Rapid capillary zone electrophoresis method for the determination of metal cations in beverages

A rapid and reliable capillary zone electrophoresis method for the determination of inorganic cations was developed. The complete separation of K⁺, Ba²⁺, Ca²⁺, Na⁺, Mg²⁺, Mn²⁺, Ni²⁺, Cd²⁺, Li⁺ and Cu²⁺ can be achieved in 4 min with a simple electrolyte composed by 10 mM imidazole as the carrier buffer and background absorbance provider and acetic acid as the complexing agent (pH 3.60). Injection was performed hydrostatically by elevating the sample at 10 cm for 30 s. The running voltage was +25 kV at room temperature. Indirect UV-absorption detection was achieved at 185 nm. The detection limit was in the range between 0.06 mg/l (Mg²⁺) and 0.57 mg/l (K⁺) and the quantification limits ranged from 0.10 mg/l (Ni²⁺) to 0.80 mg/l (Cu²⁺). The calibration graphs were linear in the concentration range from the quantification limit till at least 1 g/l in K⁺, 10 mg/l in Ba²⁺, Ca²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Cd²⁺, 40 mg/l in Na⁺ and 12 mg/l in Li⁺ and Cu²⁺. The repeatability, intraday and interday analysis were ≤1.55% and ≤3.64% for migration time and ≤3.38% and ≤3.63% for peak area. The method developed has been applied to several beverage samples with only a simple dilution and filtration treatment of the sample. The proposed method is simple, fast, cheap and it is achieved with common products in either laboratory. For these reasons, it is a very useful method for routine analysis.     

毛细管区带电泳法间接测定红细胞中的主要无机阳离子

建立了间接测定红细胞中主要无机阳离子的毛细管区带电泳方法, 考察了背景溶液pH、咪唑和酒石酸浓度等对无机离子分离效果及峰面积的影响. 以10 mmol/L咪唑-4 mmol/L酒石酸(pH 5.5)为背景, 在15 kV、214 nm的条件下, 对红细胞中K 、Mg2 、Ca2 和Zn2 进行了定性、定量分析, 回收率在96%～104%之间, 迁移时间和峰面积的相对标准偏差分别低于0.76%和2.8%(日内), 0.85%和3.7%(日间). 所建方法有望成为一种测定细胞内离子含量的辅助方法.     

Separation of metal cations in acidic solution by capillary electrophoresis with direct and indirect UV detection

Methods for the detectionn of metal cations under acidic conditions, near PH 2, in capillary electrophoresis (CE) were investigatged. Conditions for direct UV detection of UV absorbing metal cations such as Cr³⁺, Cu²⁺, Fe³⁺, UO₂²⁺, VO²⁺, and VO²⁺ were established With aqueous HCl or HClO₄ as the electroyte carrier. The speciation of vanadium(IV) and vanadium(V) at PH 2.3 by CE was achieved with direct detection at 185 nm. With the strong absorbance at 185 nm, no complexation was needed to detect the metal cations. An indirect UV detrection scheme for acidic conditions was also investigated. Several background carrier electolytes (BCES) were studied including 4-methylbenzylamince, nicontinamide, pyridazine, guanidine, 3-picoline, and chromium (III) to determine their effectivencess under very acidic conditions. The efect of ioni c surfactants and the nonionic surfactant, Trition X-100, on the peak heights and N Values was also studied.     

Development of a fast capillary electrophoresis method to determine inorganic cations in biodiesel samples

The aim of this study was to develop a fast capillary electrophoresis method for the determination of inorganic cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) in biodiesel samples, using barium (Ba²⁺) as the internal standard. The running electrolyte was optimized through effective mobility curves in order to select the co-ion and Peakmaster software was used to determine electromigration dispersion and buffer capacity. The optimum background electrolyte was composed of 10 mmol L⁻¹ imidazole and 40 mmol L⁻¹ of acetic acid. Separation was conducted in a fused-silica capillary (32 cm total length and 23.5 cm effective length, 50 μm I.D.), with indirect UV detection at 214 nm. The migration time was only 36 s. In order to obtain the optimized conditions for extraction, a fractional factorial experimental design was used. The variables investigated were biodiesel mass, pH, extractant volume, agitation and sonication time. The optimum conditions were: biodiesel mass of 200 mg, extractant volume of 200 μL and agitation of 20 min. The method is characterized by good linearity in the concentration range of 0.5-20 mg kg⁻¹ (r > 0.999), limit of detection was equal to 0.3 mg kg⁻¹, inter-day precision was equal to 1.88% and recovery in the range of 88.0-120%. The developed method was successfully applied to the determination of cations in biodiesel samples.     

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.     

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.     

Simultaneous separation of inorganic anions and cations by capillary zone electrophoresis

A new capillary electrophoretic approach for simultaneous separation of fast anions and cations is demonstrated. Indirect UV detection at 214 nm in conjunction with electromigration sampling from both ends of the capillary was developed. Two electrolyte systems based on imidazole-nitrate and copper(II)-ethylenediamine-nitrate were investigated for the simultaneous separation of chloride, sulphate, hydrocarbonate, potassium, ammonium, calcium, sodium and magnesium ions. Experimental parameters that were evaluated included a nature of UV chromophore, pH of electrolyte, a nature of complexing agent. The method permits the excellent separation of three anions and five cations in only 4 min using electrolyte system containing 2.5 mmol l⁻¹ Cu(NO₃)₂, 5 mmol l⁻¹ ethylenediamine and 1 mmol l⁻¹ fumaric acid at pH 8.5 adjusted with tetraethylammonium hydroxide.     

Quantitative determination of inorganic minor cations in sodium-, calcium-, magnesium-matrix simulated samples by capillary electrophoresis

The analysis of ammonium, alkali and alkaline-earth trace cations (0.5 ppm) in samples with a calcium, sodium or magnesium matrix (500 ppm) has been achieved using 10 mM imidazole (pH 4.5) electrolyte to which a complexing agent (15-crown-5, oxalic acid or dipicolinic acid) has been specifically added in order to decrease the electrophoretic mobility of the matrix cation and thus to allow the separation of higher mobility cations at sub-ppm concentrations. The influence of several experimental parameters (complexing agent concentration, buffer pH and temperature) have been studied in order to optimize the separation. The complexing agent concentration appears to be the main parameter governing the selectivity of the cations during the analysis of matrix samples. In optimized conditions, we have checked that the separation between minor inorganic cations is not significantly altered by an increase in the matrix cation concentration. As the concentration of the matrix cation increases, the migration times of minor cations remain unchanged even for a 1000 ppm concentration of the matrix cation. Finally, these optimized buffers allow the quantitation of minor cations down to 0.05% (w/w) for calcium- or magnesium- matrix simulated samples and 0.2% (w/w) for sodium-matrix simulated samples.     

Separation of perfluorocarboxylic acids using capillary electrophoresis with UV detection

A capillary electrophoretic method with UV detection for separation and quantitation of perfluorocarboxylic acids (PFCAs) from C6-PFCA to C12-PFCA has been developed. The optimization of measurement conditions included the choice of the most appropriate type and concentration of buffer in the background electrolyte (BGE), as well as the type and the content of an organic modifier. The optimal separation of investigated PFCAs was achieved with 50 mM phosphate buffer and 40% isopropanol in the BGE using direct UV detection. The optimum wavelength for direct UV detection was optimized at 190 nm. For indirect detection, several chromophores were studied. Five mM 3,5-Dinitrobenzoic acid (3,5-DNBA) in 20 mM phosphate buffer BGE and indirect UV detection at 280 nm gave the optimal detection and separation performance for the investigated PFCAs. The possibility of on-line preconcentration of solutes by stacking has been examined for indirect detection. The detection limits (LODs) determined for direct UV detection ranged from 2 microg/mL for C6-PFCA to 33 microg/mL for C12-PFCA. The LODs obtained for indirect UV detection were comparable to those obtained for direct UV detection.     

Determination of ammonia, creatinine and inorganic cations in urine using CE with contactless conductivity detection

CE with capacitively coupled contactless conductivity detection (C(4)D) was used to determine waste products of the nitrogen metabolism (ammonia and creatinine) and of biogenic inorganic cations in samples of human urine. The CE separation was performed in two BGEs, consisting of 2 M acetic acid + 1.5 mM crown ether 18-crown-6 (BGE I) and 2 M acetic acid + 2% w/v PEG (BGE II). Only BGE II permitted complete separation of all the analytes in a model sample and in real urine samples. The LOD values for the optimized procedure ranged from 0.8 microM for Ca(2+) and Mg(2+) to 2.9 microM for NH(4)(+) (in terms of mass concentration units, from 7 microg/L for Li(+) to 102 microg/L for creatinine). These values are adequate for determination of NH(4)(+), creatinine, Na(+), K(+), Ca(2+) and Mg(2+) in real urine samples.     

Characterization of exopolysaccharides in marine colloids by capillary electrophoresis with indirect UV detection

A method was established using capillary electrophoresis with indirect UV detection for analysis of monosaccharides liberated from exopolysaccharides by acidic hydrolysis. Tangential flow filtration was used to isolate high molecular weight polysaccharides from seawater. The capillary electrophoresis method included the use of a background electrolyte consisting of 2,6-dimethoxyphenol and cetyltrimethylammonium bromide. Several neutral sugars commonly existing in marine polysaccharides were separated under optimized conditions. The relative standard deviations were between 1.3% and 2.3% for relative migration time and 1.3-2.5% for peak height. Detection limits (at S/N 3) were in the range of 27.2-47.8 μM. The proposed approach was applied to the analysis of hydrolyzed colloidal polysaccharides in seawater collected from the Baltic Sea. Nanomolar levels of liberated monosaccharides in seawater samples can be detected by preconcentration up to 30,000 times.     

高效毛细管电泳-电导检测对四环素衍生物分离测定的研究

运用毛细管电泳-电导检测方法对4种四环素衍生物——土霉素(OTC)、金霉素(CTC)、强力霉素(DOC)和四环素(TC)的分离进行了研究。在3．5mmol/L三羟基氨基甲烷(Tris)-7．5mmol/L柠檬酸(Cit)pH4．0的运行缓冲液中，4种四环素衍生物在15min内获得完全分离。四环素衍生物的线性范围分别为5．0-500μg/mL OTC，3．6-420μg/mL CTC，4.5-470μg/mL DOC和2.5-400μg/mL TC。检测限(S／N＝3)分别为OTC2．0μg/mL，CTC 1．8μg／mL，DOC2．5μg/mL和TC1．0μg/mL。采用本法对实际样品强力霉素片中强力霉素和土霉素片中土霉素进行测定，回收率分别为97．2％和96.4％。     

Separation and determination of homovanillic acid and vanillylmandelic acid by capillary electrophoresis with electrochemical detection

A method of separation and determination of homovanillic acid (HVA) and vanillylmandelic acid (VMA) was developed based on capillary zone electrophoresis/amperometric detection with high sensitivity, good resolution and selectivity. In order to achieve complete separation and good response, several factors including pH, buffer concentration, separation voltage, detection potential and the length of separation capillary, were studied in detail. The method has been used to determine both HVA and VMA in human urine. Uric acid (UA) in human urine did not interference with their determination. The limit of detection of the method was 1.3×10⁻⁶ mol/l (1.4 fmol) for HVA and 7.9×10⁻⁷ mol/l (0.87 fmol) for VMA at a signal-to-noise ratio of 3.     

Direct determination of sialic acids in serum by capillary electrophoresis with UV detection

Summary A novel method for the determination of N-acetylneuraminic acid (NANA) and N-glycolylneuraminic acid (NGNA) has been developed using high-performance capillary electrophoresis with UV detection at 195 nm, without pre or post-column derivatisation. The acids were separated in a 50-cm, fused-silica capillary (50μ i.d, 45.5-cm effective length) with Na₂B₄O₇−Na₂HPO₄ buffer. The detection limit for NANA is a concentration of 9.6×10⁻⁶ M or, in terms of mass:3.879×10⁻¹⁴ mol (39 fmol). This method is applicable to determination of NANA in normal human serum. The results were also compared with those of the colorimetrie method.     

New preconditioning strategy for the determination of inorganic anions with capillary zone electrophoresis using indirect UV detection

It is widely accepted that preconditioning procedures are indispensable in capillary electrophoresis in order to achieve reproducibility of migration times and peak areas. Several preconditioning strategies have been employed for electrophoretic determinations of inorganic anions using indirect UV detection including simple flushing with buffer or alkaline or acid pre-rinsing followed by flushing with electrolyte. We investigated the influence of various preconditioning strategies on the reproducibility of migration times and peak areas of inorganic anions. The electrolyte systems for indirect UV detection were based on pyromellitic acid and chromic acid respectively as UV absorbing probes and hexamethonium hydroxide as electroosmatic flow modifier. Preconditioning agents under investigation were electrolyte buffer, NaOH, HCl and the free acids of the UV absorbing probes. Investigations showed that reproducibility of migration times and peak areas can be significantly improved by acid pre-rinsing using the corresponding acid of the UV absorbing probes compared to preconditioning by flushing the capillary with buffer. In contrast to acid pre-rinsing using hydrochloric acid no interfering signals within the migration time window of inorganic anions under investigation can be observed. The optimized preconditioning procedure yields relative standard deviations of migration times less than 0.25% (n=10). Relative standard deviations of corrected peak areas were below 5% applying acid preconditioning using pyromellitic acid.     

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.     

Separation of phenolic acids by capillary electrophoresis with indirect contactless conductometric detection

A new method for the electrophoretic separation of nine phenolic acids (derivatives of benzoic and cinnamic acids) with contactless conductometric detection is presented. Based on theoretical calculations, in which the mobility of the electrolyte co- and counterions and mobility of analytes are taken into consideration, the electrolyte composition and detection mode was selected. This approach was found to be especially valuable for optimization of the electrolyte composition for the separation of analytes having medium mobility. Indirect conductometric detection mode was superior to the direct mode as predicted theoretically. The best performance was achieved with 150 mM 2-amino-2-methylpropanol electrolyte at pH 11.6. The separation was carried out in a counter-electroosmotic mode and completed in less than 6 min. The LODs achieved were about 2.3-3.3 microM and could be further improved to 0.12-0.17 microM by using a sample stacking procedure. The method compares well to the UV-Vis detection.     

Determination of quinine in beverages by online coupling capillary isotachophoresis to capillary zone electrophoresis with UV spectrophotometric detection

The present study illustrates the possibilities of capillary isotachophoresis (CITP) online coupled with capillary zone electrophoresis (CZE) and hyphenated with fiber-based spectrophotometric diode array detection (DAD) for the direct, highly reliable, and ultrasensitive determination of quinine (QUI) in real multicomponent ionic matrices (beverages). Here, the CITP provided an effective online sample pretreatment (preseparation and preconcentration) prior to the CZE separation. Due to the CITP sample preconcentration, a simple UV-visible absorbance spectrophotometric detection was sufficient for obtaining very low concentration limits of detection (~2.3 ng/mL). Enhanced separation selectivity due to the combination of different separation mechanisms (CITP vs. CZE) enabled to obtain a pure analyte zone, suitable for its detection and quantitation in the directly injected real samples. The spectrophotometric DAD, unlike single wavelength UV detection, enabled to characterize the purity (i.e. spectral homogeneity) of the analyte zone and preliminary data indicate structurally related compounds via characteristic spectra recorded in the interval of 200-600 nm. The proposed CITP-CZE-DAD method was characterized by favorable performance parameters (sensitivity, linearity, precision, recovery, accuracy, robustness, and selectivity) and successfully applied to the control of QUI and potential QUI impurities in commercial beverages. This method is proposed as a routine automatized method for the highly reliable quality food control.     

Optimization of cation detection by capillary zone electrophoresis with indirect UV absorbance

Summary The indirect UV detection of cations by capillary zone electrophoresis gives peaks of very different height or area between cations. We show that the height depends on the electrophoretic mobility of the cation compared with the electrophoretic mobility of the chromophore used. Moreover, the limit of detection can be easily improved by about 4-fold by adjusting the concentration of complexing agent or by using a chromophore with the same velocity as the studied cation. Using a new parameter termedsensitization power we can optimize the limit of detection and have determined the best chromophores for each family of cations.Sensitization power is a maximum for: alkali metals and alkali earths with imidazole and UV Cat 2^?, for transition metal with pyridine, for light rare earth with ephedrine and UV Cat 1^?, for heavy lanthanides with 1-naphthylamine and phenyl-trimethyl-ammonium bromide. Corrected areas of all cations studied have normal distributions directly proportional to their ionic charge. Certain behaviour can be predicted for elements such as actinides. Detection can also be enhanced because the relation of proportionality between ionic charge and corrected area allows comparison of the performance of all chromophores.     

Analysis of inorganic cations in honey by capillary zone electrophoresis with indirect UV detection

An indirect UV detection method based on capillary electrophoresis was developed to separate eleven metal cations completely, including alkali, alkaline earth and transition metal, which are related to evaluate the quality of honey. The background electrolyte contains 15 mmol/L chromophore imidazole, and acetic acid (pH = 3.7), which functioned as pH adjustor and complexing reagent. The selected cations can be completely separated within 8 min under hydrodynamic mode injection with a running voltage of 20 kV at 25°C. Limit of detection, linearity, reproducibility relative standard deviation of migration time and recoveries are in the range of 0.01-0.21 mg/L, 0.06-60.0 mg/L, 2.1-3.4% and 95.4-104.1%, respectively. The applicability of the method is shown by the analysis of honey samples, including a comparison with results of pretreatment and unpretreatment of eight samples. The results demonstrate that the developed method can conveniently be used in routine analysis of honey.