Retention Of Inorganic Anions Research Articles

Separation of inorganic anions on reversed-phase C18 columns with a phosphomolybdate mobile phase

Reversed-phase high performance liquid chromatography (RP-HPLC) is the most widely used chromatographic method. In addition to hydrophobic interactions, additional interactions such as electrostatic interactions may participate in the retention behaviour of an analyte. This makes it possible to use RP-HPLC for many types of analyte. We describe a simple method for separating inorganic anions on a C18 column, in which retention of inorganic anions is almost entirely due to electrostatic interactions. This leads to rapid separations as well as higher theoretical plate numbers. We used 2 mM phosphoric acid containing a low concentration of disodium molybdate as the mobile phase, which allows UV detection of non-UV-absorbing anions. With this method, we determined eight inorganic anions including several non-UV-absorbing anions photometrically at 220 nm. The detection limits of the examined eight inorganic anions calculated at a signal-to-noise ratio of 3 were between 0.3 and 10 μM. The detector response was linear over three orders of magnitude of inorganic anion concentration. The proposed RP-HPLC/UV method was successfully applied to determine inorganic anions in some water samples.

Retention of inorganic anions using mesoporous zirconia spheres modified with anion-exchange groups as the stationary phase for ion chromatography.

A zirconia (ZrO2) stationary phase with a chemically fixed silane coupling agent (trimethyl [3-(trimethoxysilyl)propyl]ammonium chloride; TMA), which possesses quaternary ammonium functional groups, is evaluated as a separation column for ion chromatography (IC) of anions. The selectivity for anions varies depending on the amount of TMA immobilized on the ZrO2. The TMA-ZrO2, with an anion-exchange capacity of 17 ± 3µeq/g, shows an anion-exchange reaction that involves the specific retention of fluoride ion on ZrO2. The TMA-ZrO2 exhibits a decrease of the anion resolution with an increase of the eluent pH and an enhancement of the selective separation of fluorideion with an increase of the column temperature. Through this study, the TMA-ZrO2 stationary phase shows potential as a new medium for ion separation.

Separation of inorganic anions by capillary ion chromatography with UV detection using poly(vinylimidazole-co-ethylene dimethacrylate) monolithic column

Poly(1-vinylimidazole-co-ethylene dimethacrylate) (VIM-EDMA) monolithic stationary phase was applied for separation of inorganic anions by capillary ion chromatography (IC). The retention of inorganic anions on the VIM-EDMA column was investigated using various salt solutions as the eluent. Good separation of inorganic anions was obtained on VIM-EDMA monolithic column using NH4Cl as the eluent. Good mechanical stability and low swelling propensity values (0.12 and −0.02 for ACN and MeOH, respectively) were obtained. The column repeatability was also examined by determining the relative standard deviations (RSDs) of retention time and peak area of target anions. Relatively low RSDs (n = 7) of retention time (<2.3%) and peak area (<8.8%) were obtained on the VIM-EDMA column. The utilization of VIM-EDMA column for potential environmental application was also demonstrated by determining the occurrence of inorganic anions in various environmental water samples without sample preparation process.

Poly(ethylene oxide)-bonded stationary phase for separation of inorganic anions in capillary ion chromatography

A tosylated-poly(ethylene oxide) (PEO) reagent was reacted with primary amino groups of an aminopropylsilica packing material (TSKgel NH2-60) in acetonitrile to form PEO-bonded stationary phase. The reaction was a single and simple step reaction. The prepared stationary phase was able to separate inorganic anions. The retention behavior of six common inorganic anions on the prepared stationary phase was examined under various eluent conditions in order to clarify its separation/retention mechanism. The elution order of the tested anions was iodate, bromate, bromide, nitrate, iodide, and thiocyanate, which was similar as observed in common ion chromatography. The retention of inorganic anions could be manipulated by ion exchange interaction which is expected that the eluent cation is coordinated among the PEO chains and it works as the anion-exchange site. Cations and anions of the eluent therefore affected the retention of sample anions. We demonstrated that the retention of the analyte anions decreased with increasing eluent concentration. The repeatability of retention time for the six anions was satisfactory on this column with relative standard deviation values from 1.1 to 4.3% when 10mM sodium chloride was used as the eluent. Compared with the unmodified TSKgel NH2-60, the prepared stationary phase retained inorganic anions more strongly and the selectivity was also improved. The present stationary phase was applied for the determination of inorganic anions contained in various water samples.

Anion-exchange chromatography on short reversed-phase columns modified with amphoteric ( N-dodecyl- N, N-dimethylammonio)alcanoates

Short reversed-phase columns (50 mm × 4.6 mm Gemini C 18) were dynamically coated with carboxybetaines of the general structure, C 12H 25N +(CH 3) 2(CH 2) n COOH, namely ( N-dodecyl- N, N-dimethylammonio)undecanoate, DDMAU ( n = 10) and ( N-dodecyl- N, N-dimethylammonio)butyrate, DDMAB ( n = 3), and investigated for the separation of inorganic anions in ion chromatography. The role of the ionic strength of coating surfactant solutions on their adsorption and resultant column capacity was studied. The retention of inorganic anions was investigated with different eluents at various concentrations and pH. Interestingly, no retention for anions was found with pure water as the eluent, but the addition of small amounts of electrolytes, up to 0.1 mM, caused a sharp increase in the retention of analytes. The effect of increasing anion retention with an increase in eluent cation charge was also observed. Based on this effect a new cation charge gradient concept was proposed and applied to the separation of a standard mixture of anions.

Amphoteric surfactant-modified stationary phase for the reversed-phase high-performance liquid chromatographic separation of nucleosides and their bases by elution with water

A study on surface modification of an octadecylsilica (ODS) column with amphoteric surfactants has been carried out for efficient reversed-phase liquid chromatographic separations of hydrophobic analytes only with water eluent. Two amphoteric surfactants each with different terminal groups (betaine-type and sulfobetaine-type surfactants) were employed as the stationary phase modifier, and the separation characteristics of the modified ODS columns were evaluated by comparing the elution times of nucleosides, their bases, and inorganic ions. In both surfactant-modified ODS column systems, the adsorption of amphoteric surfactant led to a decrease in the retention of nucleosides and their bases, while an increase in the retention of inorganic anions. These results indicate that the amphoteric surfactant adsorbed on the ODS surface suppresses the hydrophobicity of the reversed-phase surface, but it also generates a specific electrostatic field. In other words, the modified ODS columns exhibit hydrophobic/electrostatic mixed-mode separation properties. The degree of the contribution of each property to the separation of analytes can be varied with the amount of the adsorbed surfactant. Consequently, nucleosides and their bases were effectively separated on the ODS column coated with 0.55 mmol of betaine-type surfactant in water elution.

Determination of inorganic anions on porous graphitic carbon using evaporative light scattering detection: Use of carboxylic acids as electronic competitors

Different volatile carboxylic acids have been investigated as electronic competitors to optimize the separation of 12 common anions (F −, H 2PO 4 −, Cl −, IO 3 −, IO 4 −, Br −, BrO 3 −, SO 4 2−, ClO 3 −, NO 3 −, I −, ClO 4 −) on a porous graphitic carbon (PGC) column with evaporative light scattering detection. The addition of pyridine in the aqueous acidic mobile phase improves the efficiency of the separation and the detector response. The retention of inorganic anions on non-modified PGC is dominated by electronic interactions based purely on donor–acceptor (charge transfer) interaction between the lone pair electrons of the solute and the π-electrons of the PGC.

Separation of inorganic anions by reversed-phase ion-pair chromatography with direct UV detection

In this paper, a separation method of the inorganic anions including I−, NO 2 − , NO 3 − , IO 3 − and SCN− on the reversed-phase ion-pair chromatography with direct UV detection has been developed, and the limits of detection of these inorganic anions were determined. The effects of the organic modifier volume fraction and concentration of the ion-pair reagent on the retention of inorganic anions were discussed.

Retention and separation of inorganic anions by reversed-phase ion-interaction chromatography on octadecyl silica

The retention behaviour of chloride, nitrite, bromide, nitrate and sulphate was investigated using Partisil 10 ODS-3 as the stationary phase and a solution of tetrabutylammonium in aqueuos phthalate or phosphate buffer as the eluent. The quaternary ammonium ion adsorption behaviour and the influence of the quatenary ammonium concentration, the pH and the buffer concentration on the retention of the inorganic anions is discussed. The major adsorption and ion-exchange equilibria in the retention process were studied and used to develop a retention model for the different analytes. This retention model was verified experimentally. Ion-interaction reversed-phase chromatography with an octadecyl-bonded silica stationary phase and tetrabutylammonium iodide—phthalate eluent was found to be successful system for the separation and determination of inorganic anions and when conductivity detection is used.