Acid-rain monitoring in East Asia with a portable-type ion-exclusion–cation-exchange chromatographic analyzer

A monitoring system consisting of a portable-type conductimetric ion-exclusion–cation-exchange chromatographic (CEC) analyzer and a meteorological satellite data analyzer has been investigated for the evaluation of the effects of acid precipitation on natural and urban environments in East Asia. The portable ion-exclusion–CEC analyzer uses a polymethacrylate-based weakly acidic cation-exchange resin column in the H⁺-form and a weak-acid eluent (tartaric acid–methanol–water) and is applied for the simultaneous determination of anions (SO₄²⁻, NO₃⁻, and Cl⁻) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) in precipitation transported from mainland China to central Japan, as mapped by the meteorological satellite data analyzer. Linear calibration graphs of peak area versus concentration for anions and cations were observed in the concentration range 0–1.0 mM for the anions and 0–0.5 mM for the cations. Detection limits at a signal-to-noise ratio of 3 were in the range 5.18–12.1 ppb for the anions and 6.58–16.5 ppb for the cations. The practical utility of this monitoring system is presented.     

Simultaneous separation of common mono- and divalent cations on silica gel modified with aluminium by non-suppressed ion chromatography with conductimetric detection and nitric acid–15-crown-5 as eluent

The modification of silica gel with aluminium by a coating method was very effective for the preparation of silica-based stationary phases which acted as a cation exchanger under strongly acidic conditions. However, the separation of common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) on an aluminium-adsorbing silica (Al-Silica) column was moderate by a conductimetric detection ion chromatography (IC) with strongly acidic eluents. Then, the addition of various crown ethers (12-crown-4, 15-crown-5 and 18-crown-6) in acidic eluent was carried out. As a result, it was found that 15-crown-5 was most effective for the improvement of peak resolution. Excellent separation of these cations was achieved in 20 min by elution with 2 mM nitric acid–2 mM 15-crown-5. The proposed IC was successfully applied to the determination of major cations in various natural waters.     

Simultaneous separation of common mono- and divalent cations on a zirconium-modified silica gel column by ion chromatography with non-suppressed conductimetric detection and tartaric acid–15-crown-5 as eluent

The application of laboratory-made zirconium-modified silica gels (Zr-silicas) as cation-exchange stationary phases to ion chromatography with conductimetric detection (IC–CD) for common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) was carried out. Zr-silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide (Zr(OCH₂CH₂CH₂CH₃)₄) in ethanol. Zr-silica adsorbed on 10 mg zirconium g⁻¹ silica gel was a suitable cation-exchange stationary phase in IC–CD for the separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection for these cations were achieved in 10 min by IC–CD using a Zr-silica column (150×4.6 mm I.D.) and 10 mM tartaric acid containing 10 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) as the eluent. The proposed IC–CD method was successfully applied to the determination of major mono- and divalent cations in natural water samples.     

On-line concentration of s-triazine herbicides in micellar electrokinetic chromatography using a cationic surfactant

A new method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was investigated using high-performance ion-exclusion/cation-exchange chromatography with conductimetric detection on a separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin in the hydrogen-form and an eluent comprising 1.5 mM sulfosalicylic acid–6 mM 18-crown-6 at pH 2.6, operated at 1.5 ml/min. Effective separation and highly sensitive conductimetric detection for the anions and the cations was achieved in about 14 min. Since the ionic balance (equivalents of anions/equivalents of cations) of acid rain waters of different pH (4.40–4.67) ranged from 0.97 to 0.94, evaluation of the water quality of acid rain was possible. This method was successfully applied to the simultaneous determination of the anions and the cations in acid rain transported from mainland China and North Korea to central Japan monitored by a meteorological satellite data analyzer.     

Manipulation of separation selectivity of inorganic anions in electrostatic ion chromatography by the use of mixed cationic–zwitterionic micelles as the column coating solution

This paper describes an electrostatic ion chromatographic system in which the separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitterionic and cationic surfactants in the column coating solution used to prepare the stationary phase. The zwitterionic surfactant used for this study was 3-(N,N-dimethyltetradecylammonio)propanesulfonate (Zwittergent-3-14) and the cationic surfactant was tetradecyltrimethylammonium (TTA). Using a reversed-phase C₁₈ column (250×4.6 mm I.D.) coated with 10/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the stationary phase and either NaHCO₃ or Na₂CO₃ aqueous solution as the eluent, together with suppressed conductivity detection, baseline separation of seven model inorganic anions was obtained. The elution order for those anions was found to be F⁻4²⁻−4²⁻2⁻−3⁻. Under the same conditions but using 1/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the column coating solution, the elution order for these model ions was F⁻4²⁻4²⁻−2⁻−3⁻. The early elution of phosphate and sulfate is a unique attribute of this system. Detection limits for F⁻, HPO₄²⁻, Cl⁻, SO₄²⁻, NO₂⁻, Br⁻ and NO₃⁻ (S/N=3, sample injection volume 100 μl) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 μM, respectively.     

Capillary electrophoresis for measuring major and trace anions in thermal water and condensed-steam samples from hydrothermal springs and fumaroles

A new application of capillary electrophoresis for measuring major and trace anions in thermal water and condensed-steam samples is presented. Ten fluid samples were collected from hydrothermal springs and fumaroles located in a volcanic zone of Deception Island, Antarctica. Anion separation was achieved in less than 6 min using indirect UV detection at 254 nm with a negative power supply (−15 kV). The electrolyte consisted of 4.7 mM sodium chromate, 4.0 mM electroosmotic flow modifier (OFM) hydroxide, 10 mM 2-(N-cyclohexylamino)ethanesulfonic acid and 0.1 mM calcium gluconate (pH 9.1). Major anions (Cl⁻, SO₄², PO₄H²⁻, and CO₃H⁻) were measured using hydrostatic injection (10 cm for 30 s) at 25°C. Trace amounts of anions (F⁻, Br⁻, and NO₃⁻) were better determined by electromigration injection (4 kV, 10 s) at 15°C. Good reproducibility of the migration times (<0.72% RSD), a satisfactory linear response and accuracy as well as acceptable detection limits were successfully obtained.     

Separation and detection of common mono- and divalent cations by ion chromatography with an ODS column and conductivity/UV detection

The retention and detection behavior of common mono- and divalent cations (M⁺, alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and ammonium ions (NH₄⁺); M²⁺, alkaline earth metal ions (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) was examined using an ODS column (150×4.6 mm I.D.) and conductivity (CD)/UV detection. The results obtained were as follows: (1) for M⁺, the mobile phase, 0.1 mM sodium dodecyl sulphate (SDS)+10 mM HNO₃ and indirect CD detection were effective. (2) Addition of Ce(III) in the mobile phase accelerated the elution of both M⁺ and M²⁺. The separation of above 10 cations on an ODS column was achieved for the first time without any coelution of cations and disturbance by system peak. Addition of higher SDS resulted in good separation of M⁺ and M²⁺ with longer retention times. CD detection was possible for M⁺ and M²⁺ and UV detection for M²⁺. (3) For M²⁺, the mobile phase, 0.8 mM Ce(III)+0.1 mM SDS+1 mM HNO₃ and indirect UV detection were effective. The IC methods were applied to real samples.     

Ion chromatography of organic-rich natural waters from peatlands II. Na, NH4, K, Mg and Ca

Organic rich natural waters from peat bogs in continental (Switzerland) and maritime (Shetland Islands, Scotland) environments were analysed for Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ using ion chromatography. These cations were determined simultaneously in surface and pore water samples from the continental bogs using a 250-μl injection loop in an isocratic separation. Using this loop, detection limits of the order of 1 ng/g were achieved. An organics-removal cartridge (Dionex OnGuard P) was used to remove humic materials. Analyses of deionized water filtered through these cartridges showed acceptably low blank values (e.g., ca. 5 ng/g) and appeared to have no significant effect on the measured cation concentration. For the maritime bog waters, the low concentrations of NH₄⁺ (ca. 1 μg/g) compared with Na⁺ (ca. 100 μg/g) required improved peak separation. This was accomplished using a gradient separation beginning with 40 mM HCl—1 mM , -2,3-diaminopropionic acid monochloride (DAP) and switching to 40 mM HCl-12 mM DAP after 2 min. Using a 25 μl injection loop, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ were determined simultaneously in less than 25 min. In this instance, even with Na⁺/NH₄⁺ > 100, there was no interference from Na⁺ in the determination of NH₄⁺ (baseline separated).     

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods

Depending on the sulfur species, picomoles of different inorganic sulfur compounds can be detected and separated by HPLC in one arrangement in a sample volume less than 50 μl. The combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S²⁻), sulfite(SO₃²⁻ and thiosulfate (S₂O₃²⁻) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample. While the derivatized sulfur compounds could be detected by their fluorescence emission at 480 nm, elemental sulfur is identified by its UV absorption at 263 nm. Sulfate in the remaining aqueous phase is detected by HPLC with indirect UV detection at 254 nm. Detection ranges for the different sulfur compounds examined are as follows: sulfide (5 μM to 1.5 mM), sulfite (5 μM to 1.0 mM), thiosulfate (1 μM to 1.5 mM), elemental sulfur (2 μM to 32 mM) and sulfate (5 μM to >1 mM).     

Histidine as a dipolar eluent component in cation chromatography: II. Prediction of retention data for alkaline and alkaline-earth ions

The utility of cation chromatography has been developed by the application of -histidine as a multiprotic and dipolar (zwitterionic) eluent component. The method simplifies the cation analysis. The chromatographic characteristics of this system were studied in detail with a view to determining the selectivity and the mechanism by which the cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) are retained. Complete separations were observed in the isocratic run over the eluent concentration range 3.0–6.0 mM at pH below 2.0. Sensitive detection was achieved using suppressed conductivity at the pH of isoelectric point of the histidine. Retention equations are derived for mono- and divalent cations eluted from ion-exchange separation column with multiple ionic eluents. The theory is based on the extension of ion-exchange equilibrium by protonation equilibria. The selectivity data for analyte and eluent species are determined using the model from the experimental retention data by computer-assisted iterative calculations. The model was utilized to predict retention data. The results in three-dimensional retention surfaces together with species distribution graphs are presented.     

Simultaneous ion-exclusion chromatography and cation-exchange chromatography of anions and cations in environmental water samples on a weakly acidic cation-exchange resin by elution with pyridine-2,6-dicarboxylic acid

A non-suppressed conductivity detection ion chromatographic method using a weakly acidic cation-exchange column (Tosoh TSKgel OApak-A) was developed for the simultaneous separation and determination of common inorganic anions (Cl-, NO3- and SO4(2-)) and cations (Na+, NH4+, K+, Mg2+ and Ca2+). A satisfactory separation of these anions and cations on the weakly acidic cation-exchange column was achieved in 25 min by elution with a mixture of 1.6 mmol L-1 pyridine-2,6-dicarboxylic acid and 8.0 mmol L-1 18-crown-6 at flow rate of 1.0 mL min-1. On this weakly acidic cation-exchange resin, anions were retained by an ion-exclusion mechanism and cations by a cation-exchange mechanism. The linear range of the peak area calibration curves for all analytes were up to two orders of magnitude. The detection limits calculated at S/N = 3 ranged from 0.25 to 1.9 mumol L-1 for anions and cations. The ion-exclusion chromatography-cation-exchange chromatography method developed in this work was successfully applied to the simultaneous determination of major inorganic anions and cations in rainwater, tap water and snow water samples.     

Ion-exchange properties of hypercrosslinked polystyrene impregnated with methyl orange

A novel bipolar stationary phase (HCPS–MO) was prepared by impregnation of hypercrosslinked polystyrene (HCPS) with methyl orange (MO; 4-dimethylamino-4′-sulfoazobenzene) and its ion-exchange properties were studied. Simultaneous separation of cations and anions on HCPS–MO is possible, although it behaves preferentially as a cation-exchanger. Unusual selectivity of HCPS-MO for alkali and alkaline-earth metal cations: Na⁺+K⁺+4⁺+ and Mg²⁺2+2+2+ was observed. The effect of temperature on retention of alkali and alkaline-earth metal cations was studied. Separation of Na⁺, K⁺, Rb⁺, NH₄⁺, Cs⁺, Mg²⁺ and Ca²⁺ on HCPS–MO with diluted cerium(III) nitrate solution as an eluent in single run is presented.     

Ion chromatography of nitrite and carbonate in inorganic matrices on an octadecyl—poly(vinyl alcohol) gel column using acidic eluents

Low levels of carbonate and nitrite contained in inorganic matrices were determined by ion chromatography on an Asahipak ODP-50 poly(vinyl alcohol) gel-based reversed-phase column. With an acidic mobile phase, inorganic matrix anions and cations eluted near the void volume of the column, whereas carbonate and nitrite were retained and separated completely from the matrix ions. After the separation column, the peak response was enhanced using a cation-exchange hollow fibre and 25 mM sodium sulphate or alkaline enhancers. Sea-water samples can be applied directly for the determination of carbonate and added nitrite at ppm levels. The maximum sample volume that can be loaded on the column without peak deformation depended on the pH of the sample solution and the sulphuric acid concentration in the eluent. A 50 μl sea-water sample was applicable with a 2.5 mM acid eluent.     

High-speed simultaneous ion-exclusion/cation-exchange chromatography of anions and cations on a weakly acidic cation-exchange resin column

The simultaneous ion-exclusion/cation-exchange separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin of 3 microm particle size was used to achieve the simultaneous high-speed separation of anions and cations (Cl(-), NO3(-), SO4(2-), Na(+), K(+), NH4(+), Ca(2+) and Mg(2+)) commonly found in environmental samples. The high-speed simultaneous separation is based on a combination of the ion-exclusion mechanism for the anions and the cation-exchange mechanism for cations. The complete separation of the anions and cations was achieved in 5 min by elution with 15 mM tartaric acid-2.5 mM 18-crown-6 at a flow-rate of 1.5 ml/min. Detection limits at S/N=3 ranged from 0.36 to 0.68 microM for anions and 0.63-0.99 microM for cations. This method has been applied to the simultaneous determination of anions and cations in several environmental waters with satisfactory results.     

Analysis of water extracts from airborne dust samples by capillary isotachophoresis

Application of capillary isotachophoresis (CITP) for the analysis of water extracts of the dust samples collected in different periods in air-filtration devices in Prague car traffic tunnels and in Parisian metro station is presented. The extracts were analyzed in cationic mode with a leading electrolyte (LE) of 10 mM KOH, 25 mM acetic acid, pH 4.4, and a terminating electrolyte (TE) of 10 mM β-alanine, adjusted to pH 4.4 with acetic acid, and in anionic mode with LE 10 mM HCl, 20 mM histidine, pH 5.8 and TE 10 mM 2-(N-morpholino)ethanesulphonic acid, pH 3.7. Extracted amounts of UV-absorbing substances, including pollen allergens and organic pollutants, the number of the found components and concentrations of some inorganic ions (e.g. Cl⁻, K⁺, Na⁺, Ca²⁺) in the dust samples were determined. It was found that the extracted amounts of anionic components and their number were much higher than those of cationic components. Significant differences have been found in the analyses of the extracts of different origin. Much more material and more components were present in the extracts of samples from the pollen-rich period than from the pollen-free period, especially in anionic CITP mode.     

Ion chromatographic separation of alkali metal and ammonium cations on a C18 reversed-phase column

The separation of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) and ammonium cations on a C₁₈ reversed-phase column using three anionic surfactants [sodium 1-eicosyl sulphate, sodium dodecyl benzenesulphonate and sodium dodecyl sulphate (SDS)] is described. Two methods were examined: (a) “permanent” coating, with the use of a C₁₈ reversed-phase column previously coated with the surfactants; and (b) dynamic coating, with addition of the surfactants to the mobile phase. With method (a) the separation of the six cations was achieved with SDS. However, the retention times gradually decreased owing to dissolution of the SDS coating. Good separation was obtained with method (b), where 10 mM HNO₃ containing 0.1 mM SDS was used as the mobile phase with conductivity detection, and it was applied satisfactorily to real samples. The effect of system peaks on determination is also discussed.     

Retention behavior of arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium iodide on a styrene-divinylbenzene column with benzenesulfonates as ion-pairing reagents

The pH-dependent retention behavior of arsenobetaine, arsenocholine, trimethylarsine oxide, tetramethylarsonium iodide (cationic arsenic compounds), arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid (anionic arsenic compounds) was studied on a Hamilton PRP-1 reversed-phase column (250×4.1 mm I.D.) with 10 mM aqueous solutions of benzensulfonic acids (X-C₆H₄SO₃⁻; X=H, 4-HO, 3-CO₂H; 4-HO-3-HO₂C-C₆H₃SO₃⁻) as ion-pairing reagents in the pH range 2–5 using flame atomic absorption spectrometry as the arsenic-specific detector. The dependencies of the k′-values of the ‘cationic’ arsenic compounds was rationalized on the basis of the protonation/deprotonation behavior of the arsenic compounds and of the four benzenesulfonates. The results provided evidence for the formation of a cationic species from trimethylarsine oxide below pH 3. Benzenesulfonate is the most hydrophobic ion-pairing reagent causing strong retention of the cationic arsenic compounds and consequently impeding their rapid separation. With the less hydrophobic, substituted benzenesulfonates the cationic arsenic compounds had retention times not exceeding 6 min. At a flow-rate of 1.5 cm³ min⁻¹ 10 mM aqueous 3-carboxy-4-hydroxybenzenesulfonate solution adjusted to pH 3.5 allowed the separation of arsenate, methylarsonic acid, arsenobetaine, trimethylarsine oxide, the tetramethylarsonium ion, and arsenocholine within 3 min. Dimethylarsinic acid coelutes with arsenobetaine at pH 3.5, but can be separated from arsenobetaine with the same mobile phase at pH 2.5. At pH 2.5 the signals for trimethylarsine oxide, the tetramethylarsonium ion, and arsenocholine are too broad to be useful for quantification. Arsenite and methylarsonic acid cannot be separated under these conditions.     

Determination of sulfur oxyanions by ion chromatography on a silica ODS column with tetrapropylammonium salt as an ion-pairing reagent

The difficulty in using conventional ion chromatography for the determination of sulfate, thiosulfate, dithionate and polythionates (tri-, tetra-, penta- and hexathionate) in their mixtures, comes mainly from very late elutions of polythionates due to their strong retentions onto a separating column. Rapid and sensitive determination of these sulfur oxyanions has been achieved by ion-pair chromatography using a silica octadecylsilane (ODS) column with mobile phases of 10% or 20% (v/v) acetonitrile in water (pH, 5.0) containing 0.2 mM phthalate and 7 mM tetrapropylammonium salt (TPAOH). The sulfur species separated on the column were monitored with a conductivity detector after passing through a micro membrane suppressor in the H⁺ form. When an acetonitrile-water (10:90, v/v) mobile phase (pH, 5.0) of 0.2 mM phthalate and 7 mM TPAOH was used at a flow-rate of 0.8 ml min⁻¹, sulfate, thiosulfate, dithionate and trithionate were eluted at short retention times of 9.1, 9.7, 11.4 and 15.8 min, respectively; however, the higher polythionates required more than 30 min to elute. When the concentration of acetonitrile in the mobile phase was raised to 20% (v/v), all polythionates of tri- to hexathionate were completely separated from their mixtures within 21 min; in this instance, both sulfate and thiosulfate failed to be resolved due to their close retention times. Good recoveries were obtained for these sulfur oxyanions when added to various hot-spring water samples.     

Separation and indirect detection by capillary zone electrophoresis of ppb (w/w) levels of aluminum ions in solutions of multiple cations

Solutions of multiple cations in aqueous solutions at concentrations as low as 200 ppb were analyzed by capillary zone electrophoresis. Aluminum ions were cleanly separated from Li⁺, K⁺, Ca²⁺, Cr³⁺, Zn²⁺, CU²⁺, and other ions less than 6 min after injection of the solution on a 50 cm × 50 μm I.D. uncoated fused-silica capillary column at 15 kV. Indirect detection at 204 nm was carried out using a pH 2.8 background electrolyte containing 5.2 mM ephedrine as a UV-absorbing co-ion and 4.7 mM -hydroxyisobutyric acid as a completing counter ion. Mobilities for Al³⁺ and 14 other complexed cations were determined for this electrolyte.     

Ion chromatography of nitrite at the ppb level with photometric measurement of iodine formed by post-column reaction of nitrite with iodide

The difficulty in ion-chromatographic determination of nitrite in aqueous solutions containing a high concentration of chloride arises mainly from incomplete resolution of the peaks for these anions on the separation column whose efficiency is not high. A photometric measurement of iodine formed by a reaction of nitrite with iodide has been found to make it possible to determine, chromatographically, trace amounts of nitrite without any interference from chloride; chloride does not oxidize iodide to produce iodine. The proposed method was based on the separation of nitrite from matrix anions on a silica-based anion-exchange column with a 1.5·10⁻³ M phthalate eluent (pH 5.0), followed by photometric measurement of the iodine (as triiodide) formed via a post-column reaction of the separated nitrite with iodide. The optimal conditions for the post-column reaction were established by varying the concentrations of iodide, copper(II) and nitric acid in a post-column-reaction solution and the length of a reaction tube. A calibration graph for nitrite, plotted as peak heights versus concentrations, was linear up to 1.50·10⁻⁵ M (690 ppb). The detection limit, defined at S/N=3, was 1.00·10⁻⁷ M (4.60 ppb) nitrite. The presence of chloride ions up to 0.01 M did not give any interference to the determination of nitrite. This method was successfully applied to the determination of nitrite in lake water, river water, sewage works water and snow samples without any pretreatment.