Determination of synthetic pharmaceuticals in phytotherapeutics by capillary zone electrophoresis with contactless conductivity detection (CZE-CD)

In this work, a method for simultaneous determination of amfepramone, fenproporex, sibutramine and fluoxetine was developed by capillary zone electrophoresis with capacitively coupled contactless conductivity detection (C⁴D) using a homemade capillary electrophoretic system. The optimized conditions for the separation of the pharmaceuticals by CZE were as follows: 50 mmol L^− 1 phosphate buffer (pH 5.0) in 50/50 (v/v) mixture of water/acetonitrile as the working electrolyte, 15 kV separation voltage, 25 °C separation temperature, hydrodynamic injection by gravity using 20 cm injection height and 60 s injection time. The detection by C⁴D was carried out by using a homemade detector, which employs a sinusoidal wave generator operating at 600 kHz frequency and 2 V_pp wave amplitude. The optimized and validated CZE-C⁴D method was applied for the determination of the studied pharmaceuticals as adulterants in phytotherapeutic formulations commercialized in Brazil for slimming purposes.     

Fast simultaneous determination of trimethoprim and sulfamethoxazole by capillary zone electrophoresis with capacitively coupled contactless conductivity detection

The association of trimethoprim and sulfamethoxazole is a very effective with antibiotic properties, and commonly used in the treatment of a variety of infections. Due to the importance in diseases treatment of humans and also of animals, the development of methods for their quantification in commercial formulations is highly desirable. In the present study, a rapid method for simultaneous determination of these compounds using CE with capacitively coupled contactless conductivity detection was developed. A favorable working region for both analytes was from 12.5 to 200 μmol/L (linear responses with R > 0.999 for N = 5). Other parameters calculated were sensitivity (1.28 ± 0.10/1.45 ± 0.11) min/(μmol L), RSD (4.5%/2.0%), and LOD (1.1/3.3) μmol/L for trimethoprim and sulfamethoxazole, respectively. Under this condition, the total run time was only 2.6 min. The proposed method was applied to the determination of trimethoprim and sulfamethoxazole in commercial samples and the results were compared to those obtained by using a HPLC pharmacopoeia method. This new method is advantageous for quality‐control analyses of trimethoprim and sulfamethoxazole in pharmaceuticals samples, because it is rapid and precise. Moreover, it is less laborious and demands minimum amounts of reagents in comparison to the recommended method.     

Separation of twenty underivatized essential amino acids by capillary zone electrophoresis with contactless conductivity detection

Twenty underivatized essential amino acids were separated using capillary zone electrophoresis and consequently detected with contactless conductivity detection (CCD). A simple acidic background electrolyte (BGE) containing 2.3 M acetic acid and 0.1% w/w hydroxyethylcellulose (HEC) allowed the electrophoretic separation and sensitive detection of all 20 essential amino acids in their underivatized cationic form. The addition of HEC to the BGE suppressed both, electroosmotic flow and analyte adsorption on the capillary surface resulting in an excellent migration time reproducibility and a very good analyte peak symmetry. Additionally, the HEC addition significantly reduced the noise and long-term fluctuations of the CCD baseline. The optimized electrophoretic separation method together with the CCD was proved to be a powerful technique for determination of amino acid profiles in various natural samples, like beer, yeast, urine, saliva, and herb extracts.     

Determination of different classes of amines with capillary zone electrophoresis and contactless conductivity detection

The use of contactless conductivity detection for the determination of different organic amines in CE was successfully demonstrated. Aliphatic non UV-absorbing species could be determined along absorbing compounds by measuring the conductivity of their protonated forms. The species tested included short-chained aliphatic primary, secondary and tertiary amines, branched aliphatic amines, diamines, hydroxyl-substituted amines as well as species incorporating aromatic and non-aromatic cyclic moieties. Highest sensitivity was obtained with BGE solutions containing solely acetic acid. A concentration of 0.5 M at a pH value of 2.5 was used. Detection limits were in the order of 1 microM. Complete separation of cis- and trans-1,2-diaminocyclohexane could be achieved by adding 18-crown-6 as modifier to the electrolyte solution.     

Separation of haloacetic acids in water by capillary zone electrophoresis with direct UV detection and contactless conductivity detection

The separation of haloacetic acids (HAAs) in water by capillary zone electrophoresis with direct UV and contactless conductivity detection was investigated using phosphate, citrate, and borate buffers, and the experimental data were compared to simulation data predicted by a computational program known as PeakMaster. Good agreement between the experimental data and simulation data predicted by PeakMaster was found. Using the phosphate buffer or the citrate buffer and electrokinetic injection it was possible to quantitate HAAs at 0.1 ppm levels in water.     

Rapid determination of partition coefficients of pharmaceuticals by phase distribution and microchip capillary electrophoresis with contactless conductivity detection

A simple microchip CE method integrated with contactless conductivity detection was developed for the direct determination of partition coefficients of selected pharmaceuticals after phase distribution equilibrium. The equilibrium of distribution between two phases for four pharmaceuticals was performed using a 1‐octanol/water system and 1‐octanol/buffer system. During the concentration determination, several major factors affecting detection were investigated in detail for each pharmaceutical to optimize the detection sensitivity. In the optimal conditions, sufficient electrophoretic separation and sensitive detection for each target analyte can be achieved within 40 s. The two systems showed a pH‐dependent partition behavior. Moreover, the measured values showed excellent agreement with those obtained by the traditional shake‐flask method with HPLC–UV detection and literature reports, respectively. The developed method can be successfully applied to measure partition coefficient values of pharmaceuticals and requires much shorter analytical time compared to traditional methods.     

Considerations on contactless conductivity detection in capillary electrophoresis

Nearly all analyses by capillary electrophoresis (CE) are performed using optical detection, utilizing either absorbance or (laser-induced) fluorescence. Though adequate for many analytical problems, in a large number of cases, e.g., involving non-UV-absorbing compounds, these optical detection methods fall short. Indirect optical detection can then still provide an acceptable means of detection, however, with a strongly reduced sensitivity. During the past few years, contactless conductivity detection (CCD) has been presented as a valuable extension to optical detection techniques. It has been demonstrated that with CCD detection limits comparable, or even superior, to (indirect) optical detection can be obtained. Additionally, construction of the CCD around the CE capillary is straightforward and robust operation is easily obtained. Unfortunately, in the literature a large variety of designs and operating conditions for CCD were described. In this contribution, several important parameters of CCD are identified and their influence on, e.g., detectability and peak shape is described. An optimized setup based on a well-defined detection cell with three detection electrodes is presented. Additionally, simple and commercially available read-out electronics are described. The performance of the CCD-CE system was demonstrated for the analysis of peptides. Detection limits at the microM level were obtained in combination with good peak shapes and an overall good performance and stability.     

Capacitively coupled contactless conductivity detection in capillary electrophoresis

Capacitively coupled contactless conductivity detection (C(4)D) has become an accepted detection method in capillary electrophoresis (CE) for a variety of analytes. Advantages of this technique over optical detection modes and galvanic contact conductivity detection include great flexibility in capillary handling and rather simple mechanical parts and electronics, as it can be performed in an on-capillary mode. Furthermore, the detection principle can be used with capillaries made of other materials than fused silica (PEEK, Teflon), with chip-based separation technologies, or with capillaries having very small inner diameters. This review presents a discussion of the published literature on C(4)D for CE and capillary electrochromatography.     

Monosaccharide profiling of glycoproteins by capillary electrophoresis with contactless conductivity detection

Saccharides form one of the major constituents of biological macromolecules in living organisms. Many biological processes including protein folding, stability, immune response and receptor activation are regulated by glycosylation. In this work, we optimized a capillary electrophoresis method with capacitively coupled contactless conductivity detection for the separation of eight monosaccharides commonly found in glycoproteins, namely D-glucose, D-galactose, D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, D-fucose, N-acetylneuraminic acid, and D-xylose. A highly alkaline solution of 50 mM sodium hydroxide, 22.5 mM disodium phosphate, and 0.2 mM CTAB (pH 12.4) was used as a background electrolyte in a 10 µm id capillary. To achieve baseline separation of all analytes, a counter-directional pressure of –270 kPa was applied during the separation. The limits of detection of our method were below 7 µg/ml (i.e., 1.5 pg or 1 mg/g protein) and the limits of quantification were below 22 µg/ml (i.e., 5 pg or 3 mg/g protein). As a proof of concept of our methodology, we performed an analysis of monosaccharides released from fetuin glycoprotein by acid hydrolysis. The results show that, when combined with an appropriate pre-concentration technique, the developed method can be used as a monosaccharide profiling tool in glycoproteomics and complement the routinely used LC-MS/MS analysis.     

Separation of enantiomers in capillary electrophoresis with contactless conductivity detection

Contactless conductivity detection is successfully demonstrated for the enantiomeric separation of basic drugs and amino acids in capillary electrophoresis (CE). Derivatization of the compounds or the addition of a visualization agent as for indirect optical detection schemes were not needed. Non-charged chiral selectors were employed, hydroxypropylated cyclodextrin (CD) for the more lipophilic basic drugs and 18-crown-6-tetracarboxylic acid (18C6H4) for the amino acids. Acidic buffer solutions based on lactic or citric acid were used. The detection limits were determined as 0.3 microM for pseudoephedrine as an example of a basic drug and were in the range from 2.5 to 20 microM for the amino acids.     

Determination of mono- and disaccharides by capillary electrophoresis with contactless conductivity detection

The separation and detection of common mono- and disaccharides by capillary electrophoresis (CE) with contactless conductivity detection (CCD) is presented. At high values of pH, the sugars are converted to anionic species that can be separated by CE and indirectly detected by CCD. The main anionic species present in the running electrolytes are hydroxide and phosphate, which have greater mobility than the ionized sugars, and, thus, the indirect detection is possible. The method was applied to analysis of glucose, fructose, and sucrose in soft drinks, isotonic beverages, fruit juice, and sugarcane spirits. Galactose was used as internal standard in all cases. Plate numbers range from ca. 70,700 to 168,200 and the limits of detection from 13 to 31 microM.     

Determination of pharmaceuticals classified as emerging pollutants using capillary electrophoresis with capacitively coupled contactless conductivity detection

A study on the simultaneous separation of 13 pharmaceutical products by capillary electrophoresis with capacitively coupled contactless conductivity detection was presented. The parameters of the background electrolyte, such as pH, organic additives as well as types and concentrations of cyclodextrins (CD) were studied. The optimal separation conditions were achieved with a background electrolyte consisting of 9 mM Tris/5 mM lactic acid at pH 8.0, containing 5% n-propanol, 0.025% gamma-CD, 0.075% hydroxyl-beta-CD and 0.15% dimethyl-beta-CD. Limits of detections ranged from 61 to 1676 microg/L (S/N=3) and the relative standard deviations for migration time and peak area were below 2 and 6%, respectively. This demonstrated the potential of the capillary electrophoresis-capacitively coupled contactless conductivity detection method for biomedical and environmental analysis, as shown in the determination of pharmaceuticals identified as emerging pollutants in water samples.     

Separation of fluoroquinolones in acidic buffer by capillary electrophoresis with contactless conductivity detection

A method to determine five fluoroquinolones (FQs), namely, rufloxacin (RUF), ciprofloxacin (CIP), enrofloxacin (ENO), gatifloxacin (GAT) and moxifloxacin (MOX), in acidic buffer by capillary electrophoresis (CE)-capacitively coupled contactless conductivity detection (C⁴D) technique is presented. Separation was carried out in a fused-silica capillary (42 cm × 50 μm) using a buffer composed of 10 mM tartaric acid, 14 mM sodium acetate and 15% (v/v) methanol at pH 3.8. The RSDs of the migration times and peak areas were 0.65% and 12.3% (intraday), 1.28% and 8.8% (interday), respectively. CE-C⁴D in combination with liquid–liquid extraction (LLE) as clean-up and preconcentration procedure, allows detection of the FQs in fortified chicken muscle samples with detection limits of 6.8–11.7 ng/g. This method shows potential in rapid determination of FQs in samples with complex matrix.     

硫酸沙丁胺醇的毛细管电泳非接触电导法检测

建立了毛细管电泳-非接触电导检测分离测定硫酸沙丁胺醇的分析方法。分别考察了分离介质、背景电解质及其浓度和pH、分离电压、进样时间、激发电压、激发频率等因素对实验结果的影响。在优化的实验条件(以15 mmol/L乳酸水溶液(pH 2.7)为电泳介质,10 kV下电动进样3 s,分离电压为10 kV,激发电压为60 V,激发频率为120 kHz)下,硫酸沙丁胺醇的检出限(信噪比为3)为1.92 mg/L,在9.60～48.0 mg/L质量浓度范围内有良好的线性关系(r=0.995),迁移时间的相对标准偏差(RSD)为2.7%。将该方法用于硫酸沙丁胺醇片和硫酸沙丁胺醇气雾剂中的硫酸沙丁胺醇含量的测定,加标回收率为90%～113%,检测结果与药厂的标示值相符合,为硫酸沙丁胺醇的检测提供了一种简便、快速、高灵敏的方法。关键词: 毛细管电泳;非接触电导检测法;硫酸沙丁胺醇;硫酸沙丁胺醇片;硫酸沙丁胺醇气雾剂     

Determination of tobramycin in human serum by capillary electrophoresis with contactless conductivity detection

A study on the determination of the antibiotic tobramycin by CE with capacitively coupled contactless conductivity detection is presented. This method enabled the direct quantification of the non-UV-absorbing species without incurring the disadvantages of the indirect approaches which would be needed for optical detection. The separation of tobramycin from inorganic cations present in serum samples was achieved by optimizing the composition of the acetic acid buffer. Field-amplified sample stacking was employed to enhance the sensitivity of the method and a detection limit of 50 microg/L (S/N = 3) was reached. The RSDs obtained for migration time and peak area using kanamycin B as internal standard were typically 0.12 and 4%, respectively. The newly developed method was validated by measuring the concentration of tobramycin in serum standards containing typical therapeutic concentrations of 2 and 10 mg/L. The recoveries were 96 and 97% for the two concentrations, respectively.     

Fingerprinting postblast explosive residues by portable capillary electrophoresis with contactless conductivity detection

A portable capillary electrophoretic system with contactless conductivity detection was used for fingerprint analysis of postblast explosive residues from commercial organic and improvised inorganic explosives on various surfaces (sand, concrete, metal witness plates). Simple extraction methods were developed for each of the surfaces for subsequent simultaneous capillary electrophoretic analysis of anions and cations. Dual‐opposite end injection principle was used for fast (<4 min) separation of 10 common anions and cations from postblast residues using an optimized separation electrolyte composed of 20 mM MES, 20 mM l ‐histidine, 30 μM CTAB and 2 mM 18‐crown‐6. The concentrations of all ions obtained from the electropherograms were subjected to principal component analysis to classify the tested explosives on all tested surfaces, resulting in distinct cluster formations that could be used to verify (each) type of the explosive.     

Fast determination of ethambutol in pharmaceutical formulations using capillary electrophoresis with capacitively coupled contactless conductivity detection

A method for the determination of ethambutol (EMB), a first‐line drug against tuberculosis, based on CE with capacitively coupled contactless conductivity detection is proposed. The separation of EMB and its main product of degradation were achieved in less than 3 min with a resolution of 2.0 using a BGE composed of 50 mmol/L histidine and 30 mmol/L MES, pH 6.30. By raising the pH to 8.03, the analysis time was reduced to 1.0 min, but with a significant loss of resolution (0.7). Using the best separation conditions, linearity of 0.9976 (R², five data points), sensitivity of 1.26×10^?4 V min μmol^?1 L, and LOD and quantification of 23.5 and 78.3 μmol/L, respectively, were obtained. Recoveries at four levels of concentration ranged from 95 to 102% and the concentration range studied ranged from 100 to 500 μmol/L. The results obtained for the determination of EMB in pharmaceutical formulations were compared with those obtained by using CE with photometric detection.     

Simultaneous determination of atenolol and amiloride in pharmaceutical preparations by capillary zone electrophoresis with capacitively coupled contactless conductivity detection

Capillary zone electrophoresis coupled with a capacitively coupled contactless conductivity detector (CE‐C⁴D) has been employed for the determination of atenolol and amiloride in pharmaceutical formulations. Acetic acid (150 mm ) was used as background electrolyte. The influence of several factors (detector excitation voltage and frequency, buffer concentration, applied voltage, capillary temperature and injection time) was studied. Non‐UV‐absorbing L‐valine was used as internal standard; the analytes were all separated in less than 7 min. The separation was carried out in normal polarity mode at 28°C, 25 kV and using hydrodynamic injection (25 s). The separation was effected in an uncoated fused‐silica capillary (75 μm, i.d. × 52 cm). The CE‐C⁴D method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 5–250 μg/mL for the studied analytes. The relative standard deviations of intra‐ and inter‐day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol and amiloride in different pharmaceutical tablet formulations. Copyright © 2010 John Wiley & Sons, Ltd.     

High-voltage contactless conductivity detection of metal ions in capillary electrophoresis

The detection of alkali, alkaline earth and heavy metal ions with a high-voltage capacitively coupled contactless conductivity detector (HV-C(4)D) was investigated. Eight alkali, alkaline earth metal ions and ammonium could be separated in less than 4 min with detection limits in the order of 5 x 10(-8) M. The heavy metals Mn2+, Pb2+, Cd2+ Fe2+, Zn2+, Co2+, Cu2+ and Ni2+ could also be successfully resolved with a 10 mM 2-(N-morpholino)ethanesulfonic acid/DL-histidine (MES/His)-buffer. Zn2+, Co2+, Cu2+ and Ni2+ showed an indirect response. The detection limits for the heavy metals were determined to range from about 1 to 5 microM.     

Miniaturized movable contactless conductivity detection cell for capillary electrophoresis

A miniaturized capacitively coupled contactless conductivity detector (mini-C(4)D) cell has been designed which is small enough to allow it to slide along the effective capillary length inside the capillary cassette of an Agilent capiillary electrophoresis system (CE) (or other CE brand of similar construction), including the possibility of positioning it close to the point of optical detection (4 cm), or even putting two such detector cells in one cassette. The cell was tested and the performance characteristics (noise, sensitivity, and peak width) were compared with those obtained with the previously used large C(4)D cell. No significant differences were observed. The mini-C(4)D was used in simultaneous separations of common cations and anions where its advantage over a larger C(4)D cell is the ability to vary the point of detection with the mini-C(4)D cell continuously at any point along the capillary length, so that the optimum apparent selectivity can be chosen. Other applications include providing a convenient second point of detection in addition to photometric detection, such as to measure accurately the linear velocity of a zone, or to allow placement of two mini-C(4)D cells in one capillary cassette simultaneously.