Environmental water monitoring by capillary electrophoresis and result comparison with solvent chemistry techniques

The aim of this work was to determine inorganic ions from natural waters by capillary electrophoresis (CE) and to compare the results obtained with those measured with conventional solvent chemistry techniques. The project was part of a larger CE study, during which we measured inorganic ions from some lake and river systems and groundwaters in Southern Finland. Results obtained from contaminated Finnish waters were compared with samples from the River Rhine in the Düsseldorf area. Two CE methods were used for analysis: one for determination of chloride, sulfate, nitrite and nitrate at pH 7.7 and the other for ammonium, potassium, calcium, sodium and magnesium at pH 3.6, both methods using identification based on indirect UV detection. Two separation methods were used in order to prevent complex formation of metals with sulfate, hydroxide and decomposed organic matter present in the environmental samples. On the basis of the CE studies dilution was needed for those samples having more than 100 mg/l of sulfate, chloride, calcium and sodium. On average, the natural waters in the study contained ammonium, magnesium, sodium, potassium and calcium below 0.3, 20, 200, 20, and 200 mg/l, respectively. The concentrations of chloride, sulfate, nitrite and nitrate were below 20, 100, 10, and 10 mg/l, respectively. Correlation of the CE results with those acquired by titration, atomic absorption spectrometry, ion chromatography and flow injection analysis were obtained; R2 values for the comparison tests varied from 0.8816 to 0.9994 depending on the ion. The repeatabilities of the anion and cation CE methods were tested using laboratory-made reference sample mixtures with high and low salt concentration.     

On-line process monitoring of water-soluble ions in pulp and paper machine waters by capillary electrophoresis

In this study, capillary electrophoresis (CE) was used for separation of inorganic and organic ions from waters of paper and paperboard machines at mills. The instrument was constructed for on-line measurements by building a batch-type sample feeding unit. Chloride, thiosulphate, sulphate, oxalate, sulphite, hydrogen sulphide, formate, carbonate, phosphate and acetate in the process water samples were separated using an ion-specific separation system in CE with dicarboxylic acid buffer (pH 8.2), with pyridinium-2,3-dicarboxylic acid modified with commercial NICE-Pak OFM-OH solution (pH 12.0) or with a cetyltrimethylammonium bromide solution modified with chromate (pH 10.6). In addition, Analis CEofix Anions 8 electrolyte solution was tested in on-line studies at mills. It allowed 5 min separation time for the anions. Aluminium was determined at pH 3.6 in 10 min by using a laboratory-made imidazole buffer modified with 18-crown 6-ether. The developed CE systems were used to monitor the concentrations of sulphur species in dithionite degradation, to estimate corrosion degree in the water tanks, to monitor formaldehyde as the biocide chemical in wire washing and, in general, to observe process disturbances resulting from chemical feedings and their sites. The CE combination was on-line coupled to eight different process machines for continuous monitoring of concentrations for periods between two weeks and one month at paper and pulp mills in Finland.     

Capillary electrophoretic determination of inorganic anions in the drainage and surface water samples.

Capillary electrophoresis was used for separation and quantitation of several inorganic anions in the drainage and surface water samples from the region with extensive use of fertilisers. Baseline separation of 13 small anions including nitrite and nitrate up to the concentrations of 100 mg/l was achieved in less than 5 min. The electrolyte consisted of 3 mM K2CrO4, 30 microM cetyltrimethylammonium bromide and 3 mM boric acid at pH 8. The method yielded precisions of 1.8-7.2% (RSD, n = 10) and detection limits from 4 micrograms/l (Cl-) up to 500 micrograms/l (citrate). The results of the CE method were compared to ion chromatography using water-acetonitrile (86:14) at pH 8.6 adjusted with NaOH as the mobile phase and consistent results were obtained.     

Separation of anions by ion-interaction chromatography with a novel cationic/zwitterionic eluent

Inorganic and organic anions can be separated on an ordinary silica C18 column using a mobile phase containing tetrabutylammonium hydroxide (TBAH) and an aminosulfonic acid zwitterion reagent (MOPS). The pH of this eluent is close to 7 and the background conductivity is about 50 microS, which is low enough to permit anion analyte detection by direct conductivity. Linear calibration curves were obtained for the six anions studied and detection limits ranged from 0.075 to 0.15 mg/l (ppm) for the five inorganic anions. The method was applied to the determination of water-soluble anions in aerosol samples at concentrations as low as 0.3 mg/l.     

Identification of inorganic ions in post‐blast explosive residues using portable CE instrumentation and capacitively coupled contactless conductivity detection

Novel CE methods have been developed on portable instrumentation adapted to accommodate a capacitively coupled contactless conductivity detector for the separation and sensitive detection of inorganic anions and cations in post‐blast explosive residues from homemade inorganic explosive devices. The methods presented combine sensitivity and speed of analysis for the wide range of inorganic ions used in this study. Separate methods were employed for the separation of anions and cations. The anion separation method utilised a low conductivity 70 mM Tris/70 mM CHES aqueous electrolyte (pH 8.6) with a 90 cm capillary coated with hexadimethrine bromide to reverse the EOF. Fifteen anions could be baseline separated in 7 min with detection limits in the range 27–240 μg/L. A selection of ten anions deemed most important in this application could be separated in 45 s on a shorter capillary (30.6 cm) using the same electrolyte. The cation separation method was performed on a 73 cm length of fused‐silica capillary using an electrolyte system composed of 10 mM histidine and 50 mM acetic acid, at pH 4.2. The addition of the complexants, 1 mM hydroxyisobutyric acid and 0.7 mM 18‐crown‐6 ether, enhanced selectivity and allowed the separation of eleven inorganic cations in under 7 min with detection limits in the range 31–240 μg/L. The developed methods were successfully field tested on post‐blast residues obtained from the controlled detonation of homemade explosive devices. Results were verified using ion chromatographic analyses of the same samples.     

Simultaneous determination of DTPA,EDTA, and NTA by capillary electrophoresis after complexation with copper

We present a method for simultaneous determination of the aminopolycarboxylic acids DTPA, EDTA and NTA in dishwashing detergents, paper mill waters, and natural waters by capillary electrophoresis (CE). The complexing agents were examined as their copper(II) complexes and separated by conventional CE with reversed polarity of the applied voltage. The optimum separation conditions were established by varying the pH and phosphate and tetradecyltrimethylammonium bromide (TTAB) concentrations in the run buffer. The separations were carried out in a fused-silica capillary (61 cm×75 m i.d.) filled with phosphate buffer (80 mmol L^–1, TTAB concentration 0.5 mmol L^–1, pH 7.1, voltage –20 kV) using direct UV detection at 191 and 254 nm. With this CE method all the peaks in the electropherograms were properly separated, the calibration plots gave good correlation coefficients and all three complexing agents could be detected in less than 4 min. Linear calibration plots were obtained for CuDTPA, CuEDTA and CuNTA; limits of detection were 0.03 mmol L^–1 for all complexing agents and recoveries for all tested samples were within the range 104±7%. Results obtained from dishwashing detergent samples were found to be reliable and comparable with those from HPLC (R²=0.989) and UV–Vis (R²=0.985) methods.     

Preparation and characterization of polyalkene membranes modified with four different ion-exchange groups by radiation-induced graft polymerization

An ion chromatographic method was developed for the determination of nine inorganic and organic acid anions at sub- to low-microg/l levels in power plant water samples. In this method, samples were injected using a large-volume direct injection technique, the analyte anions were separated on a hydroxide-selective anion-exchange column using high-purity hydroxide eluents generated by an on-line electrolytic eluent generator and detected using the suppressed conductivity detection method. The method performance was evaluated by analyzing synthetic water samples containing additives encountered in the power plant water samples and four water samples from a fossil fuel power plant. The relative standard deviations of retention times of analyte ions separated on the hydroxide-selective anion-exchange column were less than 0.4%. The recoveries of analyte ions spiked into the synthetic water samples at concentrations of 0.13-1.0 microg/l were in the range of 70-120%. The method detection limits for analyte ions in deionized water were 0.0099, 0.0056, 0.019, 0.057, 0.0084, 0.023, 0.067, 0.037, and 0.079 microg/l for fluoride, acetate, formate, chloride, nitrite, sulfate, bromide, nitrate, and phosphate, respectively.     

Use of eosin as a fluorophore in capillary electrophoresis with laser detection.

Eosin has been used to generate the background signal for indirect fluorimetric detection of inorganic and organic ions, simultaneously separated by capillary zone electrophoresis (CZE). This reagent provides constant fluorescence over the pH range of 5-10 and is compatible with the excitation by an argon ion laser at 488 nm with emission at 520 nm. The use of esosine as fluorophore, H3BO3, and Na2B4O7 as electrolyte and diethylentriamine as modifier of the electroosmotic flow in CZE were optimised. The analytical potential of the studied buffer was tested on a group of 12 anions, used as model compounds. Both, hydrodynamic and electrokinetic injection mode were optimised. The detection limits determined by the last injection mode, were in the range 0.008-0.037 mg l(-1). By using this method, the quantitation of the common anions in tap and mineral water has been carried out successfully.     

Performance of ion chromatography in the determination of anions and cations in various natural waters with elevated mineralization

The performance of ion chromatography in the determination of anions and cations in natural mineral waters of different composition and different total mineralization was evaluated. Up to 12 ions of the 20 usually included in extended chemical analysis of natural waters were successfully determined by ion chromatography alone. At least 98.60% and up to 99.96% of total cation composition of mineral waters was determined by ion chromatography. Hydrogen carbonate predominated in anion composition of mineral waters and was determined titrimetrically. The percentage of anions determined by ion chromatography in the remaining anion composition of mineral waters was between 98.90% and 99.96%. The agreement between total concentrations of anions and cations in individual mineral waters determined predominantly by ion chromatography is very good and the performance of ion chromatography for the basic and for the extended chemical analysis of highly mineralized water samples is very high. Method development was assisted by previously developed algorithms and appropriate experimental conditions are also discussed.     

Light-emitting diode-based indirect fluorescence detection for simultaneous determination of anions and cations in capillary electrophoresis

This report presents simultaneous analysis of cations and anions by capillary electrophoresis (CE) in conjunction with indirect fluorescence detection using a blue light-emitting diode (LED), based on the displacement of fluorescein with anionic EDTA-metal complexes and anions. A new focusing system combined with a plastic lens and a 40x objective was developed and used effectively to focus the diverging beam of the LED on the capillary. The optimum compositions for simultaneous analysis of metal ions and anions are the samples prepared in 5 mM borate, pH 9.2, containing 2 mM EDTA and the background electrolytes (BGEs) consisting of 5 mM borate buffer, 5 microM fluorescein, and 1 microM NaCl at pH 9.2. Using this pre-capillary complexation method, the analysis of a sample containing five metal ions and eight anions was accomplished in 8 min, with the relative standard deviation values for the migration times less than 2.0%. The peak heights against the concentrations of the metal ions and anions are linear in 10-1000 and 50-2000 microM, with correlation coefficients better than 0.998, and 0.982, respectively. The limits of detection at a signal-to-noise ratio 3 of up to 14.6 microM for formate and as low as 3.7 microM for Ni2+. The results of the analyses of pond water and a Chinese herbal soup present the advantages of this method, including simplicity, rapidity, reproducibility, and low costs.     

Study of the selectivity of inorganic anions in hydro-organic solvents using indirect capillary electrophoresis

In capillary electrophoresis (CE) analysis of small inorganic anions, the ability to control the electroosmotic flow (EOF) and the ability to alter the electrophoretic mobility of the ions are essential to improve resolution and separation speed. In this work, a CE method for separation of small inorganic anions using indirect detection in mixed methanol/water buffers is presented. The suitability of different UV absorbing probes commonly used for indirect detection including chromate, iodide, phthalate, benzoate, trimellitate, and pyromellitate, in mixed methanol/water buffers is examined. The effect of the electrolyte buffer system, including the pH, buffer concentration and the organic solvent on the electrophoretic mobility of the probes and analytes are also investigated. The EOF was reversed using cationic surfactant, cetyltrimethylammonium bromide (CTAB) so ions were separated under co-EOF mode. The organic solvent alters the electrophoretic mobility of the probes and the analytes differently and hence choice of the appropriate probe is essential to achieve high degree of detection sensitivity. Separations of six anions in less than 2.5 min were accomplished in buffers containing up to 30% MeOH. Adjustment of the methanol content helps to improve the selectivity and resolution of inorganic anions. Limit of detection, reproducibility and application of the method for quantification of anions in water samples will also be discussed.     

High performance liquid chromatographic determination of aluminium in natural waters in the form of its lumogallion chelate

A high performance liquid chromatographic method for the determination of ultra trace amount of aluminium in natural waters has been developed using lumogallion as a precolumn reagent for fluorimetric detection. The highly fluorescent Al-lumogallion chelate (lambda(ex) 500 nm, lambda(em) 574 nm) was separated on a LiChrosorb RP 18 column with an eluent containing 3:7 acetonitrile/0.02M potassium hydrogen phthalate buffer (pH 4.7) containing 10(-5)M lumogallion. The proposed system provides a simple, quick, selective and sensitive method for the determination of ultra-trace amount of aluminium in water samples. The detection limit defined as three times the standard deviation of the blank signal, was 0.05 mug/l. in water samples for 100 mul injection. The tolerance limits were 5 mg/l. for Fe(III) and F(-) and over 10 mg/l. for other foreign ions. The sensitivity of the method was independent of salinity. This method had been used for the direct determination of aluminium in both tap and coastal sea-waters without any preconcentration steps.     

Ion-exchange-based eluent-free preconcentration of some anions

Preconcentration procedures based on ion-exchange methods are often used to enhance the sensitivities of analytical techniques where the eluent used for eluting the preconcentrated ions does not influence the subsequent analytical step. Until recently, only a limited use of ion-exchange-based sample preconcentration procedures has been found in those analytical techniques where the eluent components strongly influence the separation procedure [e.g., capillary electrophoresis (CE)]. In this paper, we present a preconcentration procedure based on (i) the preconcentration of anions on an ion-exchange resin, (ii) the subsequent elution of analytes, and (iii) on-line removal of eluent components by chemical suppression using an appropriate suppressor device (either packed-bed suppressor column or micromembrane suppressor). The adjustment of the system parameters, combined with a computer-controlled, sensing/switching system, resulted in a minimal additional dilution of the eluted preconcentrated anions. The efficiency of the proposed enrichment/matrix removal procedure was tested by using off-line CE analysis of collected preconcentrated samples, reaching a LOD of 1 microg/l for a selected anion.     

In-capillary derivatization and determination of iodine in sodium chloride solution

A new capillary electrophoretic (CE) method was developed for the simple and selective determination of iodine in 0.5 mol l(-1) NaCl. The proposed method is based on the in-capillary derivatization of iodine with thiosulfate ions using the zone-passing technique and direct photometric detection of the iodide and tetrathionate formed. The optimal conditions for the separation and derivatization reaction were established by varying the concentration of iodine, electrolyte pH and applied voltage. The optimized separations were carried out in phosphate electrolyte (pH 6.86) using direct photometric detection at 253.7 nm. Common photometric detection absorbing anions such as Cl(-), NO(2)(-), S(2)O(3)(2-) did not give any interference. Valid calibration (r(2) = 0.994) is demonstrated in the range 16.5-198.1 mg l(-1) of iodine. The detection limit (calculated according to K. Doerffel, Statistik in der analytischen Chemie, 1990) was 11.53 mg l(-1) (by iodide peak area) and 8.45 mg l(-1) (by tetrathionate peak area). The proposed system was applied to the determination of iodine after oxidation of iodide in underground water.     

Development of capillary electrophoresis for the determination of metal ions using mixed partial and complete complexation techniques

A new capillary electrophoretic (CE) method was developed for the selective and sensitive determination of common metal ions. The proposed method is based on conventional CE separation of metal cations followed by complete complexation of separated analytes with 1,10-phenanthroline using the zone-passing technique. This approach combines both partial and complete complexation modes and, thus, enables rapid, selective, efficient separation together with sensitive direct UV detection of metal species. The optimal conditions for the separation and derivatization reaction were established by varying type of electrolyte, electrolyte pH, introduction time and concentration of 1,10-phenanthroline. The optimized separations were carried out in 50 mmol l(-1) glycolic acid electrolyte (pH 6.0 with imidazole) using direct UV detection at 254 nm. Five common metal cations (Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) were separated in less than 4 min. The proposed system was applied to the determination of Fe(II) and Zn(II) in snow samples. The recovery tests established for snow samples were within the range 100+/-12%.     

Preliminary results on the immobilisation of radionuclides from waters with specific adsorbers based on phosphate salts

The present paper is focused on the ability of aluminium phosphate (ALPC), magnesium ammonium phosphate (MGPC), magnesium hydrogen phosphate (MGHPC), and calcium hydrogenphosphate (CAHPC), adsorbed onto charcoal, to immobilise actinides by adsorption from natural waters. The objective of this process is to evaluate the environmental pollution due to the actinides. Europium, thorium, protactinium, neptunyl, and uranyl ions were chosen to simulate actinides in the +3, +4, +5 and +6 oxidation state. The adsorbers were tested using natural waters samples. The adsorption trends and capacities were analysed. ALPC and MGPC exhibited a similar behaviour and adsorbed demonstrating that the +5, +4 and +3 actinide ions can be easily immobilised from natural waters and may be successfully used at pH 7-8. MGHPC may be used at a higher pH, whereas CAHPC is effective in the whole pH range. In all cases, thorium, protactinium and europium were strongly     

Capillary electrophoretic determination of thiosulfate,sulfide and sulfite using in-capillary derivatization with iodine

A new capillary electrophoresis (CE) method was developed for the rapid, simple and selective determination of thiosulfate, sulfide and sulfite species. The proposed method is based on the in-capillary derivatization of separated sulfur anions by mixing their zones with the iodine zone during the electrophoretic migration and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying electrolyte pH, electrolyte counter-ion, concentration of iodine, and applied voltage. The optimized separations were carried out in 20 mmol/L Tris-chloride electrolyte (pH 8.5) using direct UV detection at 214 nm. All three sulfur species were well resolved in less than 4 min. The method gives repeatability comparable or even better than this obtained for sulfur anions using standard CE technique. The proposed CE system was applied to the monitoring of sulfur anions in spent fixing solutions during the electrolytic oxidation.     

Use of capillary electrophoresis with UV detection as a screening method to determine histamine in fish samples.

Histamine levels in fish, extracted with methanol, were determined by capillary electrophoresis (CE) using phosphate buffer pH 2.5 and U.V. detection at 210 nm. Histamine was well separated from the other co-extracted components under the given CE condition without any cleanup of the methanol extract. The average recovery of spiked histamine in various types of fish samples was 96%. Using the same methanol extracts from various fish samples, we then compared histamine concentration obtained by CE and fluorometric methods.     

Determination of organic acids in air by capillary electrophoresis and ion-exclusion chromatography

Summary A capillary electrophoretic (CE) method for the determination of organic acids in the low ppm range is described. The buffer consisted of 5 mM 2,6-pyridinedicarboxylic acid and 0.5 mM cetyltrimethylammonium bromide, pH 5.6. The former served as background electrolyte for indirect UV detection at 200 nm, whereas the latter was used to reverse electroosmotic flow. In <5 min 8 low molecular mass organic acids (oxalic, formic, malonic, glutaric, glycolic, acetic, lactic and propanoic) and two inorganic acids (hydrochloric and sulphuric) were separated. Detection limits for anions tested were 0.04 mg L⁻¹ (lactic acid) to 0.6 mg L⁻¹ (malonic acid). The method was applied to the determination of organic acids in air samples. The CE results when compared with ion-exclusion chromatography (IEC) agreed well. The use of electrokinetic injection in CE proved beneficial for preconcentration of organic acids in real samples. Using electrokinetic injection, preconcentration factors ranging from 14 (hydrochloric acid) to 3 (propanoic acid) were obtained. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Application of capillary electrophoresis in the quality control of osmotically treated water

Summary This paper discusses the use of capillary zone electrophoresis (CZE) with indirect UV detection for the separation and detection of ions. By use of a 70 cm×75 μm i.d. capillary at −15 kV and an electrophoretic buffer containing sodium chromate, 1-butanol, and cetyltrimethylammonium bromide as electroosmotic-flow modifier (pH 8) nine inorganic and organic anions were separated in less than 10 min. By use of the same type of capillary at 20 kV and an electrophoretic buffer containing imidazole and 18-crown-6 (pH 5) eight cations were separated in less than 5 min. The different variables that affect the separation were studied and optimized; the compounds were detected at low mg L⁻¹ levels after hydrodynamic injection under pressure. The method was tested with osmotically treated waters, and the results compared with those obtained by ion chromatography for anion analysis and by atomic absorption spectroscopy for cation analysis.