Analysis of aliphatic car☐ylic acids and amino acids in effluents of landfills, composting plants and fermentation plants by ion-exclusion and ion-exchange chromatography

Short chain aliphatic acids, including volatile fatty acids (VFAs), di-/tricar☐ylic acids, hydroxy- and keto-acids were analyzed in landfill leachates and related water samples by two independently operated ion-exclusion chromatographic systems, differing mainly in the retention characteristics of the separation columns (Merck Polyspher OA-HY, Dionex HPICE AS6), and in the detection mode (UV absorbance at 210 nm, conductivity). The amino acid content of the samples was determined by ion chromatography. Because methods for amino acids analysis are widely standardized, the main efforts were undertaken to optimize the determination of car☐ylic acids. The VFAs (7 compounds) contributed between 33% and 89% to the sample's dissolved organic carbon (DOC) content. The DOC proportions of the multifunctional acids (9 compounds) ranged from 1.1–49%. Between 0.9% and 13% of the DOC content was apportioned to amino acids. Main components were alanine, valine and leucine. The analytical efficiencies of the ion-exclusion chromatography systems were compared and the specific application properties are discussed.     

Ion-exclusion chromatography with conductimetric detection of aliphatic carboxylic acids on a weakly acidic cation-exchange resin by elution with benzoic acid-beta-cyclodextrin

In this study, an aqueous solution consisting of benzoic acid with low background conductivity and beta-cyclodextrin (beta-CD) of hydrophilic nature and the inclusion effect to benzoic acid were used as eluent for the ion-exclusion chromatographic separation of aliphatic carboxylic acids with different pKa values and hydrophobicity on a polymethacrylate-based weakly acidic cation-exchange resin in the H+ form. With increasing concentration of beta-cyclodextrin in the eluent, the retention times of the carboxylic acids decreased due to the increased hydrophilicity of the polymethacrylate-based cation-exchange resin surface from the adsorption of OH groups of beta-cyclodextrin. Moreover, the eluent background conductivity decreased with increasing concentration of beta-cyclodextrin in 1 mM benzoic acid, which could result in higher sensitivity for conductimetric detection. The ion-exclusion chromatographic separation of carboxylic acids with high resolution and sensitivity was accomplished successfully by elution with a 1 mM benzoic acid-10 mM cyclodextrin solution without chemical suppression.     

Ion chromatographic separation of car☐ylic acids prediction of retention data

The retention behavior of biologically relevant monovalent (formic, acetic, propionic, lactic and pyruvic) and divalent (oxalic, malonic, succinic, fumaric, maleic and tartaric acids) car☐ylic acids together with inorganic analytes (chloride and sulphate) has been studied. The separation was performed on a latex-based strong anion-exchange resin using carbonate buffer systems in suppressed IC. The retention behaviour of analytes was investigated at different pH values and [HCO₃⁻]+[CO₃²⁻] concentrations. A theoretical model, involving ion-exchange equilibria of sample and eluent anions, was derived and applied to the chromatographic data obtained. Chromatographic ion exchange selectivity values were determined and retention data were calculated for the anions using different carbonate eluent conditions. The average of errors between the predicted and the measured retention volumes of the analytes studied does not exceed 4.0%. The study effectively characteristics the behaviour of different analytes under elution conditions of practical importance.     

Retention behavior of carboyxlic acids on highly cross-linked poly(styrene-divinylbenzene)-based and silica-based cation exchangers

A highly cross-linked porous poly(styrene-divinylbenzene) resin was reacted with sulfuric acid to give strong cation-exchange resins with capacities from 0.2 to 1.9 mequiv./g. The retention behavior of mono- and dicar☐ylic acids on these resins was compared with results obtained from silica-based cation exchangers functionalized with alkylsulfonic acid or phenylsulfonic acid groups. The contribution of different retention mechanisms like ion exclusion, hydrophobic interaction and adsorption to the separation of the analytes on these chromatographic supports was discussed. Additionally the applicability of silica-based cation exchangers was tested in the field of silage analysis.     

Retention behavior of alkali, alkaline earth and transition metal cations in ion chromatography with an unmodified silica gel column

An unmodified silica gel (Develosil 30-5) column (150×4.6 mm I.D.) has been applied to the ion chromatographic separation of alkali, alkaline earth and transition metal cations. The retention behavior of the above cations on the bare substrate was investigated using a number of weak inorganic and organic acid eluents. During this investigation, several separations were achieved and the most suitable eluent conditions were identified. It was concluded that: (a) 1.5 mM HNO₃-0.5mM pyridine-2,6-dicar☐ylic acid eluent was the most effective for the simultaneous separation of common alkali and alkaline earth metal cations, (b) 1.5 mM oxalic acid eluent resulted in the best separation of alkali, alkaline earth, and transition metal cations, (c) 0.5 mM CuSO₄ eluent could be used for the separation of alkali metal cations alone and (d) 0.5 mM ethylenediamine-oxalic acid eluent at pH 5.5 resulted in themost efficient separation of both alkaline earth and transition metal cations.     

离子排斥色谱用于厌氧消化处理水中脂肪族羧酸的分析（英文）

The analysis of seven aliphatic carboxylic acids(formic,acetic,propionic,iso-butyric,n-butyric,iso-valeric and n-valeric acid) in anaerobic digestion process waters for biogas production was examined by ion-exclusion chromatography with dilute acidic eluents(benzoic acid,perfluorobutyric acid(PFBA) and sulfuric acid) and non-suppressed conductivity/ultraviolet(UV) detection.The columns used were a styrene/divinylbenzene-based strongly acidic cation-exchange resin column(TSKgel SCX) and a polymethacrylate-based weakly acidic cation-exchange resin column(TSKgel Super IC-A/C).Good separation was performed on the TSKgel SCX in shorter retention times.For the TSKgel Super IC-A/C,peak shape of the acids was sharp and symmetrical in spite of longer retention times.In addition,the mutual separation of the acids was good except for iso-and n-butyric acids.The better separation and good detection was achieved by using the two columns(TSKgel SCX and TSKgel Super IC-A/C connected in series),lower concentrations of PFBA and sulfuric acid as eluents,non-suppressed conductivity detection and UV detection at 210 nm.This analysis was applied to anaerobic digestion process waters.The chromatograms with conductivity detection were relatively simpler compared with those of UV detection.The use of two columns with different selectivities for the aliphatic carboxylic acids and the two detection modes was effective for the determination and identification of the analytes in anaerobic digestion process waters containing complex matrices.     

Qualitative analysis of some carboxylic acids by ion-exclusion chromatography with atmospheric pressure chemical ionization mass spectrometric detection

A simple, selective and sensitive method for the determination of carboxylic acids has been developed. A mixture of formic, acetic, propionic, valeric, isovaleric, isobutyric, and isocaproic acids has been separated on a polymethacrylate-based weak acidic cation-exchange resin (TSK gel OA pak-A) based on an ion-exclusion chromatographic mechanism with detection using UV-photodiode array, conductivity and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). A mobile phase consisting of 0.85 mM benzoic acid in 10% aqueous methanol (pH 3.89) was used to separate the above carboxylic acids in about 40 min. For LC-MS, the APCI interface was used in the negative ionization mode. Linear plots of peak area versus concentration were obtained over the range 1-30 mM (r2=0.9982) and 1-30 mM (r2=0.9958) for conductimetric and MS detection, respectively. The detection limits of the target carboxylic acids calculated at S/N=3 ranged from 0.078 to 2.3 microM for conductimetric and photometric detection and from 0.66 to 3.82 microM for ion-exclusion chromatography-APCI-MS. The reproducibility of retention times was 0.12-0.16% relative standard deviation for ion-exclusion chromatography and 1.21-2.5% for ion-exclusion chromatography-APCI-MS. The method was applied to the determination of carboxylic acids in red wine, white wine, apple vinegar, and Japanese rice wine.     

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.     

Evaluation of different electrolyte systems and on-line preconcentrations for the analysis of haloacetic acids by capillary zone electrophoresis

The separation of various carboxylic acids was performed on a polymethacrylate-based weakly acidic cation-exchange resin (TSKgel OApak-A) using ion-exclusion chromatography under the acidic elution conditions. When a diluted sulfuric acid solution was used as the eluent, highly sensitive conductimetric detection of carboxylic acids was achieved without increasing the background conductance of the eluent. This method was more sensitive than using benzoic acid eluent and enabled a good resolution of dicarboxylic as well as monocarboxylic acids. The addition of 5–20% methanol to the eluent considerably reduced the retention times of carboxylic acids with hydrophobic nature.     

Determination of some aliphatic carboxylic acids in anaerobic digestion process waters by ion-exclusion chromatography with conductimetric detection on a weakly acidic cation-exchange resin column

The determination of seven aliphatic carboxylic acids, formic, acetic, propionic, isobutyric, n-butyric, isovaleric and n-valeric acids in anaerobic digestion process waters was examined using ion-exclusion chromatography with conductimetric detection. The analysis of these biologically important carboxylic acids is necessary as a measure for evaluating and controlling the process. The ion-exclusion chromatography system employed consisted of polymethacrylate-based weakly acidic cation-exchange resin columns (TSKgel OApak-A or TSKgel Super IC-A/C). weakly acidic eluent (benzoic acid), and conductimetric detection. Particle size and cation-exchange capacity were 5 microm and 0.1 meq./ml for TSKgel OApak-A and 3 microm and 0.2 meq./ml for TSKgel Super IC-A/C, respectively. A dilute eluent (1.0-2.0 mM) of benzoic acid was effective for the high resolution and highly conductimetric detection of the carboxylic acids. The good separation of isobutyric and n-butyric acids was performed using the TSKgel Super IC-A/C column (150 mm x 6.0 mm i.d. x 2). The simple and good chromatograms were obtained by the optimized ion-exclusion chromatography conditions for real samples from mesophilic anaerobic digestors, thus the aliphatic carboxylic acids were successfully determined without any interferences.     

Dynamic coating ion-exchange chromatography of cations on an octadecyl-bonded silica stationary phase

It was found that common cations (Na+, NH4+, K+, Mg2+ and Ca2+) could be strongly retained on an ODS stationary phase when aqueous solutions of carboxylic acids were used as eluents. The chromatographic conditions used in this work were the same as in common cation-exchange chromatography on a cation-exchange resin and the retention behavior of the above-mentioned cations on the ODS column was quite similar to that on a cation-exchange column. The retention behavior and mechanism have been investigated using a number of carboxylic acids as eluents. The retention mechanism of the cations in these experiments was considered to be a dynamic coating ion-exchange mechanism. The carboxylic acids in the mobile phase were coated onto the surface of the ODS stationary phase and formed a dynamic carboxylic acid functional layer which could act like the functional group layer of a carboxylic group cation exchanger.     

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.     

High-performance ion chromatography applied to free-radical mechanisms in drug design the problem of ion analysis at high ionic strengths

Putative free-radical intermediates in drug action can be studied by radiolysis of model systems containing low concentrations of drug and much higher concentrations of other solutes to scavenge the primary water radicals and convert them into appropriate oxidants or reductants. The need to employ high ionic solute concentrations (typically >10 mmol dm⁻³) represents a challenge for the high-performance ion chromatographic detection of drug-derived ions (typically, <50 μmol dm⁻³). Constraints on the chromatographic method chosen are illustrated with examples of the application of high-performance ion chromatography (HPIC) to radiation chemistry studies in the oxidative decar☐ylation of the anti-tumour drugs flavone-8- and xanthenone-4-acetic acids and structurally related aromatic car☐ylic acids (CO₂ in the form of CO₃²⁻), the oxidative denitrification of nitric oxide precursor molecules (NO in the form NO₂⁻/NO₃⁻) and the generation of SO₄²⁻ from novel thiol-based (perthiol) drugs.     

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 SO₄²⁻; 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.     

Bacterial siderophores: unusual 3,4,5,6-tetrahydropyrimidine-based amino acids in pyoverdins frompseudomonas fluorescens

Two unusual natural amino acids have been identified in the pyoverdins occurring from two different strains ofPseudomonas fluorescens. They contain a 3,4,5,6-tetrahydropyrimidine moiety resulting from the condensation of 2,4-diaminobutyric acid with the car☐yl group of respectively serine and glutamine.     

Selective determination of ammonium ions by high-speed ion-exclusion chromatography on a weakly basic anion-exchange resin column

This paper describes an ion-exclusion chromatographic system for the rapid and selective determination of ammonium ion. The optimized ion-exclusion chromatographic system was established with a polymethacrylate-based weakly basic anion-exchange resin column (TSKgel DEAE-5PW) as the separation column, an aqueous solution containing 0.05 mM tetramethylammonium hydroxide (pH 9.10) as eluent with conductimetric detection for the analyte determination. Under the optimum chromatographic conditions, ammonium ion was determined within 2.3 min with a detection limit (S/N=3) better than 0.125 microM. Ammonium ion in rain and river waters was precisely determined using this ion-exclusion chromatographic system.     

Vacancy ion-exclusion chromatography of haloacetic acids on a weakly acidic cation-exchange resin

A new and simple approach is described for the determination of the haloacetic acids (such as mono-, di- and trichloroacetic acids) usually found in drinking water as chlorination by-products after disinfection processes and acetic acid. The new approach, termed vacancy ion-exclusion chromatography, is based on an ion-exclusion mechanism but using the sample solution as the mobile phase, pure water as the injected sample, and a weakly acidic cation-exchange resin column (TSKgel OApak-A) as the stationary phase. The addition of sulfuric acid to the mobile phase results in highly sensitive conductivity detection with sharp and well-shaped peaks, leading to excellent and efficient separations. The elution order was sulfuric acid, dichloroacetic acid, monochloroacetic acid, trichloroacetic acid, and acetic acid. The separation of these acids depends on their pKa values. Acids with lower pKa values were eluted earlier than those with higher pKa, except for trichloroacetic acid due to a hydrophobic-adsorption effect occurring as a side-effect of vacancy ion-exclusion chromatography. The detection limits of these acids in the present study with conductivity detection were 3.4 microM for monochloroacetic acid, 0.86 microM for dichloroacetic acid and 0.15 microM for trichloroacetic acid.     

Characterization of the properties of stationary phases for liquid chromatography in aqueous mobile phases using aromatic sulphonic acids as the test compounds

We investigated the effects of the concentration of naphthalene sulphonic acids (NSAs) as anionic test compounds in the injected sample and of the salt additives to the mobile phase on ion-exclusion. The retention behaviour of NSAs sensitively reflects even minor changes in the ionic and hydrophobic interactions and can be useful for predicting the effects of the stationary phases in reversed-phase chromatography of polar and ionic compounds, both small ones and biopolymers, e.g., oligonucleotides. We studied chromatographic properties of several stationary phases intended for separations in aqueous mobile phases: a C18 column end-capped with polar hydrophilic groups, a densely bonded C8 column doubly end-capped with short alkyl groups, a short alkyl stationary phase designed to keep full pore accessibility in highly-aqueous mobile phases and a Bidentate column with “bridged” C18 groups attached to the silica hydride support. The chemistry and pore structure of various types of column packing materials and of the salt additives to the mobile phase affect the proportion of the pore volume non-accessible to anions due to ion-exclusion and consequently the peak asymmetry and hydrophobic selectivity in reversed-phase chromatography of organic acids. We also addressed the problems connected with the determination of column hold-up volume in aqueous mobile phases. The accessibility of the stationary phase for anionic compounds in contact with the sample zone is affected by ion-exclusion due to repulsive interactions with the negatively charged surface in the pores of the stationary phase. The accessible part of the stationary phase increases and consequently the migration velocity along the column decreases with increasing concentration of the sample in the zone moving along the column. Because of a limited access to the stationary phase, its capacity can be easily overloaded. The combination of the column overload and ion-exclusion effects may result in fronting or tailing peak asymmetry. To explain this behaviour, we proposed a modified Langmuir model, respecting the variation of the column capacity due to the effects of sample concentration on ion-exclusion.     

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.     

Retention behaviour of strong acid anions in ion-exclusion chromatography on sulfonate and carboxylate stationary phases

Some factors influencing the retention of strong-acid anions on ion-exclusion columns were investigated using columns with sulfonate and carboxylate functional groups. The nature of the functional group on the resin, the eluent pH and the eluent ionic strength all significantly affected the retention and separation of these analytes. Retention was observed for all strong-acid anions over the eluent pH range 2.2-5.7 and increased with both decreasing eluent pH and increasing eluent ionic strength. Some separation of strong-acid anions was possible when using a resin with carboxylate functional groups. It has also been demonstrated that strong-acid anions are poor markers of column void volume for ion-exclusion chromatography. A more accurate value was obtained using the neutral polymeric material dextran blue. When using eluents of low ionic strength, poor or fronted peak shapes were observed. A mechanism for these observations is proposed that relates the shape to ionic strength changes across the peak. A system peak was encountered under most experimental conditions. The properties of this peak are discussed and a cause for the system peak postulated.