Recent advances in the capillary electrophoresis analysis of antibiotics with capacitively coupled contactless conductivity detection

Pushing the Limits of Capacitively Coupled Contactless Conductivity Detection for Capillary Electrophoresis

Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) has proven to be an efficient technique for the separation and detection of charged inorganic, organic, and biochemical analytes. It offers several advantages, including cost-effectiveness, nanoliter injection volume, short analysis time, good separation efficiency, suitability for miniaturization, and portability. However, the routine determination of common inorganic cations (NH4+, K+, Na+, Ca2+, Mg2+, and Li+) and inorganic anions (F-, Cl-, Br-, NO2-, NO3-, PO43-, and SO42-) in water quality monitoring typically exhibits limits of detection of about 0.3-1 μM without preconcentration. This sensitivity often proves insufficient for the applications of CE-C4D in trace analysis situations. Here, we explore methods to push the detection limits of CE-C4D through a comprehensive consideration of signal and noise sources. In particular, we (i) studied the model of C4D and its guiding roles in C4D and CE-C4D, (ii) optimized the bandwidth and noise performance of the current-to-voltage (I-V) converter, and (iii) reduced the noise level due to the strong background signal of the background electrolyte by adaptive differential detection. We characterized the system with Li+; the 3-fold signal-to-noise (S/N) detection limit for Li+ was determined at 20 nM, with a linear range spanning from 60 nM to 1.6 mM. Moreover, the optimized CE-C4D method was applied to the analysis of common mixed inorganic cations (K+, Na+, Ca2+, Mg2+, and Li+), anions (F-, Cl-, Br-, NO2-, NO3-, PO43-, and SO42-), toxic halides (BrO3-) and heavy metal ions (Pb2+, Cd2+, Cr3+, Co2+, Ni2+, Zn2+, and Cu2+) at trace concentrations of 200 nM. All electropherograms showed good S/N ratios, thus proving its applicability and accuracy. Our results have shown that the developed CE-C4D method is feasible for trace ion analysis in water quality control.

A compact and high-performance setup of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D)

Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) has the advantages of high throughput (simultaneous detection of multiple ions), high separation efficiency (higher than 105 theoretical plates) and rapid analysis capability (less than 5 min for common inorganic ions). A compact CE-C4D system is ideal for water quality control and on-site analysis. It is suitable not only for common cations (e.g. Na+, K+, Li+, NH4+, Ca2+, etc.) and anions (e.g. Cl-, SO42-, BrO3-, etc.) but also for some ions (e.g. lanthanide ions, Pb2+, Cd2+, etc.) that require complex derivatization procedures to be detected by ion chromatography (IC). However, an obvious limitation of the CE-C4D method is that its sensitivity (e.g. 0.3-1 μM for common inorganic ions) is often insufficient for trace analysis (e.g. 1 ppb or 20 nM level for common inorganic ions) without preconcentration. For this technology to become a powerful and routine analytical technique, the system should be made compact while maintaining trace analysis sensitivity. In this study, we developed an all-in-one version of the CE-C4D instrument with custom-made modular components to make it a convenient, compact and high-performance system. The system was designed using direct digital synthesis (DDS) technology to generate programmable sinusoidal waveforms with any frequency for excitation, a kilovolt high-voltage power supply for capillary electrophoresis separation, and an "effective" differential C4D cell with a low-noise circuitry for high-sensitivity detection. We characterized the system with different concentrations of Cs+, and even a low concentration of 20 nM was detectable without preconcentration. Moreover, the optimized CE-C4D setup was applied to analyse mixed ions at a trace concentration of 200 nM with excellent signal-to-noise ratios. In typical applications, the limits of detection based on the 3σ criterion (without baseline filtering) were 9, 10, 24, 5, and 12 nM for K+, Cs+, Li+, Ca2+, and Mg2+, respectively, and about 7, 6, 6 and 6 nM for Br-, ClO4-, BrO3- and SO42-, respectively. Finally, the setup was also applied for the analysis of all 14 lanthanide ions and rare-earth minerals, and it showed an improvement in sensitivity by more than 25 times.

A New Contactless Cross-Correlation Velocity Measurement System for Gas-Liquid Two-Phase Flow

Based on the principle of Contactless Conductivity Detection (CCD), a new contactless cross-correlation velocity measurement system with a three-electrode construction is developed in this work and applied to the contactless velocity measurement of gas-liquid two-phase flow in small channels. To achieve a compact design and to reduce the influence of the slug/bubble deformation and the relative position change on the velocity measurement, an electrode of the upstream sensor is reused as an electrode of the downstream sensor. Meanwhile, a switching unit is introduced to ensure the independence and consistency of the upstream sensor and the downstream sensor. To further improve the synchronization of the upstream sensor and the downstream sensor, fast switching and time compensation are also introduced. Finally, with the obtained upstream and downstream conductance signals, the velocity measurement is achieved by the principle of cross-correlation velocity measurement. To test the measurement performance of the developed system, experiments are carried out on a prototype with a small channel of 2.5 mm. The experimental results show that the compact design (three-electrode construction) is successful, and its measurement performance is satisfactory. The velocity range for the bubble flow is 0.312-0.816 m/s, and the maximum relative error of the flow rate measurement is 4.54%. The velocity range for the slug flow is 0.161 m/s-1.250 m/s, and the maximum relative error of the flow rate measurement is 3.70%.

Novel Electrochemical Aptasensor Based on Ordered Mesoporous Carbon/2D Ti3C2 MXene as Nanocarrier for Simultaneous Detection of Aminoglycoside Antibiotics in Milk

Herein, a novel electrochemical aptasensor using a broad-spectrum aptamer as a biorecognition element was constructed based on a screen-printed carbon electrode (SPCE) for simultaneous detection of aminoglycoside antibiotics (AAs). The ordered mesoporous carbon (OMC) was firstly modified on 2D Ti₃C₂ MXene. The addition of OMC not only effectively improved the stability of the aptasensor, but also prevented the stacking of Ti₃C₂ sheets, which formed a good current passage for signal amplification. The prepared OMC@Ti₃C₂ MXene functioned as a nanocarrier to accommodate considerable aptamers. In the presence of AAs, the transport of electron charge on SPCE surface was influenced by the bio-chemical reactions of the aptamer and AAs, generating a significant decline in the differential pulse voltammetry (DPV) signals. The proposed aptasensor presented a wide linear range and the detection limit was 3.51 nM. Moreover, the aptasensor, with satisfactory stability, reproducibility and specificity, was successfully employed to detect the multi-residuals of AAs in milk. This work provided a novel strategy for monitoring AAs in milk.

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 (C⁴ D). 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-C⁴ D 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-C⁴ D 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.

A Study on Double Inputs Direct Contact and Single Output Capacitively Coupled Conductivity Detector

In this paper, an improved double inputs direct contact and single output capacitively coupled conductivity detector (DISODCD) based on traditional contactless capacitively coupled conductivity detector (C⁴D) is developed. The sensor uses double inputs of the contact electrode and capacitively coupled output of the contactless electrode and a lock-in amplifier to reduce interfering noise signals and amplify gain. Parallel circuit counteracts the part of the adverse capacitance reactance introduced by electrode polarization and reduces the effect of the impedance caused by the coupled wall capacitance to measure the resistance of solution. The sensor reduces limit of detection (LOD) of analyte and improves the sensitivity of the device. The LOD of the potassium chloride solution is 1 nM, and the detection range is 0.01 μM to 10 mM in actual testing for a single sample. The ratio of the response of potassium chloride solution to background ultrapure water at low concentrations is better than that of double input capacitively coupled contactless conductivity detector (DIC⁴D) and direct contact conductivity detection (DCD) under the same condition. In the case that the test cell is contaminated with impurities, pollution of impurities has little effect on the response of DISODCD. In practical application, it has a good service life.

Sensitivity of photoelctrocehmical aptasensor using spiral nanorods for detecting antiobiotic levels in experimental and real samples

Given increasing concern regarding antibiotic environmental contamination, there is immediate need to monitor antibiotic levels to effectively control pollution. In this study, we used a photoelectrochemical aptasensor based on TiO₂@MoS₂ spiral nanoarrays to detect chloramphenicol (CAP) in antibiotics. Nanoarrays were directly grown on fluorine-doped tin oxide (FTO) conductive glass with excellent biochemical stability, while aptamer-SH were immobilized by chemical binding on a synthetic TiO₂@MoS₂ nanoarray. Results show that the photocurrents were reduced in the presence of photoelectrochemistry associated with specific selection of aptamer for CAP. When the measurement of the fabricated nanomaterial chip was carried out using a three-electrode system, we found a highly specific and stable detection of chloramphenicol that ranged between 0.1 pM and 1 μM, with the detection limit of 0.1 pM. In addition, we obtained satisfactory results when real sample were used to validate the potential of photoelectrochemical (PEC) aptasensor for detecting chloramphenicol content in milk. Our results demonstrate that photoelectrochemical aptasensor is conducive to the development of less toxic multifunctional nanomaterials, making the biosensor more robust and environmentally friendly. Therefore, photoelectrochemical aptasensor can be widely applied in the field of environmental monitoring.

Simultaneous separation of 12 different classes of antibiotics under the condition of complete protonation by capillary electrophoresis-coupled contactless conductivity detection

A novel capillary electrophoresis - capacitively coupled contactless conductivity detection (CE-C⁴D) method for the separation of 12 antibiotics, including four types of aminoglycosides, three types of fluoroquinolones, two types of tetracyclines, and three types of macrolides, was developed. Half of these antibiotics were not determined by ultraviolet (UV) because of their lack of UV-absorbing groups. Formic acid (FA) (pH 2.50) with low conductivity was employed as the background electrolyte (BGE) in comparison with three BGE systems (i.e., HAc, HCl and H₃PO₄), which not only allowed complete protonation and electrophoresis separation but provided more cost-effectiveness and shorter analysis time. Under these conditions, a UV detector was employed as an additional detection mode to evaluate the qualitative analysis of 6 antibiotics possessing UV absorbing groups. Moreover, it was found that the sensitivities of the C⁴D and UV detectors were similar. Albeit a slightly reduced sensitivity of C⁴D in the analysis of norfloxacin, enrofloxacin and tylosin compared to UV, enough points were achieved to detect all analytes by C⁴D. The repeatability with respect to peak areas and migration times was better than 4.69% and 2.48% (n = 5), respectively. Mixed liquid pharmaceutical formulations of tobramycin eye drops having non-UV absorbing groups and ofloxacin eye drops possessing UV absorbing groups have been separated and detected in a single run by this technique. The studied recoveries of the two were 100% and 103%, respectively.

Three-fold interpenetrated metal–organic framework as a multifunctional fluorescent probe for detecting 2,4,6-trinitrophenol, levofloxacin, and l-cystine

A robust Zn(ii) MOF with good chemical and thermal stability, was prepared as an effective fluorescent probe for 2,4,6-trinitrophenol (TNP), levofloxacin (LVX) and l-cystine (l-Cys) with recyclability.

Capillary and microchip electrophoresis with contactless conductivity detection for analysis of foodstuffs and beverages

The paper provides a comprehensive survey of the use of capillary and microchip electrophoresis in combination with contactless conductivity detection (C⁴D) for the analysis of drinking water, beverages and foodstuffs. The introduction sets forth the fundamentals of conductivity detection anddescribes an axialC⁴Dversion. There is also a detailed discussion of the determination of inorganic ions, organic acids, fatty acids, amino acids, amines, carbohydrates, foreign substances and poisons from the standpoint of separation conditions, sample treatment and detection limits. Special attention is paid to the analysis of foodstuffs at microchips with emphasis on the employed material and connection of the microchip with the C⁴D. The review attempts to draw attention to modern trends, such as dual-opposite injection, field-enhanced sample injection, electromembrane extraction and on-line combination of microdialysis with CE. CE/C⁴D is characterised by high universality, high speed of analysis, simple sample preparation, small consumption of sample and other chemicals.

Indirect calibration for capillary electrophoresis with conductivity detection

There is a growing interest in conductivity detection for capillary electrophoresis; especially because of capacitively coupled contactless conductivity approach. This robust and general-purpose detector has another lesser-known feature: sensitivity does not depend on the very chemical nature of the analyte, but only on its effective charge and effective mobility. Therefore, the calibration curve prepared for a given species may be used to quantify another one of same charge and mobility. In the absence of a species (calibrant) of exactly the same mobility, two or more calibrants can be used. Provided the sensitivity varies smoothly in the desired region of mobility, it can be mathematically described by a function. For small ranges of mobilities, a linear behavior is expected, and the sensitivity for the analyte can be obtained by interpolation. This technique was investigated for eight different combinations of mono- and double-charged cationic and anionic analytes using buffered and unbuffered background electrolytes (BGEs). For most of the applications, a linear model was enough to describe the sensitivity (0.988 < R² < 0.998), but for ample range of mobilities, the inclusion of a hyperbolic term was needed (0.995 < R² < 0.999). This technique has a great potential to be used in field applications and in laboratories when the analytes are unstable or they are not available to be used in the preparation of standard solutions.

Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Current challenges in the detection and analysis of falsified medicines

Falsified medicines affect public health all around the globe. Complex distribution routes, illegal online webshops and reuse of packaging materials make them hard to detect. In order to tackle this problem, detection methods for the recognition of suspicious medicines and subsequent confirmation of falsification by analytical techniques is required. In this review, we focus on the developments and challenges that existed in the last five years (2015-2020) in the detection and analysis of falsified medicines. These challenges might have not been solved yet or arisen with new types of falsifications, new analytical techniques or detection strategies. Detection of suspicious medicines starts with visual inspection of packaging materials. However, re-use of packaging materials and high-quality imitations complicate visual inspection. Recent developments in the analysis of packaging by microscopic and spectroscopic techniques such as optical microscopy, X-ray fluorescence, infrared spectroscopy and Raman spectroscopy or microscopy, in combination with multivariate analysis show promising results in the detection of falsified medicines. An ongoing big challenge in the analysis of falsified medicines is the affordability of analytical devices. Yet, recent reports showed that lower cost devices, such as Counterfeit Drug Indicator or Counterfeit Detection device version 3 show promising use in the detection of falsified medicines. Furthermore, combining the outcomes of different low-cost analytical techniques, such as Minilab, colorimetry and Counterfeit Drug Indicator significantly increased selectivity and sensitivity in the detection of falsified medicines. Also, recent developments make it possible to link a low-cost technique, such as TLC, to mobile phones. Proper training of personnel has shown room for improvement and remains a challenge, even for relatively simple techniques. With an increased use of analytical fingerprints, an upcoming challenge is the accessibility of the growing pool of data. There is also the need of validated reference libraries on both national and international levels. Developments of the last few years bring us a step closer in the fight against falsified medicines, however challenges remain in the worldwide accessibility of affordable, easily operable and sensitive techniques.

Single-chip based contactless conductivity detection system for multi-channel separations

In this work, the design and characterization of a multi-cell capacitively coupled contactless conductivity detection system are described. The operation and simultaneous acquisition from 3 detector cells are demonstrated, however, the system is capable of supplying 8 detection cells and can be easily upgraded to maintain 64 capacitively coupled contactless conductivity detection cells. On performing flow-injection analysis, the system recorded as low as 0.01 mM of acetic acid, phosphoric acid, NaH₂PO_4, and Na₂B₄O₇ solutions in water. The instrument was also capable of recording and distinguishing different mixtures of organic solvents: (a) methanol-acetonitrile, (b) hexane-acetone. The designed detection system is expected to be used coupled with multi-channel separation devices for monitoring simultaneous processes.

Capacitively coupled contactless conductivity detection for analytical techniques - Developments from 2018 to 2020

The developments of analytical contactless conductivity measurements based on capacitive coupling over the two years from mid-2018 to mid-2020 are covered. This mostly concerns applications of the technique in zone electrophoresis employing conventional capillaries and to a lesser extent lab-on-chip devices. However, its use for the detection in several other flow-based analytical methods has also been reported. Detection of bubbles and measurements of flow rates in two-phase flows are also recurring themes. A few new applications in stagnant aqueous samples, e.g. endpoint detection in titrations and measurement on paper-based devices, have been reported. Some variations of the design of the measuring cells and their read-out electronics have also been described.

Capillary electrophoretic methods for quality control analyses of pharmaceuticals: A review

Capillary electrophoresis represents a promising technique in the field of pharmaceutical analysis. The presented review provides a summary of capillary electrophoretic methods suitable for routine quality control analyses of small molecule drugs published since 2015. In total, more than 80 discussed methods are sorted into three main sections according to the applied electroseparation modes (capillary zone electrophoresis, electrokinetic chromatography, and micellar, microemulsion, and liposome-electrokinetic chromatography) and further subsections according to the applied detection techniques (UV, capacitively coupled contactless conductivity detection, and mass spectrometry). Key parameters of the procedures are summarized in four concise tables. The presented applications cover analyses of active pharmaceutical ingredients and their related substances such as degradation products or enantiomeric impurities. The contribution of reported results to the current knowledge of separation science and general aspects of the practical applications of capillary electrophoretic methods are also discussed.

Large volume sample stacking of antiepileptic drugs in counter current electrophoresis performed in PAMAPTAC coated capillary

Electrophoretic stacking is developed for sensitive determination of three zwitterionic antiepileptics, namely vigabatrin, pregabalin and gabapentin, in human serum. CE separation is performed in a 25 μm fused silica capillary covalently coated with the copolymer of acrylamide with 5% content of permanently charged 3-acrylamidopropyl trimethylammonium chloride (PAMAPTAC). In background electrolyte of 500 mM acetic acid, the 5% PAMAPTAC generates an anodic electro-osmotic flow with a magnitude of (-18.6 ± 0.5) · 10^-9 m²V^-1s^-1, which acts against the direction of the electrophoretic migration of the analytes. A sample of the antiepileptic prepared in a 25% v/v infusion solution and 75% v/v acetonitrile is injected into the capillary in a large volume attaining a zone length of up to 270 mm. After turning on the separation voltage, the antiepileptics are isotachophoretically focussed behind the zone of Na⁺ ions with a sensitivity enhancement factor of 78. For the clinical determination of antiepileptics, the human serum is diluted with acetonitrile in a ratio of 1:3 v/v and a zone with a length of 90 mm is injected into the capillary. The method is linear in the 0.025-2.5 μg/mL concentration range; the attained limit of quantification is in the range 18.3-22.8 nmol/L; the within-day precision for the migration time is 0.8-1.2% and for the peak area 1.5-2.4%.

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 (C⁴ D) for CE is reported. These systems have been employed as a simple, versatile, and cost-effective analytical tool. CE-C⁴ D 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-C⁴ D, with most recent work on determination of aminoglycoside and glycopeptide antibiotics being communicated. For aminoglycosides, the development of CE-C⁴ D 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-C⁴ D 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-C⁴ D methods was 0.5 mg/L. Good agreement between results from CE-C⁴ D 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.

Modular instrumentation for capillary electrophoresis with laser induced fluorescence detection using plug-and-play microfluidic, electrophoretic and optic modules

This study reports on the development of a novel instrument for capillary electrophoresis (CE) coupled with laser induced fluorescence (LIF) detection that is inspired by the Lego-toy concept. The Lego CE-LIF design is an evolution of purpose-made CE instrumentation, allowing the users to construct their own analytical device with a high degree of standardization (i.e. a "standard" setup) without requirement of mechanical and electronic workshop facilities. To allow instrument reproduction outside the original fabrication laboratory, which is not trivial for in-house-built CE systems, the new design is based on unprecedent 'plugging' hyphenation of various off-the-shelf parts available for microfluidics, optics and electrophoresis. To render the operation with Lego CE-LIF optimal, we developed a new background electrolyte (BGE), using for the first time extremely high concentrations of zwitterionic and large weakly charged species for much improvement of detection sensitivity. The Lego CE-LIF was demonstrated for separation and detection of oligosaccharides labelled with 8-aminopyrene-1,3,6-trisulfonic acid (APTS). The new gel-free BGE for oligosaccharide analysis also allowed simplification of the conventional CE-LIF protocol used with commercial instruments while keeping satisfactory separation performances. Furthermore, the new BGE is fully compatible with a non-thermostatted Lego CE instrument thanks to low current and therefore low heat generation under application of a high voltage.

Highly water-stable Cd-MOF/Tb3+ ultrathin fluorescence nanosheets for ultrasensitive and selective detection of Cefixime

Two-dimensional Cd-MOF/Tb³⁺ (Cd-MOF = [Cd (μ-2,3-pdc) (H₂O)₃]_n (2,3-pdc = 2,3-pyridine dicarboxylic acid)) fluorescent nanosheets with the thickness of 1.4 nm were successfully synthesized by a simple solution route with subsequent ultrasonic exfoliation at room temperature. It was found that as-obtained Cd-MOF/Tb³⁺ ultrathin nanosheets could be homogeneously dispersed in aqueous system to form a sol with excellent stability. Also, the fluorescence intensity of nanosheets remarkably increased to almost 12 times higher than that of Cd-MOF/Tb³⁺ microsheets before exfoliation. Further investigations uncovered that the above strong fluorescence of Cd-MOF/Tb³⁺ nanosheets could be highly sensitively quenched by Cefixime antibiotic in aqueous solution without interference from other antibiotics, amino acids and pesticides. Hence, the as-obtained ultrathin Cd-MOF/Tb³⁺ nanosheets could be prepared as a highly selective and sensitive fluorescence probe for the detection of Cefixime in aqueous system. Compared with the bulk Cd-MOF/Tb³⁺ sensor, the Cd-MOF/Tb³⁺ ultrathin nanosheets sensor exhibited a far lower detection limit down to 26.7 nM for CFX. Also, the as-obtained nanosheets sensor presented satisfactory recovery ranging from 98.07% to 103.01% and acceptable repeatability (RSD < 6.29%, n = 6) for the detection of CFX in domestic water. Furthermore, the sensing mechanism studies revealed that the high selection of the present fluorescent probe for detection of CFX should be attributed to the cooperation of the photoinduced electron transfer and the inner filter effect.

Separation of anaesthetic ketamine and its derivates in PAMAPTAC coated capillaries with tuneable counter-current electroosmotic flow

Capillary electrophoretic separation of ketamine, norketamine, hydroxynorketamine, and dehydronorketamine was performed in the counter-current regime under the influence of oppositely-directed electroosmotic flow. For this purpose, the fused silica capillaries were covalently coated with the poly(acrylamide-co-3-acrylamidopropyl trimethylammonium chloride) copolymer (PAMAPTAC). The content of the cationic monomer APTAC in the polymerization mixture varied in the range 0-6 mol. % and the generated electroosmotic flow increased continuously in the 0-20 · 10^-9 m²V^-1s^-1 interval. Importantly, it resulted in improved electrophoretic resolution of ketamine/norketamine, which increased from 0.8 for neutral PAM coating (i.e. 0% PAMAPTAC) to 3.0 for 6% PAMAPTAC. The determination of ketamine and its derivates in rat serum was performed in a 4% PAMAPTAC capillary with an inner diameter of 25 μm. The separation was performed in a 500 mM aqueous solution of acetic acid (pH 2.3). The clinical sample was deproteinized by the addition of acetonitrile to the serum and a large volume of the treated sample was injected directly into the capillary. The achieved limit of detection ranged from 2.2 ng/mL for dehydronorketamine to 4.1 ng/mL for hydroxynorketamine; the intra-day repeatability was 1.0-1.5% for the migration time and 2.8-3.3% for the peak area. The developed methodology was employed for time monitoring of ketamines in rat serum after intra venous administration of low doses of anaesthetic at a level of 2 μg per g of body weight.

Determination of carbapenem antibiotics using a purpose-made capillary electrophoresis instrument with contactless conductivity detection

In this study, the employment of a purpose-made capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C⁴D) as a simple and cost-effective approach for simultaneous determination of different carbapenem antibiotics is reported. The developed CE-C⁴D approach was for the first time applied for quality control of various pharmaceutical formulations in Vietnam, as well as for therapeutic monitoring of these antibiotics in plasma samples from patients under intensive care. Four of the most popular carbapenems in Vietnam, doripenem, meropenem, imipenem and ertapenem, were determined using an electrolyte composed of 10 mM Tris adjusted to pH 8.0 with acetic acid. The best detection limits achieved using the developed CE-C⁴D method were 0.36 mg/L and 0.45 mg/L for pharmaceutical and plasma samples, respectively. Good agreement between results from CE-C⁴D and the confirmation method (HPLC-PDA) was achieved, with a coefficient of determination (r²) for the two pairs of data of 0.9967.

Thiol-ene Click Derivatization for the Determination of Acrylamide in Potato Products by Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

The development of analytical methods for acrylamide formed during food processing is of great significance for food safety, but limited by its inherent characteristics, the analysis of acrylamide is a continuing challenge. In this study, an efficient derivatization strategy for acrylamide based on thiol-ene click reaction with cysteine as derivatization reagent was proposed, and the resulting derivative was then analyzed by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D). After systematic investigation including catalyst dosage (0-20 mM), reaction temperature (30-90 °C) and time (1-60 min), and cysteine concentration (0.2-3.6 mM), acrylamide could be efficiently labeled by 2.0 mM cysteine at 70 °C for 10 min using 4 mM n-butylamine as catalyst. Application of 10 mM triethylamine as separation buffer, the labeled acrylamide was analyzed within 2.0 min, and the relative standard deviations of migration time and peak area were less than 0.84% and 5.6%, indicating good precision. The C⁴D signal of acrylamide derivative showed a good linear relationship with acrylamide concentration in the range of 7-200 μM with the correlation coefficient of 0.9991. The limit of detection and limit of quantification were calculated to be 0.16 μM and 0.52 μM, respectively. Assisted further by the QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample pretreatment, the developed derivatization strategy and subsequent CE-C⁴D method were successfully applied for the determination of acrylamide in potato products.

Rapid electrophoretic monitoring of the anaesthetic ketamine and its metabolite norketamine in rat blood using a contactless conductivity detector to study the pharmacokinetics

A method of capillary electrophoresis with contactless conductivity detection has been developed for non-enantioselective monitoring the anaesthetic ketamine and its main metabolite norketamine. The separation is performed in a 15 μm capillary with an overall length of 31.5 cm and length to detector of 18 cm; inner surface of the capillary is covered with a commercial coating solution to reduce the electroosmotic flow. In an optimised background electrolyte with composition 2 M acetic acid + 1% v/v coating solution under application of a high voltage of 30 kV, the migration time is 97.1 s for ketamine and 95.8 s for norketamine, with an electrophoretic resolution of 1.2. The attained detection limit was 83 ng/mL (0.3 μmol/L) for ketamine and 75 ng/mL (0.3 μmol/L) for norketamine; the number of theoretic plates for separation of an equimolar model mixture with a concentration of 2 μg/mL was 683 500 plates/m for ketamine and 695 400 plates/m for norketamine. Laboratory preparation of rat blood plasma is based on mixing 10 μL of plasma with 30 μL of acidified acetonitrile, followed by centrifugation. A pharmacokinetic study demonstrated an exponential decrease in the plasma concentration of ketamine after intravenous application and much slower kinetics for intraperitoneal application.