Simultaneous analysis of lead, mercury and selenium species by capillary electrophoresis with combined ethylenediaminetetraacetic acid complexation and field-amplified stacking injection

Detection and Separation of Inorganic Cations in Natural, Potable, and Wastewater Samples Using Capillary Zone Electrophoresis with Indirect UV Detection

Capillary zone electrophoresis (CZE) is a sensitive and rapid technique for determining traces of inorganic cations in water samples. CZE with indirect UV-diode array detection (CZE-DAD) was utilized to identify several inorganic cations in natural, potable, and wastewater samples. A pH 4.35 background electrolyte system was employed and consisted of 15 mM imidazole, 8 mM malonic acid, 2 mM 18-crown-6 ether as complexing agents, 10% v/v methanol as an organic modifier with indirect absorbance reference at 214 nm. The CZE method involved electromigration injection at 5 kV for 5 s, a separation voltage of 20 kV at 25°C, and a detection wavelength of 280 nm. Six main cations (ammonium NH4+, potassium K⁺, calcium Ca²⁺, sodium Na⁺, magnesium Mg²⁺, and lead Pb²⁺) were tested, and all but lead, were detected in the water samples at concentrations between 0.03 and 755 ppm with a detection limit ranging between 0.023 and 0.084 ppm. The successful evaluation of the proposed methodology allowed us to reliably detect and separate six metal ions in different water samples without any pretreatment. All water samples were collected from Northern New York towns and the Raquette River water system, the third longest river in New York State and the largest watershed of the central and western Adirondacks.

Real-time Assay of Toxic Lead in In Vivo Living Plant Tissue

A method of detecting lead was developed using square wave anodic stripping voltammetry (SWASV) with DNA-carbon nanotube paste electrode (CNTPE). The results indicated a sensitive oxidation peak current of lead on the DNA-CNTPE. The curves were obtained within a concentration range of 50 ngL(-1)-20 mgL(-1) with preconcentration time of 100, 200, and 400 sec at the concentration of mgL(-1), μgL(-1), and ngL(-1), respectively. The observed relative standard deviation was 0.101% (n = 12) in the lead concentration of 30.0 μgL(-1) under optimum conditions. The low detection limit (S/N) was pegged at 8 ngL(-1) (2.6 × 10(-8) M). Results showed that the developed method can be used in real-time assay in vivo without requiring any pretreatment and pharmaceutical samples, and food samples, as well as other materials requiring water source contamination analyses.

Direct fluorometric detection of paramagnetic and heavy metal ions at sub-amol level using an aromatic polyaminocarboxylate by CZE: Combination of pre- and on-capillary complexation technique

The low sensitivity of simple CZE for detecting metal ions is a long-standing problem even when an LIF detection system is employed. We have successfully achieved an ultrasensitive CE-LIF using a simple CZE mode (typical detection limit: 10(-11)-10(-10) mol/dm(3)). Both the design of a newly synthesized ligand and the combination of a precapillary derivatizing technique with an on-capillary ternary complexing technique have enabled us to achieve this extremely low LOD and high resolution of large metal complexes. The direct fluorescent detection of the paramagnetic metal ions was achieved for the first time despite their intrinsic fluorescent quenching nature. The fluorescent ligand (L) consists of a polyaminocarboxylate chelating moiety, a strongly emissive fluorescein moiety and a spacer connecting the two portions. The migration behavior of various metal-L complexes was investigated. The resolution among the complexes was improved by the introduction of a ternary complex equilibrium of the kinetically stable mother complexes with OH(-) ion. The analytical potential of our simple system was examined, and it was proved that the system was one of the most sensitive methods without the need for any preconcentration process.

Sensitive capillary electrophoretic determination of mercury species with amperometric detection at a copper electrode after cation exchange preconcentration

A capillary electrophoretic method for the separation of four mercury species with amperometric detection was developed. Inorganic Hg2+, methyl-, ethyl-, and phenyl-mercury were complexed with L-cysteine and separated in a counterelectroosmotic mode in an electrolyte solution comprised of 20 mM sodium tetraborate at pH 9.5. Amperometric detection of separated species was achieved at passivated copper electrode under electrocatalytic oxidation conditions. The four mercury species were separated in less than 8 min with LODs ranging from 170 to 450 microg/L. Cation exchange preconcentration was used to decrease the LODs down to 1.7 microg/L.

Mercury speciation by CE: A review

CE methods for the speciation of inorganic and organomercury compounds are reviewed. Sample preparation, separation conditions and detection modes are discussed. Efficient separation and sensitive determination of mercury species by CE typically involves complexation with various thiols, chromogenic and other chelating agents; however, some methods do not require complexation. Spectrophotometric detection based on UV-visible absorption is by far the most commonly used. Hyphenated techniques, such as CE/inductively coupled plasma (ICP)-MS, hydride generation coupled to ICP-MS or atomic fluorescence spectrometry and CE/atomic absorption spectrometry are gaining popularity due to their high sensitivity and selectivity. Last, but not least, the potential and applications of electrochemical methods for detection of separated mercury species are outlined.

Highly sensitive determination of lanthanides by capillary electrophoresis with direct visible detection after precapillary complexation with aromatic polyaminocarboxylate and additionally applying dynamic ternary complexation with nitrilotriacetic acid

A newly synthesized aromatic polyaminocarboxylate (NBD-ABEDTA, H(4)L) was applied to precapillary derivatizing capillary electrophoresis as a chelating reagent for lanthanide ions (Ln(3+)). The Ln-L complexes provide both kinetic stability on dissociation due to their methyl-EDTA coordinating structure, and high light absorptivity (epsilon(max) = 2.4 x 10(4) cm(-1) mol(-1) dm(3)) in the visible region at 469 nm thanks to their nitrobenzofurazan moiety. A ligand was employed for capillary zone electrophoresis based on a unique concept: both precapillary and dynamic on-capillary complexation were carried out on one center-metal ion to achieve high resolution. As a ternary complex-formation agent, iminodiacetate (IDA), bound to the mother complex (Ln-L), was added to the carrier buffer solution. The carrier buffer solution of 9.5 mmol.dm(-3) (pH 9.45) borate and 33.5 mmol.dm(-3) IDA, drastically improved the resolution among Ln(3+) ions. Each of the Ln complexes was effectively separated, except for Pr-Sm. Furthermore, the absence of L from the carrier solution, which stabilizes the baseline fluctuation, provided low LOD (typically 4.2 x 10(-7) mol.dm(-3)). This strongly suggests that Ln-L complexes are kinetically stable even with a large excess of IDA. Quite unexpectedly, the order of migration differs from that of the atomic number, inverting at Nd. This is due to the effect of the cavity size of the residual coordination sites on the ternary complexation and the electronic density of Ln(3+).

Determination of Pb(II), Cu(II) and Fe(III) with Capillary Electrophoresis Using Ethylenediaminetetraacetic Acid as a Complexing Agent and Vancomycin as a Complex Selector

The simultaneous determination of metal ions using ethylenediaminetetraacetic acid (EDTA) as a complexing agent and vancomycin as a complex selector was successfully studied by capillary electrophoresis with the U-shaped cell. The partial filling method (counter current mode) was used in order to gain selectivity of the separation, and also to increase the detection sensitivity. The effect of the vancomycin concentration on the separation behavior of free EDTA and metal products, and the effect of the EDTA concentration on the stability of metal-EDTA products were considered. Under the optimal condition, the reproducibilities (RSD) of the migration time and the peak area were less than 3.39% and 9.61%, respectively. With the high sensitivity of the method, Pb(II), Cu(II) and Fe(III) in tap water were successfully determined, and the recoveries were 99 - 105%. The concentrations of these metal ions found in tap water did not exceed the maximum allowed concentrations regulated by the U.S. Environmental Protection Agency.

Full-capillary sample stacking/sweeping-MEKC for the separation of naphthalene-2,3-dicarboxaldehyde-derivatized tryptophan and isoleucine

In an attempt to improve the sensitivity of detection in capillary electrophoresis (CE), a novel online sample-concentration method, full-capillary sample stacking (FCSS)/sweeping-micellar electrokinetic chromatography (sweeping-MEKC) mode, is proposed. Naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized tryptophan and isoleucine were selected as model compounds. In the initial step, the weakly acidic compounds, dissolved in a low-conductivity buffer (35.1 microS/cm; apparent ph (pH*) in a mixed solution of acetonitrile/methanol/water, 4.6), fill the entire capillary, two vials of a high-conductivity buffer (2.06 mS/cm; pH* 2.0) are placed on each end, and a negative polarity is then applied. Under these conditions, the direction of the electroosmotic flow (EOF) is toward the inlet. Meanwhile, the anionic analytes move in the reverse direction and are neutralized and stacked at the boundary of a dynamic pH-junction (between the sample matrix and the nonmicellar background solution (BGS)). When the sample concentration is completed, the BGS is quickly changed to solutions containing SDS-BGS for the subsequent separation. Since the mobility of SDS-analytes is then greater than the EOF, the following steps occur by the sweeping (for focusing) and MEKC (for separation) mode. Using these steps, a full-capillary sample injection/separation can be achieved.

On-line sample concentration techniques in capillary electrophoresis: velocity gradient techniques and sample concentration techniques for biomolecules

Methods with a high sensitivity and high separation efficiency are goals in analytical separation techniques. On-line sample concentration techniques in capillary electrophoresis (CE) separations have rapidly grown in popularity over the past few years because they achieve this goal. This review describes the methodology and theory associated with a number of different techniques, including electrokinetic and chromatographic methods. For small molecules, several on-line concentration methods based on velocity gradient techniques are described, in which the electrophoretic velocities of the analyte molecules are manipulated by field amplification, sweeping, and isotachophoretic migration, resulting in the on-line concentration of the analyte zones. In addition, the on-line concentration methods for macromolecules are described, since the techniques used for macromolecules (DNAs and proteins), are different from those for small molecules, with respect to either mechanism or methodology. Recent studies relating to this topic are also discussed, including electrophoretic and chromatographic techniques on capillary or microchip.

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.

Recent advances in capillary electrophoresis and capillary electrochromatography of pollutants

An overview of major developments in capillary electrophoresis and capillary electrochromatography systems in the environmental field is presented, covering relevant publications between the second half of 1999 and early 2001. Contributions are reviewed in relation to developments in detection, sample preparation/preconcentration, precision and applications. Many interesting examples are shown and the influence of important parameters on the performance of developed methods is discussed.

Determination of trace metals by capillary electrophoresis

A new analytical procedure is developed using a strong complexing agent, 1,10-phenanthroline (Phen), for direct UV detection of Zn, Mn, Cu, Co, Cd, and Fe at microg/L concentrations in environmental water samples. The metal chelates formed showed different electrophoretic mobilities and solved the comigration problem for capillary electrophoresis (CE) separation of free metal ions. To obtain stable metal-Phen chelates during the capillary zone electrophoresis (CZE) run, both pre-column and on-column complexation are required and threefold excess of Phen over metal ions should be added to the sample. The optimized background electrolyte (BGE) consists of 30 mM hydroxylamine hydrochloride and 0.1% methanol at pH 3.6. Under hydrodynamic sampling, CE run at + 20 kV in 65 cm x 0.05 mm ID fused-silica column with detection at 265 nm, baseline separation, satisfactory working ranges (10 microg/L to 5.5 mg/L), sensitive detection limits (1-3 microg/L), good repeatability for migration times (relative standard deviation, RSD 0.36-0.81%, n = 5), peak area (RSD 3.2-4.2%, n = 5) and peak height (RSD 3.2-4.5%, n = 5) were obtained for the metal cations investigated. The reliability of the method was established by parallel determination using the inductively coupled plasma-atomic emission spectrometry (ICP-AES) method giving results within statistical variation. The procedure developed is shown to provide a quick, sensitive, precise, and economic method for simultaneous determination of metal cations that can form stable chelates with Phen.