Kazutoku Ohta

Simultaneous ion-exclusion chromatography-cation-exchange chromatography with conductimetric detection of anions and cations in acid rain waters

Abstract A simple, selective and sensitive method was investigated for simultaneously determining anions (Cl−, NO3−, SO42−) and cations (Na+, NH4+, K+, Mg2+, Ca2+) in acid rain and related environmental waters in central Japan. The method involves simultaneous ion-exclusion-cation-exchange chromatography with conductimetric detection on a polyacrylate weakly acidic cation-exchange resin column with a weak-acid eluent. With the weak-acid eluent (tartaric acid) both anions and cations were separated simultaneously, based on ion-exclusion and cation-exchange mechanism. Owing to the presence of H+ ions in the tartaric acid eluent, the detector response was positive for the anions and negative for the cations. Using a 5 mM tartaric acid-7.5% methanol-water eluent, good simultaneous separation and detection were achieved in about 30 min. The results indicated an ionic balance of about 100% between the anions (including HCO3−) and the cations (including H+).

Simultaneous ion-exclusion/cation-exchange chromatography of anions and cations in acid rain waters on a weakly acidic cation-exchange resin by elution with sulfosalicylic acid

A simple, selective, and sensitive method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was developed using ion-exclusion/ cation-exchange chromatography with conductimetric detection. A weakly acidic cation-exchange resin column (Tosho TSKgel OA-PAK-A) and a sulfosalicylic acid-methanol-water eluent was used. With a mobile phase comprising 1.25 mM sulfosalicylic acid in methanol-water (7.5:92.5) at 1.2 ml/min, simultaneous separation and detection of the above anions and cations was achieved in about 30 min. Linear calibration plots of peak area versus concentration were obtained over the concentration ranges 0-1.0 mM for anions (R=0.9991) and 0-0.5 mM for cations (R=0.9994). Detection limits calculated at S/N=3 ranged from 4.2 to 14.8 ppb for the anions and from 2.4 to 12.1 ppb for the cations. The reproducibility of retention times was 0.14-0.15% relative standard deviation (RSD) for anions and 0.18-0.31% for cations, and reproducibility of chromatographic peak areas was 1.22-1.75% RSD for anions and 1.81-2.10% for cations. The method was applied successfully to the simultaneous determination of anions and cations in aerosols transported from mainland China to central Japan, as determined by a meteorological satellite data analyzer.

Ion-exclusion chromatography of aliphatic carboxylic acids on an unmodified silica gel column

In order to demonstrate the effectiveness of a silica gel column in ion-exclusion chromatography, the elution behavior of aliphatic carboxylic acids was investigated on an unmodified silica gel column having cation-exchange characteristics. When water was used as an eluent, the elution order of the carboxylic acids was dependent on the pKa and the hydrophobicity, but the resolution between strong acids, e.g. HNO3, and carboxylic acids was not satisfactory. Therefore, the composition of eluents containing sulfuric acid and organic modifiers was investigated for the separation of HNO3 and C1–C10 aliphatic carboxylic acids. When 0.5 mM sulfuric acid containing 0.05% heptanol was used as an eluent, an excellent ion-exclusion chromatographic separation was achieved in 30 min using UV-detection at 220 nm.

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 (SO4(2)-, 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.

Ion-exclusion chromatography with conductimetric detection of aliphatic carboxylic acids on an H+-form cation-exchange resin column by elution with polyols and sugars

Abstract The Ion-exclusion chromatography (IEC) of normal aliphatic carboxylic acids of different acidity (p K a ) and hydrophobicity was investigated on a poly(styrene-divinylbenzene) (PS-DVB)-based strongly acidic cation-exchange resin column in the H + form and conductimetric detection. When water was used as the eluent, although the C 1 -C 5 carboxylic acids were separated from strong acid (HCl) depending on the p K a and the hydrophobicity, the resolution was low and the peaks were accompanied by leading depending on their hydrophobicities. To improve the peak shape and the peak resolution, aqueous eluents of polyols and sugars containing 1–8 alcoholic OH groups (methanol, ethylene glycol, glycerol, erythritol, xylitol, fructose, sorbitol, and sucrose) were tested for the IEC separation of the carboxylic acids. When aqueous eluents of polyols and sugars were used, the tendency for leading peaks was decreased drastically with increasing number of OH groups in the polyols and sugars. This is due mainly to the increase in the hydrophilicity of the PS-DVB surface by the OH groups. An aqueous eluent of 10% methanol-0.15 M sucrose gave a reasonable resolution and highly sensitive detection for carboxylic acids. This eluent has a much lower background conductivity (ca. 4 μS cm −1 ) and much higher detection sensitivity (ca. 170 times higher for valeric acid) than the 0.5 m M sulfuric acid (ca. 390 μS cm −1 ) commonly used as an eluent in conventional IEC with conductimetric detection.

Simultaneous determination of anions and cations by ion-exclusion chromatography-cation-exchange chromatography with tartaric acid/18-crown-6 as eluent.

Ion-exclusion chromatography-cation-exchange chromatography was developed for the simultaneous separation of common inorganic anions and cations (Cl-, NO3- and SO4(2-); Na+, NH4+, K+, Mg2+ and Ca2+) on a weakly acidic cation-exchange column by elution with weak acid. Generally, the resolution among these monovalent cations was only moderate, thereby hindering the determination of these analytes in natural-water samples. Therefore, 18-crown-6 was added to the eluent to improve the resolution. A good separation of these anions and cations on a weakly acidic cation-exchange column was achieved in 30 min by elution with 5 mM tartaric acid/6 mM 18-crown-6/methanol-water (7.5:92.5). The ion-exclusion chromatography-cation-exchange chromatography method developed here was successfully applied to the separation of major anions and cations in an environmental water sample.

Ion-exclusion chromatography of aliphatic car☐ylic acids on a cation-exchange resin by elution with polyvinyl alcohol

Ion-exclusion chromatography of aliphatic car☐ylic acids of different acidity (pKa) and hydrophobicity was investigated on a polystyrene-divinylbenzene (PS-DVB) based strongly acidic cation-exchange resin in the H+ form and conductivity detection by elution with polyvinyl alcohol (PVA). When water was used as an eluent, the resolution of the car☐ylic acids was very low and the peak accompanied a fronting depending on their hydrophobicities. Therefore, to improve the peak shape and the peak resolution, aqueous eluents containing PVAs (degrees of polymerization, n=500, 1500and2000) with many OH groups were tested for the ion-exclusion chromatographic separation of the car☐ylic acids. When aqueous eluents containing PVA were used, the fronting was decreased dramatically by the effect of increased hydrophilicity of the PS-DVB cation-exchange resin surface due to adsorption of OH group in PVA. The high resolution ion-exclusion chromatographic separation without the fronting and highly sensitive conductimetric detection of the car☐ylic acids was accomplished successfully by elution with a 0.2% PVA (n=1500)-10% methanol-water.

Simultaneous determination of common mono- and divalent cations by ion chromatography with an unmodified silica gel column

In order to characterize the cation-exchange properties of a silica gel column in the acidic region, the retention behavior of common mono- and divalent cations (Na+, NH4+, K+, Mg2+ and Ca2+) was investigated. When using 5 mM nitric acid (pH 2.3) as an eluent, these cations were retained on a silica gel column (150×4.6 mm I.D.) packed with Develosil 30-5 unmodified silica gel that has a very large surface area (ca. 770 m2/g), showing that such a stationary phase could be used as a cation-exchanger for ion chromatography with acidic eluents. When using 1.5 mM 2,6-pyridinedicarboxylic acid as an eluent, a good separation of these cations was obtained in 12 min using conductimetric detection. This separation was applied successfully to the simultaneous determination of the five cations in various environmental water samples.

High-performance ion-exclusion/cation-exchange chromatography of anions and cations in acid rain waters on a weakly acidic cation-exchange resin

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.

Ion-exclusion chromatographic behavior of aliphatic carboxylic acids and benzenecarboxylic acids on a sulfonated styrene–divinylbenzene co-polymer resin column with sulfuric acid containing various alcohols as eluent

The addition of C1-C7 alcohols (methanol, ethanol, propanol, butanol, heptanol, hexanol and heptanol) to dilute sulfuric acid as eluent in ion-exclusion chromatography using a highly sulfonated styrene-divinylbenzene co-polymer resin (TSKgel SCX) in the H+ form as the stationary phase was carried out for the simultaneous separations of both (a) C1-C7 aliphatic carboxylic acids (formic, acetic, propionic, isobutyric, butyric, isovaleric, valeric, 2-methylvaleric, isocaproic, caproic, 2,2-dimethyl-n-valeric, 2-methylhexanoic, 5-methylhexanoic and heptanoic acids) and (b) benzenecarboxylic acids (pyromellitic, hemimellitic, trimellitic, o-phthalic, m-phthalic, p-phthalic, benzoic and salicylic acids and phenol). Heptanol was the most effective modifier in ion-exclusion chromatography for the improvement of peak shapes and a reduction in retention volumes for higher aliphatic carboxylic acids and benzenecarboxylic acids. Excellent simultaneous separation and relatively highly sensitive conductimetric detection for these C1-C7 aliphatic carboxylic acids were achieved on the TSKgel SCX column (150 x 6 mm I.D.) in 30 min using 0.5 mM sulfuric acid containing 0.025% heptanol as eluent. Excellent simultaneous separation and highly sensitive UV detection at 200 nm for these benzenecarboxylic acids were also achieved on the TSKgel SCX column in 30 min using 5 mM sulfuric acid containing 0.075% heptanol as eluent.