Suppressed Ion Chromatography Research Articles

Asymmetric Membrane Fiber-Based Carbon Dioxide Removal Devices for Ion Chromatography

The application of hollow and filament-filled single asymmetric membrane fibers, consisting of a thin silicone layer on a tubular microporous support, for removing CO(2) in suppressed ion chromatography effluents is described. With appropriate choice of the removal device and operating conditions, the CO(2) can be essentially quantitatively (99+%) removed. For carbonate-based eluents, the use of such devices greatly reduces or eliminates the water dip, permitting better quantitation of poorly retained anions that elute close to the dip, allows practical gradient chromatography, and improves noise levels and attainable detection limits. In hydroxide eluent chromatography, the device largely removes the response from CO(2) present in the samples; this greatly aids atmospheric trace gas analysis by IC. Device dimensions are such that the dispersion introduced by the device is small.

Determination of nitrate by suppressed ion chromatography after copperised-cadmium column reduction

The nitrate-selective copperised-cadmium (Cu-Cd) reduction reaction coupled directly to the highly sensitive nitrite ion chromatographic detection, produced a more precise method for determination of nitrate than any one of the two conventional methods. A borate buffer solution used in the reduction reaction, in place of the conventional ammonium–EDTA buffer solution, eliminated interferences from co-eluting ions in the subsequent ion chromatographic detection of nitrite. Optimised experimental conditions included using a packed-bed Cu-Cd reductor column length of 12.5 cm, a solution flow rate of 3.0 ml/min, and using 10.0 ml of borate buffer solution for each 20.0 ml of nitrate-containing solution. Precision was high for results obtained within a greatly extended linear dynamic range of 0.006–1.20 mg/l NO 3 −, with a much lower limit of detection of 0.40 μg/l NO 3 −. Cu-Cd reductor column efficiency was 98.20 ± 6.03%. Validation of the method was undertaken using certified reference materials. The method was successfully applied to analysis of dam water, river water and storm water samples, producing more precise results than either the conventional colorimetric method or the conventional ion chromatographic method.

Simultaneous determination of inorganic anions, calcium and magnesium by suppressed ion chromatography

Suppressed conductimetric detection ion chromatography (IC) was investigated for the separation and detection of common inorganic anions, calcium and magnesium by anion-exchange chromatography using a sodium carbonate–EDTA mobile phase. The formation of anionic Ca 2+–EDTA and Mg 2+–EDTA complexes allowed its separation from other inorganic anions opening the way for their simultaneous determination in a single chromatographic run. The effect of the pH, carbonate and EDTA concentrations in the eluent and the previous addition of EDTA to the samples has been studied. The optimised experimental conditions were applied to the determination of Ca 2+ and Mg 2+ in mineral waters with results in agreement with alternative ICP-MS methodologies.

Determination of carbon dioxide and acid components in exhaust gas by suppressed ion chromatography.

Although anions are usually determined by suppressed ion chromatography (IC), carbonate and bicarbonate ions can not be determined, because a mixed solution of sodium carbonate and sodium hydrogencarbonate is used as the eluent. This paper describes an IC method for the determination of carbonate ion and common anions using an IonPac AG17/AS17 column, an EG 40 eluent generator and a conductivity detector. The proposed IC method could determine carbonate ion and anions within 6 min. The relative standard deviations (n = 5) for chloride (0.4 mg L(-1)), nitrite (0.8 mg L(-1)), carbonate (100 mg L(-1)), nitrate (1.0 mg L(-1)) and sulfate (2.0 mg L(-1)) ions were 5.1%, 1.1%, 4.2%, 5.1% and 1.1%, respectively. In addition, the absorbing solution of carbon dioxide was examined, and 2-amino-2-methyl-1-propanol was found to be a good absorbing solution. The proposed IC method was applied to the determination of carbon dioxide and acid components in flue gas and automobile exhaust gas.

Low-pressure gradient micro-ion chromatography with ultra-short monolithic anion exchange column.

A 1.0 x 0.4 cm silica based monolithic anion exchanger has been produced and evaluated for use within a miniature gradient suppressed ion chromatography system based upon low-pressure micro-scale peristaltic pumps.

Highly Sensitive Methods for Determination of Fluoride in Biological Samples

A total of 40 samples of shell ashes from chicken eggs and 15 samples of chicken plasma have been investigated for amounts of fluoride. Two different methods have been applied. Egg samples were analysed with a spectrophotometric method (Alizarin:cerium:fluoride complex with detection at λ = 620 nm), following prior distillation of the samples in sulfuric media. Plasma samples were analysed by suppressed ion chromatography (IC) with conductivity detection. In this case, it was necessary to develop a cleaning method for the samples before their injection into the chromatographic system. The detection limits obtained were 25 ng mL−1 for the colorimetric method and 50 ng mL−1 in the case of the chromatographic method. Both methods were successfully applied to the analysis of the samples, and the obtained results were in accordance with the results obtained with the ion selective electrode (ISE) method. On the other hand, the proposed methods turn out to be a sensitive alternative when problems with sample size or cationic interferences are present.

A SIMPLE METHOD FOR ASSAYING TOTAL GLUCOSINOLATE CONTENT OF PLANT MATERIALS VIA SULFATE-ION-RELEASE USING ION CHROMATOGRAPHY

Naturally occurring phytochemicals possessing unique medicinal properties have become a matter of high interest in recent years. A good example is the enormous increase in the use of Saint John's Wort in Europe to treat depression. The anticancerous property of the vegetables of the family cruciferae, e.g., cauliflower, kale, broccoli, cabbage, mustard, and Brussels sprouts, has been attributed to a class of sulfur-containing phytochemicals known as glucosinolates. From a practical standpoint, the total glucosinolate content is generally considered the important parameter and hence that is what would generally be needed as a marker of product quality. The most frequently used method for the assay of total glucosinolates so far has been by assaying glucose which is produced stoichiometrically by the action of enzyme myrosinase. Various approaches for glucose assay have been employed and most are time-consuming and expensive. Fortunately, all glucosinolates, as a group of compounds, posses a sulfate group along with glucose which can be easily and stoichiometrically released by the action of enzymes myrosinase or sulfatase. The resulting sulfate can be easily and conveniently assayed by the use of ion chromatography. This paper reports the results of a study undertaken to develop a simple method for assaying total glucosinolates in plant materials by sulfate-ions-release and using Suppressed Ion Chromatography. Since the method is based on the sulfate ions released from the hydrolysis of glucosinolates, endogenous sulfate ions first had to be removed from the sample extracts. This was successfully accomplished via precipitation of sulfate ions by treating the extracts with 20 mM barium ions at 40 C for 60 minutes. Further, the residual (excess) barium ions were removed via precipitation by treatment of extracts with 25 mM chromate ions at 40 C for 15 minutes. Following these steps, glucosinolates were hydrolyzed by using myrosinase enzyme at a pH of 6.0 resulting in the release of sulfate moiety. Nearly 100% recovery of added sinigrin was achieved by assaying sulfate. However, the time needed for the complete hydrolysis of sinigrin by enzyme myrosinase in the presence of other salts needed for the procedure, was much longer than in their absence. Consequently, either a greater quantity of enzyme and/or a greater incubation time was necessary to achieve complete hydrolysis. Results of nine broccoli samples analyzed for total glucosinolates using the sulfate ion release method reported here were in agreement with those using glucose release method. Various parameters of the method are discussed.

Suppressed ion chromatography for monitoring chemical impurities in steam for geothermal power plants

A suppressed ion chromatography (IC) technique has been evaluated as a chemical monitoring tool for detecting major anions (F −, Cl −, NO 3 − and SO 4 2−) of condensed steam in geothermal power plants. It is shown that the suppressed IC technique provides a suitable means for preventing possible damage to generating equipment in the geothermal industry. An electrical conductivity detector (0.1 μS sensitivity) with an anion-exchange column (IonPac AS4A-SC), a micro-membrane suppressor (AMMS II), and an isocratic high-pressure pump system were successfully used for detecting low concentrations of inorganic anions. Method detection limits for the anions of interest were <0.184 mg/L. Details of the IC methodology as well as some experimental results obtained during its application for the chemical monitoring of geothermal steam pipes are also described.

Matrix Effects in the Determination of Low Anion Concentrations using Suppressed IC

Concentrations of anions in environmental water samples such as chloride, nitrate and sulphate, may differ orders of magnitude. Conditions have been investigated under which the quality of ion chromatographic data for series of environmental water samples, comprising samples with low anion concentrations, can be affected by the matrix of previous samples in the series. Effects of a high ionic sample matrix on the elution and retention processes of analytes have also been studied by repeated analyses of standards and blanks. The study was performed using a Dionex 2000i chromatograph and an AS4ASC column. Additionally, a Dionex DX500 chromatograph, equipped with a sodium hydroxide eluent generator and a AS15 column, was applied to investigate effects of low anion concentrations in the (bi)carbonate eluent used in the Dionex 2000i system. The effects are explained by distortions of the distribution of anions over eluent and stationary phase. Simultaneous analyses of major and minor components in routine measurements in a single series is still possible using suppressed ion chromatography, even in cases where the matrices are also divergent. Remedial tools to reduce undesired effects are described.

Effects of common metal ions on the determination of anions by suppressed ion chromatography

The effects of common metal ions (Na +, K +, Ca 2+, Mg 2+, Al 3+ and Fe 3+) on the determination of nitrate, phosphate and sulfate by suppressed ion chromatography were investigated. The responses of nitrate within 1–10 mg/l were not affected in the presence of six metal ions at 10 mg/l. The peak areas of 1.0 mg/l sulfate increased significantly at 10 mg/l Fe 3+ or Al 3+ up to 51.34 and 48.37%, respectively. In the presence of 10 mg/l Fe 3+, the peak area of 1 mg/l and 10 mg/l phosphates decreased by 91.44 and 33.71%, respectively. At 10 mg/l Al 3+ the peak areas of phosphate also increased slightly. The adverse effect of Fe 3+ on the determination of phosphate could be overcome effectively by reducing the pH of the samples. The method to overcome the adverse effect was studied.

Comparison of soluble P in soil water extracts determined by ion chromatography, colorimetric, and inductively coupled plasma techniques in PPB range

The determination of soil solution phosphate ions at trace levels is questionable with colorimetric method due to both limit of sensitivity and possible hydrolysis of organic soluble phosphate (P). A simple procedure was developed to determine orthophosphate at trace levels in soil solutions by single-column, suppressed-ion chromatography with conductivity detection without prior sample concentration. The procedure requires column capacity selection and use of a 500-μL injection loop. The method shows a detection limit of 0.05 μg P L−1 as well as a high resolution with a Dionex AS9SC column. The proposed method was tested by analyzing 45 soil samples (Colombian oxisols) differently P fertilized. Phosphorus levels in solutions were also determined by green-malachite colorimetry and inductively coupled plasma as reference methods. The linear correlation between the various methods showed that analysis of orthophosphate in the ppb range by ion chromatography are likely more acceptable that value obtained with colorimetry, which hydrolyzed organic P and caused systematic error. Examination of coefficients of variation for the IC method calculated from triplicate analyses of five randomized samples (situated between 7.4 and 16.3 μg P L−1) showed value ranged from 2.0 to 6.7%. The procedure allows precise measurements of trace amounts of orthophosphate in the presence of moderate background levels of salts such as chloride, nitrate, and sulfate ions and was adequate for routine analysis.

Application of electrodes modified with ion-exchange polymers for the amperometric detection of non-redox cations and anions in combination to ion chromatography

An amperometric sensor for non-electroactive ions was designed, evaluated in flow injection analysis, and applied as a novel detector in suppressed ion chromatography. It consists of a carbon paste electrode modified with either a polycationic or a polyanionic polymer containing a suitable charge transfer mediator (Fe(CN) 6 3− or Cu 2+), operating in an indirect amperometric mode. The detection mechanism involves ion exchange between the non-redox ionic analyte and the electroactive mediator, in the polymer particles located at the electrode surface, followed by the electrochemical transformation of the mediator species leached out of the polymer at the electrode ∣ solution interface. As detection was achieved in the absence of added supporting electrolyte, the amperometric signal contains both faradic and capacitive components. Optimisation was performed to get the highest faradic signals, by varying various experimental parameters (i.e. applied potential, composition of the electrode). These systems were then successfully applied to the analysis of mixtures of cations (Li +, Na +, K +, NH 4 +, Ca 2+, Mg 2+) and anions (F −, Cl −, NO 2 −, NO 3 −, SO 4 2−, PO 4 3−) subsequent to chromatographic separation. Good operational stability was observed, with typically less than 5% signal loss for 50 successive measurements.

Suppressed ion chromatography methods for the routine determination of ultra low level anions and cations in ice cores

The concentration of trace ionic species in snow and ice samples was determined using suppressed ion chromatography (IC) with conductivity detection and ultra-clean sample preparation techniques. Trace anion species were determined in a single 24-min run by combining sample preconcentration with gradient elution using Na2B4O7 eluent. The detection limits (ranging from 0.001 to 0.006 μM) are the lowest reported in the literature. Cation species were analysed by direct injection of 0.25 ml and isocratic elution with a H2SO4 eluent. The clean preparation techniques showed no evidence of a difference (Student’s t-test) between Milli-Q water samples analysed directly and processed Milli-Q ice samples. These robust, ultra-clean IC methods were routinely applied to the analysis of large number of samples to produce a high-resolution trace ion ice core record from Law Dome, East Antarctica.

Determination of chromium(iii) and chromium(vi) using suppressed ion chromatography inductively coupled plasma mass spectrometry

We have developed a method for the determination of Cr(III) and Cr(VI) by ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) using a self-regenerating suppressor. Deposition of the dissolved solids on the cones and the ion optics was eliminated by the suppressor. Chromium(III) was derivatized with EDTA, forming a stable mono-anionic complex, which was then separated from Cr(VI) by anion-exchange chromatography. The conditions for the quantitative conversion of Cr(III) to the corresponding EDTA complex were optimized and neither oxidation of Cr(III) to Cr(VI) nor reduction of Cr(VI) to Cr(III) were observed. Using 50 mmol L−1 NH4NO3 (pH 8) as the chromatographic eluent, potential interferents, such as chloride, carbonate and sulfate, were separated from both the Cr(EDTA)− complex and from Cr(VI), and no salt deposition was observed over long periods of time. The tolerance of the method to the presence of major matrix anions (NO3−, Cl−, CO32− and SO42−) was extensively studied. With a 1 mL injection volume, the detection limits were 5 and 12 ng L−1 using 52Cr, and 7 and 16 ng L−1 using 53Cr for Cr(III) and Cr(VI), respectively. The RSD of 5 injections was less than 5% at the 50 ng L−1 level. The method was validated using reference materials SRM 1643d and SLEW-3.

Enhanced conductometric detection of cyanide in suppressed ion chromatography

Weak-acid anions such as borate and cyanide, present problems in chemically suppressed ion chromatography, since the acids are weakly ionised, giving low conductivity and therefore decreased sensitivity. For borate this problem was overcome by converting the weak acid to its sodium salt, by the use of a second anion micromembrane suppressor (AMMS) as an ion exchange reactor (IER), flushed by EDTA reagent, to supply sodium ions for the conversion. This paper will discuss the use of this IER system to determine cyanide, which is also a very weak acid, with a similar pK a to borate. The detection limit for cyanide of 50 μ M compare favourably with indirect conductivity detection.

Determination of epichlorohydrin by ion chromatography

In this work we developed a new method for epichlorohydrin determination with suppressed ion chromatography. The technique is based on a reaction between the analyte and sulfur(IV) to form a product with a terminal sulfonate group that can be analyzed by anion-exchange chromatography. The reaction conditions were optimized as a function of temperature, type and concentrations of reagents and pH. Due to the characteristics of the product formed, the columns used were an IonPac AS11 and AS11-HC with a NaOH eluent. The eluent concentration was optimized in order to achieve a complete separation of epichlorohydrin, chloride and nitrate ions, commonly occurring in drinking waters. In order to improve the detection limits, a preconcentration step, using reversed-phase materials, has been optimized. The method developed was suitable for epichlorohydrin determination in drinking water.

Determination of chloride, sulfate and nitrate in groundwater samples by ion chromatography

Groundwater is a significant source of water for both domestic and agricultural use in some regions of the Maracaibo lake basin in Venezuela. Chemically suppressed ion chromatography with a Dionex Model 2000i/sp, Ionpac AS11, ASRS-I system was used for the analysis of major inorganic anions in groundwater samples. About 50 samples of groundwater, taken over several months in three different locations, were analyzed after filtration and sometimes dilution. In all the samples, the separation between the peaks of chloride, nitrate and sulfate showed good resolution (symmetrical peaks, not broadened), even when the chloride concentration was as high as 850 mg l −1 and reproducibility (RSD) was ∼2%. No other peaks (i.e. fluoride, nitrite and phosphate) were observed at selected experimental conditions. With the chosen parameters, the method is well-suited for the routine determination of these anions in groundwater samples, giving results in less than 10 min (including column clean-up). With an appropriate combination of detector output ranges (300 and 1000 μS), only one set of calibration solutions was needed for all samples. In the Sierra Maestra location, the groundwater samples, were significantly different in total anion levels. Mean total chloride plus sulfate concentrations (∼525 mg l −1) were about 100 times higher than in the other sites. Some water quality implications of these groundwater samples are also discussed.

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 HCO 3 −:CO 3 2− 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.

Combination of suppressed and non-suppressed ion chromatography with atmospheric pressure ionization mass spectrometry for the determination of anions

Non-suppressed and suppressed ion chromatography in combination with atmospheric pressure ionization mass spectrometry are compared with special respect to sensitivity for the analysis of low-molecular-mass anions. Iodate, bromate, bromide, sulfate, thiosulfate and bromide could be separated by non-suppressed ion chromatography using a low-capacity anion-exchange column and ammonium citrate as mobile phase. Absolute detection limits between 0.4 and 0.7 ng could be achieved; employing a column requiring a flow-rate of 1 ml/min for optimum performance, splitting was necessary so that only 120 μl/min entered the interface of the mass spectrometer resulting in detection limits between 0.03 and 0.06 mg/l. The same stationary phase (packed into a narrow-bore column which allowed operation without splitting) was suitable for the separation of oxyhalides in the suppressed mode with detection limits of 0.5 μg/l (50 pg) with sodium carbonate as eluent. The method was applied to the analysis of drinking water for oxyhalides. The sample pretreatment for the removal of matrix anions (sulfate, chloride and hydrogencarbonate) is described.

Capacity gradient anion chromatography with a borate complex as eluent

Complex formation between borate compounds and vicinal diols is well recognized. Generally, in a chemically bonded anion-exchange resin, many hydroxyl groups are introduced on the surface of the resin in order to make the resin hydrophilic. The borate as an eluting reagent also reacts to these hydroxyl groups, and this complex formation decreases the apparent ion-exchange capacity of the column by being dissociated to the anion depending on the eluent pH. In the present work a method is described for the simultaneous determination of anions based on the capacity gradient for suppressed ion chromatography. A Tosoh IC-Anion-PW column and dihydroxyphenylborane–mannitol eluent system were used. To maintain baseline stability, it was helpful to keep the borate concentration constant during a gradient of 16 to 0 m M mannitol as a modifier to prevent the complex formation with the hydroxyl on the resin. The chemical composition of the eluents and gradient profiles are discussed and the application to the analysis of the condensed phosphates with widely varying retention times as food additives in a cheese sample is presented.