Ion-pair Concentration Research Articles

Development of a HPLC Method for the Determination of 17β-Estradiol-3-Phosphate in Pharmaceutical Preparations

Abstract A validated reversed-phase high-performance liquid chromatographic (HPLC) procedure for the analysis of 17β-estradiol-3-phosphate is reported. In the development of this assay, several factors were evaluated including buffer ionic strength, mobile phase pH, ion-pairing concentration, organic composition, and column type. The described method is rapid and coupled with standard HPLC procedures leads to a selective, accurate, and reproducible assay. The peak area versus 17β-estradiol-3-phosphate concentration is linear over the range of 0.1–100 μg/mL, with a detection limit of 0.02 μg/mL.

Dependence of ionic association on polymer chain length in poly(ethylene oxide)-lithium triflate complexes

Ionic association in complexes of lithium trifluoromethanesulfonate with low-molecular-weight poly(ethylene oxide) dimethyl ethers was studied using Raman and infra-red vibrational spectroscopy. The relative concentrations of ion pairs and more highly associated ionic species are quite dependent on chain length. This dependence was measured in both the CF 3 symmetric deformation mode and the SO 3 symmetric stretching mode. The effect of the terminating group was considered by comparing the dimethyl ethers with hydroxy-terminated poly(ethylene oxide) at comparable chain lengths. Hydrogen bonding effects in the hydroxy-terminated poly(ethylene oxide) compounds were also found to depend on chain length.

Effects of ion pairs on the dynamics of erbium-doped fiber lasers.

Experiments with erbium-doped fiber lasers demonstrate cw, sinusoidal, and self-pulsing operation. The obtained regimes depend on three control parameters: ion-pair concentration, photon lifetime, and pumping rate. We present a theoretical model which describes the active medium as a mixture of isolated ions and ion pairs. Starting with the adapted laser rate equations we show that the description of the dynamical behavior of this system can be reduced to only four first-order coupled equations. A linear stability analysis demonstrates the existence of self-pulsing for a finite range of pumping rates. At both ends of this range Hopf bifurcations occur: one located near the first laser threshold and the other at a higher pumping ratio, whose position is closely related to the pair concentration. Results of numerical calculations are in good qualitative agreement with our experimental data.

Influence of ion pairs on the dynamical behaviour of Er3+-doped fibre lasers

We demonstrate experimentally the influence of ion-pair concentration on the dynamical behaviour of erbium-doped fibre lasers. At low pair densities, the laser has a CW output, while at higher densities it exhibits a self-pulsing behaviour. For intermediate pair concentrations, the output intensity evolves continuously from an infinite train of pulses to a CW steady state as the pumping ratio is increased.

Determination of isomeric N-oxide metabolites of some substituted 2,4-diaminopyrimidines by reversed-phase ion-pair high-performance liquid chromatography

Reversed-phase ion-pair high-performance liquid chromatography has been investigated for the separation, detection, identification and quantitation of the isomeric 1N- and 3N-oxide metabolites of metoprine, pyrimethamine and trimethoprim. A rapid and sensitive analytical method for the simultaneous determination of the isomeric 1N- and 3N-oxides of metoprine and pyrimethamine was devised for in vitro metabolic studies by optimisation of mobile phase pH, pairing-ion concentration, secondary-ion concentration and percentage organic modifier.

Effects of organic modifier and ion-pair reagent in liquid chromatography

The capacity factors of phenylamine and naphthylamine sulphonic acids in reversed-phase, ion-pair liquid chromatography (RP-IPC) were measured. The combined effects of organic modifier (Cb) and ion-pair reagent concentration (Cp) on retention follow an equation based on the electrostatic model: $$\ln k' = a + b lnC_p + cC_b $$ the experimental value of b correlates well with the value of 0.5 z (z=charge on analyte ion) predicted for mono and divalent ions. The measured value of b is, however, lower than that predicted for trivalent ions, which may be due to the effective number of charges being less than the apparent number. The absolute values of a and c are much larger than those in RP-HPLC in the absence of an ion-pair reagent, quantitative correlation of a and c with retention values in RP-HPLC and solute charges has been observed and a good linear relationship between a and c has been obtained, strongly supporting the validity of the electrostatic retention model. A critical value, R, at which the negative effect of methanol on retention is equal to the positive effect of the ion-pair reagent (TBAI) has been proposed. The critical values obtained are related to the behaviour of the solute, the ion-pair reagent and the stationary and mobile phases, and lies between −0.04 and −0.065 in most cases, which means that the increase by exp times (=2.718×) the ion-pair concentration the original is equivalent to a decrease of 0.04–0.065 in volume fraction of methanol

The history of the development of the chemical model for seawater

From 1959 to 1962, I was working as a research assistant to Prof. R. M. Garrels in the geochemistry laboratory at Harvard University. We were measuring the solubilities of various carbonate minerals in solutions saturated with carbon dioxide. Our attempts to measure the solubilities of highly soluble minerals such as hydromagnesite and trona led us to consider that complex ions or ion pairs such as MgCO3 or [NaCO3] − might exist in some of the more concentrated solutions. Venturing into the field of aqueous electrochemistry, using the available electrodes [pH, Na +, K +] and assumptions about solution theory, charge balance, and individual ion activity coefficients, we measured dissociation constants for several carbonate and bicarbonate species. Next we attempted to extend the concept of individual ion activity coefficients and ion pairs toward understanding the factors affecting the solubility of calcite in seawater, which meant working at much higher ionic strength and also having to consider sulfate ion pairs. Finally, we were emboldened to try to calculate the major ion species distributions in seawater, assuming that Cl − was completely ionized. The first version of the manuscript, submitted to the American Journal of Science, was severely criticised by both electrochemists and marine geochemists. The manuscript was rewritten, the solubility of gypsum was discussed, and the title of the paper was changed from something like “Activities and concentrations of major ion species and ion pairs in seawater” to the final simpler and more emphatic one. Both Bob and I were very proud of the fact that the model remained valid as long as twenty-five years after publication.

Determination of tylosin and related macrolides in fermentation broth by gradient elution ion-pair liquid chromatography

A gradient elution ion-pair HPLC assay was developed for the analysis of tylosin and related macrolides in fermentation broth. The effect of the ion-pair agent concentration and identity was studied to optimize the reproducibility of the separation. The assay compares favorably with the biological assay and is sufficiently durable for the analysis of many samples per column.

Prediction of Retention in Reversed Phase Ion-Pair Chromatography Using Sodium Dodecyl Sulphate as Pairing Ion

Abstract A 3 × 3 factorial design has been applied in the study of the chromatographic behaviour of thirteen protonated amines in reversed phase HPLC using sodium dodecyl sulphate as the pairing ion. The maximum capacity factors (log k'max ) of the test compounds and the mobile phase pairing ion concentrations that produce the retention maxima (log Pmax ), have been correlated to the pKa , hydrophobicity and connectivity index of the solute, as well as the mobile phase acetonitrile and tetrabutylammonium (TBA) contents. The two dependent variables log K'max and log Pmax , have been shown to be governed mainly by the hydrophobicity of the solutes and, the acetonitrile and mobile phase TBA concentration. The mathematical models generated have been employed to predict experimental conditions for retention optimization of diltiazem and deacetylated diltiazem. The predicted log k'max and log Pmax , have been found to be in agreement with those obtained experimentally.

Retention prediction based on the electrostatic model of reversed-phase ion-pair high-performance liquid chromatography: effect of pairing ion concentration

Based on the electrostatic model of reversed-phase ion-pair chromatography, a practical equation was developed to describe the relationship between the capacity factor of ionic solutes and the eluent concentration of the amphiphilic pairing ion. At constant ionic strength and organic modifier concentration, the logarithm of solute capacity factor can be approximated as a linear function of the logarithm of the pairing ion concentration. The slope of this relationship is determined by the sign and number of charges of the solute ion and the pairing ion. The limitations and the practical use of the proposed model are discussed in detail.

Effects of eluent composition, ion-pair reagent and temperature on the separation of histones by high performance liquid chromatography

The influence of the eluent composition, ion-pair concentration, and temperature on the fractionation of chromosomal proteins by reversed-phase high performance liquid chromatography (HPLC) has been investigated. Based on this examination methods for the troublesome separation of histones H1o/H1b, H2A/H4, and H5.1/H5.2 have been developed.

Ion-pair high-performance liquid chromatography of purine compounds in the small intestinal mucosa of children with coeliac disease

Isocratic methods are described for the separation of purine compounds in specimens of jejunal mucosa available by peroral biopsy from patients with coeliac disease. The first mode provided separation of both the ionic nucleoside monophosphates and the non-ionic nitrogen bases and nucleosides. The second mode was applicable to analyses of the nucleoside mono-, di- and triphosphates only. These chromatographic procedures were carried out with tetrabutylammonium phosphate as an ion-pair modifier and different concentrations of acetonitrile in the mobile phase. The modes are flexible in that they permit the optimization of the separation of these compounds according to the purpose of the investigation. The results of studies on purine metabolite patterns in coeliac mucosa are discussed.

Mixed-alkali effect in poly(propylene oxide)-thiocyanate salt systems

Thin films of cross-linked poly(propylene oxide) containing various known ratios of NaSCN to KSCN have been prepared. Samples in which the ether oxygen to total alkali metal ion ratio was kept constant at a value of approximately 9.6 exhibit a slight minimum in the glass transition temperature versus mole fraction of alkali ion data. Conductivity values for this system do not exhibit a minimum. The absence of a mixed-alkali effect could be due to the appreciable mobility of the anion in these polymer systems and/or a high concentration of ion pairs, thus making the mixed-alkali effect less important in the conduction mechanism.

Etude par Microscopie Raman de la Couche Liquide Située au Contact d'un Cristal en Cours de Dissolution dans sa Solution Mère: Systèmes LiNO3H2O et KNO3H2O

AbstractThe composition of the dissolution layer of LiNO3 and KNO3 crystals in their respective unsaturated mother liquors was studied by Raman microscopy coupled with a multi‐channel acquisition of data. Preliminary examination of homogenous solutions at various concentrations of LiNO3 and KNO3 revealed the existence of individual Raman bands assigned to different solvated species, namely free aquated ions, solvent‐separated ion pairs and/or contact ion pairs. Weak bands due to a small amount of aggregates (LiNO3)n or (KNO3)n were also identified. Spectral parameters of each individual band were calculated. Raman spectra of dissolution layers recorded at different steps of the crystal dissolution revealed considerable reinforcement of aggregates and contact ion pair concentrations compared with that existing in the bulk of the unsaturated mother liquors. The aggregate concentration in the dissolution layer was found to be even higher than that calculated for the corresponding saturated solution. The behaviours of LiNO3 and KNO3 were shown to differ considerably.

Evidence from alkali-metal NMR spectroscopy for ion pairing in alkaline silicate solutions

Interactions between alkali-metal cations and silicate anions in silicate solutions were investigated by cation NMR spectroscopy. The concentration of cation-anion pairs was determined from the chemical shift and the resonance line widths. The concentration of ion pairs involving large anions increases with increasing cation size. For silicate solutions in which there is a distribution in cation size, the concentration of ion pairs exhibits a maximum with increasing cation size. This maximum is interpreted in terms of the selectivity of ion-pairing reactions.

SOILSOLN: A program for teaching equilibria modeling of soil solution composition

The program SOILSOLN is a chemical equilibrium model for use in teaching ion speciation in soil solutions. The program iteratively estimates concentrations of ion pairs, hydrolytic species, metal-organic complexes, and free ions in solution. Inputs of Ca, Mg, K, Na, NH4, Mn, Zn, AI, Si, CI, P, NO3, SO4, F, pH, dissolved organic carbon (DOC), and partial pressure CO 2 are supported by the program. The program outputs ionic speciation, percent free ion, and free ion activities. Additionally, ion activity products and disequilibria indices are computed for selected mineral species. Percent organic complexes are computed when DOC is included in the input data. SOILSOLN is provided as an uncompiled BASIC source program that can be modified by individual users. The program is prompt-driven and requires minimum computer proficiency, allowing students to concentrate on program structure and data interpretation rather than on program execution. This program can be used most effectively as a problem-solving tool to supplement and reinforce the concepts of ionic activity and ion speciation, typically introduced in upper level undergraduate courses. U ’~a’n. R~CEr~r~.Y, concepts of ionic activity and ion

Steady state current flow in solid binary electrolyte cells: Part 2. The effect of ion association

The steady state current flow following the application of a constant voltage to cells of the form M(s)< M +X −(s)¦M(s) where M +X −(s) is a binary solid electrolyte, such as a polymer electrolyte, containing mobile M + cations, X − anions and MX ion pairs, is discussed. General equations are derived for the effective conductivity of the electrolyte in terms of the diffusion coefficients of the three species and the association constant. A number of special cases which are of particular importance to the study of polymer electrolytes are considered briefly. It is shown (i) that measurements of steady state currents can indicate when significant concentrations of ion pairs are present, and (ii) that this technique may provide an excellent method of evaluating the practical merit of these materials for applications such as power sources or electrochromic devices. It is also noted that transference numbers cannot be obtained from this or the related ac technique when mobile ion pairs are present.

Raman and Brillouin scattering of LiClO4 complexed in poly(propylene-glycol)

Raman spectra of LiClO4 complexed in poly(propylene-glycol) (PPG) have been obtained for concentrations of the monomer to salt ratio (ether oxygen):Li in the range 30:1–5:1. Splitting of the symmetric stretching mode of the ClO4− anion was observed with an intensity profile that varied with salt concentration. This phenomenon indicates a changing environment about the anion. A two-component band analysis leads to the identification of dissociated ions on one hand and solvent-separated ion pairs on the other. The concentration of ion pairs is relatively low compared to that of the dissociated ions, which are predominant for all concentrations. Despite the observed increase in the absolute number of dissociated ions at higher salt concentration, the electrical conductivity is reported to decrease in the same range. This indicates that the number of ‘‘free’’ charge carriers is of less importance for the conductivity than the mobility, which is damped in this concentration range. Frequency shifts of the disordered longitudinal-acoustic mode and increased hypersonic velocities, measured with Raman and Brillouin scattering techniques, respectively, indicate increased stiffness of the polymer matrix for increasing salt concentration, which probably results in decreased ion mobility.

The Influence of Alkali Metal Hydroxides on Silica Condensation Rates: The Role of Ion Pairing

ABSTRACTThe condensation kinetics and the role of Ion pairing are investigated for silicate anions in alkaline solutions. Selective, and non-selective inversion recovery experiments are performed using the Si NMR spectrum of alkali metal silicate solutions. In this way the rates of condensation of silicate monomers is studied as a function of the nature of the base. These rates exhibit maxima with increasing cation size. The maxima are interpreted in terms of the concentration and activity of ion pair intermediates of the Si exchange reaction.Interactions between alkali metal cations and larger silicate anions in silicate solutions are investigated using NMR spectroscopy of the cations. The chemical shift and the resonance llnewidths are used to estimate the concentration of cation-silicate ion pairs. The concentration of pairs involving large anions increases with increasing cation size. Thus it is expected that condensation kinetics are influenced by the size of the silicate fragment.

Influence of extraction properties of PVC plasticizer membrane on the response of coated wire type ion selective electrode

The authors studied the influence of the extraction properties of a PVC membrane plasticizer of a coated-wire type ion-selective electrode on its response in titrations of brucine and atropine with sodium tetraphenyl borate, as well as in potentiometric determinations of these compounds. The highest attainable value of the ion pair concentration in the plasticizer, which is limited by the distribution coefficient of the ion pair, determines the interval in which the electrode potential can be changed; and a linear dependence of the potential range of the titration curves on the logarithm of the ion-pair distribution coefficient was found. The slope of the dependence of the electrode potential on the logarithm of the ion concentration to be determined, found in potentiometric measurements, is proportional to the distribution coefficient of the ion which forms a pair with the ion to be determined and in whose solution the electrode membrane is activated between the measurements. The dependence of the slope of the electrode function on the logarithm of the product of the mentioned distribution coefficients is linear.