Determination of Phenols,Inorganic Anions,and Carboxylic Acids in Kraft Black Liquors by Capillary Electrophoresis

Two methods are presented for the quantitative capillary electrophoretic (CE) determination of phenolic lignin degradation compounds as well as of inorganic anions and organic acids in Kraft black liquors. Important phenolic lignin degradation compounds can be rapidly separated by co-electroosmotic CE after acidification of the liquors and subsequent extraction of the compounds with chloroform. A capillary electrophoretic separation of phenolic compounds is performed by using a phosphate/borate electrolyte system and UV detection at 214 nm. In addition, a HPLC method using a gradient with water, methanol, and acetic acid is also developed. Inorganic ions which are of importance to the pulping process can be determined by simply diluting the black liquors after sampling and subsequent analysis with a chromate electrolyte system and indirect UV detection at 185 nm. In addition, the concentration of low molecular aliphatic carboxylic acids can be determined simultaneously within the same run. By method optimization it is possible to separate the anions within one minute and, at the same time, to increase the resolution of the solutes. The electrolyte systems for the CE separations were optimized by varying the pH value and by adding organic solvents. Short separation times are obtained by adding a polycationic EOF modifier (hexadimethrine bromide) to the electrolyte which reverses the electroosmotic flow. A migration of the anionic analytes in the same direction as the electroosmotic flow is thus established.     

Polymeric ionic liquid as a background electrolyte modifier enhancing the separation of inorganic anions by capillary electrophoresis

A novel and easy method for the separation of inorganic anions by capillary electrophoresis using a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium bromide) as a background electrolyte modifier has been developed. The PIL has been proved to generate a reversed electroosmotic flow which reduces the analysis time and improves the separation significantly. Effects of the PIL concentration and buffer composition (pH and concentration) were evaluated on basis of the resolution and efficiency of the sample. Under optimum conditions, good separation of six model inorganic anions was achieved with high efficiency and excellent reproducibility within 3 min. The results obtained indicate that the combination of reversed EOF and the association between the analytes and the PIL on the capillary wall or BGE play a prominent role in the separation of anions. Therefore, the PIL presents a useful alternative for the BGE modifier in the study of inorganic anions by CE.     

The use of macrocycles as electroosmotic flow modifiers in the separation of inorganic anions by capillary electrophoresis

In a novel approach to the use of macrocycles in separation systems, we report the use of macrocyclic ligands as electroosmotic flow modifiers for the separation of inorganic anions by capillary electrophoresis (CE). Inorganic anions were successfully separated through the use of 18-crown-6 or cryptand 2.2.2. as electroosmotic flow modifiers. We found that for our CE system, use of a macrocycle as the modifier resulted in better baseline stability and better efficiency than the commonly used modifier DETA. In our system, the separation efficiency and electroosmotic flow varied according to the pH of the buffer and the affinity of the macrocycle for the buffer metal cation. Results for sodium- and potassium-based buffers show that for the cryptand, pH plays a role in determining the amount of macrocycle-metal complex formed. Separations of a 12 anion standard illustrate these results. In addition, we report the effect of concentration of both macrocycle and metal ion on complex formation and resultant electroosmotic flow modification. Relationships between the macrocycle-metal complex, the buffer medium, the efficiency of separation, and the migration times of the analytes are discussed, and theoretical interpretations presented.     

电解质溶液组成对低分子量阴离子毛细管电泳分离的影响

研究了毛细管电泳间接紫外检测法测定低分子量阴离子时电解质溶液中背景电解质、电渗流改性剂、ｐＨ值、有机溶剂等对分离的影响；比较了铬酸根、邻苯二甲酸根、苯甲酸根３种背景离子对不同迁移率阴离子分离的影响，并对间接紫外检测的定量基础及灵敏度进行了讨论；考察了３种不同长链烷基三甲基季铵盐电渗流改性剂浓度对阴离子迁移时间和电渗迁移率的影响，结果表明电渗流的改性效果与烷基链的长度有关；ｐＨ影响阴离子的有效迁移率     

Separation of multiply charged anions by capillary electrophoresis using alkyl phosphonium pairing agents

Two newly developed UV transparent phosphonium-based cationic reagents were evaluated as background electrolyte additives for capillary electrophoresis for the separation of multiply charged anions, including several complex anions. These cationic reagents showed moderate suppression of the electroosmotic flow, interacted with the analytes to improve their separation and often improved the peak shape. The effects of the additives and their concentration on the separation were studied, as well as the buffer type, pH, and voltage. The dicationic reagent effectively separated eight divalent anions within 17 min and the tetracationic reagent best separated nine trivalent anions, as well as a mixture of all the anions.     

Investigations on the behaviour of acidic, basic and neutral compounds in capillary electrochromatography on a mixed-mode stationary phase

This work describes the separation of acidic, basic and neutral organic compounds as well as inorganic anions in a single run by capillary electrochromatography employing a stationary phase which exhibits both strong anion-exchange and reversed-phase chromatographic characteristics. The positive surface charge of this stationary phase provided a substantial anodic electroosmotic flow. The analytes were separated by a mixed-mode mechanism which comprised chromatographic interactions (hydrophobic interactions, ion-exchange) as well as electrophoretic migration. The influence of ion-exchange and hydrophobic interactions on the retention/migration of the analytes could be manipulated by varying the concentration of a competing ion and/or the amount of organic modifier present in the background electrolyte. Additionally the effects of pH changes on both the chromatographic interactions as well as the electrophoretic migration of the analytes were investigated.     

Parameters influencing separation and detection of anions by capillary electrophoresis

Electrolyte composition is critical in optimizing separation and detection of ions by capillary electrophoresis. The parameters which must be considered when designing an electrolyte system for capillary electrophoresis include electrophoretic mobility of electrolyte constituents and analytes, detection mode, and compatibility of electrolyte constituents with one another. An electrolyte system based on pyromellitic acid is well suited for use with indirect photometric detection, and provides excellent separations of anions. The ability to modify the electrophoretic mobility of pyromellitic acid as a function of ph provides flexibility in matching electrophoretic mobilities of analytes. Additionally, the use of alkyl amines as electroosmotic flow modifiers allows the rapid separation of anions by reversing the direction of electroosmotic flow in a fused-silica capillary. The optimization of a capillary electrophoresis electrolyte for anion analysis is also discussed in terms of pH, ionic strength and applied voltage. The effect of organic solvent on separation selectivity is also discussed.     

Capillary electrophoretic determination of inorganic selenium species

The performance of pyromellitic electrolyte for capillary zone electrophoresis of inorganic selenium species in the presence of selected common anions with indirect UV detection was investigated. The separation was achieved with pyromellitic electrolyte at pH 8.8 and hexamethonium hydroxide as the electroosmotic flow modifier. Obtained detection limits of 0.17 microg ml(-1) for Se(VI) and 0.29 microg ml(-1) for Se(IV) were improved by a factor of 5-7 in comparison with chromate electrolyte, which has been mainly employed for selenium analysis. Good resolution for nitrate-Se(VI) peaks were obtained.     

Large-volume stacking in capillary electrophoresis using a methanol run buffer

Highly sensitive nonaqueous capillary electrophoresis of weakly acidic organic compounds has been performed using methanol as the run buffer solvent. Methanol provided appropriate suppression of the electroosmotic flow and an increase in the electrophoretic mobilities of anionic solutes compared to water. These two effects allowed large-volume stacking using the electroosmotic flow pump (LVSEP) to be achieved for larger anions using a bare fused-silica capillary under an electric field of reverse polarity, whereas only fast-moving small anions were previously known to be suitable for LVSEP in aqueous media. A field-enhanced sample injection of an additional amount of analytes during the solvent plug removal further enhanced the limits of detection to below the nanomolar range with conventional UV absorption detection. Under optimum conditions, excellent linear responses and reproducibility in the migration times together with the corrected peak areas for ten analytes were obtained in the concentration range of 10-100 nM.     

Pressurized-flow anion-exchange capillary electrochromatography using a polymeric ion-exchange stationary phase

The feasibility of using capillary columns equipped with silica frits and packed with a polymer-based anion exchanger (Dionex AS9-HC) for CEC separations of inorganic anions has been investigated. Experiments using a conventional 25 cm packed bed, and mobile phase flow that is a combination of hydrodynamic and electroosmotic flow were used to demonstrate that by varying the applied voltage (electrophoresis component) or the concentration of the competing ion in the mobile phase (ion-exchange component), considerable changes in the separation selectivity could be obtained. Using an artificial neural network, this separation system was modelled and the results obtained used to determine the optimum conditions (9 mM perchlorate and −10 kV) for the separation of eight inorganic anions. When a short (8 cm) packed bed was used, with detection immediately following the packed section, the separation of eight test analytes in under 2.2 min was possible using pressure-driven flow and a simple step voltage gradient. A more rapid separation of these analytes was obtained by only applying high voltage (−30 kV), where many of the same analytes were separated in less than 20 s and with a different separation selectivity to that obtained in conventional ion-exchange or capillary electrophoresis separations.     

Separation of inorganic anions in acidic solution by capillary electrophoresis

Inorganic anions are almost always determined by capillary electrophoresis (CE) at an alkaline pH, so the analytes will be fully ionized. However, a long-chain quaternary ammonium salt usually must be added as a flow modifier to the carrier electrolyte to reverse the direction of the electroosmotic flow. By working at a sufficiently acidic pH, the electroosmotic flow in fused-silica capillaries is virtually eliminated, and anions can be separated simply by differences in their electrophoretic mobilities. Excellent separations were obtained for AuCl₄⁻ and the chloro complexes of platinum group elements in HCl solution at pH 2.0 to 2.4. No additional buffer or flow modifier was needed. This CE technique is an excellent way to follow slow hydrolytic reactions in which one or more of the chloride ligands is replaced by water. Sharp peaks and good separations were also obtained for MnO₄⁻, VO₃⁻, chromate, molybdate, ferrocyanide, ferricyanide and stable complex ions such as chromium oxalate (CrO₃³⁻).     

Speciation of inorganic and methylated arsenic compounds by capillary zone electrophoresis with indirect UV detection. Application to the analysis of alkali extracts of As2S2 (realgar) and As2S3 (orpiment)

A capillary zone electrophoresis (CZE) method with indirect UV detection was developed to simultaneously separate inorganic and organic arsenic compounds including arsenite (iAsIII), arsenate (iAsV), monomethylarsonate and dimethylarsenic acid (DMAV). 2,6-Pyridinedicarboxylic acid (PDC) and n-hexadecyltrimethylammonium hydroxide (CTAOH) were selected to compose a background electrolyte (BGE), where PDC was used as chromophore and CTAOH functioned as electroosmotic flow (EOF) modifier to reduce/eliminate EOF. The choice of detection wavelength, the optimization of BGE pH, and effects of applied electric field strength and temperature on separation were further investigated. The limits of detection for the targeted analytes were between 0.19 and 0.23 ppm as molecule. Good linearity of more than three orders of magnitude was obtained. Repeatability of migration times and peaks areas were 0.8-1.7 and 3.4-6.9% R.S.D.; whereas reproducibility were 1.2-2.2 and 3.6-7.1% R.S.D., respectively. The established CZE method was then applied to analyze the alkali extracts of realgar (As2S2) and orpiment (As2S3). The main components in both alkali extracts were identified to be iAsIII and iAsV.     

A novel method for analysis of explosives residue by simultaneous detection of anions and cations via capillary zone electrophoresis

A novel electrolyte has been developed for the simultaneous separation of cations and anions in low explosive residue by capillary electrophoresis. This electrolyte contains 15 mM α-hydroxyisobutyric acid (HIBA) as the buffer, 6 mM imidazole as the cation chromophore, 3 mM 1,3,6-naphthalenetrisulfonic acid (NTS) as the anion chromophore, 4 mM 18-crown-6 ether as a cation selectivity modifier, and 5% (v/v) acetonitrile as an organic modifier. The pH was adjusted to 6.5 using tetramethylammonium hydroxide (TMAOH), an electroosmotic flow modifier. The method was optimized by varying the concentrations of α-HIBA, imidazole, and 1,3,6-NTS at three different pH values. The results provided a simultaneous indirect photometric analysis of both anions and cations with detection limits ranging from 0.5 to 5 ppm for anions and from 10 to 15 ppm for cations with a total run time of under 7 min. The method was then applied to the analysis of Pyrodex^® RS and black powder, as well as several smokeless powders. The results obtained were consistent with previously reported results for separate anion and cation analysis and provide a faster, more complete analysis of each sample in a single chromatographic run.     

Sulfur speciation by capillary zone electrophoresis: conditions for sulfite stabilization and determination in the presence of sulfate, thiosulfate and peroxodisulfate

Capillary zone electrophoresis (CZE) was used for the separation of the sulfur species SO3(2-), SO4(2-), S2O(3-) and S2O8(2-). Using an electrolyte system with 9.5 mmol L(-1) potassium chromate as UV-absorbing probe and 1 mmol L(-1) diethylenetriamine (DETA) as electroosmotic flow modifier, various possibilities for the stabilization of sulfite and electrophoretic separation of the sulfur anions were investigated. By adding 5% propanol as a stabilizer to both the working electrolyte and the sample solution, a good stabilization for sulfite and a separation of the sulfur anions in a short analysis time (4 min) was achieved. The advantages by using propanol instead of other stabilizers often used in analytical techniques are discussed. The electrophoretic separation of the sulfur anions was optimized with respect to the pH of the working electrolyte and concentration of the electroosmotic flow modifier (DETA). The detection limits achieved for SO3(2-), SO4(2-), S2O3(2-) and S2O8(2-) were 0.35, 0.25, 0.78 and 0.80 mg L(-1), respectively.     

用聚丙烯酰胺交联涂层毛细管电泳柱分离无机阴离子

研究了用涂层柱分离Ｉ＾－，ＮＯ＾－２，ＮＯ＾－３，ＳＣＮ＾－，ＭｏＯ＾２－４等５种具有紫外吸收的阴离了的毛细管电泳方法。采用涂层柱可以有效地抑制电渗流，因此无需在载体电解质溶液中加入电流改性剂。其优越性在于改善了由于电渗流改性剂与体积较大的阴离子发生离子对相互作用所导致的峰形拖尾现象，有助于准确定理。     

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%.     

Dual-opposite injection electrokinetic chromatography for the unbiased, simultaneous separation of cationic and anionic compounds

The concept of dual opposite injection in capillary electrophoresis (DOI-CE) for the simultaneous separation, under conditions of suppressed electroosmotic flow, of anionic and cationic compounds with no bias in resolution and analysis time, is extended to a higher pH range in a zone electrophoresis mode (DOI-CZE). A new DOI-CE separation mode based on electrokinetic chromatography is also introduced (DOI-EKC). Whereas conventional CZE and DOI-CZE are limited to the separation of charged compounds with different electrophoretic mobilities, DOI-EKC is shown to be capable of separating compounds with the same or similar electrophoretic mobilities. In contrast to conventional EKC with charged pseudostationary phases that often interact too strongly with analytes of opposite charge, the neutral pseudostationary phases appropriate for DOI-EKC are simultaneously compatible with anionic and cationic compounds. This work describes two buffer additives that dynamically suppress electroosmotic flow (EOF) at a higher pH (6.5) than in a previous study (4.4), thus allowing DOI-CZE of several pharmaceutical bases and weakly acidic positional isomers. Several DOI-EKC systems based on nonionic (10 lauryl ether, Brij 35) or zwitterionic (SB-12, CAS U) micelles, or nonionic vesicles (Brij 30) are examined using a six-component test mixture that is difficult to separate by CZE or DOI-CZE. The effect of electromigration dispersion on peak shape and efficiency, and the effect of surfactant concentration on retention, selectivity, and efficiency are described.     

聚合离子液体用作毛细管电泳背景电解质添加剂快速高效分离5种核苷类化合物

将聚乙烯基-3-乙基咪唑溴盐离子液体用作毛细管电泳背景电解质添加剂,利用聚合离子液体的阳离子聚合物性质静电吸附到毛细管内表面,成功实现电渗流的有效反转,建立了共电渗流模式下5种核苷类化合物分离的新方法。考察了聚合离子液体浓度、pH值等因素对电渗流的影响。在优化实验条件下,3.1 min内实现了对5种核苷类化合物的快速高效分离;将该方法分别与不加添加剂和加入离子液体单体后的体系进行对比,结果表明,该方法大大缩短了5种核苷类化合物的分析时间,提高了分析效率,最高柱效达95万/m塔板数,分析物的迁移时间RSD均不高于0.38%。该方法简单、快速、重复性好,具有很好的应用前景。     

Ion association with alkylammonium cations for separation of anions by capillary electrophoresis

A background electrolyte (BGE) containing a 100 mM concentration of an alkylammonium cation with ethyl, propyl or butyl groups provides an excellent medium for separation of anions by capillary electrophoresis (CE). Two major effects were noted. Use of one of a series of alkylammonium cations in the BGE at a selected pH provides a simple and effective way to vary and control electroosmotic flow (EOF) over a broad range. It is believed that the alkylammonium cations are coated onto the capillary surface through a reversible dynamic equilibrium. Secondly, alkylammonium cations modify the electrophoretic migration of sample anions and the electroosmotic migration of neutral organic analytes by association interaction. This selective interaction results in improved anion separations and permits the simultaneous separation of neutral analytes. The degree of association interaction varies with the bulk and hydrophobicity of the alkylammonium cations. Incorporation of an aliphatic amine salt of moderate molecular weight in the running electrolyte provides a valuable new way to vary the migration times of sample anions and to optimize their resolution. The interactions between alkylammonium cations and sample anions or neutral organics appear to take place entirely within the liquid phase and do not require a polymeric or micellar pseudo phase.