Determination of oxoanions in river water by capillary electrophoresis

A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of ten oxoanions (CrO4(2-), SeO4(2-), MoO4(2-), WO4(2-), VO4(3-), SeO3(2-), As04(3-), TeO3(2-), TeO4(2-), and AsO3(3-)) which were baseline-separated from each other and from the interfering UV absorbing anions (NO3- and NO2-) commonly found in environmental water samples. The new background electrolyte system developed contained 5 mM potassium phosphate and 0.007 mM octadecyltrimethylammonium hydroxide, pH 11.2. The optimized working conditions were electrokinetic sampling at -5 kV for 10 s, running voltage at -15 kV with 5 microA current, and detection wavelength at 205 nm. No interference was observed for non-UV-absorbing anions and UV-absorbing anions up to 20 and 10 times higher concentrations respectively. The speed of analysis was fast, with a complete CE run within 6 min. Wide linear ranges (1-2,000 microg/L), good repeatability in migration time (relative standard deviation RSD 0.55-2.8%), satisfactory precision in peak area (RSD 3.8-5.6%) and peak height (RSD 3.9-5.3%) measurement, and detection limits (1-25 microg/L) sufficiently sensitive to detect oxoanions found in environmental water samples were obtained. The reliability of the CE procedure developed had been established by recovery test and parallel method determination using atomic absoprtion spectrophotometry for real river water sample.     

Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium

A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.     

Analysis of organic acids and inorganic anions in beverage drinks by capillary electrophoresis

To meet the need for a new and validated analytical method for simultaneous determination of inorganic and organic acid anions in beverage drinks, a capillary zone electrophoresis (CZE) procedure had been developed based on a new background electrolyte (BGE) system containing 3 mmol/L 1,3,5-benzenetricarboxylic acid (BTA), 15 mmol/L tris(hydroxymethyl)aminomethane and 1.5 mmol/L tetraethylenepentamine (TEPA) at pH 8.4. Baseline separation of anions commonly found in beverage drinks could be achieved in less than 14 min with indirect UV detection at 240 nm. Comigration problems for hydroxycarboxylic acids could be solved using TEPA as BGE additive. The results indicate excellent repeatability for migration time (RSD, 0.27-0.67%, n = 5) and good precision for both peak height (RSD, 3.2-4.2%, n = 5) and peak area (RSD, 3.1-4.5%, n = 5). Under the optimized conditions and using corrected peak area for quantitation, an excellent linear dynamic range (with correlation coefficient > 0.997 in a concentration range from 0.005 to 2.0 mmol/L) and low detection limit (1-4 micro mol/L) were obtained for all the anions investigated. The applicability and reliability of the CE procedure developed were established by parallel method determination using established ion chromatography procedure for the analysis of inorganic and organic acid anions in orange juice and wine samples. Our CZE procedure provided a sensitive and economic technique for simultaneous determination of inorganic and organic acid anions in orange juice, red and white wine samples.     

Speciation of Co(II), Co(III), and Cu(II) in ethylenediamine solutions by capillary electrophoresis

A capillary electrophoretic (CE) method for the speciation of Co(II), Co(III), and Cu(II) in electroless copper-plating baths containing ethylenediamine (En) has been developed. The method is based on the selective pre-capillary derivatization of Co(II) with 1,10-phenanthroline (Phen) followed by CE separation of stable [CoPhen(3)](2+), [CoEn(3)](3+), and [CuEn(2)](2+) chelates. The proposed derivatization procedure protects Co(II) from oxidation by dissolved oxygen and enables rapid determination of all three metal species within a single run. The optimized separations were carried out in a fused silica capillary (57 cmx75-microm I.D.) filled with an ethylenediamine sulfate electrolyte (20 mmol L(-1) H(2)SO(4), pH 7.0 with En, applied voltage +30 kV) using direct UV detection at 214 nm. The detection limits for a signal-to-noise ratio of 3 and 10 s, hydrodynamic injections were 5x10(-6) mol L(-1) for Cu(II), 1x10(-6) mol L(-1) for Co(III), and 4x10(-7) mol L(-1) for Co(II). Application of the method to the speciation of Co(II), Co(III), and Cu(II) in copper-plating bath samples is also demonstrated.     

On-line hyphenation of capillary electrophoresis with flame-heated furnace atomic absorption spectrometry for trace mercury speciation

Capillary electrophoresis (CE) was directly interfaced to flame-heated furnace atomic absorption spectrometry (FHF-AAS) via a laboratory-made thermospray interface for nanoliter trace element speciation. The CE-FHF-AAS interface integrated the superiorities of stable CE separation, complete sample introduction, and continuous vaporization for AAS detection without the need of extra external heat sources and any post-column derivation steps. To demonstrate the usefulness of the developed hybrid technique for speciation analysis, three environmentally significant and toxic forms of methylmercury (MeHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) were taken as model analytes. Baseline separation of the three mercury species was achieved by CE in a 60 cm long x 75 microm inner diameter fused-silica capillary at 20 kV and using a mixture of 100 mM boric acid and 10% v/v methanol (pH 8.30) as running electrolyte. The precision (relative standard deviation, RSD, n = 7) of migration time, peak area and peak height for the mercury species at 500 microg x L(-1) (as Hg) level were in the range of 0.9-1.2%, 1.5-1.9%, and 1.4-2.0%, respectively. The detection limit (S/N = 3) of three mercury species was 3.0 +/- 0.15 pg (as Hg), corresponding to 50.8 +/- 2.4 microg x L(-1) (as Hg) for 60 nL sample injection, which was almost independent on specific mercury species. The developed hybrid technique was successfully applied to the speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).     

Simultaneous capillary electrophoretic separation of small anions and cations after complexation with ethylenediaminetetraacetic acid

A new approach for simultaneous separation of small inorganic and organic anions and metal cations by capillary electrophoresis is demonstrated. Metal cations in the sample are transformed into their chelates with EDTA and are separated together with the anions using an anionic separation mode. Simultaneous separation of 19 common anions and cations was achieved in about 6 min with the electrolyte containing 5 mM K2CrO4, 3 mM boric acid, 35 microM cetyltrimethylammonium bromide and 12 microM EDTA at pH 8. Limits of detection (s/n = 3) were in the range from 4 ppb for Cl- up to 1250 ppb for Cu-EDTA and RSDs of peak areas ranged from 1.4% for Cl- up to 8.5% for Mn-EDTA chelate. The practical applicability of the method was demonstrated on the analysis of anions and cations in various water samples.     

Fast assay of glucosamine in pharmaceuticals and nutraceuticals by capillary zone electrophoresis with contactless conductivity detection

A novel capillary electrophoresis (CE) method with contactless conductivity detection suitable for the determination of glucosamine (GlAm) and K(+) in pharmaceuticals was devised. Under the optimum conditions (aqueous 30 mM acetate buffer of pH 5.2 as the background electrolyte; voltage 30 kV; 25 degrees C), GlAm (migrating as glucosaminium cation) was well separated from K(+) that could occur in the dosage forms as excipient. The CE analysis was performed in fused-silica capillaries (50 microm i.d., 75 cm total length, 27 cm to detector) and the separation took <3 min. The calibration graphs were linear for both GlAm (100-300 microg/mL; r(2)=0.997) and K(+) (15-75 microg/mL; r(2)=0.997) when using ethanolamine (100 microg/mL) as the internal standard. The LOD values (S/N=3) were 9.3 microg/mL for GlAm and 2.9 microg/mL for K(+). The method was applied to the assay of GlAm content in various dosage forms. Intermediate precision evaluated by determining the content of GlAm in a single formulation on 3 consecutive days was characterized by RSD 2.35% (n=15). Acceptable accuracy of the CE method was confirmed by the added/found GlAm recovery experiments (recoveries 94.6-103.3%) and by statistical comparison of the results attained by the proposed CE and a reference HPLC method.     

On-line pervaporation-capillary electrophoresis for the determination of volatile acidity and free sulfur dioxide in wines

Pervaporation has been coupled on-line to capillary electrophoresis (CE) by a simple interface consisting of a modified CE vial. The approach allows volatile analytes to be removed and injected into the capillary meanwhile the sample matrix remains in the pervaporator. By this approach volatile acidity and free sulfur dioxide have been simultaneously determined in wines. The detection limits (LODs) are 1.25 and 5.00 microg/mL, the quantification limits 4.12 and 16.50 microg/mL, and the linear dynamic ranges between LOD and 50 microg/mL and between 0.1 and 0.9 g/L for free sulfur dioxide and volatile acidity, respectively. The repeatability and within laboratory reproducibility, expressed as relative standard deviation (RSD), are 1.61% and 3.00% for free sulfur, and 3.35% and 4.58% for volatile acidity, respectively. The optimal pervaporation time and the time necessary for the individual separation-detection of the target analytes are 6 and 5 min, respectively. The analysis frequency is 7 h(-1) and the sample amount necessary is less than 7 mL. The proposed method and official methods for the analytes were applied to 32 wine samples. A two-tailed t-test was used to compare the methods, which yielded similar results. The errors, expressed as RSD for the two parameters, ranged between 1.3 and 4.1%.     

Cloud point preconcentration prior to capillary zone electrophoresis: simultaneous determination of platinum and palladium at trace levels

The incorporation of a cloud point extraction (CPE) step prior to capillary electrophoresis (CE) for simultaneously determining platinum and palladium at sub-microg/L levels is presented and evaluated. The analytes were extracted as 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complexes, at pH 2.0, mediated by micelles of the nonionic surfactant polyethyleneglycolmono-p-nonylphenyl ether (PONPE 7.5). The separation-determination step was developed from 150 microL of the extracted surfactant-rich phase diluted with 50 microL of acetonitrile (ACN). An exhaustive study of the variables affecting the cloud point extraction with PONPE 7.5 and the CZE step was done. The type and composition of the background electrolytes (BGEs) were investigated with respect to separation selectivity, reproducibility, and stability. A BGE of 50 mM monobasic sodium phosphate containing 30% ACN, pH 4.53 was found to be optimal for the separation of metal chelates. Detection was performed at 576 nm. An enrichment factor of 250 was obtained for the preconcentration of 50 mL of sample solution. The detection limits for the preconcentration of 50 mL of sample were 0.04 microg/L for Pt and 0.08 microg/L for Pd. As an analytical demonstration, ultratrace concentrations of platinum and palladium were conveniently quantitated in spiked water and urine samples.     

Rapid speciation of iron by on-line coupling of short column capillary electrophoresis and inductively coupled plasma mass spectrometry with the collision cell technique

A method for rapid speciation analysis of iron was developed by on-line coupling of short column capillary electrophoresis and inductively coupled plasma mass spectrometry. The collision cell technique was used to eliminate argon-based polyatomic interferences and a Micromist nebulizer was employed to increase the nebulization efficiency. Rapid speciation analysis of Fe(II) and Fe(III) was achieved within 1 min by short column capillary electrophoresis in a 14 cm x 50 microm id capillary at 28 kV voltage with a mixture of 15 mmol/L tris(hydroxymethyl)aminomethane + 1 mmol/L 1,10-phenanthroline + 1 mmol/L EDTA (pH 8.6) as running electrolyte. The precisions (RSD, n = 5) of migration time and peak area for Fe(II) and Fe(III) were in the range of 1.0 - 2.6 and 1.9 - 3.9%, respectively. The limits of detection (3sigma) of Fe(II) and Fe(III) were 10.0 and 8.3 microg/L, respectively.     

Direct determination of small cations in proteinaceous samples using a flow injection-capillary electrophoresis system.

A method is described for the direct determination of small inorganic cations in samples containing large amounts of proteins, such as milk or blood plasma. The method is based on electrokinetic injection in a flow injection analysis-capillary electrophoresis (CE) system. The selected CE-electrolyte, containing 5 mM 4-aminopyridine and 7 microM cetyltrimethylammonium bromide at pH 4.5, prevents detrimental protein adsorption on the capillary walls. Therefore, no sample pretreatment, except for dilution, is required. Up to 30 repeated injections in one electrophoretic run can be performed, yielding RSD values of the migration time of less than 1 and 2.5% (n=30) for milk and blood plasma samples, respectively.     

CE coupled with amperometric detection using a boron-doped diamond microelectrode: validation of a method for endogenous norepinephrine analysis in tissue

The level of endogenous norepinephrine (NE) in several tissue types was determined by CE with amperometric detection. We report herein on the method validation by HPLC using both amperometric and coulometric detection (CD). Keys to the method were the use of a diamond microelectrode for detection and off-line SPE for sample preparation. The run buffer was a 250 mM borate solution adjusted to pH 8.8 with potassium hydroxide. The diamond microelectrode exhibited a low and stable background current, and a low peak-to-peak noise < or =0.65 pA at the detection potential of +0.86 V versus Ag/AgCl. For standard solutions, the detector signal (i.e., oxidation current) changed linearly with the NE concentration (r(2) = 0.999) between 60 and 1000 nmol/L with an estimated LOD of 51 nmol/L (S/N = 3) and a response variability of 4.5% (RSD, n = 5). An Oasis MCX sorbent was used for SPE and the procedure produced an NE recovery of 95.1 +/- 5.6% (n = 6) from tissue homogenates. NE levels in the spleen, small intestine, and heart of a normotensive rat were found to be in the range of 0.77-0.97, 0.22-0.32, and 0.29-0.45 microg/g tissue (n = 3), respectively.     

Rapid determination of cyclamate in foods by solid-phase extraction and capillary electrophoresis

A method for the determination of cyclamate in food was developed using solid-phase extraction (SPE) and capillary electrophoresis (CE) with indirect ultraviolet (UV) detection. A 5-10 g sample in 0.1 mol/L hydrochloric acid was homogenized and made up to a volume of 50 mL with 0.1 mol/L hydrochloric acid. After the sample was centrifuged, 25 mL of supernatant was loaded into an Oasis HLB SPE cartridge. The cartridge was washed with 2 mL of demineralized water followed by 2 mL of 50% aqueous methanol, and cyclamate was eluted with 4.5 mL of 50% aqueous methanol. The eluate was added to a solution of sodium propionate (internal standard) for CE analysis. The cyclamate in the eluate was electrophoresed on a fused-silica capillary using 1 mmol/L hexadecyltrimethylammonium bromide and 10 mmol/L potassium sorbate as a running buffer. Detection and reference wavelengths of cyclamate determined with a UV detector were 300 and 254 nm, respectively. The calibration curves for cyclamate showed good linearity in the range of 2-1000 microg/mL and the limits of detection in beverage, fruit in syrup, jam, pickles and confectionary are sample dependent and ranged from 5-10 microg/g. The recovery of cyclamate added at a level of 200 microg/g to various kinds of foods was 93.3-108.3% and the relative standard deviation was less than 4.9% (n=3). A number of commercial samples were analyzed using the proposed method. Cyclamate was detected in one waume, two pickles, and two sunflower seeds. The quantitative values determined with CE correlated to those from high-performance liquid chromatography (HPLC) (the detected values of cyclamate in a sunflower seed measured by CE and HPLC were 3.40 g/kg and 3.51 g/kg, respectively). This analytical method for cyclamate using CE is especially suitable for use in the field.     

Determination of uranium, iron, copper, and nickel in rock and water samples by MEKC

A micellar electrokinetic capillary chromatographic (MEKC) procedure has been developed for the separation and determination of dioxouranium (VI), iron(III), copper(II), and nickel(II) using bis(salicylaldehyde)propylenediimine (H2SA2Pn) as chelating reagent with a total run time of <3 min. Sodium dodecyl sulphate (SDS) was used as micellar medium at pH 8.1 with sodium tetraborate buffer (0.1 M). Uncoated fused silica capillary with effective length 38.8 cmx75 microm id was used with an applied voltage of 30 kV and photo-diode array detection at 228 nm. Linear calibrations were established within 0.045-1000 microg/mL of each element with detection limit within 15-122 ng/mL. The method was applied to the analysis of spring water and rock samples. The presence of uranium in rock and spring water samples was established within 1.58-1739.3 microg/g and 0.047-0.712 microg/mL with relative standard deviation within 0.9-2.1% and 1.3-2.6% respectively. Uranium ore and water samples were also assayed by the standard addition technique. Recovery of uranium was >98% with RSD up to 2.7%. Copper, nickel, and iron in their combined matrix were concurrently determined within RSD 0.6-3.6% (n=5) and the results obtained were compared with those of flame AAS.     

Trace ion analysis of seawater by capillary electrophoresis: determination of iodide using transient isotachophoretic preconcentration

An improved transient isotachophoresis (tITP) procedure for the preconcentration of iodide from highly saline matrices was developed with the objective to quantify iodide in seawater by capillary electrophoresis (CE). The procedure takes advantage of introducing cetyltrimethylammonium chloride into the high-sodium chloride background electrolyte, which due to a specific interaction with iodide amended placement of the analyte at a large distance from the matrix chloride (the latter performed the role of a leading anion). Computer simulation showed that 2-(N-morpholino)ethanesulfonate could be adopted as a suitable terminating ion to enable isotachophoretic focusing at the beginning of the CE run. Under optimized tITP conditions, the sensitivity response of iodide was improved by a factor of 140 over normal CE mode. This allowed for direct UV detection of as low as 0.6 microg/L iodide and made feasible CE analysis of undiluted surface seawater samples where iodide was found at a 30 microg/L level. The applicability of the proposed tITP-CE method could apparently be extended to the determination of other trace seawater anions (e.g., iodate).     

毛细管电泳-间接紫外检测法分离和测定食品中的有机酸

有机酸毛细管电泳（CE）分析是90年代初首先被报道的[1],近年来有了较大的发展[2]．采用CE法可进行不同基质样品如食品、饮料、尿液等样品中多种有机酸的同时分析[1,3,4]．该法采用CE的阴离子分离模式,在电解质溶液中加入电渗流改性剂,使电渗流方向逆向,从而与阴离子的电泳方向一致,以缩短分析时间．常见有机酸在200um以上大多无紫外吸收,一般采用间接紫外检测方法[1,3],也可采用低波长紫外检测[4]．低分子量阴离子的CE研究报道不多[5,6],有机酸的CE分离系统研究尚未见报道．本文系统地研究了毛细管电泳-间接紫外检测法分析…     

毛细管区带电泳激光诱导荧光间接检测环腺苷单磷酸和环鸟苷单磷酸

研究了影响毛细管区带电泳激光诱导荧光间接检测环腺苷单磷酸和环鸟苷单磷酸的实验条件.cAMP和cGMP的线性范围分别为30～500mg/L和15～500mg/L,其最低检测限分别为9.0mg/L和0.5mg/L;当浓度为125mg/L时,cAMP和cGMP峰面积的RSD为4.45%和6.21%(n=4);其迁移时间的日间RSD分别为2.92%和2.04%(n=5)     

Mapping the phosphorylation sites of proteins using on-line immobilized metal affinity chromatography/capillary electrophoresis/electrospray ionization multiple stage tandem mass spectrometry

On-line immobilized metal affinity chromatography/capillary electrophoresis/electrospray ionization-mass spectrometry (IMAC/CE/ESI-MS) offers selective preconcentration of phosphorylated peptides with identification of the phosphorylated amino acid(s). The preconcentration provides low concentration limits of detection and capillary electrophoresis separates the peptides. Recently, we reported a fast, simple, and sensitive on-line IMAC/CE/ESI-MS/MS method for the determination of phosphopeptides at low-pmole levels. That work is expanded here by use of multiple stage tandem mass spectrometry (MS(n), n = 2,3) to isolate and fragment target ions to provide more reliable assignments of phosphorylated residues. The application of IMAC/CE/ESI-MS(n) is demonstrated by the analysis of tryptic digests of alpha- and beta-casein and in-gel tryptic digests of beta-casein.     

Sensitivity enhancement of chlorinated phenols by continuous flow liquid membrane extraction followed by capillary electrophoresis

This paper describes a new analytical system, based on the combination of continuous flow liquid membrane extraction (CFLME) enrichment and capillary electrophoresis (CE) separation, for analysis of chlorinated phenols in water samples. Five chlorinated phenols including 3-chlorophenol (3CP), 4-chlorophenol (4CP) 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) were separated by CE with Tris/sodium dihydrogen phosphate solution containing methanol 1% (v/v) as the run buffer. CFLME related parameters were investigated and optimal enrichment was obtained by using 0.3 mol L(-1) Tris as acceptor and with a sample pH 5.0, a sample flow rate of 4.0 mL min(-1), and an enrichment sample volume of 150 mL. The detection limit (S/N= 3) was 6.9, 1.0, and 1.7 ng mL(-1) for DCP, PCP, and TCP, respectively. The reproducibility (RSD%, n = 6) was 5.7 for DCP, 2.5 for PCP, and 2.8% for TCP (n = 6). The proposed method was applied to the determination of chlorinated phenols in spiked water samples with relatively satisfactory recoveries.     

On-line pervaporation-capillary electrophoresis for the determination of volatile analytes in food slurries

Pervaporation has been coupled on-line to capillary electrophoresis (CE) by a flow injection manifold and the replenishment system of the CE instrument. The approach allows volatile analytes to be removed, derivatisated and injected into the capillary meanwhile the sample matrix remains in the pervaporator. Acetone and four aldehydes (namely: formaldehyde, acetaldehyde, hexenal, 2-trans-hexenal) have been simultaneously determined in slurries samples by this approach. The detection limits (LOD) ranged between 0.1 and 0.6 microg/ml, the quantification limits between 0.5 and 2.0 microg/ml and the linear dynamic ranges between the limit of quantitation and 150 microg/ml. The precision, expressed as relative standard deviation (RSD), ranged between 0.76 and 4.21% for repeatability and between 1.12 and 4.78% for within laboratory intermediary precision. The errors involved in the analysis of the target analytes--expressed as RSD for all compounds--ranged between 0.13 and 4.87%. The optimal pervaporation time and that necessary for the individual separation/detection of the target analytes are 15 and 10 min, respectively. The analysis frequency is 4 h(-1). The accuracy of the method and potential matrix effects were established by analysing spiked samples. Recoveries between 96.12 and 105.67% were obtained. The proposed method was applied to 10 samples with different solid contents (namely, such yoghurt, juice and yoghurt-juice mixtures).