Maria Rey

Determination of inorganic cations and ammonium in environmental waters by ion chromatography with a high-capacity cation-exchange column.

While alkali and alkaline earth cations are commonly determined by using spectrometric techniques such as atomic absorption spectrometry or inductively coupled plasma, ammonium cation in the same sample must be measured separately by a wet chemical technique such as colorimetry, titrimetry, or ammonia-selective electrode. In a single 25-min run ion chromatography can determine all of the important inorganic cations including lithium, sodium, ammonium, potassium, magnesium and calcium. In this paper, we describe the use of ion chromatography with a new high-capacity cation-exchange column (the IonPac CS16), an electrolytically-generated methanesulfonic acid eluent and suppressed conductivity detection to determine dissolved alkali and alkaline earth cations and ammonium in drinking water wastewater and aqueous soil extracts. The IonPac CS16 is a high-capacity cation-exchange column that incorporates recent advances in polymer chemistry to enable trace-level determinations of cations even in high-ionic-strength matrices. We discuss the linear range, method detection limits, and analyte recoveries obtained with this column, and evaluate the effect of potential interferences on method performance during the analysis of typical environmental samples.

Novel cation-exchange stationary phase for the separation of amines and of six common inorganic cations

Abstract Currently available polymeric cation-exchange phases tend to be best suited to the separation of either amines as a class or the inorganic cation as a class. In this paper we will describe a new cation-exchange phase based on a polymeric, highly crosslinked macroporous substrate to which two different monomers, one with carboxylate and the other with phosphonate functional groups, have been covalently grafted. Due to the type of monomers used and the conditions under which the resin is grafted, it offers good selectivity for both inorganic cations and amines, and is more hydrophilic than its predecessor, IonPac CS12 (Dionex). It is possible to chromatograph the more hydrophilic amines without the use of solvent, and for the more hydrophobic amines solvent can be added to the eluent, as the resin is solvent-compatible. Applications in which temperature is used on the column to affect chromatography will be shown.

A new approach to dealing with high-to-low concentration ratios of sodium and ammonium ions in ion chromatography

Abstract In ion chromatography, samples of very dissimilar concentration ratios of ammonium-to-sodium are difficult to quantify since these two cations have similar selectivities for stationary phases containing commonly used sulfonic acid or carboxylic acid cation-exchange functional groups. A new column with carboxylic acid and phosphonate functional groups as well as a crown ether group has been developed to address this limitation. Selectivity of the common inorganic cations is different from conventional columns in that the separation between sodium and ammonium has been greatly increased, and potassium ion elutes after magnesium and calcium. Applications involving very dissimilar concentration ratios of cations can now be done isocratically, with a single column. Other applications of this new column will also be discussed.

Novel weak acid cation-exchange column

A cation-exchange column with carboxylate cation-exchange sites was developed. Compared with conventional surface-sulfonated or latex agglomerated resins, this weak acid cation exchanger has a high selectivity for hydronium ions. Mono- and divalent cations such as alkali and alkaline earth metals can therefore be determined simultaneously in less than 10 min using a weakly acidic eluent under isocratic conditions. Because the ethylvinylbenzene-divinylbenzene substrate is highly cross-linked, the new separator is solvent compatible, thus allowing the use of organic solvents to alter the selectivity of the separation and to remove organic contaminants from the column. The separation characteristics of this column are presented and various applications are discussed.

Determination of sodium and ammonium ions in disproportionate concentration ratios by ion chromatography.

In ion chromatography, samples of very different ammonium-to-sodium concentration ratios are difficult to quantify since these two cations have similar selectivities for stationary phases containing commonly used sulfonate or carboxylate cation-exchange functional groups. The IonPac CS15 cation-exchange column, with carboxylate and phosphonate functional groups as well as a crown ether group, was developed to address this limitation. Selectivity for the common inorganic cations on this column is different from that of conventional cation-exchange columns in that the separation between sodium and ammonium ions has been greatly increased, allowing for determinations of low levels of one in the presence of high levels of the other with an isocratic eluent. For larger than 4000:1 sodium-to-ammonium concentration ratios, an eluent step change or gradient elution is needed. For moderate ratios, combinations of this column with a carboxylate column, containing no crown ether group, can be used at room temperature with an isocratic eluent containing no organic solvent.

Determination of trace level ions by high-volume direct-injection ion chromatography

Abstract A high-volume direct-injection method was developed for the purpose of trace level determinations (low to sub-μg/l) of anions and cations by ion chromatography. The chromatographic signal was enhanced by increasing the sample volume up to 1300 μl with no significant loss in peak efficiency. The following parameters were optimized for minimizing noise: eluent flow, background conductance, suppressor chemistry, conductivity temperature and data filtering. Total analysis times were less than 30 min and the method detection limits for most ions ranged from 10 to 400 ng/l (ppt).

High-capacity cation-exchange column for enhanced resolution of adjacent peaks of cations in ion chromatography

One of the advantages of ion chromatography [Anal Chem. 47 (1975) 1801] as compared to other analytical techniques is that several ions may be analyzed simultaneously. One of the most important contributions of cation-exchange chromatography is its sensitivity to ammonium ion, which is difficult to analyze by other techniques [J. Weiss, in: E.L. Johnson (Ed.), Handbook of Ion Chromatography, Dionex, Sunnyvale, CA, USA]. The determination of low concentrations of ammonium ion in the presence of high concentrations of sodium poses a challenge in cation-exchange chromatography [J. Weiss, Ion Chromatography, VCH, 2nd Edition, Weinheim, 1995], as both cations have similar selectivities for the common stationary phases containing either sulfonate or carboxylate functional groups. The task was to develop a new cation-exchange stationary phase (for diverse concentration ratios of adjacent peaks) to overcome limitations experienced in previous trails. Various cation-exchange capacities and column body formats were investigated to optimize this application and others. The advantages and disadvantages of two carboxylic acid columns of different cation-exchange capacities and different column formats will be discussed.

Column switching for difficult cation separations

In ion chromatography, samples of very different concentration ratios of ammonium-to-sodium are difficult to quantify since these two cations have similar selectivities for stationary phases containing commonly used sulfonate or carboxylate cation-exchange functional groups. These cations, therefore, elute in close proximity, making quantification of the ion of lower concentration difficult. For example, in the power generation industry, ammonium is often used as a corrosion inhibitor in cooling waters, and determination of low concentrations of sodium in the presence of high concentrations of ammonium is required. Conversely, in environmental samples, it is necessary to determine low levels of ammonium in matrices with high concentrations of sodium. An isocratic column-switching method using two cation exchange columns of different functionalities allows either of these determinations in concentration ratios greater than 10 000:1.

Determination of Pharmaceuticals by Multi-Phase Chromatography: Combined Reversed Phase and Ion Exchange in One Column

Abstract Separations of various classes of pharmaceuticals using several HPLC retention modes simultaneously are described. The drugs including barbiturates, anti-inflammatories, cephalosporins and sulfa antibiotics are separated by a combination of reversed phase and ion exchange on a new multi-phase HPLC column. This column contains two types of particles, a macroporous substrate particle, which has adsorptive properties, and a monolayer of ion exchange latex particles which is attached to the substrate. The reversed phase and ion exchange retention modes operate independently and therefore can be controlled independently through selection of eluant components and gradient conditions. This approach to multi-mode chromatography is applied to accomplish assay reduction and on-line sample preparation. The determination of drugs in biomedical matrices such as urine, serum and saliva are discussed. Advantages of multi-mode chromatography over ion-pair reversed phase chromatography are discussed.