Determination of inorganic anions in Kraft pulping liquors by capillary electrophoresis

Various sulfur containing anions (sulfate, sulfite, and thiosulfate) in Kraft pulping process liquors are determined by capillary electrophoresis. In addition, other inorganic anions (hydroxide, chloride, oxalate, carbonate) are analyzed with the developed method. Through optimization of the separation conditions it is possible to simultaneously determine these anionic species in pulping liquors with direct and indirect UV detection at 185, 214, and 254 nm. To ensure short separation times a migration of the anionic analytes in the same direction as the electroosmotic flow (co-electroosmotic CE) is established by reversal of the electroosmotic flow with 1,5-dimethyl-1,5-diazaundecamethylene polymethobromide (hexadimethrine bromide; HDB; polybrene™) which is added to the electrolyte as EOF modifier. The impact of acetonitrile as organic modifier to improve the selectivity of the anionic analytes is also investigated. The developed method is then applied to analyze and quantify various anions in pulping liquors (white and black liquors). By simultaneously determining the hydroxide concentration it is possible to calculate effective alkalinity and sulfidity with the measured concentrations without the need of volumetric methods.     

Determination of Low-Molecular-Mass Phenolic and Non-Phenolic Lignin Degradation Compounds in Wood Digestion Solutions by Capillary Electrophoresis

 Different capillary electrophoretic techniques were investigated and compared for the separation of low-molecular-mass phenolic and neutral lignin degradation compounds. Simple capillary zone electrophoresis (CZE) was not suited for this problem. Switching to micellar electrokinetic capillary chromatography (MEKC) by adding micelle-forming reagents to the carrier electrolyte enhanced the separation performance considerably. Alternatively, microemulsion electrokinetic chromatography (MEEKC) was investigated. This is a CE technique in which analytes interact with moving oil droplets present in a microemulsion buffer. Using the optimized carrier electrolyte systems and a 60 cm×50 μm I.D. bubble cell capillary it was possible to analyse solutions of different wood digestion procedures and to investigate differences in lignin degradation products during use of different kinds of wood (eucalyptus, beech, scotch pine and acacia). Received August 25, 1999. Revision April 13, 2000     

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     

Analysis of lignin degradation products by capillary electrophoresis

Summary A method for the quantitative analysis of phenolic lignin degradation products by capillary electrophoresis (CE) with on-column UV detection has been developed. The liquid biomass solutions contain low molecular hemicellulosic sugars and phenolic lignin degradation products with various degrees of polymerization. Special attention has been paid to the monomeric phenolic components of lignin degradation fragments, e.g. derivatives of phenolic acids, aldehydes, and alcohols. Uncoated fused silica capillaries and borate-phosphate buffer systems at moderate pH conditions were used in order to separate the compounds of interest. To provide validation of the method, the same samples were analyzed independently by HPLC using gradient elution on a RP-C18 column. As sugar degradation fragment, furan-2-carboxylic acid was detected.     

Capillary electrophoretic determination of thiosulfate,sulfide and sulfite using in-capillary derivatization with iodine

A new capillary electrophoresis (CE) method was developed for the rapid, simple and selective determination of thiosulfate, sulfide and sulfite species. The proposed method is based on the in-capillary derivatization of separated sulfur anions by mixing their zones with the iodine zone during the electrophoretic migration and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying electrolyte pH, electrolyte counter-ion, concentration of iodine, and applied voltage. The optimized separations were carried out in 20 mmol/L Tris-chloride electrolyte (pH 8.5) using direct UV detection at 214 nm. All three sulfur species were well resolved in less than 4 min. The method gives repeatability comparable or even better than this obtained for sulfur anions using standard CE technique. The proposed CE system was applied to the monitoring of sulfur anions in spent fixing solutions during the electrolytic oxidation.     

Study of the selectivity of inorganic anions in hydro-organic solvents using indirect capillary electrophoresis

In capillary electrophoresis (CE) analysis of small inorganic anions, the ability to control the electroosmotic flow (EOF) and the ability to alter the electrophoretic mobility of the ions are essential to improve resolution and separation speed. In this work, a CE method for separation of small inorganic anions using indirect detection in mixed methanol/water buffers is presented. The suitability of different UV absorbing probes commonly used for indirect detection including chromate, iodide, phthalate, benzoate, trimellitate, and pyromellitate, in mixed methanol/water buffers is examined. The effect of the electrolyte buffer system, including the pH, buffer concentration and the organic solvent on the electrophoretic mobility of the probes and analytes are also investigated. The EOF was reversed using cationic surfactant, cetyltrimethylammonium bromide (CTAB) so ions were separated under co-EOF mode. The organic solvent alters the electrophoretic mobility of the probes and the analytes differently and hence choice of the appropriate probe is essential to achieve high degree of detection sensitivity. Separations of six anions in less than 2.5 min were accomplished in buffers containing up to 30% MeOH. Adjustment of the methanol content helps to improve the selectivity and resolution of inorganic anions. Limit of detection, reproducibility and application of the method for quantification of anions in water samples will also be discussed.     

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.     

Separation and determination of 10-hydroxy-2-decenoic acid in royal jelly by capillary electrophoresis

Summary The application of capillary electrophoresis (CE) to the separation and determination of the active ingredient, 10-hydroxy-2-decenoic acid, in royal jelly with direct on-column UV detection at 214 nm is described. Using a cathodic injection and anodic detection scheme, 10-hydroxy-2-decenoic acid (10-HDA) was separated and detected in less than 10 min in a fused silica capillary column with a phosphate buffer at pH 7.3 with an applied voltage of 20 KV followed by direct UV detection. The use of cetyltrimethylammonium bromide (CTAB) as electroosmotic flow modifier allows the rapid separation of 10-HDA from other constituents in royal jelly by reversing the direction of electroosmotic flow. The influence of organic solvents in the electrolyte on separation selectivity is also discussed.     

Separation of anions by ion chromatography-capillary electrophoresis

Capillary electrophoresis (CE) with a water-soluble ion-exchange polymer in the background electrolyte is very efficient for the separation of organic and inorganic anions because the ion-exchange selectivity, as well as differences in electrophoretic mobility, can be used for separating sample ions. Poly(diallyldimethylammonium chloride) (PDDAC) was employed for this purpose. A very stable electroosmotic flow was obtained between pH 2.3 and 8.5 due to the strong adsorption of PDDAC onto the capillary wall. The effect of ion exchange on the migration of sample anions and their separation was controlled by varying the concentration of PDDAC, the concentration and the type of salt used in the CE background electrolyte. Addition of organic solvent (e.g., acetonitrile) could also modify the sample migration and the separation. Baseline separations were obtained for anions with very similar mobilities, such as bromide and iodide, naphthalenesulfonates, and bi- and tricarboxylic acids. Typical separation efficiencies were between 195,000 and 429,000 theoretical plates per meter. Ten replicate separations gave an average RSD of 1.0% for migration times of the sample anions studied. Excellent separations were obtained for a variety of samples, including a separation of 17 inorganic and organic anions in less than 6 min.     

Capillary electrophoretic determination of lignin degradation products obtained by permanganate oxidation

A new capillary electrophoretic (CE) technique was developed for the separation of lignin degradation products after permanganate oxidation, yielding information about quality and quantity of various linkages in the lignin molecule. This CE method is a promising alternative to existing gas chromatographic (GC) methods. An advantage in comparison with GC is the short separation time and the fact that the oxidation products (aromatic acids) can be analyzed without derivatization. The selectivity and sensitivity of CE combined with UV detection is adequate and makes it suited for fast routine characterization of lignins. If necessary, the CE method can be coupled with electrospray ionization mass spectrometry in order to make a clear assignment of the peaks.     

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.     

卤代乙酸及其结构相近化合物的高效毛细管电泳分离

氟、氯、溴等卤代乙酸是结构非常相近的离子型化合物,对它们的分离测定比较困难。用高效毛细管电泳法在碱性或酸性缓冲液条件下可将它们分离。在酸性缓冲液条件下,可提高有机酸分离的选择性。较低的操作电压有利于提高阴离子的分离度,而改变温度对分离度的影响不大。     

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.     

Determination of organic acids in air by capillary electrophoresis and ion-exclusion chromatography

Summary A capillary electrophoretic (CE) method for the determination of organic acids in the low ppm range is described. The buffer consisted of 5 mM 2,6-pyridinedicarboxylic acid and 0.5 mM cetyltrimethylammonium bromide, pH 5.6. The former served as background electrolyte for indirect UV detection at 200 nm, whereas the latter was used to reverse electroosmotic flow. In <5 min 8 low molecular mass organic acids (oxalic, formic, malonic, glutaric, glycolic, acetic, lactic and propanoic) and two inorganic acids (hydrochloric and sulphuric) were separated. Detection limits for anions tested were 0.04 mg L⁻¹ (lactic acid) to 0.6 mg L⁻¹ (malonic acid). The method was applied to the determination of organic acids in air samples. The CE results when compared with ion-exclusion chromatography (IEC) agreed well. The use of electrokinetic injection in CE proved beneficial for preconcentration of organic acids in real samples. Using electrokinetic injection, preconcentration factors ranging from 14 (hydrochloric acid) to 3 (propanoic acid) were obtained. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

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.     

Nonionic surfactant enhanced semipermanent coatings for capillary electrophoresis of inorganic anions without use of organic additives

Separation of inorganic anions by capillary electrophoresis (CE) is usually conducted in co-electroosmotic mode due to the large electrophoretic mobilities of inorganic anions. Semipermanent surfactant coatings have been shown to be effective for CE of inorganic anions due to their strong capability of electroosmotic flow (EOF) manipulation. However, semipermanent coatings often suffer from their unsatisfactory stability. In addition, organic solvent additives are usually required to adjust the selectivity, which also aggravate the degradation of coating. In this work, a novel semipermanent coating consisting of cationic Gemini surfactant 18-10-18 and nonionic surfactant Tween 20 was developed to separate inorganic anions in CE. This coating is easy to prepare and more stable than pure Gemini coating. The introduction of nonionic surfactant in the coating not only suppresses the reversed EOF but can also adjust the selectivity of separation. Good separations of six model anions were achieved, the separation efficiency was as high as 65040-169700 plates/m and the RSDs of the migration times were less than 0.5 and 2.5% for run-to-run and day-to-day assays, respectively. Calibration curves were linear in the range of 0.05-5.0 mM; the detection limits ranged from 20 to 50 μM. More importantly, no organic solvents are required in the background buffer to achieve the satisfactory separations. This guarantees the coating stability and makes the method greener than most of other methods for CE of inorganic anions.     

Recent developments in the separation of inorganic and small organic ions by capillary electrophoresis

Which method should I use for ion analysis, ion chromatography (IC) or capillary electrophoresis (CE)? In terms of actual theoretical plates CE has a clear-cut advantage. The separation ability of IC is adequate for many sample types, and many separation scientists feel that IC offers greater reliability and confidence than CE. However, IC is a more mature technique and there has been more time to solve problems such as peak tailing and to improve reproducibility. The two techniques should be viewed as complementary. A number of recent developments in ion analysis by CE are discussed. These include some simple ways to control electroosmotic flow and improve reproducibility, separation of isotopes, improved methods of indirect photometric detection, a new contactless conductivity detector, separation of ions at low pH, and in solutions of high salt content. Progress in a new technique called IC-CE will be described in which a soluble ion-exchange polymer is added to the capillary electrolyte to separate anions based on differences in both electrophoretic mobility and ion-exchange interactions.     

Analysis of black tea theaflavins by non-aqueous capillary electrophoresis.

In this study a new capillary electrophoresis (CE) method was developed to quantify the four major theaflavins occurring in black tea. Where aqueous based CE methods showed poor selectivity and considerable band broadening, non-aqueous CE achieved baseline separation of the theaflavins within 10 min. The effects of the organic solvent composition and background electrolyte concentration on the separation selectivity and electrophoretic mobilities were investigated. Our optimized separation solution consisted of acetonitrile-methanol-acetic acid (71:25:4, v/v) and 90 mM ammonium acetate. This method was used to analyze three black tea samples.     

Separation of phenolic acids in soil and plant tissue extracts by co-electroosmotic capillary electrophoresis with direct UV detection

Summary A capillary zone electrophoretic method for the analysis of phenolic acids in soil and plant extracts was developed with direct UV detection using a phosphate electrolyte solution. The electrophoretic separation required the phenolic acids to be charged at a pH above their pKa in order to achieve their migration towards the anode. Electroosmotic flow (EOF) was reversed in direction by adding tetradecyltrimethylammonium bromide (TTAB). Factors affecting the separation selectivity, including the buffer pH and EOF modifiers, were investigated systematically. Eight phenolic acids were separated and detected in 10 min using an electrolyte containing 25 mM phosphate, 0.5 mM TTAB and 15% acetonitrile (v/v) at pH of 7.20. Linear plots for the test phenolic acids were obtained in a concentration range of 0.01–1 mM with detection limits in the range of 1.0–7.0 μM. The recoveries ranged from 92.8 to 102.3% in soil and plant tissues samples spiked at 100 μM and the relative standard deviation based on the peak area were ranged 2.0 to 4.5%. The proposed method was used for the determination of phenolic acids in plant tissue and soil extracts with direct injection.     

Polymeric ionic liquid-coated capillary for capillary electrophoresis

A new application of the polymeric ionic liquid (PIL) in capillary electrophoresis is reported. Poly(1-vinyl-3-butylimidazolium bromide) was physically adsorbed on silica capillary as the simple and effective coating for capillary electrophoresis (CE) analysis, in which the PIL is not present in the background electrolyte. The electroosmotic flow (EOF) of the PIL-coated capillary as compared with that of the bare fused-silica capillary shows a different dependence on electrolyte pH values. The EOF is reversed over a wide pH range from 3.0 to 9.0 and shows good repeatability. It is also found that the coated capillary has a good tolerance to some organic solvents, 0.1 M NaOH and 0.1 M HCl. The PIL-coated capillary has been employed in different areas. Both the basic proteins and anionic analytes can be well separated by PIL-coated capillaries in a fast and easy way. The PIL-coated capillary is also able to separate organic acid additives in a grape juice. The results showed that this type of coating provides an alternative to the CE separation of anions and basic proteins.