Rosanne W. Slingsby

Applications of ion chromatography with electrospray mass spectrometric detection to the determination of environmental contaminants in water

Ion chromatography (IC) is widely used for the compliance monitoring of common inorganic anions in drinking water. However, there has recently been considerable interest in the development of IC methods to meet regulatory requirements for analytes other than common inorganic anions, including disinfection byproduct anions, perchlorate, and haloacetic acids. Many of these new methods require the use of large injection volumes, high capacity columns and analyte specific detection schemes, such as inductively coupled plasma mass spectrometry or postcolumn reaction with UV-Vis detection, in order to meet current regulatory objectives. Electrospray ionization mass spectrometry (ESI-MS) is a detection technique that is particularly suitable for the analysis of permanently ionized or polar, ionizable compounds. The combination of IC with MS detection is emerging as an important tool for the analysis of ionic compounds in drinking water, as it provides increased specificity and sensitivity compared to conductivity detection. This paper reports on the application of IC-ESI-MS for the confirmation and quantitation of environmentally significant contaminants, i.e. compounds with adverse health effects which are either regulated or being considered for regulation, such as bromate, perchlorate, haloacetic acids, and selenium species, in various water samples.

Protein variant separations by cation-exchange chromatography on tentacle-type polymeric stationary phases

We developed a set of prototype cation-exchange column packings that are based on a hydrophilic coated, pellicular polymeric support with a grafted tentacular surface chemistry that is highly suited to resolving closely related protein variants. These column packings (1) afford minimal band spreading in conjunction with extremely high selectivity, (2) exhibit a very hydrophilic character and (3) have moderate loading capacity. Cytochrome c variants (bovine, horse, rabbit) were baseline-separated, as was native ribonuclease A and its two deamidation products, the Asp67 and isoAsp67 forms. Humanized monoclonal antibody variants differing in the presence of lysine at the C terminus of the heavy chains were baseline-resolved. Finally, the separation of hemoglobin variants found in a sample containing elevated levels of glycated hemoglobin was also demonstrated.

Anion-exchange selectivity in latex-based columns for ion chromatography

Abstract The anion-exchange columns employed in suppressed ion chromatography contain packings which are agglomerations of anion-exchange latexes and functionalized polymeric substrate. Differences in anion-exchange selectivity studied here are achieved through variations of the properties of the ion-exchange sites and charge density. Column capacity is influenced by the particle sizes of the latexes and substrate. Efficiency is most strongly effected by size of the substrate resin. This paper discusses selectivity variations that are associated with differences in the nature of the quaternary ammonium ion-exchange sites of the latexes and their relationships with various eluents employed in suppressed ion chromatography. Hypotheses are proposed to explain retention behavior of model analyte anions.

Separation and Detection of Carboxylic Acids by Ion Chromatography

Abstract Common carboxylic acids such as most Krebs cycle acids and other organic acids can be separated by either anion exchange or ion exclusion chromatography and detected by conductivity with chemical suppression. This is accomplished using a new generation of high dynamic capacity suppressors which allow separations on moderate and high capacity resins with concentrated eluants. For both anion exchange and ion exclusion chromatography, cation exchange membrane based suppressors are used to reduce the conductivity of the eluant while enhancing the conductivity of the organic acid analytes. The ability to choose between anion exchange and ion exclusion chromatography expands the versatility of ion chromatography by increasing the analysts ability to solve co-elution problems.

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.

Approaches to sample preparation for ion chromatography sulfate precipitation on barium-form ion exchangers

Abstract Clean-up and matrix elimination of samples are useful for removal of column-fouling substances and interfering ions in many ion chromatography applications. Matrix elimination is especially important in trace analysis, where preconcentration of large sample volumes is often required. Even mid-ppm concentrations of interfering ions can have a detrimental effect on preconcentration efficiency and chromatographic separation. Whereas halides are easily removed from samples by precipitation on silver-form cation exchange resin, sulfate removal on barium-form resin has been problematic. At best, the efficiency of sulfate removal is dependent on the cation content of the sample matrix. In addition, sulfate leakage from the resin bed limits the sample volume that can be applied to a barium-form device. In this paper we explore the chemical processes that are involved in the precipitation of sulfate with barium, their effects on analyte recovery and the completeness of sulfate removal, and the implications for use of barium-form ion exchange devices for removing sulfate from samples.

Gradient elution of aliphatic carboxylic acids by ion chromatography in the ion-suppression mode

Abstract The gradient ion chromatography separation and detection of aliphatic carboxylic acids in the homologous series of butyric acid through stearic acid as well as some unsaturated fatty acids are presented. The separation mode requires the ion suppression of the weak acid analytes for a reversed-phase inteaction while detection by electrical conductivity requires analyte ionization through a cation-exchange micromembrane suppressor device.

Low-level calibration study for a new ion chromatographic column to determine borate in deionized water

In the semiconductor industry, there is interest in determining borate at sub-ppb levels in ultrapure water, since borate is an early breakthrough ion from ion-exchange resin beds. Although dissolved silica is the most common species currently used to monitor the breakdown of the deionization systems, it is thought that borate probably breaks through earlier than silicate. To be of use as an early-warning indicator, borate must be determined at ppt levels. This paper discusses benchtop results with several new column products designed to deliver low-ppt detection limits for boron as borate. The system uses a prototype borate-specific concentrator column that is coupled to an ion-exclusion separator and suppressed-conductivity detection. The acidic eluent, containing mannitol, quantitatively elutes the borate from the concentrator. The analytical separation is performed using a specially designed ion-exclusion column. Data presented are from two multilevel calibration studies. Included is a discussion of detection-limit calculations and recommended formats for reporting results.