Application of Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection (CE-C4D): 2017-2020

Analysis of areca alkaloids and their conversions using CE-C4D and identification by CE-MS

As one of the four major addictive substance globally, areca nut contains areca alkaloids as its principal active ingredients, which exhibit both medicinal potential and toxic effects. In this study, a concise and effective approach was developed for the simultaneous analysis of areca alkaloids using laboratory-built capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D). The proposed method demonstrated satisfactory linearity (R2 ≥ 0.995), precision (RSDs ≤ 6.56%) and quantification limits of 0.77-1.37 μM. This method has been successfully used to quantify areca products with recoveries of 92.2-110.1%. In addition, the effect of processing on the areca alkaloid content in areca nut-containing products was analyzed. On this basis, the conversions of areca alkaloids under various alkaline conditions were investigated through experimental studies and theoretical calculations. The separation parameters for CE-C4D were effectively transferred to CE-mass spectrometry (MS), and the above analytical results for areca alkaloids were validated by incorporating CE-MS related experiments.

Advancement of microchip electrophoresis coupled with capacitively coupled contactless conductivity detection-from design to application (2018-2024)

Over the past three decades, microchip electrophoresis coupled with capacitively coupled contactless conductivity detection (ME-C4D) has garnered considerable interest due to its various merits, including minimal sample consumption, compact structure, immediate detection, and high analytical precision. Continuous technological innovation and improvement have significantly advanced ME-C4D in structural design, fabrication processes, and experimental methodologies. As a result, the application of this technology has expanded into a wider range of electrochemical analysis fields, including disease diagnosis, food safety assessment, environmental pollutant detection, and soil nutrient analysis. This review meticulously examines the forefront of ME-C4D over the last five years. It methodically categorizes and scrutinizes advancements from various dimensions, including newly emerged ME microchips, C4D electrodes, experimental protocols, and pioneering applications. Moreover, this paper critically summarizes these developments, identifying the prevailing limitations and challenges within ME-C4D. Ultimately, it projects potential future trajectories for innovation in the field of ME-C4D, suggesting pathways to overcome existing hurdles and hinting at the untapped possibilities that lie ahead.

Contactless Conductivity Detection for Capillary Electrophoresis-Developments From 2020 to 2024

The review covering the development of capillary electrophoresis with capacitively coupled contactless conductivity detection from 2020 to 2024 is the latest in a series going back to 2004. The article considers applications employing conventional capillaries and planar lab-on-chip devices as well as fundamental and technical developments of the detector and complete electrophoresis instrumentation.

Rapid Determination of Galantamine in Human Plasma by Microchip Electrophoresis With a Highly Integrated Contactless Conductivity Detector

A novel and rapid method was developed for the determination of galantamine in human plasma by microchip electrophoresis with a highly integrated contactless conductivity detector (CCD). The instrumental parameters affecting the response of the detector, such as excitation frequency and excitation voltage, were examined and optimized. The electrophoresis conditions that influenced the separation and detection of galantamine, including the composition of buffer solution, buffer pH, buffer concentration, additives, injection time, and separation voltage were systematically investigated. Under the optimal conditions, the peak height had a good linear relationship with the concentration of galantamine in human plasma from 10 to 160 µg/L, and the correlation coefficient was 0.9992, the limit of detection reached 1.1 µg/L. The recoveries were between 98.6% and 102.1%. This sensitive, rapid, and convenient method is a good alternative to existing methods for galantamine determination. Also, this highly integrated CCD holds great promise in clinical biochemical analysis.

Antimalarial analysis of pharmaceutical formulations and biological samples by capillary electrophoresis: the state of the art and applications

Malaria is a serious public health problem, being an endemic disease in 84 countries, mainly in Africa. This review explores the application of capillary electrophoresis (CE) techniques for analyzing antimalarial drugs, highlighting methods from 2000 to 2023 for the analysis of pharmaceutical formulations and human biological samples. The versatility, selectivity, high efficiency, cost-effectiveness, and high analytical frequency of CE techniques have become attractive choices for pharmaceutical analysis, focusing on quality control and impurity analysis applications. The evolution of achiral and chiral electromigration methods has been described based on the features of each mode of separation: capillary zone electrophoresis (CZE), micellar electrokinetic chromatography, microemulsion electrokinetic chromatography, and capillary electrochromatography. As expected, CZE is reported in most articles owing to its compatibility with drug properties and separation mode. However, it is necessary to perform other separation modes for a few drugs that are present in neutral form. After exhaustive research using different databases and statistical analyses, 27 articles using CE techniques for antimalarial drug analysis were found and are mentioned in this review.

Photothermal Backscatter Interferometry for Enhanced Detection in Capillary Electrophoresis

Refractive index (RI) detection using backscatter interferometry (BSI) enables universal detection in capillary electrophoresis (CE). BSI detection is a versatile on-capillary approach that is easily integrated with capillary or microfluidic channels, straightforward to miniaturize, and inexpensive. The focused BSI light source can also double as the excitation source for fluorescence, enabling simultaneous universal (BSI) and specific (fluorescence) signals from the same detection volume. To improve BSI detection and expand orthogonal content, we integrate photothermal absorption with BSI detection. Nonradiative relaxation of an excited analyte releases heat into the surroundings, which modifies both the local RI and conductivity (viscosity) of the analyte zone. We recently showed that the BSI signal is sensitive to both RI and conductivity, which makes photothermal absorption a promising route to signal enhancement. Here, we use coaxially delivered BSI and photothermal absorption beams to characterize BSI, photothermal BSI, and fluorescence detection using the separation of test samples. We show that photothermal absorption leads to 3 orders of magnitude improvement in BSI detection limits at the powers studied and provides new opportunities for studying binding interactions with CE.

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.

Application of capillary electrophoresis with capacitively contactless conductivity detection for biomedical analysis

The coupling of capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4 D) has become convenient analytical method for determination of small molecules that do not possess chromogenic or fluorogenic group. The implementations of CE with C4 D in the determination of inorganic and organic ions and amino acids in biomedical field are demonstrated. Attention on background electrolyte composition, sample treatment procedures, and the utilize of multi-detection systems are described. A number of tables summarizing highly developed CE-C4 D methods and the figures of merit attained are involved. Lastly, concluding remarks and perspectives are argued.

Determination of scopolamine and butylscopolamine in beverages, urine and Buscopan® tablets samples using electrophoresis microchip with integrated contactless conductivity detection

The number of cases in which scopolamine (SCO) was used for both recreational and predatory purposes has increased dramatically in recent decades. Linked to this, there is a concern about obtaining SCO through thermal degradation of butylscopolamine (BSCO) - an active ingredient of Buscopan® - a drug sold without a medical prescription. In this study, mixtures containing SCO and BSCO were separated and detected on a microchip electrophoresis (ME) device with integrated capacitively coupled contactless conductivity detection (C4D) using a running buffer composed of 40 mmol L-1 of butyric acid and 25 mmol L-1 of sodium hydroxide (pH 5.0). The separation was performed within ca. 115 s with a resolution of 1.3 and separation efficiency ranging from 1.4 × 105 to 1.5 × 105 theoretical plates m-1. A detection limit of 1.1 μmol L-1 was achieved for both species and the developed method revealed satisfactory repeatability with relative standard deviation (RSD) values for forty-eight injections between 4.8 and 9.4% for peak areas and lower than 3.3% for migration times. Furthermore, inter-day precision was evaluated for sixteen injections (a sequence of four injections performed over four days), and RSD values were less than 6.6% for peak areas and 2.2% for migration times. Satisfactory recovery values (95-114%) were obtained for all evaluated beverage samples (cachaça, vodka, whiskey, beer, Coca-Cola, and grape juice) as well as for artificial urine samples (95-107%). Finally, the conversion of BSCO into SCO was observed after simple heating procedure of Buscopan® sample (not subject to medical prescription), which was successfully confirmed through analysis by capillary electrophoresis coupled to the mass spectrometry (CE-MS). Based on the reported results, the use of ME-C4D devices has demonstrated a huge potential for applications in the forensic chemistry field.

Green Analytical Method for Simultaneous Determination of Glucosamine and Calcium in Dietary Supplements by Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

The need for analytical methods that are fast, affordable, and ecologically friendly is expanding. Because of its low solvent consumption, minimal waste production, and speedy analysis, capillary electrophoresis is considered a "green" choice among analytical separation methods. With these "green" features, we have utilized the capillary electrophoresis method with capacitively coupled contactless conductivity detection (CE-C⁴D) to simultaneously determine glucosamine and Ca²⁺ in dietary supplements. The CE analysis was performed in fused silica capillaries (50 μm inner diameter, 40 cm total length, 30 cm effective length), and the analytical time was around 5 min. After optimization, the CE conditions for selective determination of glucosamine and Ca²⁺ were obtained, including a 10 mM tris (hydroxymethyl) aminomethane/acetic acid (Tris/Ace) buffer of pH 5.0 as the background electrolyte; separation voltage of 20 kV; and hydrodynamic injection (siphoning) at 25 cm height for 30 s. The method illustrated good linearity over the concentration range of 5.00 to 200 mg/L of for glucosamine (R ² = 0.9994) and 1.00 to 100 mg/L for Ca²⁺ (R ² = 0.9994). Under the optimum conditions, the detection limit of glucosamine was 1.00 mg/L, while that of Ca²⁺ was 0.05 mg/L. The validated method successfully analyzed glucosamine and Ca²⁺ in seven dietary supplement samples. The measured concentrations were generally in line with the values of label claims and with cross-checking data from reference methods (HPLC and ICP-OES).

A Review of Analytical Methods for Codeine Determination

Codeine is derived from morphine, an opioid analgesic, and has weaker analgesic and sedative effects than the parent molecule. This weak opioid is commonly used in combination with other drugs for over-the-counter cough relief medication. Due to the psychoactive properties of opioid drugs, the easily obtained codeine often becomes subject to misuse. Codeine misuse has emerged as a concerning public health issue due to its associated adverse effects such as headache, nausea, vomiting, and hemorrhage. Thus, it is very important to develop reliable analytical techniques to detect codeine for both quality control of pharmaceutical formulations and identifying drug misuse in the community. This review aims to provide critical outlooks on analytical methods applicable to the determination of codeine.