Fast determination of paracetamol and its hydrolytic degradation product p-aminophenol by capillary and microchip electrophoresis with contactless conductivity detection

Paracetamol (PAC) is one of the most extensively used analgesics and antipyretic drugs to treat mild and moderate pain. P-aminophenol (PAP), the main hydrolytic degradation product of PAC, can be found in environmental water. Recently, CE has been developed for the detection of a wide variety of chemical substances. The purpose of this study is to develop a simple and fast method for the detection and separation of PAC and its main hydrolysis product PAP using CE and microchip electrophoresis with capacitively coupled contactless conductivity detection. The determination of these compounds using microchip electrophoresis with capacitively coupled contactless conductivity detection is being reported for the first time. The separation was run for all analytes using a BGE (20 mM β-alanine, pH 11) containing 14% (v/v) methanol. The RSDs obtained for migration time were less than 4%, and RSDs obtained for peak area were less than 7%. The detection limits (S/N = 3) that were achieved ranged from 0.3 to 0.6 mg/L without sample preconcentration. The presented method showed rapid analysis time (less than 1 min), high efficiency and precision, low cost, and a significant decrease in the consumption of reagents. The microchip system has proved to be an excellent analytical technique for fast and reliable environmental applications.     

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.     

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.     

Determination of vitamin C and preservatives in beverages by conventional capillary electrophoresis and microchip electrophoresis with capacitively coupled contactless conductivity detection

The separation and detection of commonly used preservatives (benzoate, sorbate) and vitamin C by both conventional CE and microchip electrophoresis with capacitively coupled contactless conductivity detection is presented. The separation was optimized by adjusting the pH-value of the buffer and the use of hydroxypropyl-beta-CD (HP-beta-CD) and CTAB as additives. For conventional CE, optimal separation conditions were achieved in a histidine/tartrate buffer at pH 6.5, containing 0.025% HP-beta-CD and 0.1 mM CTAB. LOD ranged from 0.5 to 3 mg/L (S/N = 3) and the RSDs for migration time and peak area were less than 0.1 and 2%, respectively. A considerable reduction of analysis time can be accomplished by using microchip electrophoresis without significant loss in sensitivity under optimal separation conditions. A histidine/tartrate buffer at pH 6.5, incorporating 0.06% HP-beta-CD and 0.25 mM CTAB, gave detection limits ranging between 3 and 10 mg/L and satisfactory reproducibilities of < or =0.4% for the migration time and < or =3.5% for the peak area. The methods developed are useful for the quantitative determination of food additives in real samples such as soft drinks and vitamin C tablets.     

Capacitively coupled contactless conductivity detection with dual top–bottom cell configuration for microchip electrophoresis

An optimized capacitively coupled contactless conductivity detector for microchip electophoresis is presented. The detector consists of a pair of top–bottom excitation electrodes and a pair of pickup electrodes disposed onto a very thin plastic microfluidic chip. The detection cell formed by the electrodes is completely encased and shielded in a metal housing. These approaches allow for the enhancement of signal coupling and extraction from the detection cell that result in an improved signal‐to‐noise‐ratio and detection sensitivity. The improved detector performance is illustrated by the electrophoretic separation of six cations (NH, K⁺, Ca²⁺, Na⁺, Mg²⁺, Li⁺) with a detection limit of approximately 0.3 μM and the analysis of the anions (Br^?, Cl^?, NO, NO, SO, F^?) with a detection limit of about 0.15 μM. These LODs are significantly improved compared with previous reports using the conventional top–top electrode geometry. The developed system was applied to the analysis of ions in bottled drinking water samples.     

Study on the effects of electrolytes and solvents in the determination of quaternary ammonium ions by nonaqueous capillary electrophoresis with contactless conductivity detection

A study on the separation of lipophilic quaternary ammonium cations in NACE coupled with contactless conductivity detection (NACE‐C⁴D) is presented. The suitability of different salts dissolved in various organic solvents as running electrolytes in NACE‐C⁴D was investigated. A solvent mixture of methanol/acetonitrile at a ratio of 90%:10% v/v showed the best results. Deoxycholic acid sodium salt as BGE was found to provide exceptional high stability with low baseline noise that leads to highest S/N ratios for the target analytes among all BGEs tested. Under the optimum conditions, capillaries with different internal diameters were examined and an id of 50 μm was found to give best detection sensitivity. The proposed method was validated and showed good linearity in the range from 2.5 to 200 μM, low limits of detection (0.1–0.7 μM) and acceptable reproducibility of peak area (intraday RSD 0.1–0.7%, n = 3; interday RSD 5.9–9.4%, n = 3).     

Determination of carbethopendecinium bromide in eye drops by capillary electrophoresis with capacitively coupled contactless conductivity detection

Antiseptic agent carbethopendecinium bromide (septonex) was determined by capillary electrophoresis with capacitively coupled contactless conductivity detection. Optimal separation of this quaternary ammonium ion was achieved in BGE of pH 7.0 containing 30 mM 2-(N-morpholino)ethanesulfonic acid, 12.5 mg/mL of 2-hydroxypropyl-β-cyclodextrin and 20% v/v of acetonitrile. The separation was performed at 25°C in an uncoated fused silica capillary (50 μm id; total length, 60.5 cm; effective length, 50 cm) at 30 kV. Samples were injected hydrodynamically at 50 mbar for 6 s. For quantitative analysis, L-arginine (500 μg/mL) was used as internal standard. The calibration curve was rectilinear for 25-400 μg/mL of septonex (y=0.0113x-0.0063; r(2)=0.9992). The LOD was 7 μg/mL of septonex (at S/N=3). The run-to-run repeatability (n=6) was characterized by the RSDs of 0.18% for the migration time and 1.96% for the analyte/internal standard peak area ratio. Accuracy tested by recovery experiments at three concentration levels gave recoveries of 100.27-104.22% with RSD ≤2.19%. The method was successfully applied to the assay of carbethopendecinium bromide in eye drops. Quaternary ammonium ions having structure and size close to that of carbethopendecinium may not be resolved from the analyte.     

A thin cover glass chip for contactless conductivity detection in microchip capillary electrophoresis

A microfabricated thin glass chip for contactless conductivity detection in chip capillary electrophoresis is presented in this contribution. Injection and separation channels were photolithographed and chemically etched on the surface of substrate glass, which was bonded with a thin cover glass (100 μm) to construct a new microchip. The chip was placed over an independent contactless electrode plate. Owing to the thinness between channel and electrodes, comparatively low excitation voltage (20–110 V in V_p–p) and frequency (40–65 kHz) were suitable, and favorable signal could be obtained. This microchip capillary electrophoresis device was used in separation and detection of inorganic ions, amino acids and alkaloids in amoorcorn tree bark and golden thread in different buffer solutions. The detection limit of potassium ion was down to 10 μmol/L. The advantages of this microchip system exist in the relative independence between the microchip and the detection electrodes. It is convenient to the replacement of chip and other operations. Detection in different position of the channel would also be available.     

Low-cost and versatile analytical tool with purpose-made capillary electrophoresis coupled to contactless conductivity detection: Application to antibiotics quality control in Vietnam

In this study, the development of our purpose-made capacitively coupled contactless conductivity detection (C⁴D) for CE is reported. These systems have been employed as a simple, versatile, and cost-effective analytical tool. CE-C⁴D devices, whose principle is based on the control of the ion movements under an electrical field, can be constructed even with a modest financial budget and limited infrastructure. A featured application was developed for quality control of antimicrobial drugs using CE-C⁴D, with most recent work on determination of aminoglycoside and glycopeptide antibiotics being communicated. For aminoglycosides, the development of CE-C⁴D methods was adapted to two categories. The first one includes drugs (liquid or powder form) for intravenous injection, containing either amikacin, streptomycin, kanamycin A, or kanamycin B. The second one covers drugs for eye drops (liquid or ointment form), containing either neomycin, tobramycin, or polymyxin. The CE-C⁴D method development was also made for determination of some popular glycopeptide antibiotics in Vietnam, including vancomycin and teicoplanin. The best detection limit achieved using the developed CE-C⁴D methods was 0.5 mg/L. Good agreement between results from CE-C⁴D and the confirmation method (HPLC- Photometric Diode Array ) was achieved, with their result deviations less than 8% and 13% for aminoglycoside and glycopeptide antibiotics, respectively.     

Rapid determination of NSAIDs by capillary and microchip electrophoresis with capacitively coupled contactless conductivity detection in wastewater

A simple, rapid method using CE and microchip electrophoresis with C⁴D has been developed for the separation of four nonsteroidal anti-inflammatory drugs (NSAIDs) in the environmental sample. The investigated compounds were ibuprofen (IB), ketoprofen (KET), acetylsalicylic acid (ASA), and diclofenac sodium (DIC). In the present study, we applied for the first time microchip electrophoresis with C⁴D detection to the separation and detection of ASA, IB, DIC, and KET in the wastewater matrix. Under optimum conditions, the four NSAIDs compounds could be well separated in less than 1 min in a BGE composed of 20 mM His/15 mM Tris, pH 8.6, 2 mM hydroxypropyl-beta-cyclodextrin, and 10% methanol (v/v) at a separation voltage of 1000–1200 V. The proposed method showed excellent repeatability, good sensitivity (LODs ranging between 0.156 and 0.6 mg/L), low cost, high sample throughputs, portable instrumentation for mobile deployment, and extremely lower reagent and sample consumption. The developed method was applied to the analysis of pharmaceuticals in wastewater samples with satisfactory recoveries ranging from 62.5% to 118%.     

Analysis of flavonoids by CE using capacitively coupled contactless conductivity detection

A CE method employing capacitively coupled contactless conductivity (C(4)D) compared to indirect UV-detection was developed for the analysis of phytochemically relevant flavonoids, such as 6-hydroxyflavone, biochanin A, hesperetin and naringenin. To ensure fast separation at highest selectivity, sensitivity and peak symmetry, the pH value and the concentration of the running BGE had to be optimized regarding both co- and counter-EOF mode. Optimum conditions were found to be 1.0 and 5.0 mM chromate BGE (pH 9.50) in the counter- and co-EOF mode, respectively. Validation of the established CE-C(4)D method pointed out to be approximately seven times more sensitive compared to indirect UV-detection applying the same conditions. The lower LOD defined at an S/N of 3:1 was found between 0.12 and 0.21 microg/mL for the analytes of interest using C(4)D and between 0.77 and 1.20 microg/mL using indirect UV-detection. Compared to an earlier published CE method employing direct UV-detection, C(4)D was found to be approximately two times more sensitive. Due to the lower baseline noise, C(4)D showed an excellent regression coefficient >0.99 compared to 0.93 when using indirect UV detection calibrating within a concentration range between 1 and 10 microg/mL. The influence of the sugar moiety on the conductivity of a flavonoid was studied upon the analysis of the aglycon hesperetin and the rutinosid hesperidin. The sugar moiety in hesperedin shows a higher conductivity compared to hesperetin. Finally, the optimized established CE-C(4)D method was applied to the determination and quantification of naringenin in Sinupret.     

Automated capillary electrophoresis with on-line preconcentration by solid phase extraction using a sequential injection manifold and contactless conductivity detection

An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 μm internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi.     

Electromembrane extraction of amino acids from body fluids followed by capillary electrophoresis with capacitively coupled contactless conductivity detection

Electromembrane extraction (EME) proved to be a simple and rapid pretreatment method for analysis of amino acids and related compounds in body fluid samples. Body fluids were acidified to the final concentration of 2.5 M acetic acid and served as donor solutions. Amino acids, present as cations in the donor solutions, migrated through a supported liquid membrane (SLM) composed of 1-ethyl-2-nitrobenzene/bis-(2-ethylhexyl)phosphonic acid (85:15 (v/v)) into the lumen of a porous polypropylene hollow fiber (HF) on application of electric field. The HF was filled with 2.5 M acetic acid serving as the acceptor solution. Matrix components in body fluids were efficiently retained on the SLM and did not interfere with subsequent analysis. Capillary electrophoresis with capacitively coupled contactless conductivity detection was used for determination of 17 underivatized amino acids in background electrolyte solution consisting of 2.5 M acetic acid. Parameters of EME, such as composition of SLM, pH and composition of donor and acceptor solution, agitation speed, extraction voltage, and extraction time were studied in detail. At optimized conditions, repeatability of migration times and peak areas of 17 amino acids was better than 0.3% and 13%, respectively, calibration curves were linear in a range of two orders of magnitude (r(2)=0.9968-0.9993) and limits of detection ranged from 0.15 to 10 μM. Endogenous concentrations of 12 amino acids were determined in EME treated human serum, plasma, and whole blood. The method was also suitable for simple and rapid pretreatment and determination of elevated concentrations of selected amino acids, which are markers of severe inborn metabolic disorders.     

多通道非接触电导检测装置用于自由流电泳分离在线检测

现有自由流电泳(FFE)装置因不具备在线检测功能,其实用性仍然存在明显不足.针对这一问题,该工作发展了一种多通道电容耦合式非接触电导检测(MC-C4 D)装置并开发了自动测量软件.MC-C4 D装置采用了并行分时的非接触电导检测技术,即由多个同样的非接触电导检测模块并行排列,而单个电导检测模块又由多个非接触电导检测池组...     

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     

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.     

Monitoring of amoxicilline and ceftazidime in the microdialysate of diabetic foot and serum by capillary electrophoresis with contactless conductivity detection

Determination of the broad-spectrum antibiotics amoxicilline (AMX) and ceftazidime (CTZ) in blood serum and microdialysates of the subcutaneous tissue of the lower limbs is performed using CE with contactless conductivity detection (C⁴D). Baseline separation of AMX is achieved in 0.5 M acetic acid as the background electrolyte and separation of CTZ in 3.2 M acetic acid with addition of 13% v/v methanol. The CE-C⁴D determination is performed in a 25 µm capillary with suppression of the EOF using INST-coating on an effective length of 18 cm and the attained migration time is 4.2 min for AMX and 4.4 min for CTZ. The analysis was performed using 20 µl of serum and 15 µl of microdialysate, treated by the addition of acetonitrile in a ratio of 1/3 v/v and the sample is injected into the capillary using the large volume sample stacking technique. The LOQ attained in the microdialysate is 148 ng/ml for AMX and 339 ng/ml for CTZ, and in serum 143 ng/ml for AMX and 318 ng/ml for CTZ. The CE-C⁴D method is employed for monitoring the passage of AMX and CTZ from the blood circulatory system into the subcutaneous tissue at the sites of diabetic ulceration in patients suffering from diabetic foot syndrome and also for measuring the pharmacokinetics following intravenous application of bolus antibiotic doses.     

Determination of nerve agent degradation products by capillary electrophoresis using field-amplified sample stacking injection with the electroosmotic flow pump and contactless conductivity detection

In the present study, field-amplified sample stacking injection using the electroosmotic flow pump (FAEP) was developed for the capillary electrophoretic separation of the four nerve agent degradation products methylphosphonic acid (MPA), ethyl methylphosphonic acid (EMPA), isopropyl methylphosphonic acid (IMPA) and cyclohexyl methylphosphonic acid (CMPA). Coupled to contactless conductivity detection, direct quantification of these non-UV active compounds could be achieved. Sensitivity enhancement of up to 500 to 750-fold could be obtained. The newly established approach was applied to the determination of the analytes in river water and aqueous extracts of soil. Detection limits of 0.5, 0.7, 1.4 and 2.7 ng/mL were obtained for MPA, EMPA, IMPA and CMPA, respectively, in river water and 0.09, 0.14, 0.44 and 0.22 μg/g, respectively, in soil.     

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.     

Capillary electrophoresis with contactless conductivity detection coupled to a sequential injection analysis manifold for extended automated monitoring applications

A capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C⁴D) based on a sequential injection analysis (SIA) manifold was refined. Hydrodynamic injection was implemented to avoid a sampling bias by using a split-injection device based on a needle valve for precise adjustment. For safety and reliability, the integrity of the high voltage compartment at the detection end was fully maintained by implementing flushing of the high voltage interface through the capillary. With this set-up, extended fully automated monitoring applications are possible. The system was successfully tested in the field for the determination of the concentration levels of major inorganic cations and anions in a creek over a period of 5 days.