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A simple, rapid, and sensitive technique for measuring mirtazapine and its metabolites enantiomers in human fluids, such as urine and serum, was developed by applying ultrasound-enhanced and surfactant-assisted dispersive liquid-liquid microextraction (USA-DLLME) integrated with poly(diallyldimethylammonium chloride) (PDDAC)-mediated stacking in capillary electrophoresis (CE). The parameters that affect extraction and stacking performance, such as the extraction volume, surfactant types, surfactant concentrations, salt additives, extraction time, solution pH, and background electrolytes, were comprehensively studied and optimized to achieve optimal detection performance. Under optimal extraction conditions (injection of 120 µL of C

We developed a triple-readout probe for colorimetric, fluorescent, and fluorescence-lifetime sensing of alkaline phosphatase (ALP) through the hydrolyzed ascorbic acid phosphate (AAP)-mediated formation of silver nanoparticles (AgNPs) on Ag

This study developed a new method for the extraction, clean up, chiral separation, and determination of five pairs of phenothiazine drugs using ultrasound-assisted dispersive liquid–liquid microextraction combined with capillary electrophoresis (CE). A mixture of extraction solvent (30 μL of CHCl3) and dispersive solvent (200 μL of tetrahydrofuran) was rapidly injected using a syringe, which formed tiny cloudy droplets of an organic extractant that dispersed entirely into the aqueous phase. After centrifuging, the sediment phase of volume 60 ± 0.5 μL was transferred into a small vial and evaporated to dryness. The residue was reconstituted in 5 μL of aqueous solution, analyzed using CE and then successfully baseline separated in 6 min using a background electrolyte composed of 5 mM hydroxypropyl-γ-cyclodextrin, 0.9% poly(diallyldimethylammonium chloride), and 150 mM tris-formate at pH 3.0. The developed method was linear in the 0.01–10 μM range, with R2 ≥ 0.9956 for all target analytes. The limit of detection (S/N = 3) and the limit of quantification (S/N = 10) were 2–4 nM and 10 nM, respectively. Excellent repeatability (RSD ≤ 5.5%, n = 5) was achieved. The recoveries of all phenothiazine drugs from urine were in the 83.5–104.0% range. The advantages of this approach were low cost, versatility, simplicity, and high sensitivity.

A sensitive technique for the measurement of warfarin and its metabolic enantiomers in human fluids such as urine and serum technique was developed by applying ultrasound-assisted dispersive liquid-liquid microextraction linked with poly(ethylene oxide)-mediated stacking in capillary electrophoresis. The parameters that influence extraction and stacking performance-the type of the extraction and dispersive solvents and their volume, extraction time, salt additives, sample matrix, solution pH, and the composition of background electrolyte stacking-were carefully studied and optimized based on the considering of obtaining the best detection sensitivity. Under the optimal extraction (30 μL C2H2Cl4 and 200 μL tetrahydrofuran in 1 mL of sample solution) and separation (0.5% PEO, 200 mM Tris-borate, pH 8.5, and 5 mM dimethyl-β-cyclodextrin) conditions, the enrichment factors of D-/L-warfarins and D-/L-7-OH warfarins covered from 1758 to 1859 and their limits of detection ranged from 0.34 to 0.38 nM. Calibration-related results exhibited acceptable linearity with the coefficient of determination higher than 0.99; the relative standard deviations of the peak area were determined to 4.1%–6.3% (n = 3). The recovery of four separated analytes spiked in samples of urine and serum was found to be 93%–110% and 95%–109%, respectively. We revealed that ultrasound-assisted dispersive liquid-liquid microextraction with poly(ethylene oxide)-mediated stacking in capillary electrophoresis could be a prompt and practical method for quantifying the levels of warfarin and its metabolic enantiomers in real-world samples, especially in biological fluids.

Citrate-capped gold nanoparticles (AuNPs) modified with thrombin-binding aptamer are often implemented for colorimetric, fluorescent, and electrochemical detection of thrombin in an aqueous solution. However, researchers have rarely explored the application of fibrinogen-modified AuNPs (F-AuNPs) for thrombin sensing. We present a simple, inexpensive, sensitive, and selective probe for colorimetric assay of thrombin through combining thrombin-induced inclusion of F-AuNPs into Fibrin and F-AuNPs-catalyzed reduction of 4-nitrophenol with an excess amount of NaBH4. Considering that fibrinogen stabilized citrate-capped AuNPs against a high-ionic-strength buffer, F-AuNPs efficiently catalyzed the NaBH4-mediated decrease of yellow 4-nitrophenol to colorless 4-aminophenol. The presence of thrombin converted fibrinogen into fibrin on the nanoparticle surface, leading to the inclusion of nanoparticles into fibrin. The formation of fibrin inhibited that the AuNPs catalyzed the NaBH4-mediated reduction of 4-nitrophenol. Consequently, the color of the solution gradually varied from colorless to yellow with increasing thrombin concentration. The proposed system was shown to be accurate in the quantification of small differences in the concentration of human thrombin over the range of 4–60 pM. The lowest detectable concentration of human thrombin by the naked eye was as low as 16 pM. We demonstrated the practical application of the proposed system in quantifying 1–15 nM human thrombin in human plasma.

Pesticides are a family of non-biodegradable chemical compounds which widely used in agriculture to control pests and increase yield production. However, overuse or abuse of pesticides and their metabolites may cause potential toxicity for the environment as well as human health and all other living organisms, even at deficient concentrations. Consequently, the development of sensors for monitoring these compounds is significant. Recently, nanoparticles-based sensors have been extensively employed as a potential alternative or complementary analytical tool to conventional detection methods for pesticides. Among them, gold nanoparticles (AuNPs) owing to their unique optical properties have been developed as smart sensors with high selectivity, sensitivity, simplicity, and portability. These comprehensive reviews have summarized various studies performed based on different detection strategies, i.e., colorimetric, fluorescence, surface-enhanced Raman scattering, and electrochemical, using AuNPs as sensing probes for pesticide analysis in various matrices. Additionally, the current challenges and future trends for developing novel AuNPs-based sensors for the detection of pesticides are also discussed.

This study developed a sensitive method involving capillary electrophoresis (CE) coupled with ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugs at nanomolar concentration levels. The method consists of hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector and poly (diallyldimethylammonium chloride) (PDDAC)-based CE. Five pairs of d,l-phenothiazines were baseline separated using a background electrolyte containing 0.9% PDDAC, 5 mM Hp-γ-CD, and 100 mM tris(hydroxymethyl)aminomethane (Tris)-formate (pH 3.0). The five pairs were successfully stacked on the basis of the difference in viscosity between the PDDAC-containing background electrolyte and the sample solution, with almost no loss of resolution. The combination of a solid-phase extraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazine enantiomers. Under optimal conditions, calibration graphs displayed the linear range between 6 and 1500 nM, with relative standard deviation values lower than 3.5% (n = 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-fold enhancement was achieved. The practicality of using the proposed method to determine five pairs of d,l-phenothiazines in urine is also validated, in which recoveries between recoveries of all phenothiazines from urine ranged from 89% to 101%. Keywords: Capillary electrophoresis, Chiral separation, On-line concentration, Phenothiazine, Solid phase extraction

Separation techniques are promising for the detection of adamantane analogs with various functional groups. The derivatization of adamantane analogs with chromophores or fluorophores should be conducted using a separation technique combined with a common ultraviolet–visible or fluorescence detector. However, limited research has been conducted on underivatized adamantane analogs. Therefore, we present a highly rapid and sensitive method for detecting underivatized adamantane analogs by integrating ultrasound-assisted dispersive liquid–liquid microextraction (UADLLME), field-amplified sample stacking (FASS)-related capillary electrophoresis (CE), and capacitively coupled contactless conductivity detection (C4D). In the proposed system, UADLLME is used for sample clean up and analyte enrichment, whereas FASS-related CE provides on-line concentration of underivatized adamantane analogs during CE separation. A mixture of memantine (MT), amantadine (AT), and rimantadine (RT) was separated at baseline within 8 min through the application of optimized UADLLME (mixing extraction solvent, 50 μL of 1,1,2,2-tetrachloroethane (C2H2Cl4) and dispersive solvent, 200 μL of acetonitrile; mixing solution was injected into 1 mL of the sample solution at pH 12.5), FASS (buffer, 1.5 M acetic acid; additive, 0.05 mM β-cyclodextrin; pH 2.5), and C4D (amplitude, 2 Vpp; frequency, 500 kHz). The calibration curve exhibited acceptable linearity, with a coefficient of determination higher than 0.99. The limits of detection (signal-to-noise ratio of 3) were estimated to be 0.9, 1.0, and 1.2 nM for MT, AT, and RT, respectively. The relative standard deviations of peak areas varied from 8.9% to 9.3% (n = 5), whereas the sensitivity improvement of three underivatized adamantane analogs ranged from 1342 to 1766. The feasibility and accuracy of the present method for the determination of MT, AT, and RT in human serum and urine was satisfactorily confirmed by the excellent recovery and relative error. The proposed method exhibited high enrichment factors and offers excellent precision, high accuracy, and a short analysis time.

A rapid, simple, and sensitive technique for the quantitative detection of fluoxetine and norfluoxetine enantiomers in biological fluids was developed based on the combination of field-amplified sample stacking (FASS)–related capillary electrophoresis (CE) with ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME). The extraction efficiency of UA-DLLME was strongly related to extraction time, salt concentration, type of extraction and dispersion solvents, and volume of extraction and dispersion solvents. The extracted fluoxetine and norfluoxetine enantiomers in a mixture of 50% methanol and 50% deionized water were efficiently stacked using FASS and then separated using cyclodextrin-modified CE. Under optimal conditions of FASS (chiral selector, 3 mM trimethyl-β-cyclodextrin; and background electrolyte, 100 mM phosphate buffer) and UA-DLLME (extraction solvent, 200 μL of acetone; and dispersed solvent, 50 μL of C2H2Cl4 in 1 mL of the sample solution), the obtained enrichment factors of fluoxetine and norfluoxetine enantiomers reached approximately 2000. The linear ranges for the quantification of fluoxetine and norfluoxetine enantiomers were 0.3–150 and 0.6–150 nM, respectively. The relative standard deviations in peak areas and migration time for four analytes were less than 3.3% and 6.3%, respectively. The proposed system provided limits of detection (signal-to-noise ratio of 3) for four analytes corresponding to 0.1 nM. The precision and accuracy for urine and serum samples were less than 6.8 and 8.3%, respectively. These findings suggested that the proposed system exhibited a high potential for the reliable determination of fluoxetine and norfluoxetine enantiomers in clinical samples.

Dispersive liquid-liquid microextraction was combined with acetonitrile stacking in capillary electrophoresis for the identification of three selective serotonin reuptake inhibitors (citalopram, fluoxetine, and fluvoxamine) in human fluids such as urine and plasma. Parameters that affect the extraction and stacking efficiency, such as the type and volume of the extraction and disperser solvent, extraction time, salt addition for dispersive liquid-liquid microextraction, and sample matrices, pH, and concentration of the separation buffer for stacking, were investigated and optimized. Under optimum conditions, the enrichment factors were in the range of 1195-1441. Limits of detection ranged from 1.4 to 1.7 nM for the target analytes. Calibration graphs displayed satisfied linearity with R2 greater than or equal to 0.9978, and relative standard deviations of the peak area analysis were in the range of 2.9-5.0% (n = 3). The recoveries of all tricyclic antidepressant drugs from urine and plasma were in the range of 77-117 and 79-106%, respectively. The findings of this study show that dispersive liquid-liquid microextraction acetonitrile-stacking capillary electrophoresis is a rapid and convenient method for identifying tricyclic antidepressant drugs in urine and plasma.

Cyclic diadenylate monophosphate (c-di-AMP) and P1,P5-diadenosine-5′ pentaphosphate (Ap5A) have been determined to play important roles in bacterial physiological processes and human metabolism, respectively. However, few, if any, methods have been developed that use fluorescent sensors to sense c-di-AMP and Ap5A in the real world. To address this challenge, this study presents a fast, convenient, selective, and sensitive assay for quantifying c-di-AMP and Ap5A fluorescence based on the competitive binding of diadenosine nucleotides and a polyadenosine probe to coralyne. The designed probe consists of a 20-mer adenosine base (A20), a fluorophore unit at the 5′-end, and a quencher unit at the 3′-end. Through A2–coralyne–A2 coordination, coralyne causes a change in the conformation of A20 from that of a random coil to a folded structure, thus enabling the fluorophore to be close to the quencher. As a result, fluorescence quenching occurs between the two organic dyes. When the A20·coralyne probe encounters t...

Citrate-capped gold nanoparticles (AuNPs) modified with thrombin-binding aptamer are often implemented for colorimetric, fluorescent, and electrochemical detection of thrombin in an aqueous solution. However, researchers have rarely explored the application of fibrinogen-modified AuNPs (F-AuNPs) for thrombin sensing. We present a simple, inexpensive, sensitive, and selective probe for colorimetric assay of thrombin through combining thrombin-induced inclusion of F-AuNPs into Fibrin and F-AuNPs-catalyzed reduction of 4-nitrophenol with an excess amount of NaBH

A rapid, simple and sensitive method for the detection of piperazinyl phenothiazine drugs using dispersive liquid-liquid microextraction (DLLME) combined with field-amplified sample stacking (FASS) in CE was developed. Sensitivity parameters that affect the extraction and FASS efficiency, such as the type and volume of disperser solvent, extraction time, addition of salt, and efficiency of FASS, were investigated and optimized. Note that the conductivity ratio between BGE and sample zone was measured to be 2300. Under optimal extraction and stacking conditions, the calibration curve, which ranged from 0.3 to 160 ng/mL, demonstrated good linearity with a correlation coefficient r≧ 0.9900. The LODs of prochlorperazine (Pcp), trifluoperazine (Tfp), perphenazine (Ppa), and fluphenazine (Fpa) at an S/N of 3 were 0.1, 0.1, 0.07, and 0.08 ng/mL, respectively. An approximately 1000-fold to 2500-fold improvement in sensitivity was achieved for the four tested analytes compared to conventional CZE without DLLME. The recoveries of all phenothiazines in urine and plasma ranged from 85.7 to 107.6% and 95.6 to 105.4%, respectively. The proposed method was demonstrated to be a rapid and convenient method for the determination of four piperazinyl phenothiazine drugs in human urine and plasma.

High-speed capillary electrophoresis (CE) enables the simple, rapid, and inexpensive analysis of large sets of chiral samples in the pharmaceutical industry. Hence, we developed a novel method for separating enantiomers of d,L-phenothiazines simply and rapidly, based on using poly(diallyldimethylammonium chloride) (PDDAC) as an additive and hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector in capillary electrophoresis. Adding 0.9% PDDAC to the background electrolyte generated a stable, high, and reversed electroosmotic flow (EOF). Hp-γ-CD not only worked as a complexing agent to increase the chiral resolution between d,L-phenothiazines but also decreased the effective electrophoretic mobility of these drugs. Combining PDDAC and Hp-γ-CD as buffer additives enabled CE to achieve a high-speed enantioseparation of five pairs of d,L-phenothiazines. A decrease in capillary length and an increase in the intensity of the electric field further shortened the separation time. When the background electrolyte contained 0.9% PDDAC, 5mM Hp-γ-CD, and 75 mM formic acid (pH 3.0), enantioseparation of the d,L-phenothiazines was attained within 230 s by applying a capillary length of 32.5 cm and an electric field of 292 V cm(-1). The limit of detection (LOD) of the d,L-phenothiazines at a signal-to-noise ratio of 3 ranged from 2 to 8 μM. We demonstrated the feasibility of this method by detecting the five pairs of d,L-phenothiazines in urine samples.

Dispersive liquid-liquid microextraction was combined with acetonitrile stacking in capillary electrophoresis for the identification of three selective serotonin reuptake inhibitors (citalopram, fluoxetine, and fluvoxamine) in human fluids such as urine and plasma. Parameters that affect the extraction and stacking efficiency, such as the type and volume of the extraction and disperser solvent, extraction time, salt addition for dispersive liquid-liquid microextraction, and sample matrices, pH, and concentration of the separation buffer for stacking, were investigated and optimized. Under optimum conditions, the enrichment factors were in the range of 1195-1441. Limits of detection ranged from 1.4 to 1.7 nM for the target analytes. Calibration graphs displayed satisfied linearity with R

Nowadays, owing to the increasing population and the attempts to satisfy its needs, pesticides are widely applied to control the quantity and quality of agricultural products. However, the presence of pesticide residues and their metabolites in environmental samples is hazardous to the health of humans and all other living organisms. Thus, monitoring these compounds is extremely important to ensure that only permitted levels of pesticide are consumed. To this end, fast, reliable, and environmentally friendly methods that can accurately analyze dilute, complex samples containing both parent substances and their metabolites are required. Focusing primarily on research published since 2010, this review summarizes the use of various sample pretreatment techniques to extract pesticides from various matrices, combined with on-line preconcentration strategies for sensitivity improvement, and subsequent capillary electrophoresis analysis.

This paper presents on-line simultaneous concentration and separation of cationic and anionic neurochemicals by capillary electrophoresis (CE) with UV absorbance spectroscopy. Neurochemical stacking exploits differences in local electric field and viscosity between the sample zone and the background electrolyte (BGE). To achieve these discontinuous conditions for CE, neurochemicals were prepared in a solution containing 1 mM formic acid and 20% (v/v) acetonitrile (ACN). The capillary was filled with a solution of 500 mM Tris–borate (TB) and 10% (v/v) glycerol. The buffer vial contained 500 mM TB and 0.5% (v/v) polyethylene oxide (PEO). After injecting a large sample volume, PEO enters the capillary by electro-osmotic flow (EOF). Anionic neurochemicals stacked at the sample zone and PEO-containing BGE boundary. Simultaneously, cationic neurochemicals were concentrated at the boundary between the sample zone and the glycerol-containing BGE. The concentrated cationic neurochemicals were baseline separated in the presence of glycerol, mainly due to hydrogen bonding interactions between glycerol hydroxyl groups and the neurochemical's hydroxyl and amino groups. Under optimal stacking conditions, we observed the following: (a) the maximum sample injection volume was 720 nL; (b) the limit of detection for signal-to-noise ratio of 3 ranged from 14.7 to 313.4 nM; and (c) sensitivity enhancements compared to normal injection (15 nL) ranged from 116 to 281-fold. We evaluated the proposed method by the determination of neurochemicals in urine samples.

This study combines Tween 20-capped gold nanoparticles (Tween 20-AuNPs) with capillary electrophoresis (CE) for ultrasensitive detection of thiol-containing peptides, including glutathione (GSH), γ-glutamylcysteine (γ-GCS), and phytochelatin analogs. By forming Au S bonds, Tween 20-AuNPs can selectively extract and enrich these thiols from a complicated matrix. A Tween 20 capping layer not only suppresses nonspecific adsorption, but also enables NPs to disperse in a highly salinity solution. Dithiothreitol removes thiol-containing peptides from the NP surface through ligand exchange. The released peptides are selectively derivatized with o-phthaldialdehyde (OPA) to form tricyclic isoindole derivatives. Extraction efficiency of five thiol-containing peptides with Tween 20-AuNPs was highly reliable in the Tween 20-AuNP concentration, time of extraction and desorption thiols, and sample volume. After injecting a large sample volume, the OPA-derivatized peptides migrate against the electroosmotic flow (EOF) and enter the polyethylene oxide (PEO) zone. The sensitivity of these peptides was improved by stacking them at the boundary between the sample and PEO zones. As a result, limits of detection (LODs) for five peptides were down to 0.1–6 pM. Not only is the proposed method probably the first CE example for detecting dissolved thiols in seawater; it also has the lowest LODs for GSH, γ-GCS, and phytochelatins compared to other reported methods.

We describe the stacking and separation of d- and l-aspartic acid (Asp) by capillary electrophoresis (CE) with light-emitting diode-induced fluorescence detection (LEDIF). In the presence of cyanide, d- and l-Asp were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA) to form fluorescent derivatives prior to CE-LEDIF. The separation of NDA-derivatized d- and l-Asp was accomplished using a discontinuous system - buffer vials contained a solution of 0.6% poly(ethylene oxide) (PEO), 150 mM sodium dodecyl sulfate (SDS), and 60mM hydroxypropyl-β-cyclodextrin (Hp-β-CD), while a capillary was filled with a solution of 150 mM SDS and 60mM Hp-β-CD. The role of PEO, Hp-β-CD, and SDS is to act as a concentrating media, as a chiral selector, and as a pseudostationary phase, respectively. This discontinuous system could be employed for the stacking of 600 nL of NDA-derivatized d- and l-Asp without the loss of chiral resolution. The stacking mechanism is mainly based on the difference in viscosity between sample zone and PEO as well as SDS sweeping. The limits of detection at signal-to-noise of 3 for d- and l-Asp were down to 2.4 and 2.5 × 10(-10)M, respectively. Compared to normal sample injection volume (25 nL), this stacking approach provided a 100- and 110-fold improvement in the sensitivity of d- and l-Asp, respectively. This method was further applied for determining d- and l-Asp in cerebrospinal fluid, soymilk, and beer.

We report a novel means for chiral separation and stacking of amino acids by MEKC with LED-induced fluorescence detection. Naphthalene-2,3-dicarboxaldehyde, hydroxypropyl-beta-cyclodextrin (Hp-beta-CD), SDS, and poly(ethylene oxide) (PEO) serve as a derivatized agent, chiral selector, pseudostationary phase, and concentrated medium, in sequence. To improve speed, resolution, and stacking efficiency, the analysis of chiral amino acids was performed under discontinuous conditions--the capillary was filled with a solution of 100 mM Tris-borate, 150 mM SDS, and 50 mM Hp-beta-CD, whereas buffer vials contain 20 mM Tris-borate, 150 mM SDS, 50 mM Hp-beta-CD, and 0.5% w/v PEO. A solution of nonionic PEO enters the capillary with the help of EOF during the separation. Through interaction of SDS micelles/Hp-beta-CD and chiral amino acid, the negatively charged complexes migrated into the PEO solution and stacked at the boundary between the sample zone and the PEO solution. Compared with normal sample injection (10 nL sample volume), a several hundred-fold sensitivity improvement for chiral amino acids was obtained under the injection of 270 nL sample volume (30% of the capillary volume). Meanwhile, the LOD at S/N of three for DL-amino acids were in the range of 0.18-0.22 nM. The proposed method has been applied for the determination of DL-leucine in urine and plasma samples.

A micellar electrokinetic capillary chromatography (MEKC) method, using UV detection, was developed for the determination of polyphenols in Toona sinensis (Meliaceae); the procedure involved precipitation of polyphenols from the leaves of T. sinensis using methanol. The structures can be established with fifteen compounds including methyl gallate, gallic acid, kaempferol, quercitin, quercitrin, rutin, kaempferol-glucoside, catechin, epicatechin, stearic acid, palmitic acid, β-sitosterol, stigmasterol, β-sitosteryl-glucoside, and stigmasteryl-glucoside by spectroscopic analysis. However, there has been no investigation to quantitate the polyphenols that form T. sinensis. Thus, seven polyphenols of T. sinensis with UV absorbance, catechin (C), epicatechin (EC), methyl gallate (MG), rutin (R), gallic acid (G), quercitrin (Q), and kaempferol (K) were separated within 10 min with a 40 cm uncoated fused-silica column, with the RSD < 3% (migration times), voltage at 15 kV using this method. On-column detection was carried out at 254 nm. The detection limit of this method for all analytes ranged from 19.5 to 0.02 μM (RSD < 3.1%). The method provided a rapid and sensitive identification of polyphenols of interest in T. sinensis and is suitable for biological activity studies.

In this paper, we describe a method for analyzing large-volume protein samples using capillary electrophoresis in conjunction with laser-induced fluorescence detection (CE-LIF). To improve the stacking and separation efficiencies of proteins, we added either 0.01% sodium dodecyl sulfate (SDS) or 0.01% poly(ethylene oxide) (PEO) to the Tris-borate solutions (pH 10.0) used to prepare the protein samples. After injection of the large-volume samples (ca. 1.0 microL, 0.1 microM), the proteins migrate against the electroosmotic flow (EOF) and enter the PEO zone; this process causes them to slow and stack at the boundary between the PEO and sample zones. As a result, the limits of detection (LODs) at a signal-to-noise (S/N) of 3 for most proteins are sub-nM to several nM. For instance, the LOD (S/N = 3) for alpha-lactalbumin is 0.48 nM, which is an 84-fold sensitivity enhancement over the traditional method. By applying a short plug of 0.2% SDS prior to sample injection, a greater number of peaks, representing the microheterogeneity of the proteins, were resolved and the stacking efficiency of the proteins increased slightly. This method allowed us to detect 12 peaks when injecting a large volume of sample containing six model proteins (0.1 microM). We also analyzed the microheterogeneities of the proteins by using CE with UV-Vis absorption detection when injecting a large volume of sample containing six model proteins (1.0 microM) in the presence of a 1.0% SDS plug. The practical method is validated by the detection of human serum albumin in a urine sample, obtained from a healthy female, without sample pretreatment; its concentration was 0.18 microM. We further demonstrate the capability of this method to detect low amounts of proteins through the detection of 45 nM hemoglobin after injecting ca. 1.0 microL of ultradilute lysed red blood cells. The experimental results indicate that our proposed method has great potential for use in diagnosis and proteomics applications.

This paper describes a simple, sensitive, efficient, and rapid method for simultaneous analysis of biologically active amines and acids by capillary electrophoresis in conjunction with laser-induced native fluorescence detection (CE-LINF) using a diode pumped solid state nanolaser at 266 nm. In order to optimize resolution of the amines that were prepared in 10.0 mM formate-Tris (FT) solutions, 10.0 mM FT solutions with and without containing halides were used to fill the capillary and reservoirs, respectively. The electrophoretic mobilities of tryptamine (TA) and serotonin (5-HT) at pH 4.0 decrease with the increase in halide concentration (0-10.0 mM). Taken together with a great effect of iodide than other halides, we suggest that the formation of ion pairs is a main contributor for altering the migration of the amines. In order to simultaneously analyze the amines and their metabolites (acids) at low pH, a high bulk EOF is required. The analysis of 10 anlytes including amines and acids was completed within 12 min by CE-LINF using a capillary treated with 0.5M NaOH and then filled with 10.0 mM FT solutions (pH 4.0) containing 10.0 mM KCl prior to analysis. The limits of detection for TA and 5-hydroxyindole-3-acetic acid (5-HIAA) are 0.12 and 6.0 nM, respectively. The present method has been further validated by analyzing urine samples, with an RSD less than 3.1% (migration times) and 3.9% (concentration).

This paper describes the synthesis of core-shell CdSe/CdS quantum dots (QDs) in aqueous solution by a simple photoassisted method. CdSe was prepared from cadmium nitrate and 1,1-dimethylselenourea precursors under illumination for up to 3 h using a pulsed Nd:YAG laser at 532 nm. The effects that the temperature and the laser irradiation process have on the synthesis of CdSe were monitored by a series of experiments using the precursors at a Cd:Se concentration ratio of 4. Upon increasing the temperature (80-140 degrees C), the size of the CdSe QDs increases and the time required for reaching a maximum photoluminescence (PL) is shortened. Although the as-prepared CdSe QDs possess greater quantum yields (up to 0.072%) compared to those obtained by microwave heating (0.016%), they still fluoresce only weakly. After passivation of CdSe (prepared at 80 degrees C) by CdS using thioacetamide as the S source (Se:S concentration ratio of 1) at 80 degrees C for 24 h, the quantum yield of the core-shell CdSe/CdS QDs at 603 nm is 2.4%. Under UV irradiation of CdSe/CdS for 24 h using a 100-W Hg-Xe lamp, the maximum quantum yield of the stable QDs is 60% at 589 nm. A small bandwidth (W1/2 < 35 nm) indicates the narrow size distribution of the as-prepared core-shell CdSe/CdS QDs. This simple photoassisted method also allows the preparation of differently sized (3.7-6.3-nm diameters) core-shell CdSe/CdS QDs that emit in a wide range (from green to red) when excited at 480 nm.

A partially filling technique for the analysis of DNA markers and polymerase chain reaction (PCR) products by capillary electrophoresis in the presence of electroosmotic flow using polymer solutions is presented. Either after or prior to the sample injection, a plug of salts at high pH was hydrodynamically injected. During the separation, poly(ethylene oxide) (PEO) solution entered the capillary. We have found that the position, length, and composition of the plugs affect the sensitivity, resolution, and speed on the analysis of PhiX-174/HaeIII DNA restriction fragments or a DNA mixture (pBR 322/HaeIII digest, pBR 328/BglI digest and pBR 328/HinfI digest) with different degrees. Through careful evaluation of the impact of anions and cations on the analysis of DNA, we have suggested that the optimal condition is applying a plug consisting of 32 mM NaCl and 0.01 M NaOH at 30 cm height for 60 s after sample injection. In the presence of such a plug, PEO adsorption reduces, and thus the separation is faster, as well as the sensitivity improves. Using this condition, the analysis of a DNA mixture (injected at 30 cm for 360 s) containing ten different PCR products amplified after 17 cycles was complete in 25 min. About a 2000-fold improvement in the sensitivity was achieved when compared to that by a conventional method (10 s injection) without applying a plug.

We report concentration and separation of DNA in the presence of electroosmotic flow (EOF) using poly(ethylene oxide) (PEO) solution. DNA fragments migrating against EOF stacked between the sample zone and PEO solution. To maximize the injection volume, several factors, such as concentrations of Tris-borate (TB) buffer and PEO solution, capillary size, and matrix, were carefully evaluated. The use of 25 mM TB buffers, pH 10.0, containing suitable amounts (less than 10 mM) of salts, such as sodium chloride, sodium phosphate, and sodium acetate, to prepare DNA is essential for the concentration of large-volume samples. In the presence of salts, the peaks also became sharper and the fluorescence intensity of DNA complexes increased. Using 2.5% PEO and a 150 microm capillary filled with 400 mM TB buffer, pH 10.0, up to 5 microL DNA samples (phiX 174 RF DNA-HaeIII digest or the mixture of pBR 322/HaeIII, pBR 328/Bg/I, and pBR 328/HinfI digests) have been analyzed, resulting in more than 400-fold improvements in the sensitivity compared to that by conventional injections (ca. 36 nL). Moreover, this method allows the analysis of 3.5 microL PCR products amplified after 17 cycles without any sample pretreatment.

We have demonstrated on-line concentration and separation of DNA in the presence of electroosmotic flow (EOF) using poly(ethylene oxide) (PEO) solutions. After injecting large-volumes DNA samples, PEO solutions entered a capillary filled with 400 mM Tris-borate (TB) buffers by EOF and acted as sieving matrices. DNA fragments stacked between the sample zone and PEO solutions. Because sample matrixes affected PEO adsorption on the capillary wall, leading to changes in EOF, migration time, concentration, and resolving power varied with the injection length. When injecting phiX174 RF DNA-HaeIII digest prepared in 5 mM Tris-HCl buffer, pH 7.0, at 250 V/cm, peak height increased linearly as a function of injection volume up to 0.9 microl (injection time 150 s). The sensitivity improvement was 100-fold compare to that injected at 25 V/cm for 10 s (0.006 microl). When injecting 1.54 microl of GeneScan 1000 ROX, the sensitivity improvement was 265-fold. The sensitivity improvement was 40-fold when injecting 0.17 microl DNA sample containing pBR 322/HaeIII, pBR 328/BglI, and pBR 328/HinfI digests prepared in phosphate-buffered saline. This method allows the analysis of polymerase chain reaction (PCR) products amplified after 17 cycles when injecting 0.32 microl (at 30 cm height for 300 s). The total analysis time was shorter (91.6 min) than that (119.6 min) obtained from injecting PCR products after 32 cycles for 10 s.

We report the separation of polycyclic aromatic hydrocarbons (PAHs) using 0.1% poly(ethylene oxide) (PEO) in micellar electrokinetic chromatography (MEKC). In the presence of PEO, adsorption of PAHs on the capillary wall was reduced, leading to better resolution and reproducibility. Effects of tetrapentylammonium iodide (TPAI), dextran sulfate (DS), methanol, and sodium lauryl sulfate (SDS) on the separation of PAHs were elucidated. In terms of resolution and speed, DS, compared to TPAI, is a better additive for separation of PAHs. When using 0.1% PEO solution containing 45% methanol, 50 mM SDS, and 0.02% DS, separation of 10 PAHs containing 2 to 5 benzene rings was accomplished in less than 12 min at 15 kV in a commercial CE system. The method has also been tested for separating seven PAHs with high quantum yields when excited at 325 nm using a He-Cd laser. Unfortunately, separation of the seven PAHs was not achieved and sensitivity diminished under the same conditions. To optimize sensitivity, resolution and speed, a stepwise technique in MEKC has been proposed. The seven PAHs were resolved in 35 min at 15 kV when separation was performed in 0.1% PEO solution containing 35 mM SDS, 40% methanol and 0.02% DS for 2 min, and subsequently in 0.1% PEO solution containing 20 mM SDS, 50% methanol, and 0.02% DS.

Separations of small ions were carried out under nonequilibrated conditions using capillaries treated with NaOH, HCl, or tris(hydroxymethyl)aminomethane (Tris) prior to analysis. For separations of benzoic acid isomers or acids and amines under weakly acidic conditions, capillaries flushed with 0.1 M NaOH and subsequently with running buffers prior to analysis were used. Separations of six benzoic acid isomers were accomplished in 4 min in 1 mM phosphate buffers, pH 4.01, containing 2.5 mM hydroxypropyl-beta-cyclodextrin. Without additives, the separation of biological amines and acids were also achieved in 10 min at pH 4.01. Capillaries treated with 0.1 M HCl prior to analysis were tested in separations of six phenols in 5 mM Tris solutions at pH 7.0. As a result of small electrophoretic mobilities of phenols against a small electroosmotic flow, resolution was optimized. We also found that reproducibility was improved using capillaries treated with HCl. The relative standard deviations of migration mobility of phenols were less than 1%, which were smaller than those obtained using capillaries treated with 0.1 M NaOH or Tris.

We demonstrated DNA preconcentration and separation in the presence of electroosmotic flow (EOF) using poly(ethylene oxide) (PEO) solutions. After injecting large volumes of DNA samples into a capillary filled with free tris(hydroxymethyl)aminomethane (Tris)-borate (TB) buffers, PEO solutions entered the capillary by EOF and acted as sieving matrices. In contrast to conventional methods (in the absence of EOF), controlling the EOF was also useful for resolution optimization. We have found that PEO adsorption on the capillary wall was more pronounced when low ionic strength buffers were used. Thus, the EOF decreased with increasing injection length, which led to longer migration times and changes in resolution and stacking efficiency. All resolution values were higher than 1.5 when 1.0 microg/mL DNA samples were injected at 240 V/cm for 60 s (0.67 microL). In addition, as low as 0.015 microg/mL DNA samples (an about 66-fold increase in sensitivity) were detected when the injection was performed at 250 V/cm for 60 s.

Dynamic control and pH changes in the system have been utilized for the separation of twelve organic acids in less than 3 min using capillary electrophoresis (CE). High-speed separations of organic acids under weak acidic conditions indicate the existence of high electroosmotic flow (EOF) caused by treatment of the capillaries with 0.1 M NaOH before each separation. However, strong polyprotic acids can only be detected at higher applied voltages with shorter capillaries, since local EOF decreases significantly when migration time increases. In terms of resolution and speed, the optimal voltage is around 20 kV in 22.5-cm capillaries. The effects of the electric field strength and capillary length on the resolution of organic acids have been investigated to show the existence of dynamic flow. For both methods, dynamic flow is of great importance for the enhancement of resolution for stronger acids. On comparing all of the results, the change in voltage is more efficient for improving the separation resolution in this study. More importantly, this new method can be used in any commercial CE instrument because of its features of high resolution, high speed and simplicity.

A new and very simple technique has been developed in capillary zone electrophoresis for the separation of organic acids. In this new method, capillaries were simply treated with 0.1 M NaOH via high pressure for 3 min, then flushed with running buffer solutions via high pressure for 10 s before performing separation. After this treatment, electroosmotic flow (EOF) is higher than electrophoretic mobilities (EPM) of all analytes in weak acidic conditions. Thus, eight organic acids are well separated in less than 7 min at an applied voltage of 22 kV. In addition to significant differences of EPM among analytes in weak acidic conditions, dynamic changes in EOF and pH account for the good separation results. Capillary dimensions, ionic strength and type of buffer solution all show dramatic effects on the separations of organic acids. The results also support the existence of dynamic changes in the system during a run. This new method provides the advantages of reproducibility, speed and simplicity for the separation of organic acids which cannot be easily separated in the range of pH 4–6 by any conventional means.

This study proposes a sensitive method for the simultaneous separation and concentration of 9 pairs of amino acid enantiomers by combining poly(ethylene oxide) (PEO)-based stacking, β-cyclodextrin (β-CD)-mediated micellar electrokinetic chromatography (MEKC), and 9-fluoroenylmethyl chloroformate (FMOC) derivatization. The 9 pairs of FMOC-derivatized amino acid enantiomers were baseline separated using a discontinuous system, and the buffer vials contained a solution of 150 mM Tris-borate (TB), 12.5% (v/v) isopropanol (IPA), 0.5% (w/v) PEO, 35 mM sodium taurodeoxycholate (STDC), and 35 mM β-CD, and the capillary was filled with a solution of 1.5 M TB, 12.5% (v/v) IPA, 35 mM STDC, and 35 mM β-CD. Based on the difference in viscosity between the sample zone and PEO solution and because of the STDC sweeping, the discontinuous system effectively stacked 670 nL of the 9 pairs of FMOC-derivatized amino acid enantiomers without losing chiral resolution. Consequently, the limits of detection for the 9 pairs of FMOC-derivatized amino acid enantiomers were reduced to 40−60 nM. This method was successfully used to determine d -Tryptophan (Trp), l -Trp, d -Phenylalanine (Phe), l -Phe, d -Glutamic acid (Glu), and l -Glu in various types of beers.

In this chapter, we describe a method to identify amino acids (AA) by capillary electrophoresis in conjunction with light-emitting diode-induced fluorescence (LEDIF). First, amino acids labeled with naphthalene-2,3-dicarboxaldehyde (NDA) in the presence of cyanide are converted to highly fluorescent cyanobenz[f]isoindole (CBI) derivatives. Next, they are separated by gel electrophoresis in the presence of EOF. In the process, the CBI products were excited by a violet LED to produce green fluorescence. In addition to the optical setup of light-emitting diode-induced fluorescence, the preparation of poly(ethylene) oxide for amino acid separation is also described in this chapter.

In this chapter, we describe a method to identify amino acids (AA) by capillary electrophoresis in conjunction with light-emitting diode-induced fluorescence (LEDIF). First, amino acids labeled with naphthalene-2,3-dicarboxaldehyde (NDA) in the presence of cyanide are converted to highly fluorescent cyanobenz[f]isoindole (CBI) derivatives. Next, they are separated by gel electrophoresis in the presence of EOF. In the process, the CBI products were excited by a violet LED to produce green fluorescence. In addition to the optical setup of light-emitting diode-induced fluorescence, the preparation of poly(ethylene) oxide for amino acid separation is also described in this chapter.

A novel method for the determination of sertraline using dispersive liquid–liquid microextraction (DLLME) coupled with capillary electrophoresis (CE) was developed. Acetone and dichloromethane were used as the disperser solvent and extraction solvent, respectively. A mixture of the extraction and disperser solvents was rapidly injected into a 1.0 mL aqueous sample to form a cloudy solution. After the extraction, sertraline was analyzed using CE that was equipped with UV detection. A 74-fold improvement in the sensitivity was observed when DLLME was used to extract sertraline. Since the DLLME extract residue was redissolved with 5 μL of water that contained 20% methanol, the detection sensitivity was further enhanced through the use of field-amplified sample stacking (FASS). A 11-fold improvement in the sensitivity was obtained when FASS was used to on-line concentrate sertraline. Under optimal extraction and stacking conditions, the calibration curve, which ranged from 0.01 to 1 μM was observed to be linear. The limit of detection (LOD) at a signal-to-noise ratio of 3 was 2.5 nM for sertraline. An approximately 814-fold improvement in the sensitivity was observed for sertraline compare with injection of standard solution without the DLLME and FASS procedures. This developed method was successfully applied to the determination of sertraline in human urine samples.

This paper tackles a simple and efficient method for the simultaneous separation and stacking of neurotransmitters in capillary electrophoresis with UV detection. By using poly(diallyldimethylammonium chloride) (PDDAC) as a buffer additive, the high and reversed EOF are observed. Moreover, the mobility of indolamines and catecholamines decreases as the PDDAC concentration increases. Based on the difference in mobility in the presence and absence of PDDAC, the analytes were simply stacked between the boundary of the sample zone and the background electrolyte containing PDDAC. The separation of 14 analytes including indolamines, catecholamines, and metanephrines was accomplished within 33 min under optimal conditions (1.2% PDDAC and 5 mM formic acid at pH 4.0), and the values of relative standard deviation of their migration time were less than 3.1%. By applying stacking methods for fourteen analytes, we observed: (a) the sample injection volume of sample is up to 216 nL, (b) the limits of detection at signal-to-noise of 3 range from 15.4 to 122.1 nM, and (c) the sensitivity enhancements, compared to normal injection (12 nL), range from 110- to 220-fold. Under the optimal stacking conditions, the present method has been applied to analyze of vanillomandelic acid, 5-hydroxyindole-3-acetic acid, dopamine, tryptamine, and 3-indoxyl sulfate in urine samples.

The combination of capillary electrophoresis (CE) and light-emitting diode-induced fluorescence (LED-IF) detection has been demonstrated in the analysis of major amino acids in tea leaves and beverages. The separation efficiency of amino acids, which were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA), depended on the capillary length and PEO concentration. We suggested that the interactions between the NDA derivatives and poly(ethylene oxide) (PEO) molecules are based on hydrogen bonding, hydrophobic patches, and Van der Waals forces. The magnitude of EOF and the interactions between them can be further controlled by the capillary length. The separation of 17 NDA-amino acids derivatives was completed within 16 min using 0.5% PEO and 60 cm capillary length. The relative standard deviations (R.S.D.) of their migration times (n = 5) were less than 2.7%. Additionally, the limits of detection at signal-to-noise ratio 3 for the tested amino acids ranged from 3.6 to 28.3 nM. Quantitative determination of amino acids in tea leaves and beverages was accomplished by our proposed method. This study showed that amino acid present in highest concentration in tea leaves and beverages is γ-aminobutyric acid and theanine, respectively. The experimental results suggest that our proposed methods have great potential in the investigation of the biofunction of different tea samples.

This paper describes the photosynthesis of gold nanoparticles (GNPs) in the presence of bovine serum albumin (BSA). The concentration of NaAuCl4 and the relative ratio of NaAuCl4 to BSA are important parameters for controlling the size of the GNPs. We prepared GNPs having average diameters ranging from 7 to 50 nm by illumination (Hg-Xe lamp) of phosphate-buffered solutions (pH 3.0-11.0) containing 1 mM NaAuCl4 and 10 microM BSA for 9 h. The size distribution of the GNPs synthesized at pH 7.0 is narrower relative to that of those prepared at other values of pH. Based on the observation that there are no GNPs formed at 25 degrees C in the absence of either BSA or illumination, we conclude that photolytic reduction is the main mechanism for the formation of the GNPs and that BSA acts as a capping agent to stabilize the as-synthesized GNPs. In addition to BSA, several other proteins, such as beta-casein, conalbumin, hemoglobin, beta-lactoglobulin, lysozyme, myoglobin, ovalbumin, pepsin, and trypsinogen play the same role.

The images of corneal endothelium cells obtained from specular microscopes are blurred and obscure. We use adaptive local process and lowpass filter to enhance the contrast of the images and to reduce the background noise. A special matched filter is designed to detect the edges of cell borders. Then by applying thinning technique and line tracing rules, the borders of endothelium cells can be correctly identified. This algorithm provides the quantitative informations of cell size, density, and shape which are concerning the general status, viability, and functional reserve of this important cell layer.

On-line concentration and separation of biologically active amines and acids by capillary electrophoresis (CE) in conjunction with laser-induced fluorescence using an Nd:YAG laser at 266 nm under discontinuous conditions is presented. The suitable conditions for simultaneous analysis of amines and acids were: samples were prepared in a solution (pH* 3.1) consisting of 10 mM citric acid, 89% acetonitrile (ACN), and water; a capillary was filled with 1.5 M Tris-borate (TB) buffer (pH 10.0); and the anodic vial contained PTG10 buffer (pH* 9.0) that consists of 50 mM propanoic acid, Tris, 10% glycerol, and water. After injecting a large-volume sample, amines and acids were separately stacked at the front (cathodic side) and back (anodic side) of the acidic sample zone, mainly because of changes in their electrophoretic mobilities as a result of changes in pH, viscosity, and electric field when high voltage was applied. When the sample was injected at 15 kV for 360 s, the concentration limits of detection (LODs) for 5-hydroxytryptamine (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) were 0.27 and 0.31 nM, respectively, which are about 400- and 800-fold sensitivity improvements when compared to those injected at 1 kV for 10 s. For the analysis of amines, samples were prepared in 100 mM citric acid (pH* 1.8) containing 89% ACN and both the capillary and anodic vial were filled with 400 mM PTG20 (propanoic acid, Tris, 20% glycerol, and water) at pH* 4.5. Using a large injection volume (15 kV for 360 s), we achieved concentration LODs of 17 pM and 0.3 nM for tryptamine and epinephrine, which are about 5200- and 14,000-fold sensitivity improvements, respectively, in comparison with those injected at 1 kV for 10 s. The features of simplicity (no sample pretreatment), rapidity (12 min), and sensitivity for identification of amines and acids of interest in urine samples show diagnostic potential of the two approaches developed in this study.

A method for the analysis of aliphatic carboxylic acids (ACAs) in nonaqueous capillary electrophoresis (NACE) in conjunction with indirect laser-induced fluorescence (ILIF) using merocyanine 540 (MC 540) is described. Performing the analysis in organic solvent is advantageous when using MC 540, because of its greater quantum yield in aprotic solvent. To achieve a high dynamic reserve (DR) and optimize resolution, we have tested a number of aqueous mixtures containing alcohols and acetonitrile (ACN). The optimum buffer for the analysis of C2-C18 ACAs, in terms of sensitivity, resolution, and speed, is an aqueous mixture of 40% ACN, 30% ethanol, and 1 mM Tris at apparent pH 7.4 (adjusted with ascorbic acid). Under this condition, the DR is greater than 1000, thereby the limits of detection for acids are in the range of sub-microM to microM. Linear plots show that the dynamic ranges for the analysis of ACAs are at least two decades in concentration, with regression coefficients all greater than 0.98. The relative standard deviations of the migration times and peak heights for all ACAs are less than 2.0%. Furthermore, this simple and cost-effective method has been applied to the analysis of marine lipid concentrate, with the concentrations of 1.67+/-0.03 and 4.50+/-0.05 mM (n = 5) for C14 and C16 acids, respectively, in a tablet of marine lipid concentrate sample.

DNA separations in the presence of electroosmotic flow (EOF) using poly(ethylene oxide) (PEO) solutions have been demonstrated. During the separations, PEO entered capillaries filled with Tris-borate (TB) free buffers by EOF and acted as sieving matrices. We have found that ionic strength and pH of polymer and free solutions affect the bulk EOF and resolution differently from that in capillary zone electrophoresis. The EOF coefficient increases with increasing ionic strength of the free TB buffers as a result of decreases in the adsorption of PEO molecules. In contrast, the bulk EOF decreases with increasing the ionic strength of polymer solutions using capillaries filled with high concentrations of free TB buffers. Although resolution values are high due to larger differential migration times between any two DNA fragments in a small bulk EOF using 10 mM TB buffers, use of a capillary filled with at least 100 mM TB free buffers is suggested for high-speed separations. On the side of PEO solutions, 1.5% PEO solutions prepared in 100 to 200 mM TB buffers are more proper in terms of resolution and speed. The separation of DNA markers V and VI was accomplished less than 29 min in 1.5% PEO solutions prepared in 100 mM TB buffers, pH 7.0 at 500 V/cm using a capillary filled with 10 mM free TB buffers, pH 7.0.