Separation of chromium (III) and chromium (VI) by capillary electrophoresis using 2,6-pyridinedicarboxylic acid as a pre-column complexation agent

Rapid determination of chromium species in environmental waters using a diol-bonded polymer-stationary column under water-rich conditions coupled with ICPMS

Chromium speciation analysis in environmental water is of great significance for the monitoring of water pollution and assessing its influences on human health. This study proposes a rapid analytical approach for the simultaneous determination of Cr(VI) and Cr(III) in environmental waters by hydrophilic interaction chromatography (HILIC) coupled with ICPMS under a water-rich condition. 2,6-Pyridinedicarboxylic acid (PDCA) was used to unify Cr(III) species in various chemical forms into a stable Cr(III)-PDCA anion complex and then separated from Cr(VI) oxyanion on a diol-bonded polymer-based HILIC column. An aqueous mobile phase containing 50 mmol L-1 ammonium acetate (pH 7.0), 2 mmol L-1 PDCA, and 4% acetonitrile successfully separates chromium species as well as chloride ions. In addition, our method elutes Cr(VI) preferentially over Cr(III)-PDCA, enabling rapid determination of Cr(VI), and both chromium species were analyzed within 6.2 min. The detection limits of 0.19 μg L-1 for Cr(VI) and 0.35 μg L-1 for Cr(III) at m/z 52 under He collision mode are comparable to or better than the conventional ion exchange chromatography-ICPMS methods, and quantitative recovery was obtained from spike-recovery tests on river water samples containing various levels of matrix. Optimization experiments of the HPLC conditions indicate that the retentions of Cr(VI) and Cr(III)-PDCA are characterized by electrostatic and nonpolar interactions, respectively. The retention behavior of inorganic anions and cations in water-rich conditions observed in this study will provide new insights into the separation mechanism in polymer-based HILIC columns, which has been poorly understood.

Chromium Determination in Leather and Other Matrices: A Review

Leather industry plays an essential role in the world's economy; however, it also has a negative environmental impact due to the generation of significant quantities of wastes, some of which are classified as hazardous chemicals. Chrome tanning, the most popular tanning process, employs chromium salts, acids, and some other chemicals. Some dyes can be also a source of chromium. As a result, hexavalent chromium, a known carcinogenic and mutagenic, can be found in leather products and cause allergic dermatitis or trigger other diseases. For this reason, it is important to quantify the total amount of chromium in final leather goods, as well as the oxidation state in which this element is found. This paper aims to summarize chromium contamination due to the leather production processes, and to review the analytical methods that have been used to determine chromium's most abundant species: Cr(III) and Cr(VI) in leather and other matrices (foodstuffs, cosmetic products, environmental, and pharmaceutical samples). The international and European regulations are presented as well as the last academic developments to extract and quantify chromium species. The future outlook of pretreatment and quantification techniques are also discussed in this work, with a special focus on chromium interconversions.

Importance of Clean Surfaces on the Catalyst: SnS2 Nanorings for Environmental Remediation

The focus of the work is the synthesis of SnS₂ nanomaterials with (peg-SnS₂NF) and without (sf-SnS₂NR) the involvement of the organic template and the comparative study of their catalytic activities. The synthesis of these materials was achieved in a single-step procedure aided by hexamethyldisilazane (HMDS). These nanoparticles were subjected to X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and UV-vis spectroscopy analyses to investigate their structural, topographical, surface, and optical properties. The present work suggests that the surfactant-free SnS₂ nanoring (sf-SnS₂NR) catalyst has lower surface area compared to the poly(ethylene glycol)-stabilized SnS₂ nanoflower (peg-SnS₂NF) catalyst but shows high activity under visible light for the photoreduction of Cr(VI) and the photocatalytic degradation of organic dyes. The work exposed the importance of the clean surfaces on the catalyst and is expected to have a high impact on the photocatalytic activity of the SnS₂ nanomaterial. The study also endorses the utility of the HMDS-assisted synthetic method for the production of multifunctional semiconductor tin disulfide nanomaterials with multiple potential applications.

Characterisation of Crevice and Pit Solution Chemistries Using Capillary Electrophoresis with Contactless Conductivity Detector

The ability to predict structural degradation in-service is often limited by a lack of understanding of the evolving chemical species occurring within a range of different microenvironments associated with corrosion sites. Capillary electrophoresis (CE) is capable of analysing nanolitre solution volumes with widely disparate concentrations of ionic species, thereby producing accurate and reliable results for the analysis of the chemical compositions found within microenvironment corrosion solutions, such as those found at crevice and pit corrosion sites. In this study, CE with contactless conductivity detection (CCD) has been used to characterize pitting and crevice corrosion solution chemistries for the first time. By using the capillary electrophoresis with contactless conductivity detection (CE-CCD) system, direct and simultaneous detection of seven metal cations (Cu²⁺, Ni²⁺, Fe³⁺, Fe²⁺, Cr³⁺, Mn²⁺, and Al³⁺) and chloride anions was achieved with a buffer solution of 10 mM 2,6-pyridinedicarboxylic acid and 0.5 mM cetyltrimethylammonium hydroxide at pH 4 using a pre-column complexation method. The detection limits obtained for the metal cations and chloride anions were 100 and 10 ppb, respectively. The CE-CCD methodology has been demonstrated to be a versatile technique capable of speciation and quantifying the ionic species generated within artificial pit (a pencil electrode) and crevice corrosion geometries for carbon steels and nickel-aluminium bronze, thus allowing the evolution of the solution chemistry to be assessed with time and the identification of the key corrosion analyte targets for structural health monitoring.

Simultaneous determination of Cr(III) and Cr(VI) in tannery wastewater using low pressure ion chromatography combined with flow injection spectrophotometry

Trivalent and hexavalent chromium have been successfully separated and determined using low pressure ion chromatography combined with flow injection spectrophotometric analysis (LPIC-FIA). A column packed with crosslinking starch microspheres was used for on-line separation of Cr(III) from Cr(VI) in a flow-injection system because of its absorptive effect on Cr(III). To determine the concentration of Cr(III) and Cr(VI) in samples, we used 3.0 mmol/L nitric acid to elute adsorbed Cr(III) from the column and then used ceric sulfate-sulfuric acid as oxidant to convert all Cr(III) into Cr(VI). Then, Cr(VI) directly came from the samples and Cr(VI) came from Cr(III) successively formed a amaranthine complex with diphenycarbazide and the complex shows a maximum absorption at 530 nm. Analytical parameters including the concentration of eluent and oxidant solution, oxidizing temperature, length of oxidizing reaction coil, reaction coil and injection coil, interfering effects, etc., were optimized. The limit of detection was 1.25 μg/L for Cr(VI) and 3.76 μg/L for Cr(III). The linear relationship between absorption with the concentration of Cr(VI) and Cr(III) was 0.001-1.000 mg/L and 0.030-1.000 mg/L with correlation coefficients of 0.9995 and 0.9994, respectively. The relative standard deviation of Cr(VI) and Cr(III) was 1.21% and 1.66%, respectively (n=10). Major cations and anions did not show any interference. We validated this method through certified reference materials and through measuring the recovery in tannery wastewater.

Recovering Ga(III) from coordination complexes using pyridine 2,6-dicarboxylic acid chelation ion chromatography

Ion exchange chelation chromatography is an effective means to extract metals from coordination complexes and biological samples; however there is a lack of data to verify the nature of metal complexes that can be successfully analysed using such a procedure. The aim of this study was to assess the capability of pyridine 2,6-dicarboxylic acid (PDCA) to extract and quantify Ga(III) from a range of environments using standard liquid chromatography apparatus. The PDCA chelation method generated a single Ga(III) peak with a retention time of 2.55 +/- 0.02 min, a precision of <2% and a limit of detection of 110 microM. Ga(III) hydroxide complexes (highest stability constant 15.66) were used to successfully cross-validate the chelation method with inductively coupled plasma mass spectrometry. The PDCA assay extracted 96.9 +/- 1.2% of the spiked Ga(III) from porcine mucus and 100.7 +/- 2.7% from a citrate complex (stability constant 10.02), but only ca 50% from an EDTA complex (stability constant 22.01). These data suggest that PDCA chelation can be considered a suitable alternative to inductively coupled plasma mass spectrometry for Ga(III) quantification from all but the most strongly bound coordinated complexes i.e. a stability constant of <15.

Cloud point extraction combined with high-performance liquid chromatography for speciation of chromium(III) and chromium(VI) in environmental sediment samples

A sensitive and simple method for high-performance liquid chromatography (HPLC) determination of traces of chromium species in lake sediments after preconcentration by cloud point extraction (CPE) has been developed. Simultaneous preconcentration of Cr(III) and Cr(VI) in sediment samples was achieved by CPE with 1-(2-thiazolylazo)-2-naphthol (TAN) as the chelating agent and non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) as the extractant. Baseline separation of the TAN chelates of Cr(III) and Cr(VI) was realized on a RP-C(18) column by using a mixture of methanol-water (69:31, v/v) solution and 4.5 mmol L(-1) CTMAB buffered with 0.03 mol L(-1) NaAc-HAc solution (pH 5.5) as the mobile phase at a flow rate of 0.8 mL min(-1). The variables affecting the complexation and extraction steps were examined. The precision (R.S.D.) for seven replicate injections of a mixture of 100 microg L(-1) of Cr(III) and Cr(VI) was 1.2 and 0.9% for the retention time, 4.7 and 2.7% for the peak area, respectively. The concentration factor was 45 for Cr(III) and 40 for Cr(VI). The detection limit (LOD) of this method, calculated as three times the standard deviation of the blank signals was 7.5 microg L(-1) for Cr(III) and 3.5 microg L(-1) for Cr(VI), respectively. The proposed procedure was applied to the speciation of chromium in sediment samples with satisfactory results.

Evolution of catalysts directed by genetic algorithms in a plug-based microfluidic device tested with oxidation of methane by oxygen

This paper uses microfluidics to implement genetic algorithms (GA) to discover new homogeneous catalysts using the oxidation of methane by molecular oxygen as a model system. The parameters of the GA were the catalyst, a cocatalyst capable of using molecular oxygen as the terminal oxidant, and ligands that could tune the catalytic system. The GA required running hundreds of reactions to discover and optimize catalyst systems of high fitness, and microfluidics enabled these numerous reactions to be run in parallel. The small scale and volumes of microfluidics offer significant safety benefits. The microfluidic system included methods to form diverse arrays of plugs containing catalysts, introduce gaseous reagents at high pressure, run reactions in parallel, and detect catalyst activity using an in situ indicator system. Platinum(II) was identified as an active catalyst, and iron(II) and the polyoxometalate H(5)PMo(10)V(2)O(40) (POM-V2) were identified as active cocatalysts. The Pt/Fe system was further optimized and characterized using NMR experiments. After optimization, turnover numbers of approximately 50 were achieved with approximately equal production of methanol and formic acid. The Pt/Fe system demonstrated the compatibility of iron with the entire catalytic cycle. This approach of GA-guided evolution has the potential to accelerate discovery in catalysis and other areas where exploration of chemical space is essential, including optimization of materials for hydrogen storage and CO(2) capture and modifications.

Short-column CE coupled with inductively coupled plasma MS for high-throughput speciation analysis of chromium

A method was developed for high-throughput speciation analysis of chromium by on-line coupling of short-column capillary electrophoresis (SC-CE) and inductively coupled plasma mass spectrometry (ICP-MS). Baseline separation of Cr(III) and Cr(VI) was achieved within 1 min by SC-CE in a 15 cm x 75 microm id fused-silica capillary at 6 kV using 15 mM HNO(3) as running electrolyte. The precisions (RSD, n = 5) of migration time and peak area for Cr(III) and Cr(VI) were in the range of 1.8-2.4% and 2.2-5.7%, respectively. The limits of detection (3sigma) of Cr(III) and Cr(VI) were 1.8 and 1.9 microg/L, respectively. The synthesized samples containing Cr(III) and Cr(VI) species were determined by the developed SC-CE-ICP-MS hyphenated technique, and the recoveries of Cr(III) and Cr(VI) in the synthesized samples were in the range of 103-110% and 90-108%, respectively.

Application of pneumatic flow injection-tandem spectrometer system for chromium speciation

In this approach, a pneumatic flow injection-tandem spectrometer system, without a delivery pump, has been developed to study chromium speciation. In this system, suction force of pneumatic nebulizer of a flame atomic absorption spectrometer has been used for solution delivery through the manifold. Cr(VI) and total Cr concentrations were determined using UV-Vis and FAAS spectrometers, respectively. The Cr(III) was determined by difference. The calibration curves were linear up to 10 mug mL-1 and 20 mug mL-1 for Cr(VI) and total Cr with detection limit of 0.12 mug mL-1 and 0.07 mug mL-1 for Cr(VI) and Cr(III), respectively. The midrange precision and accuracy are less than 1.98% and +/- 2.50% for two species, respectively, at a sampling rate of 100 h-1. This system was applied for the determination of the chromium species in spiked and natural waters as well as industrial waters.

Confirmation of vanadium complex formation using electrospray mass spectrometry and determination of vanadium speciation by sample stacking capillary electrophoresis

Capillary zone electrophoresis (CZE) with UV detection was used to determine vanadium species. Nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) and 2,6-pyridinedicarboxylic acid (PDCA) were investigated to determine whether these ligands formed stable anionic complexes with vanadium. Of all the ligands studied HEDTA was the most suitable ligand because it gave the largest UV response with reasonable migration time. Electrospray mass spectrometry (ES-MS) was used to confirm the formation of [VO(2)(HEDTA)](2-) and [VO(HEDTA)](1-) in solution. An electrolyte containing 25 mM phosphate, 0.25 mM tetradecyltrimethylammonium bromide (TTAB) at pH 5.5 was optimum for the separation of these anionic vanadium complexes. Sample stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were tested to improve the sensitivity. Best sensitivity was obtained using FASI, with detection limits of 0.001 microM, equivalent to 0.4 microg L(-1), for [VO(2)(HEDTA)](2-) and 0.01 microM, equivalent to 3.4 microg L(-1) for [VO(HEDTA)](1-). The utility of the method for the speciation of V(IV) and V(V) was demonstrated using ground water samples.

Fermentation reactor coupled with capillary electrophoresis for on-line bioprocess monitoring

In this paper, a filter probe integrated into a computerized pneumatic sampler for capillary electroseparations was developed for an on-line monitoring of bioprocesses. The optimization of the performance of the coupled system was done by using a response surface modeling and three-level two-factor design. The resolution was found to be the most important parameter influencing the performance of an on-line analysis of the microbial metabolism. For the on-line analysis the migration time and detection limit were also found to be important parameters. Different parameters were combined by using an overall desirability function to find optimum conditions for all parameters. The equipment with an optimized separation protocol was used to monitor the bioaccumulation of Cu, Zn, Co and Cd (with detection limits 0.46, 0.37, 1.2, 0.84 mM correspondingly) by the Rhodococcus sp. bacteria isolated from the highly polluted technogenic soil of northeastern Estonia during a 2-week experiment.

Metal ion speciation and capillary electrophoresis: Application in the new millennium

Metal ions are essential for human beings at low concentrations but they are toxic or even carcinogenic at high concentrations. Many metallic ions are found in the environment in different species which are differentiated not only by their physicochemical forms but also by their diverse toxicities with respect to living organisms (speciation). CE has been used for metal ion speciation. The present review article describes the recent trends in metal ion speciation by CE. This article deals with the speciation of metal ions, optimization of the speciation (by independent and dependent variables), hyphenation of CE, validation of the methods, mechanisms of speciation, CE versus chromatography and conclusions.

Capillary electrophoresis hyphenated to inductively coupled plasma-sector field-mass spectrometry for the detection of chromium species after incubation of chromium in simulated sweat

The presence of chromium in chromium-tanned leather represents a considerable health problem since it can lead to chronic allergic contact dermatitis. Apart from trivalent chromium (Cr(III)), which is used for tanning, leather often contains hexavalent chromium (Cr(VI)), resulting from the oxidation of Cr(III) during the tanning process. This study deals with the chromium compounds in simulated sweat when brought into contact with Cr(III) or Cr(VI) and with chromium-tanned leathers. A capillary electrophoresis (CE) method was developed, with inductively coupled plasma-sector field-mass spectrometry (ICP-SF-MS) for element-specific detection. Two different electrophoretic runs, applying once the positive and once the negative polarity mode, were necessary for the detection of positively and negatively charged chromium species. Although sometimes described in the literature, a pre-run derivatization of the chromium-species was not performed here to prevent species transformation. 50 mmol.L(-1) sodium phosphate at a pH of 2.5 was used as CE separation buffer and as make-up liquid for the CE-ICP-SF-MS interface. When applied to simulated sweat samples incubated with Cr(VI), this method showed that methionine is responsible for the reduction of Cr(VI) into Cr(III), which, at its turn, forms a complex with lactic acid. In the case of sweat plus Cr(III), the latter step was also seen. Applied to simulated sweat in contact with leather samples, the method developed showed the presence of the former species among a much more complex pattern.

Interactions of Pb2+ with fulvic acid by electrophoretically mediated on-capillary microanalysis

Electrophoretically mediated microanalysis (EMMA) was used to monitor the on-column complexation of Pb2+ and fulvic acid (FA). Electropherograms revealed several characteristic regions, the areas of which correlate with the metal concentration. The analysis of the electropherograms suggests that at least two different complexes are formed. Therefore, the EMMA is a prospective technique for structural investigation of humic substances (HS).

Speciation of V, Cr and Fe by capillary electrophoresis–bandpass reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis-dynamic reaction cell inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the speciation of iron(III/II), vanadium(V/IV) and chromium(VI/III) is described. Two different CE migration modes were employed for separating the six metal ions using pre-capillary complexation. One is counter-electroosmotic mode in which iron(III/II) and vanadium(V/IV) ions were well separated using a 60 cm x 75 microm i.d. fused silica capillary. The voltage was set at +22 kV and a 15 mmol l(-1) tris(hydroxymethyl)aminomethane (Tris) buffer (pH 8.75) containing 0.5 mmol l(-1) ethylenediaminetetraacetic acid (EDTA) and 0.5 mmol l(-1) ortho-phenanthroline (phen) was used as the electrophoretic buffer. The other is co-electroosmotic mode in which chromium(VI/III) ions were well separated while the applied voltage was set at -22 kV and a 10 mmol l(-1) ammonium citrate buffer (pH 7.7) containing 0.5 mmol l(-1) diethylenetriaminepentaacetic acid (DTPA) and 0.01% polybrene was used as the electrophoretic buffer. The mass spectra were measured at m/z 51, 52 and 56 for V. Cr and Fe, respectively. The interfering polyatomic ions of 35Cl16O+, 40Ar12C+ and 40Ar16O+ on 51V+, 52Cr+ and 56Fe+ determination were reduced in intensity significantly by using NH3 as the reaction cell gas in the DRC. The detection limits were in the range of 0.1-0.5, 0.4-1.3 and 1.2-1.7 ng ml(-1) for V, Cr and Fe, respectively. Applications of the method for the speciation of V, Cr and Fe in wastewater were demonstrated. The recoveries were in the range of 92-120% for various species.

On-column complexation capillary electrophoretic separation of Fe2+ and Fe3+ using 2,6-pyridinedicarboxylic acid coupled with large-volume sample stacking

On-column complexation of Fe2+ and Fe3+ with 2,6-pyridinedicarboxylic acid (2,6-PDCA) formed anionic complexes, which were then separated by capillary zone electrophoresis with direct UV detection at 214 nm. To achieve reasonable separation selectivity and on-column complexation, the conditions such as pH, the concentration of 2,6-PCDA and the EOF modifiers in the electrolyte were examined. The electrolyte contained 5.0 mM 2,6-PDCA, 0.25 mM tetradecyltrimethlammonium bromide (TTAB) and 5% (v/v) acetonitrile at pH 4.0 was optimised for on-column complexation and the separation of Fe[PCDA]2(2-) and Fe[PCDA]2(-). To enhance the detection sensitivity, large-volume sample stacking (LVSS) was used for the on-line preconcentration of Fe[PCDA]2(2-) and Fe[PCDA]2(-). Under the optimised conditions, satisfactory working ranges (0.5-50 microM), lower detection limits (less than 0.1 microM) and good repeatability of the peak areas (R.S.D.: 5.2-7.8%, n = 5) was achieved using LVSS (300 s). With LVSS, the detection sensitivity was enhanced more than 50-fold compared to conventional hydrodynamic injection. The proposed method was used successfully for the determination of Fe2+ and Fe3+ in water samples.

Retention of Cr(III) by high-performance chelation ion chromatography interfaced to inductively-coupled plasma mass spectrometric detection with collision cell

High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(II) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei.

Speciation of chromium by in-capillary reaction and capillary electrophoresis with chemiluminescence detection

A sensitive method for the simultaneous determination of chromium(III) (Cr3+) and chromium(VI) (CrO4(2-)) using in-capillary reaction, capillary electrophoresis (CE) separation and chemiluminescence (CL) detection was developed. The chemiluminescence reaction was based on luminol oxidation by hydrogen peroxide in basic aqueous solution catalyzed by Cr3+ ion followed by capillary electrophoresis separation. Based on in-capillary reduction, chromium(VI) can be reduced by acidic sodium hydrogensulfite to form chromium(III) while the sample is running through the capillary. Before the electrophoresis procedure, the sample (Cr3+ and CrO4(2-)), buffer and acidic sodium hydrogensulfite solution segments were injected in that order into the capillary, followed by application of an appropriate running voltage between both ends. As both chromium species have opposite charges, Cr3+ ions migrate to the cathode, while CrO4(2-) ions, moving in the opposite direction toward the anode, react with acidic sodium hydrogensulfite which results in the formation of Cr3+ ions. Because of the migration time difference of both Cr3+ ions, Cr(III) and Cr(VI) could be separated. The running buffer was composed of 0.02 mol l(-1) acetate buffer (pH 4.7) with 1 x 10(-3) mol l(-1) EDTA. Parameters affecting CE-CL separation and detection, such as reductant (sodium hydrogensulfite) concentration, mixing mode of the analytes with CL reagent, CL reaction reagent pH and concentration, were optimized. The limits of detection (LODs) of Cr(III) and Cr(VI) were 6 x 10(-13) and 8 x 10(-12) mol l(-1) (S/N=3), respectively. The mass LODs for Cr(III) and Cr(VI) were 1.2 x 10(-20) mol (12 zmol) and 3.8 x 10(-19) mol (380 zmol), respectively.

Derivatization of inorganic ions in capillary electrophoresis

This review gives a short overview of the main approaches to the derivatization of inorganic ions in capillary electrophoresis (CE) with emphasis on the most recent works. Various derivatization procedures and detection methods are discussed. A brief account of their advantages and limitations is given. More specific areas such as microchip CE, simultaneous separation of anions and cations, and speciation analysis are also briefly discussed.

Elemental speciation analysis in capillary electrophoresis

The growing awareness of the strong development of the toxicity of heavy metals upon their chemical forms has led to an increasing interest in the qualitative and quantitative determination of specific metal species. Speciation has therefore become an important topic of present-day analytical research. The development in the elemental speciation analysis by capillary electrophoresis (CE) is reviewed. Various CE separation modes and detection techniques applied are discussed. A comprehensive description of reported methods to date in CE speciation analysis including metals, metalloids and nonmetallic elements is demonstrated. Some examples are presented to demonstrate CE's ability to solve real-world speciation analysis with emphasis on the applications in biological and environmental samples. Further, some issues concerning the limitations and the future of CE with regard to speciation studies are also discussed.

Capillary electrophoresis speciation of chromium in leather tanning liquor

We present a method for the speciation of chromium by capillary electrophoresis. Cr(III) was complexed with diethylenetriaminepentaacetic acid (DTPA) to form a negatively charged complex. Using 20 mM phosphate buffer of pH 8 containing 0.5 mM tetradecyltrimethylammonium hydroxide (TTAOH) at a separation voltage of -15 kV, both forms of chromium CrDTPA(2-) and CrO(4) (2-) were separated in less than 6 min. Direct UV detection at 214 nm was used. The effect of the presence of interfering ions was investigated. The application of the developed method to speciation of chromium in tanning liquor is demonstrated. The obtained results have shown a good correlation with those of flame atomic absorbance spectrometry (FAAS), inductively coupled plasma-mass spectrometry (ICP-MS) and UV/VIS spectrophotometry.

Determination of spore concentration in Bacillus thuringiensis through the analysis of dipicolinate by capillary zone electrophoresis

A new capillary zone electrophoresis (CZE) method for the analysis of dipicolinic acid, a specific component found in spores but not in vegetative cells, was used to determine spore concentration in Bacillus thuringiensis according to the relationship between the spore concentration and the content of dipicolinate. The quantitative relationship was established by using purified spores. Electrolyte conditions that affected the separation efficiency of dipicolinate and the reproducibility were investigated. With 10 mM phosphate, 10 mM ethylenediaminetetraacetic acid and 0.25 mM tetradecyltrimethylammonium bromide at pH 6.2 as the carrier electrolyte, dipicolinate can be determined within 8 min at an applied voltage of -25 kV (anode at detector) and a capillary temperature of 25 degrees C. The method has a high separation efficiency with which the number of theoretical plates is above 300,000 plates m(-1). The relative standard deviations for migration time and peak area are less than 0.5% and 2.0%, respectively. The detection limit for dipicolinate was 10 ng ml(-1), which corresponds to 7.2 x 10(5) spores ml(-1). The method was used to determine spores in fermentation broths, and the results obtained agreed well with the values obtained by plate counting.

On-column complexation of metal ions using 2,6-pyridinedicarboxylic acid and separation of their anionic complexes by capillary electrophoresis with direct UV detection

On-column complexation of metal ions with 2,6-pyridinedicarboxylate (2,6-PDC) to form anionic complexes enabled their separation by capillary zone electrophoresis with direct UV detection at 214 nm. Nine metal ions, Cu2+, Zn2+, Ni2+, Cd2+ Mn2+, Pb2+, Fe3+, Al3+ and Ca2+, were determined in less than 7 min using 10 mM 2.6-PDC solution containing 0.75 mM tetradecyltrimethylammonium bromide at pH 4.0. Satisfactory working ranges (20-300 microM), detection limits (3-10 microM) and good repeatability of the peak areas (RSD 2.1-4.2%, n=5) were obtained using hydrodynamic injection (30 s). The proposed method was used successfully for the determination of Mn2+, Fe3+, Al3+ and Ca2+ in groundwaters.