Simultaneous ion-pair chromatography of inorganic anions and cations using on-column derivatization with chelating agents and UV detection

Six complexones have been investigated as on-column derivatizing agents for the simultaneous separation of inorganic anions and cations using ion pair chromatography. UV spectrophotometry at 210 nm has been applied for both the direct and the indirect detection of anions and anionic metal complexes. Under the experimental conditions used DCTA and DTPA have been practically applicable. Factors affecting the chromatographic behaviour of analyte ions have been studied. Chloride, nitrite, nitrate sulphate, chromate, molybdate, iron, chromium (III), copper (II), cobalt (II), nickel (II) and mercury (II) ions have been separated in 30 min with a mobile phase containing 1 mmol/1 TBA and 0.5 mmol/1 DCTA at pH 6.2 in acetonitrile-water (10:90 v/v). With DTPA as eluent and using pre-column derivatization of metal cations with DCTA eight anions and six metal cations can be separated. The detection limits are less than 0.1 mg/l for most of the investigated ions. Permanent address: Department of Analytical Chemistry, Vilnius University, Naugarduko 24, 2006 Vilnius, Lithuania     

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.     

Determination of zinc diethyldithiocarbamate released into artificial sweat from natural rubber latex vulcanizates by HPLC

A simple high-performance liquid chromatography method is adopted in order to quantitate the amount of zinc diethyldithiocarbamate (ZDEC) released into artificial sweat from natural rubber latex vulcanizates. The artificial sweat is extracted with dichloromethane, and the residue is recovered and re-dissolved in a known quantity of dichloromethane. ZDEC is quantitated as its copper complex by reacting with copper(II) sulphate. A reversed-phase C18 column and detection wavelength of 435 nm are used to measure the copper-dithiocarbamate complex. The procedure is repeated with cobalt(II) chloride, and the amount of ZDEC obtained by both the methods is compared. It is found that the recovery of ZDEC from the artificial sweat is high when copper(II) sulphate is used, indicating that the copper(II) sulphate is a better complexing agent than cobalt(II) chloride under the conditions used in the present study. The limits of detection and the quantitation of ZDEC are found to be 0.25 and 0.86 microg/mL, respectively. The present method, based on precolumn derivatization using copper(II) sulphate, facilitates the quantitation of ZDEC in latex products.     

Determination of cobalt(II), copper(II) and iron(II) by ion chromatography with chemiluminescence detection

An optimized flow-injection manifold for the chemiluminescence determination of cobalt(II), copper(II), iron(II) and chromium(III) by their catalytic effect on the luminol reaction is described. Detection limits are 0.0006, 0.08, 0.3 and 0.1 ng ml^?1, respectively. The suppression effect of several carboxylic acids on the emission intensity is discussed. A procedure for the separation of cobalt(II), copper(II) and iron(II) on a low-capacity, silica-based cation-exchange column, using 5 mM oxalic acid at pH 4.2 as the mobile phase and post-column detection via the luminol reaction, is also described. Detection limits for cobalt(II) and copper(II) are 0.01 and 5 ng ml^?1, respectively.     

Separation and detection of common mono- and divalent cations by ion chromatography with an ODS column and conductivity/UV detection

The retention and detection behavior of common mono- and divalent cations (M⁺, alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and ammonium ions (NH₄⁺); M²⁺, alkaline earth metal ions (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) was examined using an ODS column (150×4.6 mm I.D.) and conductivity (CD)/UV detection. The results obtained were as follows: (1) for M⁺, the mobile phase, 0.1 mM sodium dodecyl sulphate (SDS)+10 mM HNO₃ and indirect CD detection were effective. (2) Addition of Ce(III) in the mobile phase accelerated the elution of both M⁺ and M²⁺. The separation of above 10 cations on an ODS column was achieved for the first time without any coelution of cations and disturbance by system peak. Addition of higher SDS resulted in good separation of M⁺ and M²⁺ with longer retention times. CD detection was possible for M⁺ and M²⁺ and UV detection for M²⁺. (3) For M²⁺, the mobile phase, 0.8 mM Ce(III)+0.1 mM SDS+1 mM HNO₃ and indirect UV detection were effective. The IC methods were applied to real samples.     

Indirect ultraviolet spectrophotometric detection in the ion chromatography of common mono- and divalent cations on an aluminium adsorbing silica gel column with tyramine-containing crown ethers as eluent

The application of laboratory-made aluminium-adsorbing silica gel (Al-Silica) as a cation-exchange stationary phase to ion chromatography-indirect photometric detection (IC-IPD) for common mono- and divalent cations (Li+, Na+, NH+, K+, Mg2+ and Ca2+) was carried out by using protonated tyramine (4-aminoethylphenol) as eluent ion. When using 1.2 mM tyramine-0.2 mM oxalic acid at pH 4.5 as eluent, incomplete separation of the monovalent cations and complete separation of the divalent cations were achieved in 17 min. Then, the addition of crown ethers in the eluent was carried out for the complete separation of the mono- and divalent cations. As a result, when using 1.2 mM tyramine--0.2 mM oxalic acid at pH 4.5 containing either 5 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) or 0.5 mM and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) as eluent, excellently simultaneous separation of these cations was achieved in 21 min. The proposed IC-IPD was successfully applied to the determination of major cations in natural water samples.     

Enhancement of detection sensitivity for indirect photometric detection of anions and cations in capillary electrophoresis

This review focuses on the indirect photometric detection of anions and cations by capillary electrophoresis. Special emphasis has been placed on the sensitivity of the technique and approaches taken to enhance detection limits. Theoretical considerations and requirements have been discussed, including buffering, detection sensitivity, separation of cations, and detector linearity. A series of tables detailing highly absorbing probes and the conditions of their use for indirect photometric detection are included.     

Capillary isoelectric focusing with UV-induced fluorescence detection

Low-molecular-mass fluorescent compounds excitable in the near UV region with suitable acidobasic and electrophoretic properties are suggested as isoelectric point (pI) markers for isoelectric focusing (IEF) with UV photometric and UV excited fluorometric detection. The experimental set-up of capillary IEF with UV excited fluorometric detection and properties of new UV-induced fluorescent pI markers are given. The pI values of 18 new pI markers determined independently of IEF methods range from 2.1 to 10.3. The examples of separation of new pI markers together with derivatized proteins by capillary IEF with photometric or fluorometric detection are presented.     

Liquid chromatographic determination of cobalt(II), copper(II) and iron(II) using 2-thiophenaldehyde-4-phenyl-3-thiosemicarbazone as derivatizing reagent

The complexing reagent 2-thiophenaldehyde-4-phenyl-3-thiosemicarbazone (TAPT) was examined for high performance liquid chromatographic (HPLC) separations of cobalt(II), copper(II) and iron(II) or cobalt(II), nickel(II), iron(II), copper(II) and mercury(II) as metal chelates on a Microsorb C-18, 5-mum column (150x4.6 mm i.d.) (Rainin Instruments Woburn, MA, USA). The complexes were eluted isocratically with methanol:acetonitrile:water containing sodium acetate and tetrabutyl ammonium bromide (TBA). UV detection was at 254 nm. The solvent extraction procedure was developed for simultaneous determination of the metals, with detection limits within 0.5-2.5 mug ml(-1) in the final solution. The method was applied for the determination of copper, cobalt and iron in pharmaceutical preparation.     

Enantiomeric resolution of bupivacaine by high-performance liquid chromatography and chiroptical detection

This work reports a new analytical procedure for the separation and determination of the enantiomers of bupivacaine and the determination of the enantiomeric purity. The isomers were separated using a Chirex 3020 (250 mm x 4.6 mm) with a mobile phase of n-hexane:dichloroethane:ethanol (82:9:9, v/v/v) at a flow-rate of 1 ml min(-1) and UV, polarimetric and circular dichroism (CD) detection. Obtained retention times were 5.93 and 7.53 min (R and S) with a resolution of Rs=2.36. Precisions (RSD) were 1.83 and 2.02% (CD detection) and 3.07 and 1.26% (UV detection) for R- and S-enantiomers, respectively (at 10 microg level). Detection limits were 0.5 and 0.5 microg (R and S) with CD detection, and 0.9 and 0.3 microg with UV detection. Polarimetric detection was inadequate to perform a quantitative method at similar concentration ranges as UV and CD because of poor sensitivity. A procedure for determination of enantiomeric purity using a conventional chromatographic column (RP18, Luna) coupled to a CD detector and anisotropy factor (CD/UV) as analytical signal was also developed. Obtained results show that RSDs of 6.7-1.6% were obtained in the range of 0-100% enantiomeric purity.     

Separation and detection of angiotensin peptides by Cu(II) complexation and capillary electrophoresis with UV and electrochemical detection

The use of capillary electrophoresis (CE) with on-capillary Cu(II) complexation for the determination of angiotensin and its metabolites is described. The resulting copper-peptide complexes can be detected using either UV or electrochemical (EC) detection. Optimal reaction and separation conditions for the angiotensin peptides were first determined using CE with UV detection. With UV detection, the limit of detection (signal-to noise ratio S/N = 3) for native angiotensin II was 18 microM, while the limit of detection (LOD) obtained for the copper-angiotensin II complex is 2 microM. CE with EC detection was then evaluated, yielding significantly lower LODs--2 microM for native angiotensin II and 200 nM for the copper-angiotensin II complex. The addition of copper to the run buffer improved the separation and sensitivity for both CE-UV and CE-EC detection. The method was demonstrated by monitoring the conversion of angiotensin I to angiotensin II in plasma via angiotensin-converting enzyme (ACE) and subsequent inhibition of ACE by captopril.     

An ion-exchange separation of metal cations on a C-18 column coated with dodecylsulphate

The retention mechanism was studied for the cations of the alkaline earth metals and Zn(2+) Ni(2+), Co(2+), Cd(2+) and Bi(3+) on a C(18) column permanently coated with sodium dodecylsulphate, with aqueous mobile phases containing cupric chloride or sulphate, or cerous nitrate. The dependencies of the logarithm or the capacity ratio on the logarithm of the eluent concentration were linear, demonstrating that ion-exchange was the predominating separation mode; the slopes of these dependencies were in good agreement with the values predicted from the ion-exchange theory. Indirect UV photometric detection yielded limits of detection (LOD) of 21, 44, 120 and 275 ng in the volume injected, 20 mul, for Mg(2+), Ca(2+), Sr(2+) and Ba(2+), respectively, with the 10(-2)M copper(II) chloride mobile phase; the respective LOD values decreased to 0.8, 1.6, 3.0 and 6.7 ng with the 5 x 10(-4)M cerium(III) nitrate eluent. The method was found to be primarily suitable for determination of the alkaline earths and was applied to analyses of surface and mineral waters.     

Analytical reactions of 5-amino-orotic acid

The potential of 5-amino-orotic acid (AOA) for spectrophotometric determination of metal ions is explored. Only the reactions with copper(II), cobalt(II) and osmium(VIII) are sensitive and suitable for this purpose. Ternary complexes of copper(II) formed with AOA and ammonia or pyridine can also be used for photometric determination of the metal and given better sensitivity and selectivity than the binary complex. Optimum conditions for determination of all the three metal ions have been established.     

Synthesis and Spectrothermal Studies of Thermochromic Diamine Complexes of Cobalt(III), Nickel(II) and Copper(II) Squarate. Crystal Structure of [Co(en)3](sq)1.5 · 6H2O

New adducts of ethylenediamine (en), N,N-dimethylethylenediamine (ndmen) and N,N′-dimethylethylenediamine (dmen) with squarate as counter-ions were synthesized and characterized by physico-chemical methods (IR and UV/vis spectroscopy, magnetic susceptibility and thermoanalytical measurements). The crystal structure of tris(ethylenediamine)cobalt(III) 1.5 squarate hexahydrate, [Co(en)₃](sq)_1.5 · 6H₂O, was determined by single crystal X-ray diffraction. Co(III), Ni(II) and Cu(II) ions in the monomeric octahedral tris(ethylenediamine)cobalt(III) 1.5 squarate hexahydrate (1), tris(ethylenediamine)nickel(II) squarate 0.5 hydrate (2) and diaquabis(ethylenediamine)copper(II) squarate dihydrate (3) are chelated by ethylenediamines through two amine nitrogen atoms. Cu(II) atoms in the diaquabis(ndmen)copper(II) squarate (4) and diaquabis(dmen)copper(II) squarate (5) monomeric octahedral complexes are coordinated by ndmen and dmen molecules through two amine nitrogen atoms in a bidentate chelating manner. Water molecules complete the octahedral coordination. The orange (1), violet (4) and violet (5) complexes upon heating transform to claret, green and green species on dehydration, respectively, which revert immediately after cooling in the open atmosphere. The violet (3) complex upon heating loses water molecules yielding a deep blue dehydrated species, which on further heating undergoes an exothermic phase transition accompanied by thermochromism, deep blue to brown in the solid state. The decomposition mechanism and thermal stability of the solid complexes are interpreted in terms of their structures. The final decomposition products – the respective metal oxides – were identified by IR spectroscopy.     

Reversed phase liquid chromatographic determination of organic acids using on-line complexation with copper(II) ion

We describe a simple and sensitive liquid chromatographic method for the analysis of organic acids using on-line complexation with copper(II) ion. Organic acids complexed with copper(II) ion were separated on a reversed-phase C18 column and detected by UV absorption at 240 nm. The copper(II) ion concentration in the mobile phase had a great influence on separation and sensitivity. A mobile phase consisting of 10 mM copper(II) sulfate in 5 mM sulfuric acid (pH 2.3) was used to separate nine organic acids (tartaric, malic, malonic, lactic, acetic, citric, maleic, succinic and fumaric acids). The detection limits of the examined organic acids calculated at S/N = 3 ranged from 0.6 to 100 μM. The detector signal was linear over three orders of magnitude of organic acid concentration. The method successfully measured organic acids in juice and vinegar samples.     

Amperometric detection of amines using cobalt electrodes after separation by ion-moderated partition chromatography

A simple and low-cost amperometric sensor for amines has been developed using a cobalt wire electrode working in alkaline solution. The sensor may be used as a detector for high-performance liquid chromatography (HPLC) that avoids the need for derivatization or post-column reaction. Experimental conditions for flow injection analysis (FIA) and HPLC separation, including the applied potential, pH and concentrations of organic modifier and carrier solution, were optimized. A cobalt wire electrode, in the constant potential amperometric mode, gives an excellent response toward amines in ion-exclusion chromatography in unbuffered solution. The sensitivities of the detection and separation of amines on the column are affected by flow rate, the concentration of the mobile phase and the concentration of organic solvent in the mobile phase, whereas the applied potential only affects the sensitivity of the detector. A cobalt electrode is more sensitive than a copper electrode, and comparable in sensitivity to a UV detector for most amines tested. The detection sensitivity is comparable to that obtained with GC methods, but the procedures are far simpler. The detection limits of the order of nanomoles obtained under the chromatographic conditions used offer an alternative for the determination of amines in a variety of matrices, such as in environmental, biomedical and pharmaceutical samples.     

Flow-injection photometric determination of sub-nanogram amounts of cobalt by its catalysis of the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline in a micellar medium

A catalytic flow-injection photometric method was developed for the determination of levels of cobalt as low as 10(-10) mol 1(-1). The method is based on the catalytic action of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline to form a colored dye (lambda(max) = 590 nm) in the presence of hydrogen peroxide. The extremely activating effect was obtained in the presence of 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) and sodium hydrogencarbonate as activators. Furthermore, the sensitivity of the method was enhanced by adding sodium dodecylsulfate as a surfactant. Linear calibration graphs were obtained over the range 0.04-0.2 ng ml(-1) and 0.1-0.5 ng ml(-1) cobalt(II). respectively, at a sampling rate of 30 per hour. The detection limit (signal/noise = 3) was 5 pg ml(-1) and the relative standard deviations for 0.1 and 0.04 ng ml(-1) cobalt (n = 10) were 1.0 and 2.3%, respectively. The method was applied to the determination of cobalt in pepperbush.     

Retention,direct detection,and quantitation of palladium (II) using high-performance liquid chromatography and evaporative light scattering detection

This study demonstrates the use of high-performance liquid chromatography and evaporative light scattering detection for the direct detection and quantitation of palladium II. After evaluating the effects of buffer concentration and pH, the separation of cobalt II, copper I, copper II, nickel II, and palladium II was accomplished using a Chromolith® Performance SI monolithic column with a hydrophilic interaction chromatography mode gradient elution. Typical validation parameters were evaluated to assess the method’s quantitative performance for palladium II which included specificity, accuracy, precision, linearity, stability, and limit of detection. This technique provides a unique and practical alternative method for the accurate quantitation of palladium II.     

CoCl_2·6H_2O or LaCl_3·7H_2O Catalyzed Biginelli Reaction. One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1 H)-ones

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Spectrophotometric determination of traces of metallic ions and their mixtures with 3-methyl-1,2-cyclopentanodione dithiosemicarbazone: II. Bismuth,copper, and cobalt

The properties of bismuth, copper, and cobalt complexes of 3-methyl-1,2-cyclopentanodione dithiosemicarbazone and the optimal conditions for their formation are described. The complexes were used with success in the photometric determination of traces of bismuth, copper, and cobalt. Nine procedures are proposed for the accurate analysis of Bi(III)-Cu(II), Bi(III)-Co(II), Zn(II)-Cu(II), Cd(II)-Cu(II), Hg(II)-Cu(II), Zn(II)-Co(II), Cd(II)-Co(II), Hg(II)-Co(II), and Cu(II)-Co(II) mixtures. Satisfactory results were obtained.