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PubMed1968

Physicochemical properties of cartilage in the light of ion exchange theory.

Ion exchange theory has been applied to articular cartilage. Relationships were derived between permeability, diffusivity, electrical conductivity, and streaming potential. Systematic measurements were undertaken on these properties. Experimental techniques are described and data tabulated. Theoretical correlations were found to hold within the experimental error. The concentration of fixed negatively-charged groups in cartilage was shown to be the most important parameter. Fixed charge density was found to increase with distance from the articular surface and this variation was reflected in the other properties.

Adult↗
PubMed2000

Determination of glyphosate and aminomethylphosphonic acid residues in water by gas chromatography with tandem mass spectrometry after exchange ion resin purification and derivatization. Application on vegetable matrixes

An analytical method for the determination of glyphosate and its principal metabolite, aminomethylphosphonic acid (AMPA), in water of different hardnesses (5, 20, and 30 degrees DH, french hardness) has been developed. Samples were fortified at different levels (0.05, 0.1, 1, and 5 microg/L) and were purified by column chromatography on ion-exchange resins. After derivatization with TFAA/HFB mixture, the derivatives were quantified by using capillary gas chromatography with an ion-trap tandem mass spectrometric detector. Analytical conditions for MS/MS detection were optimized, and the quantification was carried out on the sum of areas of the three most representative ions: m/z 283, 223, and 181 for AMPA and m/z 440, 321, and 261 for glyphosate. The limit of quantification was demonstrated to be at 0.05 microg/L for each compound. The mean recovery value and the relative standard deviation (n = 65) were 93 and 12% for AMPA and 95 and 13% for glyphosate.

Journal Article↗
PubMed1999

Two ion-exchange chromatographic methods for the isolation of antibacterial peptides from lactoferrin. In situ enzymatic hydrolysis on an ion-exchange membrane.

Two ion-exchange chromatographic methods are reported for the rapid isolation of antibacterial peptides from lactoferrin (LF). Using the first method, a pepsin hydrolysate of LF was fractionated by bead-based cation-exchange chromatography. After removal of weakly bound material by washing with ammonia, highly purified lactoferricin-B (LFcin-B) was obtained in a single step by elution with 2 M NaCl. Some other cationic peptides, copurified as minor components, were also characterised by N-terminal sequencing, mass spectrometry and antibacterial activity determination. With the second method, cheese whey was filtered through a cation-exchange membrane, and the selectively bound LF was directly hydrolysed in situ with pepsin. Inactive LF fragments were washed off the membrane with ammonia, and a fraction enriched in LFcin-B was obtained by further elution with 2 M NaCl. The membrane method is more rapid and offers several economic advantages.

Amino Acid Sequence↗
PubMed1993

Chiral ion-exchange chromatography. Correlation between solute retention and a theoretical ion-exchange model using imprinted polymers.

Mobile phase effects were studied in the separation of D- and L-phenylalanine anilide (D,L-PA) on an imprinted chiral stationary phase (CSP). Using an aqueous-organic mobile phase, an improved column performance was seen, reflected in a two-fold decrease in the reduced plate height and an almost doubling of the resolution as compared to when a pure organic mobile phase was used. A strong dependence of retention (k') and enantiomer selectivity (alpha) on mobile phase pH was observed. k' reached a maximum at a pH close to the pKa value of the solute and alpha was high at low pH value but decreased when pH exceeded the solute pKa. Potentiometric titration data allowed estimation of the state of protonation of both the carboxylic acid containing CSP and the amino group containing solutes. The data are analyzed using a simple cation-exchange model to allow simulation of the retention as a function of mobile phase pH. The close agreement between the simulated and experimental curves for retention versus pH suggests that a simple cation-exchange mechanism controls the retention in this system. Moreover, the slightly lower average pKa of the imprinted polymer compared to that of a corresponding blank polymer explains the high selectivity seen at low pH values. Based on these findings, a model describing the events controlling binding and selectivity as a function of pH is proposed.

Chromatography, Ion Exchange↗
PubMed1991

Comparative performance of ion exchange and ion-paired reversed phase high performance liquid chromatography for the determination of nucleotides in biological samples.

We have compared anion exchange chromatography on APS-Hypersil (4.6 x 100 mm) eluted with a phosphate gradient with reversed phase chromatography on ODS-Hypersil (4.6 x 100 mm) in the presence of either tetrabutylammonium (TBA) or triethylammonium (TEA) ions with a methanol gradient. The systems have been compared both for ease of operation and for their resolving power with standard mixtures and acid extracts of both normal red cells (RBC) and ischaemic tissues. The two chromatographic modes exhibited similar separating efficiencies for standard mixtures of nucleotides but retention times were most stable using reversed phase liquid chromatography (RPLC) with TEA. Anion exchange columns slowly lost ion exchange capacity but selectivity was unchanged. RPLC in the presence of TBA gave reproducibile capacity factors only when operated isocratically due to irreversible changes to the silica surface. For RBCs the RPLC with TEA and anion exchange systems resolved 17 and 15 peaks, respectively, and for the ischaemic samples 22 and 14 peaks, respectively. However, nucleosides and bases were also resolved by the ODS column causing chromatographic crowding and uncertain peak identification.

Animals↗
PubMed2002

Microscale continuous ion exchanger.

A microscale continuous ion exchanger based on two liquid streams flowing in parallel is presented. The ion exchange reaction occurs through diffusional transfer of molecules between the ion exchanger phase and the eluent phase and is applied for conductivity suppression. Two approaches are demonstrated. In the first approach, a liquid ion exchanger (i.e. a strongly basic compound, e.g., tetraoctylammonium hydroxide, or a secondary amine, e.g., Amberlite IA-2) is dissolved in an organic solvent immiscible with the aqueous eluent. The system allows for sensitive suppressed conductivity detection of various inorganic cations. When the weakly basic secondary amine is used, conductometric detection of heavy metals is possible. In the second approach, a suspension of finely ground ion-exchange resin is used as the ion exchanger phase. In this case, the suspension need not involve an organic solvent. Theoretical models and computations are presented along with experimental results. The potential of such a system as a chip-scale post-separation suppressor/reactor is evident.

Cations↗
PubMed1981

An improved liquid ion exchanger for chloride ion-selective microelectrodes.

A new chloride liquid ion exchanger, Corning 477913, suitable for fabricating ion-selective microelectrodes (ISE) is described. It differs from the standard chloride exchanger. Corning 477315, in that the concentration of organophilic ligand is increased fivefold. The properties of ISE (tip diameter less than 1 micrometer) made from the new material are superior to those of ISE made from the standard material. The yield of acceptable ISE was greater (77 vs. 34%); the ISE resistance was decreased 5.3-fold; the average slope was improved (-52.8 vs. -45.5 mV); and the selectivity over some interfering anions was increased. Measurement of intracellular chloride activity in rabbit ventricle with ISE made from the new exchanger gave results similar to those reported previously with the standard exchanger. This suggests that 477913 is satisfactory for use in biological tissue. The new formulation should be particularly advantageous for measurements requiring ISE with very fine tips and in fabrication of multibarrel ISE.

Anions↗
PubMed2006

Ion-exchange voltammetry of dopamine at Nafion-coated glassy carbon electrodes: quantitative features of ion-exchange partition and reassessment on the oxidation mechanism of dopamine in the presence of excess ascorbic acid.

The incorporation/exclusion features of dopamine (DA), ascorbic acid (AA) and uric acid (UA) are evaluated for Nafion (NA)-coated glassy carbon electrodes (GCE) of different thicknesses. The ion-exchange partition of DA(+) between the NA film and the sodium phosphate electrolyte is evaluated by determining the partition coefficient (k(D)) and the apparent diffusion coefficient (D(app)) in thick NA films which were 401 and 1.5 x 10(-9) cm(2) s(-1), respectively. The solution diffusion coefficient was found to be 6.0 x 10(-6) cm(2) s(-1). Also, the effect of NA loading and of the voltammetric timescale on DA voltammetry in the presence of excess AA is assessed, at physiologic like conditions. It is demonstrated that, although AA is excluded at the NA coating, a catalytic regeneration of DA, induced by AA, occurs at the interface NA film/electrolyte resulting from the diffusion of the o-quinone product of DA oxidation from the electrode surface to that interface. The interference of AA in the voltammetric signal of DA is eliminated using 18 microg mm(-2) NA films and v> or =0.5 V s(-1). Therefore, fast, selective and sensitive voltammetric analysis of DA at concentrations<100 microM in the presence of excess AA, e.g., 1 mM is achieved.

Adsorption↗
PubMed2000

Anomaly of 155Gd and 157Gd isotope effects in ligand exchange reactions observed by ion exchange chromatography

The isotope effects of gadolinium in Gd-EDTA ligand exchange system were studied by means of ion exchange chromatography. The separation coefficients of gadolinium isotopes, epsilon, and the local enrichment factors, beta, were calculated from the observed isotopic ratios at the front and rear boundaries of the gadolinium adsorption band. Clear mass independent anomalies were observed in the isotope effects of 155Gd and 157Gd. The relation between the isotope effects of gadolinium isotopes, studied by the three-isotope plot and the separation coefficient methods, and the mass of gadolinium isotopes was found to be related to the change in the mean square radius of the nuclear charge distribution parameter, (r2), of these isotopes, which suggests that the nucleus shape and size highly affect the gadolinium isotope effects in chemical exchange reactions.

Journal Article↗
PubMed1984

Measurement of urinary vanilmandelic acid and homovanillic acid by high-performance liquid chromatography with electrochemical detection following extraction by ion-exchange and ion-moderated partition.

An improved protocol has been developed to isolate homovanillic acid (HVA) and vanilmandelic acid (VMA) from urine with strong anion-exchange resin. The sample is diluted with acetate buffer and passed through a disposable column. HVA, uric acid, and many hydrophobic organic acids are removed with 1.0 M acetic acid--ethanol. Then VMA is eluted with 0.5 M phosphoric acid. Two isocratic mobile phases allow rapid high-performance liquid chromatographic measurement of VMA (5 min) and HVA (8 mins) on a 5-micron ODS column. Selective conditions were developed with dual-electrode coulometric detection to permit specific measurement of VMA, HVA, and internal standards, with less than 5% between-run variation.

Chromatography, High Pressure Liquid↗
PubMed2003

Oxidation of cyclohexane catalyzed by metal-ion-exchanged zeolites.

The ion-exchange rates and capacities of the zeolite NaY for the Cu(II), Co(II), and Pb(II) metal ions were investigated. Ion-exchange equilibria were achieved in approximately 72 h for all the metal ions. The maximum ion exchange of metal ions into the zeolite was found to be 120 mg Pb(II), 110 mg Cu(II), and 100 mg Co(II) per gram of zeolite NaY. It is observed that the exchange capacity of a zeolite varies with the exchanged metal ion and the amount of metal ions exchanged into zeolite decreases in the sequence Pb(II) > Cu(II) > Co(II). Application of the metal-ion-exchanged zeolites in oxidation of cyclohexane in liquid phase with visible light was examined and it is observed that the order of reactivity of the zeolites for the conversion of cyclohexane to cyclohexanone and cyclohexanol is CuY > CoY > PbY. It is found that conversion increases by increase of the empty active sites of a zeolite and the formation of cyclohexanol is favored initially, but the cyclohexanol is subsequently converted to cyclohexanone.

Journal Article↗
PubMed2006

Ion-exchange of Pb2+, Cu2+, Zn2+, Cd2+, and Ni2+ ions from aqueous solution by Lewatit CNP 80.

Removal of trace amounts of heavy metals can be achieved by means of selective ion-exchange processes. The newly developed resins offered a high resin capacity and faster sorption kinetics for the metal ions such as Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) ions. In the present study, the removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) ions from aqueous solutions was investigated. Experimental investigations were undertaken using the ion-exchange resin Lewatit CNP 80 (weakly acidic) and were compared with Lewatit TP 207 (weakly acidic and chelating). The optimum pH range for the ion-exchange of the above mentioned metal ions on Lewatit CNP 80 and Lewatit TP 207 were 7.0-9.0 and 4.5-5.5, respectively. The influence of pH, contact time, metal concentration and amount of ion-exchanger on the removal process was investigated. For investigations of the exchange equilibrium, different amounts of resin were contacted with a fixed volume of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) ion containing solution. The obtained sorption affinity sequence in the presented work was Ni(2+)>Cu(2+)>Cd(2+)>Zn(2+)>Pb(2+). The metal ion concentrations were measured by AAS methods. The distribution coefficient values for metal ions of 10(-3)M initial concentration at 0.1mol/L ionic strength show that the Lewatit CNP 80 was more selective for Ni(2+), Cu(2+) than it was for Cd(2+), Zn(2+) and Pb(2+). Langmuir isotherm was applicable to the ion-exchange process and its contents were calculated. The uptake of metal ions by the ion-exchange resins was reversible and thus has good potential for the removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) from aqueous solutions. The amount of sorbed metal ion per gram dry were calculated as 4.1, 4.6, 4.7, 4.8, and 4.7mequiv./g dry resin for Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+), respectively. Selectivity increased in the series: Cd(2+)>Pb(2+)>Cu(2+)>Ni(2+)>Zn(2+). The results obtained showed that Lewatit CNP 80 weakly acidic resin had shown better performance than Lewatit TP 207 resin for the removal of metals. The change of the ionic strength of the solution exerts a slight influence on the removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+). The presence of low ionic strength or low concentration of NaNO(3) does not have a significant effect on the ion-exchange of these metals by the resins. We conclude that Lewatit CNP 80 can be used for the efficient removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) from aqueous solutions.

Cadmium↗
PubMed1985

Measurement of intracellular calcium ion activity with neutral exchanger ion sensitive microelectrodes.

Micropipettes filled with the neutral liquid ion exchanger ETH 1001 can be used to make microelectrodes that are sensitive to cytoplasmic levels of Ca2+. They are high resistance electrodes, so that care is required in order to record the low current signal. The electrodes often yield 10-15 mV change between intracellular Ca2+ activities of 10(-6) and 10(-7) M, according to a log relation. The microelectrodes are non-destructive, even in rather small cells, and can be used to monitor Ca2+ changes during experimental interventions.

Animals↗