Two-dimensional nano-liquid chromatography-mass spectrometry system for applications in proteomics

Transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte (BGE) was improved to further lower the limit of detection (LOD) for determination of nitrite and nitrate in seawater. By lowering the pH of BGE, the difference between effective mobility of nitrite and that of nitrate increased, thereby permitting increased sample volumes to be tolerated and their LOD values to decrease. Artificial seawater with pH adjusted to 3.0 using phosphate buffer was adopted as the BGE. To reverse electroosmotic flow (EOF), a capillary was flushed with 0.1 mM dilauryldimethylammonium bromide for 3 min before the capillary was filled with the BGE. Limits of detection (LODs) for nitrite and nitrate were 2.7 and 3.0 microg/l (as nitrogen), respectively. The LODs were obtained at a signal-to-noise ratio of 3. Values of the relative standard deviation (RSD) of peak area for these ions were 2.0 and 0.75%, respectively, when nitrite concentration was 0.05 mg/l and that of nitrate was 0.5 mg/l. The RSDs of peak height were 4.4 and 2.3%. The RSD values of migration time for these ions were 0.19 and 0.17%. The proposed method was applied to determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada. Results agreed with the assigned tolerance interval. This method was also applied to determination of these ions in seawater collected around Osaka Bay. Results nearly agreed with those obtained by a conventional spectrophotometric method.     

Capillary zone electrophoretic determination of iodide in seawater using transient isotachophoresis with artificial seawater as the background electrolyte

We describe an application of capillary zone electrophoresis (CZE) with transient isotachophoresis (ITP) as the on-line concentration procedure for the determination of iodide in seawater. The effective mobility of iodide was decreased by the addition of 10 mM cetyltrimethylammonium chloride (CTAC) to an artificial seawater background electrolyte (BGE) so that transient ITP functioned and iodide was separated from other coexisting anions such as bromide, nitrite, and nitrate in seawater samples. After sample injection, 600 mM acetate was separately injected into the capillary as the terminating ion to generate transient ITP. The limit of detection (LOD) for iodide was 3.0 microg/L. The LOD was obtained at a signal-to-noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area, peak height, and migration time for iodide were 2.9, 2.1, and 0.6%. The proposed method was applied to the determination of iodide in seawater collected around the Osaka Bay. The results obtained by use of the calibration graph were agreed with those obtained by the addition of the standard solutions for iodide.     

Determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater by capillary zone electrophoresis with artificial seawater as the background electrolyte using transient isotachophoresis

We describe a combination of selected ions as a terminating ion which is useful for transient isotachophoresis (ITP) in capillary zone electrophoresis (CZE) for the determination of nitrite and nitrate in seawater. In addition to 150 mM sulfate as the principal terminating ion, 10 mM bromate was added to a sample solution as the additional terminating ion. Artificial seawater containing 3 mM cetyltrimethylammonium chloride (CTAC) was adopted as a background electrolyte (BGE). The limits of detection (LODs) for nitrite and nitrate were 2.2 and 1.0 microg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.9 and 1.4%. The RSDs of peak height were 1.7 and 1.9%, the RSDs of migration time 0.11%. The proposed method was applied to the determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada (NRC). The results almost agreed with the assigned tolerance interval.     

Optimum conditions for effective use of the terminating ion in transient isotachophoresis for capillary zone electrophoretic determination of nitrite and nitrate in seawater,with artificial seawater as background electrolyte

We have examined transient isotachophoresis (ITP) conditions, e.g. the nature of the terminating ion, its concentration, and the injection procedure, to improve the limit of detection (LOD) for determination of nitrite and nitrate in seawater by capillary zone electrophoresis (CZE). Artificial seawater containing 3.0 mmol L(-1) cetyltrimethylammonium chloride (CTAC) was used as background electrolyte (BGE). After sample injection 600 mmol L(-1) acetate was separately injected into the capillary as the terminating ion for transient ITP. The LOD for nitrite and nitrate, obtained at a signal-to-noise ratio (S/N) of 3, were 15 and 7.0 microg L(-1) (as nitrogen), respectively. Relative standard deviations (RSD) of peak area for nitrite and nitrate were 7.3 and 0.8%, respectively, and the RSD of peak height were 5.7 and 1.2%, respectively, when the concentrations of nitrite and nitrate were 0.05 and 0.25 mg L(-1). The RSD of migration time for these ions was 0.2%. The proposed method was applied to the determination of nitrite and nitrate in seawater samples. The results for nitrite were nearly in agreement with those obtained by naphthylethylenediamine spectrophotometric analysis (SPA; correlation coefficient 0.9041).     

Simultaneous determination of bromide, nitrite and nitrate ions in seawater by capillary zone electrophoresis using artificial seawater as the carrier solution

We describe capillary zone electrophoresis (CZE) for the simultaneous determination of bromide, nitrite and nitrate ions in seawater. Artificial seawater was adopted as the carrier solution to eliminate the interference of high concentrations of salts in seawater. The artificial seawater was free from bromide ion to enable the determination of bromide ion in a sample solution. For the purpose of reversing the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the carrier solution. A 100 microm ID (inside diameter) capillary was used to extend the optical path length. The limits of detection (LODs) for bromide, nitrite, and nitrate ions were 0.46, 0.072, and 0.042 mg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.1, 1.5, and 0.97%. The RSDs of migration time for these ions were 0.61, 0.69, and 0.66%. Artificial seawater samples containing various concentrations of bromide, nitrite, and nitrate ions were analyzed by the method. The error was less than +/-12% even if the concentration ratio of bromide ion to nitrite or nitrate ion was 20-240. The proposed method was applied to the determination of bromide, nitrite, and nitrate ions in seawater samples taken from the surface and the seabed. These ions in other environmental waters such as river water and rainwater samples were also determined by ion chromatography (IC) as well as this method.     

Determination of bromate in sea water using multi-dimensional matrix-elimination ion chromatography

A multi-dimensional matrix-elimination ion chromatography approach has been applied to the determination of bromate in seawater samples. Two-dimensional and three-dimensional configurations were evaluated for their efficacy to eliminate the interference caused by the high concentration of ubiquitous ions present in seawater, such as chloride and sulfate. A two-dimensional approach utilising a high capacity second dimension separation comprising two Dionex AS24 columns connected in series was applied successfully and permitted the determination of bromate in undiluted seawater samples injected directly onto the ion chromatography system. Using this approach the limit of detection (LOD) for bromate based on a signal to noise ratio of 3 was 1050 μg/L using a 500 μL injection loop. Good linearity was obtained for bromate with correlation coefficients for the calibration curves of 0.9981 and 0.9996 based on peak height and area, respectively. A three-dimensional method utilising two 10-port switching valves to allow sharing of the second suppressor and detector between the second and third dimension separations showed better resolution and detection for bromate and reduced the LOD to 60 μg/L for spiked seawater samples. Good linearity was maintained with correlation coefficients of 0.9991 for both peak height and area. Ozonated seawater samples were also analysed and exhibited a non-linear increase in bromate level on increasing ozonation time. A bromate concentration in excess of 1770 μg/L was observed following ozonation of the seawater sample for 120 min. Recoveries for the three-dimensional system were 92% and 89% based on peak height and area, respectively, taken over 5 ozonated samples with 3 replicates per sample.     

Improvement of capillary zone electrophoresis sensitivity with artificial seawater as the background electrolyte utilizing transient isotachophoresis for the determination of nitrate and nitrate ions in seawater

We describe capillary zone electrophoresis (CZE) with transient isotachophoresis (ITP) for the determination of low concentrations of nitrite and nitrate ions in seawater. Bromide-free artificial seawater was adopted as background electrolyte (BGE) to eliminate the interference of high concentrations of salts in seawater. To reverse the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the BGE. High concentrations of chlorate were added to sample solutions as the terminating ion to generate the ITP process before the CZE separation. In general, the stacking effect increased with increasing amounts of chlorate injected into the capillary. The limits of detection (LODs) for nitrite and nitrate were 0.063 and 0.033 mg/L when the chlorate concentration was 600 and 200 mM, respectively; these were half of those obtained by CZE without the transient ITP. The LODs were obtained at a signal to noise ratio (S/N) of 3. The relative standard deviations (RSD, n = 10) of the peak areas for these ions were 3.2 and 2.9%. The RSDs of peak heights for these ions were 1.6 and 2.1%. The RSDs of migration times for these ions were 0.67 and 0.46%.     

Quantification of anions and cations in environmental water samples. Measurements with capillary electrophoresis and indirect-UV detection.

The aim of this study was to validate two separation methods for determination of inorganic anions and cations from natural waters with capillary electrophoresis (CE) by using indirect-UV detection. The research is related to method development for screening of groundwater samples obtained in site investigations for spent fuel of the Finnish nuclear industry. In CE analysis, anions were separated in pyromellitic acid (pH 7.7) in the order bromide, chloride, sulphate, nitrite, nitrate, fluoride and dihydrogenphosphate. Cations were separated at pH 3.6 after anions using an 18-crown-6-ether solution. In these analyses, ammonium migrated first followed by potassium, calcium, sodium and magnesium. The concentrations of the ions in the natural water samples were calculated by using two or three calibration curves made using reference solutions at concentration levels of 0.5-250 mg/l. The repeatabilities of the anion and cation methods were tested using laboratory-made reference sample mixtures with high and low salt concentrations. The limits of quantification in the analyses were between 0.02 and 0.1 mg/l, depending on the ion. Concentrations of ions tested in natural waters varied from a few milligrams to tens of grams per litre.     

Determination of ammonium in river water and sewage samples by capillary zone electrophoresis with direct UV detection

We developed capillary zone electrophoresis (CZE) with direct UV detection for determination of ammonium in environmental water samples. Ammonium in the samples was partly converted into ammonia in the alkaline background electrolyte (BGE) during migration and was detected by molecular absorption of ammonia at 190 nm in approximately 7 min. The limit of detection (LOD) for ammonium was 0.24 mg/l (as nitrogen) at a signal-to-noise ratio of three. The respective values of the relative standard deviation (RSD) of peak area, peak height, and migration time for ammonium were 2.1, 1.8, and 0.46%. Major alkali and alkaline earth metal ions coexisting in the samples did not interfere with ammonium determination by the proposed method. The proposed method determined ammonium in surface water and sewage samples. The results were compared to those obtained using ion chromatography (IC).     

Environmental water monitoring by capillary electrophoresis and result comparison with solvent chemistry techniques

The aim of this work was to determine inorganic ions from natural waters by capillary electrophoresis (CE) and to compare the results obtained with those measured with conventional solvent chemistry techniques. The project was part of a larger CE study, during which we measured inorganic ions from some lake and river systems and groundwaters in Southern Finland. Results obtained from contaminated Finnish waters were compared with samples from the River Rhine in the Düsseldorf area. Two CE methods were used for analysis: one for determination of chloride, sulfate, nitrite and nitrate at pH 7.7 and the other for ammonium, potassium, calcium, sodium and magnesium at pH 3.6, both methods using identification based on indirect UV detection. Two separation methods were used in order to prevent complex formation of metals with sulfate, hydroxide and decomposed organic matter present in the environmental samples. On the basis of the CE studies dilution was needed for those samples having more than 100 mg/l of sulfate, chloride, calcium and sodium. On average, the natural waters in the study contained ammonium, magnesium, sodium, potassium and calcium below 0.3, 20, 200, 20, and 200 mg/l, respectively. The concentrations of chloride, sulfate, nitrite and nitrate were below 20, 100, 10, and 10 mg/l, respectively. Correlation of the CE results with those acquired by titration, atomic absorption spectrometry, ion chromatography and flow injection analysis were obtained; R2 values for the comparison tests varied from 0.8816 to 0.9994 depending on the ion. The repeatabilities of the anion and cation CE methods were tested using laboratory-made reference sample mixtures with high and low salt concentration.     

Determination of magnesium and calcium ions in sea water by capillary type isotachophoresis

Summary A new analytical procedure for the determination of magnesium and calcium ions in sea water was developed with a capillary type isotachophoresis after adsorption on sodium form cation-exchange resin and elution with EDTA solution. Linear working curves were obtained for 3% sodium chloride solutions containing up to 2,000 mg/l of these ions, adjusted to pH 8 with 0.1 N sodium carbonate solution. A supporting electrolyte containing 0.01 M hydrochloric acid and 0.5% methyl cellulose buffered to pH 8.5 with tris(hydroxymethyl)aminomethane and a 40 cm long FEP tube as the main column were used. The proposed method was applied to the determination of magnesium and calcium ions in coastal sea water samples collected in Osaka Bay in April, 1984 and in artificial samples prepared with artificial or natural sea water.

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Bestimmung von Magnesium und Calcium in Meerwasser mit Hilfe der Capillar-Isotachophorese

Zusammenfassung Das Verfahren beruht auf der Isotachophorese nach vorhergehender Adsorption an Kationen-Austauscher in Na-Form und Elution mit EDTA-Lösung. Für 3%ige NaCl-Lösungen mit <2000 mg/l Mg und Ca (auf pH 8 mit 0,1 N Natriumcarbonatlösung eingestellt) wurden lineare Eichkurven erhalten. Als Trägerelektrolyt diente 0,01 M Salzsäure mit 0,5% Methylcellulose, gepuffert auf pH 8,5 mit Tris(hydroxymethyl)aminomethan. Hauptsäule war eine 40 cm lange FEP-Röhre. Das vorgeschlagene Verfahren wurde zur Mg- und Ca-Bestimmung in Küstenwasser der Osaka-Bucht sowie in synthetischen Proben eingesetzt.

     

Determination of iodide in seawater using C30 column modified with polyoxyethylene oleyl ether in ion chromatography

An ion chromatographic method for rapid and direct determination of iodide in seawater samples is reported. Separation was achieved using a laboratory-made C30 packed column (100 mm × 0.32 mm i.d.) modified with polyoxyethylene oleyl ether, with an aqueous solution of 300 mM sodium chloride as eluent and using UV detection at 220 nm. Samples containing iodate, nitrate, iodide and thiocyanate were eluted within 8 min, and the relative standard deviations of the retention time, peak area and peak height were all smaller than 4.19% for all of the analyte anions. Effects of eluent composition on retention behavior of inorganic anions have been investigated. Both cation and anion of the eluent affected the retention time of analytes. When inorganic eluents, such as ammonium chloride, ammonium sulfate, lithium chloride, sodium chloride, sodium sulfate, magnesium chloride and magnesium sulfate were used, the retention time of analytes increased with increasing eluent concentration. The limit of detection of iodide was 19 μg l⁻¹ (S/N = 3), while the limit of quantitation was 66 μg l⁻¹ (S/N = 10). The present method was successfully applied to the rapid and direct determination of iodide in seawater samples.     

Uncertainty Budget for Simultaneous Determination of Minor and Major Ions in Seawater with Ion Chromatography Confronted with Uncertainties in Concentrations of Calibration Standards

This work deals with the development and application of the detailed uncertainty budget for simultaneous determination of minor and major ions in seawater and derived saline solutions. Combination and sequence of gravimetric or/and volumetric steps involved in introducing each particular ion into stock and final combined calibration standards; cross contamination of chemicals and dilution of samples were critically assessed and their significance to the combined uncertainty was evaluated. The main uncertainty components were identified and quantified for all anions and cations determined with ion chromatography in seawater and estuary water and confronted with uncertainties associated with concentrations of ions in combined calibration standards. Similar uncertainty components reflect very differently upon different ions.     

Synthesis of o,o′-dihydroxyazo compounds and their application to the determination of magnesium and calcium by flow injection analysis

Seven _o,o′-dihydroxyazo dyes were synthesized and examined as spectrophotometric reagents for magnesium and calcium. These reagents are highly sensitive for magnesium (? = 47 000) and calcium (? = 39 000 l mol^?1 cm^?1). Of the reagents synthesized, 2-(2-hydroxy-3,6-disulfo-1-naphthylazo)-5-(N,N-diethylamino)phenol was the best because of its ease of preparation and purification, and its stability in alkaline solution. This dye was applied in the determination of magnesium and calcium by flow injection analysis. The total concentration of magnesium (0.1–1.2 mg 1^?1) and calcium (0.4–4.0 mg 1^?1) was determined by masking iron(III), aluminium(III), copper(II), zinc(II), manganese(II) and cadmium(II) with 2,3-dimercapto-1-propanol (DMP) and triethanolamine (TEA). Magnesium was determined by masking calcium and the other metal ions with a ligand buffer containing barium(II)—EGTA, DMP and TEA. The amount of calcium was obtained as the difference between the two peak heights. Results for the determination of magnesium and calcium in potable water and serum are presented.     

Dodecylsulfate-coated monolithic octadecyl-bonded silica stationary phase for high-speed separation of hydrogen, magnesium and calcium in rainwater

The high-speed determination of hydrogen, magnesium and calcium ions by ion chromatography (IC) is demonstrated on a monolithic octadecyl-boned silica (ODS) column coated with lithium dodecylsulfate (Li-DS). This stationary phase, when used in conjunction with a 2 mM ethylenediamine and 0.1 mM Li-DS solution as eluent at pH 6.0, was found to be suitable for the rapid and efficient separation of hydrogen and magnesium and calcium in the order H+ < Mg2+ < Ca2+ within 4 min at a flow rate of 4.0 ml/min. Under the conditions, linear calibration plots of conductivity versus concentration were obtained for the cations over about three orders of magnitude, and the detection limits were 1 microM for H+, 2 microM for Mg2+ and Ca2+. Rainwater was analyzed directly using this IC system with satisfactory results.     

Simultaneous determination of iodide and iodate in seawater by transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte

We developed capillary zone electrophoresis with transient isotachophoresis (ITP) as an on-line concentration procedure for simultaneous determination of iodide and iodate in seawater. The effective mobility of iodide was decreased by addition of 20 mM cetyltrimethylammonium chloride to an artificial seawater background electrolyte so that transient ITP functioned for both iodide and iodate. Limits of detection for iodide and iodate were 4.0 and 5.0 microg/l (as iodine) at a signal-to-noise ratio of 3. Values of the relative standard deviation of peak area, peak height, and migration times for iodide and iodate were 2.9, 1.3, 1.0 and 2.3, 2.1, 1.0%, respectively. The proposed method was applied to simultaneous determination of iodide and iodate in seawater collected at a pond at our university.     

Ion chromatographic determination of hydroxide ion on monolithic reversed-phase silica gel columns coated with nonionic and cationic surfactants

The determination of hydroxide by ion chromatography (IC) is demonstrated using a monolithic octadecylsilyl (ODS)-silica gel column coated first with a nonionic surfactant (polyoxyethylene (POE)) and then with a cationic surfactant (cetyltrimethylammonium bromide (CTAB)). This stationary phase, when used in conjunction with a 10 mmol/l sodium sulfate eluent at pH 8.2, was found to be suitable for the rapid and efficient separation of hydroxide from some other anions, based on a conventional ion-exchange mechanism. The peak directions and detection responses for these ions were in agreement with their known limiting equivalent ionic conductance values. Under these conditions, a linear calibration plot was obtained for hydroxide ion over the range 16 micromol/l to 15 mmol/l, and the detection limit determined at a signal-to-noise ratio of 3 was 6.4 micromol/l. The double-coated stationary phase described above was shown to be superior to a single coating of cetyltrimethylammonium bromide alone, in terms of separation efficiency and stability of the stationary phase. A range of samples comprising solutions of some strong and weak bases was analyzed by the proposed method and the results obtained were in good agreement with those obtained by conventional potentiometric pH measurement.     

Determination of calcium, magnesium and zinc in unused lubricating oils by atomic absorption spectroscopy

Varying concentrations of lanthanum and strontium were added to solutions of ashed unused lubricating oils for the determination of calcium, magnesium and zinc content using flame atomic absorption spectrophotometry. At least 3000 μg g⁻¹ of lanthanum or strontium was required to completely overcome the interference of the phosphate ion, PO³⁻₄, and give peak values for calcium. The presence of lanthanum or strontium did not cause an appreciable increase in the amount of magnesium and zinc obtained from the analyses. The method is fast and reproducible, and the coefficients of variation calculated for the elements using one of the samples were 1.6% for calcium, 3.5% for magnesium and 0.2% for zinc. Results obtained by this method were better than those obtained by other methods for the same samples.     

聚氧化乙烯絮凝-电感耦合等离子体发射光谱法测定土壤中水溶性钾、钠、钙、镁、硫酸根

建立了聚氧化乙烯絮凝-4000r/min离心,电感耦合等离子体发射光谱法（ICP-AES）测定土壤水溶性钠钾钙镁硫酸根离子的方法。本法在常规方法浸提的基础上,加入聚氧化乙烯絮凝剂使溶液中的胶体形成絮凝物聚沉,制得澄清溶液,消除了胶体对钾、钠、钙、镁吸附的干扰;采用电感耦合等离子体发射光谱法一次性测定钾、钠、钙、镁、硫酸根,相较传统方法简便快速,结果准确可靠。本法各离子检出限为0.37-2.91g/g,相对标准偏差小于5.55%,完全满足检测要求。该法操作简便,快速,实用性强,对环境无二次污染,已成功应用于土壤水溶性钾、钠、钙、镁、硫酸根离子的测试分析中,适合土壤批量样品分析。     

Optimization of square wave anodic stripping voltammetry (SWASV) for the simultaneous determination of Cd,Pb, and Cu in seawater and comparison with differential pulse anodic stripping voltammetry (DPASV)

Square wave anodic stripping voltammetry (SWASV) was optimized for the simultaneous determination of Cd, Pb and Cu in coastal seawater samples. Background subtraction was adapted to improve peak detection and quantification. Optimum background voltammograms were obtained by applying a 7.5 s equilibration potential at -975 mV (vs. Ag/AgCl, 3M KCl) before starting the background scan. Voltammetric scan parameters were optimized to obtain maximum sensitivity while retaining good peak resolution and discrimination from background. Optimal parameters were: frequency 100 Hz, pulse amplitude 25 mV, current sampling delay time 2 ms, step height 8 mV. The sensitivity of optimized SWASV proved to be more than double that of differential pulse anodic stripping voltammetry (DPASV), and analysis time was halved. Samples containing around 13 (Cd), 30 (Pb), 200 (Cu) ng/l (typical averages of the coastal area of the Marche region) can be analyzed using a 5 min deposition time and the total analysis time using three standard additions is about 1 h and half, excluding the mercury film preparation and the outgassing of the sample, which can be made in parallel using a second cell cup.