Adsorption of cationic polyelectrolyte onto a model carboxylic latex and the influence of adsorbed polycation on the charge regulation at the latex surface

 Adsorption of a well-characterized cationic polyacrylamide (CPAM) onto the surface of a model colloid (monodisperse polystyrene latex with carboxylic functional groups) was studied over a wide range of pH (4–9) and KCl concentration (c _s =10^-3–0.3 M). The surface charge density of the latex particles with and without adsorbed CPAM was also measured over the same range of electrolyte compositions. The adsorbed amount of CPAM increases with increase in c _s and pH. The polyelectrolyte adsorption alters substantially the surface charge density of the latex particles as compared to the polymer-free case. A large overcompensation of the surface charge by the adsorbed polyelectrolyte is established at high c _s and low pH. A qualitative explanation of the observed features is put forward. Received: 3 December 1996 Accepted: 20 January 1997     

Interparticle forces arising from an adsorbed strong polyelectrolyte in colloidal dispersions: charged patch attraction

Adsorbed polystyrene sulphonate (PSS) shifts the pH of the zero zeta potential, pH_ς = 0, of ZrO₂ to a lower pH. The positive charge density of ZrO₂ at pH = pH_ς=0 determined from the amount of PSS adsorbed was in excellent agreement with that obtained from charge titration. Polystyrene sulphonic acid shifts pH_ς=0 to a greater degree compared with polyacrylic acid because it is a much stronger acid. A patch is likely to just consist of one adsorbed molecule. The patch is negative when the charges of the molecule exceed the underlying positive surface charge. Attraction between the negative patch and the bare positive surface of a second particle is responsible for increasing the yield stress of concentrated ZrO₂ dispersions at pH_ς=0. Its magnitude is only of the order of the van der Waals attraction. Increasing ionic strength and patch misalignment diminish the attraction. The upper limit of the patch area was estimated from the radius of gyration of the molecule in solution. With a known patch area, the patch charged density can be calculated. With the selection of an appropriate patch area, the yield stress due to charged patch attraction increases linearly with the product of the negative and positive patch densities. Received: 30 March 1998 Accepted: 18 September 1998     

Flow behaviour of titanium dioxide dispersions in the presence of 2-hydroxyethyl cellulose

 The effects of 2-hydroxyethyl cellulose (HEC) of weight-average molecular weight 15,000, 90,000 and 7,20,000 on the rheological properties of TiO₂ dispersions were evaluated. For all three HECs, the maximum yield stress, τ_ymax, (occurred at zero zeta potential), decreased with increasing HEC concentration. Interestingly, the largest reduction in τ_ymax was observed with the HEC with the highest molecular weight. This reduction was attributed to steric interaction arising from adsorbed HEC. Adsorbed high-molecular-weight HEC formed an effectively thicker steric barrier because of its larger size and higher adsorption capacity. Bridging interactions that were expected to be important for the high-molecular-weight HEC were found to be unimportant here. In the flocculated regime, HEC enhanced the shear-thinning characteristics of the TiO₂ dispersions. Received: 8 November 1999 Accepted: 20 December 1999     

Extraction of copper(II) from weakly acid and ammonia media with <Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-dialkylhydrazides of aliphatic carboxylic acids

Dependence of physicochemical properties of N′,N′-dialkylhydrazides of aliphatic carboxylic acids (solubility in kerosene, acid-base properties) on the length of hydrocarbon radicals in the functional group was studied. The extraction capacity for copper(II) salts in weakly acid and ammonia media was examined in the range from pH 5–11 to a NH₃ content of 2.7 M. The capacity of the organic phase for copper(II) and re-extraction conditions were determined for the example of N′,N′-dibutylhydrazide of octanoic acid.     

Chelating resin preconcentration and Hg(II) assisted elution followed by differential-pulse anodic stripping voltammetry for the determination of Cd, Cu, and Pb in seawater

A new and efficient Hg(II) back-elution method for the desorption of Cd, Cu, and Pb from Chelex-100 chelating resin was developed. A smaller eluent volume and shorter elution time can be achieved using an Hg(II) containing eluent rather than pure nitric acid. Owing to the remaining Hg(II) ion in the effluent, a mercury thin-film electrode is formed in-situ during the anodic stripping voltammetric determination without any further addition of Hg(II). The results indicate that all the analytes in seawater matrix can be completely adsorbed on Chelex-100 resin from the sample at pH 6.5, and subsequently eluted from the resin with an acid solution of 5 × 10^–4 mol/L Hg²⁺ + 1 mol/L HClO₄. The detection limits obtained from the differential-pulse anodic (μg L^–1 to ng L^–1) stripping voltammetry are at sub-ppb to ppt (μg L^–1 to ng L^–1) levels permitting to determine Cd, Cu and Pb traces in seawater. The analytical reliability was confirmed by the analysis of the certified reference material CASS-II (open ocean seawater). Received: 22 April 1997 / Revised: 5 August 1997 / Accepted: 7 August 1997     

An LC method for monitoring medium-chain fatty acid permeation through CaCo-2 cell monolayers

A simple method was developed for monitoring the permeation of medium-chain fatty acids of C8 (octanoic acid) and C10 (decanoic acid) through CaCo-2 cell monolayers by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). The detection was made based on the electrochemical reduction prepeak of quinone caused by acids, requiring the fabrication of a two-channel HPLC-ECD system. In one channel, acetonitrile–water (7:3, v/v) was used as a mobile phase to separate acids by a C30 column. In the other channel, acetonitrile–water (7:3, v/v) containing 6 mmol/L 3,5-di-t-butyl-1,2-benzoquinone and 20 mmol/L LiClO₄ was used as a quinone solution to detect acids by an electrochemical cell with a glassy carbon working electrode. In this HPLC-ECD system, eluted acids were mixed with the quinone solution in a post column fashion to obtain current signals caused by acids. The peak area was found to be linearly related to the acid amount ranging from 25 to 1,000 pmol (r > 0.992). The detection limits of octanoic acid and decanoic acid were 7.5 and 8.8 pmol, respectively. Octanoic acid and decanoic acid spiked into cell culture media samples were extracted with acetonitrile and their recoveries were more than 89.5% with an RSD of less than 8.2%. This method was applied to the permeation experiment of octanoic acid and decanoic acid with CaCo-2 cell monolayers formed on the Transwell? system. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This work was partly presented at The Physical Pharma Forum 2008 on March 24, 2008 in Tokyo, Japan.     

Supercritical fluid extraction of t-resveratrol and other phenolics from a spiked solid

Supercritical fluid extraction of spiked phenolics including gallic acid, (+)-catechin, (–)-epicatechin, caffeic acid, p-coumaric acid, myricetin, t-resveratrol, quercetin and salicylic acid from an inert support using pure CO₂ and methanol-carbon dioxide mixtures was studied. Extraction and collection variables including modifier percentage, extraction temperature, flow rate, extraction time, trap packing and rinse solvent were optimized. The study revealed that the use of methanol as modifier was mandatory. Only the less hydroxylated compounds such as p-coumaric acid, t-resveratrol and salicylic acid could be quantitatively recovered (mean recovery ≥ 95%) from spiked diatomaceous earth. Mean recoveries of more polar phenolic acids and flavonoids such as gallic acid, caffeic acid, catechins and quercetin were between 30% and 70%. Myricetin was not recovered at all. Received: 19 June 1997 / Revised: 20 October 1997 / Accepted: 26 October 1997     

Supercritical fluid extraction of t-resveratrol and other phenolics from a spiked solid

Supercritical fluid extraction of spiked phenolics including gallic acid, (+)-catechin, (–)-epicatechin, caffeic acid, p-coumaric acid, myricetin, t-resveratrol, quercetin and salicylic acid from an inert support using pure CO₂ and methanol-carbon dioxide mixtures was studied. Extraction and collection variables including modifier percentage, extraction temperature, flow rate, extraction time, trap packing and rinse solvent were optimized. The study revealed that the use of methanol as modifier was mandatory. Only the less hydroxylated compounds such as p-coumaric acid, t-resveratrol and salicylic acid could be quantitatively recovered (mean recovery ≥ 95%) from spiked diatomaceous earth. Mean recoveries of more polar phenolic acids and flavonoids such as gallic acid, caffeic acid, catechins and quercetin were between 30% and 70%. Myricetin was not recovered at all. Received: 19 June 1997 / Revised: 20 October 1997 / Accepted: 26 October 1997     

Aqueous solution of phosphoric acid as the stationary liquid phase for selective separation of fatty acids under conditions of steam chromatography

An aqueous solution of phosphoric acid was used as a selective stationary liquid phase for the separation of volatile fatty acids under conditions of steam chromatography. Organic acids C₂–C₈ are eluted from the column as symmetric peaks, and the order of their elution is reverse to that observed commonly on other phases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 497–499, March, 1997.     

Dispersion of alumina-coated TiO2 slurries in the presence of poly(acrylic) acid influence of monovalent counterions

The rheological behavior of concentrated alumina-coated TiO2 slurries has been investigated in connection with the type of surface counterions (monovalent cations: X = Li+, Na+, TMA+) in the absence and in the presence of polyacrylic acid (PAA). The study has been conducted in a pH range of 4-10 and with ionic strengths lower than 0.01 M. The pH and ionic strength were adjusted with XOH and XCl, respectively. The surface properties have been investigated by titration of surface counterions and the apparent yield stress has been measured using a dynamic stress rheometer. It appears from the results that the pH at the maximum yield stress and the magnitude of the yield stress depend on the nature of the counterion. The yield stress measurements were also conducted in the presence of PAA (0.5 segment/nm2) adsorbed on the particle surface. In that case, the mineral surface and adsorbed polymer were neutralized with XOH. The results show that the dispersion efficiency depends on the polymer counterion. In general, it is found that the maximum yield stress and the corresponding counterion surface density both follow the sequence TMA+ < Na+ < Li+. The adsorption of PAA apparently amplifies the effects observed with the corresponding cation. An electrostriction effect of the hydration layer at the interface is suggested in order to explain the increasing yield stress as the surface density of Li+ increases. The so-called structure-making/structure-breaking model explains the yield stress reduction with the TMA+ surface density.     

Flow field-flow fractionation-inductively coupled optical emission spectrometric investigation of the size-based distribution of iron complexed to phytic and tannic acids in a food suspension: implications for iron availability

Flow field–flow fractionation–inductively coupled plasma optical emission spectrometry (FlFFF–ICP–OES) was applied to achieve the size-based fractionation of iron in a food suspension in order to gain insights into iron availability. The binding of iron with phytic and tannic acids, employed as model inhibitors of iron availability in foods, was investigated at pH 2.0 (representing stomach fluid), pH 5.0 (the transition stage in the upper part of the duodenum), and pH 7.0 (the small intestine). In the presence of phytic acid, iron was found as a free ion or it was associated with molecules smaller than 1 kDa at pH 2.0. Iron associated with molecules larger than 1 kDa when the pH of the mixture was raised to 5.0 and 7.0. In the presence of tannic acid, iron was again mostly associated with molecules smaller than 1 kDa at pH 2.0. However, at pH 5.0, iron and tannic acid associated in large molecules (∼25 kDa), while at pH 7.0, most of the iron was associated with macromolecules larger than 500 kDa. Iron size-based distributions of kale extract and tea infusion containing phytic and tannic acids, respectively, were also examined at the three pH values, with and without enzymatic digestion. Without enzymatic digestion of the kale extract and the tea infusion at pH 2.0, most of the iron was released as free ions or associated with molecules smaller than 1 kDa. At other pH values, most of the iron in the kale extract and the tea infusion was found to bind with ~2 kDa and >500 kDa macromolecules, respectively. Upon enzymatic gastrointestinal digestion, the iron was not observed to bind to macromolecules >1 kDa but <500 kDa, due to the enzymatic breakdown of large molecules to smaller ones (<1 kDa). Figure Flow field–flow fractionation was exploited in order to achieve size-based iron fractionation and thus investigate iron-binding behavior under gastrointestinal conditions     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Comparison of adsorption affinity of polyacrylic acid for surfaces of mixed silica–alumina

The influence of solution pH (in the range 3–9) on the adsorption of polyacrylic acid (PAA) on the mixed silica–alumina surface (SA-3: SiO₂ 97 %–Al₂O₃ 3 % and SA-96: SiO₂ 4 %–Al₂O₃ 96 %) was investigated. The following methods were applied in experiments: spectrophotometry, viscosimetry, potentiometric titration, and microelectrophoresis, which enable determination of adsorbed amount of the polymer, thickness of its adsorption layers, surface charge density, and zeta potential of solid particles in the presence and absence of PAA, respectively. The obtained results indicate that rise of solution pH causes the decrease of PAA adsorption and the increase of its adsorption layer thickness on surfaces of both solids. Moreover, significantly higher adsorption of polyacrylic acid was obtained on the SA-96 surface. This is a result of more favorable electrostatic interactions occurring between the adsorbing polymer chains and the SA-96 surface and formation of a greater number of adsorbate-adsorbent connections through hydrogen bridges.     

Oxidation of brown coal of Angren deposit with a mixture of nitric and sulfuric acids

Oxidation of brown coal of Angren deposits by a mixture of nitric and sulfuric acids was studied in respect of dependence on the concentration of nitric acid (5–30%), concentration of sulfuric acid in nitric acid solution (2.5–20%), and temperature (40–80°C) at the process duration 2 h and the ratio of coal: HNO₃ = 1: 2. Optimal conditions of the process in terms of maximum yield of humic acids and the minimum loss of nitrogen oxides were found.     

Fluorescence study of the interaction between metal ions and methyl methacrylate–methacrylic acid copolymers in aqueous solutions: thallium(I), calcium(II), and terbium(III)

 The binding of the cations thallium(I), calcium(II) and terbium(III) to methyl methacrylate– methacrylic acid copolymers with different fractions of acid groups (x) has been studied in aqueous solution at various pH values using the fluorescence of covalently bonded 9-vinyl anthracene as a probe. In all cases, the extent of binding increases as a function of the charge of the polymer with either increasing fraction of carboxylic acids or of pH. However, differences are observed in the behavior of the three cations. With Tl(I), quenching of the anthracene group fluorescence is observed, indicating that the thallium(I) approaches the probe and suggesting that the alkylanthracene is probably in a relatively polar region. Binding constants have been determined from anthracene quenching data and from studies with the fluo-rescent-probe sodium pyrenetetra-sulfonate. Good agreement is obtained between the two methods, and values for the binding constants increase from 250 to 950 M^-1 as x increases from 0.39 to 1. It is suggested that the cation is held in the polyelectrolyte domain, partly by Debye–Hückel effects and partly by more specific interactions. Stronger binding is found with calcium(II) and terbium(III), and in this case increases in fluorescence intensity are observed on complexation due to the anthracene group being in a more hydrophobic region, probably as a result of conformational changes in the polymer chain. In the former case the stoichiometry of the interaction was determined from the fluorescence data to involve two carboxylate groups bound per calcium. Association constants were found using murexide as an indicator of free calcium to vary from 8400 to 37 000 M^-1 as x increases from 0.39 to 1. It is suggested that in this case specific calcium(II)–carboxylate interactions contribute to the binding. With terbium(III), a greater increase in the probe fluorescence intensity was observed than with calcium, and it is suggested that the interaction with the polymer is even stronger, leading to a more pronounced conformational change in the polymer. It is proposed that the terbium(III) interacts with six carboxylic groups on the polymer chain, with three being coordinated and three attracted by electrostatic interactions. Received: 10 June 1997 Accepted: 24 October 1997     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples. Received: 6 October 1997 / Revised: 26 November 1997 / Accepted: 3 December 1997     

Tribological performance of fatty acid modification of sol–gel TiO<Subscript>2</Subscript> coating

In this paper, the coatings with friction-reducing properties were investigated using both sol–gel and self-assembling techniques. The thin film of TiO₂ was firstly prepared on glass substrates via a sol–gel method, followed by calcinating at 480 °C. The films of fatty acid were then deposited on the TiO₂ surface to obtain a dual-layer film. The contact angle measurement and FT IR spectroscopy were used to determine the wetting behavior and chemical structure of films, respectively. The friction-reducing behavior of films sliding against a steel ball was examined on a macro friction and wear tester. It is found that fatty acid is strongly adsorbed on sol–gel derived TiO₂ surface. Good friction-reducing behavior is observed for the glass substrate after duplex surface-modification with TiO₂ surface obtained by sol–gel method and top layer of fatty acid.     

Influence of solution pH on stability of aluminum oxide suspension in presence of polyacrylic acid

The effect of solution pH and molecular weight of polyacrylic acid (PAA) on its adsorption as well as on stabilization-floculation properties of the colloidal Al₂O₃ and electrolyte solution systems was studied. The measurements showed that at pH = 6, the presence of the polymer of molecular weight 2?000 and 240?000 does not change stability of Al₂O₃ suspension. However at pH =3 and 9 the effect of polyacrylic acid is significant. At pH = 3 it creates destabilization of the suspension while at pH = 9 PAA it improves significantly the stability of Al₂O₃. It was shown that the increase in solution pH affects conformation of adsorbed macromolecules which causes the decrease in PAA adsorbed amount and thickness of polymer adsorption layer. By comparing the values of diffusion layer and surface charges, main effects responsible for the decrease in surface charge and ζ potential of the solid in the presence of the polymer as well as suspension stability were determined.     

Flow-injection analysis based on a membrane separation module and a bulk acoustic wave impedance sensor – determination of the volatile acidity of fermentation products

A novel flow-injection analysis (FIA) system has been developed for the rapid determination of the volatile acidity of some fermentation products like vinegars and juices. The proposed method is based on the diffusion of volatile acids, mainly acetic acid, across a PTFE gas-permeable membrane from an acid stream into an alkaline stream, and the acids trapped in the acceptor solution are determined online by a bulk acoustic wave impedance sensor based on changes in the conductivity of the solution. It exhibited a linear frequency response up to 10 mmol · L^–1 acetic acid with a detection limit of 50 μmol · L^–1, and the precision was better than 1% (RSD) at a through-put of 72 h^–1. The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow rates and temperature on the FIA performance were also investigated. Received: 2 June 1997 / Revised: 7 July 1997 / Accepted: 12 July 1997