John M. Riviello

Parameters influencing separation and detection of anions by capillary electrophoresis

Abstract Electrolyte composition is critical in optimizing separation and detection of ions by capillary electrophoresis. The parameters which must be considered when designing an electrolyte system for capillary electrophoresis include electrophoretic mobility of electrolyte constituents and analytes, detection mode, and compatibility of electrolyte constituents with one another. An electrolyte system based on pyromellitic acid is well suited for use with indirect photometric detection, and provides excellent separations of anions. The ability to modify the electrophoretic mobility of pyromellitic acid as a function of ph provides flexibility in matching electrophoretic mobilities of analytes. Additionally, the use of alkyl amines as electroosmotic flow modifiers allows the rapid separation of anions by reversing the direction of electroosmotic flow in a fused-silica capillary. The optimization of a capillary electrophoresis electrolyte for anion analysis is also discussed in terms of pH, ionic strength and applied voltage. The effect of organic solvent on separation selectivity is also discussed.

Determination of eight synthetic food colorants in drinks by high-performance ion chromatography.

Eight synthetic food colorants (Amaranth, Brilliant Blue, Indigo Carmine, New Red, Ponceau 4R, Sunset Yellow, Tartrazine, Allura Red) were determined by high-performance ion chromatography on an anion-exchange analytical column with very low hydrophobicity and visible absorbance detection. Gradient elution with hydrochloric acid-acetonitrile effected both the chromatographic separation of these colorants and the on-line clean-up of the analytical column, which was very advantageous for routine analysis. High-performance ion chromatography may be a solution to the chromatographic analysis for some water-soluble, organic analytes with strong hydrophobicity. The method has been applied to the determination of colorants in drinks and in instant drink powder. No time-consuming pretreatment, as used in conventional liquid chromatography, was needed.

New strategies for determination of transition metals by complexation ion-exchange chromatography and post column reaction

Abstract A method for the simultaneous determination of metals (Fe3+, Fe2+, Cu, Ni, Zn, Co, Cd, Mn and Pb) at μg/l levels in environmental matrices is demonstrated. The metals are separated by ion chromatography on a mixed-bead ion-exchange column (IonPac CS5A) and detected by post-column reaction and spectrophotometric detection. The use of a gradient program (based on oxalic acid–hydrochloric acid–sodium chloride and sodium nitrate eluents) allows the separation of nine metals in a single run. The direct injection of a large volume of samples lowers the detection limits to below and/or few μg/l. The chromatographic conditions and colour-development reaction were optimised. Two post-column reagents, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and 4-(2-pyridylazo) resorcinol, were tested and detection limits were compared. The use of 5-Br-PADAP increased the sensibility for Cu, Cd, Zn and Mn. For the proposed method, linearity, reproducibility, detection limits and interference due to alkaline-earth metals (noticeably Mg and Ca) were discussed. Under the suggested chromatographic conditions Mg2+ and Ca2+ up to 0.2 g/l do not interfere with separation and quantitative analysis of the metals. The calibration graphs were linear (r2>0.986) in the range 5–5000 μg/l. The application of the method to the determination of metals in coastal marine sediments is shown.

Capillary electrophoresis of inorganic cations and low-molecular-mass amines using a copper-based electrolyte with indirect UV detection

An electrolyte system for the separation and detection of common inorganic cations and low-molecular-mass amines using capillary electrophoresis was developed. The electrolyte system is based on copper(II) as the primary electrolyte constituent. The method permits the determination of alkali metals, alkaline-earth metals, and ammonium in less than 5 min. Utility of the method for the separation of low-molecular-mass amines has also been demonstrated. Factors affecting separations using this electrolyte system have been investigated and include pH, buffering, and the addition of selective mobility modifiers. The analytical performance of the electrolyte system is discussed in terms of detection limits, linearity of response, migration time precision and matrix effects.

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.

On-line pretreatment and determination of Pb, Cu and Cd at the μg l−1 level in drinking water by chelation ion chromatography

A novel, highly sensitive method for the simultaneous separation and determination of lead, copper, cadmium and other transition metals in drinking water was achieved by on-line sample pretreatment of chelation ion chromatography. Manganese, which coeluted with cadmium, was oxidized to permanganate by ammonium persulfate before injection. Permanganate, with bulk quantity of alkali, alkaline earth metals, iron and aluminum, was eliminated by pyrophosphoric acid-ammonium acetate buffer solution (pH 5.5), while retaining heavy and transition metals on a selective chelating resin (MetPac CC-1 column). Then, they were disabsorbed and transferred to a sulfonated cation exchanger (TMC-1 column). Finally, the concentrated trace metals were separated on a bifunctional ion-exchange column (CS5A) by a concentration gradient of oxalic acid and sodium nitrate eluents, coupled with post-column spectrophotometric detection with 2-[(5-bromo-2-pyridyl)azo]-5-diethylaminophenol (5-Br-PADAP) at 560 nm. The separation and color-development conditions were optimized. The detection limits for the method (signal-to-noise ratio=3:1) were at or below the mu g l(-1) level. The results of drinking water analyses were satisfactory

Ion chromatography of heavy and transition metals by on- and post-column derivatizations

A new method for the simultaneous separation and determination of mercury(II) with other heavy and transition metals by ion chromatography (IC) was developed. This method involves on-column derivatization with 2,6-pyridinedicarboxylic acid (PDCA) and anion-exchange separation, followed by a post-column reaction with 2-[(5-bromo-2-pyridyl)-azo]-5-diethylaminophenol (5-Br-PADAP) to form metal-5-Br-PADAP chelates, which can be sensitively monitored by spectrophotometric detection at 565 nm. PDCA was first combined with Na2C2O4 to separate the metals within 16 min. The optimum separation and derivatization conditions were studied in detail. The detection limits of Pb2+, CU2+, Ni2+ Zn2+, Co2+, Cd2+, Mn2+ and Hg2+ were 0.2 mgl(-1) (115 mu l loop), 1.5, 5, 0.5, 5, 5, 3 and 20 mu gl(-1) (676 mu l loop), respectively. This method was applied to the analysis of standard rice sample, waste cellpacking and municipal solid waste fly ash with satisfying results

Determination of cadmium and lead at μg/1 levels in aqueous matrices by chelation ion chromatography

Abstract A method for the simultaneous determination of μg/1 or sub-μg/1 levels of cadmium and lead in sea water by chelation ion chromatography is demonstrated. The method consists in the preconcentration of a sea-water sample containing cadmium and lead on an iminodiacetate chelating resin; alkali and alkaline earth metals are removed from the resin with an ammonium acetate buffer, the metals are eluted and separated by cation-exchange chromatography, followed by postcolumn derivatization with 4-(2-pyridylazo)resorcinol and spectrophotometric detection at 520 nm. The concentration and separation steps are automated. The detection limit, when concentrating 200 ml of sea water, was found to be 2 ng for cadmium and 6 ng for lead. Relative standard deviations of 4.5% and 6.8% for 10 μg/1 of cadmium and lead, respectively, were obtained. Transition metals (Fe, Co, Ni, Zn, Cu, Mn) do not interfere in the analysis. An application of the method to the determination of cadmium and lead in sea-water samples collected in the Taranto gulf (Italy) is presented.

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).

Use of ion chromatography for the determination of transition metals in the control of sewage-treatment-plant and related waters

Transition metals [Fe(III), Fe(II), Cu, Ni, Zn, Co, Cd, Mn] were separated using a mixed-bed ion-exchange column (Dionex IonPac CS5A). A pyridine2–6-dicar☐ylic acid eluent was used and detection was accomplished using post-column reaction with 4-(2-pyridylazo)resorcinol and absorbance monitoring at 530 nm. Under the suggested chromatographic conditions both Mg2+ and Ca2+, up to 0.1 g/l and 0.3 g/l, respectively, do not interfere with separation quantitation. Detection limits from 0.06 μg/l for Co(II) to 0.38 μg/l for Fe(II). The calibration graphs were linear (r20.986) over two orders of magnitude (5–5000 μg/l). The selective separation of eight metals in 20 min was obtained and the method was applied to the analysis of natural and waste waters related to the maintenance of a sewage treatment plant.