Field-amplified Sample Injection Research Articles

Trace analysis of acetylcholinesterase inhibitors with antipsychotic drugs for Alzheimer’s disease by capillary electrophoresis with on column field-amplified sample injection

A simple and sensitive capillary zone electrophoresis (CZE) with UV detection (214 nm) was developed and validated for the simultaneous determination of the acetylcholinesterase inhibitors (AChEI), donepezil, and rivastigmine, with antipsychotic drugs in plasma. A sample pretreatment by liquid-liquid extraction and subsequent quantification by CZE with field-amplified sample injection (FASI) was used. The optimum separation for these analytes was achieved in <20 min at 25 °C with a fused-silica capillary column of 60.2 cm × 50 μm I.D. (effective length 50 cm) and a run buffer containing 120 mM phosphate (pH 4.0) with 0.1 % γ-cyclodextrin, 40 % methanol (MeOH), and 0.02 % polyvinyl alcohol as a dynamic coating to reduce analytes' interaction with the capillary wall. Using phenformin as an internal standard (40.0 ng/mL), the linear ranges of the proposed method for the simultaneous determination of donepezil, rivastigmine, aripiprazole, quetiapine, risperidone, clozapine, ziprasidone, and trazodone were over the range 4.0-80.0 ng/mL, and olanzapine was over the range 1.0-20.0 ng/mL. The method was applied for concentrations monitoring of AChEIs and antipsychotic drugs in ten Alzheimer's disease patients with behavioral and psychological symptoms of dementia after oral administration of the commercial products.

Incorporation of polyamidoamine sweeping and electrokinetic supercharging for in-line DNA fragment preconcentration

We report an approach for in-line preconcentration of DNA fragments using dendritic polyamidoamine generation 2.0 (PAMAM G 2.0) as sweeping agent. During the experiment, a plug of PAMAM G 2.0 was hydrodynamically injected first, followed by field-amplified sample injection (FASI) of DNA fragments, which were concurrently swept by PAMAMs via DNA–PAMAM complexation. Then, a segment of releasing agent, sodium dodecyl sulfate (SDS), was hydrodynamically introduced and subsequently electrophoretically driven to interact with the DNA–PAMAM complexes, forming more stable supramolecular SDS–PAMAM complexes and releasing the initially bound DNA fragments. The excess dodecyl sulfate anion also acted as terminating electrolyte in the separation, thereby the DNA fragments were enriched by the joint effects of FASI, sweeping and transient isotachophoresis. We term the approach PAMAM sweeping–electrokinetic supercharging (EKS). Because the mobility of the DNA–PAMAM complex was very low, the proposed method allowed long-time sample injection without notable loss in separation efficiency. Under the optimum conditions, the PAMAM sweeping–EKS strategy improved the detection sensitivity of DNA fragments by more than 30 folds relative to the conventional FASI. Moreover, due to the sweeping process incorporated, the approach can be applied to enrichment of DNA fragments in highly saline matrix.

Different strategies for the preconcentration and separation of parabens by capillary electrophoresis

Several strategies, namely, large volume sample stacking (LVSS), field-amplified sample injection (FASI), sweeping, and in-line SPE-CE, were investigated for the simultaneous separation and preconcentration of a group of parabens. A BGE consisting of 20 mM sodium dihydrogenphosphate (pH 2.28) and 150 mM SDS with 15% ACN was used for the separation and preconcentration of the compounds by sweeping, and a BGE consisting of 30 mM sodium borate (pH 9.5) was used for the separation and preconcentration of the compounds by LVSS, FASI, and in-line SPE-CE. Several factors affecting the preconcentration process were investigated in order to obtain the maximum enhancement of sensitivity. The LODs obtained for parabens were in the range of 18-27, 3-4, 2, and 0.01-0.02 ng/mL, and the sensitivity evaluated in terms of LODs was improved up to 29-, 77-, 120-, and 18,400-fold for sweeping, LVSS, FASI, and in-line SPE-CE, respectively. These preconcentration techniques showed potential as good strategies for focusing parabens. The four methods were validated with standard samples to show the potential of these techniques for future applications in real samples, such as biological and environmental samples.

Simultaneous determination of four β2-agonist residues in pig feed and urine by capillary electrophoresis with field amplified sample injection and electrochemiluminescent detection

A novel method for simultaneous determination of clenbuterol (CLB), terbutaline (TER), salbutamol (SAL), and procaterol (PRO) was proposed based on capillary electrophoretic (CE) separation and electrochemiluminescent (ECL) detection. Matrix solid phase dispersion (MSPD) and ion exchange coupled with mesoporous nanocarbon adsorption were adopted to pretreat solid and aqueous samples, respectively. The sensitivity was enhanced by about 9-fold due to the online stacking via field amplified sample injection. The conditions for CE separation and ECL detection were investigated in detail. The four β2-agonists were baseline separated under the optimum conditions within 10 min. The linear ranges were 0.25–10.00 μmol L−1 with detection limits (S/N = 3) of 0.081, 0.076 and 0.034 μmol L−1 for CLB, TER and SAL, respectively, and 0.5–20.00 μmol L−1 for PRO with a detection limit of 0.12 μmol L−1. The developed method was successfully applied to determine the four β2-agonists in real samples, offering average recoveries ranging from 88.9% to 107.1% for pig feed, and from 86.7% to 109.1% for pig urine.

Field-amplified sample injection for the determination of isonicotinamide and nicotinamide in whitening cosmetics and supplemented foodstuffs by MEKC

A new micellar electrokinetic capillary chromatography (MEKC) method combined with field-amplified sample injection (FASI) has been developed for the analysis of isonicotinamide and nicotinamide in whitening cosmetics and supplemented foodstuffs. Parameters affecting FASI preconcentration and MEKC separation were optimized systematically. Compared with direct MEKC, the sensitivity of FASI-MEKC was improved by 12.8- and 9.8-fold for isonicotinamide and nicotinamide, respectively. The detection limits (LODs) of isonicotinamide and nicotinamide were 0.051 μg mL−1 and 0.069 μg mL−1, respectively, with RSD (intraday) < 4.9% (n = 7, c = 0.5 μg mL−1) and RSD (interday) < 6.4% (n = 5, c = 0.5 μg mL−1). The proposed method was successfully applied in determination of isonicotinamide and nicotinamide in whitening cosmetics and supplemented foodstuffs with acceptable recoveries of 84.7–108.4%.

Simultaneous Determination of Pyridine-Triphenylborane Anti-Fouling Agent and Its Degradation Products in Paint-Waste Samples Using Capillary Zone Electrophoresis with Field-Amplified Sample Injection

We proposed a capillary zone electrophoresis (CZE) procedure using field-amplified sample injection (FASI) for the simultaneous determination of pyridine-triphenylborane (PTPB) and its degradation products: diphenylborinic acid (DPB), phenylboronic acid (MPB), and phenol. The LODs for PTPB, DPB, MPB, and phenol were, respectively, 0.85, 0.88, 44, and 28 μg L(-1). The RSDs (n = 4) for the analytes listed above were in respective ranges of 6.2 - 14, 5.9 - 10, and 0.49 - 0.62% for the peak area, peak height, and migration time. The compounds were extracted from paint-waste samples collected from shipyards using a siliga-gel column. The extract was dissolved with acetonitrile containing 1% (v/v) pyridine. The samples were then analyzed using CZE, revealing respective concentrations of 0.076 - 0.53, 0.015 - 0.36, 1.7 - 22, and 1.2 - 13 μg g(-1). The proposed FASI-CZE method is a simple and promising procedure that is expected to be useful for the determination of PTPB and its degradation products in paint wastes.

Dispersive liquid–liquid microextraction prior to field-amplified sample injection for the sensitive analysis of 3,4-methylenedioxymethamphetamine, phencyclidine and lysergic acid diethylamide by capillary electrophoresis in human urine

A novel capillary zone electrophoresis (CZE) with ultraviolet detection method has been developed and validated for the analysis of 3,4-methylenedioxymethamphetamine (MDMA), lysergic acid diethylamide (LSD) and phencyclidine (PCP) in human urine. The separation of these three analytes has been achieved in less than 8min in a 72-cm effective length capillary with 50-μm internal diameter. 100mM NaH2PO4/Na2HPO4, pH 6.0 has been employed as running buffer, and the separation has been carried out at temperature and voltage of 20°C, and 25kV, respectively. The three drugs have been detected at 205nm. Field amplified sample injection (FASI) has been employed for on-line sample preconcentration. FASI basically consists in a mismatch between the electric conductivity of the sample and that of the running buffer and it is achieved by electrokinetically injecting the sample diluted in a solvent of lower conductivity than that of the carrier electrolyte. Ultrapure water resulted to be the better sample solvent to reach the greatest enhancement factor. Injection voltage and time have been optimized to 5kV and 20s, respectively. The irreproducibility associated to electrokinetic injection has been correcting by using tetracaine as internal standard. Dispersive liquid–liquid microextraction (DLLME) has been employed as sample treatment using experimental design and response surface methodology for the optimization of critical variables. Linear responses were found for MDMA, PCP and LSD in presence of urine matrix between 10.0 and 100ng/mL approximately, and LODs of 1.00, 4.50, and 4.40ng/mL were calculated for MDMA, PCP and LSD, respectively. The method has been successfully applied to the analysis of the three drugs of interest in human urine with satisfactory recovery percentages.

Determination of nitrocellulose by capillary electrophoresis with laser-induced fluorescence detection

The industrial application of nitrocellulose depends on its nitrogen content. When nitrocellulose presents high nitrogen content is used in the manufacture of explosives whereas nitrocellulose with low nitrogen content is used to make a wide range of daily and non-explosive products (e.g. cigarettes, paints, lacquers). This fact makes really important to develop a method for the determination and discrimination of nitrocellulose samples. This work reports, for the first time, the qualitative determination of nitrocellulose previously derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS) by capillary electrophoresis (CE-LIF) with laser-induced fluorescence detection (CE-LIF). APTS-labeled nitrocellulose was determined in lowly and highly nitrated nitrocellulose samples present in collodions and smokeless gunpowders, respectively, after their pulverization in liquid nitrogen. The method described enables the visual discrimination of different nitrocelluloses on the basis of the different electrophoretic profiles obtained, and provides a useful tool to determine nitrocellulose. Additionally, the use of field-amplified sample injection (FASI) enabled enhanced sample detection, which made it possible to determine nitrocellulose contained in ∼15μg of gunpowder.

Simultaneous detection of antibacterial sulfonamides in a microfluidic device with amperometry

A highly sensitive and robust method for simultaneous detection of five sulfonamide drugs is developed by integrating the preconcentration and separation steps in a microfluidic device. An ampetrometry is performed for the selective detection of sulfonamides using an aluminum oxide–gold nanoparticle (Al2O3–AuNPs) modified carbon paste (CP) electrode at the end of separation channel. The preconcentration capacity of the channel is enhanced by using the field amplified sample stacking and the field amplified sample injection techniques. The experimental parameters affecting the analytical performances, such as pH, % of Al2O3, volume of AuNPs, buffer concentration, and water plug length are optimized. A reproducible response is observed during the multiple injections of samples with RSDs<4%. The calibration plots are linear with the correlation coefficient between 0.991 and 0.997 over the range between 0.01 and 2025pM. The detection limits of five drugs are determined to be between 0.91 (±0.03) and 2.21 (±0.09)fM. The interference effects of common biological compounds are also investigated and the applicability of the method to the direct analysis of sulfonamides in real meat samples is successfully demonstrated. Long term stability of the modified electrode was also investigated.

On‐line preconcentration of perfluorooctanoic acid and perfluorooctanesulfonic acid by nonaqueous capillary electrophoresis

Separation of major environmental pollutants as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by capillary electrophoresis is reported for the first time. It is not possible to resolve the solutes in an aqueous media. However, the use of methanol and acetonitrile as the background electrolyte (BGE) solvents allowed their rapid separation in an uncoated capillary. A major effort was put into BGE optimization in respect to both separation efficiency and detection for further on-line preconcentration. 5 mmol.L⁻¹ naphthalene-1-sulfonic acid and 10 mmol.L⁻¹ triethylamine dissolved in ACN/MeOH (50:50 v/v) provided best separation and detection conditions. Next, the large-volume sample stacking and the field-amplified sample injection were applied and compared. Large-volume sample stacking improved limits of detection (LODs) with regard to the standard injection by 69 times for PFOA and 143 times for PFOS with LODs of 280 and 230 nmol.L⁻¹, respectively. Field-amplified sample injection improved LODs 624 times for PFOAand 806 times for PFOS with LODs 31 and 40 nmol.L⁻¹, respectively. Both preconcentration methods showed repeatabilities of migration times less than 1.2% RSD intraday and 6.6% RSD interday. The method was applied on PFOA and PFOS analysis in a sample of river water treated with solid-phase extraction, which further improved LOD toward 5.6 × 10⁻¹⁰ mol.L⁻¹ for PFOS and 6.4 × 10⁻¹⁰ mol.L⁻¹ for PFOA and allows the method to be used for river water contamination screening or decomposition studies.

Ultrasound‐assisted emulsification microextraction for the determination of ephedrines in human urine by capillary electrophoresis with direct injection. Comparison with dispersive liquid–liquid microextraction

Ultrasound-assisted emulsification microextraction and dispersive liquid-liquid microextraction were compared for extraction of ephedrine, norephedrine, and pseudoephedrine from human urine samples prior to their determination by capillary electrophoresis. Formation of a microemulsion of the organic extract with an aqueous solution (at pH 3.2) containing 10% methanol facilitated the direct injection of the final extract into the capillary. Influential parameters affecting extraction efficiency were systematically studied and optimized. In order to enhance the sensitivity further, field-amplified sample injection was applied. Under optimum extraction and stacking conditions, enrichment factors of up to 140 and 1750 as compared to conventional capillary zone electrophoresis were obtained resulting in limits of detection of 12-33 μg/L and 1.0-2.8 μg/L with dispersive liquid-liquid microextraction and ultrasound-assisted emulsification microextraction when combined with field-amplified sample injection. Calibration graphs showed good linearity for urine samples by both methods with coefficients of determination higher than 0.9973 and percent relative standard deviations of the analyses in the range of 3.4-8.2% for (n = 5). The results showed that the use of ultrasound to assist microextraction provided higher extraction efficiencies than disperser solvents, regarding the hydrophilic nature of the investigated analytes.

A new nonpeptide substrate of human sirtuin in a capillary electrophoresis‐based assay. Investigation of the binding mode by docking experiments

Sirtuins are nicotinamide dinucleotide-dependent class III histone deacetylases catalyzing various physiological processes involved in cell proliferation, differentiation, apoptosis, and ageing. This makes them attractive targets in drug research. In order to simplify sirtuin substrates for assay development, two N(ɛ)-acetyllysine derivatives, N(ɛ)-acetyl-N(α)-(4-methyl-7-methoxycoumarin)lysine amide, and N(ɛ)-acetyl-N(α)-(4-methyl-7-methoxycoumarin)lysine methyl ester were synthesized and evaluated as substrates for human SIRT1 in a capillary electrophoresis-based enzyme assay. Substrate, deacetylated product, and the coproduct nicotinamide were separated in a 200 mM phosphate/Tris buffer at pH 2.85. Field-amplified sample injection was employed to achieve sufficient assay sensitivity. While the ester derivative was not recognized by the enzyme, the amide substrate was effectively converted to the deacetylated product. The assay was subsequently validated with respect to range, linearity, limit of detection, and limit of quantification. Michaelis-Menten kinetic parameters, K(m) = 83 μM and V(max) = 6.8 μM/min were determined. The applicability of the assay for inhibitor screening was demonstrated using the known inhibitors sirtinol and the suramin derivate NF258. Resveratrol did not increase the deacetylation rate at concentrations of up to 200 μM. Docking experiments revealed the necessity of an amide function at the C-terminus of nonpeptide substrates while more structural freedom is tolerated at the N-terminus of N(ɛ) -acetyllysine.

Sample stacking by field‐amplified sample injection and sweeping for simultaneous analysis of acidic and basic components in clinic application

In this study, online sample concentration method, which coupled field-amplified sample injection (FASI) and sweeping technology with micellar electrokinetic chromatography (MEKC), was used to detect and analyze acidic and basic components in a single run. In order to concentrate the acidic and basic components simultaneously in a single run sweeping step, a combination of successive anion- and cation-selective injections were used. Before sample loading, a rinse buffer containing 50 mM Tris buffer (pH 3) with 41% MeOH and 0.1% polyethylene oxide (PEO) was injected in order to suppress the electroosmotic flow (EOF). Sample loading of anionic components was achieved by electrokinetic injection at a negative voltage of -2.5 kV for 80 s, and then the cationic components were injected at a positive voltage of +5 kV for 120 s. Finally, sweeping with SDS micelles from the separation buffer (25 mM Tris buffer with 60 mM SDS, pH 3) was performed at a negative voltage of -20 kV. This capillary electrophoretic methodology was applied to the quantification of acidic and basic drugs in commercial tablets and in plasma samples. The precision and accuracy of the proposed method at different concentrations ranging from high, medium, to low were evaluated on spiked plasma samples. The intra and interday precision and accuracy values at three concentrations were all below 6.1%. The method was also successfully applied to monitor the tested drugs in the plasma of nine elderly cardiovascular and/or Alzheimer's disease patients after oral administration of the commercial products.

Simultaneous analysis of cocaine and its metabolites in urine by capillary electrophoresis–electrospray mass spectrometry using a pressurized liquid junction nanoflow interface

A new method for the simultaneous separation of cocaine and four metabolites in urine by CE-ESI-MS via a pressurized nanoliquid junction interface was developed. The resolution of cocaine, cocaethylene, benzoylecgonine, norcocaine, and ecgonine methyl ester was achieved in a polyvinyl-alcohol-coated capillary with 75 μm id × 50 cm total length, using a 15 mM ammonium formate electrolyte solution (pH 9.5) in less than 15 min. In addition, to enhance sensitivity, a field-amplified sample injection (FASI) was evaluated in terms of injection time and sample solvent composition. The limits of detection achieved with the FASI method ranged from 1.5 to 10 ng/mL for all the compounds. The detection of the studied compounds was performed using an ion-trap mass spectrometer in a positive ionization mode. A mixture of methanol:water (80:20 v/v) containing 0.1% v/v of formic acid was employed as spray liquid and delivered at ~200 nL/min. Under optimal CE-MS conditions, linearity was assessed in the concentration range of interest for all analytes with correlation coefficients r² ≥ 0.9913. Intra- and inter-day precision provided a relative standard deviation lower than 1.54% for migration times and lower than 12.15% for peak areas. Finally, urine samples, spiked with the standard mixture, were extracted using a solid-phase extraction procedure and injected under FASI conditions, providing recoveries from 80% to 94% for all analytes.

Analysis of phenolic acids and their antioxidant activity by capillary electrophoresis-mass spectrometry with field-amplified sample injection

In this study, a capillary electrophoresis-mass spectrometry (CE-MS) method with field-amplified sample stacking was developed to analyze and detect four hydrophilic active components (danshensu, salvianolic acid B, caffeic acid and lithospermic acid) present in many plant-derived samples, and to evaluate their antioxidant ability. The assay was performed on an uncoated fused-silica capillary of 95 cm × 50 μm I.D. and a positive voltage of 27 kV was applied. The sample was injected under pressure of 50 mbar for 3–300 s and the temperature of capillary was kept 25 °C. Sheath liquid constituted of 5 mM ammonium acetate in methanol solution, flowing at 4 μL min−1, and was supplied to the CE-electrospray interface. The effects of nebulizer gas pressure, the flow rate and temperature of the drying gas, sheath liquid composition and flow rate, and sample injection length were optimized in order to obtain better performance. Utilizing the preconcentration technique, the sensitivity was enhanced by approximately 30–50 fold in terms of limits of detection compared to common hydrodynamic injection without interference from matrix coextractives. The phenolic antioxidant abilities were also determined by simple and accurate free radical spiking test. Furthermore, the method has been successfully applied to a danshen sample.

Rapid, Simple and Ultrasensitive Analysis of Paraquat in Drinking Water by Field-Amplified Sample Injection Combined with Pressure-Assisted Capillary Zone Electrophoresis

Rapid, Simple and Ultrasensitive Analysis of Paraquat in Drinking Water by Field-Amplified Sample Injection Combined with Pressure-Assisted Capillary Zone Electrophoresis

Solid‐phase extraction‐field‐amplified sample injection coupled with CE‐ESI‐MS for online pre‐concentration and quantitative analysis of brain‐gut peptides

In order to improve the sensitivity of CE-ESI-MS for the analysis of brain-gut peptides, a solid-phase extraction combined with field-amplified sample injection was used for the pre-concentration of the brain-gut peptides. Compared with the conventional pressure injection method, the sensitivity in the detection of brain-gut peptides was improved more than 100-fold. The possible factors affecting sample stacking, such as the sample matrix, the composition and the length of the water column, the types and the volumes of eluent, have been investigated in detail. Under the optimum conditions, the detectable concentration of brain-gut peptides was found to be as low as 0.02 μM. A linear response concentration for the detection was developed in the range of 0.08-25 μmol/L. A real sample of human cerebrospinal fluids, which was spiked with brain-gut peptides, was also examined in order to evaluate the reliability of the proposed approach. The recovery of the method was in a range from 69.2 to 85.4%. The method was found to be reliable, accurate and potentially applicable for clinical drug analysis.

High‐sensitivity capillary and microchip electrophoresis using electrokinetic supercharging

Electrokinetic supercharging (EKS) is considered as one of the most powerful online preconcentration techniques in electrophoresis. It combines the efficient preconcentration power of field-amplified sample injection and the exceptional selective nature of transient isotachophoresis. It has a wide range of applications to different types of analytes ranging from small ions to large proteins and DNA fragments. This comprehensive review--up to date--provides listing for all the works, developments, and advances in EKS. The review will pay particular attention to innovations, new methodologies for manipulation, challenges for improving the detection sensitivity, and various applications of EKS in capillaries and microchips.

Pressure-assisted electrokinetic supercharging for the enhancement of non-steroidal anti-inflammatory drugs

Electrokinetic supercharging (EKS) combines field-amplified sample injection with transient isotachophoresis (tITP) to create a powerful on-line preconcentration technique for capillary electrophoresis. In this work, EKS is enhanced with a positive pressure (pressure-assisted EKS, or PA-EKS) during injection to improve stacking of non-steroidal anti-inflammatory drugs (NSAIDs). Several parameters, including buffer composition and concentration, terminating electrolyte, organic modifier, and injection voltage and injection time of both terminating electrolyte and sample were optimized. Detection limits for seven NSAIDs were determined and an enhancement in sensitivity of almost 50,000-fold was obtained. The PA-EKS method has the potential to be a simple MS compatible preconcentration method to improve the sensitivity of CE.

Separation and simultaneous detection of anticancer drugs in a microfluidic device with an amperometric biosensor

A simple and highly sensitive method for simultaneous detection of anticancer drugs is developed by integrating the preconcentration and separation steps in a microfluidic device with an amperometric biosensor. An amperometric detection with dsDNA and cardiolipin modified screen printed electrodes are used for the detection of anticancer drugs at the end of separation channel. The preconcentration capacity is enhanced thoroughly using field amplified sample stacking and field amplified sample injection techniques. The experimental parameters affecting the analytical performances, such as pH, temperature, buffer concentration, water plug length, and detection potential are optimized. A reproducible response is observed during multiple injections of samples with a RSD <5%. The calibration plots are linear with the correlation coefficient between 0.9913 and 0.9982 over the range of 2–60 pM. The detection limits of four drugs are determined to be between 1.2 (±0.05) and 5.5 (±0.3) fM. The applicability of the device to the direct analysis of anticancer drugs is successfully demonstrated in a real spiked urine sample. Device was also examined for interference effect of common chemicals present in real samples.