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.     

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.     

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.     

Confirmation and determination of carboxylic acids in root exudates using LC-ESI-MS

Reversed-phase liquid chromatography with UV detection is of limited applicability in the separation and identification of carboxylic acids because of the column's poor separation efficiency and the non-selective nature of the UV detector. To address this issue, RP-LC with electrospray ionization mass spectrometry has been explored for the confirmation and determination of carboxylic acids in plant root exudates, with ESI-MS providing structural information, high selectivity, and high sensitivity. The separation of 10 carboxylic acids (pyruvic, lactic, malonic, maleic, fumaric, succinic, malic, tartaric, trans-aconitic, and citric acid) was performed on a C(18) column using an eluent containing 0.1% (v/v) acetic acid within 10 min, where the acidic eluent not only suppressed the ionization of the carboxylic acids to be retained on the column, but was also compatible with ESI-MS detection. In addition, an additional standard was used to overcome the matrix effect. The results showed that peak areas correlated linearly with the concentration of carboxylic acids over the range 0.05-10 mg/L. The detection limits of target acids (signal-to-noise S/N ratio of 3) ranged from 20 to 30 microg/L. Finally, the proposed method was used for the confirmation and determination of low-molecular-weight carboxylic acids in plant root exudates, and provided a simple analytical procedure, including sample processing, fast separation, and high specificity and sensitivity.     

Non-suppressed conductivity and indirect UV detection of carboxylic acids in environmental samples by ion-exclusion chromatography using 2,6-pyridinedicarboxylic acidic eluent

2,6-Pyridinedicarboxylic acid (PDCA) was evaluated as an eluent for indirect UV and non-suppressed conductivity detection of carboxylic acids in ion-exclusion chromatography. The effect of PDCA concentration on the separation and detection sensitivity was investigated. The reasonable resolutions between carboxylic acids were achieved using 1 mM PDCA eluent. Detection limits were 1.0-7.0 microM for conductivity detection and 8-30 microM for UV detection. Compared to the eluent containing 1 mM sulfuric acid, the method offers a high resolution and high detection sensitivity for both detectors due to its high molar absorptivity and low background conductance. The proposed method was demonstrated to be useful for the determination of carboxylic acids in environmental samples with direct sample injection.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids II. Separation of aliphatic carboxylic acids with pyromellitic acid as eluent and with suppressed conductimetric detection

The application of zirconium-modified silica gels (Zr-Silica) as stationary phases for ion-exclusion chromatography with conductimetric detection (IEC–CD) for C₁–C₈ aliphatic carboxylic acids (formic, acetic, propionic, butyric, valeric, caproic, heptanoic and caprylic acids) was carried out using pyromellitic acid as the eluent. 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 solution. An ASRS-Ultra anion self-regenerating suppressor in the K⁺ form was used for the enhancement of conductimetric detector response of these aliphatic carboxylic acids. A Zr-Silica adsorbed on 10 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in IEC–CD for the separation of these aliphatic carboxylic acids. Excellently simultaneous separation and highly sensitive detection for these aliphatic carboxylic acids were achieved in 25 min by IEC–CD with the Zr-Silica column (250×4.6 mm I.D.) and a 0.2 mM pyromellitic acid containing 0.15% heptanol as the eluent.     

High-performance CE: an effective method to study lactonization of alpha2,8-linked oligosialic acid

A sensitive and efficient method using high-performance CE (HPCE) and neuraminidase hydrolysis was developed to study the lactonization and hydrolysis of alpha2,8-pentasialic acid. Eleven lactone species of pentasialic acid formed in glacial acetic acid were detected and classified into three groups based on the number of carboxylic acids: monolactones with four carboxylic acids, dilactones with three carboxylic acids, and trilactones with two carboxylic acids. These lactones eluted between the original pentamer (with five carboxylic acids) and the fully lactonized species (with one carboxylic acid) in HPCE. Eight of the isomers were identified by hydrolysis with neuraminodase. Results obtained from previous reports and from this study together reveal a general rule for predicting the subtle difference in the acidity of each carboxylic acid in oligosialic acids: the closer the carboxylic acid is to the nonreducing end, the more acidic it is. Therefore, the elution order of lactone isomers having the same number of carboxylic groups can be predicted from the position of the free carboxylic groups in pentasialic acid. We used this principle and the results of hydrolysis with neuraminidase to identify hexamer lactone isomers separated by HPCE.     

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

In this preliminary study, a new approach to ion-exclusion chromatography is proposed to overcome the relatively poor conductivity detection response which occurs in ion-exclusion chromatography when acids are added to the eluent in order to improve peak shape. This approach, termed vacancy ion-exclusion chromatography, requires the sample to be used as eluent and a sample of water to be injected onto a weakly acidic cation-exchange column (TSKgel OApak-A). Vacancy peaks for each of the analytes appear at the retention times of these analytes. Highly sensitive conductivity detection is possible and sharp, well-shaped peaks are produced, leading to efficient separations. Retention times were found to be affected by the concentration of the analytes in the eluent, and also by the presence of an organic modifier such as methanol in the eluent. Detection limits for oxalic, formic, acetic, propionic, butyric and valeric acids were 0.1, 0.2, 0.3, 0.3, 0.4 and 0.5 microM, respectively, and linear ranges for some acids extended over two orders of magnitude. Precision values for retention times were 0.21% and for peak areas were <1.90%. The vacancy ion-exclusion chromatography method was found to give detection responses four to 10 times higher than conventional ion-exclusion chromatography using sulfuric acid eluent and two to five times higher than conventional ion-exclusion chromatography using benzoic acid eluent.     

Ion-exchange properties of silica gel with covalently bonded histidine

The ion-exchange and acid-base properties of Silasorb 600 (10 μm) with immobilized histidine (His-SiO₂) were investigated. The acid-base properties of the sorbent were estimated from the dependence sof the retention of organic acids and bases on the eluent pH. The effect of various organic modifiers (benzoic, citric, oxalic, and sulfuric acids) and the eluent pH on the retention of inorganic ions was studied. It was shown that His-SiO₂ exhibits anion-exchange properties in acidic and weakly acidic media at pH < 5.7. Eight anions were separated under optimal conditions on a 150 × 4.6-mm column in 21 min using a 5 mM oxialic acid solution as an eluent.     

Novel way of separating polyfluorocarboxylic acids by ion-exclusion chromatography

Ion-exclusion chromatography has been successfully applied to the separation of a number of polyfluorocarboxylic acids. The separation of various mono- and dibasic polyfluorocarboxylic acids having a different alkyl group was investigated using a polymethacrylate-based weakly acidic cation-exchange resin (TSK gel OApak-A) in the H -form and conductimetric detection. When water was used as the eluent, polyfluorocarboxylic acids could not be resolved. When an aqueous solution of sulfuric acid, benzoic acid, o-phthalic acid, 1,3,5-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, and tartaric acid was used, the separation of polyfluorocarboxylic acids occurred for monobasic ones. While, for fluorine-containing dibasic acids, imperfect separation of peaks occurred. In order to improve their separation, the effect of an addition of organic modifiers such as methanol, 2,2,2-trifluoroethanol and 2H-hexafluoro-2-propanol in the eluent was also investigated.     

Chromatographic properties of the ion-exclusion column IonPac ICE-AS6 and application in environmental analysis. Part I: Chromatographic properties

The chromatographic performance of the Dionex IonPac ICE-AS6 ion exclusion column is investigated. Therefore, capacity factors, efficiency, peak symmetry, resolution, and selectivity are determined for various mono- and polyfunctional aliphatic carboxylic acids under selected chromatographic conditions. Except for the stronger acids (pKa1 < 3.75), the highest chromatographic efficiency is achieved at a column temperature of 40 or 50 degrees C, and peak shape is found to be optimal at approximately 60 degrees C. The separation of the stronger acids is favored by an eluent pH below 3.0 and column temperatures below 40 degrees C. The maximal effective plate numbers range between 126 (tartronic acid) and 6380 (4-oxovaleric acid). Hydroxy-substituted acids are less retained and less influenced by temperature changes than the unsubstituted compounds. It is estimated that size exclusion effects take part in the separation of aldonic acids. The addition of 1% isopropanol to the acidic eluent increases the chromatographic efficiency generally, whereas higher concentrations reduce the retention of several acids drastically.     

Use of potassium-form cation-exchange resin as a conductimetric enhancer in ion-exclusion chromatography of aliphatic carboxylic acids

In this study, a cation-exchange resin (CEX) of the K⁺-form, i.e., an enhancer resin, is used as a postcolumn conductimetric enhancer in the ion-exclusion chromatography of aliphatic carboxylic acids. The enhancer resin is filled in the switching valve of an ion chromatograph; this valve is usually used as a suppressor valve in ion-exchange chromatography. An aliphatic carboxylic acid (e.g., CH₃COOH) separated by a weakly acidic CEX column of the H⁺-form converts into that of the K⁺-form (e.g., CH₃COOK) by passing through the enhancer resin. In contrast, the background conductivity decreases because a strong acid (e.g., HNO₃) with a higher conductimetric response in an eluent converts into a salt (e.g., KNO₃) with a lower conductimetric response. Since the pH of the eluent containing the resin enhancer increases from 3.27 to 5.85, the enhancer accelerates the dissociations of analyte acids. Consequently, peak heights and peak areas of aliphatic carboxylic acids (e.g., acetic acid, propionic acid, butyric acid, and valeric acid) with the enhancer resin are 6.3-8.0 times higher and 7.2-9.2 times larger, respectively, than those without the enhancer resin. Calibrations of peak areas for injected analytes are linear in the concentration range of 0.01-1.0 mM. The detection limits (signal-to-noise ratio = 3) range from 0.10 μM to 0.39 μM in this system, as opposed to those in the range of 0.24-7.1 μM in the separation column alone. The developed system is successfully applied to the determination of aliphatic carboxylic acids in a chicken droppings sample.     

Determination of carboxylic acids by ion-exclusion chromatography with non-suppressed conductivity and optical detectors

Summary Determination of carboxylic acids using non-suppressed conductivity and UV detections is described. The background conductance of 1-octanesulfonic acid, hexane sulfonic acid and sulfuric acid at varying concentrations was determined. Using 0.2 mM 1-octanesulfonic acid as a mobile phase and an injection volume of 300 l, the detection limits range from 1 M for formic acid to 10 M for butyric acid. The conductivity detector was connected in tandem with a Waters 484 optical detector at 210 nm, which allowed the analysis of carboxylic acids from 0.01 mM to 10 mM. The dependence of the retention of carboxylic acids on the eluent pH is discussed.     

Aliphatic carboxylic acids as new modifiers for separation of 2,4-dinitrophenyl amino acids by micellar liquid chromatography

The possibilities of isocratic separation of 2,4-dinitrophenyl derivatives of 12 amino acids that considerably differ in hydrophobicity by micellar mobile phases with different organic modifiers have been discussed. For the first time aliphatic carboxylic acids have been used as modifiers of micellar eluent in micellar liquid chromatography with C18 columns. Elution strength of hybrid micellar phases on the basis of sodium dodecylsulfate and aliphatic carboxylic acids increases in sequence: acetic相似文献   

Why robust background electrolytes containing multivalent ionic species can fail in capillary zone electrophoresis

Previous models for the retention behaviour of carboxylic acids in ion-exclusion chromatography are applicable only when the degree of ionisation of the analyte is constant over the entire chromatographic peak. When solutions of sulfuric acid are used as eluents, this condition applies only when the eluent concentration is considerably higher than that of the analyte. Since it is common for dilute solutions of sulfuric acid to be used as eluents, a retention model which accounts for unbuffered eluents has been developed. This model also considers the effects on retention of hydrophobic adsorption of the undissociated and dissociated forms of the analyte onto the stationary phase substrate, as well as the effects of organic solvents added to the eluent. The derivation of this model is presented and it has been evaluated using a comprehensive set of retention data obtained using three different sulfonated stationary phases over a range of eluent conditions. The adsorption coefficients calculated from the model are in accordance with expected trends and showed that both the undissociated and dissociated forms of the analyte acids were retained by hydrophobic adsorption effects, although this adsorption was much stronger for the undissociated analytes.     

A novel derivatization reagent possessing a bromoquinolinium structure for biological carboxylic acids in HPLC‐ESI‐MS/MS

A novel bromoquinolinium reagent, i.e. 1‐(3‐aminopropyl)‐3‐bromoquinolinium bromide (APBQ), was synthesized for the analysis of carboxylic acids. A simple and practical precolumn derivatization procedure using the APBQ in RP chromatography and MS (HPLC‐MS) has been developed using bile acids and free fatty acids, as the representative carboxylic acids in biological samples. The APBQ efficiently reacted with carboxylic acids at 60°C for 60 min in the presence of N,N‐dicyclohexylcarbodiimide and pyridine as the activation reagents. Because the APBQ possesses a bromine atom in the structure, the identification of a series of carboxylic acids was easily achieved due to the characteristic bromine isotope pattern in the mass spectra. The APBQ also has a quaternary amine structure, thus the positively charged derivatives are predominate for the highly sensitive detection of carboxylic acids. The APBQ was successfully applied to the selective determination of biological carboxylic acids in human plasma. The bile acids (chenodeoxycholic acid and deoxycholic acid) and several saturated (stearic acid and palmitic acid) and unsaturated free fatty acids (oleic acid and linoleic acid) were reasonably determined by HPLC‐MS under the proposed procedure. Based on the results of analyses of human plasma and saliva, the proposed procedure using APBQ seems to be applicable for the qualitative and quantitative analyses of a series of carboxylic acids in biological samples.     

Analysis of carbonic acid in water samples by ion-exclusion chromatography with pure water as eluent.

A simple, sensitive and rapid ion-exclusion chromatographic method for the simultaneous separation of carbonic acid and short chain organic acids (formic acid, acetic acid, and propionic acid) has been developed. A weakly acidic cation exchange resin column TSKgel OApak-A was used for the separation; pure water, owing to its lower background conductance, was employed as eluent in order to obtain high detection sensitivity. A good separation of these weak acids was achieved in 16 min. The linear range of the peak area calibration curve for carbonic acid was from 3.0 mg/L to 500 mg/L. The conductivity detection limit calculated at S/N = 3 was 0.084 mg/L for carbonic acid. The method developed in this work was successfully applied to the determination of carbonic acid in several environmental water samples without any pretreatment.     

Separation of perfluoroalkylsulfinic acids and perfluoroalkylsulfonic acids by ion-exclusion chromatography

Ion-exclusion chromatography has been successfully applied to the separation of a number of perfluoroalkylsulfinic acids and perfluoroalkylsulfonic acids. The separation of various perfluoroalkylsulfinic and perfluoroalkylsulfonic acids, with different alkyl groups, was investigated on a polymethacrylate-based, weakly acidic, cation-exchange resin (TSK gel OApak-A) in the H⁺-form and using conductimetric detection. When water was used as the eluent, these perfluoroalkylsulfinic and perfluoroalkylsulfonic acids could not be resolved. When an aqueous solution of benzoic acid and o-phthalic acid was used, the separation of each of these acids occurred. In order to improve their separation, the effect of the addition of methanol and 2,2,2-trifluoroethanol, as organic modifiers, was also investigated.     

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.     

Reversed Phase High Performance Liquid Chromatography Using Carboxylic Acids in the Mobile Phase

Abstract

This report describes the use of different carboxylic acids as mobile phase modifiers. The effect on retention of acid chain length, pH, and eluent composition for a series of phenylalkanols, phenol, and the amines aniline, N-methylaniline, and benzylamine is discussed. The retention of both neutral and positively charged compounds is influenced by the dissociation equilibrium of the carboxylic acid in the mobile phase. By using l-pentanol to coat excess exposed silanol groups on the reversed phase column used, the inflection in the retention of both neutral and charged solutes as pH is changed occurs at the pK_a of the acid in the mobile phase. In addition, by using an acid and amine with the same or similar pK_a values, selective ion-pairing of this pair over others with dissimilar pK_a values can be promoted. Application of this technique to the selective retention of amino acids and peptides was unsuccessful.