Anion chromatography using on-line recycled eluents

Non-suppressed anion chromatography, using on-line recycled eluents, was investigated. Cations and anions from samples were excluded from the eluents using a mixture of strongly acidic cation-exchange resins and strongly basic anion exchange resins in the eluent reservoir. This exclusion was performed after determination of the anions in the non-suppressed anion chromatography, and the eluents were then recycled on-line. The performance of consecutive determinations was evaluated from the relative standard deviation (RSD) of peak heights and retention times of chloride, bromide, nitrite, nitrate, and sulfate ions, with a concentration of 3 microg ml(-1) each, compared to that of normal anion chromatography. Over 50 consecutive determinations could be achieved with an eluent volume of only 200 ml for a 100 microl sample volume. Almost all the RSD values for retention time, and peak heights of these anions, were smaller than 3%. Over fifty consecutive determinations of chloride, nitrate, and sulfate ions in a river water sample could be achieved with an eluent volume of only 100 ml. All the RSD values for retention time and peak heights of these anions were smaller than 3%. The eluent volume could be decreased to one tenth of that used in normal anion chromatography. The performance of the anion chromatography, using on-line recycled eluents, was the same as that for normal anion chromatography under the same conditions.     

Determination of nitrite, nitrate, and glucose-6-phosphate in muscle tissues and cured meat by IC/MS

The endogenous nitrate concentration in fresh meat and the residual nitrate and nitrite contents after curing are related to food quality and safety. Most ion chromatography (IC) methods suffer from interferences, especially in fresh meat samples, in which the endogenous nitrate content is low, and in cured meat products, in which other nitrogenous compounds can interfere with the separation of inorganic anions. One of the major classes of interfering compounds in fresh meat are sugar phosphates, which originate from glycolysis during the conversion of muscle glycogen to lactic acid. Nitrate can be separated from interfering compounds with a high-capacity anion-exchange column that was manufactured for use with hydroxide eluents (i.e., hydroxide-selective). This column has a different selectivity than traditional IC columns that use carbonate eluents and facilitates the determination of nitrate in both fresh and cured meats. Nitrate was detected by both suppressed conductivity measurement and mass spectrometry (MS). The identifications of nitrate and glucose-6-phosphate were confirmed by MS detection. The described IC/MS method is robust, sensitive to nitrate concentrations as low as 0.10 mg/kg, and can determine sugar phosphates that are useful for monitoring meat freshness. We successfully used this method to determine nitrate in nearly 100 muscle tissues and cured meat samples.     

Determination of tungstate in soils and sludges by using single-column ion chromatography

A procedure has been developed for the determination of tungstate at trace levels in aqueous extracts of soil and sludge by single-column ion chromatography (SCIC). Chromatographic parameters based on ion selectivity, time of determination and signal response were optimized for tungstate with the simultaneous detection of nitrate and sulfate. Chloride, phosphate, chromate, molybdate and vanadate were found not to interfere in the determination. A low-capacity resin-based column was used for the separation with p-hydroxybenzoic acid (5 mM) at pH 8.5 as the eluent. The limit of detection defined as three times the signal-to-noise ratio was 170 μg l^?1 (2-ml sample). The resolution between tungstate and sulfate was R_s=2.84. The results for aqueous extracts agree closely with those obtained by an accepted spectrophotometric method.     

Determination of free and total sulfate and phosphate in glycosaminoglycans by column-switching high-performance size-exclusion and ion chromatography and single-column ion chromatography

Analytical procedures for the determination of free and total sulfate and phosphate in glycosaminoglycans by high-performance liquid chromatography were studied. A column-switching method coupling high-performance size-exclusion chromatography (HPSEC) and ion chromatography (IC) is proposed for the determination of free anions. Good run-to-run and day-to-day precision values (RSD) of < 4.7% were obtained for both anions. Total anion contents were determined after wet acid hydrolysis with nitric acid-hydrogen peroxide (5 + 1) by single-column IC and ICP-AES elemental analysis in order to validate the results. Recoveries ranging from 94.6 to 99.0% for sulfate and from 80.8 to 94.0% for phosphate were obtained. Both HPSEC-IC and single-column IC methods were applied to the analysis of a low molecular mass heparin, a non-fractionated heparin and a chondroitin 4-sulfate. From the free and total sulfate determinations, the content of linked sulfur was calculated and ranged from 5.1 to 12.2% m/m.     

Onboard determination of submicromolar nitrate in seawater by anion-exchange chromatography with lithium chloride eluent.

Ion-exchange chromatography using a high-capacity anion exchanger with UV detection was applied to the determination of nitrate in seawater. Major ions in seawater samples did not affect the peak shape and the retention time of the nitrate when an alkaline metal cation-chloride solution was used as an eluent at high concentrations (0.5-2 mol/l). At a wavelength of 220 nm, the peak of bromide was very small because of low absorption, while its separation from the nitrate peak was good at high concentrations. Among the eluents tested, lithium chloride gave the best separation of nitrate from bromide. It was estimated that the lithium ion had the least potential for ion-pair formation with nitrate, and its retention time was prolonged compared with the retention times when using other cations; with bromide and nitrite, such an effect was not observed. The results of shipboard seawater nitrate determination by our method in the South Pacific Ocean and Antarctic Sea showed good agreement with those by the conventional photometric method using continuous flow.     

The determination of lactate,acetate, chloride and phosphate in an intravenous solution by non-suppressed ion chromatography

Summary The determination of acetate, lactate, chloride and phosphate in an intravenous solution is investigated using non-suppressed ion chromatography with indirect UV absorption detection. When phthalate eluents are used with low capacity anion-exchange columns, the above solute species cannot be resolved unless acetonitrile is added to the eluent. Optimum results are obtained with 0.3 mM phthalate (pH 6.0) containing 30% acetonitrile as eluent. The improved resolution with this eluent is attributed to the existence of a partial reversed-phase retention mechanism operating on the unfunctionalised portions of the styrene-divinylbenzene polymeric ion-exchange material.     

Trace anion determination in concentrated hydrofluoric acid solutions by two-dimensional ion chromatography II. Method performance study with a hydroxide eluent and a low noise suppressor

The two-dimensional ion exclusion chromatography/ion chromatography (ICE-IC) approach is considered to be the method of choice for the determination of trace anions in concentrated hydrofluoric acid (48-50%, w/w). In order to achieve lower detection limits, this method was for the first time used with electrolytically generated and purified hydroxide eluents in combination with a low noise electrochemical suppressor. Compared to carbonate based eluents, the achieved gain in peak height sensitivity for chloride, sulfate, nitrate and phosphate is a factor of 6, 7, 16 and 13, respectively. The instrumental detection limits, based on the background noise, are 2, 0.2, 0.4 and 1.4 microg/kg HF 50% (w/w) for the same anions. Their method detection limits, calculated according to SEMI, are all within the 6-10microg/kg HF 50% (w/w) range and thus at least 10 times lower than the current Tier C grade requirements. The chromatographic run time could be shortened with some 10 min by the use of a relatively fast high-capacity hydroxide selective anion exchange column.     

Simultaneous analysis of selenate and selenite by single-column ion chromatography

Summary A rapid, selective and sensitive method has been developed for the simultaneous determination of selenate [Se(VI)] and selenite [Se(IV)] at trace levels by single-column ion chromatography. p-Hydroxybenzoic acid (4 mM) at pH 8.0 was used as the eluent. A low capacity resin-based anion-exchange column was employed for the separation with conductometric detection for quantification. The method requires minimal sample pretreatment. Resolution (R_s) between Se(VI)/Se(IV) was 6.76. Chloride, nitrate and sulfate did not interfere with selenium separation. The detection limits for Se(VI) and Se(IV) were 0.06 μg/ml and 0.110 μg/ml, respectively. The relative standard deviation using a 500-μl loop was 0.90 to 1.86% for Se(VI) and Se(IV), respectively. The method was applied to analyze seleniferous soil samples.     

Determination of traces of inorganic anions by means of high-performance liquid chromatography on zipaxsax columns

Zipax-SAX pellicular beads are used as the anion-exchanger material ; a high-pressure packing technique is described. A Zipax-SAX column (200 × 4.5 mm) is used in a separation system with eluent suppression and conductivity detection as in ion-chromatography. Good separation of chloride, nitrite, bromide, nitrate and sulfate is obtained with 1.4 × 10^-3 M succinate or adipate eluents at pH 7. A complete separation takes about 6 min at a flow rate of 3 ml min^-1. Detection limits of 2 μg l^-1 chloride, 4 μg l^-1 nitrate and 10 μg l^-1 sulfate can be reached if 2 ml of sample is preconcentrated.     

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.     

Reversed-phase liquid chromatography/electrospray ionization/mass spectrometry with isotope dilution for the analysis of nitrate and nitrite in water

A new method was developed for the analysis of nitrate and nitrite in a variety of water matrices by using reversed-phase liquid chromatography/electrospray ionization/mass spectrometry in the negative ion mode. For this direct analysis method, nitrate and nitrite anions were well separated under the optimized LC conditions, detected by monitoring m/z 62 and m/z 46 ions, and quantitated by using an isotope dilution technique that utilized the isotopically labeled analogs. The method sensitivity, accuracy, and precision were investigated, along with matrix effects resulting from common inorganic matrix anions. The isotope dilution technique, along with sample pretreatment using barium, silver, and hydrogen cartridges, effectively compensated for the ionization suppression caused by the major water matrix anions, including chloride, sulfate, phosphate, and carbonate. The method detection limits, based on seven reagent water replicates fortified at 0.01 mg N/L nitrate and 0.1 mg N/L nitrite, were 0.001 mg N/L for nitrate and 0.012-0.014 mg N/L for nitrite. The mean recoveries from the replicate fortified reagent water and lab water samples containing the major water matrix anions, were 92-103% for nitrate with an imprecision (relative standard deviation, RSD) of 0.4-2.1% and 92-110% for nitrite with an RSD of 1.1-4.4%. For the analysis of nitrate and nitrite in drinking water, surface water, and groundwater samples, the obtained results were generally consistent with those obtained from the reference methods. The mean recoveries from the replicate matrix spikes were 92-123% for nitrate with an RSD of 0.6-7.7% and 105-113% for nitrite with an RSD of 0.3-1.8%.     

Determination of trace anions in high-nitrate matrices by ion chromatography

An ion chromatography method was developed to determine trace anionic contamination in matrices that have a high concentration of nitrate ion. Contaminant anions of interest were separated on an IonPac AS15 high-capacity anion-exchange column and detected by suppressed conductivity detection. An EG40 eluent generator was used to prepare high-purity and carbonate-free potassium hydroxide. Using the EG40, performance at trace levels was enhanced because background conductivity decreased and retention time reproducibility improved. Trace anionic contamination from the mobile phase was minimized when using the eluent generator compared to using conventionally prepared sodium hydroxide eluents. The signal-to-noise ratio was also improved with the use of a temperature controlled conductivity cell and chromatography hardware in the microbore (2-mm) format. The eluent concentration was optimized to separate the contaminant anions from the excess of the nitrate matrix ions. The procedure was demonstrated for a solution of reagent-grade sodium nitrate and high-purity 0.7% nitric acid. Method detection limits for chloride, sulfate and phosphate of 150 μg/l and lower were achieved.     

Monitoring trace anion contamination in disk drive components

Ion chromatography was used to determine trace anionic contamination on the surface of hard disk drive components. These contaminants can have a detrimental effect on device reliability and yield. Disk drive components were soaked in deionized water and these extracts were analyzed for anions. The anions fluoride, acetate, formate, acrylate, methacrylate, chloride, nitrite, bromide, nitrate, benzoate, sulfate, oxalate, phthalate and phosphate were separated on a high-performance anion-exchange column and determined at concentrations less than 1 microg/l with suppressed conductivity detection. The extract solutions were analyzed either by injecting 1 ml or by preconcentrating 5 ml. We evaluated the performance of both methods.     

HPLC of anions on coated reversed phase columns using indirect UV-detection and eluents containing nitrophthalic acids

Analysis of anions by HPLC has been optimized in the direction of reduced analysis times with standard reversed phase columns and UV detection. This was achieved by use of a new eluent containing 3-nitrophthalic acid and small proportions of acetonitrile. Resin-based and silica-based anion exchangers of varying ion-exchange capacities are prepared with cetyltrimethylammonium bromide by a rapid dynamic coating technique. Some new, strong eluents containing nitrophthalic acids are evaluated and compared with an eluent containing potassium hydrogen phthalate. Addition of acetonitrile was found to improve the retention behavior of mono- and divalent anions. An automatic system was developed for the analysis of chloride, nitrate, and sulfate in drinking water. It is shown that a water sample can be analyzed in less than two minutes on a column of 25 mm length.     

Direct extraction of urinary analytes from undeveloped reversed-phase thin layer chromatography plates using a solvent gradient combined with on-line electrospray ionisation ion mobility-mass spectrometry

The direct extraction of urinary analytes deposited on reversed-phase thin-layer chromatography (RP-TLC) plates is demonstrated using a solvent gradient extraction procedure without prior chromatographic development. The surface sample probe TLC-MS interface used for the gradient extraction is compared to direct loop injection into the electrospray ion source for biofluid profiling. The gradient elution is shown to enhance ion intensities, as urinary salts are eluted in aqueous formic acid in the early part of the gradient reducing ion suppression. The retention of urinary components on the C18 RP-TLC plate was confirmed by monitoring analyte responses with, and without, an aqueous wash phase prior to the solvent gradient extraction. The use of gradient elution allows fractionation of the complex biological matrix as a result of differential retention of urine components on the undeveloped RP-TLC plate. The direct gradient analysis of TLC plates has also been combined with ion mobility-mass spectrometry to further resolve the complex urinary profile and identify co-eluting compounds.     

Electrospray ionization-ion mobility spectrometry: a rapid analytical method for aqueous nitrate and nitrite analysis

This paper reports the first example of electrospray ionization (ESI) for the separation and detection of anions in aqueous solutions by ion mobility spectrometry (IMS). Standard solutions of arsenate, phosphate, sulfate, nitrate, nitrite, chloride, formate, and acetate were analyzed using ESI-IMS and distinct peak patterns and reduced mobility constants (K(0)) were observed for respective anions. Real world water samples were analyzed for nitrate and nitrite to determine the feasibility of using ESI-IMS as a rapid analytical method for monitoring nitrate and nitrite in water systems. The data showed satisfactory correlation between the measured value ([similar]0.16 ppm) and the reported maximum nitrate-nitrogen concentration (0.2 ppm) found in a local drinking water system. For on-site measurement applications, direct sample introduction and air as an alternate drift gas to nitrogen were evaluated. The identities of the nitrite and nitrate mobility peaks were verified by comparison of reduced mobility constants with mass identified nitrate and nitrite ions reported in literature. In the mixing ratio, a linear dynamic range of 3 orders of magnitude and instrument detection limits of 10 ppb for nitrate and 40 ppb for nitrite were obtained. The calibration curves showed r(2) value of 0.98 and slope of 0.06 for nitrate and r(2) value of 0.99 and slope of 0.11 for nitrite.     

Determination of nitrite and nitrate in human serum

A simple and effective assay for nitrite and nitrate in human serum has been developed using ion chromatography. Initial experiments using isocratic carbonate-bicarbonate elution with conductivity detection on a Dionex QIC system with an AS4A-SC column showed promise but were unsatisfactory because of co-elution problems with nitrite. Carbonate and chloride were investigated as eluents using a gradient system, and direct UV detection at 214 nm was used in place of conductivity detection. Dionex AS4A, AS9A, AS12, Nucleopac PA-100 and Carbopac PA-100 columns were compared for selectivity and resistance to overload. The final method, using a chloride concentration gradient, pH buffering and direct UV detection with a Carbopac PA-100 column, shows good resolution, does not suffer from chloride overload and is simple to use. The method is being used in an investigation of the role of nitric oxide in pre-eclampsia, a hypertensive disorder during pregnancy.     

单柱离子色谱分析若干无机阴离子的初步研究

本文所提出的单柱离子色谱分离阴离子混合物的技术,不用抑制柱,树脂也无需再生。用国产多孔乙基苯乙烯-二乙烯苯共聚物制备了不同交换度的低容量阴离子交换树脂。以苯甲酸盐为洗脱液,F~-、Cl~-、Br~-可以分离,F~-峰尖锐,Br~-峰较宽。以邻苯二甲酸氢盐为洗脱液,保留时间均减小,但F~-峰被进样峰所掩盖,Cl~-、Br~-、SO_4~-:可满意地得到分离,洗脱液的浓度和pH对阴离子分离的保留时间和峰高有较大的影响。邻苯二甲酸氢盐中不同的阳离子,由于它们的电导背景不同(Li~+Na~+>K~+>NH_4~+。     

Critical comparison of retention models for the optimisation of the separation of anions in ion chromatography: II. Suppressed anion chromatography using carbonate eluents

Seven theoretical retention models, namely the linear solvent strength model (using the dominant equilibrium approach and competing ion effective charge approach), the dual eluent species model, the Kuwamoto model, the extended dual eluent species model, the multiple species eluent/analyte model and the empirical end-points model, were used to describe the retention behaviour of anions in suppressed ion chromatography (IC). An extensive set of experimental retention data was gathered for 24 anions (fluoride, formate, bromate, chloride, hexanesulfonate, bromide, chlorate, nitrate, iodide, thiocyanate, perchlorate, sulfite, succinate, sulfate, tartrate, selenate, oxalate, tungstate, phthalate, molybdate, chromate, thiosulfate and phosphate) on a Dionex AS4A-SC column using carbonate eluents of varying concentration and HCO₃⁻:CO₃²⁻ ratios. Statistical comparison of the predicted and experimentally obtained retention factors showed that the performance of the theoretical models improved with the complexity of the model. However the empirical model (in which a linear relationship is assumed between the logarithm of retention factor and the logarithm of eluent strength, but the slope is determined empirically) gave the most consistent performance across the widest range of anions. The empirical end-points model was also shown to be the most satisfactory model due to its low knowledge requirements and easy solution. Compared with non-suppressed IC (see Part I), the retention behaviour in suppressed IC was found to be easier to model by all retention models.     

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.