Determination of thiocyanate ions at nanolevel in real samples using coated graphite electrode based on synthesised macrocyclic Zn(II) complex

The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating the newly synthesized zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N₂-1,5-O₂ (I ₁ ) and zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N₂-1,5-O₂ (I ₂ ) are reported here. The best response was observed with the membrane having a composition of I₂:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with detection limit of 2.2 × 10⁻⁷ mol L⁻¹. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics w.r.t Nernstian slope 59.0 ± 0.2 mV decade⁻¹ activity, wide concentration range of 8.9 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹ and detection limit of 6.7 × 10⁻⁸ mol L⁻¹. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in potentiometric titration of SCN⁻ ion.     

A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin in palladium nanoparticles/graphene-chitosan nanocomposite film

Thermally two-dimensional lattice graphene (GR) and biocompatibility chitosan (CS) act as a suitable support for the deposition of palladium nanoparticles (PdNPs). A novel hydrogen peroxide (H₂O₂) biosensor based on immobilization of hemoglobin (Hb) in thin film of CS containing GR and PdNPs was developed. The surface morphologies of a set of representative membranes were characterized by means of scanning electron microscopy and showed that the PdNPs are of a sphere shape and an average diameter of 50 nm. Under the optimal conditions, the immobilized Hb showed fast and excellent electrocatalytic activity to H₂O₂ with a small Michaelis–Menten constant of 16 μmol L⁻¹, a linear range from 2.0 × 10⁻⁶ to 1.1 × 10⁻³ mol L⁻¹, and a detection limit of 6.6 × 10⁻⁷ mol L⁻¹. The biosensor also exhibited other advantages, good reproducibility, and long-term stability, and PdNPs/GR–CS nanocomposites film would be a promising material in the preparation of third generation biosensor.     

A new amperometric H<Subscript>2</Subscript>O<Subscript>2</Subscript> biosensor based on nanocomposite films of chitosan–MWNTs,hemoglobin, and silver nanoparticles

A new H₂O₂ biosensor was fabricated on the basis of nanocomposite films of hemoglobin (Hb), silver nanoparticles (AgNPs), and multiwalled carbon nanotubes (MWNTs)–chitosan (Chit) dispersed solution immobilized on glassy carbon electrode (GCE). The immobilized Hb displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ′) of −22.5 mV in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) in the Chit–MWNTs film was evaluated as 2.58 s⁻¹ according to Laviron’s equation. The surface concentration (Γ*) of the electroactive Hb in the Chit–MWNTs film was estimated to be (2.48 ± 0.25) × 10⁻⁹ mol cm⁻². Meanwhile, the Chit–MWNTs/Hb/AgNPs/GCE demonstrated excellently electrocatalytical ability to H₂O₂. Its apparent Michaelis–Menten constant (K _M^app) for H₂O₂ was 0.0032 mM, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H₂O₂ ranging from 6.25 × 10⁻⁶ to 9.30 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.47 × 10⁻⁷ mol L⁻¹ (S/N = 3). Furthermore, the biosensor possessed rapid response to H₂O₂ and good stability, selectivity, and reproducibility.     

Application of inorganic sorbents for removal of Cs, Sr, Pu and Am from contaminated solutions

A sorption ability of titanium silicates (TiSi) and iron oxides towards Cs, Sr, Pu and Am was tested using the laboratory batch method. The obtained results are expressed as distribution coefficients (K_d). TiSi synthesised using TiOSO₄ revealed better sorption ability towards all studied radionuclides in comparison with TiSi produced on the basis of TiCl₄. The K_d values ranged from 3.9 × 10² to 1.6 × 10⁵ mL g⁻¹ for Sr, from 6 to 4.1 × 10⁴ mL g⁻¹ for Cs, from 2.2 × 10² to 2.6 × 10⁵ mL g⁻¹ for Pu and from 50 to 1.6 × 10⁴ mL g⁻¹ for Am. The highest Pu K_d values (9 × 10³–6.2 × 10⁴ mL g⁻¹) and better kinetics were found for iron oxides.     

Simple sensor for simultaneous determination of dihydroxybenzene isomers

A simple sensor based on bare carbon ionic liquid electrode was fabricated for simultaneous determination of dihydroxybenzene isomers in 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0). The oxidation peak potential of hydroquinone was about 0.136 V, catechol was about 0.240 V, and resorcinol 0.632 V by differential pulse voltammetric measurements, which indicated that the dihydroxybenzene isomers could be separated absolutely. The sensor showed wide linear behaviors in the range of 5.0 × 10⁻⁷–2.0 × 10⁻⁴ mol L⁻¹ for hydroquinone and catechol, 3.5 × 10⁻⁶–1.535 × 10⁻⁴ mol L⁻¹ for resorcinol, respectively. And the detection limits of the three dihydroxybenzene isomers were 5.0 × 10⁻⁸, 2.0 × 10⁻⁷, 5.0 × 10⁻⁷ mol L⁻¹, respectively (S/N = 3). The proposed method could be applied to the determination of dihydroxybenzene isomers in artificial wastewater and the recovery was from 93.9% to 104.6%.     

Dispersive liquid–liquid microextraction coupled to liquid chromatography for thiamine determination in foods

A miniaturized dispersive liquid–liquid microextraction (DLLME) procedure coupled to liquid chromatography (LC) with fluorimetric detection was evaluated for the preconcentration and determination of thiamine (vitamin B₁). Derivatization was carried out by chemical oxidation of thiamine with 5 × 10⁻⁵ M ferricyanide at pH 13 to form fluorescent thiochrome. For DLLME, 0.5 mL of acetonitrile (dispersing solvent) containing 90 μL of tetrachloroethane (extraction solvent) was rapidly injected into 10 mL of sample solution containing the derivatized thiochrome and 24% (w/v) sodium chloride, thereby forming a cloudy solution. Phase separation was carried out by centrifugation, and a volume of 20 μL of the sedimented phase was submitted to LC. The mobile phase was a mixture of a 90% (v/v) 10 mM KH₂PO₄ (pH 7) solution and 10% (v/v) acetonitrile at 1 mL min⁻¹. An amide-based stationary phase involving a ligand with amide groups and the endcapping of trimethylsilyl was used. Specificity, linearity, precision, recovery, and sensitivity were satisfactory. Calibration graph was carried out by the standard additions method and was linear between 1 and 10 ng mL⁻¹. The detection limit was 0.09 ng mL⁻¹. The selectivity of the method was judged from the absence of interfering peaks at the thiamine elution time for blank chromatograms of unspiked samples. A relative standard deviation of 3.2% was obtained for a standard solution containing thiamine at 5 ng mL⁻¹. The esters thiamine monophosphate and thiamine pyrophosphate can also be determined by submitting the sample to successive acid and enzymatic treatments. The method was applied to the determination of thiamine in different foods such as beer, brewer’s yeast, honey, and baby foods including infant formulas, fermented milk, cereals, and purees. For the analysis of solid samples, a previous extraction step was applied based on an acid hydrolysis with trichloroacetic acid. The reliability of the procedure was checked by analyzing a certified reference material, pig’s liver (CRM 487). The value obtained was 8.76 ± 0.2 μg g⁻¹ thiamine, which is in excellent agreement with the certified value, 8.6 ± 1.1 μg g⁻¹.     

CO<Subscript>2</Subscript> corrosion inhibition of X-70 pipeline steel by carboxyamido imidazoline

The corrosion inhibition of X-70 pipeline steel in saltwater saturated with CO₂ at 50 °C with carboxyamido imidazoline has been evaluated by using electrochemical techniques. Techniques included polarization curves, linear polarization resistance, electrochemical impedance, and electrochemical noise measurements. Inhibitor concentrations were 0, 1.6 × 10⁻⁵, 3.32 × 10⁻⁵, 8.1 × 10⁻⁵, 1.6 × 10⁻⁴, and 3.32 × 10⁻⁴ mol l⁻¹. All techniques showed that the best corrosion inhibition was obtained by adding 8.1 × 10⁻⁵ mol l⁻¹ of carboxyamido imidazoline. For inhibitor concentrations higher than 8.1 × 10⁻⁵ mol l⁻¹ a desorption process occurs, and an explanation has been given for this phenomenon.     

LC–MS–MS determination of ibuprofen, 2-hydroxyibuprofen enantiomers,and carboxyibuprofen stereoisomers for application in biotransformation studies employing endophytic fungi

The purpose of this study was the development and validation of an LC–MS–MS method for simultaneous analysis of ibuprofen (IBP), 2-hydroxyibuprofen (2-OH-IBP) enantiomers, and carboxyibuprofen (COOH-IBP) stereoisomers in fungi culture medium, to investigate the ability of some endophytic fungi to biotransform the chiral drug IBP into its metabolites. Resolution of IBP and the stereoisomers of its main metabolites was achieved by use of a Chiralpak AS-H column (150 × 4.6 mm, 5 μm particle size), column temperature 8 °C, and the mobile phase hexane–isopropanol–trifluoroacetic acid (95: 5: 0.1, v/v) at a flow rate of 1.2 mL min⁻¹. Post-column infusion with 10 mmol L⁻¹ ammonium acetate in methanol at a flow rate of 0.3 mL min⁻¹ was performed to enhance MS detection (positive electrospray ionization). Liquid–liquid extraction was used for sample preparation with hexane–ethyl acetate (1:1, v/v) as extraction solvent. Linearity was obtained in the range 0.1–20 μg mL⁻¹ for IBP, 0.05–7.5 μg mL⁻¹ for each 2-OH-IBP enantiomer, and 0.025–5.0 μg mL⁻¹ for each COOH-IBP stereoisomer (r ≥ 0.99). The coefficients of variation and relative errors obtained in precision and accuracy studies (within-day and between-day) were below 15%. The stability studies showed that the samples were stable (p > 0.05) during freeze and thaw cycles, short-term exposure to room temperature, storage at −20 °C, and biotransformation conditions. Among the six fungi studied, only the strains Nigrospora sphaerica (SS67) and Chaetomium globosum (VR10) biotransformed IBP enantioselectively, with greater formation of the metabolite (+)-(S)-2-OH-IBP. Formation of the COOH-IBP stereoisomers, which involves hydroxylation at C3 and further oxidation to form the carboxyl group, was not observed.     

Sensitive fluorescent probes for determination of hydrogen peroxide and glucose based on enzyme-immobilized magnetite/silica nanoparticles

Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme horseradish peroxidase (HRP) on Fe₃O₄/SiO₂ magnetic core–shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe₃O₄/SiO₂ nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able to activate hydrogen peroxide (H₂O₂), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm. Under optimized conditions, a linear calibration curve was obtained over the H₂O₂ concentrations ranging from 5.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 2.1 × 10⁻⁹ mol L⁻¹. By simultaneously using glucose oxidase and HRP-immobilized Fe₃O₄/SiO₂ nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity of the product responded well linearly to glucose concentration in the range from 5.0 × 10⁻⁸ to 5.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 1.8 × 10⁻⁸ mol L⁻¹. The proposed method was successfully applied for the determination of glucose in human serum sample.     

Radiolysis of 1-naphthol in aqueous solutions

The effects of absorbed doses, initial pH and 1-naphthol concentration onto its radiolysis in aqueous sulphuric and hydrochloric acids by gamma rays from ⁶⁰Co were investigated. Under the experimental conditions, 1-naphthol degradation yields increased with increasing the absorbed doses (0.3–3.0 kGy) and with decreasing the initial 1-naphthol concentration (20–1 ppm). It was found out that the hydrated electrons did not play any significant roles in 1-naphthol radiolysis, as the degradation yields were higher at pH₀ ~ 0.46 compared to those at pH₀ ~ 2.0–5.0. The corresponding radiolytic yields G(−1-naphthol) were (6.13 ± 1.00)) × 10⁻² and (5.11 ± 0.22) × 10⁻² μmol/J in sulphuric acids, (15.61 ± 3.85) × 10⁻² and (4.76 ± 0.48) × 10⁻² μmol/J in hydrochloric acids. 1-Naphthol degradation rates could be described by the kinetic equations of pseudo-first-order reactions. An empirical relation between the observed reaction constants k _D and the initial 1-naphthol concentrations was established, enabling to predict the absorbed doses required for a given treatment efficiency. Three products of 1-naphthol degradation were revealed using an HPLC/UV procedure.     

Development of a liquid chromatography-mass spectrometry method for the determination of ursolic acid in rat plasma and tissue: application to the pharmacokinetic and tissue distribution study

A fast and sensitive liquid chromatography–mass spectrometry method was developed for the determination of ursolic acid (UA) in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate using gradient elution. Quantification was performed by selected ion monitoring with (m/z)⁻ 455 for UA and (m/z)⁻ 469 for the IS. The method was validated in the concentration range of 2.5 − 1470 ng mL⁻¹ for plasma samples and 20 − 11760 ng g⁻¹ for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7% to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 − 106.9% and 82.1 − 108.1%, respectively. Recoveries in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL⁻¹ or 4.0 ng g⁻¹. The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The main pharmacokinetic parameters obtained were T _max = 0.42 ± 0.11 h, C _max = 1.10 ± 0.31 μg mL⁻¹, AUC = 1.45 ± 0.21 μg h mL⁻¹ and K _a = 5.64 ± 1.89 h⁻¹. The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats.     

A compact miniaturized continuous flow system for the determination of urea content in milk

A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the urea concentration range from 1.0 × 10⁻⁴ to 5.0 × 10⁻³ mol L⁻¹ with a limit of detection of 8.0 × 10⁻⁶ mol L⁻¹. The relative standard deviation (RSD) for a 2.0 × 10⁻³ mol L⁻¹ urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h⁻¹. To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the data are in close agreement, at a 95% confidence level.     

Electro-catalysis by immobilised human flavin-containing monooxygenase isoform 3 (hFMO3)

Human flavin-containing monooxygenases are the second most important class of drug-metabolizing enzymes after cytochromes P450. Here we report a simple but functional and stable enzyme-electrode system based on a glassy carbon (GC) electrode with human flavin-containing monooxygenase isoform 3 (hFMO3) entrapped in a gel cross-linked with bovine serum albumin (BSA) by glutaraldehyde. The enzymatic electrochemical responsiveness is characterised by using well-known substrates: trimethylamine (TMA), ammonia (NH₃), triethylamine (TEA), and benzydamine (BZD). The apparent Michaelis–Menten constant (K′_M) and apparent maximum current (I′_max) are calculated by fitting the current signal to the Michaelis–Menten equation for each substrate. The enzyme-electrode has good characteristics: the calculated sensitivity was 40.9 ± 0.5 mA mol⁻¹ L cm⁻² for TMA, 43.3 ± 0.1 mA mol⁻¹ L cm⁻² for NH₃, 45.2 ± 2.2 mA mol⁻¹ L cm⁻² for TEA, and 39.3 ± 0.6 mA mol⁻¹ L cm⁻² for BZD. The stability was constant for 3 days and the inter-electrode reproducibility was 12.5%. This is a novel electrochemical tool that can be used to investigate new potential drugs against the catalytic activity of hFMO3.     

FAD-modified SiO2/ZrO2/C ceramic electrode for electrocatalytic reduction of bromate and iodate

SiO₂/ZrO₂/C carbon ceramic material with composition (in wt%) SiO₂ = 50, ZrO₂ = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image showed that ZrO₂ and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks of the material was 18 S cm⁻¹, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide (FAD) prepared by immersing the solid SiO₂/ZrO₂/C, molded as a pressed disk, inside a FAD solution (1.0 × 10⁻³ mol L⁻¹) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl) were: BrO₃ ⁻, lrr = 4.98 × 10⁻⁵–1.23 × 10⁻³ mol L⁻¹ and dl = 2.33 μmol L⁻¹; IO₃ ⁻, lrr = 4.98 × 10⁻⁵ up to 2.42 × 10⁻³ and dl = 1.46 μmol L⁻¹ for iodate.     

Sensitive voltammetric sensor of dihydromyricetin based on Nafion/SWNT-modified glassy carbon electrode

A novel voltammetric sensor, based on single-walled carbon nanotubes (SWNT) dispersed in Nafion and modified glassy carbon electrode (GCE), was fabricated and used to determine the trace amounts of dihydromyricetin (DMY). The electrochemical behavior of DMY at this sensor was investigated in 0.1 mol L⁻¹ sulfuric acid solutions + 0.1 mol L⁻¹ NaCl by cyclic voltammetry and squarewave voltammetry. Compared with bare GCE, the electrode presented an excellent response of DMY through an adsorption-controlled quasi-reversible process. Under the optimum conditions, the response peak currents were linear relationship with the DMY concentrations in the range of 1.0 × 10⁻⁷–1.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 9 × 10⁻⁸ mol L⁻¹. Based on this voltammetric sensor, a simple and sensitive electroanalytical method for DMY was proposed and applied to quantitative determination of DMY in Ampelopsis grossedentata samples. In addition, the oxidation mechanism was proposed and discussed, which could be a reference for the pharmacological action of DMY in clinical study.     

Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m²⋅g⁻¹ and 487 m²⋅g⁻¹ for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant K _i,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g⁻¹ and more than twice as high as obtained from Henry’s law with K _i is 26.8 mL⋅g⁻¹. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K _i is 17.1 mL⋅g⁻¹. Adsorption enthalpy Δh _Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol⁻¹ for extrudates and −29.6 kJ⋅mol⁻¹ for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.     

Electrocatalytic oxidation of nitrite at a terpyridine manganese(II) complex modified carbon past electrode

A carbon past electrode modified with [Mn(H₂O)(N₃)(NO₃)(pyterpy)], ( \textpyterpy = 4￠- ( 4 - \textpyridyl ) - 2,2￠:\text6￠,\text2￠￠- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and nitrite can be determined in the ranges of 5.00 × 10⁻⁶ to 1.55 × 10⁻² mol L⁻¹, with a detection limit of 8 × 10⁻⁷ mol L⁻¹. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10⁻², 0.56× 10⁻⁶, and 7.99 × 10⁻⁶ cm² s⁻¹, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed. This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior, anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Solid Phase Spectrophotometry for the Determination of Cobalt in Pharmaceutical Preparations

 A new sensitive method exploiting solid-phase spectrophotometry is proposed for the determination of cobalt in pharmaceutical preparations. The chromogenic reagent 1-(2-thiazolylazo)-2-naphthol (TAN) was immobilized on C18 bonded silica loaded into a home-made cell with 1.5 mm of optical path for cobalt determination. Cobalt(II) reacts with TAN on C18 material, at pH 6.0–7.5, to give a coloured complex which has maximum absorption at 572 nm. In this way, the sample was passed through the cell and Co(II) ions were quantitatively retained on the solid-phase. After the direct measurement of light-absorption in the solid phase, only the cobalt was eluted with 0.1 mol L⁻¹ hydrochloric acid. The cell was washed with water and then another sample solution could be passed through the cell. The procedure allowed the determination of cobalt in the range of 10–160 μg L⁻¹ with coefficient of variation of 4.7% (n=10) and apparent molar absorptivity of 2.62 × 10⁶ L mol⁻¹ cm⁻¹ using sample volume of 3-mL. Received May 15, 2000. Revision August 28, 2000.     

Effects of Temperature and Common Ions on Binding of Puerarin to BSA

The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding constants (K _a) between puerarin and BSA are 1.13×10⁴ L⋅mol⁻¹ (20 °C) and 1.54×10⁴ L⋅mol⁻¹ (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results in a lower binding constant (1.58×10³ L⋅mol⁻¹) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu²⁺ and Fe³⁺ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex.     

Development of electrochemical DNA biosensor for Trichoderma harzianum based on ionic liquid/ZnO nanoparticles/chitosan/gold electrode

Electrochemical DNA biosensor was successfully developed by depositing the ionic liquid (e.g., 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][Otf])), ZnO nanoparticles, and chitosan (CHIT) nanocomposite membrane on a modified gold electrode (AuE). The electrochemical properties of the [EMIM][Otf]/ZnO/CHIT/AuE for detection of DNA hybridization were studied. Under optimal conditions using cyclic voltammetry, the target DNA sequences could be detected in the concentration range of 1.0 × 10⁻¹⁸ to 1.82 × 10⁻⁴ mol L⁻¹, and with the detection limit of 1.0 × 10⁻¹⁹ mol L⁻¹. This DNA biosensor detection approaches provide a quick, sensitive, and convenient method to be used in the identification of Trichoderma harzianum.