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

Quantification of Ions in Human Urine-A Review for Clinical Laboratories

Urine is an organic fluid produced by the kidney, and its analysis is one of the most requested laboratory tests by clinicians. The ionic composition of urine has been shown to be a good health indicator: it is useful for the diagnosis of several diseases, as well as monitoring therapeutics. This review considers laboratorial techniques that have been used throughout time for the quantification of ions in urine, and also considers some methodologies that can potentially be used in clinical laboratories for this kind of analysis. Those methods include gravimetry, titration, flame emission spectrophotometry (flame photometry), fluorimetry, potentiometry (ion selective electrodes), ion chromatography, electrophoresis, kinetic colorimetric tests, enzymatic colorimetric tests, flow cytometry, atomic absorption, plasma atomic emission spectrometry, and paper-based devices. Sodium, potassium, chloride, calcium, and magnesium are among the most important physiological ions, and their determination is frequently requested in hospitals. There have been many advances regarding the analysis of these ions in 24 h urine. However, there is still some way to go concerning the importance of intracellular ions in this type of sample as well as the use of occasional urine for monitoring these parameters.

Capillary electrophoresis for the investigation of two novel aminoalkanol derivatives of 1,7-diethyl-8,9-diphenyl-4-azatricyclo[5.2.1.02,6] dec-8-ene-3,5,10-trione as potential anticancer drugs in water solution and serum

A simple, rapid, capillary zone electrophoresis method was developed and validated for the analysis of two novel aminoalkanol derivatives (I) and (II) of 1,7-diethyl-8,9-diphenyl-4-azatricyclo[5.2.1.0^2,6 ]dec-8-ene-3,5,10-trione, which were found in earlier studies as potential anticancer drugs. Samples were analyzed to demonstrate the specificity and stability indicating ability of the developed method. The samples were extracted using n-hexane-ethyl acetate mixture in the ratio of 90:10. Electrophoretic separation was performed on a eCAP fused silica capillary (37 cm length, 50 µm inside diameter) with a 50 mM tetraborate buffer as a background electrolyte adjusted to pH = 2.5. The separation time of (I) and (II) was achieved within 7 min. In addition, analysis of the two compounds in the serum was conducted. Limits of detection of (I) and (II) by UV absorbance at 200 nm were achieved in the range of 87.4-92.1 ng/mL. The sufficient recovery was observed in the range of 90.3-99.8%. The quantification limits for the compounds (I) and (II) were in the range of 279.71-291.03 ng/mL, respectively. The method has been successfully applied to the analysis of compounds (I) and (II) in serum samples.

Analysis and characterization of aluminum chlorohydrate oligocations by capillary electrophoresis

Aluminum chlorohydrates (ACH) are the active ingredients used in most antiperspirant products. ACH is a water soluble aluminum complex which contains several oligomeric polycations of aluminum with degrees of polymerization up to Al₁₃ or Al₃₀. The characterization and quantification of ACH oligo-cations remain a challenging issue of primary interest for developing structure/antiperspirant activity correlations, and for controlling the ACH ingredients. In this work, highly repeatable capillary electrophoresis (CE) separation of A_l3⁺, Al₁₃ and Al₃₀ oligomers contained in ACH samples was obtained at pH 4.8, owing to a careful choice of the background electrolyte counter-ion and chromophore, capillary I.D. and capillary coating. This is the first reported separation of Al₁₃ and Al₃₀ oligomers in conditions that are compatible with the aluminum speciation in ACH solution or in conditions of antiperspirant application/formulation. Al₁₃ and Al₃₀ effective charge numbers were also determined from the sensitivity of detection in indirect UV detection mode. The relative mass proportion of Al₁₃ compared to Al₁₃+Al₃₀ could be determined in different aluminum chlorohydrate samples. Due to its simplicity, repeatability/reproducibility, minimal sample preparation and mild analytical conditions, CE appears to be a promising analytical separation technique for the characterization of ACH materials and for the study of structure/antiperspirant activity correlations.

Determination of Inorganic Ion Profiles of Illicit Drugs by Capillary Electrophoresis

A portable capillary electrophoresis instrument with dual capacitively coupled contactless conductivity detection (C⁴ D) was used to determine the inorganic ionic profiles of three pharmaceutical samples and precursors of two illicit drugs (contemporary samples of methylone and para-methoxymethamphetamine). The LODs ranged from 0.10 μmol/L to 1.25 μmol/L for the 10 selected cations, and from 0.13 μmol/L to 1.03 μmol/L for the eight selected anions. All separations were performed in less than 6 min with migration times and peak area RSD values ranging from 2 to 7%. The results demonstrate the potential of the analysis of inorganic ionic species to aid in the identification and/or differentiation of unknown tablets, and real samples found in illicit drug manufacture scenarios. From the resulting ionic fingerprint, the unknown tablets and samples can be further classified.

Analysis of Small Ions with Capillary Electrophoresis

Small inorganic ions are easily separated through capillary electrophoresis because they have a high charge-to-mass ratio and suffer little from some of the undesired phenomenon affecting higher molecular weight species like adsorption to the capillary wall, decomposition, and precipitation. This chapter is focused on the analysis of small ions other than metal ions using capillary electrophoresis. Methods are described for the determination of ions of nitrogen, phosphorus, sulfur, fluorine, chlorine, bromine, and iodine.

Determination of potassium, sodium, calcium and magnesium in total parenteral nutrition formulations by capillary electrophoresis with contactless conductivity detection

A simple method based on capillary electrophoresis with a capacitively coupled contactless conductivity detector (CE-C(4)D) was developed for the determination of potassium, sodium, calcium and magnesium in parenteral nutrition formulations. A hydro-organic mixture, consisting of 100 mM Tris-acetate buffer at pH 4.5 and acetonitrile (80:20, v/v), was selected as the background electrolyte. The applied voltage was 30 kV, and sample injection was performed in hydrodynamic mode. All analyses were carried out in a fused silica capillary with an internal diameter of 50 microm and a total length of 64.5 cm. Under these conditions, complete separation between all cations was achieved in less than 4 min. The CE-C(4)D method was validated, and trueness values between 98.6% and 101.8% were obtained with repeatability and intermediate precision values of 0.4-1.3% and 0.8-1.8%, respectively. Therefore, this method was found to be appropriate for controlling potassium, sodium, calcium and magnesium in parenteral nutrition formulations and successfully applied in daily quality control at the Geneva University Hospitals.

Capillary electrophoresis for pharmaceutical analysis

This chapter describes the application of capillary electrophoresis (CE) to pharmaceutical analysis. The areas of pharmaceutical analysis covered are enantiomer separation, analysis of small molecules such as amino acids or drug counter-ions, pharmaceutical assay, related substances determinations, and physiochemical measurements such as log P and pKa of compounds. The different electrophoretic modes available and their advantages for pharmaceutical analysis are described. Recent applications of CE for each subject area are tabulated with electrolyte details. Information on electrolyte choice and method optimization to obtain optimal separations is included.

Determination of organic acids by CE and CEC methods

A comprehensive overview of the analysis of low-molecular-mass organic acids employing electromigration methods in the capillary format is given. This review includes papers published since 2003 and can be seen as an update of the review paper published by Galli et al. in 2003. Tables included in this review contain application papers describing the determination of organic acids from a variety of fields like the analysis of food and beverages, environmental samples, samples from clinical origin, and from natural products.

Potential of CE for the determination of inorganic and acidic anions in cyanoacrylate adhesives

In this work, a CZE method with indirect UV detection was developed for the simultaneous determination of the inorganic and acidic anions, chloride, sulfate, nitrate, fluoride, formate, phosphate, diethylphosphate, methyl sulfonate, cyanoacetate, and methacrylate present in cyanoacrylate adhesives. Chromate was employed as the probe ion, and the EOF was reversed by incorporating CTAB into BGE. Detection limits of 0.7-4.6 microg/mL were obtained for all the anions studied. The CE method developed is a significant improvement on traditionally used chromatographic methods such as ion chromatography, as it resulted in shorter analysis times with enhanced separation efficiencies. This method was successfully employed for the analysis of inorganic and acidic anions in cyanoacrylate adhesive samples.

Highly efficient protein separations in capillary electrophoresis using a supported bilayer/diblock copolymer coating

A surfactant/polymer wall coating consisting of the doubly chained cationic surfactant dimethyldioctadecylammonium bromide (DODAB) and polyoxyethylene (POE) 40 stearate is investigated. The coating is formed by simply rinsing a capillary with a solution containing DODAB and POE 40 stearate. The resultant coating is semi-permanent--demonstrating stable electroosmotic flow (EOF) even after a 60 min high pressure rinse with buffer. The EOF (-0.45+/-(0.23) x 10(-4) cm(2) V(-1) s(-1) at pH 7.4) is suppressed by more than a factor of ten compared to that observed for DODAB alone. Model protein mixtures were separated over a pH range of 3-10 with efficiencies of up to greater than 1 million plates/m for the basic proteins cytochrome c, lysozyme, ribonuclease A and alpha-lactalbumin, and the acidic proteins insulin chain A, trypsin inhibitor, and alpha-chymotrypsinogen A. Migration time reproducibility was 0.5-4.0% from run to run and 0.6-4.3% from day to day. Protein recoveries with this coating ranged from 84% to 97%.

General theory of indirect detection in chromatography

Indirect detection is used in liquid chromatography to detect sample components that more or less lack detectable properties. A detectable component, the probe, is added to the mobile phase and the sample containing the components is injected. Every solute, even those not normally detectable, will give rise to detectable peaks due to the presence of the probe. The theory currently used to describe this situation is different for different adsorption isotherm models and also restrictions have to be imposed on the adsorption isotherm parameters. We present a general theory that describes both the retention times and areas of the detected peaks without making any a priori adsorption isotherm assumptions. Our general theory is compared with the current theory and validated by computer simulations. An alternative quantification method is suggested based on the measurement of the relative areas of the sample components without the requirement of having standard curves of known solutions of the sample components. Using this approach, the new theory is able to predict the solute concentrations in cases when the current theory did not, i.e., when the saturation capacities of the sample components and the probe differed from each other. In addition, a new application is proposed: the estimation of adsorption isotherm parameters.

Capillary electrophoresis for the analysis of small-molecule pharmaceuticals

This paper reviews the application of CE to the analysis of small-molecule pharmaceuticals. The areas of pharmaceutical analysis covered are enantiomer separation, the analysis of small molecules such as amino acids or drug counter-ions, pharmaceutical assay, determination of related substances and physicochemical measurements such as log P and pK(a) of compounds. The different electrophoretic modes available and their advantages for pharmaceutical analysis are described. Recent applications of CE for each subject area are tabulated with electrolyte details.

Secondary isotope effects in liquid chromatography behaviour of 2H and 3H labelled solutes and solvents

The separation of solutes that differ only in the extent of isotopic substitution of their hydrogen atoms, using either mixtures of isotopically non-modified or perdeuterated solvents as mobile phases, is described. The occurrence of a secondary isotope effect is demonstrated in reversed-phase liquid chromatography, which is independent of the nature of the stationary phase (different octadecyl-bonded silicas, an embedded alkylamide-bonded silica, as well as one polymeric stationary phase were tested), and the water content and the nature of organic modifier of the mobile phase. The separation of 24 structurally different isotopologue pairs (apolar compounds and polar compounds with exchangeable or non-exchangeable hydrogen atoms) is examined using reversed-phase liquid chromatography. It is found that the greater the number of isotopically substituted hydrogen atoms in a given organic solute, the better is the separation of a particular isotopologue pair. The single secondary isotope effect is shown to be dependent on the number of isotopic substitutions. The greater the number of these substitutions, the smaller is the single isotope effect. The single secondary isotope effect is higher for aromatic hydrocarbons than for aliphatic hydrocarbons. A secondary isotope effect is also observed in chiral chromatography and normal-phase liquid chromatography, as well as on changing the nature of the substituting isotope, i.e.: tritium instead of deuterium. Thus, we have demonstrated that the total secondary isotopic effect for hydrogen/tritium is higher than for hydrogen/deuterium. This isotope effect involves only the consequences of changes in interactions due to nuclear motions. Overall this study confirms the predominance of hydrophobic effects in retention processes in reversed-phase liquid chromatography. In reversed-phase liquid chromatography, a secondary isotope effect related to mobile phase composition is also observed. The behaviour of deuterium oxide and water in mobile phases of the same composition (%, w/w) is compared. Independent of the nature of the organic modifier (methanol, acetonitrile or ethanol), the effect of replacing H2O with 2H2O in the mobile phase, is an increase in the retention factors and an improvement in the chromatographic resolution of isotopologue pairs. This increase in the resolution is not accompanied by a change in the chromatographic selectivity. The measurement of liquid-liquid extraction coefficients proves that the effect is mainly due to the modification of the phase ratio. In general the effect of 2H-labelled solvents (2H2O and C2H3CN) as mobile phase components, compared to their isotopically non-modified isomers, can be rationalized on the basis of their lower polarisabilities. Overall the use of perdeuterated rather than isotopically non-modified solvents as mobile phase components leads to the most efficient separation systems.

Capillary electrophoresis screening of poisonous anions extracted from biological samples

A method was developed for screening human biological samples for poisonous anions using capillary electrophoresis (CE) employing indirect UV detection. The run buffer consisted of 2.25 mM pyromellitic acid, 1.6 mM triethanolamine, 0.75 mM hexamethonium hydroxide and 6.5mM NaOH at pH 7.7. Biological samples were pretreated using solid phase extraction. The method was applied to the analysis of human blood, plasma, urine, and intestinal contents. Twenty-nine different anions were detectable at aqueous concentrations of 1 part per million (ppm) with a typical analysis time less than 20 min. Intraday migration time R.S.D. and peak area R.S.D. for blood samples were less than 1.1% and 6.3%, respectively. Interday migration time R.S.D. for plasma samples ranged from 7.5% to 10.4%. The new method produced efficient separations of various target anions extracted from complex biological matrices.

Analysis of anions in ambient aerosols by microchip capillary electrophoresis

We describe a microchip capillary electrophoresis method for the analysis of nitrate and sulfate in ambient aerosols. Investigating the chemical composition of ambient aerosol particles is essential for understanding their sources and effects. Significant progress has been made towards developing mass spectrometry-based instrumentation for rapid qualitative analysis of aerosols. Alternative methods for rapid quantification of selected high abundance compounds are needed to augment the capacity for widespread routine analysis. Such methods could provide much higher temporal and spatial resolution than can be achieved currently. Inorganic anions comprise a large percentage of particulate mass, with nitrate and sulfate among the most abundant species. While ion chromatography has proven very useful for analyzing extracts of time-integrated ambient aerosol samples collected on filters and for semi-continuous, on-line particle composition measurements, there is a growing need for development of new compact, inexpensive approaches to routine on-line aerosol ion analysis for deployment in spatially dense, atmospheric measurement networks. Microchip capillary electrophoresis provides the necessary speed and portability to address this need. In this report, on-column contact conductivity detection is used with hydrodynamic injection to create a simple microchip instrument for analysis of nitrate and sulfate. On-column contact conductivity detection was achieved using a Pd decoupler placed upstream from the working electrodes. Microchips containing two Au or Pd working electrodes showed a good linear range (5-500 microM) and low limits-of-detection for sulfate and nitrate, with Au providing the lowest detection limits (1 microM) for both ions. The completed microchip system was used to analyze ambient aerosol filter samples. Nitrate and sulfate concentrations measured by the microchip matched the concentrations measured by ion chromatography.

A sulfonated capillary that gives reproducible migration times for capillary zone electrophoresis and micellar electrokinetic chromatography

To obtain reproducible migration times and rapid analyses of analytes, sulfonate groups were chemically introduced to the inner wall of untreated fused-silica capillary with 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane. The sulfonated capillary showed relatively constant electroosmotic mobility which was greater than that obtained by an untreated fused-silica capillary over the pH range studied (pH 2-9). In both CZE and MEKC, the RSDs of the migration times of analytes with the sulfonated capillary were less than 0.2% which were significantly lower than those obtained with an untreated fused-silica capillary (0.5-3.5%). When BGE were set at pH 7.0 for CZE and MEKC, the analysis times with the sulfonated capillary were about half those obtained with an untreated fused-silica capillary. These results indicate that the sulfonated capillary can provide highly reproducible and rapid analyses in CE.

Ion chromatographic method development for monitoring of seawater quality used in over-the-counter pharmaceutical industry

A methodology is developed for the analysis of inorganic anions (fluoride, chloride, bromide, sulphate) in seawater used for over-the-counter (OTC) nasal spray production. The eluent flow rate and concentration of eluent competing ions are optimised by using an artificial neural network resolution model in combination with normalised resolution product criterion function. The developed artificial neural network resolution model shows good predictive ability R2 > or = 0.9973. The determined ion chromatographic parameters enable baseline separation of all components of interest. By performing a validation procedure and a number of statistical tests, it is shown that the developed ion chromatographic method has superior performance characteristics: linearity R2 > or = 0.9993, recovery = 99.77-100.65%, repeatability RSD < or = 1.85%. This result proves that the proposed method can be used for routine quality assurance analysis in OTC pharmaceutical industry.

Utilisation of crown ethers in microemulsion electrokinetic chromatography for the separation of inorganic cations

A new method to influence the separation selectivity of inorganic cations in capillary electrophoresis is presented. This method combines the use of certain crown ethers to form complexes with a specific cation (changing its ionic radius/charge ratio and thereby its electrophoretic mobility) with partitioning of the crown ether/analyte complex between an aqueous phase and a pseudo-stationary phase, such as the oil droplet of a microemulsion. Several microemulsions, including uncharged oil droplets and oil droplets with different degrees of surface charge were tested to evaluate their ability to improve the separation of the selected analytes.

Separation of purine and pyrimidine bases by capillary electrophoresis using β-cyclodextrin as an additive

Capillary electrophoresis was applied to separate purine and pyrimidine bases in the basis of their partial ionization in the alkaline buffer. The effects of buffer pH, buffer and beta-cylclodextrin concentration were systematically investigated using a commercial capillary electrophoresis instrument with UV detector at 254nm. We found that the resolutions of bases (especially for adenine and thymine) were significantly improved in the presence of beta-cylclodextrin. The satisfactory separation of five bases such as cytosine, thymine, adenine, guanine and uracil were achieved by capillary electrophoresis using beta-cylclodextrin as an additive. Under the optimal conditions, the linear range was from 2 to 200microg/ml for bases (R= 0,991-0,9977 ) and the detection limits were from 0.8 to 1.8microg/ml (S/N = 2). The detection limit of 0.05microg/ml ( S/N=2 ) for uracil was obtained by stacking injection mode. The assay was used to determine the deamination of cytosine to uracil by heating in the presence of sodium hydroxide. Our primarily results show that capillary electrophoresis is a very useful tool for determination of purine and pyrimidine bases and study on nucleic acids.

Quantitative capillary zone electrophoresis of inorganic anions

Despite the availability of commercial capillary electrophoresis systems for over ten years, where quantitative analysis is required, capillary zone electrophoresis (CZE) has often failed to replace ion chromatography as the method of choice for a large number of analytes, not least inorganic anions. To investigate the reasons for this apparent failing, a review is presented of work that has been carried out to-date involving the quantitative application of CZE to the determination of inorganic anions in industrial and environmental samples. This review summarizes work both investigating and improving the quantitative aspects of the CZE of inorganic anions. A complete survey of how CZE has been applied to the determination of inorganic anions in real samples is given, including what, if any, analytical performance parameters were investigated and quoted, and if quality assurance data and validation methods were briefly considered, thoroughly investigated or simply ignored.

Derivatization of inorganic ions in capillary electrophoresis

This review gives a short overview of the main approaches to the derivatization of inorganic ions in capillary electrophoresis (CE) with emphasis on the most recent works. Various derivatization procedures and detection methods are discussed. A brief account of their advantages and limitations is given. More specific areas such as microchip CE, simultaneous separation of anions and cations, and speciation analysis are also briefly discussed.

Analytical separations of lanthanides and actinides by capillary electrophoresis

The separation of lanthanide and actinide elements belongs to one of the most challenging tasks of the separation science, due to a great similarity in their physical and chemical properties. The electrophoretic separation can be accomplished in the presence of suitable complex-forming agents, from which alpha-hydroxyisobutyric acid (HIBA) has been used most often. In the most effective capillary electrophoretic mode--capillary zone electrophoresis (CZE)--a complete separation of lanthanide ions can be accomplished within a few minutes. Various electrophoretic methods can be relatively easily adopted for the determinations of individual lanthanide elements in certain kinds of technical materials, concentrates, precursors, etc., where the high speed and low costs of analysis characteristics of capillary electrophoresis (CE) may be advantageously exploited. Electrophoretic techniques may also be employed for speciation studies, especially for examinations of the behavior of actinides in the environment.

The importance of capillary electrophoresis, capillary electrochromatography, and ion chromatography in separations of inorganic ions

The importance of capillary electrophoresis (CE), capillary electrochromatography (CEC), and ion chromatography (IC) in inorganic ion analyses is outlined. Methods for improving the reliability of the CE measurements are briefly described. Selectivity optimization in CE analyses of inorganic cations and anions is discussed. Using the Peakmaster program, CE system peaks (system zones, eigenmobilites) and some important CE parameters, such as effective mobilities, electromigration dispersion, indirect UV, and direct conductivity signals, are predicted and compared with experimental analyses.

Enhancement of detection sensitivity for indirect photometric detection of anions and cations in capillary electrophoresis

This review focuses on the indirect photometric detection of anions and cations by capillary electrophoresis. Special emphasis has been placed on the sensitivity of the technique and approaches taken to enhance detection limits. Theoretical considerations and requirements have been discussed, including buffering, detection sensitivity, separation of cations, and detector linearity. A series of tables detailing highly absorbing probes and the conditions of their use for indirect photometric detection are included.

Simultaneous analysis of metabisulfite and sulfate by CE with indirect UV detection. Application to and validation for a pharmaceutical formulation

Metabisulfite is used as an antioxidant agent in a number of pharmaceutical formulations. In order to quantify simultaneously both metabisulfite and its oxidation product (sulfate), a capillary zone electrophoretic (CZE) method with indirect UV detection was developed. Best results were achieved with a background electrolyte (BGE) constituted of 15 mM pyromellitic acid, 15 mM tris-(hydroxymethyl)-aminomethane and 0.2 mM tetradecyltrimethylammonium bromide at pH 8.3 and an applied electrical field of 123 V/cm in a 32.5 cm fused silica capillary. Indirect UV detection was performed at a wavelength of 225 nm. In order to validate this method, an internal standard (IS), namely ammonium formate, was used. Moreover, due to the high chloride concentration in the pharmaceutical formulation, conductivity was adjusted by adding sodium chloride into standard solutions to prevent matrix effect. Linearity and accuracy were successfully tested in a concentration range of 33.3-250 microg/ml for sodium metabisulfite and of 50-375 microg/ml for sodium sulfate. Method precision was determined on six samples each day. Thereby, relative standard deviations (R.S.D.) of 6% and 12-13% were obtained for intra-day and inter-day precision, respectively. Considering the instability of metabisulfite and its use as an antioxidant agent and not as an active principle, the method was accepted and used for routine analyses.