Fluorescent detection of peptides and amino acids for capillary electrophoresis via on-line derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole

An in-capillary derivatization of amino acids and peptides with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was developed for their subsequent capillary electrophoretic analysis with laser-induced fluorescence detection (λ _ex=488 nm). The in-capillary derivatization was achieved in zone-passing mode by introducing successive plugs of sample and NBD-F into a fused silica capillary previously equilibrated with an alkaline borate buffer. To prevent NBD-F hydrolysis and to achieve a reliable derivatization, NBD-F was prepared daily in absolute ethanol and a plug of absolute ethanol was introduced between the sample and NBD-F reagent plugs. Various parameters influencing the derivatization efficiency were investigated and the optimum conditions were as follows: background electrolyte (BGE), 20 mM borate buffer (pH 8.8); introduction time, 4 s for sample and 2 s for NBD-F; molar ratio of NBD-F/sample, above 215; temperature, 45 °C for amino acids and 35 °C for peptides; applied voltage, +15 kV. The validation of the in-capillary derivatization method under optimal conditions showed a good linearity between the heights of the derivative peaks and the concentrations of the amino acids. The intra-day relative standard deviations of the migration times and the peak heights were less than 1.3% and 4.6%, respectively. The efficient derivatization and separation of a mixture of valine, alanine, glutamic acid and aspartic acid were achieved using this technique. Peptides such as buccaline and β-protein fragment 1–42 could also be derivatized using the developed in-capillary derivatization procedure. In‑capillary derivatization and separation of amino acids with different concentrations. From the top to bottom the concentrations are 1.11×10⁻⁵ M, 5.55×10⁻⁶ M, 2.78×10⁻⁶ M, 6.95×10⁻⁷ M. for valine; 1.26×10⁻⁵ M, 6.30×10⁻⁶ M, 3.15×10⁻⁶ M, 7.88×10⁻⁷ M for alanine; 3.78×10⁻⁵ M, 1.89×10⁻⁵ M, 9.45×10⁻⁶ M, 2.36×10⁻⁶ M for glutamic acid;, 4.27×10⁻⁵ M, 2.14×10⁻⁵ M, 1.07×10⁻⁵ M, 2.68×10⁻⁶ M for aspartic acid. Experiment conditions: injection order: 4s for sample, 1s for absolute ethanol, and then 2s for 5.24×10⁻² M NBD‑F; BGE: 20 mM borate pH 8.77; Applied voltage: 15 kV.     

The potentiometric behavior of polymer-supported metallophthalocyanines used as anion-selective electrodes

Liquid polymer membrane electrodes based on nickel and manganese phthalocyanines were examined for use as anion-selective electrodes. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) membranes, which were directly coated onto the surfaces of graphite electrodes. The resulting electrodes demonstrate near-Nernstian responses over a wide linear range of perchlorate anion (5 × 10⁻⁷ to 1 × 10⁻¹ M). The electrodes have a fast response time, submicromolar detection limits (5 × 10⁻⁷ M perchlorate), and could be used over a wide pH range of 3.5–10. The influences of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The proposed sensors revealed high selectivity for perchlorate over a number of common inorganic and organic anions. The highest selectivity was observed for the electrode based on manganese phthalocyanine in the presence of the lipophilic anionic additive sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. Application of the electrodes to determine perchlorate in tap water and human urine is also reported.      

Simultaneous determination of uric acid and ascorbic acid at a ferrocenium–thioglycollate modified electrode

Self-assembled monolayers (SAMS) of chemisorbed thioglycollate on a gold electrode surface have been used as a base interface for the electrostatic adsorption of ferrocenium ion. Electrochemical impedance spectra (EIS) and cyclic voltammetry (CV) were used to evaluate the electrochemical properties of the supramolecular film. The bare gold electrode failed to distinguish the oxidation peaks of ascorbic acid (AA) and uric acid (UA) in phosphate buffer solution (PBS, pH 7.0), while the ferricinium–thioglycollate modified electrode could separate them efficiently. In differiential pulse voltammetric measurements, the prepared gold electrode could separate AA and UA signals, allowing the simultaneous determination of AA and UA. Under optimal conditions and within the linear range of 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ M, the detection limits of AA and UA achieved were 2.0 × 10⁻⁷ and 1.0 × 10⁻⁷ M, respectively. The applicability of the prepared electrode was demonstrated by measuring AA and UA in human urine without any pretreatment. Figure Fabrication process for the modified electrode     

Circular dichroism thermal lens microscope in the UV wavelength region (UV-CD-TLM) for chiral analysis on a microchip

We have developed a circular-dichroism thermal lens microscope for UV wavelengths (UV-CD-TLM), for the first time, to realize sensitive chiral analysis on a microchip. Quasi-continuous-wave phase modulation of a pulsed UV laser was used to generate left-circularly polarized light and right-circularly polarized light and to detect the generated TL signal amplitude and phase with a lock-in amplifier. The amplitude and phase were used to determine the concentration and chirality, respectively, of a sample. The basic principle of UV-CD-TLM for chiral analysis on a microchip was verified by measuring aqueous solutions of optically active camphorsulfonic acids (CSA). Lower limits of detection (LOD) were calculated at S/N = 2 and were 8.7 × 10⁻⁴ mol L⁻¹ (ΔA = 5.2 × 10⁻⁶ Abs.) for (+)-CSA and 8.4 × 10⁻⁴ mol L⁻¹ (ΔA = 5.0 × 10⁻⁶ Abs.) for (−)-CSA. In terms of number of molecules, LODs for UV-CD-TLM were calculated to be 8.7 fmol and 8.4 fmol, respectively. This is at least three orders of magnitude lower than previously obtained. The applicability of UV-CD-TLM for chiral analysis on a microchip was verified. Figure Sensitive chiral analysis by thermal lens microscope (TLM)     

Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE–AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L⁻¹ borate–0.40 mol L⁻¹ phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁷ mol L⁻¹ (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0–108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples. Figure Electropherograms obtained from 10 mg mL⁻¹ hair dye sample solutions at a platinum working electrode under optimum CZE–AD conditions: (a) natural black (I), (b) golden: (1) p-phenylenediamine, (2) m-phenylenediamine, (3) o-phenylenediamine, (4) resorcinol, and (5) catechol     

Determination of norfloxacin in human urine by capillary electrophoresis with electrochemiluminescence detection

A fast and sensitive approach that can be used to detect norfloxacin in human urine using capillary electrophoresis with end-column electrochemiluminescence (ECL) detection of is described. The separation column was a 75-μm i.d. capillary. The running buffer was 15 mmol L⁻¹ sodium phosphate (pH 8.2). The solution in the detection cell was 50 mmol L⁻¹ sodium phosphate (pH 8.0) and 5 mmol L⁻¹ The ECL intensity varied linearly with norfloxacin concentration from 0.05 to 10 μmol L⁻¹. The detection limit (S/N=3) was 0.0048 μmol L⁻¹, and the relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μmol L⁻¹ norfloxacin (n=11) were 2.6% and 0.8%, respectively. The method was successfully applied to the determination of norfloxacin spiked in human urine without sample pretreatment. The recoveries were 92.7–97.9%.      

Investigating the post-chemiluminescence behavior of phenothiazine medications in the luminol–potassium ferricyanide system: molecular imprinting–post-chemiluminescence method for the determination of chlorpromazine hydrochloride

A new post-chemiluminescence (PCL) phenomenon was observed when phenothiazine medications were injected into the reaction mixture after the chemiluminescence (CL) reaction of luminol and potassium ferricyanide had finished. A possible reaction mechanism was proposed based on studies of the kinetic characteristics of the CL, CL spectra, fluorescence spectra, and on other experiments. The feasibility of determining various phenothiazine medications by utilizing these PCL reactions was examined. A molecular imprinting–post-chemiluminescence (MI-PCL) method was established for the determination of chlorpromazine hydrochloride using a chlorpromazine hydrochloride-imprinted polymer (MIP) as the recognition material. The method displayed high selectivity and high sensitivity. The linear range of the method was 1.0×10⁻⁸∼1.0×10⁻⁶, with a linear correlation coefficient of 0.9985. The detection limit was 3×10⁻⁹ g/ml chlorpromazine hydrochloride, and the relative standard deviation for a 1.0×10⁻⁷ g/ml chlorpromazine hydrochloride solution was 4.0% (n=11). The method has been applied to the determination of chlorpromazine hydrochloride in urine and animal drinking water with satisfactory results.      

Surface modification of amine-functionalised graphite for preparation of cobalt hexacyanoferrate (CoHCF)-modified electrode: an amperometric sensor for determination of butylated hydroxyanisole (BHA)

A cobalt hexacyanoferrate (CoHCF)-modified graphite paraffin wax composite electrode was prepared by a new approach. An amine-functionalised graphite powder was used for the fabrication of the electrode. A functionalised graphite paraffin wax composite electrode was prepared and the surface of the electrode was modified with a thin film of CoHCF. Various parameters that influence the electrochemical behaviour of the modified electrode were studied by varying the background electrolytes, scan rates and pH. The modified electrode showed good electrocatalytic activity towards the oxidation of butylated hydroxyanisole (BHA) under optimal conditions and showed a linear response over the range from 7.9 × 10⁻⁷ to 1.9 × 10⁻⁴ M of BHA with a correlation coefficient of 0.9988. The limit of detection was 1.9 × 10⁻⁷ M. Electrocatalytic oxidation of BHA was effective at the modified electrode at a significantly reduced potential and at a broader pH range. The utility of the modified electrode as an amperometric sensor for the determination of BHA in flow systems was evaluated by carrying out hydrodynamic and chronoamperometric experiments. The modified electrode showed very good stability and a longer shelf life. The modified electrode was applied for the determination of BHA in spiked samples of chewing gum and edible sunflower oil. The advantage of this method is the ease of electrode fabrication, good stability, longer shelf life, low cost and its diverse application for BHA determination. Figure Cyclic Voltammogram of () CoHCF modified electrode, () in presence of 1.9 x 10⁻⁵ M of BHA and () bare electrode, () in the presence of 1.9 x 10⁻⁵ M of BHA in 1.0 M NaCl, pH 7.0     

Adsorptive stripping voltammetric determination of netilmicin in the presence of formaldehyde

A linear sweep adsorptive stripping voltammetric method for the determination of netilmicin in the presence of formaldehyde has been proposed for the first time. In the presence of 3.0×10⁻³ g ml⁻¹ formaldehyde, netilmicin exhibits a sensitive cathodic peak at −1.30 V (vs. the saturated calomel electrode, SCE) in a medium of Britton–Robinson buffer (pH 8.7) with a scan rate of 100 mV s⁻¹ after a preconcentration period of 120 s at −1.10 V (vs. SCE). The peak current showed a linear dependence on the netilmicin concentration over the range 4.2×10⁻⁹–1.0×10⁻⁷ g ml⁻¹. The achieved limits of detection and quantitation were 1.0×10⁻¹⁰ and 3.3×10⁻¹⁰ g ml⁻¹ netilmicin, respectively. It was deduced from the experiments that the amine–aldehyde condensation product formed between netilmicin and formaldehyde is mainly responsible for the appearance of the peak. The electrochemical behavior of netilmicin in the presence of formaldehyde has been studied. The method was applied to the direct determination of netilmicin in injectable formulations and spiked human urine and serum samples.      

Sequential preconcentration by coupling of field amplified sample injection with pseudo isotachophoresis–acid stacking for analysis of alkaloids in capillary electrophoresis

A novel on-column sequential preconcentration method based on the combination of field-amplified sample injection induced by acetonitrile and pseudo isotachophoresis (ITP)–acid stacking is developed for simply but efficiently concentrating alkaloid cations in a high-salt sample matrix in capillary electrophoresis. Acetonitrile (70%) added to a sample solution with a high-salt sample matrix not only induces field-amplified sample stacking by decreasing conductivity but also acts as a termination reagent in the succeeding pseudo ITP. After sample injection had been completed, a plug of H⁺ was injected electrokinetically and a neutralization reaction between H⁺ and tartrate from the buffer solution produced a low conductivity zone, in which the injected analyte cations were further concentrated. With the sequential preconcentration method, a 3 orders of magnitude detection sensitivity (1,400-fold) increase could be observed compared with the conventional electrokinetic injection method, without compromising separation efficiency and peak shape, and detection limits of 0.1 ng/mL for myosmine and 0.3 ng/mL for anabasine with the conditions selected were achieved. The calibration curves demonstrated good linearity in the concentration ranges 1.3–600 ng/mL for myosmine and 4.9–900 ng/mL for anabasine, respectively. The proposed method has been used to analyze successfully trace alkaloids in cigarette samples. Figure Sequential preconcentration processes: a sample injection; b introduction of HCl; c capillary zone electrophoresis separation. A ⁻ tartrate, white circles acetonitrile, black circles Na⁺, sample zone, myosmine, anabasine     

Fluorescence-detecting cationic surfactants using luminescent CdTe quantum dots as probes

A novel fluorescence quenching method for the determination of cationic surfactants (CS), specifically cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and cetylpyridinium chloride (CPC), has been developed using water-soluble luminescent CdTe quantum dots (QDs) modified with thioglycolic acid (TGA). The possible interference from heavy and transition metals (HTM) has been efficiently eliminated through simple sample treatment with mercapto cotton made in-house. Under optimum conditions, the extent of fluorescence quenching of CdTe QDs is linearly proportional to the concentration of CS from 2.0 × 10⁻⁷ to 7.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation for 1.0 × 10⁻⁶ mol L⁻¹ CTAB is 2.5% (n = 6). The proposed method exhibits high sensitivity and selectivity and furthermore avoided the use of toxic organic solvents and tedious solvent extraction procedures. It has been applied to the determination of trace CS in natural river water and commodity samples with satisfactory results. Potential interference from heavy and transition metals is eliminated during photoluminescence detection of CS through simple sample pre-treatment with mercapto cotton     

Online phototransformation–flow injection chemiluminescence determination of triclosan

A highly selective and sensitive chemiluminescence method for the determination of triclosan is proposed. The method is based on the phototransformation of triclosan to a light-emitting precursor in the presence of fluorescein in alkaline medium and the chemiluminescence reaction is then triggered by strong base or oxidants such as N-bromosuccinimide. Based on this reaction an online phototransformation–flow injection manifold was developed, in which the photoreactor comprises a 150-cm-long × 0.8-mm-i.d. piece of PTFE tubing coiled around a 25-W fluorescent lamp, and the phototransformed products were then injected into a carrier stream of borate buffer. After mixing with the oxidant stream the produced light was detected by a photomultiplier. A wide calibration range from 8.0 × 10⁻⁸ to 1.0 × 10⁻⁴ mol L⁻¹ was obtained under the optimized conditions, and the detection limit was as low as 5.0 × 10⁻⁸ mol L⁻¹. The whole process of analysis, including the online phototransformation and subsequent chemiluminescence detection, could be completed in 6 min. Most of the foreign substances tested showed high tolerance levels, and the proposed method was directly applied to the determination of triclosan in toothpaste samples without any pre-separation procedure. Figure Schematic representation of the phototransformation of triclosan and subsequent chemiluminescence reaction     

A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay

A microfluidic system incorporating chemiluminescence detection is reported as a new tool for measuring antioxidant capacity. The detection is based on a peroxyoxalate chemiluminescence (PO-CL) assay with 9,10-bis-(phenylethynyl)anthracene (BPEA) as the fluorescent probe and hydrogen peroxide as the oxidant. Antioxidant plugs injected into the hydrogen peroxide stream result in inhibition of the CL emission which can be quantified and correlated with antioxidant capacity. The PO-CL assay is performed in 800-μm-wide and 800-μm-deep microchannels on a poly(dimethylsiloxane) (PDMS) microchip. Controlled injection of the antioxidant plugs is performed through an injection valve. Of the plant-food based antioxidants tested, β-carotene was found to be the most efficient hydrogen peroxide scavenger (SA _HP of 3.27 × 10⁻³ μmol⁻¹ L), followed by α-tocopherol (SA _HP of 2.36 × 10⁻³ μmol⁻¹ L) and quercetin (SA _HP of 0.31 × 10⁻³ μmol⁻¹ L). Although the method is inherently simple and rapid, excellent analytical performance is afforded in terms of sensitivity, dynamic range, and precision, with RSD values typically below 1.5%. We expect our microfluidic devices to be used for in-the-field antioxidant capacity screening of plant-sourced food and pharmaceutical supplements. Figure Assembled PDMS microchip sandwiched between two glass plates with the top plate containing capillary reservoirs     

The electrochemical behavior of p-benzenediol on a self-assembled monolayers Pt electrode modified with N-(2-mercapto-1,3,4-thiadiazol-5-yl)-N′-(4-substituted-arylacetyl) urea

Two novel N-(2-mercapto-1,3,4-thiadiazol-5-yl)-N′-(4-substituted-arylacetyl) urea compounds have been synthesized, characterized by NMR and MS, and used as self-assembly reagents to form self-assembled monolayers (SAMs) on Pt electrodes. The modified electrodes were characterized by electrochemical methods. The electrochemical behavior of p-benzenediol at the SAMs electrodes was investigated. It was found that the electrochemical response to p-benzenediol is controlled by diffusion and can be electrocatalyzed to obtain more symmetrical redox peaks and higher voltammetric current response at the SAMs electrodes, with a peak separation of 80 mV. For p-benzenediol the process at the SAMs electrodes is quasi-reversible with a rate constant of 0.6742 s⁻¹. The SAMs electrodes have been used to determine p-benzenediol by differential pulse voltammetry. The peak current was linear for concentrations of p-benzenediol in the range 1×10⁻⁷−5×10⁻⁴ mol L⁻¹ and the detection limit was 4.0×10⁻⁸ mol L⁻¹. The SAMs electrodes were used to determine p-benzenediol in real photographic developer and in a synthetic waste water sample; the standard addition recovery was in the range 96.6–100.4%.      

Electrochemical deposition of silicate–cetyltrimethylammonium bromide nanocomposite film on glassy carbon electrode for sensing of methyl parathion

A novel electrochemical sensor for methyl parathion based on silicate– cetyltrimethylammonium bromide nanocomposite film has been fabricated by electro-assisted deposition onto glassy carbon electrode in one-step via an electrochemical modulation of pH at the electrode/solution interface to promote controlled gelification of tetraethylorthosilicate sol, and was characterized with scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The electrochemical sensing of methyl parathion on the film-modified electrode was investigated applying cyclic voltammetry and square wave voltammetry. Compared to the unmodified electrode, the shapes of the redox peaks were improved and the peak currents significantly increased. Experimental parameters such as deposition time, pH value, and accumulation conditions have been optimized. A linear relationship between the peak current and methyl parathion concentration was obtained in the range from 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.04 × 10 ⁻⁸ mol L⁻¹ (S/N = 3) after accumulation at 0 V for 120 s. The film electrode shows great promise for determination of methyl parathion in real samples.      

Molecularly imprinted solid-phase extraction and flow-injection chemiluminescence for trace analysis of 2,4-dichlorophenol in water samples

Highly sensitive flow-injection chemiluminescence (CL) combined with molecularly imprinted solid-phase extraction (MISPE) has been used for determination of 2,4-dichlorophenol (2,4-DCP) in water samples. The molecularly imprinted polymer (MIP) for 2,4-DCP was prepared by non-covalent molecular imprinting methods, using 4-vinylpyridine (4-VP) and ethylene glycol dimethacrylate (EGDMA) as the monomer and cross-linker, respectively. 2,4-DCP could be selectively adsorbed by the MIP and the adsorbed 2,4-DCP was determined by its enhancing effect on the weak chemiluminescence reaction between potassium permanganate and luminol. The enhanced CL intensity was linear in the range from 1 × 10⁻⁷ to 2 × 10⁻⁵g mL⁻¹. The LOD (S/N = 3) was 1.8 × 10⁻⁸g mL⁻¹, and the relative standard deviation (RSD) was 3.0% (n = 11) for 1.4 × 10⁻⁶g mL⁻¹. The proposed method had been successfully applied to the determination of 2,4-DCP in river water. Figure Effect of 4-VP content on the ultraviolet spectrum of 2,4-DCP in chloroform     

Capacitive biosensor for detection of endotoxin

A capacitive biosensor for the detection of bacterial endotoxin has been developed. Endotoxin-neutralizing protein derived from American horseshoe crab was immobilized to a self-assembled thiol layer on a biosensor transducer (Au). Upon injection of a sample containing endotoxin, a decrease in the observed capacitive signal was registered. Endotoxin could be determined under optimum conditions with a detection limit of 1.0 × 10⁻¹³ M and linearity ranging from 1.0 × 10⁻¹³ to 1.0 × 10⁻¹⁰ M. Good agreement was achieved when applying endotoxin preparations purified from an Escherichia coli cultivation to the capacitive biosensor system, utilizing the conventional method for quantitative endotoxin determination, the Limulus amebocyte lysate test as a reference. The capacitive biosensor method was statistically tested with the Wilcoxon signed rank test, which proved the system is acceptable for the quantitative analysis of bacterial endotoxin (P < 0.05). Figure The flow-injection capacitive biosensor system and the capacitive properties of the transducer surface, where C_SAM is the capacitance change of the self-assembled thiol monolayer, C_P is the capacitance change of the protein layer, C_a is the capacitance change of the analyte layer and C_Total is the total capacitance change measured at the working electrode/solution interface (modified from Limbut et al., 2006. Biosens Bioelectron 22: 233-240)     

Electrogeneration of polyluminol and chemiluminescence for new disposable reagentless optical sensors

A performant reagentless electrochemiluminescent (ECL) detection system for H₂O₂ is presented, based on an electropolymerized polyluminol film prepared under near-neutral conditions. Such an original polyluminol electrodeposition is reported for the first time and on a screen-printed electrode (SPE) surface. Electropolymerized luminol acts as an active luminophore of the electrochemiluminescent reaction, as the monomer does. Polymerization conditions have been optimized in order to obtain the best ECL responses to H₂O₂. By performing electrodeposition in a potentiostatic mode, at 425 mV vs. Ag|AgCl, in 0.1 mol L⁻¹ phosphate/0.1 mol L⁻¹ KCl pH 6 and 1 mmol L⁻¹ luminol, with a total charge of 0.5 mC, the linear range for H₂O₂ detection extends from 7.9 × 10⁻⁸ mol L⁻¹ to 1.3 × 10⁻³ mol L⁻¹. Such performant disposable reagentless easy-to-use miniaturized systems based on SPEs should be applicable to the electrochemiluminescent detection of many oxidase-substrate compounds. Figure An original polyluminol electrodeposition process on a screen-printed electrode surface is reported for the first time. The polymeric structure is demonstrated to behave as an electrochemiluminescent luminophore, allowing disposable reagentless easy-to-use optical sensors for hydrogen peroxide detection to be designed.     

Study of multiple binding constants of dexamethasone with human serum albumin by capillary electrophoresis–frontal analysis and multivariate regression

Studies into the interactions between drugs and human serum albumin (HSA) are extremely important for drug discovery, since HSA behaves as a carrier for external drugs and internal biological molecules. In this paper, to evaluate the pharmacokinetic and pharmacodynamic properties of dexamethasone (DXM), the interaction between DXM and HSA was studied by capillary electrophoresis–frontal analysis (CE-FA). According to the Klotz equation, four binding sites between DXM and HSA were obtained, and the average binding constant was 1.05 × 10³ M⁻¹. Furthermore, according to multiple equilibrium theory, based on the assumption that there are two types of binding site, the binding constant at one site was calculated to be 3.539 × 10³ M⁻¹, and the average of the other three was 1.234 × 10³ M⁻¹. In addition, to obtain the detailed binding information at each binding site, new equations were deduced by multivariate regression. The four binding constants of DXM and HSA were calculated to be 5.558 × 10¹ M⁻¹, 2.158 × 10⁴ M⁻¹, 7.312 × 10³ M⁻¹ and 2.043 × 10³ M⁻¹, respectively, which is helpful for detailed studies into the interactions between drugs and proteins with multiple binding sites. Figure Electropherograms of DXM sodium phosphate and HAS mixtures for different protein to drug concentration ratios, obtained by CE-FA     

Determination of Etofenprox in environmental samples by HPLC after anionic surfactant micelle-mediated extraction (coacervation extraction)

A method is described for determination of residues of the insecticide Etofenprox in environmental samples. Anionic surfactant micelle-mediated extraction (coacervation extraction) was evaluated for isolation of Etofenprox before HPLC. The optimum conditions used for extraction included: 0.09 g sodium dodecanesulfonate (SDoS), 3.1 mL (3.3, for concentrations below 0.04 mg L⁻¹) 12 mol L⁻¹ HCl, 5 min vortex stirring, 5 min centrifugation at 4000 rpm, 2 h equilibration time. The limits of quantification (LOQ) and detection (LOD) were 0.01 and 0.004 mg L⁻¹, respectively, and recoveries obtained from five real samples ranged from 94.33±2.48 to 100.13±2.71%. The precision of the method was good; relative standard deviations (RSD) were less than 7%.