equivalent to a single pitch of the helix. In addition, the apparent viscosity of 0.1 and 0.2% (w/w) aqueous gellan dispersions was examined over a range of Ca 2+ concentrations and shear rates. Results indicated an increase in apparent viscosity to a maximum, which corresponded to a 0.5:1 ratio of Ca 2+ ions to gellan carboxyl groups. Upon further Ca 2+ addition, apparent viscosity declined, indicating a weakening or breakdown of pre-gel structure.

Temperature Transition of Human Hemoglobin at Body Temperature: Effects of Calcium

We studied the effects of calcium ion concentration on the temperature dependence of rheological behavior of human red blood cells (RBCs) and concentrated hemoglobin solutions. Our previous study (G. M. Artmann, C. Kelemen, D. Porst, G. Büldt, and S. Chien, 1998, Biophys. J., 75:3179–3183) showed a critical temperature ( T c) of 36.4 ± 0.3°C at which the RBCs underwent a transition from non-passage to passage through 1.3- μm micropipettes in response to an aspiration pressure of −2.3 kPa. An increase in intracellular Ca 2+ concentration by using the ionophore A23187 reduced the passability of intact RBCs through small micropipettes above T c; the micropipette diameter needed for >90% passage increased to 1.7 μm. Viscometry of concentrated hemoglobin solutions (45 and 50 g/dl) showed a sudden viscosity transition at 36 ± 1°C ( T c η ) at all calcium concentrations investigated. Below T c η , the viscosity value of the concentrated hemoglobin solution at 1.8 mM Ca 2+ was higher than that at other concentrations (0.2 μM, 9 mM, and 18 mM). Above T c η , the viscosity was almost Ca 2+ independent. At 1.8 mM Ca 2+ and 36 ± 1°C, the activation energy calculated from the viscometry data showed a strong dependence on the hemoglobin concentration. We propose that the transition of rheological behavior is attributable to a high-to-low viscosity transition mediated by a partial release of the hemoglobin-bound water.

Gelling of alginate fibres

AbstractEquipment was developed to measure the time for complete gelling of sodium alginate fibres in calcium chloride solution, taken as the time to achieve maximum tensile strength. The effects of fibre diameter, alginate concentration, alginate composition and calcium chloride concentration on gelling time were investigated. A diffusional model, developed to predict the gelling time, agreed with experimental results except for the effect of calcium ion concentration which was modelled empirically.

Influence des ions metalliques liberes par un charbon actif sur l'adsorption de micropolluants organiques. Le role des ions calcium

Recent studies concerning the removal, by activated carbon adsorption, of natural organics or micropollutants found in water supplies, have focused attention on the ionic composition of the treated water. Many workers have demonstrated that both the ionic composition and the salt concentration affect the ability of activated carbon to remove humic substances (Randtke and Jepsen, 1982; Weber et al., 1983; Lafrance and Mazet, 1985) or organic micropollutants (Lafrance et al., 1983; Souabi et al., 1986) from solution. In particular, calcium ions have been shown to significantly increase the adsorption of organics onto activated carbon (Lafrance et al., 1983; Weber et al., 1983). Although calcium salt residues have been found on the surface of commercial activated carbon (Lafrance and Mazet, 1986), no studies have considered the effects of this cation on the adsorption of organics in batch equilibrium experiments. The purpose of the present study is to quantify the effect of calcium ion concentration on the adsorptive capacity of a powdered activated carbon (PAC) for an anionic tensio-active agent: sodium lauryl sulfate. In one series of experiments, measurements of sorption kinetics of lauryl sulfate were made using a PAC treated in three ways: (1) untreated PAC; (2) PAC washed with distilled water before use; and (3) PAC washed with HCl 1N before use. Our results (Fig. 3) show that washing the PAC before conducting an adsorption study diminishes the effectiveness of the carbon in removing lauryl sulfate. These results may be related to the surface ionic content of the PAC, especially the calcium content: the untreated PAC may contain 50 μmol Ca 2+ g −1 of carbon (Fig. 4). The PAC washed with distilled water releases 42 μmol Ca 2+ g −1 of carbon, and the PAC washed with HCl 1N releases 75 μmol Ca 2+ g −1 of carbon (Table 1). In a second series of batch experiments, the effect of micromolar concentrations of Ca 2+ on the adsorptive capacities of the PAC (treated with HCl) for lauryl sulfate was studied. Decreasing the molar ratio [lauryl sulfate]/[Ca 2+] causes an increase in the removal of the lauryl sulfate (isotherms on Figs 5 and 7, and Langmuir equilibrium parameters on Fig. 8). The influence of the order of mixing, of the adsorbates lauryl sulfate and Ca 2+ with the PAC (Table 3), is shown by the sorption kinetic curves in Fig. 6. Results indicate that the residual concentration of lauryl sulfate in solution is not affected by the order of mixing adsorbates and PAC when the molar ratio [lauryl sulfate]/[Ca 2+] is 1.0. Such results support the assumption that calciums ions specifically interact with the carbon surface in order to increase the adsorption of lauryl sulfate. The electrostatic interactions between PAC and Ca 2+, which are probably responsible for an increase in adsorption of lauryl sulfate, are examined by zeta potential measurements of the PAC. Whereas micromolar concentrations of lauryl sulfate causes a marked increase in the negative surface charges of the PAC (Figs 9 and 10), calcium ion induces a rapid neutralization of this zeta potential (Figs 10 and 11). Such neutralization of the negative functional groups of both lauryl sulfate molecules and the PAC surface is strongly related to the increase of the maximum adsorption capacity (Γ ∞) of the PAC for lauryl sulfate (Fig. 11). Batch adsorption experiments using this PAC can lead to different measures of the efficiency of the carbon for the adsorption of some organics, depending on the treatment of the PAC before and use on the release of the ionic content of the PAC. The particular role of calcium ion in the adsorption of lauryl sulfate indicates, that the carbon efficiency in removing anionic compounds can be significantly improved by the addition of micromolar quantities of salt in solution.