Ion Chromatographic determination of trace anions and cations in high-purity water

An ion chromatographic measuring system for the off-line and on-line determination of some trace anions and cations in high-purity water is presented. The ng/L level of anions and cations in 20–130 mL high-purity water can be analyzed after preconcentration on ion exchange columns. The concentrated solutes are eluted by eluents from the trap column and separated using a Dionex analytical column. The quantification of each ion is achieved using the suppressor technique and conductivity detector. The influence of various parameters on the results is discussed. The detection limits of cations and anions are between 10 and 30 ng/L for chloride, bromide, nitrate, phosphate, sulphate, sodium, ammonium, potassium, magnesium and calcium ions.     

Ion Chromatographic determination of trace anions and cations in high-purity water

An ion chromatographic measuring system for the off-line and on-line determination of some trace anions and cations in high-purity water is presented. The ng/L level of anions and cations in 20-130 mL high-purity water can be analyzed after preconcentration on ion exchange columns. The concentrated solutes are eluted by eluents from the trap column and separated using a Dionex analytical column. The quantification of each ion is achieved using the suppressor technique and conductivity detector. The influence of various parameters on the results is discussed. The detection limits of cations and anions are between 10 and 30 ng/L for chloride, bromide, nitrate, phosphate, sulphate, sodium, ammonium, potassium, magnesium and calcium ions.     

Ion-chromatographic determination of trace anions with direct sample injection

The influence of the sample volume on the ion-chromatographic determination of anions was examined using various separation columns. Unlike conventionally used columns, Akvilain Al columns exhibit higher capacity factors for weakly retained anions. Thus, increasing the injected sample volume does not result in the masking of peaks of weakly retained anions by the negative system peak. The determination of anions at a level of several Μg/L is possible over a wide pH range. A double-loop system was used to eliminate the effect of residual ions in water used for the preparation of calibration solutions.     

Reproducible digestion method for ion-chromatographic analysis of anions in 30% hydrogen peroxide

Reboxetine is a new norepinephrine reuptake inhibitor (NRI) drug recently introduced in the therapy for depressed patients. It is effective in the treatment of severe depression and safer to use than traditional tricyclic antidepressants. In this paper an original high-performance liquid chromatography (HPLC) method with ultraviolet detection for the determination of reboxetine in human plasma is described. It uses a C8 reversed-phase column and a mobile phase composed of acetonitrile and aqueous tetramethylammonium perchlorate. For the analysis of plasma samples containing very low levels of reboxetine, another HPLC method with fluorimetric detection was developed (limit of quantitation, LOQ=11 ng ml(-1); limit of detection, LOD=4 ng ml(-1)). The fluorimetric method is based on precolumn derivatisation of reboxetine with 9-fluorenylmethyl chloroformate. An accurate sample pretreatment of human plasma samples has been implemented by means of solid-phase extraction (SPE) on Oasis HLB (hydrophilic-lipophilic balance) cartridges with very high extraction yields (>95%). Both methods were applied to the analysis of plasma samples from depressed patients undergoing therapy with reboxetine and gave satisfactory results in terms of precision (RSD<4.5%) and accuracy (mean recovery>94%).     

Comparison of two methods for the optimization of the analytical conditions for the determination of total sulfur

Response surface and simplex methods were used for optimizing the determination of total sulfur present in gaseous samples using a quartz crystal microbalance. The optimization methodology increased the analytical signal from three to five times. The simplex method showed the highest efficiency in the search for the maximum sensor response. However, the response surface allows ranking the variables according to their effects and highlights the existence of a plateau in the optimal region.     

Development of visual analytical methods for trace determination.

In this paper our recent progress in the field of simple analytical methods is reviewed, with particular focus on the development of rapid, inexpensive, yet sensitive techniques to visualize trace elements of medical, industrial, and environmental importance. Our objective is to solve long-standing practical problems in these fields. We have repeatedly shown that visual perception is remarkably sensitive when used with our new techniques. The applicability of the proposed methods to real samples is also discussed. Making measurements visually is a method free from machinery malfunctions and serves as a simple and sensitive analytical technique, avoiding all of the practical disadvantages associated with sophisticated instrumentation as well as tedious procedures.     

New leading electrolyte for the direct determination of chloride and other anions in analytical isotachophoresis.

In a number of experiments it was shown that the dithionate ion possesses a higher effective mobility than the chloride ion in aqueous solution, thus enabling the direct and simultaneous isotachophoretic determination of chloride and other anions. Using an acid-base titration, we found only one pKa value for dithionic acid, which is in contrast to the two pKa values stated in the literature. Based on this pKa value, theoretical calculations and the experimentally observed effective mobility of the dithionate ion indicate a higher effective mobility compared to the chloride ion from pH 3. Taking into account the physico-chemical properties of the dithionate, its unrestricted use as isotachophoretic leading ion was confirmed. Based on the dithionate ion, new electrolyte systems for the determination of chloride were used. One system was optimised for the determination of chloride and other low-molecular-mass anions and applied to the analysis of waste water and drinking water. The water samples were analysed in parallel by ion chromatography and compared with the isotachophoretic results.     

Comparison of three analytical methods for the determination of trace elements in whole blood

Three different analytical techniques were compared in a study of the role of trace elements in multiple sclerosis. Data for eight elements (Cd, Co, Cr, Cu, Mg, Mn, Pb, Zn) from neutron activation, flame atomic absorption and electrothermal atomic absorption methods were compared and evaluated statistically. No difference (probability less than 0.001) was observed in the elemental values obtained. Comparison of data between suitably different analytical methods gives increased confidence in the results obtained and is of particular value when standard reference materials are not available.     

Green analytical chemistry in sample preparation for determination of trace organic pollutants

The principles of green chemistry are applied to not only chemical engineering and synthesis, but also increasingly analytical chemistry. We describe environment-friendly analytical techniques applied to isolate and to enrich trace organic pollutants from solid and aqueous samples. Amounts of organic solvents used in analytical laboratories are reduced by applying solventless extraction, extraction using other types of solvent, assisted solvent extraction and miniaturized analytical systems.     

离子色谱法同时测定离子液体中六氟磷酸根及痕量杂阴离子

建立了一种同时测定离子液体中六氟磷酸根(PF~6)和痕量杂阴离子氟、氯、溴(F~,Cl~,Br~)的离子色谱方法(IC)。样品经溶解、稀释、过滤后用Dionex IonPac AS22分离柱(250 mm×4 mm)分离,淋洗液为碳酸盐-乙腈体系(体积比为70:30),流速1.0 mL/min,采用Dionex DS6电导检测器检测,外标法定量。F~,Cl~,Br~和PF~6的线性范围分别为0.5～50 μg/L、10～200 μg/L、10～200 μg/L和0.9～45 mg/L,线性相关系数分别为0.9999,0.9998,0.9999和0.9998,加标回收率为94.5%～100.5%,相对标准偏差为0.63%～1.03%,检出限(以信噪比为3计)分别为0.5 μg/L、2.0 μg/L、5.0 μg/L和0.9 mg/L。该方法用于离子液体中六氟磷酸根和痕量杂阴离子的同时测定,结果令人满意。     

Development and validation of analytical methodology using capillary electrophoresis for separation and determination of anions in rainwater

A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of both organic and inorganic anions in rain water using a background electrolyte (BGE) containing 5 mM molybdate, 0.15 mM CTAH, 0.01% PVA and 5 mM Tris buffer to adjust pH at 7.9. Under optimised conditions, good repeatability (RSD for sulphate in migration time=0.36% and peak area=4.2%), low detection limit (2 ppb for chloride) and satisfactory working range (50 ppb-20 ppm for hydrodynamic injection, 10 ppb-3 ppm for electrokinetic injection for chloride) were obtained. The reliability of the CE procedure developed was established by satisfactory recovery tests and good agreement of results obtained by both the CE and ion chromatography (IC) methods. The procedure developed had been successfully applied for field monitoring of rainwater showing good repeatability and capability of detecting trace anions at ppb levels beyond the IC working range. Thus, the new CE procedure developed provides a quick, sensitive, economic and reliable method to meet the need for the simultaneous determination of both organic and inorganic anions in the acid rain monitoring programme.     

Reversed flow injection spectrophotometric determination of trace amount of ammonia in natural water by oxidation of ammonia to nitrite

A new sensitive flow injection method for determination of ammonia in natural water samples have been developed, based on the oxidation of ammonia to nitrite by hypochlorite in the presence of large amount of potassium bromide. The oxidant solution obtained by on-line mixing of hypochlorite and potassium bromide was injected into a water carrier stream, and then mixed with sample stream. Ammonia in the sample solution was oxidized to nitrite. Nitrite was then determined by spectrophotometry with sulfanilamide and N-1-naphthylethylenediamine. By reversed injection of the oxidant solution, the interference of nitrite and turbidity of the sample can be removed. The linear range of the method for ammonia is 0.2-12 muM. The proposed method is simple and sensitive. It had been applied to the determination of ammonia in lake water samples. Recoveries of 95-104% were obtained.     

Application of copper sulfate pentahydrate as an ammonia removal reagent for the determination of trace impurities in ammonia by gas chromatography

Rapid analysis of trace permanent gas impurities in high purity ammonia gas for the microelectronics industry is described, using a gas chromatograph equipped with a phtoionization detector. Our system incorporates a reactive precolumn in combination with the analytical column to remove the ammonia matrix peak that otherwise would complicate the measurements due to baseline fluctuations and loss of analytes. The performance of 21 precolumn candidate materials was evaluated. Copper sulfate pentahydrate (CuSO₄·5H₂O) was shown to selectively react with ammonia at room temperature and atmospheric column pressures, without affecting the hydrogen, oxygen, nitrogen, methane or carbon monoxide peak areas. To prevent loss of trace carbon dioxide, an additional boron trioxide reactant layer was inserted above the copper sulfate pentahydrate bed in the reactive precolumn. Using the combined materials, calibration curves for carbon dioxide proved to be equivalent in both ammonia and helium matrix gases. These curves were equivalent in both matrix gases. The quantitative performance of the system was also evaluated. Peak repeatabilities, based on eight injections, were in the range of 4.1–8.2% relative standard deviation; and detection limits were 6.9 ppb for H₂, 1.8 ppb for O₂, 1.6 ppb for N₂, 6.4 ppb for CH₄, 13 ppb for CO, and 5.4 ppb for CO₂.     

Effect of inorganic anions on the titanium dioxide-based photocatalytic oxidation of aqueous ammonia and nitrite

In this study, we investigated the effects of four inorganic anions (Cl⁻, SO₄²⁻, H₂PO₄⁻/HPO₄²⁻, and HCO₃⁻/CO₃²⁻) on titanium dioxide (TiO₂)-based photocatalytic oxidation of aqueous ammonia (NH₄⁺/NH₃) at pH ∼ 9 and ∼10 and nitrite (NO₂⁻) over the pH range of 4–11. The initial rates of NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation are dependent on both the pH and the anion species. Our results indicate that, except for CO₃²⁻, which decreased the homogeneous oxidation rate of NH₄⁺/NH₃ by UV-illuminated hydrogen peroxide, OH scavenging by anions and/or direct oxidation of NH₄⁺/NH₃ and NO₂⁻ by anion radicals did not affect rates of TiO₂ photocatalytic oxidation. While HPO₄²⁻ enhanced NH₄⁺/NH₃ photocatalytic oxidation at pH ∼ 9 and ∼10, H₂PO₄⁻/HPO₄²⁻ inhibited NO₂⁻ oxidation at low to neutral pH values. The presence of Cl⁻, SO₄²⁻, and HCO₃⁻ had no effect on NH₄⁺/NH₃ and NO₂⁻ photocatalytic oxidation at pH ∼ 9 and ∼10, whereas CO₃²⁻ slowed NH₄⁺/NH₃ but not NO₂⁻ photocatalytic oxidation at pH ∼ 11. Photocatalytic oxidation of NH₄⁺/NH₃ to NO₂⁻ is the rate-limiting step in the complete oxidation of NH₄⁺/NH₃ to NO₃⁻ in the presence of common wastewater anions. Therefore, in photocatalytic oxidation treatment, we should choose conditions such as alkaline pH that will maximize the NH₄⁺/NH₃ oxidation rate.     

Optimization of injection technique in capillary ion electrophoresis for the determination of trace level anions in environmental samples

Capillary ion electrophoresis (Waters' trade name: Capillary Ion Analysis) offers several advantages compared to ion chromatography for the analysis of ionic solutes, primarily simplicity, matrix independence, and a different separation selectivity. The use of electromigration sample introduction leads to on-capillary enrichment of ionic analytes at the sample—buffer interface, permitting the determination of low ng/ml levels of anions in environmental samples of moderate ionic strength. This injection method allows improved sensitivity compared to hydrostatic injection; and is significantly more rapid than precolumn concentration ion chromatography. The analyte enrichment rate, hence peak response, is strongly dependent upon ionic strength and appropriate measures, such as standard addition or internal standard techniques, must be used to account for differences in standard and sample conductance.     

Single-column ion-chromatographic determination of chromium(VI) in aqueous soil and sludge extracts

Single-column ion-chromatography (SCIC) was investigated as a routine, rapid, precise and selective analytical method for the determination of chromium(VI) in aqueous extracts of soil and sewage sludge. Chromatographic parameters were optimized for determination of Cr(VI), NO(-)(3) and SO(2-)(4). A low-capacity resin-based column was used for the separation and the anions were determined by conductometric detection. p-Hydroxybenzoic acid (5mM) at pH 8.5 was used as the eluent. The limit of detection, defined as S/N = 3, was 92 mug/l. The resolution between Cr(VI) and SO(2-)(4) was 2.8, the precision ranged from 0.9% for NO(-)(3) to 2.0% for Cr(VI) with a 500-mul injection. The SCIC results for Cr(VI) agreed closely with those obtained by inductively coupled argon-plasma emission and spectrophotometry.