Capillary electrophoresis for the analysis of short-chain organic acids in coffee

A simple and rapid capillary electrophoresis method for low-molecular mass carboxylic acids measurement in coffee has been optimised and validated. Regarding separation conditions, phosphate concentration in the background electrolyte, surfactant type [cetyltrimethylammonium bromide (CTAB), tetradecyltri methylammonium bromide (TTAB) and hexadimethrine bromide (HDB)], percentages of organic modifier and pH were assayed. The best conditions were: 500 mM phosphate buffer at pH 6.25 with CTAB 0.5 mM. The separation was carried out with an uncoated fused-silica capillary (57 cm x 50 microm i.d.) which was operated at -10 kV potential. Detection was performed at 200 nm. In such conditions 17 short-chain organic acids: oxalic, formic, fumaric, mesaconic, succinic, maleic, malic, isocitric, citric, acetic, citraconic, glycolic, propionic, lactic, furanoic, pyroglutamic, quinic acids plus nitrate were separated, identified and measured. Validation parameters of the method allow us to consider it lineal, accurate and precise and, therefore, reliable for its employment in food composition studies or for quality control. Results in coffees with different industrial treatment allow the detection of important differences in the organic acid profile.     

Capillary electrophoresis of inorganic anions

This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.     

Analysis of organic acids and inorganic anions in beverage drinks by capillary electrophoresis

To meet the need for a new and validated analytical method for simultaneous determination of inorganic and organic acid anions in beverage drinks, a capillary zone electrophoresis (CZE) procedure had been developed based on a new background electrolyte (BGE) system containing 3 mmol/L 1,3,5-benzenetricarboxylic acid (BTA), 15 mmol/L tris(hydroxymethyl)aminomethane and 1.5 mmol/L tetraethylenepentamine (TEPA) at pH 8.4. Baseline separation of anions commonly found in beverage drinks could be achieved in less than 14 min with indirect UV detection at 240 nm. Comigration problems for hydroxycarboxylic acids could be solved using TEPA as BGE additive. The results indicate excellent repeatability for migration time (RSD, 0.27-0.67%, n = 5) and good precision for both peak height (RSD, 3.2-4.2%, n = 5) and peak area (RSD, 3.1-4.5%, n = 5). Under the optimized conditions and using corrected peak area for quantitation, an excellent linear dynamic range (with correlation coefficient > 0.997 in a concentration range from 0.005 to 2.0 mmol/L) and low detection limit (1-4 micro mol/L) were obtained for all the anions investigated. The applicability and reliability of the CE procedure developed were established by parallel method determination using established ion chromatography procedure for the analysis of inorganic and organic acid anions in orange juice and wine samples. Our CZE procedure provided a sensitive and economic technique for simultaneous determination of inorganic and organic acid anions in orange juice, red and white wine samples.     

Capillary electrophoresis with capacitively coupled contactless conductivity detection for low molecular weight organic acids in different samples

CE with capacitively coupled contactless conductivity detection (CE-C(4)D) was explored and validated for the identification and quantification of organic acids in various types of samples. The analyses were performed under optimized conditions, using a buffer system composed of 20 mM MES-histidine (His), pH 6.0, 0.1 mM CTAB, 0.025% HP-beta-CD, and 10% methanol. The investigation included a study of the effects of buffer pH, concentration of CTAB, type and concentration of organic additives, on the migration behavior, resolution and selectivity of the organic acids. The intra- and interday RSDs (n = 6) obtained for migration time and peak area were typically in the range of 0.12-2% and 0.5-4%, respectively. Linearity, detection limits, and repeatability were evaluated. In order to evaluate the application potential of the developed method, real samples from different sources were analyzed. The results demonstrate that CE-C(4)D is a versatile tool for analyzing organic acids in beverages, Chinese herbal medicines (CHM) and plants as it allows for their detection, identification, and quantification.     

Capillary electrophoresis method for the analysis of inorganic anions, organic acids, amino acids, nucleotides, carbohydrates and other anionic compounds.

A previously developed capillary zone electrophoresis (CZE) method with indirect UV detection for the simultaneous determination of inorganic and organic anions, amino acids and carbohydrates using 20 mM 2,6-pyridinedicarboxylic acid (PDC) as the background electrolyte was extended to allow determination of 206 anions including those above--mentioned and physiological amino acids, nucleotides, aromatic acids, haloacetic acids, alcohols, phosphorylated saccharides, oxyhalides, metal oxoacids, metal-ethylenediaminetetraacetic acid (EDTA) complexes, forensic anions, Good's buffers and herbicides. Every compound could be analyzed and their electrophoretic mobility determined simply by selecting detection wavelength. This method is simple and universal for anion analysis, and could be readily applied to the simultaneous determination of anionic compounds. In this work, it was used to identify and quantify important anions in sea urchin and sake.     

Capillary electrophoresis method for analysis of inorganic and organic anions related to habitability and the search for life

In situ missions of exploration require analytical methods that are capable of detecting a wide range of molecular targets in complex matrices without a priori assumptions of sample composition. Furthermore, these methods should minimize the number of reagents needed and any sample preparation steps. We have developed a method for the detection of metabolically relevant inorganic and organic anions that is suitable for implementation on in situ spaceflight missions. Using 55 mM acetic acid, 50 mM triethylamine, and 5% glycerol, more than 21 relevant anions are separated in less than 20 min. The method is robust to sample ionic strength, tolerating high concentrations of background salts (up to 900 mM NaCl and 300 mM MgSO₄). This is an important feature for future missions to ocean worlds. The method was validated using a culture of Escherichia coli and with high salinity natural samples collected from Mono Lake, California.     

Capillary electrophoretic analysis of inorganic anions in atmospheric hailstone samples

Micellar electrokinetic capillary chromatography (MEKC) coupled with sample stacking and polarity switching was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320, UK) in human serum in the concentration range of clinical interest. Human serum samples spiked with SC and UK were eluted with methanol from a C18 cartridge, the extract was evaporated and regenerated in a solution that contained 1 mM phosphate buffer (pH 12.3) and 20% methanol. The MEKC separation was performed using an injection time of 275 s, a polarity switching time of 93 s, a phosphate buffer, (pH 12.3, 15 mM) containing 25 mM sodium dodecyl sulfate as separation electrolyte and a fused-silica capillary. The analysis takes about 6 min and gives satisfactory inter-day precision with respect to migration times and linear responses over the 80-900 ng/ml concentration range investigated for SC and UK. Intra-day RSDs (n=4 graphs) for the slopes of the calibration graphs were 4.86% for SC and 3.50% for UK. Inter-day RSDs for the slopes were 4.37% for SC and 5.39% for UK. Detection limits (S/N=3) were about 17 ng/ml for both compounds in human serum. A 1-ml volume of blood serum was necessary to do this determination.     

毛细管电泳定量检测环境水样中无机阴离子

详细讨论了胶束浓度、间接吸收背景物质的浓度及有机添加剂组成等对部分卤素及其含氧酸根的毛细管电泳分离影响;在优化的条件下,3.5min内高效、快速地完成了Cl-、Br-、ClO3-、BrO3-四种无机阴离子的分离分析,分离的理论塔板数在1.6×106～2.8×105/m之间,检出限在11.2～23.3mg/L之间,迁移时间的相对标准偏差小于1%,峰面积的相对标准偏差在5.2%～2.2%之间;并将方法用于环境水样的分析。     

Capillary electrophoretic method for the determination of inorganic and organic anions in real samples. Strategies for improving repeatability and reproducibility

Selectivity and robustness of the pyromellitic acid (PMA) based background electrolyte was improved in order to increase its applicability for routine analysis of inorganic and organic anions in real samples. An electrolyte composed of 6.75 mM PMA, 0.5 mM hexamethonium hydroxide as electroosmotic flow (EOF) modifier, Ca(2+) 0.05 mM as complexation agent and pH adjusted to 7.6 with TEA 1M allows for the separation of 22 inorganic and organic anions in less than 17 min. Good RSDs for within-day migration time reproducibility (0.03-0.9%) and day-to-day analyses (0.04-1.4%) were obtained by the use of two internal standards, allowing for an accurate compound identification. The detection limits ranged from 0.1 to 0.4 mgL(-1) (S/N=3) for hydrodynamic injection (1250 mbars). The applicability of the proposed method was demonstrated by the analysis of inorganic and organic anions in diverse real samples. The recoveries obtained ranged from 93 to 106%.     

Capillary zone electrophoresis for the determination of light-absorbing anions in environmental samples.

A rapid and simple method for separation and determination of inorganic anions by capillary zone electrophoresis was described. The detection was carried out directly with a diode array detector. The experimental conditions, such as concentration of carrier electrolyte, capillary length, voltage, and temperature were optimized. In order to improve selectivity, different organic modifiers were also investigated. The baseline separation of 10 light-absorbing anions was accomplished within 3.5 min with a background electrolyte consisting of 50 mM sodium tetraborate containing 5% MeOH. Linear plots were obtained in the concentration range of 0.1-10 microg/ml. With sample stacking injection, the quantitation limits of the anions were found to be in the range of 0.02-0.1 microg/ml. The proposed method was successfully applied to the determination of inorganic anions in environmental samples and in effluents of a power plant.     

Optimization and validation of a capillary electrophoresis methodology for inorganic anions in atmospheric aerosol samples

Optimization and validation of a method for the determination of inorganic anions, such as chloride, nitrate, sulphate, fluoride and phosphate, in atmospheric particulate matter is described. Ultrasonic extraction followed by CE, using CTAB as EOF modifier, has been established for this separation using chromate as visualization reagent for the indirect UV/vis detection. Optimization of the experimental chemical conditions (pH, surfactant concentration, chromate concentration and acetonitrile concentration) and instrumental parameters (temperature, applied voltage and injection time) is described. Linear calibrations plots are obtained for the five ions, with detection limits in the high ng/mL range. A standard reference material, SRM 1648 Urban Particulate Matter, has been used to validate the proposed method. Satisfactory reproducibility and acceptable agreement to the matter atmospheric samples has been found (recoveries ranging from 86 to 96%). Application to real particulate matter atmospheric samples, collected on high volume samplers from the air quality surveillance network of Extremadura, southwest Spain, is shown.     

Capillary electrophoresis of organic and inorganic cations with indirect UV detection

Summary The determination of alkali and alkaline earth metal ions by capillary electrophoresis using indirect UV detection is described. With the identical system it is also possible to determine short chain aliphatic amines and alkanol amines within 4 minutes. Indirect UV detection is achieved at 214 nm with a background electrolyte containing 5 mmol L^–1 imidazole. Linear calibration curves could be obtained for peak areas between 0.5 and 10 ppm. The detection limits are around 0.1 ppm (corresponding to 10 fmol in about 10 nL sample volume) for all cations and amines and 0.05 ppm for lithium. Practical applications demonstrate the applicability of this system in routine analysis.     

Capillary electrophoretic determination of inorganic anions in the drainage and surface water samples.

Capillary electrophoresis was used for separation and quantitation of several inorganic anions in the drainage and surface water samples from the region with extensive use of fertilisers. Baseline separation of 13 small anions including nitrite and nitrate up to the concentrations of 100 mg/l was achieved in less than 5 min. The electrolyte consisted of 3 mM K2CrO4, 30 microM cetyltrimethylammonium bromide and 3 mM boric acid at pH 8. The method yielded precisions of 1.8-7.2% (RSD, n = 10) and detection limits from 4 micrograms/l (Cl-) up to 500 micrograms/l (citrate). The results of the CE method were compared to ion chromatography using water-acetonitrile (86:14) at pH 8.6 adjusted with NaOH as the mobile phase and consistent results were obtained.     

Capillary electrophoresis of inorganic anions in hydro-organic media. Influence of ion-pairing and solvation phenomena

The capillary electrophoresis separation of four inorganic anions (NO3-, I-, Br- and SCN-) was investigated over the whole range of methanol-water mixture composition. As the separation selectivity was strongly dependent on the solvent composition, the influence of ion-pairing and solvation phenomena was examined in depth in an attempt to explain this modification. First, a series of experiments was performed in methanolic background electrolytes, with counter-ions of different size. Ion-pair formation involving electrolyte ions was assessed to allow for a correction for free electrolyte ion concentration. Ion-pair formation constants between each inorganic anion and electrolyte counter-ion were next determined from the variations of the anion mobility as a function of the free counter-ion concentration. In view of the low values obtained, ion-pair formation alone failed to explain the selectivity variations. Solvation phenomena were then investigated with the help of a theoretical quantum model, the density functional theory (DFT), coupled with a polarizable continuum model to mime non-specific solvent effects. Whereas this model proved successful at predicting the mobility order at infinite dilution in water, it failed to predict the correct order in methanol.     

离子色谱法测定乙二醇中微量有机酸和无机阴离子

建立了以YSA-8阴离子交换柱的离子色谱法分析乙二醇中微量有机酸和无机阴离子的方法,比较了进样乙二醇浓度对F-及有机酸测定结果的影响,进样乙二醇质量分数低于8.5%时,能够得到较准确的数据.用本法对所测的有机酸和无机阴离子检出限均在8.9 μg/L以下,线性相关系数r在0.996～0.999范围内,标准样中各物质的离子峰面积的相对标准偏差(RSD)在4.2%以下(n＝11),对乙二醇质量分数约为8.5%的样品中F-及有机酸的加标回收率在91.6%～100.0%之间,乙二醇含水料直接测定无机阴离子的加标回收率在91.8%～104.8%之间.     

Simultaneous determination of inorganic anions and organic acids in amine solutions for sour gas treatment by capillary electrophoresis with indirect UV detection

A new CE method has been developed for the simultaneous determination of selected inorganic anions (bromide, chloride, thiosulfate, nitrite, nitrate, sulfate, thiocyanate, fluoride and phosphate) and organic acids (oxalic, malonic, formic, tartric, acetic, glycolic, propionic, butyric and cyclohexanoic) in amine solutions from sour gas treatment units. An electrolyte composed of 10 mM trimellitic acid, 200 mM Tris (pH 9.0), 0.1% polyvinyl alcohol provides a satisfactory separation of all analytes of interest. The electroosmotic flow is reversed by using hexadimethrine bromide as a semi-permanent positively charged coating, making the electrolyte free of additive. Indirect UV detection at 240 nm is used because of the weak absorbing properties of most of analytes. The addition of 1% diethanolamine in standard mixtures permits to better preserve them, inhibiting potential degradation processes, especially for thiosulfate. The quantification is performed using internal standardization, by which molybdate is used as internal standard. Moreover, the use of relative migration times and the excellent repeatabilities obtained allow unambiguous identification of analytes in real samples by comparison with standard mixture. It has been shown that no significant matrix effect came from the presence of 30% diethanolamine in amine solution samples and the developed method was characterized in terms of calibration linearity and accuracy using recovery tests. In short, the developed method allows the simultaneous and rapid determination, in difficult matrices, of numerous inorganic anions and organic acids characterized by a large range of electrophoretic mobilities.     

Determination of inorganic anions, carboxylic acids and amino acids in plant matrices by capillary zone electrophoresis

Summary Physiological investigations of solute transport in plants affords knowledge of solute distribution between different tissues. Capillary electrophoresis using indirect UV and laser induced fluorescence (LIF) detection is demonstrated as a useful technique for the simultaneous determination of inorganic anions, amino acids and carboxylic acids in plant samples. Cell sap obtained from plant tissues as well as simple ethanolic or aqueous plant extracts can be analysed directly without any pretreatment. This matrix stability and the very small volumes required allow fast determinations of various compounds in small plant tissue sections. In the case of carboxylic acids, resolution can be optimized using calcium for selective complexation of some of the compounds. Selective and sensitive determination of amino acids is possible using precolumn derivatisation with orthophthaldialdehyde (OPA) and laser induced fluorescence detection. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

离子色谱法同时分析啤酒中的有机酸和无机阴离子

建立了以NaOH-甲醇混合淋洗液,离子交换色谱柱,电导检测器检测,分离啤酒中有机酸和无机阴离子的离子色谱法.结果表明：在20 min内分离出啤酒中的11种主要有机酸与无机阴离子,方法回收率和相对标准偏差分别为96.30%～104.8%和0.02%～4.0%.     

Determination of various inorganic anions and organic acids in the atmospheric particulate matter using capillary zone electrophoresis with indirect UV detection

Capillary zone electrophoresis with indirect UV detection was developed for the simultaneous analysis of inorganic anions and organic acids using a mixed solution of 2,6-pyridinedicarboxylic acid and cetyltrimethylammonium hydroxide as the background electrolyte (BGE). The parameters which influence the separation, such as indirect UV detection wavelength, BGE conditions, applied voltage and extraction conditions were investigated. Thirteen inorganic anions and organic acids were detected within 20 min. The calibration curves of each analyte were linear with correlation coefficients greater than 0.991. The relative standard deviations (n = 10) of the peak areas ranged from 0.6% to 3.3%. The detection limits for these species ranged from 0.4 to 1.4 mg/L at a signal-to-noise ratio of 3. The recovery rate of each analyte was more than 80% under optimised extraction conditions, except for nitrite. The proposed method was applied towards the analysis of inorganic anions and organic acids in the atmospheric particulate matter using an Andersen sampler. The particle size of the particulate matter was determined, but not the size of the anions.     

A new capillary electrophoresis buffer for determining organic and inorganic anions in electroplating bath with surfactant additives

Monitoring of trace impurities in electroplating bath is needed to meet EU requirements for WEEE and RoHS and for quality control of electrodeposits. Methods using IC and 100% aqueous CE buffer were found producing non-repeatable results attributed to interference of surfactants and major methanesulphonate anion. A new CE buffer containing 1.5 mM tetraethylenepentaamine, 3 mM 1,3,5-benzenetricarboxylic acid and 15 mM Tris in 20% (v/v) methanol at pH = 8.4 was shown to enhance the separation window, reduce interaction between buffer and bath constituents, and give satisfactory repeatability with baseline separation for 14 organic and inorganic anions within 14 min, good repeatability for migration time (0.32–0.57% RSD), satisfactory peak area and peak height (2.9–4.5 and 3–4.7% respectively), low detection limit (S/N = 2, 20–150 ppb), and wide working ranges (0.1–100 ppm). The CE buffer with 20% (v/v) methanol has demonstrated its capability for identifying anion impurities causing problem in aged tin bath and the use of only 10-fold dilution to produce reliable results for quality assessment in plating bath containing high surfactant additives.