Determination of hexavalent chromium and accompanying anions in one run using isocratic ion chromatography with column switching

A method for the simultaneous determination of hexavalent chromium and other inorganic anions like chloride, nitrate and sulfate in aqueous solutions was developed using isocratic ion chromatography with suppressed conductometric detection and column switching. Owing to the large differences in distribution coefficient between chromate and the other species, the chromate is separated from the other anions in a first short column, whereas the other anions are led to a longer second column via a column-switching valve, and separated there. Using standard anion separation conditions the length of the columns and the switching procedure were optimized. The time of analysis for eight anions is less than 12 min and the method can be easily automated. Detection limit and precision are not effected by the switching procedure.     

In-line respeciation: an ion-exchange ion chromatographic method applied to the separation of degradation products of chemical warfare nerve agents in soil

The natural background of anions encountered when analyzing soil samples by ion chromatography (IC) present significant problems in the separation, detection and quantification of isopropyl methylphosphonic acid (IMPA) and methylphosphonic acid (MPA), the degradation products of sarin, a chemical warfare nerve agent. Using chemically-suppressed IC with conductivity detection, a commercially available ion-exchange column, and an isocratic binary eluent system, IMPA and MPA were determined in aqueous extracts of soil at sub-ppm (μg/g) concentrations without the need for gradient elution or organic solvent eluent modifiers. Common soil anions such as chloride, nitrate, sulfate and phosphate do not interfere with the analysis method due to the composition of the binary eluent allowing for greater mobilization of multivalent anions (e.g., MPA, carbonate, and sulfate) while monovalent anions (e.g., IMPA and nitrate) are relatively unaffected. Carbonate is selectively removed by in-line respeciation to bicarbonate.     

Development of a polypyrrole-based amperometric detector for the determination of certain anions in water samples

The development of a polypyrrole-based modified electrode for use in the detection of anions in flow-injection analysis and ion chromatography is described. Chloride, nitrate, nitrite, perchlorate, bromide, carbonate, sulphate and phosphate were detected by using flow-injection analysis combined with the polypyrrole-based CME electrochemical detector. All of the anions were detected conveniently and reproducibly over a linear concentration range 1-100 mug/ml. A detection limit of 0.1 mug/ml was obtained for chloride and a limit of 1.0 mug/ml for all of the other anions. Chloride, nitrate, sulphate and phosphate, following separation using ion chromatography, were detected simultaneously by using a conductivity detector and the polypyrrole-based CME electrochemical detector in series. Both methods of detection yielded similar results with comparable sensitivity, linearity and limits of detection. This method was then applied to the analysis of fresh water samples. The electrode was stable over a 2-week period of operation with no evidence of chemical or mechanical deterioration.     

Determination of monovalent inorganic anions in high-ionic-strength samples by electrostatic ion chromatography with suppressed conductometric detection

A new ion chromatographic (IC) system has been established by using micelles of 3-(N,N-dimethylmyristylammonio)propanesulfonate (Zwittergent 3-14) loaded onto a reversed-phase packed column as the separation column with an electronic rotary switching valve packed-bed suppressor for conductometric detection of inorganic anions. An aqueous H3BO3-Na2B4O7 solution has been demonstrated to be the most desirable eluent for this IC system. The relationship between retention time and the concentration of the borate eluent was determined for a series of model anionic analytes and this relationship was found to be opposite to that exhibited in a conventional anion-exchange IC system. The rapid elution and complete separation of monovalent inorganic anions were obtained by initially using a high-concentration borate solution as the eluent for a short-period, and then switching to a lower-concentration borate eluent to complete the separation. Detection limits for nitrite, bromide, nitrate, and chlorate were 0.85, 0.88, 0.95 and 4.8 microM, respectively, when a 7.0 mM Na2B4O7 eluent was used. Moreover, the ability to directly detect these monovalent anions in samples containing high concentrations of sulfate and/or chloride ions provided a major advantage of this approach.     

Determination of glyphosate and phosphate in water by ion chromatography--inductively coupled plasma mass spectrometry detection

Quantitative determination of trace glyphosate and phosphate in waters was achieved by coupling ion chromatography (IC) separation with inductively coupled plasma mass spectrometry (ICP-MS) detection. The separation of glyphosate and phosphate on a polymer anion-exchange column (Dionex IonPac AS16, 4.0 mm x 250 mm) was obtained by eluting them with 20 mM citric acid at 0.50 mL min(-1), and the analytes were detected directly and selectively by ICP-MS at m/z = 31. Parameters affecting their chromatographic behaviors and ICP-MS characteristics were systematically examined. Based on a 500-microL sample injection volume, the detection limits were 0.7 microgL(-1) for both glyphosate and phosphate, and the calibrations were linear up to 400 microgL(-1). Polyphosphates, aminomethylphosphonic acid (the major metabolite of glyphosate), non-polar and other polar phosphorus-containing pesticides showed different chromatographic behaviors from the analytes of interest and therefore did not interference. The determination was also interference free from the matrix anions (nitrate, nitrite, sulphate, chloride, etc.) and metallic ions. The analysis of certified reference material, drinking water, reservoir water and Newater yielded satisfactory results with spiked recoveries of 97.1-107.0% and relative standard deviations of < or = 7.4% (n = 3). Compared to other reported methods for glyphosate and phosphate, the developed IC-ICP-MS method is sensitive and simple, and does not require any chemical derivatization, sample preconcentration and mobile phase conductivity suppression.     

Coupled ion chromatography for the determination of chloride, phosphate and sulphate in concentrated nitric acid

A coupled ion chromatography (IC) system was used for the determination of chloride, sulphate and phosphate in high-purity nitric acid. Such a high ionic strength matrix causes a selectivity problem in single IC systems. The first part of the system is used for a pre-separation of the analytes from the nitrate matrix. A specially designed high-capacity anion exchanger with low retention for the analytes and high retention for nitrate was developed. The eluent stream containing the analytes was transferred to the second part of the system via a heart-cut valve and a pre-concentration column. The second system utilizes a high performance anion exchanger and is used to quantify the analytes. Recoveries of the analytes are 80-100% for phosphate, and around 100% for sulphate and chloride. Detection limits for chloride, sulphate and phosphate in concentrated nitric acid (69% w/w) are 0.1, 1 and 5 mg/l, respectively.     

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.     

Determination of anions with capillary electrophoresis and indirect ultraviolet detection

A method is validated for the determination of anions with capillary electrophoresis (CE) in combination with indirect UV detection. The method described here is used for the analysis of eight of the most common anions (fluoride, chloride, bromide, sulphate, nitrate, nitrite, thiosulphate and phosphate). Next, the method is compared with a another buffer system for the determination of anions with CE and indirect UV detection. Typical limits of detection are obtained between 1 and 3 mg/l for the above-mentioned compounds. The repeatability and reproducibility of the system differs per compound and is, with the exception of fluoride and phosphate, between 4 and 6% and 5–10%, respectively. Linearity was observed between 1 and 10 mg/l. The method is applied for the determination of anions in drinking water, serum and urine.     

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.     

Analysis of wastewater for anionic and cationic nutrients by ion chromatography in a single run with sequential flow injection analysis

To prevent nutrient enrichment and, hence the undesirable ecological impacts, the nutrients monitored in wastewater samples include two anionic species, i.e., nitrate and orthophosphate, and a cationic species, ammonium. Ion chromatography (IC) is one of the popularly used techniques for determinations of nitrate and phosphate in these samples, whereas determination of ammonium in wastewater samples is typically done using manual or automated wet chemistry, e.g., flow injection analysis (FIA). We have developed a sequential IC–FIA method, using Lachat’s QC8000 IC system, which allows determinations of nitrate, phosphate and ammonia in a single injection. In this system, a QuikChem Small Suppressor cartridge is regenerated in between the samples. A sample is injected while leaving the suppressor off-line. Ammonium, a cation, elutes in the void volume of an anion-exchange column. The unsuppressed column effluent, exiting the conductivity flow cell, up to this point is used for FIA determination of ammonia. When ammonia exits the conductivity flow cell, a fully regenerated suppressor is brought in-line for conductometric detection of the anions. Analog data are simultaneously acquired from colorimetric and conductometric detectors, for the cationic and anionic nutrients, respectively. The method is accurate with spike recoveries in wastewater samples ranging from 91% for nitrate to 114% for chloride. It is precise with RSD values, for replicate analyses (n=7) of a mid-range standard, ranging from 0.4% for phosphate to 1% for nitrate.     

Determination of glycerophosphate and other anions in dentifrices by ion chromatography

Simple, reliable and sensitive analytical methods to determine the anions, such as fluoride, monofluorophaosphate, glycerophosphate related to anticaries are necessary for basic investigations of anticaries and quality control of dentifrices. A method for the simultaneous determination of organic acids, organic anions and inorganic anions in the sample of commercial toothpaste is proposed. Nine anions (fluoride, chloride, nitrite, nitrate, sulfate, phosphate, monofluorophaosphate, glycerophosphate and oxalic acid) were analyzed by means of ion chromatography using a gradient elution with KOH as mobile phase, IonPac AS18 as the separation column and suppressed conductivity detection. Optimized analytical conditions were further validated in terms of accuracy, precision and total uncertainty and the results showed the reliability of the IC method. The relative standard deviations (RSD) of the retention time and peak area of all species were less than 0.170 and 1.800%, respectively. The correlation coefficients for target analytes ranged from 0.9985 to 0.9996. The detection limit (signal to noise ratio of 3:1) of this method was at low ppb level (<15 ppb). The spiked recoveries for the anions were 96-103%. The method was applied to toothpaste without interferences.     

Simultaneous determination of six inorganic anions in drinking water by non-suppressed ion chromatography.

A non-suppressed ion chromatographic method with conductometric detection is described for the simultaneous determination of six inorganic anions: fluoride, chloride, nitrite, bromide, nitrate and sulphate. The separation was achieved on a low-capacity anion-exchange column Metrohm IC Anion Column Super Sep, with a mobile phase consisting of phtalic acid dissolved in high-purity water, 2-amino-2-hydroxymethyl-1,3-propendiol and acetonitrile. In this work computer optimization procedures, using computer programs to select chromatographic conditions have been used, leading to the achievement of a desired separation. By using the different optimization methods in an integrated manner it is, however, possible to both speed method development, by reducing unnecessary experimentation, and to overcome the many shortcomings of each method, because of the different approaches. The purpose of this work is to improve and characterise the method for simultaneous determination of six inorganic anions in drinking water by non-suppressed ion chromatography, using optimization procedures, in order to be applied to the routine analysis. The proposed method has numerous advantages over the other widely used non-suppressed ion chromatography methods: higher selectivity, shorter analysis time, lower quantitation and detection limits. The performance characteristics of the method were established by determining the following validation parameters: precision and accuracy, linearity, detection limits and quantitation limits.     

Determination of thyroid hormones in pharmaceutical preparations,after derivatization with 9-anthroylnitrile,by high-performance liquid chromatography with fluorescence detection

Fast ion-exchange chromatography has been developed and applied to the separation of common inorganic anions. Using a didodecyldimethylammonium bromide (DDAB) coated short (30 mm x 4.6 mm) ODS analytical column (3-microm particle size) and a 5 mM phthalate eluent (pH 7.5) the isocratic separation of nine common anions in 160 s was possible, with the first seven anions, including phosphate, chloride and sulphate, separated within 65 s. Detection was achieved using indirect UV at 279 nm. The high capacity, highly hydrophobic ion-exchange coating demonstrated excellent stability over time, even at elevated temperatures (45 degrees C) and exhibited unusual selectivity for common anions (retention order=fluoride, carbonate, phosphate, chloride, bromate, nitrite, sulphate, bromide and nitrate). The developed chromatography was successfully applied to the rapid analysis of river water and seawater samples.     

A simple ion chromatography method for inorganic anion analysis in edible seaweeds

A new, simple, fast and sensitive ion chromatography (IC) method, for the simultaneous analysis of fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulphate in edible seaweeds was developed and reported for the first time. The validation of the analytical method was studied in terms of linearity, sensitivity, precision and accuracy. All standard calibration curves showed very good correlation between anion peak area and concentration (r > 0.999). Limits of detection and quantitation ranged between 0.002-0.05 mg/L and 0.01-0.1 mg/L, respectively and indicated the high sensitivity of the method. Relative standard deviation values of repeatability and inter-day precision for standard anions with the same sample were less than 2%. Anion recoveries ranged from 97 to 113% for chloride and from 87 to 105% for sulphate, respectively and showed the fairly good accuracy of the method. The method was applied to the analysis of inorganic anions in brown and red edible seaweeds. Brown seaweeds were characterized by higher chloride content up to 33.7-36.9%, while red seaweeds were characterized by higher sulphate content (45-57%). Sulphate content in seaweeds is related to the presence of sulphated polysaccharides of biological importance. The method developed was well applicable to mineral anion analysis in edible seaweeds and shows suitability and reliability of use in other food samples of nutritional importance.     

Matrix elimination ion chromatography method for the determination of trace levels of anionic impurities in high purity cesium iodide

In the present study an ion chromatographic method based on matrix elimination has been developed for the determination of anionic impurities in high purity cesium iodide crystals. The presence of impurities has a detrimental effect on the characteristics of detectors based on cesium iodide crystals. In particular, oxygen-containing anions inhibit the resolving power of scintillators and decrease the optical absorption. The quantitative determination of anions (fluoride, chloride, bromide, nitrate, phosphate, and sulphate) simultaneously in the high-purity cesium iodide crystals has not been carried out before. The large concentration of iodide poses a challenge in the determination of anions (especially phosphate and sulphate); hence, matrix elimination is accomplished by adopting a sample pretreatment technique. The method is validated for linearity, accuracy, and precision. The limit of detection for different anions is in the range of 0.3-3 μg/g, and the relative standard deviation is in the range of 4-6% for the overall method.     

Determination of trace anions in organic solvents.

Ion chromatography along with matrix elimination was used to reliably determine trace levels of anionic contaminants in organic solvents. A 5-ml sample volume was injected directly into the instrument without any sample pretreatment. High-purity deionized water was used to deliver the sample to a preconcentration column, where the anions of interest were retained while the organic matrix was rinsed to waste. A sodium carbonate eluent eluted concentrated anions from the preconcentration column and separated them on a 2-mm pellicular anion-exchange column. The separated anions were detected by suppressed conductivity. This method was used to determine the anionic contaminants of isopropanol, acetone and N-methylpyrrolidone. Method detection limits for chloride, nitrate, sulfate and phosphate were all lower than 1 microg/l.     

Application of artificial neural networks for gradient elution retention modelling in ion chromatography

Gradient elution in ion chromatography (IC) offers several advantages: total analysis time can be significantly reduced, overall resolution of a mixture can be increased, peak shape can be improved (less tailing) and effective sensitivity can be increased (because there is little variation in peak shape). More importantly, it provides the maximum resolution per time unit. The aim of this work was the development of a suitable artificial neural network (ANN) gradient elution retention model that can be used in a variety of applications for method development and retention modelling of inorganic anions in IC. Multilayer perceptron ANNs were used to model the retention behaviour of fluoride, chloride, nitrite, sulphate, bromide, nitrate and phosphate in relation to the starting time of gradient elution and the slope of the linear gradient elution curve. The advantage of the developed model is the application of an optimized two-phase training algorithm that enables the researcher to make use of the advantages of first- and second-order training algorithms in one training procedure. This results in better predictive ability, with less time required for the calculations. The number of hidden layer neurons and experimental data points used for the training set were optimized in terms of obtaining a precise and accurate retention model with respect to minimization of unnecessary experimentation and time needed for the calculation procedures. This study shows that developed, ANNs are the method of first choice for retention modelling of inorganic anions in IC.     

Determination of nitrite, sulphate, bromide and nitrate in human serum by ion chromatography

An ion chromatographic method has been developed for the determination of trace amounts of nitrite, sulphate, bromide and nitrate in human serum, using an ODS column dynamically coated with cetylpyridinium chloride. The anions studied were eluted with 1 mM citrate - 2.5% methanol (pH 6.5) as the mobile phase and detected by an ultraviolet detector. The interfering proteins in human serum were removed by an initial filtration through an ultrafilter-paper. The many inorganic and organic anions commonly found in serum had little effect on the determination of the four anions. Recoveries of nitrite, sulphate, bromide and nitrate in serum were 107-110, 94-106, 106-110 and 92-100%, respectively. The proposed method was also applied to human saliva and urine.     

Identification of homemade inorganic explosives by ion chromatographic analysis of post-blast residues

Anions and cations of interest for the post-blast identification of homemade inorganic explosives were separated and detected by ion chromatographic (IC) methods. The ionic analytes used for identification of explosives in this study comprised 18 anions (acetate, benzoate, bromate, carbonate, chlorate, chloride, chlorite, chromate, cyanate, fluoride, formate, nitrate, nitrite, perchlorate, phosphate, sulfate, thiocyanate and thiosulfate) and 12 cations (ammonium, barium(II), calcium(II), chromium(III), ethylammonium, magnesium(II), manganese(II), methylammonium, potassium(I), sodium(I), strontium(II), and zinc(II)). Two IC separations are presented, using suppressed IC on a Dionex AS20 column with potassium hydroxide as eluent for anions, and non-suppressed IC for cations using a Dionex SCS 1 column with oxalic acid/acetonitrile as eluent. Conductivity detection was used in both cases. Detection limits for anions were in the range 2-27.4ppb, and for cations were in the range 13-115ppb. These methods allowed the explosive residue ions to be identified and separated from background ions likely to be present in the environment. Linearity (over a calibration range of 0.05-50ppm) was evaluated for both methods, with r(2) values ranging from 0.9889 to 1.000. Reproducibility over 10 consecutive injections of a 5ppm standard ranged from 0.01 to 0.22% relative standard deviation (RSD) for retention time and 0.29 to 2.16%RSD for peak area. The anion and cation separations were performed simultaneously by using two Dionex ICS-2000 chromatographs served by a single autoinjector. The efficacy of the developed methods was demonstrated by analysis of residue samples taken from witness plates and soils collected following the controlled detonation of a series of different inorganic homemade explosives. The results obtained were also confirmed by parallel analysis of the same samples by capillary electrophoresis (CE) with excellent agreement being obtained.