Ion-interaction Reagent Research Articles

Simultaneous separation and determination of Ti and Fe in uranium alloy by ion chromatography

A simple and reliable ion chromatographic (IC) method for the simultaneous separation and quantification of Ti and Fe in U-Ti alloys is proposed. The developed method does not require pre-separation of matrix uranium and hence direct injection of the dissolved sample into IC is feasible. Separation was realized on a reversed phase column dynamically modified with ion interaction reagent (IIR). Suitability of three IIRs was evaluated and Camphor-10-sulphonic acid (CSA) was selected. Separation of Ti and Fe was achieved by mandelic acid whereas the strongly retained U(VI) was eluted with tartaric acid. The developed method was calibrated for Ti and Fe in presence of U(VI). The limit of detection (LOD) for Ti and Fe is 0.2 µg/mL and 0.02 µg/mL, respectively. The precision of measurements was better than 5 % (RSD) at 1 ppm of Ti and 0.2 ppm of Fe. The real samples were analysed with the developed method.

Fluoroalkylamines: Novel, Highly Volatile, Fast-Equilibrating, and Electrospray Ionization-Mass Spectrometry Signal-Enhancing Cationic Ion-Interaction Reagents.

A new class of cationic ion-interaction reagents for reversed-phase chromatography is introduced in the present work. Compounds belonging to a homologous series of linear fluoroalkyl chains including trifluoroethylamine (TFEAm), pentafluoropropylamine (PFPAm), heptafluorobutylamine (HFBAm), and nonafluoropentylamine (NFPAm) were tested and compared with ammonia and triethylamine (TEA) for the separation of selected organic acids of general interest such as the herbicides glyphosate, ethephon, and fosamine and arsenic metabolites methylarsonic acid and dimethylarsinic acid as well as other compounds. Depending on the carbon and fluorine atom number, the fluoroalkylamines were shown to be effective cationic ion-interaction reagents, significantly enhancing the retention of organic acids on a C18 reversed-phase column. Contrary to the general behavior of ion-interaction reagents (a broader term than ion-pairing reagent), significant (up to 5-fold) and consistent enhancement in the electrospray ionization mass spectrometry signal (ESI-MS) was observed relative to ammonia and triethylamine. Overall, among the tested series HFBAm was found to offer the best overall properties among the tested series as it provided a good compromise between column equilibration time (ca. 25 column volumes) and retention behavior (up to a 10-fold increase in the retention factor of acids relative to ammonia) while providing the same general advantages found for the fluoroalkylamines such as fast washout times from the ESIMS system (ca. 30 min) and a 3–5-fold signal enhancement. The fluoroalkylamines are a new class of cationic ion-interaction reagents with clear advantages over the currently employed alkylamines and may revive the general interest in ion-interaction chromatography.

Reversed-Phase High-Performance Liquid Chromatography for the Determination of 15 Rare Earth Elements in Surface Water Sample Collected in a Mining Area from Lavras do Sul/RS, Brazil

A methodology was developed to assay 15 rare earth elements (REE) (La to Lu and Y) in a surface water sample from a mining area. The samples were collected in the mining area of Lavras do Sul, RS, Brazil. Reversed phase high-performance liquid chromatography employing α-hydroxyisobutyric acid (HIBA), sodium dodecyl sulfate as the ion interaction reagent, and acetonitrile as the organic modifier was used. Analytical detection was performed by spectrophotometry after post-column derivatization with 4-(2-pyridylazo)-resorcinol (PAR). Different chromatographic parameters such as ionic interaction reagent, HIBA concentration, pH, and PAR reagent concentration were studied to achieve the best conditions for the individual separation of REE. The method was validated in terms of the main analytical characteristics (linearity, limits of detection and quantification, precision, interferences, and accuracy). A method for sample cleanup was discussed. Under optimized conditions, it was possible to separate 15 REE (La to Lu and Y) in less than 15 min, with resolution of peaks Y and Dy. The cleanup procedure ensured the selectivity required to determine REE in natural water samples. The accuracy was assessed by regression analysis against measurements by ICP-MS. The calculated quantification limits ranged from 0.07 to 0.48 µg mL−1, for the most sensitive (Dy) to least sensitive (La), respectively.

Selective separation of yttrium from rare earth elements by ion interaction chromatography. Analytical and larger scale applications

ABSTRACTNew ion interaction chromatographic (IIC) method employing Kromasil 100 C18 column and tetra-n-butylammonium hydroxide (TBAOH) as an ion interaction reagent (IIR) is able to separate yttrium from Rare Earth Elements (REE) as anionic complexes with nitrilotriacetic acid (NTA). New method for the chromatographic determination of Y in REE mixture was devised and validated by the analysis of the certified reference material (CRM). Potential possibilities of the new chromatographic system for larger scale applications including macro-micro events were demonstrated.

Thermodynamic study of HPLC enantioseparations of some sulfur-containing amino acids on teicoplanin columns in ion-pairing reversed-phase mode

ABSTRACTHomocysteine is an essential amino acid produced in the metabolism of methionine. It can be regulated through two metabolic routes either to cysteine or back to methionine. The imbalance in the methionine or homocysteine metabolism is connected with many disorders. In this work, HPLC enantioseparations of cysteine, homocysteine, and methionine were performed. Enantiomers were separated on natural teicoplanin and teicoplanin aglycone chiral stationary phases when buffered mobile phase with the presence of an ion-interaction reagent was used. The column temperature effect on the enantiomeric retention, selectivity, and resolution was studied in the range of 5–45°C at 5°C increment. Thermal stability of homocysteine standard was investigated by X-ray powder-diffraction measurements at elevated temperature in the range of 25–100°C at 5°C increment in air. Moreover, the thermodynamic analysis was used to quantify contributions of entropic and enthalpic terms on separations of investigated amino acid enantiomers. The elution order of enantiomers was determined in all cases.

New reversed phase-high performance liquid chromatographic method for selective separation of yttrium from all rare earth elements employing nitrilotriacetate complexes in anion exchange mode

Separation of Y from other rare earth elements (REE) is difficult because of similarity of its ionic radius to ionic radii of Tb, Dy and Ho. In the new RP-HPLC system with C18 column, tetra-n-butyl ammonium hydroxide (TBAOH) as an ion interaction reagent (IIR), nitrilotriacetic acid (NTA) as a complexing agent at pH=2.8–3.5, and post column derivatization with Arsenazo III, yttrium is eluted in the region of light REE, between Nd and Sm and is base line separated from Nd and Sm and even from promethium. Simple model employing literature data on complex formation of REE with NTA and based on anion exchange mechanism was developed to foresee the order of elution of individual REE. The model correctly predicted that lanthanides up to Tb will be eluted in the order of increasing Atomic Number (At.No.) but all heavier REE will show smaller retention factors than Tb. Concurrent UV/VIS detection at 658nm and the use of radioactive tracers together with γ-ray spectrometric measurements made possible to establish an unique elution order of elution of REE: La, Ce, Pr, Nd, Pm, Y, Sm, Er, Ho, Tm, Yb, Eu, Lu, Dy+Gd, Tb, Sc. The real place of Y however, in this elution series differs from that predicted by the model (Y between Sm and Eu). The method described in this work enables selective separation of Y from La, Ce, Pr, Nd, Pm, Sm and all heavier REE treated as a group.

HPLC Method for Determination of Th, U and Pu in Irradiated (Th,Pu)O2 using Mandelic Acid as an Eluent

Abstract Studies for chromatographic separation of Th, U(VI) and Pu(IV) were carried out using mandelic acid as an eluent. The different chromatographic conditions like concentration of mandelic acid, pH of the mobile phase, presence of MeOH and effect of ion interaction reagent (IIR) were studied. The method was optimized for the separation of Th, U(VI) and Pu(IV). At pH < 3.5 of mobile phase, Pu(IV) was more retained compared to U(VI) whereas at pH > 3.5, reverse trend was observed. The optimized parameters were employed for the separation and determination of Th, U(VI) and Pu(IV) in a dissolved solution of irradiated (Th, Pu)O2. Sample treatment was optimized to minimize loss of Pu and Th during chromatographic determination. Studies were carried out using two IIRs to understand the anomalous chromatographic behavior of Pu(IV). Retention behavior of different oxidation states of Pu viz. Pu(III), Pu(IV) and Pu(VI) was also studied in mandelic acid.

DETERMINATION OF LANTHANIDES AND YTTRIUM IN HIGH PURITY DYSPROSIUM BY RP-HPLC USING α-HYDROXYISOBUTYRIC ACID AS AN ELUENT

An HPLC method is presented for the determination of lanthanides viz. lutetium (Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho), terbium (Tb), and yttrium (Y) in high-purity dysprosium oxide (Dy2O3) matrix. In view of their similar chemical and physical properties, determination of rare-earth elements in bulk of a rare-earth element is a difficult task. Studies were carried out on C18 and C8 reversed phase columns employing α-hydroxyisobutyric acid (α-HIBA) as an eluent. n-Octane was used as an ion interaction reagent (IIR). Different chromatographic parameters e.g., ion interaction reagent, pH and concentration of α-HIBA were studied simultaneously to arrive at the optimum condition for the individual separation of lanthanides. When n-Octane sulphonate was used as the IIR, C8-based stationary phase was found to give significantly better resolution as compared to C18-based stationary phase. Under the optimized conditions, it was possible to resolve Y from Dy using α-HIBA as the single eluent. Separation and quantification of rare-earth elements were possible in samples with Dy/Tb and Dy/Y amount ratios up to 200. The method was validated using the simulated sample containing above lanthanides, Y and Dy matrix. Quantification was done using standard addition method. The method was successfully applied for the quantification of lanthanides and Y in high purity Dy2O3 sample. Concentrations of Lu, Yb, Tm, Er, Ho, Tb, and Y were found to be 74 ppmw, 432 ppmw, 22 ppmw, 57 ppmw, 3325 ppmw, 1207 ppmw, and 4463 ppmw, respectively.

Enantiomeric Separation of Drugs Using Ion Interaction Reagents in Combination with β-Cyclodextrin in HPLC

This work describes the use of β-cyclodextrin (β-CD) as a mobile phase additive in combination with ion interaction reagents (IIR) for the enantioresolution of cyclopentolate, 2,6-diketopiperazine derivative and methylphenobarbital. The effect of concentration and type of IIR and temperature on retention and enantioseparation were studied. It has been found that the addition of an IIR to β-CD solution can lead to the improvement in enantioresolution. Interestingly, the most significant enhancement of enantioresolution was achieved for cyclopentolate, most probably due to its highest basicity. Also the stability constants of the complexes formed between β-CD and model compounds in the presence of IIR were estimated. Significant increase of complexation rate of cyclopentolate with β-cyclodextrin in presence of IIRs was observed.

Determination of Uranium in Seawater Samples by Liquid Chromatography using Mandelic Acid as a Complexing Agent

The determination of uranium at different stages of the recovery process as well as in seawater is important in its recovery study. A previous study developed a high-performance liquid chromatography (HPLC) method for uranium determination in seawater using α-hydroxy isobutyric acid as a chelating agent. However, this method causes turbidity in process samples containing high amounts of iron, resulting in the clogging of the HPLC column. In the present work, use of mandelic acid as a chelating agent for uranium has been explored. Elution conditions were optimized for the separation of iron [Fe(III)] and uranium [U(VI)] by studying the effect of an ion interaction reagent, the concentration of mandelic acid, and methanol content in the mobile phase. Different parameters were optimized to develop off- line pre-concentration of uranyl-mandelate on the reversed stationary phase. The method offers quantitative recovery of uranium and linearity in the U(VI) concentration range of 0.5 ppb to 500 ppb and can be used for the determination of U(VI) in process samples with Fe/U amount ratios up to 3,000. The method has been successfully used for the determination of U(VI) in seawater samples and process samples. The developed methodology was validated by comparing the results with those of isotope dilution-thermal ionization mass spectrometry.

Comparative Study of Ion Interaction Reagents for the Separation of Lanthanides by Reversed-Phase High Performance Liquid Chromatography (RP-HPLC)

A study of two ion interaction reagents (IIRs) viz. n-octadecane sulphonate (C18-sulphonate) and eicosyl sulphate (C20-sulphate) was carried out for the separation of lanthanides by reversed-phase high performance liquid chromatography (RP–HPLC). The objective of the study was to identify a suitable IIR offering long term adsorption onto the RP column, thereby obviating the need to introduce the IIR in the mobile phase during the separation of lanthanides. This avoids the rigorous treatment of purified fractions before their mass spectrometric analysis. Resolution was used for comparing different IIRs for separation of lanthanides under identical chromatographic conditions, employing α-hydroxy isobutyric acid (α-HIBA) as an eluent. The volume and composition of IIR solution required for the modification of the column, as well as their long term adsorption, were studied. Columns coated with C18-sulphonate and C20-sulphate allowed the separation of lanthanides without introducing the IIR in the mobile phase. Between these two IIRs, C18-sulphonate offered higher resolution and provided good long term adsorption stability. A RP column modified with C18-sulphonate, as per the optimised procedure, was used for the separation of lanthanides from a geological reference sample without the need to include IIR into the mobile phase.

Reversed-phase liquid chromatography using mandelic acid as an eluent for the determination of uranium in presence of large amounts of thorium

Studies were carried out for the separation of uranium (U) and thorium (Th) on reversed-phase (RP) C18 columns using mandelic acid as an eluent. Retention of thorium–mandelate on the unmodified stationary phase was found to be greater than that of uranyl–mandelate under the pH conditions employed. Th retention capacity of the stationary phase was determined as a function of pH and MeOH content of the mobile phase. The optimised parameters allowing U elution prior to Th were utilized for the determination of small amounts of U in the presence of large amounts of Th. The method has been used for the determination of U in synthetic samples with Th/U amount ratios up to 100,000 (10μg/g of U) without any pre-separation, employing a particulate C18 column. Effect of concentration of ion interaction reagents (IIRs) on the retention was studied to understand the mechanism of adsorption of their mandelate complexes onto the stationary phase. The experiments conducted unequivocally prove that thorium–mandelate complex is neutral whereas uranyl–mandelate complex is anionic in nature.

Effect of mobile phase composition on the retention of selected alkaloids in reversed-phase liquid chromatography with chaotropic salts

Sodium hexafluorophosphate, perchlorate and trifluoroacetate were applied as ion–ion interaction reagents in reversed-phase liquid chromatography. The separation of chosen alkaloids was performed by changing the kind of the organic modifier (methanol, acetonitrile, tetrahydrofuran), concentration of the ion–ion-interaction reagents and the concentration of phosphate buffer at constant pH (2.7) in the mobile phase. Obtained results were analyzed in connection to a dynamic ion-exchange model of retention and ion–ion interaction effects. The perturbation method was applied to test proposed retention theories. The formation of ion-complexes controlling the retention in chaotropic systems was confirmed. On the basis of the relationships of capacity factors ( k) versus salt concentrations derived experimentally, absolute increases in capacity factors, the desolvation parameters and the limiting retention factors were calculated and compared for all the investigated compounds in eluent systems studied. The selectivity of the proposed mobile phases was compared on the basis of the separation of alkaloid mixture.

Developments in ion chromatography using monolithic columns

The focus of this review is on current status and on-going developments in ion chromatography (IC) using monolithic phases. The use and potential of both silica and polymeric monoliths in IC is discussed, with silica monoliths achieving efficiencies upwards of 10(5) plates/m for inorganic ions in a few minutes or less. Ion exchange capacity can be introduced onto the monolithic columns through the addition of ion interaction reagents to the eluent, coating of the monolith with ionic surfactants or polyelectrolyte latexes, and covalent bonding. The majority of the studies to date have used surfactant-coated columns, but the stability of surfactant coatings limits this approach. Applications of monolithic IC columns to the separation of inorganic anions and cations are tabulated. Finally, a discussion on the recent commercialization of monolithic IC columns and the use of monolithic phases for IC peripherals such as preconcentrator columns, microextractors and suppressors is presented.

Ethylammonium Formate as an Organic Solvent Replacement for Ion-Pair Reversed-Phase Liquid Chromatography

Ethylammonium formate (EAF), an inexpensive and easily synthesized room-temperature ionic liquid, acts like a conventional organic solvent for reversed-phase liquid chromatography (LC). In this report, the use of standard ion-pair reagents with this ionic liquid LC mobile phase and a polystyrene-divinylbenzene PRP-1 column is explored. Starting with the column equilibrated with a methanol mobile phase, the required equilibration time of the column by the EAF ion-pair mobile phase is determined by the plate number profile. Chromatograms of six aromatic carboxylic acids, with either methanol or EAF as the mobile phase, at room temperature (in the absence of an ion-pairing agent) lack resolution with significant peak overlap of nitro-substituted benzoic acids. The addition of 30mM tetrabutylammonium ion to the EAF or methanol mobile phase provides baseline resolution for all peaks in approximately 10 min. Analogous studies using a mixture of four aromatic amines, including protonated tyramine, diphenhydramine, and neutral nitroanilines in the absence or presence of 30mM sodium dodecylsulfate (SDS) in the mobile phase are similar to those for the aromatic acids, indicating baseline resolution with only the ion-pair reagent. Raising the column temperature to 55 degrees C improves the plate count by a factor of approximately 1.2 when using the EAF mobile phase. The retention factor profiles for either the carboxylic acids or the amines, as a function of the organic modifier percentage or ion-pair reagent concentration, are similar for both EAF and methanol. The polymerized acyl monoglycinate surfactant, poly(sodium-N-undecenoyl glycinate), is used for the first time as an LC ion-interaction reagent and is about as effective as SDS for the resolution of organic amines.

Direct determination of lanthanides in simulated irradiated thoria fuels using reversed-phase high-performance liquid chromatography

Studies were carried out to develop an HPLC method for the determination of lanthanides, in presence of Th and U, without involving any pre-separation procedure for the matrix elements (Th, U). The effect of concentration of the ion interaction reagent on the retention pattern of lanthanides, thorium and uranium was studied using a reversed-phase C18 column. The chromatographic parameters were optimized for maximizing the capacity of the column to hold thorium. Dual gradient elution was used for the separation of lanthanides from a mixture of thorium and uranium present in large proportion. The method facilitates the use of a minor fission product as an internal standard for the accurate and precise quantification of lanthanides by HPLC. The developed methodology was validated by using synthetically prepared samples with different proportions of lanthanides. Studies were also carried out for the separation and determination of U and Th on a reversed-phase column. A gradient of methanol and α-hydroxy isobutyric acid was employed for the separation and determination of uranium in presence of large amounts of thorium.

Simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples by ion-pair high-performance liquid chromatography

A simple, fast, sensitive and accurate reversed-phase ion-pair HPLC method for simultaneous determination of nitrite and nitrate in atmospheric liquids and lake waters has been developed. Separations were accomplished in less than 10 min using a reversed-phase C 18 column (150 mm × 2.00 mm i.d., 5 μm particle size) with a mobile phase containing 83% 3.0 mM ion-interaction reagent tetrabutylammonium hydroxide (TBA-OH) and 2.0 mM sodium phosphate buffer at pH 3.9 and 17% acetonitrile (flow rate, 0.4 mL/min). UV light absorption responses at 205 nm were linear over a wide concentration range from 100 μg/mL to the detection limits of 10 μg/L for nitrite and 5 μg/L nitrate. Quantitation was carried out by the peak area method. The relative standard deviation for the analysis of nitrite and nitrate was less than 3.0%. This method was applied for the simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples collected in southeast Massachusetts. Nitrate was found being present at 4.79–5.99 μg/mL in dew, 1.20–2.63 μg/mL in rain, 0.32–0.60 μg/mL in snow and 0.12–0.23 μg/mL in lake water. Nitrite was only a minor species in dew (0.62–0.83 μg/mL), rain (<0.005–0.14 μg/mL), snow (0.021–0.032 μg/mL) and lake water (0.12–0.16 μg/mL). High levels of nitrite and nitrate observed in dew water droplets may constitute an important source of hydroxyl radicals in the sunny early morning.

The Fractional Charge Approach in Ion‐Interaction Chromatography of Zwitterions: Influence of the Stationary Phase Concentration of the Ion Interaction Reagent and pH

The fractional charge approach to Ion‐interaction chromatography (IIC) of zwitterions was used to quantitatively explain their retention behavior as a function of the Ion Interaction Reagent (H) concentration in the stationary phase and also to account for the influence of the zwitterion ionization degree, according to the mobile phase pH. The theory was validated using two Hs and two reversed phase columns. The good predictive abilities of the retention equations lend strong support to the hypotheses made by the fractional charge approach in the IIC of zwitterions. For the investigated homologous series the increase in retention upon H addition can be quantitatively related to the estimated fractional charge. The estimates of the operative charges and bonded phase coverages are very reasonable since they make sense physically. This way, they offer a cross validation of the fractional charge approach, since they compare well with those obtained from the fitting of parallel retention data, obtained as a function of the mobile phase concentration of H. This confirms that retention modelling may instruct the chromatographer through the optimization procedure in the parameter space.

Extended thermodynamic approach to ion interaction chromatography. Influence of the chain length of the solute ion: a chromatographic method for the determination of ion-pairing constants

The influence of the chain length in Ion Interaction Chromatography (IIC), previously named Ion Pair Chromatography, was investigated. The system examined is a C18 stationary phase and a variable, salt-controlled, mixture of a phosphate buffer pH 2.1 in methanol containing tetrabutylammonium bromide as Ion Interaction Reagent. IIC proves to be a good alternative to the well established spectrophotometric and conductometric methods of obtaining thermodynamic ion-pairing constants. The latter increase with increasing analyte chain length and decrease with increasing methanol concentration in the eluent: both results support a physical chemical description of the hydrophobic ion-pairing process at variance with the classical, Bjerrum-type modelling of the purely electrostatic interaction between inorganic ions. The calculated deltaG(o) are reliable because they compare to non-chromatographic estimates of deltaG(o) for similar systems. The present extended thermodynamic approach is able to predict and explain why the purely electrostatic approach works better for lower analyte lipophilicity or higher organic modifier concentration.

Extended thermodynamic approach to ion interaction chromatography. A mono‐ and bivariate strategy to model the influence of ionic strength

Recent breakthroughs in the theory of ion interaction chromatography (IIC) permit new analyses of the dependence of retention on different interdependent factors. The influence of the ionic strength / on the surface potential, the Donnan effect, and salting effects are taken into account to model the chromatographic behaviour of charged analytes in IIC. The most reliable experimental results found in the literature were used to test the retention equations that were developed following both a monovariate (/ changes as the concentration of H, ion interaction reagent, changes) and a bivariate (/ changes because of the simultaneous variation of H and of the background electrolyte concentrations) approach. The present extended thermodynamic model builds on the sound intuition of the electrostatic approach and proves to provide the most successful and exhaustive quantitative explanation of experimental evidence. It is also able to rationalise the less extensive agreement between the pure electrostatic approach predictions and experimental results. The adequacy of the model is supported by physically reliable estimates of the adjustable constant (ion-pair constants, deltaG degrees). Moreover statistical practice demonstrates that all the adjustable parameters (three at most) are statistically significant. A linear, zero crossing function with unit slope is obtained when k(pred) is plotted against k(exp). The mean percent error between k(pred) and k(exp) is 4.5% at most. In the absence of H the present retention equation reduces, as expected, to the relationship that describes the influence of / on the retention behaviour in reversed-phase liquid chromatography.