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.     

Separation and sweeping of metal ions with EDTA in CZE-ESI-MS

Ethylenediaminetetraacetic acid (EDTA) in the background electrolyte (BGE) of capillary zone electrophoresis coupled to an electrospray ionization mass spectrometer is presented as an approach for the determination of metal ions. Significant signals for the metal-ligand complexes were observed even when EDTA was continually eluted from the capillary during the entire electrophoretic run. The signal-to-noise ratio was improved by the addition of ammonia to the sheath liquid and by using an acquisition m/z range above the m/z of EDTA. The LODs for the test metal ions (i.e. calcium(II), manganese(II), and zinc(II)) with conventional injection were around 1-2 mg/L with corrected peak areas that are linear from 8 to 100 mg/L. The presence of EDTA in the BGE was critical not only for the separation but also for sweeping via complexation as an on-line sample concentration technique. The peak height of the test metal ions was improved at least tenfold with sweeping via EDTA complexation and yielded LODs in the μg/L range.     

Solid-phase extraction and subsequent capillary zone electrophoresis of trace metal ions as soluble dithiocarbamate complexes

Summary Modest detectability in capillary electrophoresis is often a challenge for the determination of trace-level metal ions. This limitation has been addressed by the development of an enrichment procedure combining the formation of metal bis(carboxymethyl)dithiocarbamate complexes, water soluble at basic pH and sparingly soluble in an acidic environment, and solidphase extraction. Appropriate conditions were developed for a solid-phase extraction step well compatible with subsequent capillary electrophoretic separation in terms of the composition of electrophoresis and eluting buffers. At pH below 4 when the ligand carboxyl groups are non-ionized, metal ion complexes have no apparent charge and are efficiently retained on a conventional C₁₆ cartridge. Application of a basic eluent, a borate buffer at pH9, causes the complexes to be ionized and eluted rapidly and quantitatively. Parameters affecting the retention/recovery behavior, such as the pH and ligand concentration of the loading solution, flow-rate, eluting buffer pH and concentration, etc, were examined to attain the best possible enrichment factors for trace metal ions. As a result, an increase in sensitivity over two orders of magnitude was gained that permitted lowering the detection limits for copper(II), lead(II), cadmium(II), nickel(II), and mercury(II) down to a low-μg L⁻¹ level.     

On-column complexation and simultaneous separation of vanadium(IV) and vanadium(V) by capillary electrophoresis with direct UV detection

An on-column complexation method has been developed for the simultaneous determination of V(IV) and V(V). Vanadium species were chelated with aminopolycarboxylic acids to form anionic complexes which were separated by capillary zone electrophoresis (CZE) with direct UV detection. Ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetric acid (DTPA), nitrilotriacetic acid (NTA), and N-2-hydroxyethylethlendiaminetriacetric acid (HEDTA) were investigated as both ligand and running electrolyte. Of the ligands studied the complexes of EDTA with V(IV) and V(V) resulted in the highest selectivity and UV response.The conditions used for on-column complexation and separation, including pH, and electrolyte ligand concentration, were examined to achieve reasonable separation selectivity and detection sensitivity. The optimum separation of the anionic forms of V(IV) and V(V) was obtained by use of CZE with UV detection at 185 nm and an electrolyte containing 5 mmol L(-1) EDTA at pH 4.0. Linear calibration plots were obtained in the concentration range10-300 micro mol L(-1); detection limits were 3 micro mol L(-1) for V(IV) and 1 micro mol L(-1) for V(V). The proposed method was demonstrated for the determination of vanadium in groundwater spiked with V(IV) and V(V).     

Investigation of Mixed Chiral Selectors of Different Metal Ion-L-Alanine Complex and β-Cyclodextrin on the Chiral Separation of Dansyl Amino Acids with Capillary Electrophoresis

Chiral separation of dausyl amino acids by capillary electrophoresis using mixed selectors of Mn(ll)-L-alanine complex and β-cyclodextrin (β-CD) was studied. Resolution was considerably superior to that obtained by using either Mn (Ⅱ)-L-alanine complex or β-CD alone. The effects of separation parameters, such as pH value of buffer solution, capillary temperature, the concentration of Mn (Ⅱ)-L-alanine complex, the types of CD and ligand on the migration times and resolutions were investigated. Six different transition metal complexes,Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Hg(Ⅱ) and Cd(Ⅱ)-L-alanine complexes have been employed and compared with Mn(Ⅱ)complex. Differences in retention and selectivity were found.The substitution of Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ) and Ni(Ⅱ) for Mn(Ⅱ) resulted in a better chiral resolution while Hg(Ⅱ) and Cd(Ⅱ) showed poorer resolution abilities. The chiral separation mechanism was also discussed briefly.     

All Solid State Nickel(II)‐Selective Potentiometric Sensor Based on an Upper Rim Substituted Calixarene

A new ionophore, i.e. p‐(2‐thiazolazo)calix[4]arene ( I ) has been explored for its selective behavior towards Ni(II) ions. A poly(vinyl chloride) based membrane containing ( I ) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and nitrophenyloctyl ether in the ratio 10 : 100 : 3 : 150 (I:PVC:NaTPB:NPOE) (w/w) was used to fabricate an all solid state nickel(II)‐selective sensor. The developed sensor exhibited a working concentration range of 1.0×10^?6–1.0×10^?1 M, with a Nernstian slope of 28.9±1.0 mV/decade of activity and a response time of 10–15 s. This sensor shows a detection limit of 9.0×10^?7 M. Its potential response remains unaffected of pH in the range 3.0–7.6, and the cell assembly could be used successfully in partially nonaqueous medium (up to 10 % v/v) without any significant change in the slope value or the working concentration range. The sensor worked satisfactorily for about ten weeks and exhibited excellent selectivity over a number of mono‐, bi‐, and tri‐valent cations including alkali, alkaline earth metal, and transition metal ions. It could be used as an indicator electrode for the end point determination in the potentiometric titration of nickel ions against ethylenediaminetetraacetic acid (EDTA) as well as for the determination of nickel ion concentration in real samples.     

Confirmation of iron complex formation using electrospray ionization mass spectrometry (ESI-MS) and sample stacking for analysis of iron polycarboxylate speciation by capillary electrophoresis

The use of capillary electrophoresis (CE) and UV detection for the determination of metal speciation is based on the standards via matching migration time. Consequently, it requires that the metal species are stable during electrophoresis. Migration time of the metal species is dependent on the electrolyte composition. However, the stability for such metal complexes is also dependent on electrolyte composition and electrolyte-specific stability is not always well known. In this paper, the stability of iron (Fe) polycarboxylate complex formation was determined using electrospray ionization mass spectrometry (ESI-MS). Mass spectra indicates that Fe[DTPA]²⁻, Fe[EDTA]⁻, Fe[HEDTA] and Fe[NTA] were present in solution but the mass spectrum for Fe[NTA] was found to be weak. An electrolyte containing 25 mM NaH₂PO₄ and 0.25 mM tetradecyltrimethylammonium bromide (TTAB) at pH 6.0 was used to successfully separate Fe[DTPA]²⁻, Fe[EDTA]¹⁻ and Fe[HEDTA]. The instability of Fe[NTA] meant it was not observed due to its instability during electrophoresis. To improve UV detection limits sample stacking techniques, such as large volume sample stacking (LVSS) without polarity switching and filed-amplified sample injection (FASI), were investigated. The results show that less than 0.01 μM detection limits for the Fe complexes were obtained using FASI. The calibration plots were linear from 0.05-3.0 with good reproducibility (peak area: 6.5-8.1%) when a water plug was used. Finally, the proposed method was demonstrated for the determination of trace Fe complexes in river waters.     

Analysis of metacycline by capillary electrophoresis

The development and validation of an optimized capillary electrophoresis method for the determination of metacycline in the presence of its related substances by capillary electrophoresis is shown. The influence of methanol as organic modifier, buffer pH, buffer concentration, capillary length, column temperature, Triton X-100 and methyl-beta-cyclodextrin was investigated. A central composite design was performed in order to optimize the method. The optimal separation conditions were: uncoated fused-silica capillary (39 cm total length, 31 cm effective length, 50 microm ID); as background electrolyte a solution of 160 mM sodium carbonate and 1 mM EDTA (pH 10.35)/methanol (89:13 v/v); temperature, 15 degrees C; voltage, 12 kV. The method showed good selectivity, repeatability, linearity, and sensitivity. The limits of detection and quantitation are 0.024% and 0.06%, respectively, relative to a 2.5 mg/mL solution. Six commercial samples were analyzed quantitatively.     

Fast enantiomeric separation with vancomycin as chiral additive by co-electroosmotic flow capillary electrophoresis: increase of the detection sensitivity by the partial filling technique

A fast and sensitive method is described by using vancomycin as a chiral additive for enantiomeric separation by capillary electrophoresis (CE). In order to overcome disadvantages associated with use of vancomycin as chiral additive in CE, several strategies including the dynamic coating technique, the co-electroosmotic flow technique, and the partial filling technique were employed sequentially in this method. Using the polycationic polymer hexadimethrine bromide (HDB) as a buffer additive, the capillary wall was dynamically coated with a thin film formed by the adsorbed HDB. Consequently, the adsorption of vancomycin onto the capillary wall was minimized via electrostatic repulsion between the coating of the capillary wall and the vancomycin molecule. In addition, the reversed electroosmotic flow (from cathode to anode) produced by the positively charged capillary wall migrates in the same direction of negatively charged analytes (co-electroosmotic flow electrophoresis). Thereby the electrophoretic mobility of negatively charged analytes were drastically accelerated leading to a short separation time of less than 3.4 min. The separation time was further reduced by the use of a short-end-injection technique. For example, the analysis time was achieved by as short as 55 s for a baseline separation of dansyl-alpha-amino-n-butyric acid. Concurrently, the partial filling technique was used to avoid the loss of detection sensitivity caused by the presence of vancomycin in the running buffer. The effect of several parameters, such as HDB concentration, buffer pH, plug length of the chiral selector, concentration of the chiral selector and applied voltage, on enantioselectivity were investigated toward optimization. Besides the advantage of a very short separation time, the method is characterized by high detection sensitivity, high selectivity, and high efficiency.     

Metal ion capillary zone electrophoresis with direct UV detection: Separation of metal cyanide complexes

Mixtures of cyanide complexes of iron(III), copper(I), iron(II), nickel(II), chromium(III), mercury(II), palladium(II), silver(I), cadmium(II), zinc(II), cobalt(II), and cobalt(III) have been separated by capillary zone electrophoresis using a fused silica capillary and 20 mM phosphate buffers containing 1–2 mM sodium cyanide. The complexes were detected by direct UV absorpticn at 214 nm; detection limits are in the mid ppb range for all metals except cadmium and zinc. The different detectability of various metal cyanide complexes enables the application of the method to the analysis of complex matrices such as cyanide plating bath solutions.     

Complexometric determination of palladium(II) using thioacetamide as a selective masking agent

A simple, rapid and accurate complexometric method for the determination of palladium(II) is proposed, based on the selective masking property of thioacetamide towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-5.5 (acetic acid-sodium acetate buffer) with standard lead nitrate solution using xylenol orange as indicator. An excess of a 0.5% aqueous solution of thioacetamide is then added to displace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard lead nitrate solution as before. Reproducible and accurate results are obtained in the concentration range 0.5 mg - 17.80 mg of palladium with relative error of +/- 0.16% and coefficient of variation not exceeding 0.26%. The effect of diverse ions is studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixtures.     

Highly Selective and Sensitive Copper(II) Membrane Sensors Based on 6‐Methyl‐4‐(1‐phenylmethylidene)amino‐3‐thioxo‐1,2,4‐triazin‐5‐one as a New Neutral Ionophore

A new Cu(II) ion‐selective PVC membrane sensor based on 6‐methyl‐4‐(1‐phenylmethylidene)amino‐3‐thioxo‐1,2,4‐triazin‐5‐one (MATTO) as an excellent sensing material was developed. The electrode exhibits a Nernstian slope of 29.2±0.4 mV per decade over a very wide concentration range between 1.0×10^?1 and 1.0×10^?6 M, with a detection limit of 4.8×10^?7 M (30.5 ng/mL). The sensor possesses the advantages of short conditioning time, fast response time (<10 s), and especially, very good selectivity towards transition and heavy metal, and some mono, di and trivalent cations. The proposed electrode was successfully applied to the determination of copper in wastewater of copper electroplating samples and as an indicator electrode in potentiometric titration of Cu(II) ions with EDTA.     

Surfactant‐assisted dispersive liquid–liquid microextraction combined with field‐amplified sample stacking in capillary electrophoresis for the determination of mexiletine and lidocaine

A sensitive method for the determination of mexiletine and lidocaine using surfactant‐assisted dispersive liquid–liquid microextraction coupled with capillary electrophoresis was developed. Triton X‐100 and dichloromethane were used as the dispersive agent and extraction solvent, respectively. After the extraction, mexiletine and lidocaine were analyzed using capillary electrophoresis with ultraviolet detection. The detection sensitivity was further enhanced through the use of field‐amplified sample stacking. Under optimal extraction and stacking conditions, the calibration curves were linear over a concentration range of 0.05–1.00 μM for mexiletine and 0.03–1.00 μM for lidocaine. The limits of detection (signal‐to‐noise ratio of 3) were 0.01 and 0.01 μM for mexiletine and lidocaine, respectively. An approximately 1141‐ to 1250‐fold improvement in sensitivity was observed for the two analytes compared with the injection of a standard solution without the surfactant‐assisted dispersive liquid–liquid microextraction and field‐amplified sample stacking procedures. This developed method was successfully applied to the determination of mexiletine and lidocaine in human urine and serum samples. Both precision and accuracy for urine and serum samples were less than 8.7 and 6.7%, respectively. The recoveries of the two analytes from urine and serum samples were 54.7–64.9% and 16.1–56.5%, respectively.     

Original paper application of cyclodextrins as modifiers in electrophoretic separation of metalloporphyrins

Several metallocomplexes of tetrakis-carboxyphenylporphyrin (TCPP) were separated on fused-silica capillary using CZE with UV-VIS detection. Metalloporphyrins of Co(II), Cu(II), Mn(II), Ni(II), and Zn(II) were formed directly in TCPP solution with addition of Cd(II) to increase the formation reaction rate. The composition of BGE, its concentration, and pH were optimized to ensure the stability of complexes and proper resolution. In particular, the problem of signals' shape was investigated and discussed. The presence of beta-CD in borate buffer significantly improved separation efficiency and signal shapes due to formation of inclusion complexes. Under the best separation conditions (50 mM borate running buffer at pH 9 with addition of 2 mM beta-CD, 30 kV applied voltage) a separation of metal complexes with TCPP was accomplished in 16 min.     

Quantitative complexometric determination of mercury(II) in synthetic alloys and complexes using 2-thiazolinethiol as a masking agent

A simple, rapid and selective complexometric method is proposed for the determination of mercury(II). Mercury(II) and other related metal ions are first complexed with an excess of EDTA and the surplus EDTA is back-titrated with a standard lead nitrate solution at pH 5.0–6.0 (hexamine buffer) using xylenol orange as an indicator. A 0.2% solution of 2-thiazolinethiol in acetone is then added to displace EDTA from the Hg(II)-EDTA complex. The released EDTA is titrated with a standard lead nitrate solution as before. Reproducible and accurate results are obtained in the range of 0.8 g l^?1?15.8 g l^?1 of mercury with a relative error less than ±0.25% and a coefficient of variation (n = 6) not higher than 0.28%. The interference of various ions was studied and the method was employed for the analysis of mercury in its synthetic alloy mixtures and in complexes.     

Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detection

The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel combined with a 500 nL sample injection channel) and a pair of on‐chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in beer was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (3.8), implemented by aspartic acid and bis‐tris propane, provided an adequate selectivity in the separation of oxalate from anionic beer constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 0.5 μmol/L concentration also in samples containing chloride (a major anionic constituent of beer) at a 1800 higher concentration. Such a favorable analyte/matrix concentration ratio made possible accurate and reproducible [typically, 2–5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample] determination of oxalate in 500 nL volumes of 20–50‐fold diluted beer samples. Short analysis times (about 200 s), minimum sample preparation, and reproducible migration times of this analyte (0.5–1.0% RSD values) were characteristic for ZE on the chip.     

Dual-cloud point extraction as a preconcentration and clean-up technique for capillary electrophoresis speciation analysis of mercury

A novel dual-cloud point extraction (dCPE) technique is proposed in this paper for the sample pretreatment of capillary electrophoresis (CE) speciation analysis of mercury. In dCPE, cloud point was carried out twice in a sample pretreatment. First, four mercury species, methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) formed hydrophobic complexes with 1-(2-pyridylazo)-2-naphthol (PAN). After heating and centrifuging, the complexes were extracted into the formed Triton X-114 surfactant-rich phase. Instead of the direct injection or analysis, the surfactant-rich phase containing the four Hg species was treated with 150 microL 0.1% (m/v) l-cysteine aqueous solution. The four Hg species were then transferred back into aqueous phase by forming hydrophilic Hg-l-cysteine complexes. After dCPE, the aqueous phase containing the Hg-l-cysteine complexes was subjected into electrophoretic capillary for mercury speciation analysis. Because the concentration of Triton X-114 in the extract after dCPE was only around critical micelle concentration, the adsorption of surfactant on the capillary wall and its possible influence on the sample injection and separation in traditional CPE were eliminated. Plus, the hydrophobic interfering species were removed thoroughly by using dCPE resulted in significant improvement in analysis selectivity. Using 10 mL sample, 17, 15, 45, and 52 of preconcentration factors for EtHg, MeHg, PhHg, and Hg(II) were obtained. With CE separation and on-line UV detection, the detection limits were 45.2, 47.5, 4.1, and 10.0 microg L(-1) (as Hg) for EtHg, MeHg, PhHg, and Hg(II), respectively. As an analysis method, the present dCPE-CE with UV detection obtained similar detection limits as of some CE-inductively coupled plasma mass spectrometry (ICPMS) hyphenation technique, but with simple instrumental setup and obviously low costs. Its utilization for Hg speciation was validated by the analysis of the spiked natural water and tilapia muscle samples.     

Separation and Determination of Stereoisomeric Impurity of Folinic Acid Diastereomers by CE with Vancomycin as a Selector

A highly sensitive and rapid method was developed that involves capillary electrophoresis for separation and determination of the stereoisomeric impurity of folinic acid diastereomers. In this method, vancomycin was used as the chiral selector, and a solution of poly(dimethylacrylamide) (PDMA) was prepared for dynamic coating of the capillary wall to minimize the adsorption of vancomycin. This method was optimized for six factors including concentrations of the organic modifier and vancomycin, pH and concentration of the background electrolyte, column temperature, and separation voltage. The following conditions were established: 100 mM Tris-phosphate buffer (pH 6.0) containing 1.0 mM vancomycin and 5 % acetonitrile at 30 °C, and −15 kV applied voltage on the PDMA dynamically coated capillary. Preliminary validation was performed with the determination of limit of quantification and detection, accuracy, precision, and linearity. Under our optimized method, the folinic acid diastereomers were baseline-separated within 7.5 min, and a (6S,2′S)-calcium folinate sample with 0.08 % stereoisomeric impurity was determined.

     

Baeyer‐Villiger oxidation of cyclopentanone over zeolite Y entrapped transition metal‐Schiff base complexes

Transition metal [M = VO (IV) and/or Cu (II)] complexes with Schiff base ligand, (Z)‐2‐((2‐hydroxybenzylideneamino)phenol (H₂L) have been entrapped in the super cages of zeolite‐Y by Flexible Ligand Method. Synthesized materials have been characterized by preferential physico‐chemical techniques such as inductively coupled plasma optical emission spectroscopy (ICP‐OES), elemental analyses (CHN), fourier transmission infrared spectroscopy (FTIR), electronic and UV‐reflectance spectra, Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron micrographs (SEMs), X‐ray diffraction patterns (XRD) and thermogravimetric analysis (TGA). The catalytic competence of zeolite‐Y entrapped transition metal complexes was examined in Baeyer‐Villiger (BV) oxidation of cyclopentanone using 30% H₂O₂ as an oxidant beside neat complexes to check the aptitude of heterogeneous catalysis over the homogeneous system. The effect of experimental variables such as mole ratio of substrate to an oxidant, amount of catalyst, reaction time, varying oxidants and solvents on the conversion of cyclopentanone was also tested. Under the optimized reaction conditions, one of the zeolite‐Y entrapped transition metal complex viz. [VO(L)H₂O]‐Y [where L = (Z)‐2‐((2‐hydroxybenzylideneamino)phenol] was found to be a potential contender by providing 80.22% conversion of cyclopentanone (TON: 10479.42), and the selectivity towards δ‐valerolactone was 83.56%.     

Metal ion capillary zone electrophoresis with direct UV detection: determination of transition metals using an 8-hydroxyquinoline- 5-sulphonic acid chelating system

The application of capillary zone electrophoresis to the separation and determination of metal ions after the precolumn formation of negatively charged chelates is described. Multi-component mixtures of transition metal complexes with 8-hydroxyquinoline-5-sulphonic acid (HQS) were separated in about 10 min in a fused-silica capillary column with a borate buffer of pH 9.2 at an applied voltage of 15 kV followed by direct UV detection. The capillary pretreatment with an electroosmotic flow modifier, namely a tetraalkylammonium salt, is necessary to achieve resonable migration times of these metal complexes. Incorporating the chelating reagent in the electrophoretic buffer markedly improves the detectability of relatively unstable chelates, such as those of Co(II), Zn(II) and Cd(II), and allows the separation of metal ions that form unstable HQS chelates, such as Mn(II) and alkaline earth metals. The effects of electrophoretic buffer parameters affecting the complexation reaction and migration behaviour are discussed. Linearity of calibration graphs is observed for about three orders of magnitude with sub-ppm detection limits. The applicability of the method to the analysis of real samples is demonstrated.